From Embryology
Revision as of 08:45, 14 November 2019 by Z8600021 (talk | contribs)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Embryology - 14 Jun 2024    Facebook link Pinterest link Twitter link  Expand to Translate  
Google Translate - select your language from the list shown below (this will open a new external page)

العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt    These external translations are automated and may not be accurate. (More? About Translations)

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link


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? Neural System Development | Stem Cells | OMIM | PMID 18391221)


(Greek, tachypnea = rapid breathing) Clinical term describing an increased respiratory rate of greater than 60 breaths/minute in a quiet resting baby.
(More? Postnatal Respiratory)

Talairach-Tournoux atlas

(TT atlas) A human stereotactic brain atlas published in 1988 (Talairach J, Tournoux P (1988). Co-planar stereotaxic atlas of the human brain. Thieme, New York) used in many neural studies.
(More? neural | Talairach Org | list of labels | PMID 16284412)
Talipes equinovarus
Talipes equinovarus

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 Abnormalities | Medline Plus - Clubfoot)

Tanner stages

(Tanner scale) An anatomical staging system for measuring male/female sexual development at puberty. Stages were based upon genital and secondary sex characteristic development and named after James M. Tanner. Tanner, along with W.A. Marshall, published the stages for both girls (1969 PMID 5785179) and boys (1970 PMID 5440182), see also the review (1968 PMID 4297619). It is not a system for determining age.
(More? puberty | Tanner stages | PMID 5785179 | PMID 5440182)

TARP syndrome

TARP is an acronym for a set of abnormalities that include: Talipes equinovarus, Atrial septal defect, Robin sequence, and Persistence of left superior vena cava. This condition has also a lay description Pierre Robin syndrome with congenital heart malformation and clubfoot. Recently identified as caused by mutations in the RBM10 gene (located Xp11.23-q13.3), which encodes RNA binding motif 10.
(More? Musculoskeletal System - Abnormalities | Head Development - Abnormalities | Cardiovascular System - Abnormalities | PMID 20451169)
Tongue taste map
Tongue taste map


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 - Taste Development)


(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 | OMIM - tastin)


(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 PMID 12235714)


(Greek, taxis = order; nomos= science) Term used to describe the science of classification of organisms and has three key elements: characterization, classification and nomenclature.


(T-box) A family of transcription factors that are differentially expressed within the limb buds of the embryo: Tbx2 and Tbx3 are expressed in both limbs, Tbx5 is expressed in the forelimb and Tbx4 is expressed in the hindlimb. Transcription factors bind DNA and can activate or inhibit new gene expression.
(More? Developmental Signals - Tbx | Limb Development)
tectorial membrane
tectorial membrane

tectorial membrane

In the inner ear, the specialised extracellular matrix that cover the sensory epithelial hair cells of the organ of corti within the cochlea.
(More? Hearing - Inner Ear Development)


(singular, tooth) Integumentary system specializationarising evolutionarily as a tooth-like structure on the outer body surface of jawless fishes. Tooth development requires epitheilal/mesenchymal (ectoderm of the first pharyngeal arch and neural crest) interactions during early formation. Humans have 2 sets of teeth, 20 deciduous teeth (shed at different times over 20 year period) and 32 permanent teeth (ranging in shape and size).
(More? tooth | PMID19266065)


(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 System - 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 System Development)


(endbrain) The 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.
Secondary brain vesicles: telencephalon - diencephalon - mesencephalon - metencephalon - myelencephalon
(More? Neural System Development | Neural - Ventricular System Development)


Cell biology term referring to the enzyme that maintains the chromosome ends, the telomeres, involved in cellular ageing and the capacity for division. Absence of telomerase activity leads to the chromosome ends shorten during each cell division, becoming critically short and cell senescence then occurs.
(More? Cell Division - Mitosis)

telomerase reverse transcriptase

(TERT) An enzyme involved in the processes of telomere elongation. The process of telomere elongation can be detected in oocytes undergoing the pre-antral to antral stage of follicle development.


