Abortion is the termination of a human pregnancy by removal of the fetus or embryo from the womb before it has acquired the ability to survive on its own. There are two types of abortion: spontaneous and induced. A spontaneous abortion, often called a miscarriage, occurs naturally as the result of genetic, developmental, or physiological problems developed during pregnancy. An induced abortion is the termination of a pregnancy by medical or surgical methods. An induced abortion can be either therapeutic or elective. Therapeutic abortions are performed when continued pregnancy threatens the life of the mother. Elective abortions are performed at the mother’s request for other reasons.
Abstinence, in relation to reproduction, is a voluntary act or practice of refraining from sex. Often times, people are abstinent in order to prevent pregnancy, as abstinence is the only form of birth control that is 100% effective. However, abstinence may be practiced for personal, religious, or other medical reasons.
The acrosome is a vesicle or membrane enclosed organelle that covers the anterior portion of the head of a spermatozoon until the acrosome reaction occurs.
As a spermatozoon approaches the zona pellucida (outer glycoprotein membrane) of the oocyte, the membrane of the acrosome will fuse with the plasma membrane of the oocyte, allowing the contents of the acrosome (including enzymes and antigens) to break through the egg’s tough coating. This reaction is necessary for fertilization of the egg to occur.
Activin is a powerful protein that regulates and participates in many cellular functions, including the menstrual cycle, and more specifically, the production and release of a reproductive hormone called follicle stimulating hormone (FSH). Activin is made by most organs and controls cellular proliferation and differentiation. Loss of activin can result in profound early developmental defects. Activin is regulated by a closely related protein called inhibin. Both activin and inhibin control male and female reproduction, and an imbalance in either of these hormones can result in infertility in both men and women.
The adenohypophysis is the anterior lobe of the pituitary gland and consists of the distal, intermediate, and infundibular parts. The adenohypophysis develops from a group of cells, Rathke’s pouch, that migrate toward the center of the base of the brain from the roof of the embryonic oral cavity. The post-embryonic anterior lobe contains five cell types that produce six hormones in response to the presence of releasing hormones produced by the hypothalamus: corticotropes make corticotropin (adrenocorticotropichormone, ACTH), gonadotropes make follitropin (follicle stimulating hormone, FSH) and luteotropin (luteinizing hormone, LH), lactotropes (mammotropes) make prolactin (PRL), somatotropes make somatotropin (growth hormone, GH), and thyrotropes make thyrotropin (thyroid stimulating hormone, TSH). These hormones are central to maintaining either metabolic balance in essential physiological systems (ACTH, GH, TSH) or are central to successful reproduction (FSH, LH, PRL).
The adrenal cortex is the outer tissue later of the adrenal gland and is the production site of corticosteroid and androgen hormones. It is sub-divided into three layers (zones), each structurally unique and producing a separate class of hormones. The zona glomerulosa is the most superficial layer and produces mineralcorticoids, such as aldosterone, which is involved in the regulation of blood pressure. The zona fasciculata is the middle layer and produces glucocorticoids such as cortisol, which is involved in regulating metabolism. The innermost layer is the zona reticularis and produces androgens, including androstenedione, which is the precursor to testosterone. Because the gonadal tissues normally produce more androgens than the adrenal cortex, the latter is often considered a secondary site of androgen synthesis.
The adrenal glands are endocrine glands situated directly on top of the kidneys. They are an important part of the endocrine system, producing many different types of hormones involved in biological functions, such as the stress response.
The adrenal medulla is the central, reddish-brown portion of the adrenal gland and is surrounded by the adrenal cortex. It consists of irregularly shaped cells grouped around blood vessels, which are intimately connected by the sympathetic division of the autonomic nervous system. The cells of the adrenal medulla produce, store, and release epinephrine (adrenaline), norepinephrine (noradrenaline), and a small amount of dopamine. These are the hormones involved in the fight-or-flight response, where the production of epinephrine increases heart rate and blood pressure, blood vessel constriction in the skin and gastrointestinal tract, smooth muscle dilation, and metabolism; norepinephrine has the opposite effect.
Adrenocorticotropic hormone (ACTH), also known as corticotropin, is a polypeptide hormone produced in the anterior pituitary gland. Its release often results in greater production and release of corticosteroids.
Also called placental expulsion, afterbirth refers to the placenta and fetal membranes that are expelled from the uterus via the birth canal following the birth of the baby.
In endocrinology, an agonist is a chemical or hormone that is capable of stimulating a cell in a manner akin to another hormone. It usually acts as a hormone mimic and binds to the same receptor used by the mimicked hormone in order to induce a biological response.
Alginate is a polysaccharide found in the cell walls of algae. When mixed with calcium, alginate will form a solid-like gel used to encapsulate cells.
The allantois is a fetal membrane that develops from a small vesicle at the hindgut of the very early embryo. Its function is to collect liquid waste from and to exchange gases used by the embryo. The fetal bladder is connected to the allantois. With advancing embryonic development, the size of the human allantois is decreased and becomes an elongated sac and part of the umbilical cord. The allantois is vestigial in humans.
An allosome differs from a typical autosome in that it determines the sex of an individual (e.g. the X and Y chromosomes are allosomes). In humans, an ovum contains the X allosome, and a sperm contains either the X or Y allosome.
Amenorrhea is the absence of menstrual bleeding or suppression of the normal menstrual cycle for three or more consecutive months in a woman who previously had normal menstrual cycles (secondary amenorrhea). Amenorrhea also refers to the absence of menses by age 14 in an adolescent with no development of secondary sexual characteristics, or by age 16 in an adolescent who has had normal sexual development (primary amenorrhea). Common causes of amenorrhea include pregnancy, lactation during the months following pregnancy, underlying issues with one’s reproductive organs or functions, contraceptive medication or other drugs/therapies (like chemotherapy or radiation), menopause, low levels of energy stores or malnutrition, stress or anxiety disorders, and excessive weight loss or exercise.
Amniocentesis is a prenatal test that allows one’s healthcare practitioner to diagnose health concerns, genetic diseases, and chromosomal abnormalities in the womb by extracting a sample of amniotic fluid. This is the fluid that surrounds the baby in the uterus during development, where fetal cells that contain important health information are present. Amniocentesis is typically performed when an expectant mother is between 15 and 18 weeks pregnant and, due to the small level of risk, is often times only advised for women who have an increased risk of giving birth to a baby with genetic defects. Amniocentesis cannot detect structural birth defects. It is also the most accurate way to determine the sex of the baby before birth.
The amnion is the pouch-like tissue present in the early embryo that lies over the dorsal surface of the epiblast portion of the developing inner cell mass. It is formed from cells that detach from the cytotrophoblast layer of the trophoblast stage of the embryo. As gestation progresses, the amnion grows outward and eventually surrounds the entire embryo and, in live-bearing animals, the umbilical cord, for which it forms an epithelial covering. In the latest stages of gestation, the amnion adheres to the inner cell layer of the chorion, forming the inner of the two membranes (the two together serving as the amniotic sac) surrounding the fetus. During later development, the amnion serves as a reservoir for urine, which is mixed with fluid that derives from maternal serum; this mixture cushions the developing fetus and provides a buoyant environment that allows for symmetrical growth and prevents embryonic adherence and growth onto the placental tissues. The amnion remains present at birth in most species but is absent in fish and amphibians altogether.
The amniotic cavity is the fluid-filled space within the amniotic sac where the developing fetus resides.
Amniotic fluid is the protective liquid that surrounds the developing fetus within the amniotic sac. Most of the amniotic fluid consists of fetal urine, so low amounts can indicate a lack of placental flow.
The amniotic sac is a thin but tough pair of membranes (namely, the chorion and amnion) filled with fluid. The amniotic sac surrounds the growing embryo, and later, the fetus. It is tough, yet pliable and transparent and is crucial for a successful pregnancy outcome, as it provides necessary support and cushioning.
An amniotomy, or manual puncture of the amniotic sac, is usually performed at the time of labor to induce delivery of the baby.
The fallopian tube is comprised of three parts. The ampulla is the secondary, dilated section of the tube and is the main site where fertilization commonly occurs in both mice and humans.
Anabolic steroids (the proper scientific term being ‘anabolic-androgenic steroids’, abbreviated AAS) are synthetic testosterones prescribed to treat a medical condition where hormonal deficiencies are present, or used illegally with the desire of increasing muscle mass and/or the appearance of masculine sex characteristics. Use is most common among young men. Anabolic steroids can be taken orally, injected into the muscles, or rubbed on the skin in the form of a cream. There are many effects of the unregulated use of anabolic steroids by young men, including testicle shrinkage, reduced sperm count or infertility, baldness, development of breasts (gynecomastia), and an increased risk for prostate cancer.
Anaphase is the stage of cell division (mitosis or meiosis) during which chromosomes separate and are pulled toward opposite poles of the cell by the spindle in preparation for cell division. In meiosis I, homologous pairs of chromosomes separate, resulting in two haploid sets of chromosomes, a reduction from the diploid set of chromosomes present at the start. In mitosis and meiosis II, sister chromatids separate.
Androgens are a class of steroid hormones produced in the testes, adrenal cortex, ovaries, and to some extent, fat cells. In males, androgens are essential for the growth and maintenance of male sex organs and secondary sex characteristics. In females, androgens serve as the precursor to estrogen. Testosterone is an example of an androgen.
Androstenedione is an intermediate steroid horome produced in the adrenal glands and gonads (the testes and ovaries) as a precursor to the androgen, testosterone, and the estrogens, estrone and estradiol. It is, in part, produced in response to the release of ACTH by the anterior pituitary gland.
Anencephaly is a neural tube defect in which a fetus never develops parts of its brain and skull. Almost all babies born with this disorder will die shortly after birth, however, a mother may choose to terminate her pregnancy beforehand.
Aneuploidy traces back to the point of cell division when chromosomes are not separated properly and refers to a state in which a cell or cells has/have too many or too few chromosomes. This is often seen in the form of trisomy, such as Trisomy 21 (Down syndrome), or monosomy, such as Turners Syndrome. In female gametes, aneuploidy can lead to miscarriages, infertility, and birth defects.
Anovulation is the absence of ovulation, or oocyte release from the ovary, in the menstrual cycle. Anovulation may be physiological before puberty, during pregnancy and lactation, or after menopause. It may also be pathological due to disorders affecting the ovaries, pituitary gland, or hypothalamus. Chronic anovulation accounts for about 30% of all cases of female infertility. The most common cause of chronic anovulation is polycystic ovarian syndrome (PCOS).
In endocrinology, an antagonist is a chemical or hormone that is capable of blocking the binding of an agonist to its receptor but does not induce a biological response upon binding itself.
The anterior pituitary gland is the front portion of the pituitary gland. It secretes hormones that regulate many physiological processes, including growth, reproduction, lactation, and stress.
Anti-mullerian hormone (AMH) is a hormone secreted by the Sertoli cells in the embryonic developing testes of males. AMH represses the development of the Mullerian Duct (also called paramesonephric ducts, developing female reproductive tract). AMH is also secreted by granulos cells of preantral and smaller antral follicels in the adult ovary. During male embryonic development, AMH insures the regression of female structures (fallopina tubes, uterus, cervix, and upper vagina), enabling the proper development of the wolffian duct (male reproductive tract, vas deferens, seminal vesicles). In the female, AMH secretion occurs during the reproductive lifespan until menopause; because of this, AMH can be used as a marker of the ovarian reserve.
An antral follicle (or Graafian follicle) has reached the most mature ovarian follicle stage of folliculogenesis. An antral follicle is characterized by its large diameter and the presence of a liquid-filled space, otherwise know as an antrum.
The anus is the ring-shaped opening at the end of the gastrointestinal tract opposite from the mouth. It is also the end of the alimentary canal and the posterior most opening on the perineum. It controls the removal of feces (solid waste material) from the body.
Apoptosis is a type of programmed cell death in multicellular organisms. It is a natural mechanism by which a cell intentionally destroys itself without causing damage to the organism. However, excessive apoptosis may cause atrophy (shrinking or shriveling), while lack of apoptosis in the body can lead to cancer and uncontrolled cell proliferation.
Aromatase (also referred to as estrogen synthetase or estrogen synthase) is the key enzyme responsible for estrogen production. Aromatase enzymes act by accelerating the conversion of testosterone, an androgen, into estrogens. Estrogens have been shown to promote the growth of some breast cancers. Aromatase inhibitors can decrease estrogen levels and have been used for treating breast cancer, as well as other disorders.
Artificial insemination (AI) consists of introducing sperm directly into the female genital tract, without sexual intercourse. This technique is used for fertility purposes in humans (with the use of assisted reproductive technology or a sperm donation program) and in animals (to employ genetic selection for productivity or by using a sperm bank of endangered species). Fresh or frozen washed sperm is placed in the vagina using a conception device or in the uterus by means of a catheter at the time of ovulation to improve the chances of fertilization of the released oocyte(s).
Assisted hatching is a special technique used as an assisted reproductive technology. A protective coating, called the zona pellucida, shields the developing embryo as it travels through the fallopian tube and enters the uterus. In order for the embryo to attach to the uterine wall, the zona must be dissolved and the embryo released. This is a naturally occurring process called embryo hatching. Assisted hatching was developed to overcome barriers to this process due to zona hardening or thickening. The zona can be penetrated using chemical agents, mechanical pressure, or a laser to assist in the release of the embryo and to promote implantation.
Assisted reproductive technology (ART) refers to a set of clinical procedures developed to help women conceive (become pregnant). Examples of ART include in vitro fertilization, intracytoplasmic sperm injection, preimplantation genetic diagnosis, cryopreservation, and intrauterine insemination. Currently, it is estimated that four million children worldwide have been conceived using ART procedures.
