UNSW Embryology

Glossary T

© Dr Mark Hill (2008)

Acknowledgements

T cell leukemia 3

(Tlx3) gene which specifies spinal cord glutamatergic sensory neurons and is a a selector gene in embryonic stem (ES) cells undergoing neural differentiation. Also called Respiratory Neuron Homeobox (Rnh) or HOX11L2. (More? Factors - Tlx | Neural Notes | Stem Cell Notes)

talipes equinovarus

(Latin, talipes = ankle bone, pes = foot, equinus = horse) or "club foot" congenital deformity of the foot (occurs approximately 1 in 1,000 births). Condition starts in the first trimester of pregnancy, the foot is then turned inward and downward at birth, postnatally it affects how children walk on their toes with the foot pointed downward like a horse. (More? Limb Development Abnormalities | Medline Plus - Clubfoot)

taste

refers to the sensory neurological perception begining with the taste buds of the tongue of at least five distinct qualities: sweet, bitter, sour, salty, and umami (savoury). (More? Sensory Notes - Taste)

tastin

(trophinin-assisting protein) a cell surface protein that along with trophinin involved with blastocyst implantation, mediates adhesion and is expressed on both blastocyst and endometrial epithelium. From week 6 of pregnancy it is found only on the apical side of the syncytiotrophoblast. (More? Week 2 Notes | OMIM - tastin)

taurine

(Latin, taurus = bull, after source of original isolation from ox bile) the most abundant free amino-acid in the body and has an important role in several essential biological processes. (More? Reference Aerts L, Van Assche FA. Taurine and taurine-deficiency in the perinatal period. J Perinat Med. 2002;30(4):281-6. Review.)

telangiectasias

"spider veins", small veins that appear on the face (cheeks, ears, corner of eyes) associated with the neurodegenerative disease Ataxia Telangiectasia. The disease has no current cure and children die in their teens or early 20's. (More? NINDS (USA) Ataxia Telangiectasia | Neural Abnormalities)

tentorial notch

the opening in the tentorium cerebelli fold of dura mater for the brainstem. (More? Neural CSF)

teratogen

any agent that causes a structural abnormality following fetal exposure during pregnancy. The overall effect depends on dosage and time of exposure. Absolute risk - the rate of occurrence of an abnormal phenotype among individuals exposed to the agent. (e.g. fetal alcohol syndrome) Relative risk - the ratio of the rate of the condition among the exposed and the nonexposed. (e.g. smokers risk of having a low birth weight baby compared to non-smokers) A high relative risk may indicate a low absolute risk if the condition is rare.

teratoma

(Greek, teraton = monster) tumours arising from more than one germ layer. Term first used by Virchow in 1863. Typically a germ cell tumor that may contain several different types of tissues, not all teratomas are malignant.

tetraploidy

in humans four sets of 23 chromosomes instead of 2 (diploid) due to a failure of the first mitotic division after fertilization, these fertilization events do not development.

thawed cycle

an IVF cycle in which previously frozen embryos are thawed for embryo transfer. (More? Week 1 - In Vitro Fertilization)

theca folliculi

stromal cells in the ovary, cells surrounding the developing follicle that form a connective tissue sheath. This layer then differentiates into 2 layers (theca interna, theca externa). This region is vascularized and involved in hormone secretion. Theca cells do not begin secreting estrogen until puberty. (More? Week 1 Notes - Oogenesis | Urogenital Notes)

theca externa

stromal cells forming the outer layer of the theca folliculi surrounding the developing follicle. Consisting of connective tissue cells, smooth muscle and collagen fibers. (More? Week 1 Notes - Oogenesis | Urogenital Notes)

theca interna

stromal cells forming the inner layer of the theca folliculi surrounding the developing follicle. This vascularized layer of cells respond to LH (leutenizing hormone) synthesizing and secreting androgens which are processed into estrogen. Theca cells do not begin secreting estrogen until puberty. (More? Week 1 Notes - Oogenesis | Urogenital Notes)

thrombophilia

increased tendency of blood to clot due to impaired natural anticoagulant or fibrinolytic pathways. (More? Heart Notes - Blood)

