T lymphocytes or T-cells: Lymphoid cells concerned with cell-mediated immunity. They originate from lymphoid stem cells that migrate from the bone marrow to the thymus and differentiate under the influence of the thymic hormones. Various subpopulations have been described. Tamoxifen: A nonsteroidal anti-estrogen, used in the palliative treatment of breast cancer and to stimulate ovulation in infertility. T-cells: Lymphocytes that originate from lymphoid stem cells that migrate from the bone marrow to the thymus and differentiate under the thymic hormones thus are thymus-dependent. These cells are primarily responsible for cell-mediated immunity. Telomerases: A DNA polymerase with rather unusual properties that will only elongate oligonucleotides from the telomere and not other sequences. The enzyme contains an essential 159 residue RNA sequence that provides a template for the replication of the G rich telomere sequences (so that the enzyme could in fact be considered a reverse transcriptase). Telomere: The end of a chromosome. This is made up of guanine tetrads as shown below. Template: A strand of DNA or RNA that specifies the base sequence of a newly synthesized strand, the two strands being complementary. See transcription below. Teratogens: An agent or factor that causes the production of physical defects in the developing embryo. Terminal differentiation: Induction of proliferating immature cells into nonproliferating specialized mature cells. The follicular phase: The pre-ovulatory phase of a woman's reproductive cycle during which the follicle (ovarian follicle, an oocyte surrounded by one or more layers of granulosa cells. As the ovarian follicle develops a cavity forms and it is then termed a Graafian follicle) grows and high estrogen levels cause the uterine lining to grow. The luteal phase: The post-ovulatory phase of a woman's cycle, the corpus luteum (a yellow glandular mass in the ovary formed by an ovarian follicle that has matured and discharged its ovum) produces progesterone, which in turn causes the uterine lining to secrete substances to support the implantation and growth of the early embryo. ThinPrep® Pap: The Pap test that collects cell samples using a special brush and immediately washes in a special fluid seems to reduce some of the technical problems inherent to traditional Pap smear in which cells are collected and spread on glass slide as thin film. Thoracentesis: Surgical puncture of the chest wall into the parietal cavity for aspiration of fluid. Thoracostomy: Surgical creation of an opening in the wall of the chest for the purpose of drainage. Thrombin: A protease generated in blood clotting that acts on fibrinogen to produce fibrin. Thrombocytopenia: A decrease in the number of platelets in the blood, resulting in the potential for increased bleeding and decreased ability for clotting. Thromboembolic: Pertaining to thromboembolism, obstruction of a blood vessel with thrombotic material carried by the blood stream from the site of origin to plug another vessel. Thrombosis: Presence of thrombus, an aggregation of blood factors, primarily platelets and fibrin with entrapment of cellular elements, frequently causing blood vessel obstruction at the point of its formation. Thymidine kinase: The enzyme catalyzing the transfer of phosphate from ATP to thymidine forming thymidilic acid. Thymocytes: Cells of the thymus which is a lymphoid gland (structures containing lymph, a part of defense system) in the upper chest. Thymoma: A tumor of thymus gland. Thymus: A lymphoid organ, which is the site of T lymphocytes. Thyroglobulin: An iodine-containing glycoprotein of high molecular weight occurring in the follicles of the thyroid gland; the iodinated tyrosine part of the thyroglobulin form the active hormones thyroxine and triiodothyronine, which are released into the blood on proteolysis of thyroglobulin. Thyroiditis: Inflammation of thyroid gland. The inflamed thyroid gland can release an excess of thyroid hormones into the blood stream, resulting in a temporary hyperthyroid state. Once the thyroid gland is depleted of thyroid hormones, the patient commonly goes through a hypothyroid (low thyroid) phase. This phase can last 3-6 months until the thyroid gland fully recovers. TNM: Tumor-node-metastasis. Topoisomerase I: An enzyme that changes the degree of supercoiling in DNA by cutting one strand. Trachelectomy (Cervicectomy): Excission of cervix. Trans conformation: Denotes a chemical structure in which designated atoms reside on the opposite sides of a chemical bond between two other atoms. Transaminase: A group of enzymes that catalyzes the transfer of an amino group from a donor (generally an amino acid) to an acceptor (generally a keto acid). Transcription: The process by which a single-stranded RNA with a base sequence complementary to one strand of a double-stranded DNA is synthesized by RNA polymerase. Transcription factors: Endogenous substances, usually proteins, which bind to DNA and are effective in the initiation, or stimulation of genetic transcription process. Transcriptome: The complete set of RNA transcripts produced by the genome at any one time. The transcriptome changes under different conditions due to different patterns of gene expression. Transducin: A GTP binding protein found in the disc membrane of retinal rods and cones. And is a part of the cascade involved in transduction of light to a nervous impulse. Transfected cells: Artificially infected cells; in biotechnology it means transfer of foreign DNA into a cell. Transgenic mouse: Mouse produced by the introduction of a foreign into the fertilized cell at one cell stage. Translocation: A structural chromosome aberration in which one segment of a chromosome is transferred to another chromosome. Transversion mutation: When mutation involves changing a purine (adenine or guanine) to a pyrimidine (cytosine or thymine) or vise versa. Triglyceride: A compound consisting of three molecules of fatty acids esterified to glycerol; it is a neutral fat synthesized from carbohydrates for storage in animal fatty tissue. Trisomy: Indicate presence of additional whole chromosome. Trochanter: One of two processes near the head of the femur, the outer being called the great trochanter, and the inner the small trochanter. Trophoblast: A layer of extraembryonic tissue that attaches ovum to the uterine wall and supply nutrition to the embryo. Trypsin: A hydrolytic enzyme that catalyzes the cleavage of linkages in proteins involving the carboxyl group of either arginine or lysine. TSH: Thyroid-stimulating hormone is produced by the anterior pituitary gland and has a strong influence on the growth and function of thyroid gland. Tumor Infiltrating Leukocytes: White blood cells that are present near tumors. Tumor suppressor gene: Gene, the protein product of that is necessary for normal growth of cell and prevents abnormal uncontrolled growth. Tumor-infiltrating Lymphocytes: Lymphocytes that are attracted to solid tumor sites. Tumorocidal Agents: Agents that destroy or kill tumors. Turner's syndrome: A rare genetic disorder (1 in 3,000 births) in women that is characterized by the absence of an X chromosome. This disorder inhibits normal sexual development and causes infertility. Type 2 Diabetes: One of the two major types of diabetes in which the pancreas produces insulin but the body cannot use it effectively because the cells are resistant to insulin. Tyrosine kinase: Kinases are a group of enzymes that catalyzes phosphorylation (addition of phosphate to a molecule) of proteins. Tyrosine kinase adds phosphate specifically to amino acid tyrosine present in proteins.