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Acronym for Experimental Autoimmune Encephalomyelitis, an animal model of autoimmune demyelination diseases such as in immune encephalomyelitis and multiple sclerosis (MS)
(More? experimental autoimmune encephalomyelitis).

early fetal loss

Previously called blighted ovum or missed abortion, the term in fact generally describes embryo loss in first trimester.
Adherens junction cadherin


A calcium ion-dependent cell adhesion molecule, expressed on the cell membrane and shown to be required for the process of morula compaction in the preimplantation embryo.
(More? Blastocyst Development)


(icosanoids) Family of lipid signaling molecules (prostaglandins, prostacyclins, thromboxanes and leukotrienes) made from essential fatty acids (EFAs) oxidation (arachidonic acid). Act locally in autocrine or paracrine signaling pathways.


A serious clinical condition occuring during pregnancy leading to seizures or coma, which can occur in women with preeclampsia (high blood pressure and protein in the urine).
(More? Placenta - Abnormalities | Placenta Development)


Acronym for ExtraCorporeal Membrane Oxygenation an invasive therapy that has been investigated and utilized in newborn infants with cardiorespiratory failure.
(More? Birth)

E. coli

(Escherichia coli) Shortened version of Escherichia coli.
(More? Bacterial Infection)


(Greek, ecto = outside + derma = skin) One of the initial 3 germ cell layers (ectoderm, mesoderm, endoderm) formed during gastrulation. Ectoderm will form the nervous system (from the neural tube and neural crest ), sensory placodes and also generates the entire epithelial layer of the skin covering the embryo. The ectoderm is formed from the epiblast following gastrulation, with a central columnar epithelium (neural plate) and lateral cuboidal epithelium and is continuous with and forms the epithelium that lines the amniotic cavity. In humans, the ectoderm forms during week 3 and 4 of development.
(More? ectoderm | Week 3 | Gastrulation | Neural System Development | Neural Crest Development | Integumentary Development)


(Greek, ecto = outside; "enchyma" = tissue) The term used to describe ectoderm derived neural crest which contributes in the head region skeletogenic mesenchyme (cartilage, bone, dentine, and connective tissue) which in the body region are typically derived from mesoderm. The head region non-ectomesenchymal derivatives are neurons, glia and pigment cells.
(More? Neural Crest Development | | Head Development | Tooth Development | PMID 18224711 PMID 27493992 )

ectopic implantation

(ectopic pregnancy, Greek, ektopos = out of place) Term referring to blastocyst implantation at (abnormal) sites other than within the body of the uterus (uterine body), this can result in an ectopic pregnancy. The opposite term is eutopic.
(More? Ectopic Implantation | Week 2 Abnormalities | Week 2 | Category:Ectopic Pregnancy)

ectopic pregnancy

(Greek, ektopos = out of place) A pregnancy in which the fertilized egg implants outside of the uterus usually in the fallopian tube, but also on the ovary, or the abdominal cavity. Ectopic pregnancy is a dangerous condition that must receive prompt treatment.
(More? Ectopic Implantation | Week 2 Abnormalities | Week 2 | Category:Ectopic Pregnancy)

ectoplacental cone

In early rodent development, proliferating trophoblast cells at the attachment site extend towards the uterine epithelial cells forming a "cone". In the mouse, the polar trophoblast of the blastocyst gives rise to the ectoplacental cone and initiates on day 6 (E6.0) and is completed by day 8 post-coitum (E8.0).
(More? Mouse Development)

ectoplasmic specialization

(ES) A specialized cell junction located between Sertoli cells with blood-testis barrier (basal ES) and Sertoli cells with developing spermatids (apical ES). This histological feature of sperm development is described as a "hybrid" of several tyical junction types (adherens junctions, tight junctions and focal contacts).
(More? Spermatozoa Development)


Clinical acronym for estimated date of delivery. See also gestational age GA.


Clinical term for the tissue swelling due to accumulation of fluid. Used to describe the uterine changes during and following implantation of the conceptus. Term is also used in describing pathological changes in tissues due to excess fluid accumulation.
(More? Implantation)


A birth (parturition) term, referring to the shortening or thinning of the cervix, in preparation for birth.
(More? Birth)


Acronym for Episcopic Fluorescence Image Capture.


(oocyte or ovum) An alternative term used to describe the haploid female reproductive cell Germ Cell). The term is also used to describe the avian and reptilian shell enclosed structure.
(More? Week 1 | Chicken Development | Frog Development)

egg coat

(vitelline layer, zona pellucida) The specialized extracellular matrix surrounding the egg and has different names in different species. In non-mammalians, (sea urchins, chickens) it is the vitelline layer. in mammals, this layer is called the zona pellucida.
(More? Oocyte Development | Chicken Development)

egg retrieval

(oocyte retrieval) A clinical in vitro fertilization (IVF) procedure to collect the eggs contained in the ovarian follicles.
(More? Assisted Reproductive Technology)

egg transfer

(also called oocyte transfer) A clinical in vitro fertilization (IVF) technique to transfer of retrieved eggs into a woman's fallopian tubes through [L.htm#laparoscopy laparoscopy]. This procedure is used only in gamete intrafallopian transfer (GIFT) (see definition).
(More? Assisted Reproductive Technology)