Genetic and cell biology term referring to the regions found at the ends of each chromosome and involved in cellular ageing and the capacity for division. The regions consist of repeated sequences protecting the ends of chromosomes and harbour DNA repair proteins. In the absence of the enzyme telomerase, these regions shorten during each cell division and becoming critically short, cell senescence occurs.
(More? Cell Division - Mitosis | Cell Division - Meiosis | Early human telomeres | Early human telomere length)


Cell division term referring to the fifth mitotic stage, where the vesicles of the nuclear envelope reform around the daughter cells, the nucleoli reappear and the chromosomes unfold to allow gene expression to begin. This phase overlaps with cytokinesis, the division of the cell cytoplasm.
Mitosis Phases: prophase - prometaphase - metaphase - anaphase - telophase
(More? Cell Division - Mitosis | Cell Division - Meiosis | Week 1)

tensor tympani

A muscle in the middle ear, contraction of this muscle pulls the malleus and tenses the tympanic membrane, dampening auditory ossicle movement. The muscle arises from auditory tube (cartilaginous portion) and is inserted into the malleus (manubrium near the root). Innervated by CN V mandibular nerve.

tensor veli palatini

A muscle which functions to open the auditory tube by pulling its lateral wall laterally and inferiorly.
(More? hearing | middle ear)

tentorial notch

The anatomical opening in the tentorium cerebelli fold of dura mater for the brainstem.
(More? Neural - Ventricular System Development)


(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)


Clinical term for a spermatozoa with abnormal morphology (small, large, defects in the head, tail, and/or mid-piece) present in the semen or ejaculate.
(More? spermatozoa)


(Greek, teraton = monster) The study of agents (teratogens) that can or may cause a structural abnormality following exposure during pregnancy.
(More? abnormal development)


(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.
(More? abnormal development)

term birth

(term) A clinical term for birth occurring within a defined range, 3 weeks before until 2 weeks after, the estimated delivery date. The American College of Obstetricians and Gynecologists Committee recently (2013) recently gave an opinion (no 579) definition of "term pregnancy" PMID 24150030 that attempts to give better uniformity: "the label "term" be replaced with the designations early term (37 0/7 weeks of gestation through 38 6/7 weeks of gestation), full term (39 0/7 weeks of gestation through 40 6/7 weeks of gestation), late term (41 0/7 weeks of gestation through 41 6/7 weeks of gestation), and postterm (42 0/7 weeks of gestation and beyond) to more accurately describe deliveries occurring at or beyond 37 0/7 weeks of gestation."
(More? Gestational Age | Birth)

terminal sac stage

(saccular 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.
Lung stages: respiratory embryonic stage - pseudoglandular stage - canalicular stage - terminal sac stage - alveolar stage
(More? respiratory | Lecture - Respiratory Development)

terminologia embryologica

Terminologia Embryologica (TE) A standardized list of terms/words used in the description of human embryonic and fetal structures. Produced by the Federative International Committee on Anatomical Terminology on behalf of the International Federation of Associations of Anatomists. A new second edition is in preparation for approval in 2019. The TE system replaces the earlier Nomina Embryologica. Terminologia Anatomica (TA) is a similar standard terminology for adult human anatomy.
(More? Terminologia Embryologica)

tertiary follicle

(antral follicle, small and large antral follicle or type 6 (3001-500 cells), type 7 (501-1000 cells)) Term used to describe the developmental stage of ovarian follicle development following preantral (primary) in describing the sequence primordial follicle, preantral follicle, antral follicle development within the ovary. In humans, a number of primordial follicles will begin to develop into primary follicles, some of which will then form antral follicles (secondary), with only a single antral follicle developing into the ovulating follicle (Graafian follicle) each menstrual cycle. Note that some classifications only refer to a primary (preantral) and secondary (antral) stage of follicle development.
Ovarian Follicle Stages: primordial follicle - primary follicle - secondary follicle - tertiary follicle - preovulatory follicle
(More? ovary | menstrual cycle | fertilization | Lecture - Fertilization)