Asthenospermia is the medical term for a condition in which a male’s sperm have reduced motility (the ability to swim or move). Genetic, idiopathic, and iatrogenic factors can result in this condition. Although male infertility is most commonly attributed to a low sperm count, having sperm with poor motility can lead to infertility, as well, because, once ejaculated, the sperm must be able to travel through the vagina, cervix, and uterus before reaching the fallopian tubes where fertilization will take place. To overcome infertility due to asthenospermia, assisted reproductive technology procedures can be utilized, such as intracytoplasmic sperm injection.
Atresia, with regard to ovarian follicles, is the degeneration of follicles after they have formed (but before they have fully matured) through hormonally regulated apoptosis. Atresia may occur at any follicular stage of the menstrual cycle but seems to be more frequent at the primordial and late secondary stages before puberty and at the late secondary stage during adult cycling.
Attrition, with regard to germ cells, is the death of germ cells before follicle formation. This process most likely occurs through apoptosis but may also involve autophagy or other forms of cell death.
Autophagy is a form of programmed cell death in which lysosomes degrade unnecessary and dysfunctional cells. Autophagy can be a way to maintain energy levels in cells during periods of starvation. Autophagy and apoptosis can be differentiated by several morphological and biochemical markers.
Autosomes are non-sex-determining chromosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes (allosomes).
Azoospermia is the medical term for a condition in which no measurable amount of sperm is present in a male’s semen. Genetic, idiopathic, and iatrogenic factors can result in this condition. There are two types of azoospermia: obstructive azoospermia, which refers to problems in sperm transport from the testis to the penis, and non-obstructive azoospermia, which refers to defects in sperm production. Because of the lack of sperm in the ejaculate, azoospermia results in infertility and sterility. However, depending on the type of azoospermia, certain assisted reproductive technology procedures, such as TESE and ICSI, can be used to help a man affected by this condition conceive a child.
Bacterial vaginosis is a bacterial infection in the vagina that occurs when the balance of bacteria is upset. Symptoms include a grayish-yellow discharge and fishy smell. Douching, smoking, and having multiple sexual partners can increase a woman's risk of getting bacterial vaginosis. Women who are pregnant and get bacterial vaginosis may have a higher risk of miscarriage or pre-term labor.
The barrier method refers to birth control methods used during sexual intercourse that pose a physical barrier to sperm that would otherwise enter the uterus. These methods include a diaphragm, cervical cap, male or female condom, and spermicidal foam, sponges, and film. It is important to note that male and female condoms are the only birth control methods that may prevent the contraction of STIs.
Bioengineering (also referred to as biological engineering) is a field of science in which the principles of engineering are applied to biology and medicine. Often times, bioengineering is applied to human health in order to develop new technologies that model, modify, or control biological systems.
A bioethicist is a person who studies the moral and ethical issues that surround biological advances in science, technology, and medicine by drawing from other surrounding disciplines, including law, philosophy, and politics.
Bioethics is the study of ethical issues that arise due to advancements in biology, medicine, health care, health policy, and health science.
Bioidentical hormones are synthesized or artificial hormones that are structurally identical to hormones made within the body. Common bioidentical hormones include synthesized estrogen and progesterone, both often used in hormone therapy. Bioidentical hormones are often made using chemicals extracted from plants, and they are finely ground to make them more absorbent in the body.
Biomarkers are proteins or small molecules which can be measured in the blood, urine, or other bodily fluids in order to diagnose conditions, identify disease, track disease progression, and/or monitor therapeutic interventions.
A biomaterial is any natural or synthetic material that is used for biological application. For example, the components of an artificial joint are biomaterials.
Birth refers to the process where an offspring is produced from the womb (in mammals).
A birth defect is any developmental abnormality present at birth that can be caused by a variety of factors, including drug and alcohol use by the mother during prenancy, exposure of the mother to pathogens during pregnancy, abnormalities in chromosome number, issues with gene expression, etc.
Bisphenol A (BPA) is an industrial chemical and endocrine disruptor that has been used to make certain plastics and resins since the 1960s. BPA remains controversial because of its potential to seep into foods or beverages kept in containers that are made with the compound. It also has the ability to seep into the body when handling products that contain the chemical. Studies with rodents have shown that exposure to BPA can interfere with reproductive function.
Bisphosphonates are drugs that can slow or stop the activity of bone-dissolving cells and preserve bone density, bone strength, and reduce the risk of fracture. Bisphosphonates are commonly used to prevent and treat osteoporosis, especially in post-menopausal women who have the disease.
Black cohosh is an herbal supplement that is used to treat the symptoms of menopause, such as hot flashes, mood disturbances, and vaginal dryness. It is also sometimes used to treat the symptoms of menstruation, premenstrual syndrome, and to induce labor in pregnant women. Research is inconclusive as to its effectiveness.
A blastocoel is the fluid-filled cavity of the blastula.
A blastocyst is an early embryo that is less than a week old, usually forming five days after fertilization from the morula in the uterus and implanting into the uterine wall six days after fertilization. Blastocysts are composed of two distinct cell lineages: the inner cell mass (ICM) that will become the embryo and the trophoblast that will become the placenta. The trophoblast surrounds the ICM and the inner, fluid-filled cavity called the blastocoel.
A blastomere is a single cell of a pre-implantation stage embryo formed by cell division of the zygote following fertilization. Using the specific assisted reproductive technology known as preimplantation genetic diagnosis, a single blastomere is removed from an embryo, and genetic testing is performed on this cell, so that embryos free of genetic abnormalities are transferred back into the recipient.
Blastulation is the formation of the blastula and blastocoel following the morula stage of embryo development.
Bone mineral density refers to the amount of calcium and other minerals that exist in a segment of bone. A bone mineral density test is used to assess bone strength, predict the risk of fracture, and can be used to diagnose osteoporosis (a common ailment in post-menopausal women).
Braxton Hicks contractions, also known as practice contractions or false labor pains, are irregular uterine contractions that may begin as early as the second trimester of pregnancy but are more commonly felt during the third trimester. These contractions are usually experienced as an uncomfortable cramping sensation in the lower abdomen. They do not lead to the onset of labor and usually disappear with rest. Braxton Hicks contractions are acknowledged as the body’s way of preparing for the birthing process. The term “Braxton Hicks” dates back to the first description of these contractions by an English doctor named John Braxton Hicks in 1872.
The breast is the tissue located on the right and left sides of the front of the chest and contains the mammary glands. The mammary glands secrete milk for the purpose of feeding an infant, and they are sensitive to ovarian hormones and prolactin.
A breech birth is the birth of a baby from a breech presentation, which refers to the baby exiting the pelvis feet or buttocks first. It accounts for about 3-4 % of all singleton deliveries. Factors associated with breech birth include high parity with uterine relaxation, twin or multiple fetuses, preterm labor, changes in amniotic fluid volume (poly- or oligo-hydramnios), previous breech birth, placental anomalies (placenta previa or fundal placental implantation), fetal head anomalies (hydrocephaly or anencephaly), uterine anomalies, and pelvic tumors. Generally, a baby in the breech position will be delivered by Caesarean section, as vaginal delivery is associated with high risks to the life of the mother and child.
Breech presentation refers to the positioning of the baby inside the mother’s womb, where the buttocks and/or legs occupy the lower section of the uterus, while the baby's head occupies the upper section of the uterus. Types of breech presentation include: Frank Breech 65%, Complete Breech 10%, and Incomplete Breech 25 % (Footling and Kneeling). Frank Breech is when the baby's hip joints are flexed and knee joints are extended. Complete Breech is when the baby's hip and knee joints are flexed. Footling Breech is when the baby's hip and knee joints are extended. Kneeling Breech is when the baby's hip joints are extended and knee joints are flexed.
The two bulbourethral glands (also known as Cowper's glands) are accessory glands of the male reproductive tract located on either side of the prostate gland. They produce secretions that become a component of semen during ejaculation.
A Caesarian section (C-section) is a surgical procedure performed as an alternative to natural (vaginal) delivery in which cuts are made into both the abdomen and uterus in order to deliver a baby (or babies). C-sections are usually performed when vaginal delivery might pose threats to the health of the mother or baby, but they might also be performed at the request of the mother for other reasons and can be scheduled ahead of time.
Cancer is any type of malignant growth or tumor caused by abnormal and uncontrolled cell division.
Capacitation is a biochemical maturation process that mammalian sperm must go through in the female reproductive tract after they are ejaculated from the male and before they are able to fertilize an oocyte.
Caspases are a class of cysteine proteases, or a type of enzyme, that break up or cleave other proteins. Caspases are involved in the initiation and execution of apoptosis (programmed cell death). The caspases transmit intracellular signals through a "caspase cascade" where one caspase cleaves a second caspase, and this cleavage activates the second caspase. Once activated, the second caspase could then cleave other caspases (thereby activating them) or other downstream ligands.
Castration refers to the removal or loss of function of the gonads (testes or ovaries) by various means, rendering the individual sterile (unable to reproduce).
The cervix is a small, tube-like structure located at the bottom of the uterus and extending into the vagina. When a woman is in labor, the cervix dilates to allow for the passage of the baby through the birth canal. Cells from the cervix are sampled during a Pap smear to test for signs of cancer.
Chemotherapy is the use of drugs, either administered orally or intravenously, to kill cancer cells. Many drugs used in standard chemotherapy regimens are cytotoxic and act to kill cells that divide rapidly. Unfortunately, for this reason, rapidly dividing healthy cells will be killed along with the unwanted cancer cells.
The chorion is a transient, multi-layered, extra-embryonic membrane that matures to form part of the placenta and the connection to the umbilical cord.
A chromatid is one half of a replicated chromosome. Two chromatids are joined by a centromere until they separate during cell division.
Chromatin is the complex of DNA, RNA, and proteins that compact chromosomes into a smaller volume, so that they fit inside the nucleus of a cell. The array of proteins in chromatin can also change the activity of genes.
A chromosome is a compact chromatin structure made up of DNA and an assortment of proteins. DNA is packaged into chromosomes early in meiosis or mitosis in preparation for cell division.
Cilia are small, hair-like projections that line the fallopian tubes. They wave back and forth to help guide the egg from the ovaries to the uterus. If the cilia have been previously damaged by infection, they may not move the egg to the uterus as efficiently. This can lead to the development of an ectopic pregnancy.
Cilia beating occurs in the fallopian tube (or oviduct), where the cilia beat (wave) back and forth to move along the ovum or embryo. They also facilitate fertilization by moving the sperm toward the egg.
Circumcision refers to the surgical procedure where the foreskin (prepuce) covering the head of the penis is removed. This procedure is usually performed on infants or young children in religious ceremonies. In parts of Africa and in other high-risk populations, the procedure is recommended to prevent the contraction of the HIV/AIDS virus.
Cleavage, with regard to the embryo, is a term that refers to the first few mitotic divisions of the pre-implantation embryo. These cell divisions, which begin shortly after fertilization, transform a single cell zygote into a multicellular embryo. Up until the blastocyst stage, the cell divisions serve to increase the embryo’s cell number but do not increase the embryo’s actual size.
The clitoral hood is a flap of skin that covers and protects the female clitoris, functioning like the foreskin in males.
The clitoris is the female erectile organ located at the top of the vulva, directly above the urethra, and it is the homologue of the male penis. It contains many nerve endings and is considered to be the primary source of sexual pleasure in the female.
A clutch refers to all of the eggs that are produced at a single time. In rodents, a clutch of eggs surrounded by cumulus cells can be found in the oviduct following ovulation.
Cohesin is a protein complex that holds sister chromatids together, thereby regulating their separation in anaphase of both mitosis and meiosis.
Colostrum, also known as “first milk”, is the first form of lacteal secretion produced by the mammary glands before the production of milk. Colostrum, in humans, is produced in the late stages of pregnancy and contains antibodies to protect the newborn from disease. Colostrum is very rich in nutrients, such as proteins, antibodies, growth factors, and vitamin A, but contains lower amounts of carbohydrates, lipids, and potassium compared to normal milk. The antibodies in colostrum provide passive immunity, while growth factors stimulate further development of the gut.
The moment that a sperm fertilizes an egg (in humans) to produce a zygote, which eventually develops into an embryo.
A conception device is a medical device used in assisted reproductive technology in order to help achieve pregnancy by means other than intercourse.
A technique to delete a specific gene in a specific tissue to understand the role of the individual gene. In contrast to traditional gene knockout that deletes genes in the whole body, this is induced by a Cre-LoxP recombination system that can eliminate tissue-specific genes at specific times.
Contraception refers to any preventative measure taken to avoid a pregnancy from occurring. In males, the options include condoms, rhythm method, withdrawal, vasectomy, and abstinence. In females, the options include condoms, rhythm method, abstinence, barrier methods, hormonal methods, implantable devices, sterilization surgery, and emergency contraception.
A contraceptive is a drug, chemical, or physical barrier/device that aids in pregnancy prevention.
The corpus albicans (Latin for "white body") is an ovarian scar composed of connective tissue that forms after the corpus luteum degenerates, a process called luteolysis. The corpus albicans is primarily made of collagen and persists on the ovary for a few months.
The corpus luteum (Latin for "yellow body") is a hormone-secreting gland that forms after a mature egg is released from an ovarian follicle. It is composed of granulosa- and theca-lutein cells and primarily secretes the steroid hormone, progesterone. If the egg is not fertilized, the corpus luteum will degenerate and form the corpus albicans.
Corticosteroids are any of the steroid hormones produced in the adrenal cortex.