(Greek, emboly = "a putting into") Historic term referring to the formation of a gastrula from a blastula by cellular invagination.
(More? gastrulation)


(Greek, en = in + bryein = to be full of) An egg that has been fertilized by a sperm and undergone one or more divisions. Also the set of early developmental stages in which a plant or animal differs from its mature form. See also human embryo.
(More? Embryonic Development | Australia NHMRC - A biological Definition)


(inner cell mass, Greek, en = in + bryein = to be full of and -blast, a primordial cell) The cellular mass component of the blastocyst that will give rise to the embryo. The remainder of cells that form the wall are the trophoblast cells.
(More? Embryonic Development | Week 2)


(Greek, en = in + bryein = to be full of) The science of studying embryo development, usually applied to all development before birth (in humans, included both the embryonic and fetal period).
(More? UNSW Embryology | Embryonic Development | Fetal Development)

embryonic cell cycle

Term describing the rapid rounds of mitosis occurring in early development following fertilisation. Cells alternate between mitosis and duplication of DNA without intervening growth periods (M, S, M phases) compared to the normal adult cell cycle that includes growth periods between each of these phases (M, G1, S, G2, M phase). Each round of cell division results in cells smaller in cytoplasm size that divide again before growth occurs.
(More? Mitosis)

embryonic diapause

A developmental term to describe a delay in implantation, during this period embryonic development also pauses. This can occur in many species but best characterised in the marsupial kangaroo. Insects can also have such a delay, described simply as diapause. Among placental mammals (Eutheria), it has been described in species in all the highly represented orders (Rodentia, Insectivora, Carnivora, Chiroptera, Edentata and Artiodactyla), but not in Primates.
(More? Kangaroo Development | PMID 22427933)
embryonic disc
Carnegie stage 5 embryonic disc

embryonic disc

(germ disc) Term used to describe the structure that will contribute the entire embryo within the conceptus. It is often used from the implanting bilaminar embryo stage epiblast and hypoblast), through to the trilaminar embryo (ectoderm, mesoderm and endoderm) following gastrulation. The term is no longer used after the disc folds. In humans, this can apply approximately from the middle of the second week through the third week of development when disc folding commences. Historically called the "germ disc" as it refers to this being the cellular source of the entire embryo, the term "embryonic disc" is now preferred to describe this stage of development.
(More? Carnegie stage 5 | Carnegie stage 6 | Carnegie stage 7 | Week 2 | Week 3 | Lecture - Week 3 Development | Practical - Week 3 Summary)

embryonic period

(embryonic stage, organogenic period) In humans, the first 8 weeks of development is considered the embryonic stage and is divided into 23 Carnegie stages based upon developmental milestones. This has also been described as the "organogenic period". The following time (week 9 to 36) is considered the fetal period.
(More? Embryonic Development)

embryonic testicular regression

(anorchia, vanishing testis syndrome) See anorchia.

embryo transfer

Placement of an embryo or embryos into a woman's uterus through the cervix after in vitro fertilization (IVF) or in the case of zygote intrafallopian transfer (ZIFT) (see definition), into her uterine (fallopian) tube.
(More? Week 1)


(tuberosity, a protuberance) An anatomical description for a narrow extension from a larger structure.
(More? hypopharyngeal eminence | median eminence | Head Development)


Visual development term describing the postnatal growth in eye size, resulting in an increased axial length, as the normal neonate eye first shows hyperopia (farsightedness).
(More? Sensory - Vision Development)

empty follicle syndrome

(EFS) Clinical, assisted reproductive technology term referring to when no oocytes are retrieved from mature ovarian follicles with apparently normal follicular development and estradiol levels, after controlled ovarian hyperstimulation (COH) despite repeated aspiration and flushing (incidence of 0.2 to 7%).
(More? Assisted Reproductive Technology | PMC2700670)


A chemistry term describing a chemical or compound that the basic molecular structure can occur as non-superposable mirror images. Some of these compounds can have identical chemical and physical properties, except for their ability to rotate plane-polarized light (+left/-right). While other compounds may possess in biological systems different carcinogenicity and teratogenicity. For example, the laevo (+) form of thalidomide appears to be the teratogenic compound.
(More? PMID 19414517)


A clinical syndrome of the central nervous system resulting in inflammation of the brain parenchyma and caused by a range of pathogens (viral, bacterial and protozoal infections). This infectious disease is due mainly to viral pathogens: Herpes simplex encephalitis 10%–20% of cases, Murray Valley encephalitis virus, Japanese encephalitis virus, Australian bat lyssavirus, West Nile virus, Hendra virus and Nipah virus. The pathogen is generally included in the specific encephalitis naming; Varicella encephalitis and Toxoplasma meningoencephalitis.
(More? Neural System - Abnormalities | TORCH Infections | PMC2700670)


