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A calcium-binding protein produced by glial cells (astrocytes, radial glia cells) with a trophic functions. A member of the S-100 protein family that have diverse cellular functions.
(More? Neural System Development | OMIM - S100B | PMID 17362503)


A general anatomical term meaning to formed a series of sac-like expansions. In lung development, the term refers to the process of lung epithelial cell differentiation, vascular remodeling and thinning of the mesenchyme. This process leads to enlargement of the diameter and surface area of the alveolar sacs. Distal epithelial cells form 2 populations: 1. cells flattens, thins, and spreads to form type I cells; 2. cells remain cuboidal, acquire surfactant filled lamellar bodies and differentiate into type II cells. Term is also used in describing the anatomical appearance of the large intestine.
(More? Respiratory System Development | Lecture - Respiratory Development)


(Latin, sagitta = "arrow") The anatomical plane dividing the body left and right. The plane section running exactly through the midline are the median plane or mid-sagittal plane. The plane sections away from the midline are parasagittal planes.


Acronym for Senescence-Associated Heterochromatic Foci, which are dense nuclear chromatin blobs found in cells undergoing senescence.


A zinc finger transcription factor putatively involved in inner cell mass development. Nomenclature from Sal-like gene, homologus to Drosophila homeotic gene spalt (sal) which influences development of the fly's gut.
(More? Week 2 | OMIM - SALL4 | Flybase - splat | MBoC image - DNA binding by a zinc finger protein)


(pelvic inflammatory disease) Clinical term referring to an inflammation of the uterine (fallopian) tube that can cause epithelial scarring leading to fertility problems and ectopic pregnancy. For example, salpingitis isthmica nodosa whcih is a nodular swelling of the isthmic segment of the uterine tube.
(More? Menstrual Cycle | Uterus Development | Bacterial Infection)


Acronym for Society for Assisted Reproductive Technology.

Santorini's duct

(accessory pancreatic duct, APD) A pancreatic duct which may be present as an anatomical variation due to the embryological origin of the pancreas from two pancreatic buds (dorsal and ventral). Named after Giovanni Domenico Santorini (1681 - 1737) an Italian anatomist who dissecting and delineating many anatomical features. Note the main pancreatic duct (MPD) from the dorsal bud, present in the body and tail of the pancreas (also called Wirsung's duct).
(More? Gastrointestinal Tract Development | Lecture - Gastrointestinal Development | Endocrine - Pancreas Development)


Acronym for Shaken Baby Syndrome, spectrum of neurological (eye, brain, subdural haemorrhage) and other (skeletal) injuries resulting from forcibly shaking an infant.
(More? Shaken Baby)


A chemical compound which has been found to allow embryonic stem cell in vitro propagation under chemically defined conditions in the absence of feeder cells, serum, and leukemia inhibitory factor. This chemical (a heterocycle compound) inhibits Ras-GAP (Ras remains activated) then enhancing stem cell renewal through the phosphatidylinositol 3-kinase (PI3K) pathway.
(More? Stem Cells)

scalp vascular plexus

A vascular feature visible on the head surface during late embryonic development from Carnegie stage 20 (week 8, day 50). Its development and position was used historically to stage late Carnegie embryos.
(More? Skull Development | Head Development)


One of several skull deformities (scaphocephaly, oxycephaly, plagiocephaly, trigoncephaly) caused by premature fusion (synostosis) of different developing skull sutures. Scaphocephaly results from premature sagittal suture synostosis.
(More? Skull Development | Head Development)

Scarpa's ganglion

(vestibular ganglion) The primary afferent vestibular neuron ganglion of the vestibular nerve, located within the internal auditory meatus.
(More? Inner Ear Development)


A disease caused by the parasitic blood flukes of the genus Schistosoma and one of the infectious diseases for humans and animals worldwide.

Schmidt-Lanterman cleft

(Schmidt-Lanterman incisures, clefts of Schmidt-Lanterman, segments of Lanterman, medullary segments) A histological term describing the small amounts of Schwann cell cytoplasm located within the myelin sheath surrounding a myelinated neuronal axon. These spaces form channels for nutrient and other substances to be exchanged.
(More? Neural System Development)

Schwann cell

Glial cell surrounding axons of peripheral nerves. Named after Theodor Schwann (1810 – 1882) a German physiologist who originally identified these cells.
(More? Neural System Development)

schwannoma-derived growth factor

(SDGF) A growth factor also called amphiregulin (AREG), imember of the epidermal growth factor (EGF) family having a role in regulating the epithelial proliferation.


(SOST) A protein produced by the bone-forming cells osteocytes that inhibits bone formation. This is required in maintaining bone remodeling and bone density. Mutations in the SOST gene cause sclerosteosis (high bone mass and sometimes hand defects). Over-expression in development, can cause loss of posterior limb structures through perturbing signaling centers in the developing limb by inhibiting the WNT signaling through LRP5/6.PMID20359476
(More? Bone Development | Limb Abnormalities | Limb Development | OMIM - sclerostin)


The ventromedial half of each somite that differentiates to form the axial skeleton (vertebral body and intervertebral disc).
(More? 2009 Lecture - Mesoderm Development | Musculoskeletal System Development | Week 3)


An acronym for subcortical maternal complex.


A diagnostic term used to describe the scanning or testing of a large population to detect specific changes in a smaller subset of this population.
(More? Prenatal Diagnosis | Neonatal Diagnosis)


(oscheoplasty) Clinical surgical term for the repair or plastic surgery of the scrotum. This procedure is often associated with the repair of hypospadia.
(More? Genital Abnormality - Hypospadia | Genital System - Abnormalities)


Acronym for Sexually Transmitted Infection, this term replaces the older term Sexually Transmitted Disease, any infection that can be transmitted by sex between partners. Some of these infections have been shown to impact upon embryonic and fetal development.
(More? Abnormal Development - Bacterial Infection)

second heart field

(SHF) Mesodermal region that forms adjacent to the earlier forming primary heart field and contribute to the rapid growth of the heart by elongating the tube and providing specific components (right ventricle and outflow tract field) of cardiac development (endocardium, myocardium, and smooth muscle). Recently suggested that this primary/secondary terminology should be replaced with gene specific expression domains or fields.
(More? Cardiovascular System Development | original Heart Notes | PMID: 19609448)

second polar body

The small cytoplasmic exclusion body formed when the oocyte (egg) completes meiosis 2 at fertilization. This exclusion body contains the excess DNA from the second reductive division (the first was formed from meiosis 1 at ovulation, and the third polar body is from division of this first body). These polar bodies do not contribute to the genetic complement of the zygote, embryo or fetus. Recent research in some species suggest that the space formed by the peripheral polar body (between the oocyte and the zona pellucida) can influence site of spermatozoa fertilization.
(More? Oocyte | Week 1)

second 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? Second Trimester | Fetal Development | Human Fetal Period | Development Week by Week)

secondary brain vesicle

The five cranial neural tube enlarged sac-like regions that differentiate to form the central nervous system brain. These regions form from the three primary brain vesicles. The caudal remainder of the neural tube not contributing to the secondary brain vesicles forms the spinal cord.
Secondary brain vesicles: telencephalon - diencephalon - mesencephalon - metencephalon - myeloncephalon
(More? Neural System Development | 2009 Lecture - Early Neural Development)

