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UNSW Embryology Glossary T

Link to the Original UNSW Embryology Glossary T

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

sensory neurological perception of flavour 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 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.)

telangiectasia

(Latin, tel + angi + ectasia, ectasis) plural 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)

telencephalic glial cells

(telencephalon = endbrain) supporting cerebral cortex glial cells. Telencephalic glial cells (oligodendrocytes) are formed from a small region of the ventral neuroepithelium of the telencephalon under the influence of sonic hedgehog (SHH) signaling and migrate into cortical regions. Oligodendrocytes are a subset of the various glial cell types, the myelinating macroglial cells.

(More? Neural Notes)

telencephalon

( = endbrain) embryonic neural tube region that will form cerebral hemispheres (neocortex, basal nuclei, palaeocortex, archicortex). The telencephalon is the most anterior of the 5 secondary brain vesicles formed from division of the prosencephalon (forebrain) primary brain vesicle (there are 3 primary brain vesicles). The telencephalon lumen (cavity of the neural tube) will form the lateral ventricles.

(More? Neural Notes | Ventricular System)

tensor veli palatini

A muscle which functions to open the auditory tube by pulling its lateral wall laterally and inferiorly.

(More? Hearing Notes)

tentorial notch

the opening in the tentorium cerebelli fold of dura mater for the brainstem.

(More? Neural CSF)

teratogen

(Greek, teraton = monster) Any agent that causes a structural abnormality following 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 non-exposed. (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.

(More? Abnormal Development)

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.

terminal sac stage

(terminal sac phase, immature alveoli) Term used to describe the second last histological/developmental stage (Pseudoglandular, Fetal Canalicular, ===Terminal sac===, Alveolar) of lung development. This stage occurs from late fetal week 24 to 36. During this stage branching and growth of the terminal sacs occurs, with cellular differentiation of the type -II pneumonocytes and type - I pneumonocytes The final functional sac of the respiratory tree occurs at the next neonatal period, where gas exchange occurs between the alveolar space and the pulmonary capillaries.

(More? Respiratory Notes)

testes

(Latin testis = "witness") The two male gonads (singular testis) where male germ cells (spermatozoa) are generated and also the source of testosterone (male hormone). Embryonically formed from primordial germ cells entering region of the paired mesonephric ducts (Wolffian ducts) which are preserved in male gonad development and lost in females.

(More? Genital System - Male)

testis

(Latin testis = "witness", plural testes) The male gonad where male germ cells (spermatozoa) are generated and also the source of testosterone (male hormone). Embryonically formed from primordial germ cells entering region of the paired mesonephric ducts (Wolffian ducts) which are preserved in male gonad development and lost in females.

(More? Genital System - Male)

testis-determining factor

(TDF, Sry, Testis-Determining Factor on Y, TDY ) Protein name for the protein transcription factor product of the Sry gene on the Y chromosome responsible for maleness. This protein is a member of the high mobility group (HMG)-box family of DNA binding proteins. See also the transcription factor SRY-related protein, SOX9 (SRY-related high-mobility group (HMG) box 9)

(More? Molecular Notes | Week 1 Notes | OMIM)

tetralogy of Fallot

Cardiac abnormality possibly stemming from abnormal neural crest migration. Named after Etienne-Louis Arthur Fallot (1888) who described it as "la maladie blue".

(More? Heart Abnormalities)

tetraploidy

Term used to describe a cell with duplicated chromosomal abnormality, in humans four sets of 23 chromosomes instead of 2 (diploid) due to a failure of the first mitotic division after [F.htm#fertilization fertilization], these types of fertilization events fail to develop.

(More? Abnormal 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

(Greek, thek = box) The ovarian follicle stromal cells forming the outer layer of the theca folliculi surrounding the developing follicle within the ovary. Consisting of connective tissue cells, smooth muscle and collagen fibers.

(More? Week 1 Notes - Oogenesis | Urogenital Notes)

theca interna

(Greek, thek = box) The ovarian follicle endocrine cells forming the inner layer of the theca folliculi surrounding the developing follicle within the ovary. This vascularized layer of cells respond to leutenizing hormone (LH) synthesizing and secreting androgens (androstendione) transported to glomerulosa cells which process initially into testosterone and then by aromatase into estrogen (estradiol). Theca cells do not begin hormonal functions until puberty.

(More? Week 1 Notes - Oogenesis | Urogenital Notes)

third trimester

Clinical term used to describe and divide human pregnancy period (9 months) into three equal parts of approximately three calendar months. The third trimester corresponds to the fetal period of growth in weight, as well as continued differentiation of existing organs and tissues. The respiratory system matures late in teh third trimester. The first trimester corresponds approximately to embryonic development (week 1 to 8) of organogenesis and early fetal period, the second trimester is the fetal period of growth in size.

(More? Embryo Stages | Human Fetal Period | Development Week by Week)

thrombophilia

An 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, the origin of the name reflects the organs anatomical structure. 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) An inflammatory process affecting the thyroid epithelium.

(More? Endocrine Notes | Thyroid Gland | Abnormal Development - Iodine Deficiency)

tissue fusion

A 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 ===l===eukemia ===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

Term used for any medication that inhibits labor, slowing or halting uterine contractions. These drugs are used clinically 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

An acronym for pregnancy related 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

Term that describes the ability of a cell (stem cell) to form an entire organism or any tissue from that organism. Totipotential suggests a wider differentiation ability than pluripotential, where there is a restriction to a particular group of cell types such as that seen for bone marrow blood stem cells.