tertiary villi

(tertiary chorionic villi) Term describing the final stage of embryonic placenta development. In humans, the conceptus after week 3 the chorionic secondary villi now develop placental blood vessels within the core extraembryonic mesoderm. The villi form finger-like extensions that are either anchoring chorionic villi attached to the maternal decidua or floating chorionic villi in maternal lacunae. The villi stages are ongoing as the placenta continues to grow through both the embryonic and fetal development.
Placental villi stages: primary villi - secondary villi - tertiary villi
(More? placenta | Lecture - Placenta Development)


(Latin testis = "witness") Anatomically 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 cell entering region of the paired mesonephric ducts (Wolffian ducts) which are preserved in male gonad development and lost in females.
(More? testis | Lecture - Genital Development | Male)


(Latin testis = "witness", plural testes) Anatomically 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? testis | Male | Lecture - Genital Development)

testis cord

The embryonic precursor of the seminiferous tubule. These form embryonically initially as a complex series of parallel Transverse loops separated by interstitial cells. During fetal development these cords elongate and expand leading to the convoluted structure of the seminiferous epithelium.
(More? testis | Male | Lecture - Genital Development)

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? testis | Male | Lecture - Genital Development | OMIM)


Testosterone structure cartoon
A steroidal hormone secreted by the gonad (testis and ovary) and in males is the androgen which regulates genital (gonadal and tract), secondary sex characteristics and neural development. The steroid is converted to the active metabolite dihydrotestosterone (DHT) by the enzyme 5-alpha reductase for the genital effects and estradiol by the enzyme aromatase for the neural effects.
(More? testosterone | Genital - Male_Development | Lecture - Genital Development)

tetralogy of Fallot

Tetralogy of Fallot
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". ICD-10 Q21.3 Tetralogy of Fallot Ventricular septal defect with pulmonary stenosis or atresia, dextroposition of aorta and hypertrophy of right ventricle.
(More? Tetralogy of Fallot |Cardiovascular System Development | Cardiac Tutorial | Lecture - Heart Development)


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 fertilization, these types of fertilization events fail to develop.
(More? abnormal development)


(Greek, thalassa = sea, haema = blood; US spelling, "thalassemia") A common human monogenetic haemoglobin disease. Three main forms; alpha-thalassaemia (α), beta-thalassaemia and delta-thalassaemia. Affected homozygote embryos of alpha-thalassaemia (Hb Bart’s hydrops fetalis) die either in utero, in late gestation or within a few minutes after birth.
(More? Prenatal Diagnosis)


(Greek, thalamos= bedchamber; plural, thalami) A central nervous system paired structure within the adult brain lying lateral to the 3rd ventricle, between the cerebral cortex and midbrain. The thalamus is formed from the secondary brain vesicle the diencephalon forming from primary brain vesicle, the prosencephalon. Functions include relaying both sensory and motor information to the overlying cortex and also the regulation of consciousness, sleep and alertness. The thalamus is then anatomically divided into 2 major components (dorsal and ventral) formed by clusters of nuclei.
Primary brain vesicles: prosencephalon (forebrain) - mesencephalon (midbrain) - rhombencephalon (hindbrain)
Secondary brain vesicles: telencephalon - diencephalon - mesencephalon - metencephalon - myelencephalon
(More? Neural | Lecture - Ectoderm Development | Lecture - Neural Development)

thawed cycle

An in vitro fertilization cycle in which previously frozen embryos are thawed for embryo transfer.
(More? Assisted Reproductive Technology)


(Greek, thek = box, case or sheath) Term used to describe an encasing structure.

