Anatomy
MBBS Anatomy question bank: general anatomy and osteology, regional gross anatomy (upper limb, lower limb, thorax, abdomen, pelvis, head and neck), neuroanatomy, histology and embryology.
12chapters144questions84High-Yield
Definition
The heart develops from cardiogenic mesoderm as a heart tube that folds, septates and forms four chambers with the great vessels.
Steps
- Heart tube forms (cardiogenic area)
- Cardiac looping (~day 23)
- Septation → four chambers
- Great vessels from the truncus arteriosus
Septation
- Atrial septum (foramen ovale)
- Ventricular septum
- Truncus → aorta + pulmonary trunk (spiral septum)
A single heart tube loops and septates into the four-chambered heart. Structure Forms Truncus arteriosus Aorta, pulmonary trunk Bulbus cordis Outflow tract Primitive ventricle Ventricles Applied
- VSD (commonest congenital defect)
- Tetralogy of Fallot
- Transposition (spiral septum defect)
🔑KEY POINTS TO REMEMBER- Heart tube → looping → septation → 4 chambers.
- Truncus arteriosus → aorta + pulmonary trunk (spiral septum).
- Defects: VSD, Fallot, transposition.
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).Definition
The primitive gut forms foregut, midgut and hindgut; the midgut herniates and rotates to attain the adult arrangement.
Divisions
- Foregut — to duodenum (coeliac trunk)
- Midgut — to 2/3 transverse colon (SMA)
- Hindgut — to rectum (IMA)
Midgut Rotation
- Physiological herniation (week 6)
- Rotates 270° anticlockwise (around SMA)
- Returns to the abdomen (week 10)
The midgut herniates, rotates 270°, then returns to the abdomen. Gut Artery Foregut Coeliac Midgut SMA Hindgut IMA Applied
- Malrotation, volvulus
- Omphalocele (failed return)
🔑KEY POINTS TO REMEMBER- Gut: foregut, midgut, hindgut (coeliac, SMA, IMA).
- Midgut herniates week 6, rotates 270°, returns week 10.
- Malrotation → volvulus.
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).Definition
The urogenital system develops from intermediate mesoderm, forming the kidneys, gonads and genital tracts.
Kidney Development (3 stages)
- Pronephros — rudimentary
- Mesonephros — temporary
- Metanephros — permanent kidney
Genital Development
- Gonads from the genital ridge
- Male — mesonephric (Wolffian) duct
- Female — paramesonephric (Müllerian) duct
Three kidney stages appear in sequence; genital ducts then differentiate by sex. Duct Forms Mesonephric (Wolffian) Male ducts Paramesonephric (Müllerian) Female tract Applied
- Horseshoe kidney
- Ectopic / pelvic kidney
🔑KEY POINTS TO REMEMBER- Kidney: pronephros → mesonephros → metanephros (permanent).
- Wolffian → male; Müllerian → female tract.
- Horseshoe / pelvic kidney anomalies.
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).Definition
The pharyngeal (branchial) apparatus consists of arches, pouches, clefts and membranes that form structures of the head and neck.
Components
- Arches (mesoderm) — six pairs
- Pouches (endoderm) — inner
- Clefts (ectoderm) — outer
- Membranes
Each Arch Contains
- A nerve, an artery, cartilage and muscle
Arches, pouches and clefts each form defined head-and-neck structures. Component Germ layer Arch Mesoderm Pouch Endoderm Cleft Ectoderm Applied
- Branchial cyst / fistula
- DiGeorge syndrome (pouches 3, 4)
🔑KEY POINTS TO REMEMBER- Apparatus: arches (mesoderm), pouches (endoderm), clefts (ectoderm).
- Each arch has a nerve, artery, cartilage, muscle.
- DiGeorge from pouches 3, 4.
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).Definition
The nervous system develops from the neural tube (CNS) and neural crest (PNS), both derived from ectoderm.
Neurulation
- Neural plate → neural folds → neural tube
- Neural tube → brain + spinal cord
- Neural crest → PNS and others
Brain Vesicles
- Forebrain (prosencephalon)
- Midbrain (mesencephalon)
- Hindbrain (rhombencephalon)
The neural tube becomes the CNS; the neural crest forms the PNS and more. Structure Forms Neural tube Brain, spinal cord Neural crest PNS, adrenal medulla Applied
- Neural tube defects (spina bifida)
- Neural crest — wide derivatives
🔑KEY POINTS TO REMEMBER- Neural tube → CNS; neural crest → PNS.
- Brain vesicles: fore-, mid-, hindbrain.
- Neural tube defects (spina bifida).
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).Definition
Fetal circulation has shunts that bypass the non-functional lungs and liver; these close at birth.
Fetal Shunts
- Ductus venosus — bypasses the liver
- Foramen ovale — right → left atrium
- Ductus arteriosus — pulmonary artery → aorta
Changes at Birth
- Lungs expand → ↓ pulmonary resistance
- Shunts close
- Foramen ovale → fossa ovalis
At birth the lungs open and the fetal shunts close. Fetal Adult remnant Ductus venosus Ligamentum venosum Foramen ovale Fossa ovalis Ductus arteriosus Ligamentum arteriosum Applied
- Patent ductus arteriosus (PDA)
- ASD (patent foramen ovale)
🔑KEY POINTS TO REMEMBER- Shunts: ductus venosus, foramen ovale, ductus arteriosus.
