Comprehensive Embryology Lecture Review

Vocabulary practice flashcards covering early embryogenesis, gastrulation, neurulation, cardiovascular morphogenesis and defects, gut rotation, and urogenital development.

Morula

A solid ball of dividing blastomeres produced by rapid cleavage divisions of the fertilized ovum prior to blastocyst formation.

Blastocyst

The early stage of development consisting of an inner cell mass (embryoblast), a fluid-filled blastocyst cavity, and an outer cell layer (trophoblast).

Trophoblast

The outer cell mass of the blastocyst that differentiates into the cytotrophoblast and syncytiotrophoblast to contribute to placental development.

Embryoblast

The inner cell mass of the blastocyst that differentiates into epiblast and hypoblast, ultimately giving rise to all tissues of the embryo.

Bilaminar Embryonic Disc

A two-layered flat disc formed during week 2 composed of a dorsal epiblast layer and a ventral hypoblast layer.

Epiblast

The dorsal cell layer of the bilaminar embryonic disc adjacent to the amniotic cavity that gives rise to all three definitive germ layers during gastrulation.

Hypoblast

The ventral cell layer of the bilaminar embryonic disc adjacent to the primitive yolk sac.

Gastrulation

The developmental process occurring during week 3 whereby the bilaminar disc is converted into a trilaminar embryo consisting of ectoderm, mesoderm, and endoderm.

Primitive Streak

A transient structure on the caudal dorsal surface of the epiblast through which epiblast cells invaginate to establish the primary germ layers.

Ectoderm

The outermost germ layer that gives rise to the skin, central nervous system (CNS), peripheral nervous system (PNS), eyes, and internal ear.

Mesoderm

The middle germ layer that gives rise to bones, connective tissue, skeletal muscle, the urogenital system, and the cardiovascular system.

Endoderm

The innermost germ layer that gives rise to the lining of the gut tube and its derived tissues, including the liver, pancreas, and lungs.

Neurulation

The process by which the neural plate forms, elevates its folds, and closes along the midline to create the neural tube.

Anterior Neuropore

The cranial opening of the developing neural tube that normally closes at $24$ days.

Posterior Neuropore

The caudal opening of the developing neural tube that normally closes at $28$ days.

Spina Bifida

A congenital neural tube defect resulting from failure of the posterior neuropore to close at $28$ days.

Anencephaly

A severe neural tube defect resulting from failure of the anterior neuropore to close, characterized by an open brain and absence of the skull vault.

Prosencephalon

The primary brain vesicle forming the embryonic forebrain, which later divides into the telencephalon and diencephalon.

Mesencephalon

The primary brain vesicle forming the midbrain that does not subdivide into secondary vesicles.

Rhombencephalon

The primary brain vesicle forming the embryonic hindbrain, which later divides into the metencephalon and myelencephalon.

Branchial (Pharyngeal) Arches

A series of embryonic arches that develop during week 4 to form the lower face, neck, throat, jaw and ear bones, and facial and neck muscles.

Cardiogenic Mesoderm

A specialized region of lateral plate mesoderm originally positioned cranial to the neural tube that forms blood islands (haemangioblasts and myoblasts) and the endocardial heart tubes.

Truncus Arteriosus

The distal arterial outflow segment of the primitive heart tube that gives rise to the proximal aorta and pulmonary artery.

Bulbus Cordis

The portion of the primitive heart tube that develops into the ventricular outflow tracts and the right ventricle.

Primitive Ventricle

The chamber of the embryonic heart tube that develops into the left ventricle.

Sinus Venosus

The caudal venous inflow segment of the primitive heart tube that gives rise to the smooth part of the right atrium and the coronary sinus.

Endocardial Cushions

Mesenchymal swellings appearing around day $28$ in the atrioventricular canal that fuse by day $35$ to divide the canal into right and left channels.

Septum Primum

The initial interatrial septum that grows down from the atrial roof toward the fusing endocardial cushions, bordered first by the ostium primum and later by the ostium secundum.

Septum Secundum

The thick, muscular second interatrial septum that develops adjacent to the septum primum, leaving an aperture termed the foramen ovale.

Foramen Ovale

A physiological shunt in the interatrial septum that directs oxygenated blood from the right atrium directly into the left atrium during fetal life.

Fossa Ovalis

The anatomical depression in the adult interatrial septum formed by the functional closure of the foramen ovale following the postnatal increase in left atrial pressure.