theca folliculi

The 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? ovary | Genital System Development)
theca externa and interna
theca externa and interna

theca externa

(tunica externa, Greek, thek = box, case or sheath) 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? Lecture - Genital Development | ovary | Genital System Development)

theca interna

(tunica 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. These cells also have a role in the corpus luteum.
(More? Lecture - Genital Development | Ovary Development | Genital System Development)

Theiler stages

One system for staging mouse development, which divides development into 26 prenatal and 2 postnatal stages and is based upon the publication The House Mouse: Atlas of Mouse Development by Theiler Springer-Verlag, NY (1972, 1989). There are other mouse staging systems available: Staging of gastrulating mouse embryos by morphological landmarks in the dissecting microscope. Downs KM, Davies T Development 1993 Aug;118(4):1255-66 PMID: 8269852
(More: Mouse Development | Mouse Timeline)


(sodium ethylmercurithiosalicylate, C9H9HgNaO2S) The common (USA) name for an organomercury compound used as an antiseptic and antifungal agent. Used originally as a preservative in many vaccines Currently removed from most childhood vaccines due to the presence of mercury in the compound, the potential effects of its metaboic products and a potential linkage to autism.

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? Third Trimester | Fetal Development | Timeline human development)

third ventricle

(3rd ventricle) A fluid-filled space formed from neural tube lumen, located within the diencephalon (from the primary vesicle prosencephalon, forebrain).
(More? Lecture - Ectoderm Development | Neural - Ventricular System Development)


An increased tendency of blood to clot due to impaired natural anticoagulant or fibrinolytic pathways.
(More? Cardiovascular System - Blood Development)


(Greek, thyreos = sheild , eidos = form) endocrine gland located in the neck, the origin of the name reflects the organs anatomical structure. In the human fetus, the thyroid gland has an important role in metabolism and neurological development.
(More? Endocrine - Thyroid Development | Lecture - Endocrine Development | Abnormal Development - Iodine Deficiency)

thyroid diverticulum

(Greek, thyreos = sheild , eidos = form; Latin, diverticulum = by-road)) The primordium of the thyroid gland, beginning as an median endodermal thickening in the floor of pharynx. These epithelial cells then form an out-pocketing in the foregut (between the pharyngeal pouch 1 and 2) proliferating and extending ventrally and downward into mesenchyme as cords of cells. The pathway of their descent forms the thyroglossal duct, eventually loosing contact with the pharyngeal surface.
(More? Endocrine - Thyroid Development | Lecture - Endocrine Development)


(Greek, thyreos = sheild , eidos = form) An inflammatory process affecting the thyroid epithelium.
(More? Lecture - Endocrine Development | Endocrine - Thyroid Development | 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? PMID 16927301)

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.


An acronym for T cell leukemia 3 gene, which specifies spinal cord glutamatergic sensory neurons and is a selector gene in embryonic stem (ES) cells undergoing neural differentiation. Also called Respiratory Neuron Homeobox (Rnh) or HOX11L2.
(More? Hox | Molecular Development | Neural System Development | Stem Cells)

tocolytic agent

(Greek, tokos = "childbirth"; lysis = "to release") A clinical term used for any medication that inhibits labor (labor-inhibiting), slowing or halting uterine contractions. These drugs are used clinically to treat premature labor and permit continued fetal growth before parturition. The drugs inhibit contractility by affecting signaling pathways to contractile proteins (β-adrenergic re ceptor agonists, nitric oxide donors, magnesium sulphate, calcium channel blockers) or actions of known myometrial stimulants (prostaglandin synthesis inhibitors, oxytocin antagonists). A recent Cochrane study identified "no evidence that to suggest that ethanol is an effective tocolytic compared to placebo". PMID 26544539
(More? Birth)


(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 - Viral Infection)


Acronym for trial of labor.


Acronym for Termination Of Pregnancy.