secondary follicle

(preantral follicle or type 5 (101-300 cells)) Term used to describe the developmental stage of ovarian follicle development following primary follicle when there are more than one layer of follicular cells around the oocyte. Used in describing the sequence primordial follicle, primary follicle, secondary follicle, tertiary follicle, preovulatory 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 tertiary follicle, 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 Development | Menstrual Cycle | Fertilization | Lecture - Cell Division/Fertilization | Oocyte Development)

secondary spermatocyte

Intermediate cell in spermatozoa development, within the testis seminiferous tubule they lie in the cell layer luminal to the primary spermatocyte. These smaller cells rapidly enter and complete meiosis II, forming the spermatids.
Spermatozoa development: primordial germ cell - spermatogonia - primary spermatocyte - secondary spermatocytes - spermatid - spermatozoa
(More? Spermatozoa Development | Cell Division - Meiosis | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)

secondary villi

(secondary chorionic villi) Term describing the second stage of embryonic placenta development. In humans, the conceptus during week 3 onward this stage of chorionic villi development consists of the trophoblastic shell cells (syncitiotrophoblasts and cytotrophoblasts) filled with extraembryonic mesoderm forming finger-like extensions into maternal decidua. Initially these finger-like projections cover the entire surface of chorionic sac and later become restricted to the placental surface. 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 Development | Lecture - Placenta)

secretory phase

(luteal phase) The phase of the menstrual cycle following ovulation, refers to the uterine lining (endometrium) endometrial glands secreting substances to support the growth and development of the conceptus both before and after implantation.
(More? Menstrual Cycle)


An inhibitory chaperone protein important cell division. Destruction of this protein leads to activation of separase. which then allows separation of sister chromatids (chromosomes) at mitosis metaphase-to-anaphase transition.
(More? Week 1)

Seessel's pouch

In early head development, an endodermal bud underlying the nasofrontal bud will form Sessel's pouch which later degenerates. In the chick embryo, this structure patterns first the nasal septum and later the nasal capsule, the ethmoid bone, and the upper beak.
(More? Chicken Development)


Term used to describe at the cell level the tendency of branches from the same neuron (self-branches) to selectively avoid one another in the developing nervous system. Thought to involve the neural cell adhesion molecule down syndrome cell adhesion molecule.


Term used to describe the process of breaking a solid structure into a number of usually equal size pieces. For example, in the development of body paraxial mesoderm into somites or sclerotome development into vertebra and intervertebral disc.


(Latin, sacire = "to take possession of") A clinical condition associated with discharge (abnormal, excessive, hypersynchronous) of a group of cortical neurons. Recurrent seizures of unknown etiology occur in Epilepsy.
(More? Neural System Development | Neural System - Abnormalities | Neural System Development)

sella turcica

(Latin sella = saddle, turcica = Turkish) A bony cavity within the head sphenoid bone in which the pituitary gland resides (pituitary fossa) The term refers to the shape of the cavity within the sphenoid bone. It lies just behind the lamina terminalis.
(More? Endocrine - Pituitary Development | Lecture - Endocrine Development | Image - Fetus week 10)

semicircular canals

Structure within the inner ear membranous labyrinth forming a series of fluid-filled loops of required for both balance and sensing acceleration. These loops are anatomically arranged in 3 different planes.
(More? 2009 Lecture - Hearing Development)

semaphorin 3a

(Sema3a, Collapsin 1, Coll1) A secreted protein (human 771 aa) that binds binds to the transmembrane protein neuropilin and acts as a chemorepellent factor during neural, renal, cardiac and peripheral vascular patterning. In the developing kidney glomeruli, it acts as a negative regulator of endothelial cell survival and has a role in podocyte differentiation.
(More? OMIM | Protein | OMIM neuropilin 1 | PMID: 19906865)

seminiferous tubule

Male genital structure within the testis where spermatozoa develop.
Spermatozoa Duct Pathway: seminiferous tubule - straight tubule - rete testis - ductuli efferentes - ductus epididymidis - ductus deferens
(More? Testis Development | 2009 Lecture - Genital Development)


In aging, generally at a cellular level with the accumulation of various ageing effects. Cells no longer carrying out their differentiated function and begine to decline. In many cases cells can divide a limited number of times before they become senescent, while oncogenic (cancer) cells can "escape" senescence and become proliferative.


See prenatal screening sensitivity


An important cell division protease allows the separation of sister chromatids (chromosomes) at mitosis metaphase-to-anaphase transition. This enzyme is activated by destruction of an inhibitory chaperone (securin).
(More? Week 1)


Bacteria present in the blood lead to an amplified and dysregulated immune response. Common infection sites for bacterial entry into the blood are infections in: lungs, urinary tract, abdominal cavity, and primary infections of the bloodstream.
(More? Circulatory Notes | Placenta Development)


Term used to describe the process of dividing a space or region by growth of a wall, forming a septum and can be applied to many anatomical and developmental processes. The term is often used in describing how the developing heart is divided into the two atria (atrial septation) and the two ventricles (ventricular septation).

septum primum

(primary septum) In early heart development in the atrial wall a superior region in the midline extends downward, forming the initial incomplete separation (septation) of the right and left atria leaving an opening the ostium primum. This initial structure partially breaks down forming the ostium secundum and later fuses with the septum secundum. Note that complete functional and anatomical separation of the right and left atria occurs after birth with activation of the pulmonary system.
(More? Heart Notes | 2009 Lecture - Heart | original Heart Notes)

septum secundum

(secondary septum) In early heart development, atrial septation is completed by an atrial wall growth to the right of the initial septum primum. Note that complete functional and anatomical separation of the right and left atria occurs after birth with activation of the pulmonary system.
(More? Heart Notes | 2009 Lecture - Heart | original Heart Notes)

septum transversum

(transverse septum) A mesodermal region in the early embryo. Identified externally as the junctional site between amnion and yolk sacs, and internally (within the embryo) lying directly beneath the heart and at the foregut/midgut junction. This ventro-dorsal "plate" of mesoderm contributes several structures including: the central tendon of diaphragm and some of the liver. The transverse septum has an important structural role in early embryonic development and is pierced by the gastrointestinal tract.
(More? Gastrointestinal Tract Development | Gastrointestinal Tract - Liver Development | Respiratory System - Diaphragm)


An acronym for sarcoplasmic/endoplasmic reticulum Ca2+-ATPase. This family of proteins are thought to be active calcium ion (Ca2+) uptake during mammalian sperm capacitation.


(Serpina14) Hormonally induced proteins secreted in large quantities by the endometrial epithelium during pregnancy in several species (ruminants, horses, pigs, dolphins and some carnivores) and not others (primates, rodents, lagomorphs and marsupials). These proteins belong to the serine proteinase inhibitor family.
(More? Uterus Development | PMID20678169)

Sertoli cell

The supporting cells in the testes (male gonad) that induce primordial germ cells to commit to sperm development. Support is nutritional and mechanical, as well as forming a blood-testis barrier. In development these cells secrete anti-Mullerian hormone (AMH), which causes the Mullerian duct (paramesonephric duct) to regress, and help to induce other somatic cells to differentiate into Leydig cells. The cells are named after Enrico Sertoli (1842 - 1910), and italian physiologist and histologist.
(More? Genital System Development | Lecture - Genital Development | Enrico Sertoli | UWA Blue Histology - Male Reproductive System)

Sertoli, Enrico

(1842 - 1910) An early italian physiologist and histologist who identified the support cells located in the male gonad, testes. His name is also used to identify a rare tumour of these cells, Sertoli's cell tumour (Leydig cell tumour).
(More? Lecture - Genital Development | Enrico Sertoli)

serum response factor

(SRF) A nuclear transcription factor of the MADS (MCM1, Agamous, Deficiens, SRF) box family, that interacts as a dimer with DNA at the serum response element (SRE). The SRE is a 10 base pair AT-rich sequence [CC(AT)6GG] also known as the CArG box and is present in a wide variety of genes. Expression of SRF is essential in early development for mesoderm and later during vascular development for endothelial cell function.