Corticotropes are specialized cells of the anterior pituitary gland that produce and secrete the hormone corticotropin (ACTH).
A site-specific recombinase technology that is targeted to a specific time and cell type of gene deletions and insertions. The Cre-Lox system is performed by Cre recombinase that recombines the LoxP sites derived from bacteriophage P1. It has been a very useful tool to understand the role of tissue-specific genes and mutant genes that are lethal, if expressed globally.
Cross-linking is the process of linking two molecules with the use of chemical reactions; cross-links may be covalent bonds, electrostatic bonds, or hydrogen bonds.
The process of crossing over that occurs during prophase I of meiosis refers to the exchange of genetic material between homologous chromosomes. The homologous chromosomes attach to one another and exchange small pieces of DNA, effectively increasing genetic variation.
Cryopreservation refers to the process of storing cells, tissues, or organs at very low temperatures, so they can remain viable and functional again when thawed. Cryopreservation is often used to preserve embryos created by in vitro fertilization, so they can be implanted into a woman’s uterus at a later date.
A cryostat is a cold temperature chamber containing a microtome, or slicer, used to prepare thin sections from frozen tissues. The tissues are often maintained at -20 degrees Celsius.
Cumulus cells are one of two functionally divided classes of granulosa cells in the antral follicle. They surround the oocyte to form the cumulus-oocyte complex and are released with the egg during ovulation. In order for fertilization to occur, the sperm must penetrate through the layer of cumulus cells. An abundance of cumulus cells is necessary for the development of a healthy embryo, as they provide the necessary nutrients and energy for oocyte maturation.
The cumulus-oocyte complex is ovulated during the ovulatory phase of the menstrual cycle and is just what it seems: an oocyte surrounded by specialized granulosa cells, called cumulus cells. The cumulus cells surrounding the oocyte ensure healthy oocyte and embryo development.
Ovarian cysts are fluid-filled sacs formed in the ovaries. There are a few different types, but the most common are follicular or luteal cysts, which are formed during ovulation when the egg is not properly released from the follicle and remains in the ovary, or when the corpus luteum does not break down and dissolve after release of the oocyte. These cysts often disappear in a matter of months, but more serious cysts may cause abdominal pain and bleeding.
Cytokinesis is the division of the cytoplasm in a single cell for the purpose of forming two new daughter cells during mitosis and meiosis.
Diploid is the designation given to cells with two sets of chromosomes; this is characteristic of somatic cells. In humans, this is 46 chromosomes (or 23 pairs).
Ductal is a term used to describe channels leading from glands or organs in the body. Ductal is commonly referenced in discussion of lactiferous ducts, which are responsible for carrying milk from the mammary gland to the nipple of a breast.
The ectocervix is the lower, vaginal portion of the cervix consisting of stratified squamous epithelium.
The ectoderm is the outermost layer of cells of a eukaryote or the outermost layer of cells in the developing embryo once it has reached the gastrula stage. This cell layer ultimately gives rise to nervous tissue, skin, mammary glands, pituitary gland, and enamel of the teeth.
An ectopic pregnancy is a pregnancy that results when an egg implants itself anywhere outside of the uterus, such as the fallopian tube or abdominal cavity. These pregnancies can be dangerous to the health of the mother and are rarely viable.
An effector is a protein, often an enzyme, within a hormonally stimulated cell that helps produce the end result of the hormonal stimulation. Known effectors include transcription factors involved with altering cellular gene transcription, enzymes controlling the storage and retrieval of intracellular glucose, enzymes that produce steroid hormones, and intracellular structural proteins that control cellular shape and movement. These molecules often use intracellular energy stores and result in the amplification of hormonal signals, so that binding of a few hormone molecules can make cells do things that would otherwise be impossible, if they only depended on the energy from binding the hormone molecules, themselves.
An egg, also known as an ovum, is the female reproductive cell or gamete. Eggs are arrested at metaphase of meiosis II, and following ovulation, they can be fertilized in the presence of sperm. In addition to containing DNA, the egg contains critical stores of maternal mRNAs and protein that will support fertilization and subsequent embryo development.
Egg activation refers to a series of events that occur in the egg after it is fertilized by a sperm. These events include completion of meiosis, initiating the block to polyspermy, and translation of specific mRNAs from the egg that are necessary for embryonic development prior to the maternal to zygotic transition. In all animal species studied to date, a rise in calcium levels within the egg triggers all events of egg activation.
Egg banking is an assisted reproductive technology procedure in which multiple eggs are retrieved from a woman following hormonal hyperstimulation. Although similar to embryo banking, the eggs are not fertilized prior to cryopreservation. Thus, this is a good option for women who do not have a male partner and who do not want to use donor sperm. Although this relatively new technology is successful, it is still considered experimental. The process of egg banking can take up to one month to complete.
Egg donation is the process in which a woman (egg donor) volunteers to donate an egg/oocyte or several oocytes to another woman in the hopes of helping her become pregnant through the process of in vitro fertilization (IVF). Egg donation can be part of the process of third–party reproduction. Known egg donation is reserved for those individuals or couples who select a family member or friend to be their egg donor. Anonymous egg donation is when the donor is unknown to the patient or intended couple. Many times, egg donation is anonymous. An egg donor is typically given a thorough medical exam before being treated with hormones to induce hyperovulation. Following hormonal treatment, approximately 10-15 eggs are harvested to be screened for future IVF.
Egg freezing (or oocyte cryopreservation) is the freezing of eggs (oocytes) to preserve the fertility of female cancer patients before they undergo chemotherapy or radiotherapy. Egg freezing may be an alternative to embryo freezing in order to avoid the immediate need for a fertilizing sperm in cases where a male partner or sperm donation are not available or acceptable to the patient. The typical egg freezing procedure includes the use of injectable hormones to stimulate the ovaries to promote the growth of multiple mature eggs, a surgical procedure to collect oocytes from the ovary, rapid freezing of mature oocytes, and storage of cryopreserved oocytes for a period of time (e.g. years). In the future, these oocytes can be thawed and used for in vitro fertilization by sperm to create embryos, which can then be transferred into the uterus to achieve pregnancy. Egg freezing is now considered to be an established technology by the American Society of Reproductive Medicine due to significant improvements in pregnancy rates.
Ejaculation is the release of semen from the urethral opening of the penis and is usually accompanied by orgasm.
The ejaculatory ducts are paired structures in the male reproductive system formed by the union of the vas deferens with the duct of the seminal vesicle.
Embedding refers to the placement of fixed tissue into a matrix (such as paraffin wax) that provides support for further manipulation of the tissue during processes like sectioning.
An embryo is an organism in its early stages of development. In humans, this stage extends from the time an egg undergoes fertilization to eight weeks after fertilization. Beyond that point, the organism is then referred to as a fetus.
Embryo banking is an ART procedure in which embryos are created through in vitro fertilization. These embryos are then cryopreserved and stored for future reproductive use. The process of embryo banking can take up to one month to complete.
Embryo donation utilizes unused embryos or embryos specifically created via donor eggs and donor sperm. The donated embryo is placed into the uterus of the future mother or the surrogate mother.
The embryonic disk is the flat, disk-shaped conceptus that forms prior to gastrulation in some vertebrates.
Embryonic stem cells are undifferentiated cells taken from the inner cell mass of an embryo. These cells have the ability to give rise to all three of the primary germ cell layers, the ectoderm, endoderm, and mesoderm. Because of this quality, these cells are useful in laboratory work. The stem cells are taken from both unused embryos in IVF and from cloned embryos created using donor eggs.
Emergency contraception is a form of birth control that may be used for up to five days after sexual intercourse has taken place. Emergency contraception is often used when no contraceptive methods were used, when the one or more birth control methods used may have failed, or when a woman was made to have sex against her will. The options for emergency contraception are emergency contraceptive pills and the Copper-T Intrauterine Device. These methods are not as effective as primary birth control methods used before or during sex.
The endocervix is the inner, mucosal layer of the cervix.
An endocrinologist is a physician who focuses on the treatment of diseases and conditions associated with the body’s glands and balance of hormones.
Endocrinology is the study of the body’s endocrine glands and their secretions (known as hormones).
The endoderm is the innermost layer of cells of a eukaryote or the innermost layer of cells in the developing embryo once it has reached the gastrula stage. This cell layer ultimately gives rise to the inner (epithelial) linings of the gut and associated glands, liver, respiratory tract, urinary bladder, ear passages, and the functional portions of the thyroid, parathyroid, pancreas, and thymus.
Endometriosis is a condition in which cells of the uterine lining, or endometrium, grow outside of the intrauterine environment, often on or around surrounding structures. This results in potential pain, bleeding, and scarring of internal reproductive structures, and, in some cases, infertility.
The endometrium is the highly dynamic uterine tissue lining the uterine cavity. Its cellular and molecular composition changes daily throughout the menstrual cycle in fertile women, and the outer functional layer is shed at each menstruation. The endometrium provides the "soil" into which an embryo implants to establish a pregnancy.
Enzyme-Linked Immunosorbent Assay, or ELISA, is a method used to measure reproductive hormones (eg. proteins or steroids) in blood samples. The technique uses antibodies that are linked to an enzyme. The antibodies specifically bind to the hormone in the blood sample. At the end of the reaction, a chemical is added and the enzyme causes a change in color (from clear to blue). The amount of hormone in the sample is directly proportional to the change in color.
The epiblast is a tissue type of the upper side of the embryonic disk, which arises from the inner cell mass during the late blastula and early trophoblast stages of embryonic growth. These cells give rise to the tissues of the embryo proper.
The epididymis is a long, tightly coiled tube connected to the testis. Its function is to bring non-motile sperm incapable of fertilization to functional maturity before moving into the vas deferens.
Episiotomy is a small surgical incision along the midline of the perineum, the tissue between the vagina and anus, to enlarge the vaginal opening and facilitate vaginal delivery. It can be performed under local or epidural anesthesia, and it is sutured immediately after the delivery.
Erectile dysfunction (or impotence) is the inability to achieve or maintain a firm erection for sex. There are many potential causes of erectile dysfunction, including other underlying health issues or behaviors. For example, chronic alcohol consumption is a risk factor for erectile dysfunction. Alcohol is a central nervous depressant, so it is theorized that this in addition to other physiological changes that occur when consuming alcohol contribute to erectile dysfunction.
Estrogen is a steroid hormone that is produced primarily in the female ovaries and, in small amounts, in the adrenal cortex, male testes, and placenta. Estrogen helps regulate and guide female sexual development and reproductive system functions, such as the estrous and menstruation cycles.
Estrone, also known as oestrone, is an estrogen hormone secreted by the ovary. It is a known carcinogen for women and is the least abundant of the three estrogens in the body.
The estrous cycle, which has been studied extensively in rodents, refers to the cyclic alterations that occur in the female reproductive tract and in sexual receptivity. The estrous cycle is often likened to the menstrual cycle in humans. It is composed of four distinct stages – proestrus, estrus, metestrus, and diestrus – that are each characterized by distinct physiology as well as animal morphology and behavior. Proestrus is the portion of the cycle when eggs reach full maturity within the follicles. External examination of the female genitalia reveals a swollen vulva and open vagina. Estrus is the stage of the cycle when ovulation occurs. The vagina remains open, and, at this stage, females are maximally receptive to males. Metestrus is the stage when the mature egg moves through the fallopian tube, and the vagina is closed. If successful copulation and fertilization occur, pregnancy will occur. If pregnancy does not occur, diestrus will ensue. Diestrus is the final stage of the estrous cycle in which unfertilized eggs are eliminated, and the vagina remains closed. During this stage, a new cohort of follicles begins rapid growth to prepare for ovulation in the next cycle.
Eumenorrhea refers to normal menstruation.
ex situ refers to any procedure where the cells of interest are examined outside of their native environment.
ex vivo refers to occurrences outside of a living organism. An ex vivo experiment is one that is completed outside of a living organism, where cells are directly isolated from the living organism.
An extra-amniotic pregnancy occurs when the amniotic sac ruptures, and the baby develops in the extra-embryonic coelom.
The fallopian tubes, also know as uterine tubes, are two thin tubes that connect the ovaries and uterus. An ovum (egg) that is released from an ovary will travel through a fallopian tube and into the uterus. Each fallopian tube is comprised of three sections: the isthmus, ampulla, and infundibulum.
Fecundity is a term that refers to the potential for successful reproduction.
Fertility is the ability to conceive a baby.
Fertility preservation is the use of specific medical interventions to protect the fertility of individuals whose disease or disease treatment may lead to infertility.
Fertilization is the event that occurs when a sperm and an egg unite to produce a zygote. During normal fertilization, the haploid male and female gametes fuse to produce a diploid zygote.
A fertilization membrane is a membrane that forms around the egg after fertilization in order to prevent polyspermy.
A fetal membrane is the tissue surrounding the fetus that works to protect, nourish, and assist in the excretion and respiration of the developing fetus. The fetal membranes include the chorion, amnion, and allantois. Healthy fetal membranes are required for favorable pregnancy outcomes.
The fetal origins of adult disease (FOAD), also known as Barker's hypothesis, claims that fetal stresses encountered during gestation can ultimately lead to adult diseases, such as hypertension, heart disease, stroke, and diabetes. Twenty years ago, a professor in the United Kingdom, Dr. David Barker of the University of Southampton, showed that low birth weight is a risk factor that may later contribute to the development of coronary heart disease. This is a problem both in the Western and in the developing world. In the Western world, expectant mothers often do not nourish themselves with the correct balance of vitamins and nutrients, and they may even be underweight or overweight due to this problem. This can cause their child to be born with a low birth weight. In the developing world, chronic malnutrition is still a significant problem, and this is often due to a lack of resources available for expectant mothers in these countries. In 1995, the British Medical Journal named this theory “Barker's hypothesis.”