thyroid

(Greek, thyreos = sheild , eidos = form) endocrine gland located in the neck. In the fetus, the thyroid gland has a role in neurological development. (More? Endocrine Notes | Thyroid Gland | Abnormal Development - Iodine Deficiency)

thyroiditis

(Greek, thyreos = sheild , eidos = form) inflammatory process affecting the thyroid epithelium. (More? Endocrine Notes | Thyroid Gland | Abnormal Development - Iodine Deficiency)

tissue fusion

term used in development to describe the process by which epithelial sheets migrate and or drawn together to fuse, in some cases forming new structures. (More? Perez-Pomares JM, Foty RA. Tissue fusion and cell sorting in embryonic development and disease: biomedical implications. Bioessays. 2006 Aug;28(8):809-21.)

tissue transglutaminase

(TGase) enzymes which catalyze a calcium-dependent transamidation reaction, generating covalent cross-links between proteins or proteins and polyamines. In development also involved in cell survival and apotosis signaling.

Tlx3

acronym for T cell leukemia 3 gene, which specifies spinal cord glutamatergic sensory neurons and is a a selector gene in embryonic stem (ES) cells undergoing neural differentiation. Also called Respiratory Neuron Homeobox (Rnh) or HOX11L2. (More? Factors - Tlx | Neural Notes | Stem Cell Notes)

tocolytic agent

any medication that inhibits labor, slowing or halting uterine contractions. These drugs are used to treat premature labor and permit continued fetal growth before parturition. (More? Normal Development- Birth)

togaviridae

(Latin, toga = coat) a virus family, named due to the virion having an envelope or coat. Members of the togaviridae family include: Chikungunya virus, Eastern equine encephalitis virus, O'nyong-nyong virus, Ross river virus, Rubella virus, Sindbis virus, Semliki forest virus, Venezuelan equine encephalitis virus, Western equine encephalitis virus. (More? Abnormal Development - Rubella Virus | Abnormal Development - Virus)

TORCH

acronym for infections Toxoplasma, Other organisms (parvovirus, HIV, Epstein-Barr, herpes 6 and 8, varicella, syphilis, enterovirus), Rubella, Cytomegalovirus and Hepatitus. (More? Toxoplasmosis | Viral Infection | Rubella | Cytomegalovirus | Hepatitis | Abnormal Development)

totipotent

describes the ability of a cell to form an entire organism. (More? Stem Cell Notes)

toxicogenomics

study of the interaction between the genome, chemicals in the environment, and disease. Cells exposed to a stress, drug or toxicant respond by altering the pattern of expression of genes within their chromosomes. Based on new genetic and microarray technologies.

toxoplasmosis

is an infection caused by the parasite toxoplasma gondii, present in the environment (undercooked, infected meat, handling soil or cat feces that contain the parasite). Maternal active infection during pregnancy can lead to congenital toxoplasmosis, and the toxoplasmosis parasite can also cross the placenta. Fetal infection can result in miscarriage, poor growth, early delivery or stillbirth. Children born with toxoplasmosis can experience eye problems, hydrocephalus, convulsions or mental disabilities. (More? Toxoplasmosis | Abnormal Development)

tp53

(formerly p53) a cell cycle related transcription factor that promotes transcription of genes that induce cell cycle arrest or apoptosis in response to DNA damage or other cell stresses. This tumor suppressor gene is mutated in about half of all human cancers. Nomenclature is t for tumor, p for protein and 53 is molecular size (53,000 daltons). (More? Week 1 Mitosis) See also : OMIM Entry for p53

transcription factor

a factor (protein or protein with steroid) that binds to DNA to alter gene expression, usually to activate. (eg steroid hormone+receptor, Retinoic acid+Receptor, Hox, Pax, Lim, Nkx-2.2). (More? Molecular Notes)

transcriptome

cell/molecular biology term used to cover a cell's total expression of genes at a particular point in time and usually analysed by microarray. (More? Molecular Development Notes | Week 1- Blastocyst)

TRC

acronym for taste-receptor cell, cells associated with the initial sense of taste located on the tongue. (More? Sensory Notes - Taste)

chemical whose derivatives (Triadimefon) are potent antifungal agents used systemically in agriculture and in fungal diseases in humans and domestic animals. Acts by inhibiting the cytochrome P-450 conversion of lanosterol to ergosterol and has been shown to be teratogenic.