Acronym for Single-Embryo Transfers, a single embryos transferred when women undergo in vitro fertilization (Assisted Reproduction Technology) compared to double-embryo transfer (DET).
(More? In Vitro Fertilization)

sex chromosome

Term used to describe both the male Y chromosome and the female X chromosome. All other chromosomes that are not the sex chromosomes in the genome are described as autosomes. These terms are also used in describing the location or inheritance of genes and/or genetic disorders.

sexually transmitted infection

(STI) A term describing any infection, bacterial fungal or viral, that can be transmitted by sex between partners. Some of these infections have been shown to impact upon embryonic and fetal development. This term replaces the older one of Sexually Transmitted Disease (STD).
(More? Human Abnormal Development | Viral Infection | Bacterial Infection)


acronym for soluble vascular endothelial growth factor (VEGF) receptor-1 also known as sVEGFR-1. A soluble receptor which has been shown to trap VEGF-A stopping it from stimulating the formation of blood vessels in the cornea.
(More? Eye Notes | Ambati BK, etal. Corneal avascularity is due to soluble VEGF receptor-1. Nature. 2006 Oct 18)


An acronym for Split Hand Foot Malformation

Shigella flexneri

(S. flexneri) Gram-negative bacteria that can the infect human intestine and cause bacillary dysentery (shigellosis). The infection effects lead to severe colitis and diarrhea that dehydrates afflicted patients. The bacteria gain passage into the host cell through a type III secretion apparatus, injecting invasin proteins (IpaA–D) into intestinal epithelial cells.
(More? Human Abnormal Development | Abnormal Development - Bacterial Infection)

signal recognition particle

(SRP) Protein expression term for the cytoplasmic and abundant ribonucleoprotein (protein-RNA complex) that recognizes and targets proteins to the endoplasmic reticulum. Functions in the sorting of proteins being translated to different cytoplasmic compartments by binding the SRP receptor located on the endoplasmic reticulum membrane.
(More? Molecular Development)


A mammalian homologue of Sir2 (Silent information regulator 2) a NAD-dependent deacetylase that links metabolism with longevity in several species. Mammals have 7 homologues (SIRT1 to 7) which together potentially regulate several functions associated with physiology, calorie restriction, and aging.

shotgun sequencing

DNA sequencing method. Breaks chromosomal DNA into small overlapping fragments which are individually sequenced, the entire sequence is then "reconstructed" by linking overlapped sequences together. This method has been used for whole genome sequencing.
(More? Molecular Development)

shoulder dystocia

Clinical term describing a birth related condition where the fetal bisacromial diameter is greater than the maternal pelvic inlet antero-posterior diameter. This leads to the fetal anterior shoulder becoming impacted behind the maternal pubic symphysis. More simply, the shoulder becomes "stuck" during birth.
(More? Shoulder Dystocia | Birth)


(Seven in absentia homolog 1) Acronym for Seven in absentia homolog 1. A member of the RING finger proteins with E3 ligase activity. Null mice have low birth frequency and embryos exhibit developmental abnormalities. Other functions include induction by p53, inhibition of cell proliferation and promotion of apoptosis.
(More? PMID 22132158)

simple meningocele

A neural tube defect where herniation of the meninges occurs into the subcutaneous tissue of the back with overlying intact skin. One of the three classes of spinal meningocele. (simple, lateral and anterior sacral meningocele)
(More? Neural System - Abnormalities | Neural System Development)

Simpson-Golabi-Behmel syndrome

(SGBS) Abnormality very similar to Beckwith-Wiedemann syndrome (BWS) that is due to a gene mutation in glypican-3 (Gpc3), a member of the heparan sulfate proteoglycans that are linked to the cell surface through a glycosyl-phosphatidylinositol anchor.
(More? PMID10402475)

single letter amino acid code

The individual amino acids that form proteins can be represented by a standardised single letter code, three letter code or by their entire name.
A - Alanine (Ala) | C - Cysteine (Cys) | D - Aspartic Acid (Asp) | E - Glutamic Acid (Glu) | F - Phenylalanine (Phe) | G - Glycine (Gly) | H - Histidine (His) | I - Isoleucine (Ile) | K - Lysine (Lys) |L - Leucine (Leu) | M - Methionine (Met) | N - Asparagine (Asn) | P - Proline (Pro) | Q - Glutamine (Gln) | R - Arginine (Arg) | S - Serine (Ser) | T - Threonine (Thr) | V - Valine (Val) | W - Tryptophan (Trp) | Y - Tyrosine (Tyr)
(More? Molecular Development)

single umbilical artery

(SUA) Placental cord with only a single placental artery (normally paired). This abnormality can be detected by ultrasound (colour flow imaging of the fetal pelvis) and is used as an indicator for further prenatal diagnostic testing for chromosomal abnormalities and other systemic defects.
(More? Placenta Development | Placenta - Abnormalities | Prenatal Diagnosis | Ultrasound | Trisomy 21)

sinoatrial node

Heart region consisting of modified/specialized myocardial cells that initiate the heart beat. This cardiac pacemaker region lies at the junction of the right atrium and the superior vena cava (superior caval vein) and is initially formed from embryonic myocardial cells bordering the inflow tract of the early heart tube.
(More? Heart | Embryonic Heart Rate)

sinovaginal bulbs

The caudal ends of thepaired Wolffian ducts (mesonephric ducts) thought to be involved in vaginal development, they are under negative control by androgens.
(More? Vagina Development | Genital System Development)

sinus venosus

Functions as the vein that returns blood to the embryonic heart. An early developmental cardiovascular structure, thin walled cavity, forming the input to developing heart which has 3 venous inputs (vitelline vein, umbilical vein, common cardinal vein). Later in heart development this structure gets incorporated into the wall of the future right atrium. Abnormalities of sinus venosus development contribute about 10% of all atrial septal defects.
Blood Pathway: sinus venosus -> atrium -> ventricle -> bulbus cordis (outflow tract)
(More? Heart | Atrial Septal Defects)


Acronym for small interfering RNAs, a class of regulators of gene expression. They are generated from double-stranded RNA (dsRNA) precursors. There is also another class of small RNAs involved in gene expression present in cells, MicroRNA, based upon "Dicer".


(sirenomelia sequence) Human developmental malformation of the lower body characterized by fusion of the legs and a variable combination of visceral abnormalities, reported incidence of varies between 1.1 and 4.2 per 100,000 births. Classified into type I to type VII according mainly to the presence of skeletal elements in the thigh and leg ( Stocker and Heifetz, 1987). Two mouse models; 1. lacking Cyp26a1, an enzyme that degrades retinoic acid (RA), 2. reduced bone morphogenetic protein (Bmp) signaling in the caudal embryonic region.
(More? Developmental Signals - Retinoic acid | PMID21504909)


(Szl) A member of the secreted Frizzled receptor related protein (Sfrp) family identified in chicken. These proteins are antagonists and modifiers of Wnt and BMP signalling and is expressed in early heart development.
(More? Heart)

slipped disc

(disc = intervertebral disc) A vertebral column condition in which, due to a tear in the outer ring of fibrous connective tissue, the intervertebral cartilage disc bulges and protrudes into the spinal canal, pushing on the spinal cord or on the nerve roots. The subsequent pressure on the nerve can cause pain, numbness and/or weakness in the part of the associated skin and muscle.