In humans, the term fetus is used to describe a developing organism that has reached the eighth week of developmental age (following fertilization).
A fibroid, also known as a uterine leiomyoma, is a benign (non-cancerous) tumor of the uterus. Fibroids are fairly common, occurring in 20-40% of women. They are typically asymptomatic but can result in painful intercourse, heavy menstruation, frequent urination, and, rarely, infertility.
Fimbria is a fringe or fingerlike structure located at the ends of fallopian tubes. Fimbriae facilitate egg movement through the fallopian tubes.
Fixation is the process of preserving tissue through chemical means to retain its structure.
Folic acid is a B vitamin that is important for women to take before becoming pregnant and in the early weeks after fertilization occurs. 400 micrograms of folic acid a day is proven to help prevent neural tube defects (NTDs), which are brain defects of the spinal cord and brain that occur in the first trimester of development.
The follicle is the basic functional unit of the ovary.
Follicle stimulating hormone (FSH) is a hormone made by the pituitary gland that affects the gonads (female ovaries and males testes). In females, it stimulates growth of the ovarian follicles.
A follicle that has progressed from the primary to the secondary, more mature stage of growth will display an accumulation of follicular fluid known as the follicular antrum.
Follicular fluid is a liquid component present inside the antrum of a mature follicle, surrounding the oocyte. The follicular fluid contains hyaluronic acid.
The follicular phase is the portion of the menstrual cycle in which the ovarian follicle develops and matures. This half of the menstrual cycle begins on the first day of menses and ends with ovulation. The follicular phase is characterized by a gradual rise in the steroid hormone, estrogen.
Folliculogenesis is the process of ovarian follicle development. In order to reach the ovulatory stage, an ovarian follicle will pass through the following stages: primordial (resting), primary, secondary (pre-antral), tertiary (antral), and, finally, the pre-ovulatory (Graafian) follicle stage. According to dogma in the field, in females, the peak number of ovarian follicles occurs in the fetus at mid-gestation and is approximately seven million. This number then declines to two million at birth, half a million at puberty, 25 thousand at the age of 37 years, and less than one thousand at menopause. This progressive decline in follicle count with age is due to a natural breakdown process called follicular atresia that affects 99.9% of all follicles.
Follistatin is a protein that binds to the hormone activin. It is produced in the ovary and pituitary gland and is one of several proteins that regulate FSH secretion by controlling the activating hormone, activin.
Follitropin alpha is an endogenous form of FSH that is often used in women undergoing IVF.
A gamete is a reproductive cell that exists in both males and females and is haploid in its mature form. The egg (ovum) is the female gamete, and the sperm is the male gamete. Fertilization occurs when the male and female gametes unite to form a zygote.
Gamete intrafallopian tube transfer (GIFT) is an assisted reproductive technology. First, eggs are removed from the woman’s ovary, and a sperm sample is collected from the man. Then, the two are delivered via catheter to the woman’s fallopian tube, where fertilization will hopefully take place. This differs from IVF, in that the fertilization occurs in the woman’s body as opposed to inside a petri dish.
Gametogenesis is the combination of all the processes needed to make gametes (or sex cells, the egg and the sperm). Gametogenesis refers to spermatogenesis in the male and oogenesis in the female. During gametogenesis, diploid precursor cells go thorough meiosis to produce haploid cells, and these haploid cells go through processes of differentiation to form mature gametes capable of undergoing fertilization.
The gastrula is an early post-implantation embryo that develops from the blastula. It consists of three layers of cells: the ectoderm, mesoderm, and endoderm. The process of differentiation into three germ layers is called gastrulation.
In vertebrates, gastrulation is a major morphogenetic event that results in organization of the overall body plan and generation of the primary germ layers.
Gelation is the transition of a liquid to a solid-like gel. Gelation occurs when a solution of dilute polymers is cross-linked into a network.
Gender refers to the socially constructed concepts of women and men based on appearances, actions, thoughts, and behaviors. Gender does not necessarily refer to biological differences, such as genitalia present at birth or chromosomal differences, and it can vary depending on specific sociocultural expectations of women and men.
Proteins are the functional units in cells that are encoded within defined regions of DNA. These regions are called genes, and genes are inherited from parents. Humans contain ~20,000 protein-coding genes. Collectively, all the genes in an organism are referred to as a genome.
A technique that manipulates one of an organism's genes to understand its function, either by deletion (gene knockout: abbreviation KO) or insertion (gene knockin: abbreviation KI). Gene knockout/knockin is induced by a Cre-LoxP system that deletes or inserts genes of interest. Double knockout (abbreviation DKO) is the deletion of two genes simultaneously.
A germ cell is a reproductive, haploid cell (in humans, a germ cell - either an egg or sperm cell - has 23 chromosomes).
In gametogenesis, a germ cell nest is a collection of immature primordial follicles connected by intercellular bridges due to incomplete cytokinesis thus far in the process. It is thought that this early connection is important in avoiding the production of defective germ cells.
The germinal vesicle is the nucleus of an oocyte that is arrested in prophase of meiosis I. The nuclear envelope of the germinal vesicle will break down in a process known as germinal vesicle break down (GVBD) when the oocyte resumes meiosis in response to the luteinizing hormone (LH) surge that occurs prior to ovulation.
Germinal vesicle breakdown (GVB) refers to the dissolution of the nucleus of an oocyte that is arrested in prophase of meiosis I (the breakdown of the germinal vesicle). In this stage, the oocyte resumes meiosis in response to the luteinizing hormone (LH) surge that occurs prior to ovulation. The oocyte will arrest in meiosis II at the metaphase (MII) stage, where it stays until fertilized by sperm.
The gestation period refers to the length of time between conception and birth (in humans, this is 266 days, which is just short of nine months). The gestation period varies among different species.
A gestational carrier, also referred to as a gestational surrogate, is a woman who agrees to carry and give birth to a child for another woman or couple who may be infertile. Gestational carriers use a fertilized embryo created using in vitro fertilization that is then surgically placed into their uterus. In order to prepare the uterus for conception and to carry the fetus to term, gestational carriers will need to take hormones. They are expected to surrender the infant to the genetic parents upon birth. The gestational carrier has no biological relationship to the embryo she is carrying. Gestational carriers differ from a traditional surrogate, as a surrogate, along with giving birth, provides the egg for fertilization. Several legal issues are related to gestational surrogacy and are typically addressed in advance of an arrangement. These legal issues vary from state to state.
The glans penis refers to the tip of the male penis, often known as the “head.” In uncircumcised males, the glans penis is covered by prepuce (foreskin) when the penis is not erect.
A gonad is a reproductive gland that produces ova (eggs) in females and sperm in males. Female gonads are ovaries, whereas male gonads are testes (testicles). Both organs also produce hormones.
Gonadotoxicity is the temporary or permanent damage to ovaries or testes after exposure to certain substances or drugs. Aggressive chemotherapy and radiotherapy used for the treatment of some cancers and autoimmune diseases are the most common causes of gonadotoxicity and subsequent infertility.
Gonadotropes are specialized cells of the anterior pituitary gland that produce the gonadotropins, FSH and LH.
Gonadotrophin releasing hormone (GnRH) is a hormone secreted in pulses by the hypothalamus, which stimulates the synthesis of gonadotrophins by the pituitary gland. Gonadotrophins are essential for the development of ovarian follicles (FSH) and for ovulation (LH).
Gonadotropins are protein hormones, the most principal of these being LH and FSH, secreted by the anterior pituitary gland.
Granulosa cells are somatic cells that surround the oocyte, providing it with the physical support and nutrients needed for proper oocyte development.
Growth hormone (GH) is a hormone produced by somatotropes and acts on the liver and adipose tissue to control growth, and the metabolism of lipids, proteins, and carbohydrates.
A gynecologist is a physician who focuses on the health care of women and, in particular, the female reproductive system.
Haploid is the designation given to a cell with a single set of chromosomes, characteristic of gametes. In humans, a single set is 23 chromosomes.
Hematoxylin and eosin (H&E) staining refers to the process in which hematoxylin and eosin reagents are used to visualize the morphology of tissue within sections. Hematoxylin commonly stains nuclei of cells blue while eosin acts as a counterstain, which will color other structures pink/red.
Histology is the study of cells and tissues at the microscopic level. It is a branch of anatomy dealing with tissue structure.
A histone is a protein located in the nucleus of eukaryotic cells that organizes DNA into compact structures.
Histotroph is the complex mixture of molecules secreted into or transported into the uterine lumen. Histotroph includes nutrient transport proteins, ions, mitogens, cytokines, lymphokines, enzymes, hormones, growth factors, proteases and their inhibitors, amino acids, glucose, fructose, vitamins, and other substances. Histotroph is a primary source of nutrition for mammalian conceptus development. In humans, its importance continues throughout the first trimester of pregnancy until hematotrophic nutrition is established.
The term homologous refers to chromosomes that have the same pattern of genes.
Hormonal contraception or hormonal birth control refers to any medication or medical preparation that contains either estrogen or progesterone or a combination of the two hormones that a woman takes in order to prevent a pregnancy from occurring. Hormonal birth control is often prescribed to treat other medical conditions, as well, such as acne, heavy periods, and relief for the symptoms of PCOS, endometriosis, etc. Hormonal contraception may be taken orally, implanted, injected, absorbed via a patch on the skin’s surface, or placed inside the vagina. Hormonal contraception acts by either preventing the ovulation of a matured egg from the ovary each month, by making the cervix more difficult for the sperm to pass through, or by making the lining of the uterus less capable of supporting the implantation of an embryo.
A hormone is a molecule synthesized by specialized cells in an organ that travels through the blood stream and affects other cells in the body.
Hormone (or endocrine) disruptors are substances that interfere with the proper functioning of the endocrine system (i.e., the production, release, transport, and regulation of hormones in the body). Classes of endocrine disruptors include synthetic chemicals found in the environment, plastics, pesticides, and various pollutants. Exposure to such substances has been linked to various pathologies in both animals and humans.
Hormone replacement therapy (HRT) is a medical treatment used to lessen the symptoms of menopause, such as hot flashes, night sweats, and vaginal dryness. Doctors may prescribe pills, creams, or skin patches containing the hormones estrogen or progesterone (alone or in combination) to mimic naturally-occurring levels of hormones produced by the ovaries prior to the onset of menopause.
Hormone therapy is a medical treatment for cancer. Because certain cancers are hormonally responsive, especially those involving the reproductive system, the goal of hormone therapy is to suppress tumor growth and spread by altering hormone production and activity in the body.
Hot flashes (or flushes) are common symptoms of menopause characterized by a sense of significantly increased bodily temperature, rapid heart rate, perspiration, and a flushed appearance of the face. Hot flashes occur with great frequency in the early stages of menopause, from a few times per week to multiple times per day. Though most menopausal women experience hot flashes to some degree, it is possible to go through menopause without ever experiencing a hot flash.
Human chorionic gonadotropin (hCG) is a protein hormone produced by a developing embryo which stimulates progesterone production essential for the maintenance of pregnancy. It can be detected in maternal blood as early as 10 days after fertilization occurs. It is often used as a biomarker to detect pregnancy.
Hydrocephaly refers to a build-up of cerebrospinal fluid in the brain. This is dangerous, as the excess fluid increases pressure and can compress and permanently damage the brain. Hydrocephaly usually accompanies spina bifida and is often a result of obstructed flow of cerebrospinal fluid in the ventricular system before birth.
A hydrogel is a polymer network that is highly swollen with water and has a solid-like structure.
The hymen is a ring of tissue on the rim of the vaginal opening. This tissue can be torn during sexual intercourse or other means of penetration, such as tampon use during menstruation.
Hyperovulation in humans refers to the production and release of more than one egg during a menstrual cycle. Hyperovulation can occur naturally or be stimulated via hormone treatments for the purposes of egg donation in third-party reproduction. Under normal conditions, when more than one egg is released, the chances of conceiving fraternal twins or triplets is increased. Stimulated hyperovulation involves several drugs and the careful monitoring of hormone levels and ovarian status using an ultrasound. Once mature, follicles are punctured during the egg retrieval procedure and evaluated for quality before being used for in vitro fertilization (IVF).
Hyperplasia is an increase in cell number in an organ or tissue, which could be an indication of abnormal or precancerous changes.
Hyperploidy is a state in which cells contain one or more extra chromosomes. Humans normally have 46 chromosomes per cell, but if a human has 47 or more chromosomes per cell, then that person is hyperploid. Trisomy 21 (commonly called Down Syndrome) is one example of hyperploidy because there are three copies of chromosome 21.
Hypoblast is the underside of the embryonic disk, which arose from the inner cell mass during the late blastula and early trophoblast stages of embryonic growth. These cells give rise to the yolk sac, the extra-embryonic tissue that will help support embryonic growth.
Hypogonadism is a condition of insufficient function of the gonads. The gonads produce gametes and sex hormones. In females, the ovaries produce ova (eggs), estrogens, and progestins; in males, the testes produce sperm and androgens. Sexual development and fertility may be impaired in hypogonadal individuals.
Hypoploidy is a state in which cells contain one or more fewer chromosomes than what is normal. Humans normally have 46 chromosomes per cell, but if a human has 45 or less chromosomes per cell, that person is hypoploid. One example of a hypoploid human disorder is Turner syndrome, where females have only one copy of the X sex chromosome.
