Skip to main content
Anatomy 3% exam weight

Abdomen and Pelvis Anatomy

Part of the INI CET (AIIMS PG) study roadmap. Anatomy topic anatom-009 of Anatomy.

→ See in Roadmap Build 1-Month Plan

Abdomen and Pelvis — GI Organs, Peritoneum, Kidneys, Pelvic Viscera and Nerves

Quick Review

Abdominal and pelvic anatomy are frequently tested in INI CET, especially the peritoneal relations of abdominal organs, blood supply to GI organs, and the course of the ureters. Focus on the portocaval system, the three layers of the abdominal wall, and the anatomy of the pelvis.

High-Yield Facts for INI CET:

  • Peritoneum: Parietal (lines wall) vs visceral (covers organs); peritoneum forms mesenteries, omenta, and ligaments
  • Lesser sac (omental bursa): Posterior to stomach and lesser omentum; communicates with greater sac via omental (Epiploic) foramen (of Winslow)
  • Liver: Right lobe (larger), left lobe (smaller), caudate and quadrate lobes; portal triad (hepatic portal vein, hepatic artery, bile duct); supplied by hepatic artery (25%) and portal vein (75%); venous drainage by hepatic veins to IVC
  • Kidneys: Retroperitoneal; right kidney lower (liver); left kidney higher (protected by spleen); cortex + medulla (pyramids)

Exam tip: Stomach has lesser curvature (supplied by left gastric artery) and greater curvature (supplied by short gastric and left gastro-omental artery). Pancreas: head (uncinate process touching IVC), neck, body, tail; crosses anatomical structures at L1-L2 — the “submarines” behind the stomach.

Abdominal Wall and Regions

Quadrants and Regions

  • 9 regions: Right hypochondrium, epigastrium, left hypochondrium; right lumbar, umbilical, left lumbar; right iliac fossa, suprapubic, left iliac fossa
  • McBurney’s point: 1/3 distance from ASIS to umbilicus — marks the surface projection of the appendix
  • Costal margin: Formed by costal cartilages of ribs 7-12; contains: Right hypochondrium (liver, gallbladder, right kidney), epigastrium (stomach, pancreas, aorta), left hypochondrium (spleen, left kidney, stomach tail)

Anterior Abdominal Wall — Layers

Skin → Camper’s fascia (fat) → Scarpa’s fascia (membranous) → external oblique aponeurosis → internal oblique → transversus abdominis → transversalis fascia → extraperitoneal fat → parietal peritoneum.

Muscles of the Anterior Abdominal Wall

  • External oblique: Fibres inferomedial (“hands in pockets”); forms inguinal ligament (Poupart’s ligament) at its lower free border; also forms lacunar ligament (Gimbernat’s) at medial attachment
  • Internal oblique: Fibres superomedial; cremaster muscle (from internal oblique) covers spermatic cord
  • Transversus abdominis: Deepest; transverse fibres; forms conjoint tendon medial to rectus

Rectus Sheath

Formed by aponeuroses of external oblique, internal oblique, and transversus. Above the arcuate line (halfway between umbilicus and pubic symphysis): anterior wall formed by external oblique aponeurosis + half of internal oblique aponeurosis; posterior wall formed by rest of internal oblique aponeurosis + transversus aponeurosis. Below the arcuate line: all three aponeuroses go to anterior wall; posterior wall has only transversalis fascia.

Inguinal Canal

Site of potential weakness; 4cm long; runs from deep (internal) inguinal ring (midpoint of inguinal ligament) to superficial (external) inguinal ring (aperture in external oblique aponeurosis). Contains: spermatic cord in males, round ligament in females; ilioinguinal nerve (C1 — emerges from superficial ring).

Direct vs Indirect Hernia:

  • Indirect inguinal hernia: Lateral to inferior epigastric vessels; congenital (patent processus vaginalis); covered by all three layers
  • Direct inguinal hernia: Medial to inferior epigastric vessels; acquired (weakness in Hesselbach triangle); covered by transversalis fascia only
  • Hesselbach triangle: Medial border = lateral edge of rectus abdominis; Lateral border = inferior epigastric vessels; Inferior border = inguinal ligament

Peritoneum and GI Organs

Peritoneum

Parietal peritoneum: Lines abdominal and pelvic walls; sensitive to pain (somatic) — parietal peritoneal irritation causes localised, well-defined pain.

Visceral peritoneum: Covers abdominal organs; sensitive only to stretch — deep visceral pain is poorly localised, often referred to T5-L1 dermatomes.

