Embryology Hub
Developmental origins and key embryologic processes shaping human anatomy.
Embryology Hub
Pre-Embryonic Phase
Gametogenesis, fertilization, cleavage, blastocyst formation, and extraembryonic membranes.
Cell Division & Gametogenesis – Mitosis, Meiosis Explained
An overview of the fundamental processes of cell division (mitosis and meiosis) and the formation of male and female gametes (spermatogenesis and oogenesis).
Spermatogenesis – Stages from Spermatogonia to Sperm
An overview of spermatogenesis, the process by which spermatozoa are formed in the testes, including spermatocytogenesis, meiosis, and spermiogenesis.
Oogenesis – Ovum Formation & Follicular Development
An overview of oogenesis, the formation of the female gamete (ovum), detailing follicular development, meiotic divisions, and the formation of the corpus luteum.
Fertilization – Fusion of Sperm & Ovum
An overview of fertilization, the process of fusion between male and female gametes in the uterine tube to form a zygote, initiating embryonic development.
Cleavage & Blastocyst – Morula to Implantation
An overview of the early embryonic stages, from the mitotic cleavage of the zygote into blastomeres to the formation of the morula and the blastocyst.
Embryonic Phase
Germ layers, primitive streak, mesoderm subdivisions, notochord, neurulation, and folding.
Germ Layers – Gastrulation & Trilaminar Disc
An overview of gastrulation, the crucial process in the third week where the bilaminar disc transforms into a trilaminar embryo with ectoderm, mesoderm, and endoderm.
Primitive Streak – Axis Formation & Mesoderm
An overview of the primitive streak, a key structure that appears in the embryonic disc and is essential for establishing the body axes and forming mesoderm.
Intraembryonic Mesoderm – Paraxial, Intermediate, Lateral
An overview of the differentiation of the intraembryonic mesoderm into the paraxial (somites), intermediate (urogenital), and lateral plate (body wall) mesoderm.
Notochord – Embryonic Axis & Neural Induction
An overview of notochord development from the primitive knot. Learn its role as the primary inductor for the neural tube and its fate as the nucleus pulposus.
Neurulation – Neural Tube Formation
An overview of neurulation, the process where the ectodermal neural plate folds to form the neural tube, the precursor to the brain and spinal cord.
Placental Development
Placenta, umbilical cord, and twinning with fetal membranes.
Placenta Development – Chorionic Villi & Circulation
An overview of placental development, from the formation of chorionic villi to the establishment of the maternal-fetal circulation for nutrient and gas exchange.
Umbilical Cord – Structure & Vessels
An overview of the umbilical cord, the lifeline connecting the fetus to the placenta, detailing its formation, structure with Wharton's jelly, and its two arteries and one vein.
Twinning – Monozygotic vs Dizygotic & Membranes
An overview of twinning, distinguishing between dizygotic (fraternal) and monozygotic (identical) twins, and how the timing of division affects fetal membranes.
Body Cavities & Diaphragm
Formation of body cavities and development of the diaphragm.
Body Cavities Development – Pericardial, Pleural, Peritoneal
An overview of how the single intraembryonic coelom is partitioned by membranes and the diaphragm to form the three major body cavities: pericardial, pleural, and peritoneal.
Diaphragm Development – 4 Embryonic Components
An overview of diaphragm development from four key sources: the septum transversum, pleuroperitoneal membranes, dorsal mesentery, and body wall mesoderm.
Skeletal System & Skin
Integumentary system, skeletal development, limbs, skull, ribs/sternum, and muscle development.
Skin Development – Epidermis, Dermis & Appendages
An overview of the development of the skin and its appendages, including the epidermis from ectoderm, dermis from mesoderm, and the formation of hair, nails, and glands.
Bone & Cartilage Development – Ossification Types
Learn how cartilage and bone develop from mesenchyme. This guide covers both membranous ossification (flat bones) and endochondral ossification (long bones).
Vertebral Column Development – Sclerotomes & Resegmentation
An overview of how the vertebral column develops from sclerotomes, including the resegmentation process that allows muscles to span between vertebrae.
Ribs & Sternum Development – Thoracic Cage
An overview of the development of the ribs from costal processes and the sternum from paired sternal bars that fuse in the midline to form the thoracic cage.
Skull Development – Neurocranium & Viscerocranium
An overview of skull development, detailing the formation of the neurocranium (cranial vault and base) and the viscerocranium (facial skeleton) from different sources.
Head, Neck & Face
Pharyngeal apparatus and development of face, palate, tongue, teeth, and glands.
Pharyngeal Apparatus – Arches, Pouches & Clefts
An overview of the pharyngeal apparatus, a key embryonic structure, detailing the arches, pouches, clefts, and the nerves and muscles they give rise to.
Tongue Development – Pharyngeal Arch Contributions
An overview of tongue development from multiple pharyngeal arch swellings, explaining its complex innervation pattern for general sensation, taste, and motor control.
Thyroid Development – Thyroglossal Duct
An overview of thyroid gland development from an endodermal diverticulum at the foramen cecum of the tongue and its descent via the thyroglossal duct.
