Abdomen
First module for the walls; second for the visceraThe abdominal wall is usually dissected with the back and thoracic wall as body-wall anatomy, and the inguinal canal alone accounts for a disproportionate share of exam questions. The viscera follow once the cavity is opened: the peritoneal folds first (they are the map), then the foregut, midgut, and hindgut with their arteries, the liver and biliary tree, and the retroperitoneum. The written exam loves the three embryologic gut segments because their blood supply, innervation, and referred pain all follow from them.
High-Yield Pearl
The inferior epigastric vessels decide the hernia (indirect lateral, direct medial), the foregut–midgut–hindgut split decides the artery, the referred pain, and the innervation, and the hepatoduodenal ligament is the one structure you must be able to draw from memory — triad inside, omental foramen behind.
What the written exam asks
Relationships, supply, levels, and what happens when each fails.
- Layers of the anterolateral wall. Skin → Camper's fascia (fatty) → Scarpa's fascia (membranous; fuses with the fascia lata below the inguinal ligament, so urine from a ruptured urethra tracks up the abdomen, not down the thigh) → external oblique → internal oblique → transversus abdominis → transversalis fascia → extraperitoneal fat → parietal peritoneum. Fiber directions: external oblique hands-in-pockets (down and medial), internal oblique up and medial, transversus horizontal.
- Rectus sheath and arcuate line. Above the arcuate line (midway between umbilicus and pubis) the internal oblique aponeurosis splits to wrap the rectus front and back; below it ALL three aponeuroses pass in front, leaving only transversalis fascia behind the muscle — the weak spot where the inferior epigastric vessels enter the sheath. The linea alba is the midline fusion; the linea semilunaris the lateral edge of the rectus.
- Inguinal canal. Runs from the deep ring (an opening in the transversalis fascia LATERAL to the inferior epigastric vessels) to the superficial ring (a split in the external oblique aponeurosis above the pubic tubercle). Floor: inguinal ligament (and lacunar ligament medially). Roof: arching fibers of internal oblique and transversus. Anterior wall: external oblique aponeurosis (reinforced laterally by internal oblique). Posterior wall: transversalis fascia, reinforced medially by the conjoint tendon. Contents: spermatic cord (or round ligament) and the ilioinguinal nerve.
- Hernias. Indirect inguinal: through the deep ring, LATERAL to the inferior epigastric vessels, inside the spermatic cord, often into the scrotum — a patent processus vaginalis, the common hernia of young males. Direct inguinal: through the posterior wall in Hesselbach's triangle (inferior epigastric vessels laterally, rectus medially, inguinal ligament below), MEDIAL to the vessels, an acquired weakness of older men. Femoral: below the inguinal ligament through the femoral ring medial to the femoral vein (NAVEL: Nerve, Artery, Vein, Empty space, Lymphatics) — more common in women, most likely to strangulate.
- Peritoneum and its folds. Intraperitoneal organs hang on a mesentery; retroperitoneal organs lie behind it — primarily (kidneys, ureters, adrenals, aorta, IVC, rectum, bladder) or secondarily, having lost their mesentery (duodenum parts 2–4, ascending and descending colon, pancreas). "SAD PUCKER" lists the retroperitoneal set. The greater omentum hangs from the greater curvature; the lesser omentum (hepatogastric + hepatoduodenal ligaments) spans liver to stomach; the lesser sac lies behind the stomach and opens into the greater sac through the omental (epiploic) foramen of Winslow.
- Omental foramen borders. Anterior: the hepatoduodenal ligament carrying the portal triad (portal vein behind, proper hepatic artery left, common bile duct right). Posterior: the IVC. Superior: the caudate lobe of the liver. Inferior: the first part of the duodenum. Pinching the anterior border (the Pringle maneuver) controls hepatic bleeding.