The hypothalamus synthesizes and releases GnRH and is the portion of the brain that links the endocrine system to the nervous system. The release of GnRH stimulates the synthesis of gonadotrophins (LH and FSH) by the pituitary gland.
A hysterectomy is the surgical removal of a woman’s uterus.
Implantation refers to the process that occurs when a blastocyst attaches to the uterine wall. The optimal implantation site is at the top of the uterus, in humans. If implantation occurs outside of the uterus, it is called an ectopic pregnancy and is not usually viable.
Imprinting is a mechanism that involves the placement of methyl groups onto DNA to prevent expression of one copy of a gene, either from the mother or from the father. Syndromes such as Beckwith-Wiedemann, Silver-Russell, Angelman, and Prader-Willi are associated with errors in imprinting.
in situ is a term used as an intermediate between in vivo and in vitro. For example, examining cells within an organ removed from the body would be an in situ experiment, as the organ has been removed from its native environment (the body), but the cells are being studied in the context of their usual place within the organ.
in vitro refers to occurrences outside of a living organism. An in vitro experiment is one that is completed outside of a living organism, in an artificial environment.
in vitro fertilization (IVF) is an assisted reproductive technology procedure in which eggs are combined with sperm outside of the body, so that fertilization can occur. The embryos that are created can then be implanted back into a woman’s uterus or frozen (cryopreserved) for future use.
in vivo refers to occurrences inside of a living organism. An in vivo experiment is one that is completed inside of a living organism.
Incontinence is the inability to control urination or defecation.
Induced menopause is menopause caused earlier than expected due to the use of prescription drugs, treatments, or surgical removal of the ovaries. It is a common cause of concern among women facing a cancer diagnosis, as the life-saving treatments used to fight cancer, such as radiation and chemotherapy, can also lead to premature menopause.
Infertility is the inability to become pregnant after one full year of trying to conceive a child (or six months, if a woman is 35 years of age or older).
The fallopian tube is comprised of three sections. The infundibulum is the distal end of the tube closest to the ovary. It has finger-like projections called fimbrae that sweep the oocyte, which is released from the ovary after ovulation, to guide it into the fallopian tube.
Inhibin is a protein hormone made by the female ovaries and male testes and provides feedback messages to the anterior pituitary regarding the status of the reproductive tissues. In females, inhibin rises during follicle development and falls once a mature egg is released from the ovary. Inhibin blocks the hormone activin, and the loss of this hormone results in infertility or sterility.
The inner cell mass (ICM) is the part of the blastocyst that is fated to become the embryo, amnion, and yolk sac. In contrast, the trophectoderm cells of the blastocyst will contribute to extra-embryonic tissues, such as the placenta and umbilical cord. Cells of the ICM are pluripotent, meaning they can give rise to all the cell lineages (ectoderm, endoderm, and mesoderm) found in the body. The ICM is, thus, a source of embryonic stem cells.
Intracytoplasmic sperm injection (ICSI) is an ART procedure in which a single sperm is microinjected directly into an egg to achieve fertilization. This procedure is primarily used in situations where the male patient has very few sperm.
The term intrauterine refers to occurrences within the uterus. However, since the uterus has a cavity that is accessible through the cervix, the term is often used to mean "within the uterine cavity." Thus, intrauterine development refers to development of the embryo within the uterus (both before and after implantation), while an intrauterine device (IUD) is a contraceptive device inserted into the uterine cavity.
The Intrauterine Device (IUD) is a T-shaped device implanted into the uterus for the purpose of contraception by preventing sperm from reaching the egg. There are four different IUDs available in the United States. Three of them, Liletta, Mirena, and Skyla, release a small amount of progestin similarly to a birth control pill, which usually makes periods lighter. One of them, ParaGard, also known as ‘the copper T IUD’, is hormone free and lasts longer than the hormonal options, but can cause heavier periods. IUDs are more than 99% effective, but they do not prevent against STIs.
Intrauterine growth retardation (or restriction) (IUGR) is the term applied to the condition resulting in a baby that is born of low birth weight (<10th percentile). It generally results from insufficient placental support.
Intrauterine insemination (IUI) refers to the transfer of "washed" semen or sperm directly into the uterine cavity though a catheter. By bypassing the mucosal surface of the cervix, which acts as a barrier, it increases the chance of sperm reaching the uterine cavity and tubes. Intrauterine insemination is most often used when the male has reduced sperm count or motility.
The fallopian tube is comprised of three parts. The isthmus is the thick-walled portion of the fallopian tube that enters the body of the uterus at the cornua.
A karyotype refers to the number and appearance (including physical structure, size, and banding pattern) of chromosomes in a cell. To generate a karyotype, metaphase chromosomes are obtained from a population of dividing cells from virtually any cell or tissue (blood, amniotic fluid, blastomere, etc). These chromosomes are spread onto a glass slide and stained with a dye specific for DNA that produces a characteristic banding pattern. The chromosomes are then imaged with a microscope and with the assistance of computer programs, chromosome pairs are identified and arranged in descending order of size. Finally, the banding patterns of each chromosome are analyzed. This assists in the detection of genetic anomalies including chromosome structure defects or various aneuploidies. For example, Trisomy 21 also commonly known as Down’s Syndrome, would be evident on a karyotype as three copies of chromosome 21 instead of only two that would be present in a euploid autosome or somatic cell.
The labia majora is a part of the vulva (the external portion of the female genital organs) and includes the two outermost folds of skin. The skin over the labia majora contains hair and surrounds the clitoris, urethra, and vaginal opening.
The labia minora is a part of the vulva (the external portion of the female genital organs) and includes the two innermost folds of skin between the labia majora. The skin over the labia minora does not contain hair and surrounds the clitoris, urethra, and vaginal opening.
Lactation is the process of milk secretion that occurs in female mammals in order to provide nourishment and immune protection for offspring. Lactation is dictated by the production and release of specific hormones designed to develop the ductal system of the breasts, which begins around the second trimester of pregnancy.
Lactotropes are specialized cells in the anterior pituitary gland that produce the hormone prolactin.
Lanugo is a soft downy hair that grows on the fetus as a normal part of gestation. Lanugo appears by about the fifth month of gestation and is shed at around 33-36 weeks of gestational age. Although lanugo can be seen on the shoulders of a newborn, more extensive presence on a newborn is a sign of premature birth. Most lanugo still present on newborns, commonly referred to as “peach fuzz,” is shed within a couple weeks after birth.
Laparoscopy is a key-hole surgical procedure that allows surgeons to see inside the abdomen. This type of surgery is very useful for viewing the female reproductive organs (uterus, ovaries, etc.). It normally requires a general anesthetic, but patients can often go home the same day as surgery.
Also known as Gregor Mendel’s third law, this law states that one allele is always dominant over the other and is expressed, unless both alleles are recessive, and therefore, both expressed.
Also known as Gregor Mendel’s second law, this law states that any given two traits are inherited independently of one another, and the probability that they are both inherited is left to chance.
Also known as Gregor Mendel’s first law, this law states that during the production of gametes, genes are separated, so that the offspring will inherit one from each parent.
Leydig cells are cells within the male testes that produce the hormone testosterone in response to the release of luteinizing hormone (LH) from the pituitary gland. Leydig cells are found within the interstitial space of the testes between the seminiferous tubules.
The LH surge occurs at the halfway point of the menstrual cycle (usually between days 12 and 16) and induces ovulation and formation of the corpus luteum. It is accompanied by a smaller FSH surge. A woman trying to conceive can use a kit to detect the point of the LH surge, where 24-36 hours after a positive result is usually the optimal time for intercourse.
Libido is a term for sexual desire or the degree of sexual appetite and is the psychological and emotional energy attached to one’s sex drive. Low libido is associated with a decreased desire to have sexual intercourse.
The limbic system is comprised of a set of structures located in the brain involved in the control of emotion, behavior, and memory.
Lobular is a term used to describe lobules or glands found in breast tissue that produce milk. Lobular is a descriptor of abnormal breast cell growth that begins in the lobules, e.g. lobular carcinoma and lobular neoplasia.
The luteal phase is the portion of the menstrual cycle in which the corpus luteum forms and matures. This half of the menstrual cycle begins with ovulation and ends when menstruation begins. The luteal phase is characterized by a gradual rise in the steroid hormone progesterone.
Luteinization is the set of processes by which differentiation of the theca cells and granulosa cells of the post-ovulatory ovarian follicle results in the formation of a corpus luteum.
Luteinizing hormone (LH) is a hormone released by the pituitary gland that regulates a female’s menstrual cycle and ovulation. LH also plays an important role in a male’s sperm production, as it stimulates the production of male sex hormones.
The mammary gland is an organ unique to mammals that produces milk for feeding their offspring. In humans, the mammary glands are also called breasts.
The maternal to zygotic transition occurs in the zygote during the first days after fertilization but before implantation into the uterine wall. Prior to this transition, all messenger RNAs are supplied from the egg that came from the mother. After the transition, maternal messages are destroyed, and new messages from the zygote are generated.
Meiosis is a type of cell division that produces gametes (sperm and egg cells). Unlike regular somatic cells, which contain 46 chromosomes, gametes contain only 23 chromosomes.
Melatonin is a chemical found in the human body and is part of the biological machinery that regulates the sleep-wake cycle of an individual over the course of a day. It is also found in other living species, including animals, plants, and microorganisms. In humans, high levels of melatonin are secreted by the pineal gland at night, which causes drowsiness. Medications containing melatonin have been used to treat jet lag and insomnia, although efficacy is still debatable.
Menarche is a woman’s first menstruation and occurs at an average age of 13 in the United States.
Menopause is the phase that marks the end of a woman’s reproductive cycle and occurs at an average age of 52 in the United States. Menstrual cycles permanently cease to occur, and ovarian follicles no longer mature. Clinically, menopause is marked by high levels of the hormone FSH and is associated with hot flashes, osteoporosis, and heart disease.
Menorrhagia refers to abnormally heavy bleeding and/or cramping during the menstrual period.
Menses is the period of time in which female menstruation occurs.
The menstrual cycle is the recurring cycle of physiological changes that occur in females and other primates of reproductive age. The menstrual cycle results from the coordinated actions of hormones made by the brain and pituitary gland acting on the ovaries and uterus in order to coordinate ovulation and fertilization. Hormones like FSH, LH, and activin made in the pituitary gland respond to and control the release of estrogen, progesterone, and inhibin by the ovary. These hormones then control and prepare the uterus for an egg, if fertilized. If the egg that is released each month is not fertilized, the uterine wall is shed. The shedding of the uterine wall is known as menstruation and is the more obvious external evidence of a functional reproductive cycle.
Menstruation is bleeding that occurs when the endometrial lining is shed from the uterus.
Mesoderm is the layer of cells in a eukaryote that lies between the ectoderm and the endoderm. It is also the layer of cells that lies between the ectoderm and the endoderm in the developing embryo once it has reached the gastrula stage. This cell layer ultimately gives rise to the muscles, cartilage, bones, blood, and lymph, forming tissues and vessels, spleen, kidney, gonads, genital tract, linings of the body cavities, and adrenal cortex.
Metaphase is the stage of cell division during which chromosomes are aligned at the equator of the spindle. The cell is stalled in this stage until all chromosomes are properly aligned. This is known as the metaphase to anaphase checkpoint. Mistakes in aligning the chromosomes (e.g. lagging chromosomes) or in the metaphase to anaphase checkpoint can result in aneuploidy.
A microtome is a machine designed for cutting uniform and often very thin sections of tissue following fixation and embedding. These thin sections obtained from the microtome can be used for downstream applications, such as hematoxylin and eosin staining.
The sperm mid-piece is the part of the sperm tail closest to the head where the mitochondria are located. The mitochondria provide the sperm with energy as they travel through the female reproductive tract.
A miscarriage is a spontaneous termination or abortion of pregnancy prior to 20 weeks of fetal development. Miscarriages are the most common complication during the first trimester, and they can occur due to hormonal, genetic, uterine, or reproductive abnormalities.
Mitochondria are organelles responsible for producing ATP, which is the cellular energy source. Additionally, they can synthesize steroids. Mitochondria are considered to be a semi-autonomous organelle because they replicate by self-division, have their own protein synthesis machinery, and have their own genome. Unlike the genome of the cell, which is inherited maternally and paternally, the mitochondrial genome is inherited only from the mother through mitochondria present in the egg at fertilization.
Mitosis is the process of cell division in which daughter cells receive the exact chromosomal and genetic makeup of the parent cell. This occurs during growth and repair.
Monosomy is a form of aneuploidy and occurs when only one chromosome in a pair is present. All instances of monosomy are lethal except for Turner Syndrome.
Mons pubis is the tissue that covers a woman’s pubic area. The skin covering the mons pubis contains hair and lies between the abdominal wall and labia majora.
Morphology refers to the shape and structure of a cell, tissue, organ, or organism.
The morula is an embryonic mass of blastomeres formed at the early stages of embryonic development before formation of the blastula and resulting from cleavage of the zygote.
Mosaicism exists when cells undergo changes during development such that one group of cells differs from a neighboring group. It can occur in both somatic and germ cells. Mosaicism can be caused by spontaneous DNA mutations (in either nuclear or mitochondrial DNA), spontaneous reversion of an existing DNA mutation, epigenetic changes in chromosomal DNA, and chromosomal abnormalities. Symptoms that occur as a result of mosaicism depends on the extent of the mosaic cell population. Mosaicism is important in terms of human disease. It also provides variations at the molecular level among humans, including between identical twins.
mRNA, also known as messenger RNA, is transported from the DNA in the nucleus to the ribosome in the cytoplasm containing the genetic code. It will be translated into its corresponding amino acid sequence at the ribosome.
