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 used by way of genetic engineering techniques to manipulate genes in a living organism. It is used to change genes of interest by isolating and introducing a gene sequence from one organism to another one. It can alter the phenotype of an organism by modifying at the DNA level to study the function or pathology involved with that particular gene.
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.