A gene homologue 4 of Mothers Against Decapentaplegic (drosophila gene), tumor suppressor gene, its mutation causes 90% of human pancreatic carcinomas (pancreatic ductal adenocarcinomas). Deletion of SMAD4 in embryonic pancreatic epithelium had no apparent effect on pancreatic development.
(More? OMIM - SMAD4 | Endocrine Development - Pancreas | Article - knockout SMAD4)

small intestine

The gastrointestinal tract region lying between the stomach and large intestine. Functions include digestion and absorption of nutrients and is subdivided further in order into 3 regions: duodenum, jejunum and ileum.
Small intestine: duodenum - jejunum - ileum
(More? Intestine Development | Gastrointestinal Tract Development | Lecture - Gastrointestinal Development)


The zinc finger transcriptional repressors involved in regulation of epithelial to mesenchymal transitions in vertebrates.
(More? Molecular Development)

single-nucleotide polymorphism

(SNP) places in the genome sequence where one fraction of the human population has one nucleotide, while another fraction has another. SNPs are the most abundant form of DNA variation in the human genome with an estimated 7 million common SNPs with a minor allele frequency (MAF) of at least 5% across the entire human population. Most SNPs have no effect on phenotype, though a subset of SNPs are the genetic basis of human variability. Reference: DA Hinds etal., Whole-Genome Patterns of Common DNA Variation in Three Human Populations


Acronym for SPARC (secreted acidic cysteine rich glycoprotein) related modular calcium binding 1 matricellular protein. Expressed in developing gonad and mesonephros, downregulated in an anterior-to-posterior sequence in granulosa cells but persists in Sertoli cells.


Acronym for SPARC (secreted acidic cysteine rich glycoprotein) related modular calcium binding 2 matricellular protein. Expressed in developing gonad and mesonephros, in mesonephroi and Leydig cells.


Acronym for single-nucleotide polymorphism

Society for Assisted Reproductive Technology

(SART) An affiliate of the American Society for Reproductive Medicine composed of clinics and programs that provide ART (Assisted Reproductive Technology). SART reports annual fertility clinic data to the Centers for Disease Control and Prevention (CDC). SART Website
(More? Week 1 Notes - IVF)

soft marker

Ultrasound diagnostic term describing a structural change identified on scanning that may be transient and has little or no pathological significance. These markers may also be found in fetuses with congenital abnormalities, particularly trisomies and other karyotypic abnormalities. The most frequent soft markers identified are choroid plexus cysts and an echogenic intracardiac focus.
(More? Ultrasound | Prenatal Diagnosis)

soft palate

(velum, muscular palate) The muscular posterior portion of the palate forming the roof of the oral cavity. The bony anterior portion of the palate is called the hard palate, formed by maxillary and palatine bones.
(More? Palate Development | Lecture - Head Development | Head Development)

somatic mesoderm

Mesoderm derived from lateral plate mesoderm, and found closest to the ectoderm and separated from other component of lateral mesoderm (splanchnic, near endoderm) by the intraembryonic coelom. The somatic mesoderm forms connective tissue of the body wall and the skeletal elements of the appendicular skeleton and sternum. Note: Students often confuse the terms, and therefore the derivatives of, somatic mesoderm with "somitic mesoderm" (which is the somite).
(More? Mesoderm)


(Greek, soma = body) Cell biology term used to describe the cell body of a neuron. Also used in relation to body structures (somatic, somatosensory).
(More? Neural System Development)


(Greek, soma = body) Relates to the somatosensory system, sense perception.


Segmental block ("ball") of mesoderm formed from paraxial mesoderm adjacent to notochord (axial mesoderm). Form in lateral pairs in a rostro-caudal sequence, the number of pairs formed is used to stage many embryos. Somite structure is developmentally transient, dispersing and and differentiating to muscle, bone and connective tissues of the body. Two intermediate components called the sclerotome and dermamyotome (then dermatome and myotome). Note the paraxial mesoderm of the head region does not segment.
(More? Musculoskeletal System Development | Week 3 | Movie - Somitogenesis)


A transient cavity that appears within each of the early forming somite, which is then lost as cells proliferate within the somite.
(More? Musculoskeletal System Development | Week 3)


The process of segmentation of the paraxial mesoderm within the trilaminar embryo body to form pairs of somites, or balls of mesoderm. A somite is added either side of the notochord (axial mesoderm) to form a somite pair. The segmentation does not occur in the head region, and begins cranially (head end) and extends caudally (tailward) adding a somite pair at regular time intervals. The process is sequential and therefore used to stage the age of many different species embryos based upon the number visible somite pairs. In humans, the first somite pair appears at day 20 and adds caudally at 1 somite pair/90 minutes until on average 44 pairs eventually form.
(More? Musculoskeletal System Development | Week 3 | Movie - Somitogenesis)

sonic hedgehog

(SHH) A secreted growth factor that binds patched receptor (ptc) on cell membrane. SHH function is different for different tissues in the embryo. In the nervous system, SHH is secreted by the notochord, ventralizes the neural tube, inducing the floor plate and motor neurons. In the limb, SHH is secreted by the zone of polarizing activity (ZPA) organizing limb axis formation. SHH has still others roles in organ development in lung, pancreas, etc. SHH name derives from homology to the original fruitfly (drosophila) "hedgehog" mutation, where these flies have hairs in regions (ventral) which are normally hair-free, and therefore have a disrupted body pattern. Nomenclature note lower case shh for other species, upper case SHH in humans.
(More? sonic hedgehog | Musculoskeletal System Development | Neural System Development | Molecular Notes)


Acronym for Sry-related HMG-Box 2, a 317-amino acid protein transcription factor involved in regulating many different systems. It is a major regulator of stem cell function and has also been described as an oncogene in lung squamous cell carcinoma, the most common lung cancer.
(More? OMIM Sox2)


Gene and protein name for SRY-related high-mobility group (HMG) box 9, a 509-amino acid transcription factor protein involved in regulating many different systems, including mammalian testis determination and pancreas organogenesis (a progenitor cell specific marker and maintenance factor). See also Sry.
(More? Endocrine - Pancreas Development | Molecular Development | OMIM Sox9 | Protein Sox9 | PNAS Seymour PA, Freude KK, Tran MN, Mayes EE, Jensen J, Kist R, Scherer G, Sander M. SOX9 is required for maintenance of the pancreatic progenitor cell pool. Proc Natl Acad Sci U S A. 2007 Jan 31)


Term used to describe "position and time", usually in relation to a fate map of cells during developmental processes.

space of Nuel

Within the cochlea, an organ of Corti space between the outer pillar cells and the phalangeal and hair cells. Named after Jean-Pierre Nuel (1847-1920) a Belgian ophthalmologist.
(More? Inner Ear Development)


Drosophila homeotic zinc finger transcription factor gene (sal) which influences development of the fly's gut. Human homologue are SALL (sal-like) genes.
(More? Flybase - splat | MBoC image - DNA binding by a zinc finger protein)