A mucus plug is present during pregnancy and is located at the cervix to block bacteria from passing into the uterus.
The Müllerian ducts are paired, mesodermal ducts present in the early embryo that will develop into the fallopian tubes, uterus, cervix, and upper vagina in females. In males, they are lost during the early stages of development.
Mutagenesis is the process by which genetic mutations occur.
A mutation is a change in the DNA sequence that can alter amount, structure, or function of a protein. Mutations can arise spontaneously, be inherited from a parent, or be chemically induced.
The myometrium is the middle layer of the uterine wall, consisting mostly of smooth muscle cells, with some vascular and stromal tissue. The myometrium contracts during menses and labor.
A negative feedback system is any circuit that leads to the suppression of one of its components or of the global state. In many systems, negative feedback serves an adaptive advantage to achieve balance/homeostasis. Some examples of negative feedback systems in the human body are temperature and blood sugar regulation.
Neo-oogenesis is the production of new oocytes throughout the lifetime of an organism. Neo-oogenesis commonly occurs in lower vertebrates (amphibians and reptiles), but is thought not to occur in higher vertebrates, especially mammals.
The term neonatal refers to the period of time from birth to 28 days of life.
Neural tube defects (NTDs) are birth defects of the brain, spine, and spinal cord that usually occur during the first month or trimester of pregnancy, often before a woman realizes she is pregnant. This is why women of childbearing age are advised to take a multivitamin with 400 micrograms of folic acid a day, as this is proven to help prevent NTDs.
Night sweats are episodes of excessive nighttime perspiration that can interfere with sleep.
An obstetrician is a physician who focuses on the branch of medicine associated with pregnancy and childbirth.
Oligospermia is the medical term for a condition in which low numbers of sperm are present in the semen or ejaculate. Genetic, idiopathic, and iatrogenic factors can result in oligospermia. This condition often results in infertility, which can sometimes be overcome through the use of assisted reproductive technology.
Oncofertility is a new discipline that bridges oncology and reproductive medicine in order to discover and apply new fertility preservation options for young patients facing fertility-threatening diseases or treatments.
An oncologist is a physician whose focus is cancer diagnosis and treatment.
Oncology is the field of medicine that focuses on cancer.
An oocyte is a female germ cell that is not yet ready for fertilization. The oocyte matures into an ovum (egg) that will be released during ovulation.
Oogenesis is the production of oocytes, the female gamete. It is the female form of gametogenesis. Oogenesis begins early in development with the migration of primordial germ cells to the gonads. Oogenesis is unique in that it is halted midway through the process and does not resume until fertilization occurs.
Female germ cells with diploid and stem cell characteristics that can self-proliferate and differentiate (in invertebrate and some lower vertebrate species). OSCs produce new female oocytes through oogenesis during the life-cyle of reproduction. In mammals, the existence of OSCs has been debated.
An oophorectomy is the surgical removal of one or both of a woman’s ovaries.
Oophoropexy or ovarian transposition is a surgical procedure in which one ovary or both ovaries are either suspended (disconnected from the uterus) or undergo fixation, a procedure in which the ovary is elevated and fixed to the abdominal wall. Patients requiring radiation therapy may undergo oophoropexy via laparoscopy prior to the first radiation treatment, where their ovaries are repositioned in the abdominal cavity away from the radiation field, reducing exposure to radiation.
An orgasm refers to the peak of physical response to sexual stimulation characterized most often by intense pleasure, involuntary muscular contractions of the lower pelvic region, and ejaculation (possible for both men and women). Orgasms are controlled by the limbic system, a set of structures in the brain, including the hypothalamus, which plays a role in sexual response.
An osteoclast is a large, multinucleate cell that exists in growing bone and breaks down bony tissue.
Osteopenia is a condition in which the bone mineral density is low when compared to normal levels but not low enough to qualify as osteoporosis.
Osteoporosis is a loss of bone density that can result in increased risk of fractures and structural body deformities. It is defined as a bone mineral density greater than 2.5 standard deviations below the mean bone mineral density of young, healthy adults. Because estrogen is important in the maintenance and remodeling of bone, post-menopausal women naturally lose bone density with age and are at increased risk of osteoporosis.
Ovarian cancer is a cancer of the ovaries, the female reproductive organs that produce eggs and release hormones.
The ovarian cortex is the outer layer of the ovary consisting of stroma, located just inside the tunica albuginea. The ovarian follicles are contained in the cortex.
The ovarian follicle is the functional unit of the ovary composed of an oocyte surrounded by companion somatic cells, including granulosa cells and theca cells. The somatic cell component of the follicle produces hormones important for oocyte development and proper endocrine function. Communication between the granulosa cells and the oocyte, which are mediated by transzonal projections, is essential for proper oocyte growth during oogenesis. The fully-grown oocyte is released from the follicle in response to hormonal cues at the time of ovulation.
Ovarian hyperstimulation is an assisted reproductive technology in which fertility medications are used to induce the ovaries to grow multiple follicles and eggs in a single cycle. In addition to the woman having more eggs released than normal (usually one egg per menstrual cycle), she experiences much higher hormone levels, particularly estrogen released from the growing follicles. In some cases, the supraphysiologic levels of hormones may trigger an exaggerated response, resulting in ovarian hyperstimulation syndrome. The syndrome has a broad spectrum of clinical features ranging from a mild illness needing only close observation to a severe illness with cardiovascular collapse requiring hospitalization and intensive care treatment.
Ovarian protection methods are various surgical and non-surgical methods used to reduce the risk of ovarian damage during chemotherapy and radiotherapy. Surgical protection is a prophylactic transposition of the ovaries away from the field of pelvic irradiation (oophoropexy), while non-surgical protection includes pelvic shielding and the use of GnRH analogues and fractionated doses of chemotherapy and radiotherapy.
The ovarian reserve refers to the fixed number of primordial follicles that is established prior to birth in humans. In the absence of neo-oogenesis, the ovarian reserve dictates a female’s reproductive lifespan. Factors, including various chemotherapeutics, which deplete the ovarian reserve can result in premature ovarian failure and the early onset of menopause.
Ovarian tissue banking is the process in which one entire ovary (or part of an ovary) is removed surgically, and the outer surface (cortex), which contains the eggs, is frozen in strips for later use. Women who are survivors of some types of cancer can have pieces of the tissue thawed and transplanted back into the body. A number of pregnancies have resulted from using this technique. Transplantation is not always safe following some types of cancer (e.g. leukemia) because of the risk of re-seeding the original cancer. The Oncofertility Consortium® is actively researching new ways to use this tissue. New techniques are still experimental but may be the best option for women who must begin their treatments immediately.
Ovarian transposition is the process by which surgeons move the ovaries away from the area receiving radiation therapy. The goal of the surgery is to move the ovaries within the pelvis where they can still function but will be out of the way of harmful radiation. This technique will not protect against the effects of chemotherapy.
The ovary is one of two female reproductive organs that produce eggs and release hormones, like estrogen.
The oviduct is a structure that leads from the ovaries to either the uterus or outside the body, depending on the species. In mice, eggs are ovulated from the ovary into the oviduct where fertilization occurs. The fallopian tubes are analogous to the oviducts in humans.
Ovulation is the process in which an ovarian follicle bursts, and the mature egg is released from the ovary into the fallopian tube. Ovulation usually occurs halfway though a woman’s menstrual cycle and marks the transition between the follicular and luteal phases.
The ovum, also known as the egg, is the female reproductive cell or gamete. Eggs are arrested at metaphase of meiosis II, and following ovulation, they can be fertilized in the presence of sperm. In addition to containing DNA, the egg contains critical stores of maternal mRNAs and proteins that will support fertilization and subsequent embryo development.
A Pap smear is a method to screen for cervical cancer. Squamous cells (flat, scale-like cells) are obtained from the outer surface of the cervix as well as columnar cells (tall, thin cells) from the inner canal leading to the uterus. The junction where these two cell types meet is called the transformation zone and is where most cell abnormalities are found.
Parthenotes are the products of parthenogenesis, the process in which eggs become activated to begin dividing without fertilization. Parthenotes contain genetic material from only the maternal source. In contrast, embryos are created through fertilization and contain genetic material from two genetically distinct cells. No viable human parthenote has been reported.
With regard to oncofertility, the patient navigator is a medical professional that provides female and male cancer patients with information about their fertility preservation options and helps to coordinate their care.
The pelvis is the basin-shaped structure of the vertebrate skeleton that supports the upper torso and spine and protects the rectum, bladder, and reproductive organs.
The penis is the external male sex organ. It functions in urine output and is also responsible for the delivery of sperm to the female tract during sexual intercourse.
Perimenopause, also called the "menopausal transition," is the time frame in which a woman's body shifts from regular cycles of ovulation and menstruation to menopausal symptoms, including hot flashes, vaginal dryness, night sweats, absence of menstruation, and permanent infertility. This period typically begins when women reach their 40s, though symptoms can be detected earlier.
Perinatal refers to the period around the time of birth – either directly before or after.
In females, the perineum is the area between the vagina and anus, and in males, it is the area between the scrotum and anus. The perineum is considered to be an erogenous zone in both sexes, and the female perineum is highly susceptible to damage during childbirth.
A pharmacological chaperone (or pharmacoperone from "protein chaperone") is a small molecule that enters cells and serves as a molecular scaffolding in order to cause otherwise-misfolded mutant proteins to fold and route correctly within the cell. Mutation of proteins often causes molecular misfolding, which results in protein misrouting within the cell. Accordingly, mutant molecules may retain proper function but end up in parts of the cell where the function is inappropriate, or even deleterious, to cell function. Misfolded proteins are usually recognized by the quality-control system of the cell and retained (and often destroyed or recycled) in the endoplasmic reticulum. Pharmacoperones correct the folding of misfolded proteins, allowing them to pass through the cell's quality-control system and become correctly routed. Since mutations often cause disease by causing misfolding and misrouting, pharmacoperones are potentially therapeutic agents, since they are able to correct this defect.
Ref.: Conn, P.M. and Janovick, J.A., A New Understanding of Protein Mutation Unfolds, American Scientist 93:314-321, 2005.
The pituitary gland is a very small organ, located at the base of the brain, which produces and releases hormones (signals) that control other organs and body processes. The pituitary gland responds to signals from the hypothalamus. The anterior pituitary gland is the front portion of the pituitary gland, and it secretes hormones that control physiological processes including growth, reproduction, and stress. The posterior pituitary gland is behind the anterior portion and secretes hormones involved with water balance and uterine contractions during labor.
The placenta is an organ that connects the fetus to a woman’s uterus during pregnancy. It functions in nutrient uptake, waste elimination, and gas exchange in supporting the growth of the fetus.
A polar body is the product of asymmetric cell division that occurs during meiosis. Both phases of meiosis produce a polar body, and the final result of completed meiosis is two polar bodies and one haploid egg. The formation of polar bodies allows the DNA content of the egg to be reduced while still maintaining critical stores of maternal components in the egg that are important for supporting future fertilization and pre-implantation embryo development.
Polycystic ovary syndrome is a common hormonal disorder that affects many women of reproductive age. The name of the disorder came from the observation that women with PCOS often have the appearance of “cysts” along the outer edge of their ovaries when viewed by ultrasound. These “cysts” correspond to immature follicles that have stopped developing due to hormonal imbalance. Polycystic ovaries develop as a consequence of excess ovarian androgen. PCOS can disrupt ovulation or stop it altogether, often leading to subfertility. Women with PCOS may experience excessive hair growth, weight gain, acne, and many other symptoms, ranging from mild to severe.
Polyhydramnios is the accumulation of excess amniotic fluid in the amniotic sac during pregnancy. This may be treated, if severe, by the withdrawal of amniotic fluid. Polyhydramnios can cause pre-term labor and various symptoms in the mother (e.g. shortness of breath).
A polymer is a large molecule composed of repeating structural units. Polymers may be natural (e.g. DNA or alginate) or be synthetic (e.g. plastics).
Polyploidy occurs when a cell or an organism has more than two sets of homologous chromosomes. This can be the result of failure to undergo nuclear division after DNA replication. Polyploidy differs from aneuploidy in that aneuploidy refers to when a cell or an organism has too few or too many chromosomes.
Polyspermy occurs when more than one sperm enters the egg during fertilization. Polyspermy results in a zygote that contains too much DNA (polyploidy) and that is often non-viable. During normal fertilization, the egg has several mechanisms to prevent this from occurring, including the block to polyspermy established by the zona pellucida.
A positive feedback mechanism is a model in which the behavior of the system grows/amplifies through self-activation.
Post-implantation refers to the time of embryo development that occurs after implantation in the uterus has occurred.
Postmenopause refers to the time period after menopause.
Postnatal refers to occurrences after giving birth.
An ovarian follicle that has no antrum during folliculogenesis. Most growing follicles at the early stages of folliculogenesis are preantral follicles. Preantral follicles consist of ocytes, granulosa cells, and theca cells, which grow and mature during folliculogenesis.
Preeclampsia is a pregnancy specific condition that usually develops in the late second or third trimester. It is marked by the onset of hypertension and excess protein in the woman’s urine. If left untreated, preeclampsia can lead to serious health complications for both the mother and fetus.
In humans, pregnancy refers to the development of offspring (either a single offspring or multiple) in the uterus of a woman in preparation for the birth of independent human life.
Preimplantation refers to the time of embryo development that occurs prior to implantation in the uterus.
