Anterior abdominal wall
Surface landmarks: The linea alba is a midline tendinous raphe between the rectus abdominis muscles, extending from xiphoid to pubis. The linea semilunaris marks the lateral border of the rectus sheath.
Layers (superficial to deep)
- Skin & superficial fascia: Camper (fatty) and Scarpa (membranous) layers. Scarpa fascia is continuous with Colles' fascia and dartos.
- External oblique – forms the inguinal ligament, lacunar ligament (medial border of femoral canal), and superficial inguinal ring.
- Internal oblique – contributes to the conjoint tendon (with transversus abdominis) and forms the cremasteric muscle/fascia.
- Transversus abdominis – deepest flat muscle; also contributes to the conjoint tendon.
- Transversalis fascia – lines the cavity; forms the deep inguinal ring and internal spermatic fascia.
- Extraperitoneal fat and parietal peritoneum.
Vascular supply & innervation
- Arteries: superior epigastric (from internal thoracic), inferior epigastric & deep circumflex iliac (from external iliac).
- Nerves: ventral rami T7–T12 (subcostal) plus iliohypogastric and ilioinguinal (L1).
- Lymph: above umbilicus → axillary nodes; below → superficial inguinal nodes.
Inguinal region & canal
The inguinal canal is a 4‑cm oblique passage superior and parallel to the medial inguinal ligament. It transmits the spermatic cord (male) or round ligament (female) and the ilioinguinal nerve.
Boundaries
- Roof: arching fibers of internal oblique & transversus abdominis.
- Anterior wall: external oblique aponeurosis (entire length) + internal oblique laterally.
- Floor: inguinal ligament (laterally) and lacunar ligament (medially).
- Posterior wall: transversalis fascia (lateral, weak area) and conjoint tendon (medial, reinforced).
Contents (male)
- Testicular artery (from aorta)
- Pampiniform plexus → testicular vein
- Vas deferens + artery
- Autonomic nerves & lymphatics (to aortic nodes)
female round ligament + ilioinguinal nerve.
Descent of testis
The testis develops in the urogenital ridge and descends via the gubernaculum through the inguinal canal during the last trimester. The processus vaginalis normally obliterates; its distal remnant forms the tunica vaginalis.
Inguinal & femoral hernias
Indirect inguinal
- Lateral to inferior epigastric vessels; through deep ring.
- Follows spermatic cord; covered by all 3 fascial layers.
- Congenital or acquired; more common in males.
Direct inguinal
- Medial to inferior epigastric vessels (Hesselbach’s triangle).
- Protrudes through posterior wall (transversalis fascia).
- Covered only by external spermatic fascia.
Femoral hernia: passes below the inguinal ligament, through the femoral canal. More common in women. At risk for strangulation.
Embryology of the gut tube
The primitive gut forms from endoderm (epithelium) and mesoderm (muscle, CT). Divided into foregut, midgut, hindgut with distinct arterial supply and autonomic innervation.
| Division | Artery | Parasympathetic | Sympathetic | Derivatives |
|---|---|---|---|---|
| Foregut | Celiac | Vagus | T5–T9 splanchnic → celiac ganglion | Esophagus, stomach, duodenum (1st & 2nd), liver, pancreas, biliary |
| Midgut | Superior mesenteric | Vagus | T9–T12 → superior mesenteric ganglion | Duodenum (2nd–4th), jejunum, ileum, cecum, appendix, ascending colon, proximal ⅔ transverse |
| Hindgut | Inferior mesenteric | Pelvic splanchnic | L1–L2 → inferior mesenteric ganglion | Distal ⅓ transverse, descending, sigmoid, rectum, upper anal canal |
referred pain foregut → epigastrium; midgut → periumbilical; hindgut → hypogastrium.
Foregut rotation
The foregut rotates 90° clockwise. The original left side becomes ventral; the anterior border becomes the lesser curvature. The ventral mesentery forms the lesser omentum and falciform ligament; the dorsal mesentery forms the greater omentum, gastrosplenic, and splenorenal ligaments.
The liver and gallbladder develop from the ventral mesentery; the spleen and dorsal pancreas from the dorsal mesentery.
Midgut rotation & peritoneal relations
During weeks 6–10, the midgut herniates into the umbilical cord and rotates 270° counterclockwise around the SMA. This positions the jejunum on the left and the cecum/ileum on the right, forming the inverted‑U colon.
Peritoneum & peritoneal cavity
Parietal peritoneum lines the wall – somatic innervation (sharp pain). Visceral peritoneum covers organs – autonomic (dull pain).
- Lesser sac (omental bursa): behind the stomach and lesser omentum.
- Greater sac: the rest of the cavity.
- Epiploic foramen (of Winslow): communication between the two sacs. Boundaries: anterior – hepatoduodenal ligament; posterior – IVC; superior – caudate lobe; inferior – duodenum.
Intraperitoneal vs retroperitoneal
Intraperitoneal (mobile)
- Stomach, liver, spleen
- 1st part of duodenum
- Jejunum, ileum
- Cecum, appendix
- Transverse & sigmoid colon
Retroperitoneal (fixed)
- Secondary: 2nd–3rd duodenum, pancreas (head/body/tail), ascending/descending colon, upper rectum
- Primary: kidneys, adrenals, ureters, aorta, IVC
Liver, pancreas & spleen development
Liver & biliary
Hepatic diverticulum from foregut endoderm grows into the ventral mesentery. It forms the liver, gallbladder, and bile ducts. The ventral mesentery becomes the lesser omentum and falciform ligament.
Pancreas
Ventral and dorsal pancreatic buds arise from the duodenal endoderm. The ventral bud rotates and fuses with the dorsal bud. The dorsal bud becomes the neck, body, and tail; the ventral bud becomes the head and uncinate process.
Spleen
Develops from mesoderm in the dorsal mesentery. The gastrosplenic ligament connects it to the stomach; the splenorenal ligament connects to the posterior wall.
Congenital anomalies of the gut
- Hypertrophic pyloric stenosis: hypertrophy of muscularis externa → projectile non‑bilious vomiting, olive‑shaped mass.
- Duodenal atresia: failed recanalization → bilious vomiting, polyhydramnios, “double bubble” on x‑ray.
- Omphalocele: herniation into umbilical cord (sac of amnion).
- Gastroschisis: defect in anterior wall (no sac), usually right of umbilicus.
- Meckel’s diverticulum: vitelline duct remnant; rule of 2s (2% population, 2 feet from ileocecal valve, 2 inches long).
- Hirschsprung disease: aganglionosis (no myenteric plexus) in sigmoid/rectum → megacolon.
- Malrotation: incomplete midgut rotation → volvulus.
Liver & biliary apparatus
The liver has a diaphragmatic and visceral surface. The porta hepatis transmits the portal triad (portal vein, hepatic artery, common bile duct). The gallbladder lies in a fossa on the visceral surface, stores bile, and empties via the cystic duct.
- Ligaments: falciform (between liver and anterior wall), coronary, triangular, lesser omentum (hepatogastric + hepatoduodenal).
- Hepatic veins drain into the IVC.
- Quadrate and caudate lobes are functionally part of the left lobe (blood supply from left portal triad).
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- Varicocele: pampiniform plexus dilation; “bag of worms”; reduces when supine.
- Cremasteric reflex: L1 (ilioinguinal sensory) + genitofemoral motor.
- Testicular lymph: drains to aortic nodes (not inguinal).
- Hydrocele: fluid in tunica vaginalis; does not reduce with lying down.
- Peritonitis: parietal peritoneum irritation → localized sharp pain.