See spermatazoa, this shortened term is used to describe the male haploid reproductive cell, often used generically (and incorrectly) to describe these cells and the fluid of the ejaculate. Term is a shortened form of scientifically correct term spermatazoa, singular term is spermatazoon.
(More? Spermatozoa | Fertilization | Week 1 - Spermatogenesis)

sperm annulus

(Jensen's ring; Latin, annulus = ring) A region of the mammalian sperm flagellum connecting the midpiece and the principal piece. The annulus is a septin-based structure formed from SEPT1, 4, 6, 7 and 12. Septins are polymerizing GTPases that can act as a scaffold forming hetero-oligomeric filaments required for cytokinesis and other cell cycle roles.
(More? Spermatozoa | Fertilization)


Intermediate cell in spermatozoa development, within the testis seminiferous tubule they lie in the luminal cell layer to the secondary spermatocyte. These small cells are haploid and in spermiogenesis change their cellular structure and shape to form spermatozoa.
Spermatozoa development: primordial germ cell - spermatogonia - primary spermatocyte - secondary spermatocytes - spermatid - spermatozoa
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)


(Greek, genesis = origin, creation, generation) The term used to describe the process of diploid spermatagonia division and differentiation to form haploid spermatazoa within the testis (male gonad). The process includes the following cellular changes: meiosis, reoorganization of DNA, reduction in DNA content, reorganization of cellular organelles, morphological changes (cell shape). The process following meiosis is the change in cell shape and organization, called spermiogenesis.
Spermatozoa development: primordial germ cell - spermatogonia - primary spermatocyte - secondary spermatocytes - spermatid - spermatozoa
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization | Week 1 - Spermatogenesis)


(Greek, genesis = origin, creation, generation) The maturation process of the already haploid spermatids into the mature spermatozoa shape and organization. This process involves reorganization of cellular organelles (endoplasmic reticulum, Golgi apparatus, mitochondria), cytoskeletal changes (microtubule organization) and morphological changes (cell shape, acrosome and tail formation). The process of maturation of the spermatids into spermatozoa: chromatin condenses, nucleus becomes smaller, the Golgi apparatus is modified to form the acrosome, microtubules are reorganised to form the tail, mitochondria are relocated to the initial segment of the tail and the majority of cell cytoplasm is discarded.
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)


(spermatogonial stem cell) These cells form in the embryo from the primordial germ cell and are located in the seminiferous tubule adjacent to the basal membrane. The cells can either divide and separate to renew the stem cell population, or they divide and stay together as a pair (Apr spermatogonia) connected by an intercellular cytoplasmic bridge to begin to differentiate and eventually form spermatazoa. Cells express the markers α6- and β1-integrin, GFRα1, CD9, Thy-1, and EpCAM but are negative for c-kit (Kit) or SSEA-1.
Spermatozoa development: primordial germ cell - spermatogonia - primary spermatocyte - secondary spermatocytes - spermatid - spermatozoa
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)

spermatogonial stem cell

(SSC) See spermatogonia
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)


(spermatozoon, singular term) The male haploid gamete cell produced by meiosis in the testis (male gonad) seminiferous tubule. In humans, produced from puberty onwards and develop from the diploid stem cell the spermatogonia. The developmental meiosis is called spermatogenesis and the final morphologiccal (shape) change is called spermeiogenesis. The mature human spermatozoon formed from the spermatid has a head, neck and tail and is about 60 µm long. At ejaculation these cells undergo capacitation are activated and become motile.
Spermatozoa development: primordial germ cell - spermatogonia - primary spermatocyte - secondary spermatocytes - spermatid - spermatozoa
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)

spermatozoa head

Following spermiogenesis, the first region of the spermatozoa containing the haploid nucleus and acrosome. In humans, it is a flattened structure (5 µm long by 3 µm wide) with the posterior part of nuclear membrane forming the basal plate region. The human spermatozoa is about 60 µm long, actively motile and divided into 3 main regions (head, neck and tail).
Spermatozoa development: primordial germ cell - spermatogonia - primary spermatocyte - secondary spermatocytes - spermatid - spermatozoa
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)

spermatozoa neck

Following spermiogenesis, the second region of the spermatozoa attached to basal plate, transverse oriented centriole, contains nine segmented columns of fibrous material, continue as outer dense fibres in tail. In humans, it forms a short structure (1 µm). The human spermatozoa is about 60 µm long, actively motile and divided into 3 main regions (head, neck and tail).
Spermatozoa development: primordial germ cell - spermatogonia - primary spermatocyte - secondary spermatocytes - spermatid - spermatozoa
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)

spermatozoa tail

Following spermiogenesis, the third region of the spermatozoa that has a (head, neck and tail). The tail is also divided into 3 structural regions a middle piece, a principal piece and an end piece. In humans: the middle piece (5 µm long) is formed by axonema and dense fibres surrounded by mitochondria; the principal piece (45 µm long) fibrous sheath interconnected by regularly spaced circumferential hoops; the final end piece (5 µm long) has an axonema surrounded by small amount of cytoplasm and plasma membrane.
Spermatozoa development: primordial germ cell - spermatogonia - primary spermatocyte - secondary spermatocytes - spermatid - spermatozoa
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)


The term describing a single spermatazoa.
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)

spermatogenic wave

Spermatozoa development term describing the helical patterns of development and maturation that along the length of the seminiferous tubule. There have been studies in human that suggest that these "waves" of consecutiveness of stages could be randomly generated and that the arrangement of stages in human seminiferous tubules may simply be a random occurrence (PMID8650667).
(More? Spermatozoa Development | Testis Development)

spermatogonial stem cells

(SSCs) The spermatagonia cells located beside the seminiferous tubule basal membrane that either divide and separate to renew the stem cell population, or they divide and stay together as a pair (Apr spermatogonia) connected by an intercellular cytoplasmic bridge to differentiate and eventually form spermatazoa.
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)

sperm protein 56

A component of the spermatozoa acrosomal matrix released to the sperm surface during capacitation.
(More? Spermatozoa Development | Testis Development | Fertilization | Lecture - Cell Division/Fertilization)

spina bifida

(spina bifida = "split spine") A neural tube defect (NTD) caused by failure of the early neural tube to close correctly. This defect can occur anywhere along the length of the neural tube at the level of the spinal cord. The defect can also occur at the spinal cord end of the neural tube, the posterior neuropore. Because the neural tube remains open in adddition to the neural effects, the surrounding spinal column/vertebra, connective tissue and skin may also be affected. The two main forms are open (neural elements are exposed to the external environment) or closed (occult, covered with skin).
(More? Neural System - Abnormalities | Folic Acid and Neural Tube Defects)

spinal anaesthesia

(epidural, sub-arachnoid block, US spelling; spinal anesthesia) 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)

spinal anesthesia

US spelling for spinal anaesthesia.