Preimplantation genetic diagnosis (PGD) is an ART procedure in which genetic testing is done on biopsied cell(s) from a preimplantation-stage embryo. With this technology, only unaffected embryos are transferred back to the recipient uterus to initiate a pregnancy. PGD was originally developed to screen for single gene disorders but is currently used to detect different factors, including HLA-type, chromosome abnormalities, and aneuploidy. Genetic testing can be done on biopsies of the first or second polar bodies, a single blastomere from a cleavage-stage embryo, or several trophectoderm cells from a blastocyst.
Premature menopause is menopause that happens early, before the age of 40. It can be the result of medical treatments, genetic issues, or it can occur naturally.
Premature ovarian failure (POF) is also referred to as premature menopause or primary ovarian insufficiency, and it is characterized by the inability to ovulate and an early loss of function of the ovaries altogether due to a lack of or no follicles in the ovary in women who are under the age of 40 (prior to the typical onset of menopause). POF leads to subfertility or infertility and is also linked to osteoporosis and other autoimmune disorders. It can be a result of genetic abnormalities, removal of the ovaries, or prior radiation therapy or chemotherapy. Premature ovarian failure differs from menopause in that women with premature ovarian failure may have occasional or irregular periods and may possibly become pregnant.
Premenstrual syndrome refers to symptoms that might occur between the time of ovulation and menstrual bleeding. These symptoms can include bloating, mood swings, cramping, headaches, etc.
Prenatal refers to occurrences during pregnancy (before giving birth).
The prepuce (often referred to as "foreskin" in males and the "clitoral hood" in females) is a piece of retractable skin. In uncircumcised males, it covers and protects the glans penis when the penis is not erect. In females, it covers and protects the glans clitoris.
The primary germ layers are the ectoderm, mesoderm, and endoderm. Primordial germ cells are typically considered distinct from primary germ layers, although all are derived from the inner cell mass of the embryo.
A primary ovarian follicle is an immature follicle consisting of an oocyte surrounded by a single layer of tall, supporting granulosa cells.
The primordial follicle is the most immature stage of an ovarian follicle’s development. The primordial follicle consists of an oocyte surrounded by a single layer of flat, supporting granulosa cells.
Progesterone is a steroid hormone released by the corpus luteum and placenta that prepares the uterus to receive and support a fertilized egg. It is the predominant hormone secreted during the luteal phase of the menstrual cycle and is essential in establishing and maintaining a pregnancy.
Progestin is any natural or synthetic substance, which has some or all of the biological effects of progesterone.
Prolactin (PRL) is a hormone released by the pituitary gland. It primarily acts on the mammary gland to initiate and maintain milk production after pregnancy.
The pronucleus is the nucleus of either the sperm or the egg that develops after fertilization. Following fertilization and completion of meiosis II, the egg’s DNA will decondense, and the female pronucleus will form. Similarly, the sperm DNA will also decondense and the male pronucleus will form. In many species, the male pronucleus is larger than the female one. A diploid zygote will be produced when the haploid male and female pronuclei fuse just prior to the first mitotic division.
Prophase is a phase of cell division during which DNA is packaged and condensed into chromosomes.
The prostate gland is a large gland in the male reproductive system that sits just below the bladder. It functions in the control of urination and secretes a fluid that is a component of semen.
Prostate specific antigen (PSA) is a protein produced by the prostate which facilitates sperm motility in semen. It is used as a biomarker to detect prostate enlargement or prostate cancer.
A protein is a molecule comprised of many amino acids in a linear array; proteins accomplish the major functions that cells carry out (metabolism, production of specialized molecules, and their self-reproduction by mitosis).
Puberty is the period of human development during which young people become capable of sexual reproduction. Puberty is marked by physiological changes, such as the development of secondary sex characteristics (e.g. breast development in females and facial hair in males) and the maturation of genital organs. It generally occurs between the ages of 10 and 14 in girls and 11 and 16 in boys.
Radiation therapy is the use of high-energy, ionizing rays to harm malignant cancer cells in order to stop them from dividing and growing.
A receptor is a protein molecule on the surface or interior of a cell that allows it to recognize specific molecules like hormones, reversibly bind to them, and respond with a change in the cell or in the chemicals it produces. The receptors are involved in the first step of a cascade also involving transducers and effectors that allow cells to capture, translate, and respond to chemical signals from within the body or from the environment.
Recombination is the exchange of genes between chromosomes (typically by crossing-over) that occurs during the production of gametes and results in a unique combination of genetic material. Recombination allows for the introduction of genetic variation and is a key aspect of sexual reproduction.
The rectum is the final portion of the large intestine, measuring approximately 12 centimeters in length. It is the temporary storage site for feces before defecation.
A regimen is a plan of health maintenance, often with respect to diet, therapy, and/or general prescribed treatment.
Relaxin is a protein hormone produced by the corpus luteum of the ovary, as well as other male and female reproductive organs. It is thought to play important roles in preparing the reproductive tract for birth and the changes that occur in the mother's cardiovascular system during pregnancy. Loss of relaxin in pregnant female mice results in an inability to feed their newborn pups due to impaired nipple development.
Sexual reproduction refers to the creation of new offspring by parents, while asexual reproduction occurs when organisms are able to reproduce on their own.
The scrotum is a pouch consisting of skin and muscle that contains the male testicles. It is located between the penis and the anus.
A secondary ovarian follicle is a maturing ovarian follicle consisting of an oocyte surrounded by two or more layers of tall, supporting granulosa cells.
In histology, sectioning is the process of using a microtome or cryostat to slice thin sections of tissue (~ 5 microns) that are adhered to microscope slides for further analysis.
Semen is the fluid expelled during ejaculation, usually at the point of orgasm. Semen contains sperm and the secretions of the seminal vesicles, as well as the prostate and bulbourethral glands.
The seminal vesicles are paired structures located immediately above the prostate gland. They combine with the vas deferens to form the ejaculatory duct and secrete a fluid that is a component of semen.
The seminiferous tubules in the testes are the location of sperm cell differentiation and development.
Sertoli cells are somatic cells (non-germ cells) within the seminiferous tubules of the testis that support the germ cells as they develop, providing them with nutrients and growth factors.
Sex refers to the differences in physiology and biology between women and men, such as chromosomal differences (xx versus xy) and genitalia appearance/function. Sex is also a term used to describe the physical acts of intimacy performed between individuals, which can include (but are not limited to) sexual intercourse, caressing, and oral stimulation.
Sex chromosomes are a type of chromosome that determine the sex and sexual characteristics of an organism. In mammals, the XY system determines sex, where females contain two X chromosomes and males contain one X and one Y chromosome.
Sexual intercourse refers to the insertion and thrusting of the erect male penis into the female vagina for the purposes of reproduction (semen is released at the point of ejaculation from the male into the female) or sexual pleasure.
Sexual reproduction is the process in which the male gamete (sperm) and the female gamete (egg) fuse to create a genetically distinct offspring.
A sexually transmitted infection (STI) or a sexually transmitted disease (STD) is an infection that is transmitted through intimate sexual acts, such as anal, vaginal, or oral sex, or simply by genital contact.
Simple cuboidal epithelial tissue, which is a single layer of cube-like cells with centrally located nuclei, lies on the surface of the ovary, performing excretion and absorption.
Sister chromatids are identical copies of a chromosome joined together by a centromere.
Skene's glands, also known as paraurethral glands, are found in females and are the counterpart to the prostate in males. They are tubular glands found in the upper vagina and are adjacent to the urethra. They drain fluid into the urethra and urethral opening.
Social egg freezing (or social oocyte cryopreservation) is a form of fertility preservation that allows healthy women to freeze their eggs (oocytes) for use in the future. The procedures and techniques are the same used in conventional egg freezing performed for cancer patients. Egg freezing procedures include the use of injectable hormones to stimulate the ovaries to promote the growth of multiple mature eggs, a surgical procedure to collect oocytes from the ovary, rapid freezing of mature oocytes, and the storage of cryopreserved oocytes for a period of time (e.g. years). In the future, these oocytes can be thawed and used for in vitro fertilization by sperm to create embryos, which can then be transferred into the uterus to achieve pregnancy. Social egg freezing is generally accepted in the United States, although it is prohibited in many countries.
Somatic cells are diploid cells that make up all organs and tissues within an organism. In contrast, germ cells (or gametes) and stem cells within an organism are not somatic cells.
Somatotropes, the most abundant cell type of the anterior pituitary gland, produce growth hormone (GH).
The sperm (spermatozoon) is the male reproductive cell that carries the paternal (father’s) haploid genome. Each sperm cell consists of a head (containing the sperm nucleus), a midpiece (containing mitochondria), and a flagellar tail. Spermatozoa are fully formed when they leave the testis but must undergo additional maturation processes in the epididymis and female reproductive tract (capacitation) before they are capable of fertilizing an egg.
Sperm banking is the process in which sperm cells are collected and frozen for future use.
Sperm donation refers to the act of a man (the sperm donor) providing his sperm to another infertile man or couple having difficulty conceiving their own biological child in the hopes of allowing them to become pregnant. Sperm donation is part of the process of third–party reproduction. Sperm donation is typically facilitated through a sperm bank or clinic and can occur either privately or openly with the intended mother or recipient couple. Pregnancies using sperm donations are typically achieved using artificial insemination rather than in vitro fertilization.
Analysis performed on sperm to charecterize their shape. Parameters such as the shape and size of the head and tail can highly influence the sperms ability to fertilize an egg.
A spermatid is a haploid male germ cell that has completed the process of meiosis. Immediately after meiosis, spermatids are round cells that do not resemble mature sperm. Round spermatids must go through the process of spermiogenesis in the testis to form structures, such as the head, tail, and acrosome and to become elongated spermatids.
A spermatocyte is a male germ cell that is going through the process of meiosis. Recombination of genetic material between homologous chromosomes (crossing over) occurs in each primary spermatocyte, which will then divide to produce two haploid secondary spermatocytes. Each secondary spermatocyte divides again to produce a total of four spermatids.
Spermatogenesis is the process by which male gametes (spermatozoa) are formed in the seminiferous tubules of the testis. Spermatogenesis consists of three phases: mitotic division of the spermatogonia (proliferation), meiotic division of the spermatocytes to produce spermatids (meiosis), and differentiation of round spermatids to form elongated spermatids (spermiogenesis). Germ cells remain in contact with Sertoli cells throughout spermatogenesis. After spermatogenesis in the testis, spermatozoa are still immotile and must go through further maturation processes in the epididymis and female reproductive tract before they are able to fertilize an egg.
A spermatogonium is a male germ cell along the basement membrane of the seminiferous tubule in the testis that divides by mitosis. When spermatogonia stop dividing mitotically and enter meiosis, they become spermatocytes. There are different types of spermatogonia at different stages of differentiation, and some undifferentiated spermatogonia are the stem cells of the male germ line.
A spermicide is a substance that destroys sperm. It is often used in conjunction with contraceptives like condoms or diaphragms to reduce the risk of pregnancy.
Spermiogenesis is part of the process of spermatogenesis (they are not the same thing). During spermiogenesis, haploid, round spermatids change their shape and structures to become elongated spermatids and acquire the specialized parts needed to become mature sperm.
A spindle is a structure made up of microtubules that brings about chromosomal movement during cell division.
Steroid hormones are natural hormones produced in the adrenal glands, testes, and ovaries (and in the placenta during pregnancy). There are five major classes of steroid hormones that are derived from the same cholesterol precursor: 1) androgens, 2) estrogens, 3) progestins, 4) mineralcorticoids, and 5) glucocorticoids. Androgens and estrogens function in sexual development, differentiation, and the development of secondary sex characteristics and behaviors. Progestins act to regulate the menstrual cycle and pregnancy. Mineralcorticoids and glucocorticoids do not have established functions in reproduction but do influence a wide variety of vital biological functions.
Steroidogenesis refers to the process of generating steroid hormones, such as estrogen and progesterone. Enzymes, such as aromatases, are required for converting hormone precursors into active steroid hormones.
Stromal cells are the connective tissue cells of an organ found in the loose connective tissue. They function as a framework of the organ, and the most common types are fibroblasts, immune cells, pericytes, endothelial cells, and inflammatory cells. They are most commonly associated with the haematopoietic system, uterine mucosa (endometrium), prostate gland, ovaries, and other organs.
Subfertility refers to decreased fertility but not a complete inability to become pregnant. Some common causes of subfertility in women include ovulatory disorders, such as premature ovarian failure (POF) and polycystic ovarian syndrome (PCOS), or uterine abnormalities, such as endometriosis. Subfertility also occurs with advanced female age.
Surgical menopause refers to the surgical removal of both ovaries, also known as a bilateral oophorectomy, that often occurs in conjunction with a hysterectomy. This procedure results in premature menopausal symptoms, such as hot flashes, vaginal dryness, night sweats, and fatigue.
Surrogacy is an arrangement in which a woman carries and delivers a child for another couple or person. Surrogacy may be traditional or gestational. Traditional surrogacy is the treatment in which a third-party woman carries an embryo created after artificial insemination in her uterus. In this case, the third-party woman has a genetic link to the fetus she might carry and deliver. Gestational surrogacy (using a gestational carrier/uterine carrier) is the treatment in which a third-party woman carries an embryo created after in vitro fertilization in her uterus. In this case, the third-party woman has no genetic link to the fetus she might carry and deliver.
A surrogate or surrogate mother is a woman who agrees to carry and give birth to a child for another woman or couple. In traditional surrogacy, the surrogate is the genetic mother. In this case, she is artificially inseminated with the father’s sperm and carries the pregnancy to term. Traditional surrogacy entails a variety of legal issues, including the birth mother's formal abandonment of parental rights, among others. The legal issues are typically addressed in the pre-arrangements and vary from state to state. In gestational surrogacy, the surrogate serves as a gestational carrier and is not the genetic mother. In this case, the surrogate is implanted with an embryo created using in vitro fertilization.