- Foregut, midgut, hindgut. Foregut (distal esophagus to the major duodenal papilla; plus liver, gallbladder, pancreas, spleen): celiac trunk at T12, pain referred to the epigastrium, parasympathetics from the vagus. Midgut (papilla to the proximal two-thirds of the transverse colon): superior mesenteric artery at L1, periumbilical pain, vagus. Hindgut (distal transverse colon to the upper anal canal): inferior mesenteric artery at L3, hypogastric pain, pelvic splanchnics S2–S4. Watershed zones at the splenic flexure and the rectosigmoid junction.
- Celiac trunk. Left gastric (lesser curvature, esophageal branches), splenic (pancreas, short gastrics, left gastro-omental), common hepatic → proper hepatic (right and left hepatic, cystic from the right) and gastroduodenal (right gastro-omental and superior pancreaticoduodenal). The gastroduodenal artery lies behind the first part of the duodenum — the vessel a posterior duodenal ulcer erodes.
- Portal system. Splenic vein + superior mesenteric vein → portal vein (the inferior mesenteric usually joins the splenic). Portosystemic anastomoses become the signs of portal hypertension: left gastric ↔ esophageal veins (varices), paraumbilical ↔ epigastric (caput medusae), superior rectal ↔ middle/inferior rectal (hemorrhoids), retroperitoneal colic veins ↔ lumbar veins.
- Liver and biliary tree. Falciform ligament (with the ligamentum teres, the obliterated umbilical vein) divides the anatomical right and left lobes; the functional division runs through the gallbladder fossa and IVC. Cystic duct + common hepatic duct → common bile duct, which joins the main pancreatic duct at the hepatopancreatic ampulla (of Vater) and enters the second part of the duodenum at the major papilla. Calot's triangle (cystic duct, common hepatic duct, inferior liver edge) contains the cystic artery.
- Retroperitoneum. Kidneys at T12–L3 (the right lower, under the liver) with the hilum at L1 — vein, artery, pelvis front to back. Ureters descend on the psoas, cross the pelvic brim at the bifurcation of the common iliac artery, and pass under the uterine artery or ductus deferens ("water under the bridge"). The abdominal aorta gives the inferior phrenic, celiac, SMA, renal, gonadal, IMA, lumbar, and common iliac branches, bifurcating at L4.
- Lumbar plexus on the posterior wall. From L1–L4 on the psoas: iliohypogastric and ilioinguinal (L1), genitofemoral (pierces the psoas), lateral femoral cutaneous (L2–L3, meralgia paresthetica), femoral (L2–L4, lateral to the psoas), obturator (L2–L4, medial to the psoas).
What the practical tags · 37 structures
In the order a dissection meets them — each with the one relationship that identifies it. Your lab's study list is the authority; use this to check yours against.
- 1Linea alba, linea semilunaris, tendinous intersections — the midline raphe, the lateral edge of the rectus, and the bands that make the six-pack
- 2Rectus abdominis and its sheath — the strap muscle in the aponeurotic envelope; note where the posterior layer ends
- 3Arcuate line — the lower edge of the posterior rectus sheath
- 4External oblique and its aponeurosis — hands-in-pockets fibers; its rolled lower edge is the inguinal ligament
- 5Internal oblique — fibers up and medial; the cremaster derives from it
- 6Transversus abdominis and the conjoint tendon — the horizontal deepest muscle; its lower fibers fuse with internal oblique behind the superficial ring
- 7Transversalis fascia, extraperitoneal fat, parietal peritoneum — the three layers between muscle and cavity; the deep ring is a hole in the first
- 8Superficial inguinal ring — the triangular gap in the external oblique aponeurosis above the pubic tubercle, between two crura
- 9Deep inguinal ring — lateral to the inferior epigastric vessels
- 10Spermatic cord (or round ligament) — the bundle traversing the canal; the ilioinguinal nerve rides on it, outside the coverings
- 11Inferior epigastric artery and vein — the landmark of Hesselbach's triangle
- 12Superior epigastric artery continuing the internal thoracic