(More? Stem Cell Notes)

toxicogenomics

The 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.

(More? Abnormal Development | Abnormal Development - Drugs)

toxoplasmosis

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 | OMIM Entry for p53)

trabeculae carneae

(columnae carneae) (carneae = meaty) The heart ventricular muscular bundles which project from the wall into the lumen of the ventricle, except in the region of the conus arteriosus.

(More? Heart Notes)

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

A 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)

transverse septum

(septum transversum) see [S.htm#septum_transversum septum transversum] a mesodermal region in the early embryo.

(More? Gastrointestinal Tract Notes | Liver Notes | Respiratory Development - Diaphragm)

TRC

Acronym for ===T===aste-Receptor Cell, the cells associated with the initial sense of taste located on the tongue.

(More? Sensory Notes - Taste)

triazole

A 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.

(More? Abnormal Development)

trigoncephaly

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)

trilaminar embryo

Term meaning three (3) layered embryo, used to describe the early embryo development following gastrulation when it now has a structure consisting of the 3 germ cell layers (ectoderm, mesoderm, endoderm). In humans, this developmental stage occurs during week 3.

(More? Week 3 - Trilaminar Embryo | Week 3 | Embryo Stages | Development Week by Week)

trimegestone

A synthetic progesterone potentially used in postmenopausal women (with an intact [U.htm#uterus 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)

trimester

Clinical term used to describe and divide human pregnancy period (9 months) into three equal parts of approximately three calendar months. The first trimester corresponds approximately to embryonic development (week 1 to 8) of organogenesis and early fetal. The second and third trimester correspond to the fetal period of growth in size (second trimester) and weight (third trimester), as well as continued differentiation of existing organs and tissues.

(More? Embryo Stages | Human Fetal Period | Development Week by Week)

trimethadione syndrome

A 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

Term in humans for three sets of 23 chromosomes instead of 2 (diploid) combine to form the embryo. This occurs mainly by [F.htm#fertilization 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.

(More? Abnormal Development)

trizygotic triplet

(TZ) Term for triplets resulting from three seperate [F.htm#fertilization fertilization] events, that is of three seperate ova (oocyte) and sperm (spermatozoa).

(More? Week 1 Twinning)

trophinin

A cell surface molecule along with [#tastin 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)

trophoblast

(Greek, trophe = "nutrition") the trophoblast cells have an important contribution to extraembryonic tissues (fetal placenta and membranes) and processes of early development (adplantation, implantation and endocrine support of pregnancy). Week 1 blastocyst formation the outer layer of cells (adjacent to the zona pellucida) form a flat squamous epithelial layer of cells, the trophoblast layer. Week 2 following blastocyst hatching the trophoblast layer is involved with initial adhesion to the uterine wall and subsequent implantation within the wall. During this period the trophoblast layer differentiates into two distinct layers ([S.htm#syncitiotrophoblast syncitiotrophoblast], [C.htm#cytotrophoblast cytotrophoblast]).

(More? Week 2 Notes | Week 3 Notes | Placenta Notes)

truncus arteriosus

An embryological heart outflow structure, that forms in early cardiac development and will later divides into the pulmonary artery and aorta. Term is also used clinically to describe the malformation where only one artery arises from the heart and forms the aorta and pulmonary artery.

(More? Heart Notes)

TTTS

Acronym for [#Twin-twin_transfusion_syndrome Twin-twin transfusion syndrome]

tubal factor

A 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) The structural or functional damage of one or both fallopian (uterine) tubes that reduces fertility.

(More? Week 1 - Abnormalities)

tubal sterilization

A 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)

tubulogenesis

Term used to describe the development of branched tubes from an initially unbranched epithelial bud. A fundamental process in the development of many organ systems (pancreas, mammary gland, lung, and kidney).

(More? Week 1 Notes)

tubulus rectus

(straight tubule) Anatomical structure within the testis (male gonad) a tubular system connecting seminiferous tubule to the rete testis within the mediastinum. (Spermatozoa Duct Pathway: seminiferous tubule ‚Üí straight tubule ‚Üí rete testis ‚Üí ductuli efferentes ‚Üí ductus epididymidis ‚Üí ductus deferens)

(More? Spermatogenesis)

Tumor Rejection Antigen 1

(TRA-1-60, GRP94, HSP90B1) A cell surface marker (antigen) expressed on the surface of human teratocarcinoma stem cells (EC), human embryonic germ cells (EG) and human embryonic stem cells (ES). It is a sialylated keratan sulfate proteoglycan.

(More? Stem Cell Notes | OMIM - HSP90)

tunica albuginea

A dense mesenchymal connective tissue layer lying between germinal epithelium and cortical region of female ovary, or the equivilaent capsule of the male testis forming a thick fibrous capsule. Male forms the testicular septations and the mediastinal testis. Female lies under the surface epithelium of the ovary.

(More? Week 1 Notes)

twinning

Term for 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) A developmental syndrome that 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)

Comments

Use this page to access brief definitions of specific 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 this glossary list includes: texts listed on page 1 Reading of each notes section, Department of Anatomy Publications, WWW resources from NCBI, NIH, OMIM, NHMRC (Australia), AMA (USA), Office of Rare Diseases (USA), PubMed Medline Dictionaries, MSDS, Merck Manual home edn.

These notes are for Educational Purposes Only Please email Dr Mark Hill if you wish to make a comment about this current project.

Copyright: Dr Mark Hill Created: 01.06.1997 Updated: 11.05.2009

UNSW CRICOS Provider Code No. 00098G