Intraperitoneal vs Retroperitoneal

  • Intraperitoneal: Covered by visceral peritoneum; has mesentery connecting to posterior abdominal wall; examples: stomach, jejunum, ileum, transverse colon, sigmoid colon, liver, spleen, appendix
  • Retroperitoneal: Only partially covered by peritoneum (anterior surface); examples: duodenum (except first part), pancreas (except tail), ascending and descending colon, kidneys, adrenal glands, aorta, IVC

Peritoneal Folds

  • Greater omentum: Double layer from greater curvature of stomach → drapes over transverse colon and small intestine; contains fat; has immune function (contains macrophages); surgical barrier
  • Lesser omentum: Connects lesser curvature of stomach and proximal duodenum to liver; contains hepatic portal triad (portal vein, hepatic artery, bile duct); divided into hepatogastric ligament + hepatoduodenal ligament (forms anterior boundary of omental foramen)
  • Omental (Epiploic) foramen (of Winslow): Entry to lesser sac; bounded anteriorly by hepatoduodenal ligament, posteriorly by IVC, superiorly by caudate lobe of liver, inferiorly by duodenum

Stomach

Surfaces and borders: Lesser curvature (right border) — supplied by left gastric artery; Greater curvature (left border) — supplied by short gastric + left gastro-omental artery; Anterior surface and posterior surface.

Regions: Cardia, fundus (above oesophageal opening), body, pyloric antrum and canal.

Innervation: Vagal trunks (parasympathetic) — anterior (left) and posterior (right) vagal trunks; sympathetics from coeliac plexus (T6-T10).

Duodenum

Four parts (C-shaped around head of pancreas):

  • D1 (superior): Short, intraperitoneal; first part; contains entry of common bile duct and pancreatic duct (hepatopancreatic ampulla of Vater)
  • D2 (descending): Retroperitoneal; contains major duodenal papilla (entry of bile + pancreatic duct)
  • D3 (horizontal): Retroperitoneal; crosses IVC and aorta
  • D4 (ascending): Retroperitoneal; ascends to duodojejunal flexure; suspended by ligament of Treitz (suspensory muscle of duodenum — bands of smooth muscle + CT from right crus of diaphragm)

Pancreas

Head (in C-shaped curve of duodenum): Uncinate process extends behind superior mesenteric vessels.

Neck: Anterior to portal vein; between head and body.

Body: Crosses L1; posterior to stomach; tail reaches splenic hilum.

Pancreatic duct: Runs through tail to head → joins bile duct at hepatopancreatic ampulla (Vater’s); sphincter of Oddi controls entry.

Exocrine function: Digestive enzymes — trypsin, chymotrypsin, carboxypeptidase (all secreted as inactive proenzymes), amylase, lipase, nucleases.

Endocrine function: Islets of Langerhans — alpha (glucagon), beta (insulin), delta (somatostatin), PP (pancreatic polypeptide).

Liver and Biliary System

Liver Anatomy

  • Anatomical: Right lobe (larger), left lobe (smaller), caudate (dorsal), quadrate (ventral)
  • Functional: 8 segments by Couinaud classification (based on portal triad distribution)
  • Porta hepatis: Entry of hepatic portal vein and hepatic artery, exit of hepatic ducts; lies between caudate and quadrate lobes

Gallbladder

Attached to liver by cystic duct; Hartmann’s pouch (constriction at neck — common site of gallstone impaction); fundus (projects beyond liver edge); body; neck.

Biliary Tree

Right hepatic duct + left hepatic duct → common hepatic duct → joins cystic duct → common bile duct (CBD) → runs in lesser omentum → behind D1 → through head of pancreas → hepatopancreatic ampulla of Vater → major duodenal papilla (D2).

Portal Venous System

Splenic vein + superior mesenteric vein → hepatic portal vein → liver. Portal vein supplies 75% of liver blood supply.

Portocaval anastomoses (sites where portal and systemic venous systems connect — portal hypertension leads to dilation and bleeding):

  1. Oesophageal varices: Oesophageal veins ↔ left gastric (portal)
  2. Rectal varices: Superior rectal (portal) ↔ middle and inferior rectal (systemic)
  3. Paraumbilical: Paraumbilical veins ↔ superficial epigastric → caput medusae
  4. Retroperitoneal: Colic veins (portal) ↔ renal and lumbar veins (systemic)

Large Intestine

Key Features

Taeniae coli (three longitudinal muscle bands — haustra between them), omental appendices (fatty tags).