spinal canal

The mature space in the core of the spinal cord (filled with CSF) formed from the original lumen of the neural tube.
(More? Neural System Development)

spinal cord

The caudal (tail) end of neural tube that, together with the brain (rostral end of neural tube), forms the central nervous system (CNS). Note: the process of secondary neuralation contributes the very caudal end of the spinal cord.
(More? Neural System Development)

spinal dysraphism

(neural tube defects, NTD) abnormality resulting from a developmental incomplete closure of the neural tube leading to not only neural but also spinal column defects. The two main forms are open (neural elements are exposed to the external environment) or closed (occult, covered with skin).
(More? Neural System Development)

spinal ganglia

(dorsal root ganglia, DRG) A peripheral nervous system sensory ganglia derived from the neural crest, lying laterally paired and embryonically dorsal to the spinal cord, in the adult found anatomically ventral to the spinal cord. Connects centrally with the dorsal horn of the spinal cord. The term spinal ganglia tends to now replace the historic term dorsal root ganglia.
(More? Neural Crest Development | Neural System Development)

spinal muscular atrophy

(SMA) A childhood disease due to a reduction in spinal survival motor neuron (SMN) protein. The SMN protein has several functions including axonal transport of beta-actin mRNA. See also the transport ribonucleoproteins (RNPs) granules containing Gemin2 and Gemin3.
(More? Neural System Development)

spinal nerve

A mixed nerve (motor and sensory) arising as lateral pairs at each vertebral segmental level.
(More? Neural System Development)

spiral ganglion neurons

(SGN) The neurons within the cochlea of the inner ear that innervate the inner (Type I) and outer (Type II) hair cells.
(More? 2009 Lecture - Hearing Development)

splanchnic mesoderm

Gastrointestinal tract (endoderm) associated mesoderm formed by the separation of the lateral plate mesoderm into two separate components by a cavity, the intraembryonic coelom. Splanchnic mesoderm is the embryonic origin of the gastrointestinal tract connective tissue, smooth muscle, blood vessels and contribute to organ development (pancreas, spleen, liver). The intraembryonic coelom will form the three major body cavities including the space surrounding the gut, the peritoneal cavity. The other half of the lateral plate mesoderm (somatic mesoderm) is associated with the ectoderm of the body wall.
(More? Week 3 | Gastrointestinal Tract Development | Heart Notes )


The spleen develops within the gastrointestinal tract dorsal mesogastrium mesenchyme. With folding it is located on the left side of the abdomen and has a role initially in blood (haematopoisis, blood cell formation) and later immune system development. The spleen's haematopoietic function is lost with fetal development and lymphoid precursor cells migrate into the developing organ.
(More? Spleen Development | Gastrointestinal Tract Development)


The structure formed within the cell nucleus a complex assembly of proteins and RNA required for processing RNA, removing introns to generate the exon only mRNA sequence. The complex is formed from five small nuclear ribonucleoprotein particles (snRNPs) and more than 300 different proteins.

split hand foot malformation

(SHFM, ectrodactyly, cleft hand, central ray deficiency) highly variable malformation (genetic heterogeneous, 5+ loci mapped) of hand and foot abnormalities occuring in isolation or in association with other systematic anomalies (congenital heart defects).
(More? Musculoskeletal - Limb Development Abnormalities)

spontaneous abortion

(miscarriage) A pregnancy ending in the spontaneous loss of the embryo or fetus before 20 weeks of gestation.


(Spry) An embryonic developmental regulator that stimulates or inhibits several growth factor receptor tyrosine kinase (RTK) signaling pathways. First identified in Drosophila as a negative regulator of FGF (tracheal development) and EGF (eye development) signaling. Vertebrates have four Sprouty proteins (Spry1-4) expressed in many different tissues craniofacial structures (inner ear, tooth development), kidney, cardiac and limb buds. Recently also identified as regulating neural crest cell proliferation and survival.
(More? Molecular Development | PMID20459789)


(Serine, Proline, Serine) A protein general nuclear translocation signal (NTS) sequence. SPS is the single amino acid code for a 3 amino acid domain that when phosphorylated binds to importin7 and gets released from nuclear pore proteins.
(More? Molecular Cell, Vol 31, 850-861, 26 September 2008)

Src homology 2-containing protein tyrosine phosphatase

(Shp2) A non-receptor protein tyrosine phosphatase implicated in intracellular signaling controlling cell proliferation, differentiation and migration. Recently shown to be involved with guiding central nervous system cerebellar granule cell migration.
(More? PMID: 19635473)


(Sry, human; Testis-Determining Factor, TDF; Testis-Determining Factor on Y, TDY ) Gene name sex-determining region of Y, the gene locus on the Y chromosome encoding the male "testis determining factor", a protein transcription factor and 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? Y Chromosome | Lecture - Genital Development | Week 1 | OMIM)


Acronym for Selective Serotonin Reuptake Inhibitors, drugs used in the treatment of depression, antidepressants. Some examples include: citalopram (brand name of Celexa), fluoxetine (brand name of Prozac), paroxetine (brand name of Paxil) and sertraline (brand name of Zoloft). Some of these drugs are known teratogens.
(More? Abnormal Development - Maternal Drugs | Australia healthinsite - SSRIs)

Stage-Specific Embryonic Antigen-1

(SSEA-1) A cell surface embryonic marker (antigen) which has a role in cell adhesion, migration and differentiation and is often differentially expressed during stem cell development. Can be identified by Davor Solter monoclonal antibody MC-480 (SSEA-1).
(More? Stem Cells)

Stage-Specific Embryonic Antigen 4

(SSEA-4) A cell surface embryonic marker (antigen) of human teratocarcinoma stem cells (EC), human embryonic germ cells (EG) and human embryonic stem cells (ES) which is down-regulated following differentiation of human EC cells. This antigen is not expressed on undifferentiated murine EC, ES and EG cells but upregulated on differentiation of murine EC and ES cells. Can be identified by Davor Solter monoclonal antibody MC-813-70 (SSEA-4).
(More? Stem Cells)

Standard Event System

(SES) A new suggested standardised staging system for comparing development in different vertebrate species, initially based upon turtle embryology.

stapedius muscle

In the middle ear, a muscle that contracts to pull the stapes and therefore dampens auditory ossicle movement. The muscle is innervated by CN VII tympanic branch.
(More? Hearing - Middle Ear Development | Lecture - Hearing Development)


(stirrup) One of the 3 middle ear auditory ossicles (bones) that connects by the stapes footplate. The embryonic origin is from the second pharyngeal arch cartilage, Reicherts cartilage, which differs from the other two ossicles from the first arch cartilage.
(More? Hearing - Middle Ear Development | Lecture - Hearing Development)

stations of presentation

See fetal head station.


(fatty change, fatty degeneration, adipose degeneration) Pathology term referring to the process of abnormal retention of lipids within a cell.

stem cell

Term used to describe a cell with the potential to reproduce itself indefinitely, as well as differentiate into any other embryo tissue cell types. There are also a number of different specialised stem cell definitions: totipotential stem cell (as described above), pluripotential stem cell (capable of forming a number of different cell types), embryonic stem cell (derived from the blastocyst), cord blood stem cell (derived from placental cord blood), mesenchymal stem cell and adult stem cell (derived from adult or postnatal tissue).
(More? Stem Cells)

Stem Cell Antigen 1

(Sca-1) A cell surface marker (antigen) for mouse hematopoietic progenitor/stem cell subset. It is a member of the Ly-6 family of GPI-linked surface proteins (Mr 18 kDa).
(More? Stem Cells)

Stenson's duct

(parotid duct) Historic term for the major duct of the parotid gland that allows salivary gland secretions to empty into the oral cavity. Named after Niels Stensen (1638 - 1686) a Danish anatomist, natural scientist, and theologist.


Term used to describe an abnormal narrowing, usually in relation to a tube. For example, blood vessel, gastrointestinal tract or respiratory tract.
(More? Gastrointestinal Tract - Abnormalities)


The finger-like projections from the apical surface of sensory hair cells forming the hair bundle in the cochlea. Formed by tightly cross-linked parallel actin filaments in a paracrystalline array with cell surface specializations (tip links, horizontal top connectors, and tectorial membrane attachment crowns).