A congenital anomaly characterised by herniation of the brain and/or meninges through a defect in the skull. In congenital anomalies statistics, encephalocele is not counted when present with either spina bifida or anencephaly. International Classification of Diseases, 9th Revision codes: 742.00–742.09 ICD-10-AM codes: Q01.0- Q01.2, Q01.8, Q01.9. The Australian rate of encephalocele in births from 2002–2003 was 0.5 per 10,000 births (24 women).
(More? Neural System Development)


Term used to describe the mass of an organism’s brain compared to that expected for its body weight.
(More? Neural System Development)


Term used to describe any diffuse disease of the brain that alters brain structure or function due to a wide range of teratogens.
(More? Neural System - Abnormalities)
Hearing - Neural Pathway
Hearing - Neural Pathway

endbulb of Held

Neural term for synapses in the auditory brainstem that are formed by auditory nerve fibers onto bushy cells in the cochlear nucleus.
(More? Hearing - Neural Pathway)


Clinical term for infections that are present all the time in a community.
(More? Abnormal Development - TORCH Infections | Bacterial Infection | Viral Infection)

endocardial cushion

Early heart development structures formed before atrial and ventricular septation occurs. These four heart wall in-folds (ventral, dorsal and two lateral) lie between the future atria and ventricles, later the posterior and anterior cushions fuse forming the primordial atrioventricular canals.
(More? Cardiovascular System Development | Cardiac Tutorial | Lecture - Heart Development)

endocardial cushion defect

(atrioventricular canal defect, septal defect) Term describing a cardiac abnormality due to partial or complete endocardial cushion developmental failure. This family of abnormalities can involve the atrial septum, the ventricular septum, and one or both of the atrioventricular valves.
(More? Cardiovascular System Development | Cardiac Tutorial | Lecture - Heart Development)

endocardial tube

At the embryonic disc stage the cardiogenic splanchnic mesoderm, lying above the notochord (prechordal) and buccopharyngeal membrane, forms the early heart tube. This primitive tube later forms the of the heart (atria and the ventricles) and outflow tract (truncus arteriosus). Initially a thin-walled tube, until myocardium development. In the human embryo, this stage of heart development begins during week 3.
(More? Cardiovascular System Development | Cardiac Tutorial | Lecture - Heart Development)


The epithelial membrane lining the inside surface of heart, which along with the endothelial layer forms a continuous lining of the entire cardiovascular system. The other two cardiac layers are the pericardium and myocardium. The heart embryonic origin is from the cardiogenic region of prechordal splanchnic mesoderm.
Heart layers: epicardium -> myocardium - > endocardium
(More? Cardiovascular System Development | Cardiac Embryology tutorial | Lecture - Heart Development)
Endochondral ossification
Endochondral ossification

endochondral ossification

(Greek, endon = within) The developmental term used to describe the process of the replacement of the embryonic body skeleton "template" formed by cartilage with bone. The osteoblasts are the bone-forming cells. The other bone formation process is intramembranous ossification.
(More? Bone Development | Musculoskeletal System Development)


(Greek, endon = within) Glands which release hormones into the blood stream. There are many specialized organs and tissues that release hormones into the bloodstream.
(More? Endocrine System Development)

endocrine disruptors

Term used to describe environmental chemicals that interfere with hormone function. Three main forms of interference: Mimic (effects of natural hormone), Block (binding of hormone to receptor or synthesis), Interfere (with hormone transport or elimination).
(More? Endocrine System - Abnormalities | Endocrine System Development)

endocrine gland

(Greek, endon = within) A gland (organ, tissue) that is specialized for secretion of a hormone into the bloodstream for general circulation.
(More? Endocrine System Development)


(Greek, endon = within) The process of taking in materials from outside a cell in vesicles that arise by the inward folding ("invagination") of the plasma membrane.


(Greek, endo = inside + derma = skin) One of the initial 3 germ cell layers (ectoderm, mesoderm, endoderm) formed by the process of gastrulation. The endoderm forms as a cuboidal epithelium and contributes not only to the trilaminar embryo, but also lines the yolk sac. It will form the entire epithelial lining of the gastrointestinal tract (GIT), contribute to the accessory organs of GIT and also forms the epithelial lining of the respiratory tract. Note that in the GIT it contributes both epithelium and the associated epithelial glands. In humans, endoderm forms during week 3 of development.
(More? Gastrulation | Endoderm | Week 3)


A cell surface transmembrane receptor for members of the transforming growth factor-beta (TGF-β) superfamily. Expressed on cardiovascular progenitors and then restricted to endothelial cells. In mouse, during formation of the cardiac endocardial cushions, expression is required for the endocardial to mesenchymal transition.
(More? PMID: 19703439)


(endolymphatic fluid, Scarpa's fluid) See endolymphatic fluid.