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? TORCH Infections | Toxoplasmosis | Viral Infection | Rubella Virus | Cytomegalovirus | Hepatitis Virus | Abnormal Development)


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 Cells)

touch dome

Integumentary specialised sensory structure that contain innervated Merkel cells for light touch sensation. These Merkel cells (keratin 8 positive, K8+) develop in association with primary hair follicles and are organised among columnar basal keratinocytes expressing hair follicle keratin (keratin 17 positive, K17).
(More? touch)

Townes-Brocks syndrome

(TBS) Human autosomal dominant disorder associated with a SALL1 mutation. Characterized by: imperforate anus (82%), dysplastic ears (88%) frequently associated with hearing impairment (65%), and thumb malformations (89%). Other related abnormalities include: renal impairment (27%), including end-stage renal disease (ESRD) (42%), may occur with or without structural abnormalities (mild malrotation, ectopia, horseshoe kidney, renal hypoplasia, polycystic kidneys, vesicoutereral reflux); congenital heart disease occurs in 25%; foot malformations (52%) (flat feet, overlapping toes) and genitourinary malformations (36%) are common and mental retardation occurs in approximately 10% of cases. Rare features include iris coloboma, Duane anomaly, Arnold-Chiari malformation type 1, and growth retardation.
(More? renal abnormalities | PMID 20301618)


(poisonous) The ability of a substance to cause damage to cells or tissue whether or not at the point of contact. Toxicity is the potential ability of a substance to cause deleterious effects and is generally ranked: low (causes readily reversible changes which disappear after exposure stops), moderate (may cause reversible or irreversible changes to exposed tissue but not permanent injury) or high (capable of causing death or permanent injury in normal use). The term "toxic to reproduction" refers to teratogenic.
(More? chemicals)


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 | drugs)


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? TORCH | Abnormal Development)


(formerly p53) Acronym for tumor, protein 53 based on the molecular size (53,000 daltons). 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.
(More? 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 | cardiovascular)


(windpipe) In the embryo, a ventral out-pocket of pharynx endoderm that branches in week 4 stage 13 into the right and left bronchi within the lung buds. The endoderm has associated mesoderm that later differentiates to form most structures outside the respiratory epithelium. In the adult, the trachea forms the functional connection between the pharynx and larynx to the lungs.

(More? respiratory)

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 Development)


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 | blastocyst)

transforming growth factor-beta


(More? TGF-beta | Molecular Development)

transforming growth factor-beta receptor 2

(Tgfbr2, TGFβRII) Cell surface trans-membrane receptor for TGFβ and a constitutively active serine/threonine kinase. Ligand binding triggers heterotetrameric receptor complex formation (2 x TGFβ type 2, 2 x TGFβ type I). Receptor phosphorylation then phosphorylates downstream Smad targets which translocate into nucleus and act as transcription factors.

(More? TGF-beta | Molecular Development)

transient neonatal diabetes

(TNDM) One of the two main forms of neonatal diabetes mellitus diagnosed within the first 6 months of life. This form of diabetes is remitting and frequently relapsing. The other clinical subtype is the persistent permanent neonatal diabetes (PNDM).
(More? pancreas | maternal diabetes)


A cell cytoskeleton protein of the intermediate filament system. This intermediate filament protein is similar to nestin and is expressed, along with vimentin, in avian myogenic and neurogenic precursor cells.
(More? Muscle Development)
Transverse plane

transverse plane

The Transverse plane (cross-section, horizontal plane, axial plane, or transaxial plane) is plane that divides the body into superior and inferior parts and is perpendicular to the coronal and sagittal planes.
(More? coronal plane | sagittal plane | transverse plane | axes formation)

transverse septum

(septum transversum) see septum transversum a mesodermal region in the early embryo.
(More? liver | Gastrointestinal Tract Development | Respiratory Development - Diaphragm)

transzonal projection

(TZP) An ovarian follicle term describing the cellular membraneous extension from the granulosa cell through the zona pellucida to the oocyte cell membrane where it forms gap junctions or adherens junctions allowing signalling and adhesion between the two cells.
(More? ovary | oocyte)