- 13Greater and lesser omentum — the fatty apron from the greater curvature; the thin sheet from liver to lesser curvature and duodenum
- 14Omental (epiploic) foramen — a finger passes from greater to lesser sac behind the portal triad
- 15Falciform ligament and ligamentum teres; coronary and triangular ligaments of the liver
- 16Mesentery of the small intestine, transverse mesocolon, sigmoid mesocolon
- 17Stomach: cardia, fundus, body, pylorus — the pyloric sphincter is the thick ring you can pinch at the duodenal junction
- 18Duodenum, four parts — the C around the pancreatic head; the major papilla opens on the medial wall of the second part
- 19Jejunum vs ileum — jejunum thicker, redder, long vasa recta, few arcades; ileum thinner, short vasa recta, many arcades, more fat in the mesentery
- 20Ileocecal junction, cecum, appendix — follow the taeniae coli to its base
- 21Ascending, transverse, descending, sigmoid colon; taeniae coli, haustra, omental appendices
- 22Liver lobes and porta hepatis — caudate behind, quadrate in front of the porta; the bare area has no peritoneum against the diaphragm
- 23Gallbladder and the biliary tree — cystic duct joins common hepatic duct to make the common bile duct, which passes behind the duodenum
- 24Portal vein, proper hepatic artery, common bile duct — the triad in the hepatoduodenal ligament
- 25Pancreas, head to tail — head in the duodenal C, uncinate hooking behind the SMA, tail touching the splenic hilum
- 26Spleen with its hilum and the splenorenal and gastrosplenic ligaments
- 27Celiac trunk; left gastric, splenic, common hepatic arteries; gastroduodenal artery
- 28Superior mesenteric artery and vein crossing the third part of the duodenum
- 29Inferior mesenteric artery and its left colic, sigmoid, superior rectal branches
- 30Splenic vein joining the SMV to form the portal vein behind the pancreatic neck
- 31Kidney in section — cortex, medullary pyramids, minor and major calyces, pelvis; the hilum carries vein, artery, pelvis front to back
- 32Renal artery and vein — left renal vein passes in front of the aorta under the SMA
- 33Ureter — on the psoas, crossing the bifurcation of the common iliac
- 34Suprarenal glands — cap the superior pole of each kidney
- 35Abdominal aorta and IVC — aorta left of the midline bifurcating at L4; the IVC forms at L5; gonadal vessels run down on the psoas
- 36Psoas major, iliacus, quadratus lumborum; the diaphragmatic crura
- 37Lumbar plexus branches on the posterior wall: genitofemoral, lateral femoral cutaneous, femoral, obturator
What everyone misses
The distinctions that lose points on the practical, year after year.
- Deep ring vs superficial ring. The deep ring is a gap in the transversalis fascia felt lateral to the inferior epigastric vessels; the superficial ring is the triangular split in the external oblique aponeurosis just above the pubic tubercle. Students tag the cord at the superficial ring and call it the deep ring.
- Arcuate line. Turn the rectus over and find the crisp lower edge of the posterior sheath midway between umbilicus and pubis — below it, the muscle rests directly on transversalis fascia. Tagged on nearly every wall practical.
- Jejunum vs ileum. Hold a loop to the light: long straight vasa recta with few arcades and little mesenteric fat = jejunum; short vasa recta, stacked arcades, fat to the gut wall = ileum. Name the features, not just the segment.
- The portal triad and its arrangement. In the hepatoduodenal ligament: bile duct right (anterior), hepatic artery left (anterior), portal vein behind both. A tag on the wrong tube is the classic lost point.
- Omental foramen. Known by its borders — probe it from the right with the caudate lobe above, the IVC behind, the duodenum below, and the portal triad in front — not by the opening itself.
- Cystic artery and Calot's triangle. The cystic artery (a branch of the right hepatic) sits in the triangle formed by the cystic duct, the common hepatic duct, and the liver — the structure a surgeon must identify before clipping anything.
