A Reproductive Lexicon


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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.

A gene found on the Y chromosome that encodes for the testis determining-factor protein which induces male sex determination

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.

The modification of spiral arteries in the maternal decidua which is necessary for the establishment of a maternal vascular system that can adequately support the fetus.


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.