- Close at birth as lungs expand.
- PDA / ASD if they persist.
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).Definition
Midgut rotation is the 270° anticlockwise rotation of the herniated midgut loop around the superior mesenteric artery.
Steps
- Physiological herniation (week 6)
- Rotates 90° anticlockwise (while herniated)
- Returns to the abdomen (week 10)
- Further 180° rotation (total 270°)
The midgut rotates 90° while herniated, then 180° more on return. Stage Rotation Herniated 90° On return 180° Total 270° Applied
- Malrotation → volvulus
- Reversed rotation
🔑KEY POINTS TO REMEMBER- Midgut rotates 270° anticlockwise around the SMA.
- 90° herniated + 180° on return.
- Malrotation → volvulus.
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).Definition
Meckel’s diverticulum is the commonest congenital anomaly of the GI tract, a remnant of the vitellointestinal (omphalomesenteric) duct.
Rule of 2s
- ~2% of the population
- 2 feet from the ileocaecal junction
- ~2 inches long
- 2 types of ectopic tissue (gastric, pancreatic)
- Often presents by age 2
A persistent vitelline duct leaves an ileal pouch that may bleed or inflame. Feature Detail Origin Vitelline duct Site Ileum Content Ectopic gastric / pancreatic tissue Applied
- Painless GI bleeding (children)
- Mimics appendicitis
🔑KEY POINTS TO REMEMBER- Meckel’s = vitellointestinal duct remnant (ileum).
- Rule of 2s.
- Ectopic gastric mucosa → painless bleeding.
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).Definition
Each pharyngeal arch gives rise to specific cartilage, muscles, a nerve and an artery.
Arch Nerves
- 1st — trigeminal (V)
- 2nd — facial (VII)
- 3rd — glossopharyngeal (IX)
- 4th & 6th — vagus (X)
Key Derivatives
- 1st — muscles of mastication; malleus, incus
- 2nd — muscles of expression; stapes
- 3rd — stylopharyngeus
Each arch carries its own nerve and forms set muscles and cartilage. Arch Nerve 1st Trigeminal (V) 2nd Facial (VII) 3rd Glossopharyngeal (IX) 4th / 6th Vagus (X) Applied
- Arch-based nerve / muscle defects
🔑KEY POINTS TO REMEMBER- Arch nerves: 1st V, 2nd VII, 3rd IX, 4th/6th X.
- 1st → mastication, malleus/incus; 2nd → expression, stapes.
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).Definition
Neural crest cells are a migratory population from the neural tube margins that form a wide variety of tissues.
Derivatives
- Peripheral nervous system (sensory, autonomic ganglia)
- Adrenal medulla (chromaffin cells)
- Melanocytes
- Schwann cells
- Facial skeleton (some), odontoblasts
Neural crest cells migrate widely to form many different tissues. Derivative Example Nervous Sensory/autonomic ganglia Endocrine Adrenal medulla Pigment Melanocytes Applied
- Neurocristopathies (e.g. Hirschsprung)
- Neuroblastoma
🔑KEY POINTS TO REMEMBER- Neural crest → PNS, adrenal medulla, melanocytes, Schwann cells.
- Also facial skeleton, odontoblasts.
- Hirschsprung, neuroblastoma.
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).Definition
The kidney develops from intermediate mesoderm through three successive stages, the last being permanent.
Three Stages
- Pronephros — rudimentary, non-functional
- Mesonephros — temporary, partly functional
- Metanephros — permanent kidney
Metanephros
- Ureteric bud → collecting system
- Metanephric blastema → nephrons
- Ascends from pelvis to lumbar region
Three kidney stages appear; the metanephros persists and ascends. Stage Fate Pronephros Regresses Mesonephros Temporary Metanephros Permanent kidney Applied
- Horseshoe kidney (fusion)
- Pelvic kidney (failed ascent)
🔑KEY POINTS TO REMEMBER- Pronephros → mesonephros → metanephros (permanent).
- Ureteric bud → collecting system; blastema → nephrons.
- Failed ascent → pelvic kidney.
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).Definition
The aortic arches are paired vessels of the pharyngeal arches that remodel to form the great arteries.
Key Derivatives
- 3rd arch — common carotid + internal carotid
- 4th arch — (left) arch of aorta; (right) subclavian
- 6th arch — pulmonary arteries + ductus arteriosus
The paired arches remodel asymmetrically into the great arteries. Arch Derivative 3rd Carotids 4th Aortic arch / subclavian 6th Pulmonary + ductus Applied
- Coarctation of the aorta
- PDA (6th arch remnant)
🔑KEY POINTS TO REMEMBER- 3rd → carotids; 4th → aortic arch/subclavian; 6th → pulmonary + ductus.
- Coarctation, PDA.
📚SOURCES: Langman’s Medical Embryology; Inderbir Singh’s Human Embryology; The Developing Human (Moore).