Ductus Venosus

A fetal vascular shunt that directs oxygenated blood from the umbilical vein directly to the inferior vena cava (IVC), bypassing the hepatic microcirculation.

Ductus Arteriosus

A fetal vascular bypass channel connecting the pulmonary trunk to the aorta, which shunts blood away from the fluid-filled lungs and fibroses to become the ligamentum arteriosum.

Ventricular Septal Defect (VSD)

The most common congenital cardiac malformation (accounting for $25\%$ of cardiac defects), occurring $90\%$ of the time in the membranous septum and $10\%$ in the muscular septum.

Foregut

The anterior segment of the primitive gut tube supplied by the coeliac trunk; forms the stomach, first part of the duodenum, liver, pancreas, and spleen.

Midgut

The middle segment of the primitive gut tube supplied by the superior mesenteric artery; extends from the caudal duodenum to the splenic flexure.

Hindgut

The posterior segment of the primitive gut tube supplied by the inferior mesenteric artery; extends from the splenic flexure to the upper anal canal.

Physiological Midgut Herniation

The normal temporary protrusion of the rapidly growing midgut into the umbilical cord during early development, followed by two rotations and return to the abdominal cavity by weeks $11\text{–}12$.

Omphalocele

A congenital anterior abdominal wall defect in which the midgut fails to return to the abdominal cavity by the $11\text{th}$ or $12\text{th}$ week, remaining herniated within the umbilical cord coverings.

Pronephros

The earliest, non-functional embryonic kidney system that develops transiently in the cervical region and completely regresses.

Mesonephros

The second embryonic kidney system extending from upper thoracic to lumbar ($L3$) segments; its duct persists in males as the ductus deferens.

Metanephros

The definitive third kidney system formed by the reciprocal interaction between the ureteric bud and the metanephric blastema.

Horseshoe Kidney

A congenital renal anomaly caused by the fusion of the lower poles of the kidneys as they develop in the pelvis, preventing their normal ascent to the upper abdomen.

Gubernaculum

A mesenchymal condensation that guides the descent of the gonads; in females, it persists as the proper ovarian ligament and the round ligament of the uterus.

Ectoderm

The primary embryonic germ layer that develops into the skin, central nervous system (CNS), peripheral nervous system (PNS), eyes, and internal ear.

Mesoderm

The middle embryonic germ layer that develops into bones, connective tissue, skeletal muscle, the urogenital system, and the cardiovascular system.

Endoderm

The innermost embryonic germ layer that gives rise to the epithelial lining of the gut tube and its derived tissues, including the liver, pancreas, and lungs.

Morula

A solid ball of dividing blastomeres formed by approximately $3\,\text{days}$ post-fertilisation during the period of rapid cleavage.

Blastocyst

An early embryonic structure formed at $4\frac{1}{2}\text{ to }5\,\text{days}$ comprising an inner cell mass (embryoblast), an outer cell mass (trophoblast), and a central fluid cavity.

Embryoblast

The inner cell mass of the blastocyst that gives rise to the tissues of the embryo proper.

Trophoblast

The outer cell mass of the blastocyst that contacts the uterine epithelium and differentiates into the cytotrophoblast and syncytiotrophoblast to support implantation.

Bilaminar Disc

The two-layered embryonic disc established during the second week of development, consisting of an upper epiblast layer and a lower hypoblast layer.

Gastrulation

The developmental process occurring in week 3 characterised by the formation of the primitive streak and primitive node, during which invaginating cells convert the bilaminar embryo into a trilaminar embryo with three germ layers.

Anterior Neuropore

The cranial opening of the developing neural tube that normally completes closure at $24\,\text{days}$ of development.

Posterior Neuropore

The caudal opening of the developing neural tube that normally completes closure at $28\,\text{days}$ of development.

Spina Bifida

A congenital neural tube defect resulting from the failure of the posterior neuropore to close.

Anencephaly

A severe neural tube defect resulting from failure of the anterior neuropore to close, characterised by an open brain and absence of the cranial vault.

Prosencephalon

The primary brain vesicle representing the embryonic forebrain at $4\,\text{weeks}$, which subsequently divides into the telencephalon and diencephalon by $6\,\text{weeks}$.

Rhombencephalon

The primary brain vesicle representing the embryonic hindbrain at $4\,\text{weeks}$, which subsequently differentiates into the metencephalon and myelencephalon.