Several different definitions.
1. Biological, a type of hormone signaling molecule and due to membrane solubility the receptor is cytoplasmic or nuclear.
2. Clinical, in birth glucocorticoids (e.g., betamethasone, dexamethasone) for fetal lung maturation, received by the mother before delivery in anticipation of preterm delivery.
(More? Birth)

steroidogenic factor 1

(SF-1, Ad4BP, NR5A1) Molecular term for a nuclear receptor that regulates many aspects of adrenal and reproductive development and function. Roles include the expression control of steroidogenic enzymes and cholesterol transporters required for steroidogenesis, as well as the expression of steroidogenesis-stimulating hormones and their cognate receptors.
(More? Genital System Development | OMIM - NUCLEAR RECEPTOR SUBFAMILY 5 | Review - SF-1)


A fetus or infant delivered without signs of life after 20 weeks or more of gestation.


A term named by Pierre-Paul Grasse studying ants and termites used to describe a self-organising system arising from individuals interacting with their environment. This mechanism is suggested to have a role in the developing neural system, responding to a series of attractive and repulsive extracellular cues.
(More? Neural)

stimulated cycle

An ART cycle in which a woman receives drugs to stimulate her ovaries to produce more follicles.
(More? Week 1)


(stapes) An alternative name for the stapes of the 3 middle ear auditory ossicles (bones) that connects by the stapes footplate to the inner ear.
(More? Lecture - Hearing Development)


Gastrointestinal tract (GIT) foregut organ that has a major function in digestion. In humans, during week 4 initially as a dilatation of the foregut lying behind the heart. Differential growth of the ventral and dorsal walls establishes the greater curvature of the stomach and second rotation (of 90 degrees) occurs on the longitudinal axis establishing the adult anatomical orientation of the stomach.
(More? Stomach Development | Gastrointestinal Tract Development)


See (stomodeum).


(stomatodeum) The primordial mouth region of the developing head. Initially a ventral surface depression on the early embryo the region lies between the forebrain bulge (cranially) and the heart bulge (caudally) and between the maxillary and mandibular components of the first pharyngeal arch. At the floor of this surface depression lies the buccopharyngeal membrane, which breaks down (Carnegie stage 11) opening the gastrointestinal/respiratory tract to the amniotic space and fluid.
(More? Stage 11 - Buccopharyngeal Membrane | Gastrointestinal Tract Development | Head Development)

straight tubule

(tubulus rectus) A 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)


A neural term for the region of the basal ganglia that when sectioned had a "striped appearance". This region forms a connection and processing region between the cerebral cortex and the thalamus via the globus pallidus with the reticular part of the substantia nigra. Within the striatum, early cholinergic interneurons, from tangential migrating neuroblasts, development requires Gbx2 (homeodomain transcription factor) expression.
Neural tube: prosenecephalon (forebrain) - telencephalon - basal ganglia - striatum
(More? Neural System Development)

stria vascularis

In the inner ear, forms the outer wall of the cochlear duct of the mammalian cochlea and is composed primarily of three types of cells. Marginal cells line the lumen of the cochlear duct and are of epithelial origin. Basal cells also form a continuous layer and they may be mesodermal or derived from the neural crest. Intermediate cells are melanocyte-like cells, presumably derived from the neural crest, and are scattered between the marginal and basal cell layers. The stria forms endolymph and also contains a rich supply of blood vessels.
(More? Lecture - Hearing Development)


(Greek, stroma = "a cover, table-cloth, bedding") Histological term used to describe supportive cells within an organ, tissue or structure. The term is often paired with parenchyma, which describes the functional cells of an organ, tissue or structure. All organs can therefore be functionally divided into these 2 components, stromal/parenchymal.

stromal cell

(Greek, stroma = "a cover, table-cloth, bedding") Descriptive term in the ovary, for cells surrounding the developing follicle that form a connective tissue sheath (theca folliculi). This layer then differentiates into 2 cellular layers (theca interna, theca externa). This region is vascularized and involved in hormone secretion.
(More? Week 1)

styloid process

(SP) Term given to the cylindrical, long cartilaginous bone located on the temporal bone to which the muscles and ligaments involved in mastication and swallowing are attached. Elongated styloid process (Eagle’s syndrome), when clinical symptoms such as neck and cervicofacial pain occur.


Limb development term describing the proximal region the limb in the proximo-distal sequence: stylopod, zeugopod and autopod. The skeletal component of the upper limb (forelimb) is the humerus, and for the lower limb (hindlimb) is the femur.
(More? Limb Development | Bone Development)

subacrosomal layer

Part of the region located in the developing spermatozoa head perinuclear region, this intracellular region will form the acroplaxome and is located between the inner acrosomal membrane and the nuclear envelope. The other part of the perinuclear region is the post-acrosomal sheath (PAS) at the post-acrosomal region.
(More? Spermatozoa Development | Testis Development | Fertilization)

sub-arachnoid block

Alternate clinical term for an epidural or spinal anaesthesia.
(More? Birth)

subcapsular sinus

(marginal sinus) A space lying under the connective tissue capsule or covering, which receives lymph from afferent lymphatic vessels.
(More? Lymphatic Development)

subcortical maternal complex

(SCMC) A peripheral cellular region identified in mouse oogenesis, required for determining the first cleavage-stages of division.

subcutaneous injection

(SC) Clinically, an injection into the tissue lying between the skin and the underlying muscle often used in vaccination.

subventricular zone

(SVZ) A region/layer in the developing nervous system near the ventricular layer from which newly formed neuroblasts migrate. Also the site of adult neurogenesis (neural stem cells) in the anterior lateral ventricles.
(More? Neural System Development)

submucosal plexus

(Meissner's plexus) Neural network part of of the gastrointestinal tract enteric nervous system, lies within the submucosal layer between the external smooth muscle and the mucosa of the small and large intestines from the duodenum to the internal anal sphincter. The other network is the myenteric plexus (Auerbach's plexus) within the smooth muscle wall. Both are embryologically derived from neural crest migrating into the splanchnic mesoderm.
(More? Gastrointestinal Tract Development | Neural Crest Development)


The process of brain growth, which forms sulci, grooves or folds visible on fetal brain surface as gyri grow (gyration). In human brain development this occurs in the second to third trimester. Abnormalities of these processes can lead to a smooth brain (lissencephaly).
(More? Neural System Development | 2009 Lecture - Late Neural Development)


(pl. sulci) Term referring to the brain surface anatomy forming an infold on the cerebral cortex surface. The corresponding surface ridge is a gyrus.
(More? Neural System Development | 2009 Lecture - Late Neural Development)

sulfa drug

(sulfonamides) Historic antibacterial and antifungal drug family (sulfadiazine, sulfamethizole, sulfamethoxazole, sulfasalazine, sulfisoxazole) still in use today mainly to treat urinary tract infections, due to their concentration in urine before being excreted. Can interact with other medications and sunscreen compounds and some recent studies suggest a linkage between these drugs and developmental abnormalities. Discovered by Gerhard Domagk, a German physician and chemist, in 1935.


(sulfa drug) Historic antibacterial and antifungal drug family (sulfadiazine, sulfamethizole, sulfamethoxazole, sulfasalazine, sulfisoxazole) still in use today mainly to treat urinary tract infections, due to their concentration in urine before being excreted. Can interact with other medications and sunscreen compounds and some recent studies suggest a linkage between these drugs and developmental abnormalities. Discovered by Gerhard Domagk, a German physician and chemist, in 1935.