endolymphatic fluid

(endolymph, Scarpa's fluid) The fluid that fills all the membranous labyrinth of the inner ear, except for the cochlea scala tympani and scala vestibuli, which are filled with perilymph (perilymphatic fluid).
(More? Hearing Development | Inner Ear)
=endolymphatic sac
=endolymphatic sac

endolymphatic sac

(Greek, endo = inside) An inner ear structure of the membranous labyrinth that has anatomically both an intraosseous and extraosseous component. The sac is connected to membranous labyringth by the endolymphatic duct and has functions regulating endolymph that are both secretory and absorptive. Also the site of endolymphatic sac tumours (papillary cystadenoma of the vestibular aqueduct) either occurring sporadically or associated with the autosomal-dominant von Hippel-Lindau (VHL) disease, due to a germ line mutation.
(More? Hearing Development | Inner Ear)

endometrial gland

The mucous secreting gland associated with the epithelium lining the uterus. These glands develop and secrete each menstrual cycle and are thought to provide initial blastocyst nutrition prior to implantation.
(More? Menstrual Cycle | Week 1)


A chronic gynecological disease characterized by the growth of endometrial tissue outside the uterine cavity. The endometrial tissue is incorrectly located possibly in the muscular layer of the uterus. Can also be seen as the presence of tissue similar to the uterine lining in locations outside of the uterus, such as the ovaries, uterine (fallopian) tubes, and abdominal cavity.
(More? Genital System - Abnormalities | Genital System Development | Uterus Development)


(PID, pelvic inflammatory disease) See pelvic inflammatory disease.


The epithelium lining of the non-pregnant uterus. During pregnancy this epithelium undergoes changes described as the decidual reaction and is renamed the "decidua".
(More? Week 1 | Menstrual Cycle)

endoplasmic reticulum

(ER) (Greek, endon = within + plasmein = to mold + Latin, reticulum = network) An extensive and convoluted network of membranes within a eukaryotic cell continuous with the outer nuclear membrane and divided into two distinct functional regions (smooth = SER and rough = RER).
Endoreplication and cell cycle
Endoreplication and cell cycle. PMID 24556841


(endoreduplication) Cell cycle term referring to a cell cycle when mitosis cytokinesis is skipped and DNA is re-replicated leading to polyploid cells (polyploidy). For this to occur a cell exits the mitotic cell cycle in G2 phase and undergoes multiple S phases without entering mitosis and subsequent cytokinesis. Endoreplication occurs in specific cell populations in different species: plants; drosophila follicle and nurse cells; trophoblast stem cells forming rodent giant cells and some cancer cells. Note that multi-nucleated syncitotrophoblasts and osteoclasts form by cell fusion not endoreplication. Megakaryocytes form by a press called endomitosis.

(More? PMID 23284048 PMID 24556841 PMID 19884253)

endoscopic retrograde cholangiopancreatography

(ERCP) A medical procedure that allows an endoscope injected dye to display the pancreatic duct system on an x-ray (pancreatograms). A similar procedure can be used to display the liver biliary duct system.
(More? Gastrointestinal Tract - Abnormalities | Gastrointestinal Tract - Pancreas Development)

endoscopic third ventriculostomy

(ETV) A clinical operative procedure used for the treatment of patients with obstructive hydrocephalus.
Endosulfan environmental breakdown
Endosulfan environmental breakdown


The commercial name for a chemical (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro- 6,9-methano-2,4,3-benzodioxathiepin-3-oxide) broad-spectrum insecticide and acaricide to control agricultural insect and mite pests in crops. Technical-grade endosulfan is composed of two stereochemical isomers, alpha-endosulfan (70%) and beta-endosulfan (30%). An Indian study has suggested that it acts as an endocrine disruptor, exposure in male children may delay sexual maturity and interfere with sex hormone synthesis.
(More? Endosulfan | Endocrine System - Abnormalities | INCHEM | Endosulfan Phase-out 2010 | PMID 14644673 )


(Greek, endon = within + syn = together + bios = life) The close association of two organisms, one of which lives inside the other. The mitochondria within all our cells today are thought to have been derived from just such an arrangement.
(More? Mitochondria)


A 22 amino acid peptide with potent vasoconstrictive activity on vascular smooth muscle. There are three different isoforms (ET-1, ET-2 and ET-3) and their activity is mediated through G-protein coupled receptors (GPCR) on the cell membrane. Endothelins also have a role in regulating renal function and in retina following stress.
Blood capillary endothelium
Blood capillary endothelium


A simple squamous epithelium lining blood vessels.
(More? Blood Vessel Development)


(Lipopolysaccharides, LPS, lipoglycans) A cell wall component of Gram negative bacteria.
(More? Bacterial Infection)


A molecular term referring to a cis-regulatory sequence that can regulate levels of transcription from an adjacent promoter. Many tissue-specific enhancers can determine spatial patterns of gene expression in higher eukaryotes. Enhancers can act on promoters over many tens of kilobases of DNA and can be 5' or 3' to the promoter they regulate.
(More? Molecular Development)


Acronym for the enteric nervous system of the gastrointestinal tract.