Caecum and Appendix

Caecum is intraperitoneal; ascending colon begins here; vermiform appendix attaches at posteromedial wall at McBurney’s point. Appendix has mesoappendix (contains appendicular artery — branch of ileocolic artery). Different positions: retrocaecal most common, then pelvic, then subcaecal, then pre-ileal. McBurney’s point = surface marking for appendicitis.

Blood Supply

  • SMA (superior mesenteric artery): Midgut derivatives — duodenum D1 to proximal 2/3 transverse colon
  • IMA (inferior mesenteric artery): Hindgut derivatives — distal 1/3 transverse colon to upper rectum

Kidneys

Location and Structure

Retroperitoneal; T12-L3; right slightly lower (liver); left slightly higher (spleen). Each kidney ~11cm; weighs 120-170g; surrounded by perirenal fat and renal fascia (of Gerota).

Structure:

  • Capsule: Smooth, fibrous; can be stripped
  • Cortex: Outer, contains glomeruli; extends as medullary rays into medulla
  • Medulla: 8-12 pyramids; each pyramid has base (cortical side) and papilla (apex pointing to minor calyx); papillae open into minor calyces → major calyces → renal pelvis → ureter

Blood Supply

Renal artery (from aorta at L1-L2) → segmental arteries → interlobar → arcuate → interlobular → afferent arterioles → glomerulus → efferent arteriole → peritubular capillaries → interlobular → arcuate → renal vein → IVC.

Ureter

25cm long; has three constrictions:

  1. UPJ (where renal pelvis narrows to ureter)
  2. Pelvic brim (crosses bifurcation of common iliac)
  3. UVJ (where ureter enters bladder trigone — posterolateral)

Pelvis and Pelvic Viscera

Pelvic Walls

Pelvic brim divides pelvis into true (below brim) and false (above brim) pelvis. Bones: two hip bones (ilium, ischium, pubis), sacrum, coccyx.

Pelvic floor: Pelvic diaphragm — levator ani (pubococcygeus, iliococcygeus, puborectalis) + coccygeus; supports pelvic organs; has urogenital hiatus (urethra in both, vagina in females, rectum).

Male Pelvic Organs

Urinary Bladder: Extraperitoneal; stores urine; capacity ~500mL; trigone (smooth triangle between ureteric orifices and internal urethral orifice) — common site of infection.

Prostate: Below bladder; surrounds prostatic urethra. Contains ejaculatory ducts (from seminal vesicles and vas deferens) which open into prostatic urethra at verumontanum.

  • BPH: Causes urinary frequency, nocturia, hesitancy, weak stream; arises from transitional zone (periurethral); treated with 5-alpha reductase inhibitors (finasteride), alpha blockers (tamsulosin), surgery (TURP)
  • Prostate cancer: Arises from peripheral zone (70%); PSA, digital rectal examination (DRE), transrectal ultrasound (TRUS), biopsy; spreads to bone (osteoblastic secondaries)

Female Pelvic Organs

Uterus: Retroverted and anteflexed (normal); supported by broad ligament, round ligament, cardinal ligament, uterosacral ligaments.

Parts: Fundus (above cornua), body, isthmus, cervix.

Layers: Perimetrium (serosa), myometrium (thick smooth muscle — contracts during labour), endometrium (functional and basal layers — menstruates if no implantation).

Hysterectomy types: Total (cervix removed), subtotal (cervix left), radical (parametrium removed).

Ovaries: Intraperitoneal; attached to uterus by ovarian ligament, to pelvic wall by suspensory ligament (contains ovarian vessels). Blood supply: Ovarian artery (from aorta at L2); ovarian vein → IVC (right) and left renal vein (left).

Vagina: 8cm; connections: Cervix above, vestibular glands laterally; fornices (anterior, posterior, lateral); contains vaginal flora (Lactobacillus — produces lactic acid → pH 4); no glands — mucus from cervical glands.

Suprarenal Glands

Retroperitoneal; right triangular (pyramidal) on right kidney; left crescentic on left kidney.

Cortex (from mesoderm):

  • Zona glomerulosa: Mineralocorticoids — aldosterone
  • Zona fasciculata: Glucocorticoids — cortisol
  • Zona reticularis: Androgens

Medulla (from ectoderm): Chromaffin cells; secretes adrenaline and noradrenaline; innervated by sympathetic preganglionic fibres (splanchnic nerve).

Blood supply: Superior suprarenal (from inferior phrenic), middle suprarenal (from aorta), inferior suprarenal (from renal artery).