Syngamy is the permanent fusion of two individual cells (or gametes) to produce a unique organism (the zygote). This is also called sexual reproduction or fertilization.
The tail of the sperm, or the flagellum, moves in a way that propels the sperm and allows it to move after it is deposited in the female reproductive tract.
Telophase is the stage of cell division following anaphase during which chromosomes have been pulled to each spindle pole. New nuclei begin to form, and chromosomes begin to unravel.
Teratospermia is the medical term for a condition in which sperm with abnormal morphology are present in the semen or ejaculate. Typically, more than 40% of the sperm in the semen will have abnormal morphology, including small sperm, large sperm, and sperm with defects in the head, tail, and/or mid-piece. The causes of teratospermia are largely unknown. This condition may result in infertility, which may be overcome through the use of assisted reproductive technologies.
Testicular cancer refers to the cancer of one or both testicles. Testicular cancer is more common among younger men, as the average age of diagnosis is 33, but older men are also susceptible. This cancer is highly treatable and quite often curable.
Testicular tissue banking is the process in which testicular tissue, including cells that produce sperm and sperm itself, is removed and frozen.
A testis, also known as a testicle, is the primary tissue of the male reproductive system and is located below the penis inside the scrotum. It is the site of spermatogenesis and is also involved in the synthesis and secretion of masculinization hormones.
Testosterone is a steroid hormone that is produced primarily in the male testes and, in small amounts, in the adrenal cortex and female ovaries. Testosterone helps regulate and guide male sexual and reproductive development.
Thalidomide was an over-the-counter drug used by pregnant women experiencing morning sickness in late 1950s Germany. Unfortunately, thalidomide caused severe birth defects in the children of the women who took the drug while pregnant, and many of these children did not survive. This catastrophe highlighted the need for more stringent drug-testing regulations. Now, the drug is only available by prescription for the treatment of cancer, leprosy, etc.
Theca cells are somatic cells of the developing follicle that form an enveloping sheath around the granulosa cell layers. Activated follicles at the secondary stage of development recruit theca stem cells from the surrounding stroma cells to differentiate. Active theca cells produce androgens, which provide important hormonal communications between granulosa cells and oocytes during follicle maturation. The theca cell layer also provides structural and vascular support for the growing follicle until ovulation. Following ovulation, theca cells become a source of hormonal support for pregnancy.
Third-party reproduction refers to the use of donor eggs, sperm, embryos, or the use of a surrogate mother or gestational carrier to allow an infertile person or couple to become parents. Donor eggs and sperm can be used in assisted reproductive technology procedures such as in vitro fertilization or artificial insemination to produce an embryo(s). Donor embryos or embryos derived from the biological parents can then be placed in the uterus of the future mother or gestational carrier. The third party’s involvement is typically limited to the reproductive process and does not extend to parenthood.
The thyroid hormones, triiodothyronine (T3) and thyroxine (T4), are produced by the thyroid glands and are mainly responsible for growth and metabolism.
Thyroid stimulating hormone (TSH) is produced by thyrotropes and acts on the thyroid gland to promote thyroid hormone secretion.
Thyrotropes are specialized cells in the anterior pituitary gland that produce thyroid stimulating hormone (TSH).
Tissue culture (or cell culture) is the maintenance of tissue or cells in an environment outside of an organism, typically with artificial medium as a source of nutrients.
A transdermal patch is an adhesive patch placed on the skin for the delivery of a specific, controlled dose of medication into the body. An advantage of this method is the ease in controlling finite amounts of administered medication. A disadvantage is the patch's limitations for the type of pharmaceuticals used. Transdermal patches can be used to deliver hormones in order to treat the symptoms of menopause and to serve as a form of contraception.
Transdermal therapy is a form of treatment where medication is delivered through the surface of the skin and into the bloodstream. Transdermal therapy can be administered in the form of a transdermal patch, lotion, or gel and is often used to deliver hormones for the purpose of contraception or to treat the symptoms of menopause.
A transducer is a protein that converts chemical information from a hormone that binds to its receptor into a language that the biochemical machinery within a cell can understand and act upon. Transducers normally act as liaisons between receptors that have bound to a particular hormone and the effector proteins that actually generate the final cellular responses. They are frequently arranged in a series of steps, a cascade, which allows amplification of the original hormonal signal by recruitment of cellular energy stores. Typical transducers include enzymes like protein kinases that incorporate phosphate groups into cellular proteins, thereby changing the charge, shape, position and/or functionality of the proteins targeted. They also include small molecules, such as cyclic AMP or diacyl glyceride, that act as secondary messengers within cells by binding to proteins and altering their activities.
A transgene is a gene or genetic material that is artifically added into an organisms's genome. Transgenes are used by genetic engineers to change or insert genes of interest into an organism. They are often associated with a phenotype, making them very useful for biomedical research studies.
Transzonal projections (TZPs) are membraneous extensions from the granulosa cells of ovarian follicles through the zona pellucida to the oocyte cell membrane. At the oocyte cell membrane, the transzonal projections form gap junctions or adherens junctions with the oocyte membrane, which allow for information or cargo exchange between the two cells.
A trimester is a three-month stage of pregnancy. Classically, pregnancy is nine months (40 gestational weeks) and is divided into three trimesters: the first trimester is the first three months (1-12 gestational weeks), the second trimester is the middle three months (12-28 gestational weeks), and the third trimester is the last three months (28-40 gestational weeks).
The trophectoderm is part of the blastocyst that is fated to develop into extra-embryonic tissues, such as the placenta and umbilical cord.
Trophoblasts are a heterogeneous population of cells derived from the trophectoderm (the outer cell layer of the blastocyst) that mediate and contribute to the construction of the connection between the mother and fetus at the site of implantation (the placenta). There are considerable species differences in terms of trophoblast differentiation. In humans, the differentiated forms are cytotrophoblasts, syncytiotrophoblasts, and extravillous trophoblasts.
True labor pains are regular, painful uterine contractions that begin at the onset of labor. These contractions are usually felt as strong abdominal, pelvic, and back pains and do not disappear with rest or pain killers. They increase in intensity and frequency and serve to efface and dilate the cervix in order to allow for the baby to pass through the birth canal during delivery.
Tubal ligation is a surgical procedure in which a woman's fallopian tubes are "tied" or ligated. This procedure prevents eggs from being released from the ovaries into the fallopian tubes, where fertilization normally occurs. Tubal ligation is, thus, a contraceptive method and is 99% effective in pregnancy prevention. While tubal ligation is considered a permanent form of birth control, it can be reversed through a microsurgical procedure in which the fallopian tubes are reconnected.
Tumor necrosis factors (TNFs) are a family of cytokines (signal molecules) which signal by binding to two specific receptors, TNF-receptor type I and TNF-receptor type II. Activation of the TNF signaling pathway controls cell survival, death, proliferation, and differentiation. This pathway, therefore, is responsible for the development, organization, and homeostasis of many tissues, including the breast and brain/nervous system.
Turner Syndrome occurs when a woman has inherited only one X chromosome instead of two. This syndrome is an instance of monosomy, and it is the only one that is not lethal.
The umbilical cord is a thin organ that connects the fetus to the placenta while in utero. The umbilical cord contains two arteries and a vein that facilitates oxygen and nutrient transport to the fetus. It also transports fetal waste back to the placenta to be filtered in the maternal circulation.
In both males and females, the urethra is the tube that connects the bladder to the urethral opening. Urine travels from the bladder to the urethra and then to the outside of the body via the urethral opening. In the male, semen also travels through the urethra.
A urinary tract infection (UTI) is an infection caused by bacteria that occurs in the urinary system (kidneys, ureters, bladder, and the urethra). Symptoms are often uncomfortable and can include pain or burning upon urination, fever, and fatigue.
The uterine glands are in the epithelial, glandular compartment of the endometrium, which is contiguous with the luminal epithelium. The glands synthesize and secrete most of the proteins and other components of uterine fluid (histotroph). Glandular secretions are necessary for embryo implantation and survival.
The uterine horns are the points where the fallopian tubes and uterus meet.
Uterine leiomyoma is a benign tumor that originates from the smooth muscle layer (myometrium) of the uterus. It is also known as a uterine fibroid. Fibroids are the most common benign tumors of the female genital tract. While fibroids can be asymptomatic, they can also cause irregular or heavy vaginal bleeding and other symptoms due to pressure on neighboring organs.
Uterine leiomyosarcoma is a rare but malignant tumor of the myometrium. This condition is independent of a uterine leiomyoma; the presence of uterine leiomyomas does not increase a woman's chance of developing uterine leiomyosarcoma.
The uterus, also known as the womb, is a muscular, pear-shaped organ located between a woman’s rectum and her bladder. During pregnancy, this is where the fetus develops. In women of child-bearing age, the inner layer of the uterus (endometrium) thickens in preparation for the implantation of a fertilized egg each month. If there is no fertilized egg, the endometrium is shed through the vagina. This process is called menstruation.
The vagina is a muscular canal that extends from the bottom of the cervix (the cervix connects the uterus to the vagina) to the outside of the female body. During sexual intercourse, the penis enters the vagina.
Vaginal atrophy is the thinning and inflammation of the vaginal walls due to declining estrogen levels. This condition typically occurs post-menopause, but it can also occur during breastfeeding or at other times when the body’s estrogen levels are lower than usual. Symptoms include painful intercourse, vaginal burning, dryness, painful urination, and urinary tract infections.
Vaginitis, or inflammation of the vagina, occurs when there is an upset in the balance of vaginal bacteria, during infection, or even after menopause when estrogen levels are extremely low. Symptoms of vaginitis include abnormal or smelly discharge, itching or burning, and pain during intercourse. Vaginitis can refer to bacterial vaginosis, a yeast infection (vaginal candidiasis), trichomoniasis, or vaginal atrophy (atrophic vaginitis).
The vas deferens is a duct of the male reproductive system that connects the testes to the urethra. It runs from the end of the epididymis toward the prostate, where it joins with the seminal vesicle to form the ejaculatory duct. The vas deferens functions in the transport of mature spermatozoa and secretes a fluid that is a component of semen.
Vasectomy is a surgical procedure that results in male sterilization and is performed for the purpose of serving as permanent birth control. The vasa deferentia (the tubes carrying the sperm) are tied to prevent sperm from being ejaculated, thereby preventing fertilization from occurring.
The vitelline membrane is a structure that directly surrounds the oocyte in lower organisms, such as insects, mollusks, amphibians, and birds. Its functional homologue in mammals is the zona pellucida.
Vitrification refers to a specific method of cryopreservation. Normally, when cells or tissues are frozen, ice crystal formation can damage the cells. Vitrification involves adding an antifreeze-like cocktail of chemicals to the cells or tissue before deep-freezing, thus preventing "freezer-burn."
The vulva is the external portion of the female genital organs. It includes the labia (majora and minora), clitoris, and the openings to both the vagina and urethra.
Vulvodynia is a condition where chronic pain is experienced in the vulva. There are many factors that are thought to contribute to vulvodynia, but it is a rather newly discovered condition, so further research must be done to pinpoint what exactly tends to cause this pain. It is thought that antibiotic use, sensitivity or allergies to different chemicals that may come into contact with the vulva, yeast infections, and various genetic factors may play some role.
The withdrawal method refers to pulling the penis out of the vagina and away from the woman’s external genitals before the moment of ejaculation in order to prevent a pregnancy from occurring. However, this method of birth control is not highly effective, as sperm can reside in pre-ejaculation fluid. Also, this method does not prevent against any STIs.
The Wolffian ducts are paired, mesodermal ducts present in the early embryo that will develop into the epididymis, vas deferens, and seminal vesicles in males. In females, they are lost during the early stages of development.
The yolk sac is a pouch-like tissue in the early embryo that lies adjacent to the embryonic hypoblast portion of the developing inner cell mass. Its earliest stage during implantation in the mammal is derived from the blastocyst cavity and is termed the primary yolk sac. This is followed by the development of a secondary yolk sac, which develops within the primary yolk sac and displaces it; the secondary yolk sac is derived from the cells of the hypoblast. As development proceeds, the yolk sac is partially incorporated into the tissues of the intestines. Early in mammalian gestation and throughout gestation in other animals, the yolk sac serves as the reservoir for stored lipids, fats, and proteins, and it is also the site of early production of blood. Stem cells for both germ cells and hematopoietic cells reside within the yolk sac, close to the embryo, and migrate into the embryonic abdomen early in gestation. The yolk sac is resorbed into the embryo abdomen at varying times across species (e.g. it is still present at the time that hatching occurs in fish and amphibians and has been resorbed in birds, while in mammals, resorption takes place mid-gestation).
Hatching of the zona pellucida from the outside of the blastocyst must occur before implantation in the uterine wall is possible. Assisted zona hatching (AZH) is also used as an assisted reproductive technology to further increase the chances of implantation in the uterus.
The zona pellucida is a membrane composed of four glycoproteins (ZP1-4) that surrounds the plasma membrane of the mammalian oocyte. It is important for inducing the acrosome reaction during fertilization and preventing polyspermy. The zona pellucida persists through pre-implantation embryo development, but the blastocyst must hatch out of the zona pellucida in order to undergo implantation in the uterus.
A zygote is the diploid cell that is produced following fertilization of the female egg by the male sperm. In contrast to a zygote, which is unicellular, an embryo has begun to undergo cell divisions and is multicellular.