enteral nutrition

(tube feeding) Nutritient delivery as fluid into the gastrointestinal tract. Can be used to describe postnatal nutrition through milk as well as a clinical method for delivering nutrition to patients. The method usually involves either a nasogastric or nasoenteral feeding tube into the stomach. An alternative is a surgical tube placed directly through the skin into the stomach or intestine (gastrostomy or jejunostomy). Enteral nutrition is often required for preterm or sick infants.
(More? Birth - Preterm | Milk | Postnatal Gastrointestinal Tract)

enteric nervous system

(ENS) Gastrointestinal tract neural network located within the tract wall that locally controls and coordinates intestinal functions (motility, epithelial secretion and blood flow) derived from the neural crest. It forms part of the autonomic nervous system with parasympathetic and sympathetic inputs as well as afferent nerve fibres, through the vagus nerves and spinal afferent pathways. The two main networks in the gastrointestinal tract (gut) wall are the myenteric plexus (Auerbach's plexus) and the submucosal plexus (Meissner's plexus). In humans, there are and estimated 200-600 million neurons that form the adult enteric nervous system.
(More? Gastrointestinal Tract Development | Neural Crest Development)

enteroendocrine cells

Endocrine cells found within the epithelium of the gastrointestinal tract that secrete enterohormones.
(More? Endocrine Development | Gastrointestinal Tract Development)

enterohepatic circulation

Term describing the cycle where bile salts and other substances excreted by the liver are absorbed by the intestinal mucosa and returned to the liver by the portal circulation.
(More? Gastrointestinal Tract Development | Cardiovascular System Development | Liver Development)


The insertion sites where tendons and ligaments meet bone (osteotendinous junctions, osteoligamentous junctions).


Historic term for "endodermal" germ cell layer and the embryonic structures which it forms.
(More? Week 3)


Acronym for N-ethyl-N-nitrosourea. ENU is a mutagen which can induce point mutations in DNA. Mutagenesis is by transferring an ethyl group to oxygen or nitrogen radicals in DNA, resulting in mispairing and base-pair substitution if not repaired. This chemical has been used to generate mutations in animal model systems.

epaxial muscle

Anatomical term describing skeletal muscles which lie dorsal (posterior) to the vertebral column developing from the somite myotome. In humans, this is only a small muscle group formed by the transversospinalis, longissimus, and iliocostalis muscles. Also at the ribcage level the levatores costarum muscles involved with rib elevation during respiration. The body muscles lying ventral (anterior) to the vertebral column are the hypaxial muscles.
{More? Muscle Development | Musculoskeletal System Development)


(Greek ependyma = upper cloak or garment) cell (ciliated squamous to columnar) epithelial membrane lining the cerebral ventricles (brain) and central canal (spinal cord).


(pl., ephilides; freckle) Clinical term describing a "freckle", that is a small brown or tan mark on the skin. These inherited features result from a copy of variant Melanocortin 1 Receptor (MC1R) gene and are common on fair skinned Celtic children. Melanocytes produce locally more melanin, this can also increase following exposure to ultraviolet radiation in sunlight.
(More? Integumentary | Neural Crest | OMIM MC1R)


A family of ligands for the transmembrane Eph-receptors, a group of receptor tyrosine kinases. Ephrins are involved with many development processes including neural development (cell adhesion, cell migration, boundary formation, axonal pathfinding, axon guidance, layer-specific arborisations, target area, topographic mapping and apoptosis). There are 9 members divided into two sub-families consisting of 6 ephrin A (A1-A6) and 3 ephrin B (B1-B3) ligand types. Ephrin A are glycosylphosphatidylinositol (GPI)-linked proteins. Ephrin B have a transmembrane domain and a cytoplasmic region.
(More? Neural System Development)


(Eph) A receptor protein-tyrosine kinase, mutations in this gene in human generates craniofrontonasal syndrome (CFNS): ocular hypertelorism, face malformation, cranium bifidum occultum, and craniosynostosis.
(More? OMIM - ephrin-B1)


(Greek, epi = above, upon) the layer of the bilaminar embryo (epiblast and hypoblast) that generates all three germ cell layers: ectoderm, endoderm and mesoderm. Bothe the endoderm and mesoderm are formed by epiblast cell migration through the primitive streak during gastrulation in week 3.. The remaining epiblast cells then form ectoderm and line the amniotic cavity. In human development, the epiblast layer forms in week 2 within the implanting blastocyst, at the bilaminar embryo stage (epiblast and hypoblast) of development.
(More? Week 2 | Week 3 | Gastrulation)


(Greek, "epibol" = a throwing or laying on) Term describing the division and movement of ectoderm cells during gastrulation, thinning and spreading this layer to cover the whole of the embryo.Cellular movements are thought to occur in all vertebrates, but have been most clearly identified in both zebrafish and frog (xenopus laevis).
(More? Zebrafish Development | Gastrulation)

epibranchial placode

Ectodermal thickened patches (paired placodes) in the cranial region that give rise to sensory neurons of the peripheral nervous system.