Face Development – Facial Prominences & Fusion
An overview of facial development from five prominences—frontonasal, maxillary, and mandibular—that fuse to form the lips, cheeks, and nose.
Nose Development – Nasal Pits & Sinuses
An overview of the development of the external nose from facial processes and the nasal cavities and paranasal sinuses from invaginations of the nasal pits.
Digestive System
Foregut/midgut/hindgut derivatives and development of liver, biliary system, pancreas, and spleen.
Esophagus Development – Tracheoesophageal Septum
An overview of esophagus development from the foregut and its separation from the trachea by the tracheoesophageal septum, including common clinical anomalies.
Stomach Development – Rotation & Lesser Sac
An overview of stomach development from a fusiform dilation of the foregut, detailing its 90-degree clockwise rotation and the formation of the lesser sac.
Duodenum Development – Rotation & Recanalization
An overview of duodenum development from both foregut and midgut, its rotation to a retroperitoneal position, and the process of recanalization of its lumen.
Midgut Development – Herniation & Rotation
An overview of midgut development, including its physiological umbilical herniation, 270-degree anticlockwise rotation, and return to the abdominal cavity.
Hindgut Development – Anal Canal & Pectinate Line
An overview of hindgut development, which forms the distal colon and upper anal canal. Learn about the dual origin of the anal canal above and below the pectinate line.
Respiratory System
Development of the respiratory system from early lung bud to branching morphogenesis.
Cardiovascular & Lymphatics
Heart development, arterial/venous remodeling, fetal circulation, and lymphatic development.
Heart Development – Looping, Septation & Defects
An overview of heart development, from the fusion of heart tubes and cardiac looping to the complex septation process that forms the four-chambered heart.
Aortic Arches – Development of Major Arteries
An overview of arterial development, detailing how the six pairs of pharyngeal arch arteries give rise to the major arteries of the head, neck, and thorax.
Venous Development – Vitelline, Umbilical & Cardinal Veins
An overview of venous system development from three paired veins (vitelline, umbilical, cardinal) and the complex remodeling that forms the IVC, SVC, and portal vein.
Fetal Circulation – Shunts & Postnatal Closure
An overview of fetal circulation, highlighting the three shunts (ductus venosus, foramen ovale, ductus arteriosus) that bypass the liver and lungs, and their closure at birth.
Lymphatic Development – Sacs, Ducts & Nodes
An overview of lymphatic system development from primary lymph sacs, detailing the formation of the thoracic and right lymphatic ducts, and the development of lymph nodes.
Urinary System
Kidney, ureter, bladder, and urethral development.
Kidney Development – Pronephros to Metanephros
An overview of kidney development through three successive systems: the pronephros, the mesonephros, and finally the metanephros, which forms the permanent kidney.
Ureteric Bud – Ureter & Collecting System Development
An overview of how the ureter and the entire kidney collecting system (pelvis, calyces, ducts) develop from the branching of the embryonic ureteric bud.
Bladder Development – Urogenital Sinus & Trigone
An overview of bladder development from the urogenital sinus, explaining the dual origin of its mucosa (endodermal) and trigone (mesodermal).
Urethra Development – Male vs Female
An overview of the development of the urethra, detailing the simpler formation of the female urethra and the more complex, multi-part development of the male urethra.
Genital System
Gonads, ducts, external genitalia, and relocation of testes and ovaries.
Gonadal Development – Sex Determination & Differentiation
An overview of genital system development, from the indifferent gonad to the differentiation of testes (SRY gene) or ovaries based on genetic sex (XX/XY).
Genital Ducts – Wolffian vs Müllerian Derivatives
An overview of how the mesonephric (Wolffian) ducts form the male genital tract and the paramesonephric (Müllerian) ducts form the female reproductive tract.
External Genitalia – Development in Male & Female
An overview of external genitalia development, from the indifferent stage to the differentiation of the penis and scrotum (male) or clitoris and labia (female).
Gonadal Descent – Testes, Ovaries & Gubernaculum
An overview of the descent of the testes into the scrotum and the ovaries into the pelvis, guided by the gubernaculum, and the clinical anomalies that can result.
Nervous System & Sense Organs
Neural tube, brain/spinal cord, pituitary/adrenal development, and eye/ear development.
Neurulation – Neural Tube & Neural Crest
An overview of neurulation, the process where the neural plate folds to form the neural tube, the precursor to the brain and spinal cord, and the origin of neural crest cells.
Brain Development – Vesicles to Cerebral Hemispheres
An overview of brain development from the three primary vesicles (forebrain, midbrain, hindbrain) to the complex structures of the cerebral hemispheres and brainstem.
Spinal Cord Development – Grey Horns & White Tracts
An overview of how the caudal part of the neural tube develops into the spinal cord, detailing the formation of its grey matter horns and white matter tracts.
Pituitary Development – Rathke’s Pouch & Infundibulum
An overview of pituitary gland development, detailing its dual origin from the ectodermal Rathke's pouch (anterior lobe) and the neuroectodermal infundibulum (posterior lobe).
Adrenal Development – Cortex vs Medulla Origins
An overview of adrenal gland development, highlighting its dual origin: the cortex from mesoderm and the medulla from migratory neural crest cells.
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