Acronym for Taste-Receptor Cell, the cells associated with the initial sense of taste located on the tongue.
(More? Sensory - Taste Development)

Treacher Collins syndrome

(TCS) A genetic developmental abnormality results from autosomal dominant mutations of the gene TCOF1 encoding the protein Treacle, identified in 2006. The syndrome is characterized by hypoplasia of the facial bones, cleft palate, and middle and external ear defects. These defects may relate to the effects on neural crest migration.
(More? neural crest | OMIM - TCOF1 | PMID 8563749)

trial of labor

(TOL, trial of labor after cesarean, TOLAC) Birth term related to the offer for a normal vaginal delivery after a previous cesarean delivery.
(More? Birth | Caesarean Delivery | USA Guideline, updated 2005)


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)
trigeminal ganglion
trigeminal ganglion (stage 14)

trigeminal ganglion

(CN V, semilunar ganglion or Gasserian ganglion) Cranial nerve 5 is the largest of all the cranial ganglia. Embryonically first appears in week 4 (stage 10) from neural crest and later in week 8 (stage 22) lies beside the early cochlea and pontine flexure of the hindbrain. In the adult, it is mixed motor/sensory and has three major branches - ophthalmic nerve (V1), maxillary nerve (V2), mandibular nerve (V3); sensory - provide tactile, proprioceptive, and nociceptive afferents to the face and mouth, motor - innervate the skin of the face via ophthalmic (V1), maxillary (V2) and mandibular (V3) divisions. Special visceral efferent (SVE) axons innervate the muscles of mastication via the mandibular (V3) division.

(More? cranial nerve | Neural Crest Development | Head Development)


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 Development | Head Development)


(trigonum vesicæ) Urinary bladder triangular region bounded by the two ureters and the urethra. Historically thought to be formed mesonephric duct mesoderm, current research shows purely endoderm origin.
(More? Urinary Bladder Development)

trilaminar embryo

Term used to describe the early three (3) layered embryo 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. Do not confuse the term "germ cell layers" with "germ cells", which refer to the egg and sperm.
(More? gastrulation | Week 3 | Lecture - Week 3 Development | | Timeline human development)


A 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? Menstrual Cycle)


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? Embryonic Development | Fetal Development | Timeline human development)

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 | Medline Plus - trimethadione)


(alprim) An antibiotic used to treat urinary tract infections caused by bacteria. The drug inhibits bacterial nucleic acid and protein biosynthesis. USA FDA drug rating was B3.


Term describing multiple pregnancy of three embryos. There can be both monozygotic or dizygotic forms and triplets are often born premature and with a low birth weight.
(More? twinning)


Term in humans for 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.
(More? Abnormal Development)


(triptorelin acetate) A gonadotropin-releasing hormone (GnRH) agonist used clinically in an acetate or pamoate form inreproduction for assisted reproductive technologies (ART, in vitro fertilization, IVF). This decapeptide (pGlu-His-Trp-Ser-Tyr-D-Trp-Leu-Arg-Pro-Gly-NH2) agonist stimulates the pituitary to decrease secretion of gonadotropins luteinizing hormone (LH) and follicle stimulating hormone (FSH). The other clinical applications are for hormone-responsive cancers (prostate cancer or breast cancer), precocious puberty, and other estrogen-dependent conditions (endometriosis or uterine fibroids).
(More? Ovarian Stimulation | In Vitro Fertilization | Menstrual Cycle)

triradiate cartilage

The Y-shaped growth plate region within the developing hip seen in childhood x-rays. This cartilage region in humans does not postnatally completely ossify until about 14 to 16 years of age.
(More? Musculoskeletal System Development | Bone Development Timeline)

trizygotic triplet

(TZ) Term for triplets resulting from three seperate fertilization events, that is of three separate oocyte (egg) and spermatozoa (sperm).
(More? twinning)


Cell biology and immunology term for the process of T cell and B cell capture antigens through membrane fragments of antigen presenting cells (APC).