The outermost layer of the heart, generated by progenitor cells lying outside and cells migrating into the developing heart.
Heart layers: epicardium -> myocardium - > endocardium
(More? Cardiovascular System Development | Cardiac Embryology tutorial | Lecture - Heart Development)


(Greek, epi = above) The axis of a developing plant above the attachment point of the cotyledons.

epidermal differentiation complex

(EDC) human chromosome region (1q2) containing 63 linked genes within four gene families (filaggrin and FLG-like, small proline-rich region including loricrin and involucrin, and S100) that are molecular markers for adult stratified epidermis keratinocyte terminal differentiation.
(More? Integumentary System Development)

epidermal melanin unit

(EMU) Within the skin, the unit formed by a single melanocyte and the population of keratinocytes that receive the melanin that it has synthesised.
(More? Neural Crest Development | Integumentary Development)


Histological term describing the external cellular epithelial layer of the integumentary (skin) covering the entire body. This surface layer of keratinocytes is ectoderm in origin, while the underlying connective tissue layers of dermis and hypodermis are mesoderm in origin.
(More? Integumentary System Development)


Clinical term used to describe infections that spread rapidly in a community, a small epidemic is an outbreak. For example: measles and influenza viruses.
(More? Abnormal Development - Viral Infection)


(spinal anaesthesia, sub-arachnoid block) Clinical term for the administration to the mother of a regional anesthetic to control the pain of birth labor. The distribution of the analgesic effect is limited to the lower body.
(More? Birth)

epidural space

The space existing between the duramater of the spinal cord and the periosteum of the vertebral canal appears during the last week of the embryonic period (stages 20-23) around the circumference of the spinal cord. Patelska-Banaszewska M, Wozniak W. The development of the epidural space in human embryos. Folia Morphol (Warsz). 2004 Aug;63(3):273-9. PMID: 15478101
(More? Neural System Development | Ventricular System | Axial Skeleton)


(Greek, epi = above, upon) gene silencing that occur without changes in the genes (DNA) sequence, this changes can also be inherited.
(More? Molecular Development - Epigenetics | Science - Epigenetics: A web tour | The Welcome Trust - Epigenetics)


(Greek, epi = above, upon) entire genome including silencing that occur without changes in the genes (DNA) sequence, this changes can also be inherited.
(More? Molecular Development - Epigenetics)


(Greek, epi = above, upon) cartilaginous part of the larynx above the glottis, which in infancy directs food into the esophagus and not the trachea . Embryologically it develops in the foregut from the hypobranchial eminence, behind the undeveloped tongue, from which it separates at about 7 weeks. Postnatal anatomical development in humans involves a maturational descent in infancy (4 and 6 months of age). Contains lymphoid tissue (larynx-associated lymphoid tissue, LALT and Bronchus-associated lymphoid tissue, BALT).
(More? Gastrointestinal Tract Development | Respiratory Development)


(Greek, epi = upon, phenomena = observable occurrence) Term used to describe a secondary symptom or effect unrelated to the original disease or disorder. A side-effect is a specific kind of epiphenomenon that does occur as a direct consequence of the original disease or disorder.

epiphyseal plate

(Greek, epi = upon) The region within growing bones initially occupied by cartilage (hyaline) region (between the epiphysis and diaphysis) allows lengthwise growth of a bone. In the puberty, rapid growth in this region leads to height increase, which then ossifies in the adult.
(More? Musculoskeletal System Development)

episcopic fluorescence image capture

(EFIC) A microscopic imaging technique that serially sections embedded biological specimens and photographs the tissue autofluorescence (epifluorescence) from the block surface. This generates an in register 2D image stack. Technique was described for the mouse in 2002 (PMID 11743576).
(More? EFIC stage 13)


Neural term referring to the central nervous system region formed from the diencephalon that lies superior and posterior to the thalamus. This region develops into the pineal body and nearby structures; the posterior commissure, and the medullary layers of thalamus.
(More? Neural - Epithalamus Development)

epithelial cell rests of Malassez

(ERM, epithelial rests of Malassez) are a developmental part of the periodontal ligament cells that form around a tooth. These cells are initially derived from Hertwig's epithelial root sheath and are named after Louis-Charles Malassez (1842–1909) who first described them.
(More? Tooth Development)

epithelial tissue

(Greek, epi = upon + thele = nipple) Cells tightly linked together to form a sheet with little extracellular matrix.


(Greek, epi = upon + thele = nipple) Cells tightly linked together to form a sheet with little extracellular matrix. In contrast to the second main cellular organization, connective tissue or embryonic connective tissue, mesenchyme. Most epithelia (plural) in the body are embryonically derived from either ectoderm or endoderm germ layers with some also differentiating from mesoderm. Note: not "skin", which is the epithelium and includes the underlying connective tissue layers (dermis and hypodermis) mesoderm derived connective tissue layers, neural crest melanocytes, sensory structures, and other cells forming a complex tissue.
(More? Week 3 | Integumentary System Development)


A type II transmembrane serine protease, identified in mouse for compaction of the morula during preimplantation embryonic development. Expressed from 8-cell stage at blastomere contacts and co-localises in the morula with E-cadherin.
(More? Blastocyst Development | PMID 15848395)