- Left renal vein. Crosses in FRONT of the aorta and UNDER the superior mesenteric artery (the "nutcracker"); it receives the left gonadal and left suprarenal veins, which the right counterparts send straight to the IVC.
- Appendix by the taeniae. The three taeniae coli converge on the base of the appendix — follow them when the appendix is retrocecal and hidden. McBurney's point marks it on the surface.
Clinical correlations
Where this region shows up again — in clinical medicine, on rotations, and on the boards.
- Inguinal and femoral hernias. Indirect (lateral to the inferior epigastrics, into the scrotum, congenital) vs direct (medial, through Hesselbach's triangle, acquired) — a finger in the canal feels the impulse at the tip for indirect and on the pulp for direct. Femoral hernias sit below the inguinal ligament, lateral to the pubic tubercle, and strangulate early because the femoral ring is rigid.
- Appendicitis. Visceral pain starts periumbilical (midgut, T10) and migrates to McBurney's point once the parietal peritoneum is inflamed (somatic, T12–L1). Rovsing, psoas (retrocecal appendix on the psoas), and obturator (pelvic appendix) signs are each an anatomical relationship.
- Gallbladder and biliary disease. Biliary colic is foregut pain in the epigastrium or right upper quadrant, referred to the right shoulder and scapula when the diaphragm is irritated (phrenic, C3–C5). Murphy's sign is the inflamed fundus meeting the examiner's fingers below the right costal margin. A stone at the ampulla obstructs both bile and pancreatic ducts — jaundice plus pancreatitis.
- Peptic ulcer bleeding and perforation. A posterior duodenal ulcer erodes the gastroduodenal artery (massive hematemesis); an anterior one perforates into the peritoneal cavity (free air under the diaphragm). A posterior gastric ulcer can erode the splenic artery or the pancreas.
- Portal hypertension. Cirrhosis backs blood into the portosystemic anastomoses: esophageal varices (left gastric ↔ esophageal), caput medusae (paraumbilical ↔ epigastric), hemorrhoids (superior ↔ middle/inferior rectal), plus ascites and splenomegaly.
- Splenic injury. Ribs 9–11 on the left protect the spleen; a fracture there, or any blunt left-upper-quadrant trauma, can rupture it — left shoulder pain (Kehr's sign) from blood under the diaphragm, and the splenorenal ligament carries the splenic vessels that bleed.
- Pancreatitis. A retroperitoneal organ, so the pain bores through to the back; Grey Turner (flank) and Cullen (periumbilical) signs are retroperitoneal blood tracking along fascial planes. The head sits in the duodenal curve next to the common bile duct — a head tumor causes painless jaundice.
- Abdominal aortic aneurysm. Below the renal arteries in most cases, bifurcating at L4; a pulsatile mass above the umbilicus. Rupture bleeds retroperitoneally first. The artery of the lumbar segments and the IMA's loss explains ischemic colitis at the watershed after repair.
- Ureteric stones and "water under the bridge". Stones lodge at the three narrowings — pelvi-ureteric junction, the pelvic brim crossing, and the ureterovesical junction — with pain from loin to groin along the T11–L2 dermatomes. The ureter passes under the uterine artery (and the ductus deferens), which is where it is cut in pelvic surgery.
- Umbilical and incisional hernias; diastasis. The linea alba is the weak midline: umbilical hernias in infants and the obese, epigastric hernias through it above the umbilicus, and diastasis recti as a stretched rather than torn line. Incisional hernias follow the pattern of the cut fascia.
Frequently asked
This guide is the map. Drop this region's lecture slides on the dashboard to get flashcards and questions from your lecture, group them into a module, and run a timed module exam the week before. The gross anatomy playbook has the weekly loop.
AI-authored study notes, not faculty-reviewed and not medical advice. Verify every structure against your atlas, your dissector, and your lab instructors; programs differ in what they tag.