one of several skull deformities (scaphocephaly, oxycephaly, plagiocephaly, trigoncephaly) caused by premature fusion (synostosis) of different developing skull sutures. Trigoncephaly (wedge skull) results from metopic suture (beginning at nose and runs superiorly to meet sagittal suture) synostosis. (More? Skull Notes | Head Notes)

trimegestone

synthetic progesterone potentially used in postmenopausal women (with an intact uterus) in combination with estrogen as hormone-replacement therapy (HRT). (Other Progestins: levonorgestrel, 3-keto-desogestrel, dienogest, drospirenone, Nestorone and nomegestrol acetate ) Note that Trimegestone and Nestorone are currently the most potent fourth-generation progestins with no androgenic or estrogenic actions. (More? Human Menstrual Cycle)

trimethadione syndrome

fetal disorder caused by exposure of a fetus to the anticonvulsant drug trimethadione (Tridione) used in treatment of epilepsy, which acts as a teratogen leading to fetal malformations. (More? Abnormal Development Notes | Medline Plus - trimethadione)

triploidy

in humans three sets of 23 chromosomes instead of 2 (diploid) combine to form the embryo. This occurs mainly by fertilization of a single egg by two sperm and less frequently by a diploid egg or sperm. Most human triploids abort spontaneously, with very rare survival to term.

trizygotic triplet

(TZ) triplets resulting from three fertilization events, of three seperate ova and sperm. (More? Week 1 Twinning)

trophinin

cell surface molecule along with tastin involved with blastocyst implantation, mediates adhesion and is expressed on both blastocyst and endometrial epithelium. In humans, it is internalized from the surface by 6 weeks and is absent from the placenta after 10 weeks of pregnancy. (More? Week 2 Notes | OMIM - trophinin)

truncus arteriosus

| entry to be edited | (More? Heart Notes)

TTTS

acronym for Twin-twin transfusion syndrome

tubal factor

structural or functional damage of one or both fallopian tubes that reduces fertility, described as tubal factor infertility (TFI). (More? Week 1 - Abnormalities)

tubal factor infertility

(TFI) structural or functional damage of one or both fallopian (uterine) tubes that reduces fertility. (More? Week 1 - Abnormalities)

tubal sterilization

method of female sterilization involving physical closure of the uterine tube (fallopian tube) by a surgical technique (tying, banding, clipping, or sealing with electric current). (More? Week 1 Notes)

tubulus rectus

(straight tubule) within the testis (male gonad) a tubular system connecting seminiferous tubule to the rete testis within the mediastinum. (Spermatozoa Duct Pathway: seminiferous tubule → straight tubule → rete testis → ductuli efferentes → ductus epididymidis → ductus deferens) (More? Spermatogenesis)

tunica albuginea

dense connective tissue layer lying between germinal epithelium and cortical region of female ovary, or the equivilaent capsule of the male testis. (More? Week 1 Notes)

twinning

more than a single pregnancy (singleton), the two major twinning forms are monozygotic (identical, from one fertilised egg and a single spermatazoa, 3-5 per 1000 pregnancies) or dizygotic (fraternal, from two eggs fertilised by two different spermatazoa). Late monozygotic twins can result in both a shared placenta and a shared amniotic sac (monochorionic monoamniotic twins). (More? Twinning)

Twin-twin transfusion syndrome

(TTTS) occurs in monozygotic (identical) twins with monochorionic and diamniotic placenta that results from an unbalanced blood flow from one to the other in utero. (More? Twinning - Twin-twin transfusion syndrome | Twinning - Monozygotic)

Alphabetical Links

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External Resources

Comments

Use this page to access brief definitions of specific alphabetically listed embryology terms. Additional information can be accessed from links listed at the end of each definition. Glossary from the UNSW Embryology program compiled and written by Dr Mark Hill. Reference Material used in preparing Glossary List: Texts listed on page 1 Reading of each notes section, Department of Anatomy Publications, WWW resources from NCBI, AMA (USA), Office of Rare Diseases (USA), PubMed Medline Dictionaries, MSDS, Merck Manual home edn., NHMRC (Australia). These notes are for Educational Purposes Only. Please email Dr Mark Hill if you wish to make a comment about this current project.

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