An acronymn for Small Ubiquitin-like Modifier protein, which are a family of small proteins that modify the function of other proteins by covalently attaching to and detaching from the other proteins.
(More? Molecular Development | Placenta Development)


A post-translational protein modification involving SUMO proteins attaching/detaching to other proteins and has a role in many different cellular processes. Similar to the degradation ubiquitination process.
(More? Molecular Development | Placenta Development)


(pulmonary surfactant) A mixture of lipids and proteins secreted by Type 2 alveolar cells between alveolar epithelium that reduces surface tension (detergent) at the air-liquid interface. The function is to prevent collapse of the lung at the end of expiration. In humans, these cells and their secretion develop towards the very end of the third trimester, just before birth. Hence the respiratory difficulties associated with premature births (Newborn Respiratory Distress Syndrome, Hyaline membrane disease).
(More? Respiratory Development | Lecture - Respiratory Development | Respiratory Abnormalities)

surfactant replacement therapy

A clinical birth term referring to the endotracheal instillation of a surface-active suspension for treating surfactant deficiency due to either preterm birth or pulmonary injury resulting in respiratory distress.
(More? Respiratory Development | Lecture - Respiratory Development | Respiratory System - Abnormalities)


Human reproductive arrangement where a woman (gestational carrier) agrees to carry a child for another person or couple (commissioning parent(s)) with the intention that the child will be raised by those commissioning parents. The oocytes (eggs) and/or spermatozoa (sperm) used to create the embryo(s) in the surrogacy cycle can be either from the commissioning parents or from a donor(s).
(More? In Vitro Fertilization)

survival motor neuron

(SMN) A motor neuron protein reduced in the disease childhood spinal muscular atrophy (SMA). The protein has several functions including axonal transport of beta-actin mRNA. See also the transport ribonucleoproteins (RNPs) granules containing Gemin2 and Gemin3.
(More? Neural System Development)


("join") Anatomical term used to describe in the skull to describe a form of articulation where the contiguous margins of the cranial vault bones are united by a thin layer of strong fibrous tissue. Term is also used to describe a surgical stitch.
(More? 2009 Lecture - Musculoskeletal | Medicine Practical - Bone Development | Musculoskeletal System - Bone Development)


Acronym for State Wide Infant Screening Hearing program. A government organised newborn hearing testing program using an automated auditory response technology. The program was introduced in NSW Australia in 2002 across 17 area health service coordinators.
(More? Hearing Development | Neonatal Development)


Surgical procedure for the division of the pubic symphysis cartilage during childbirth to aid obstructed labour. This historical surgical technique, developed in Europe late in the 18th century, has been used to save the lives of mother and child in obstructed labour and is still used in remote areas of some countries without easy access to medical facilities.
(More? Birth | Image - Symphysiotomy)

synacthen test

(synthetic ACTH test) A diagnostic test to both measure the amount of cortisol in the body and to determine the ability to produce cortisol.
(More? Lecture - Endocrine Development | Adrenal Development)

synaptonemal complex

A cell division structure that that forms between two pairs of homologous chromosomes. In meiosis prophase I, this structure initially assembles (synapsis) and then disassembles (desynapsis) leading 5 discrete stages (leptotene, zygotene, pachytene, diplotene, diakinesis ) based upon nuclear appearance.
(More? Cell Division - Meiosis | Oocyte Development | Spermatozoa Development | Week 1)

synaptotagmin VI

A calcium ion (Ca2+) sensor protein located human spermatozoa acrosomal membrane, the protein thought to be required at a step downstream of the intra-acrosomal Ca2+ efflux.
(More? Spermatozoa Development | Fertilization)


The process of cellular fusion to form a multinucleated cytoplasmic mass, occurs in placenta (syncytiotrophoblast) and skeletal muscle (myoblast to myotube) development. The process involves cellular recognition, migration, adhesion and finally cell fusion between the two interacting cells.
(More? Week 2 | Placenta Development | Musculoskeletal Development - Muscle Development)


A multinucleated cell currently thought to form by the fusion of another trophoblast cell the cytotrophoblasts, within the trophoblast layer (shell) of the implanting conceptus. In early development, these cells mediate implantation of the conceptus into the uterine wall and secrete the hormone (human Chorionic Gonadotrophin, hCG) responsible for feedback maintainance of the corpus luteum (in maternal ovary) and therefore maintaining early pregnancy.
(More? Trophoblast | Week 2 | Placenta Development | human Chorionic Gonadotrophin)


(human endogenous retrovirus, HERV) Envelope gene of a human endogenous defective retrovirus and a factor specifically expressed in syncytiotrophoblasts with several suggested roles. 1. may contribute towards immune tolerance of the developing embryo (human syncytin-2 and mouse syncytin-B). 2. may mediates cell-cell fusion to initially form multinucleated syncytiotrophoblast from cytotrophoblasts on the trophoblast layer (shell) of the implanting conceptus (human syncytin-1 and mouse syncytin-A).
(More? Week 2 | Placenta Development | OMIM)


(syncitium) A cellular term describing a single cell cytoplasm containing a number of nuclei that can be formed during development in two ways. Firstly, by incomplete cell division, as occurs in spermatogenesis when maturing spermatozoa do not complete cytokinesis and remain joined by cytoplasmic bridges. Secondly, by fusion of initially separate cells together, as occurs in placentation with syncytiotrophoblast formation and during skeletal muscle development when myoblasts fuse to form myotubes (he primordial skeletal muscle fibre).


Term used to describe the combined effect of exposure to more than one chemical at one time, or to a chemical in combination with other hazards (heat, radiation, infection), that results in an overall effect of such exposure to be greater than the sum of the individual effects of each hazard by itself.
(More? Human Abnormal Development)


Premature fusion of bones, in particular in relation to the different developing skull sutures.
(More? Skull Development | Head Development)


Term used to describe anatomically normally separate skeletal bones that are fused together.

synthetic ACTH test

(synacthen test) A diagnostic test to both measure the amount of cortisol in the body and to determine the ability to produce cortisol.
(More? Lecture - Endocrine Development | Adrenal Development)


An operation carried out to increase the size of the pelvic outlet to permit vaginal delivery of a baby. The procedure can be carried out under a local anaesthesia and involves a skin incision about 1.5–3 cm long and surgically dividing the cartilage of the pubic symphysis.
(More? Birth | PMID17388656)


(Greek, syn = together; daktulos = finger or digit) Term describing the presence of webbing between fingers, which may be single or multiple and may affect: skin only, skin and soft tissues or skin, soft tissues and bone.
(More? Limb Abnormalities)


(Synovial Apoptosis Inhibitor 1, SYVN1, HRD1) protein enzyme (ubiquitin ligase) expression is induced by the unfolded protein response (UPR) following an endoplasmic reticulum (ER) stress. Protein is also overexpressed in the synovial cells of patients with rheumatoid arthritis.
(More? Joint Development | OMIM - Synovial Apoptosis Inhibitor 1)


A sexually transmitted disease (STD) caused by the bacteria Treponema pallidum, a spirochete with a relatively small genome and requires a host to survive. First recognized in the 15th century in Europe, it can kill the early embryo or fetus or later in development lead to congenital deafness in an older fetus.
(More? Syphilis | Abnormal Development - Bacterial Infection | CDC - syphilis | Medline Plus - syphilis)


(Greek, syringo = tube, cele = swelling) An abnormality of a duct system. For example, seen in bulbourethral gland with dilatation of the Cowper's duct.
(More? Genital Male)

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. 2017 Embryology S. Retrieved October 23, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/S

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© Dr Mark Hill 2017, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G