(rete ovarii, broad ligament cyst) A group of epithelial tubules that can be located in the mesosalpinx possibly mesonephric duct in origin. Occurs when a segment of the mesonephric duct remains in the female, associated with either the ovary and broad ligament. This "male remnant" will appear as a cyst (broad ligament cyst, adnexal papillary cystadenoma of probable mesonephric origin, APMO) with an appearance that differs depending upon the state of differentiation when the original abnormality occurred.
(More? Uterus Development | Genital System Development)


(Greek, glotta = "tongue") Anatomical structure which covers the trachea during swallowing, preventing substances from entering the trachea and then lung. The epiglottis develops from hypobrachial eminence.
(More? Gastrointestinal Tract Development)


A serine protease inhibitor within the epididymis that coats the surface of human spermatozoa. The eynzme has an unknown function, though it has been shown to modulate prostate specific antigen (PSA) hydrolysis of semenogelin (a major protein of seminal fluid).
(More? Spermatozoa Development | Fertilization)


A statistical physics theory that states: anything that can happen will happen.


Form of apoptosis cell death associated with red blood cells.
(More? Cardiovascular System Development)


a protein hormone (from kidneys) that stimulates bone marrow stem cells to produce red blood cells. Can now be artifically manufactured in the laboratory to treat anaemia (following kidney failure).

ES cell

An acronym for Embryonic Stem cell, originally derived from the inner cell mass of the blastocyst, which is totipotential and can be grown undifferentiated in tissue culture (in vitro).
(More? Stem Cells)

Escherichia coli

(E. coli) A common eubacterial resident of the human gut. Also one of the leading gram-negative bacteria that cause neonatal meningitis and sepsis.
(More? Gastrointestinal Tract Development)

estimated date of delivery

(EDD) Clinical term for the birth date, calculated as the date 40 weeks from the first day of the last menstrual period.
(More? Birth)


Sex hormone found in both male and female. In the female, this hormone is produced by the ovaries and is responsible for development of secondary feminine sex characteristics. Together with progesterone these hormones also regulate changes that occur each menstrual cycle. During female development the fetal adrenal gland synthesises DHEA, an oestrogen precursor, converted by the placenta into estrogen (estradiol). In the male, Leydig cells produce estrogen into the rete testis fluid at variable levels in different species. During male embryonic development exposure to high levels of estrogen can lead to genital abnormalities.

(More? Menstrual Cycle | Endocrine - Adrenal Development | Placenta Development | Endocrine System Development)

estrous cycle

(oestrous cycle Latin, oestrus = gadfly, madness)The cyclic alterations in the animal female tract and in sexual receptivity related to hormone changes. When searching for related topics use the American (estrous) and British (oestrous cycle) spellings, which are both used in the literature.
Estrous cycle stages: proestrus - estrus - metestrus - diestrus
(More? Estrous Cycle | Mouse Estrous Cycle)


(heat) In most female mammals, the second stage in the estrous cycle immediately before metestrus characterized by a receptivity to a male and to mating. Pheromones may also be secreted only at this stage of her cycle.
Estrous cycle stages: proestrus - estrus - metestrus - diestrus
(More? Estrous Cycle | Mouse Estrous Cycle)


(French, etioler= to blanch or whiten) Having a thin, spindly appearance, poor leaf development, and no chlorophyll production.


(Greek, eu = true) The commonly occurring prokaryotes that live in water or soil, or within larger organisms; Archaebacteria and Eubacteria differ from each other in their metabolic abilities, the composition of their membranes, and the structure of their ribosomes.


(Greek, eu = true + karyon = nucleus) Referring to cells that contain a nucleus and other membrane bounded organelles. Note American spelling eucaryotic.

eukaryotic flagellum

(Latin, flagellum = whip) Plural is flagella. A protein assembly, consisting of microtubules, that can move a cell through a liquid medium (or a liquid medium over a cellular surface); a single cell usually contains only one or two flagella; eukaryotic flagella have the same organizational plan as cilia but flagella are much longer.


(EUROCAT) A European network of population-based registries for the epidemiologic surveillance of congenital anomalies. Started in 1979 with more than 1.5 million births surveyed per year in Europe, 43 registries in 20 countries, and 29% of European birth population covered. High quality multiple source registries, ascertaining terminations of pregnancy as well as births. The Australian classification system is called Australian Congenital Anomalies Monitoring System (ACAMS)
(More? Human Abnormal Development | eurocat | Prevalence Tables)


(euploid) Genetic term used to describe the normal cell genome chromosomal set (n, 2n, 3n) or complement for a species, in humans this is diploid (2n). The terms used to describe the classes of numerical chromosomal abnormalities include aneuploidy, polyploidy and mixoploidy.
(More? Genetics | Abnormal Development - Genetic | Cell Division - Meiosis | Trisomy 21 | Trisomy 18 | Trisomy 13)

eustachian tube

(auditory tube, otopharyngeal tube, pharyngotympanic tube) A narrow canal connecting the middle ear space to the back of the oral cavity. The tube allows ventilation, protection and clearance for the middle ear cavity. Ventilation is the pressure equalization in the middle ear. Clearance is to allow fluid drainage from the middle ear. Embryonic origin is from the first pharyngeal pouch. In development, the canal is initially both horizontal, short and very narrow leading to poor drainage and easy blockage.
(More? Middle Ear | Hearing | Hearing Abnormalities)