(TE. trophoblast layer, Greek, trophe = "nutrition") Embryology term used to describe the earliest layer formed in the blastocyst that will for the trophoblast layer. These cells contribute to extra-embryonic structures of the placenta.
(More? Week 1 | Week 2)


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 | OMIM - trophinin)


(TE; trophectoderm, Greek, trophe = "nutrition" and blast = a primordial cell) 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 (Template:Syncitiotrophoblast, cytotrophoblast).
(More? trophoblast | Week 2 | Week 3 | placenta)

truncus arteriosus

An embryological heart outflow structure, that forms in early endocardial tube stage and will later divides into the pulmonary artery and aorta. Term is also used clinically to describe the malformation of the cardiac outflow pattern, where only one artery arises from the heart and forms the aorta and pulmonary artery. There are several different, but comparable, classifications of this abnormality (Collett & Edwards type I-IV, Van Praagh A1-A4).
(More? Cardiovascular System Development | Cardiac Tutorial | Lecture - Heart)

Ts65Dn mouse

(Ts(1716)65Dn) The most widely used genetic and phenotypic mouse model for the human genetic disorder trisomy 21 or Down syndrome. The mouse strain contains a small translocation chromosome resulting in triplication of approximately half of the gene orthologs found on human chromosome 21.
(More? Trisomy 21 | mouse | PMID 7550346)


Acronym for 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)

tuberous sclerosis

(TSC) An autosomal-dominant disorder that presents with highly variable clinical indicators including: seizures, mental retardation, skin lesions, and hamartomas (benign, focal malformation that resembles a neoplasm in the tissue of its origin) affecting multiple organ systems such as the heart, brain, eye, and kidney. The survival rate is low (approximately 20%) and associated with a high incidence of perinatal morbidity and mortality.
(More? PMID 19452429)


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)

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 - straight tubule - rete testis - ductuli efferentes - ductus epididymidis - ductus deferens)
(More? Spermatozoa Development)

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 Cells | OMIM - HSP90)


(Latin, tunica = jacket) An anatomical and histological term for a layer (membrane) covering or lining a structure. Examples include tunica albuginea, tunica vaginalis, tunica muscularis, tunica mucosa.
(More? Ovary Development)

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? Ovary Development | Week 1)

tunica muscularis

Anatomical and histological term for the muscular layer of a tubular anatomical structure.

tunica vaginalis

The serous membrane pouch covering the testis formed from the saccus vaginalis of the peritoneum.
(More? testis descent image | Genital System Development)


Term used for more than a single pregnancy (singleton). The two major twinning forms are named according to the zygote number fertilized; monozygotic and dizygotic. Monozygotic (identical) resulting from one fertilised oocyte (egg) egg and a single spermatazoa (sperm) occurs at 3-5 per 1000 pregnancies. Dizygotic (fraternal) resulting from two eggs fertilised by two different spermatozoa, these twins do not share a placenta or fetal membranes. Monozygotic twins can share either placenta or membranes (monochorionic monoamniotic twins) depending when the twinning event occurs.
(More? Twinning)
Twin-twin transfusion syndrome

twin-twin transfusion syndrome

(TTTS) A developmental syndrome that occurs in monozygotic (identical) twins with monochorionic and diamniotic placenta with intrauterine blood transfusion from one twin (donor) to another twin (recipient) where there is an imbalance of blood flow from the donor twin to the recipient twin. Condition occurs in about 10% of monochorionic twins and clinically diagnosed by the alternate presence of polyhydramnios in one fetus and oligohydramnios in the co-twin.

(More? Twin-twin transfusion syndrome | twinning)

Glossary 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. and WHO ART terminology (2009).

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

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

Cite this page: Hill, M.A. (2024, June 14) Embryology T. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/T

What Links Here?
© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G