Branchial Arches

A series of paired embryonic structures appearing in week 4 that form the lower face, neck, and throat; in humans, they develop into jaw and ear bones, facial and neck muscles, and parts of the larynx and pharynx.

Cleft Lip and Cleft Palate

Congenital facial malformations resulting from incomplete fusion of the maxillary, medial nasal, and palatal prominences derived from the branchial arch apparatus.

Truncus Arteriosus

The most cranial arterial outflow region of the primitive heart tube that gives rise to the proximal aorta and pulmonary artery.

Bulbus Cordis

A component of the developing heart tube that gives rise to the ventricular outflow tracts and the right ventricle.

Primitive Ventricle

The segment of the primitive heart tube that develops into the adult left ventricle.

Sinus Venosus

The venous inflow tract of the embryonic heart tube that develops into the smooth part of the right atrium (sinus venarum) and the coronary sinus.

Heart Tube Looping

The folding of the primitive heart tube within the pericardial cavity between days $23$ and $28$, which repositions the cardiac chambers into an adult-like anatomical alignment.

Endocardial Cushions

Mesenchymal swellings that arise around day $28$ from the walls of the common atrioventricular canal, growing and fusing to divide it into right and left canals.

Ductus Venosus

A foetal vascular shunt that directs oxygenated blood from the umbilical vein directly into the inferior vena cava (IVC), bypassing the liver, and fibroses postnatally to form the ligamentum venosum.

Foramen Ovale

A foetal shunt located between the septum primum and septum secundum that directs blood from the right atrium to the left atrium, bypassing pulmonary circulation, and closes at birth to form the fossa ovalis.

Ductus Arteriosus

A foetal vascular channel connecting the pulmonary trunk to the ascending aorta to bypass non-functioning lungs, which fibroses postnatally into the ligamentum arteriosum.

Probe Patent Foramen Ovale

An anatomical variation present in up to $25\%$ of individuals where an atrial probe can pass between atria; it is usually small and clinically insignificant.

Atrial Septal Defect (ASD)

A congenital cardiac defect with an incidence of $7:10{,}000$ births and a $2:1$ female-to-male ratio, resulting from defective development of the septum primum or septum secundum.

Ventricular Septal Defect (VSD)

The most common cardiac malformation, accounting for $25\%$ of all congenital heart defects, with approximately $90\%$ occurring in the membranous septum and $10\%$ in the muscular septum.

Foregut

The embryonic gut segment that develops into the stomach, first part of the duodenum, liver, pancreas, and spleen, supplied by the coeliac trunk.

Midgut

The embryonic gut segment developing into the caudal duodenum, small intestine, and large intestine up to the splenic flexure, supplied by the superior mesenteric artery.

Hindgut

The embryonic gut segment extending from the splenic flexure through the descending colon, sigmoid colon, rectum, and upper anal canal, supplied by the inferior mesenteric artery.

Omphalocele

A congenital anterior abdominal wall defect in which herniated midgut loops fail to return to the abdominal cavity by the $11\text{th}\text{ to }12\text{th}\,\text{week}$ of gestation.

Pronephros

The earliest, non-functional renal system formed at the cranial end of the embryo that completely regresses early in development.

Mesonephros

The intermediate kidney system spanning upper thoracic to lumbar ($\text{L3}$) segments; its duct persists in males to form the ductus deferens.

Metanephros

The definitive functional adult kidney system, formed when the ureteric bud branches from the mesonephric duct and invades the metanephric blastema.

Horseshoe Kidney

A congenital renal anomaly where the inferior poles of the left and right kidneys fuse together across the midline during their early development in the pelvis.

Pelvic Kidney

An ectopic kidney that fails to ascend normally from its embryonic origin in the pelvic cavity to its adult position in the lumbar region.

Bifid Ureter

A renal developmental anomaly caused by premature division or bifurcation of the ureteric bud prior to penetrating the metanephric blastema.

Descent of the Testes

The anatomical migration of the male gonads from the posterior abdominal wall through the inguinal canal into the scrotum, starting around the $7\text{th}\,\text{week}$ and finishing by the $9\text{th}\,\text{month}$.

Gubernaculum

The embryonic mesenchymal cord that guides gonadal descent; in females, its remnants form the ovarian ligament and the round ligament of the uterus.