A block of protein encoding sequence of DNA in a gene. Many proteins are made of several exons "stitched" or spliced together by editing out non-coding (intron) sequences.
(More? DNA Notes)


The macromolecular complexe that post-transcriptionally regulate gene expression by degrading messenger RNAs.
(More? Molecular Notes | UNSW Cell Biology)

expectant management

A clinical term associated avoiding treatment and letting the miscarriage take its natural course, often associated wit first trimester miscarriage (early fetal loss).

experimental autoimmune encephalomyelitis

(EAE) an animal model of autoimmune demyelination, such as in multiple sclerosis (MS).
(More? PMID: 16632554)


(Greek, ekstriphein = "turn inside out", bladder exstrophy, cloacal exstrophy) Term used to describe developmental abnormalities where the structure has been anatomically inverted. For example, bladder exstrophy, a congenital malformation with bladder open to ventral wall of abdomen (between umbilicus and pubic symphysis) and may have other anomolies associated with failure of closure of abdominal wall and bladder (epispadias, pubic bone anomolies).
(More? bladder exstrophy | Renal System - Abnormalities)

exstrophy of the bladder

See bladder exstrophy


Anatomical term describing a body movement by skeletal muscle contraction to straighten and increase the angle between two skeletal parts. The opposite movement is flexion.

external auditory canal

See external auditory meatus.

external auditory meatus

(external auditory canal) The canal running from the external ear (auricle) to the tympanic membrane (eardrum). Embryonically this structure is formed by the first pharyngeal cleft (groove) ectoderm.
(More? Outer Ear | Hearing | Lecture - Sensory Development)

external cephalic version

Clinical (obstetric procedure) term for attempted conversion of a fetus from a nonvertex to a vertex presentation by external manipulation.
(More? Birth)

extracellular matrix

(ECM) The material secreted by cells and which they are embedded. Connective tissues contain large amounts of extracellular matrix and epithelial cells sit on a specialized extracellular matrix, the basal lamina. The oocyte is surrounded by a specialized extracellular matrix, the zona pellucida. Extracellular matrix can be different in different tissues and consists of fibers (mainly collagen) and ground substance.
(More? Cell Biology Lecture - Extracellular Matrix)

extrahepatic bile ducts

(EHBDs) Gastrointestinal term used to describe the liver and gall bladder hepatic, cystic, and common bile ducts.
(More? GIT Notes - Liver | GIT Notes - Gall Bladder)

extra-embryonic membrane

Term used to describe each of the amnion, yolk sac, allantois and chorion membranes. Amniotic membrane, ectoderm origin innermost membrane, produces amniotic fluid (reptiles, bird, and mammals are amniotes). Yolk sac, endoderm origin, associated with nutrition in reptiles and birds (mammals source of primordial germ cells and blood cells). Allantois, endoderm origin, in reptiles and birds acts as a reservoir for wastes and mediates gas exchange; in mammals is associated/incorporated with connecting stalk/placental cord fetal-maternal interface. Chorioic membrane, mesoderm origin, outermost layer in reptiles and birds acts in gas exchange; in mammals incorporated into the placenta and its functions.
(More? Placenta Development | Week 2 |Gastrointestinal Tract Development)

extraembryonic coelom

The space found outside the embryo, amniotic cavity, yolk sac and chorionic cavity.
(More? Coelomic Cavity Development)

extraembryonic mesoderm

Cells from the conceptus that contribute to placenta and fetal membranes. Described as "extraembryonic" because it is tissue lying outside the embryonic trilaminar disc (ectoderm, mesoderm and endoderm) and "mesoderm", because of the connective tissue cellular organization. In animal models, this extraembryonic mesoderm has been shown to arise from the same source as embryonic mesoderm during gastrulation.
(More? Placenta Development | Week 2 |Gastrointestinal Tract Development)

extravillous cytotrophoblasts

(EVCTs) The trophoblasts which invade the uterine endometrium along with syncytiotrophoblasts and also secrete human chorionic gonadotropin hormone (hCG).
(More? Placenta Development | Week 2)

extreme preterm deliveries

Clinical term to describe birth between 23 to 27 weeks gestation.
(More? Birth - Preterm)


Histology/pathology term used to describe cellular growth beyond the surface epithelium from which the cells originates. Used to describe the type of growth seen in epithelial cancer (cervical cancer).

Extracorporeal Membrane Oxygenation

(ECMO) an invasive therapy that has been investigated and utilized in newborn infants with cardiorespiratory failure.
(More? Respiratory System Development | Bookshelf - HSTAT)

eye field

Early embryonic region located at the anterior end of the neural plate and is the first indication of vertebrate optic development. Occurs initially a large single domain.
(More? Sensory - Vision Development | Lecture - Sensory Development)

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

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Cite this page: Hill, M.A. (2024, May 24) Embryology E. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/E

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