Anatomy: Oesophagus, Stomach and Peritoneum

Anatomy: Oesophagus, Stomach and Peritoneum

Embryological Basis

The GI tract is divided by its arterial supply into three embryological segments: foregut (pharynx to mid-duodenum, supplied by the coeliac trunk), midgut (mid-duodenum to two-thirds of transverse colon, supplied by the superior mesenteric artery), and hindgut (remaining colon to upper anal canal, supplied by the inferior mesenteric artery). This explains referred pain patterns: foregut pain is referred to the epigastrium; midgut to the periumbilical region; hindgut to the hypogastrium.

Peritoneum

The peritoneum is a serous membrane consisting of parietal peritoneum (lining the abdominal wall) and visceral peritoneum (covering organs). The peritoneal cavity is the potential space between them, normally containing a small amount of serous fluid. Intraperitoneal organs are almost completely invested by visceral peritoneum (stomach, jejunum, ileum, transverse colon, sigmoid colon, liver, spleen). Retroperitoneal organs lie posterior to the peritoneum (kidneys, ureters, aorta, IVC, pancreas body/head, duodenum 2nd–4th parts, ascending and descending colon, rectum).

A mesentery is a double layer of visceral peritoneum that connects an intraperitoneal organ to the posterior abdominal wall and transmits its vasculature, lymphatics, and nerves. The greater omentum (4 layers of peritoneum) hangs from the greater curvature of the stomach and drapes over the transverse colon; it is rich in adipose tissue and macrophages ("abdominal policeman" — limits spread of infection). The lesser omentum (2 layers) runs from the lesser curvature of the stomach and proximal duodenum to the liver (hepatogastric + hepatoduodenal ligaments). The epiploic foramen (foramen of Winslow) connects the greater and lesser sacs.

Oesophagus

The oesophagus (25 cm) runs from C6 (cricopharyngeal sphincter) to T11 (oesophageal hiatus in right crus of diaphragm). It has three natural constrictions: cricopharyngeus (C6), arch of aorta + left main bronchus (T4/5), and diaphragmatic hiatus (T10). The right crus of the diaphragm acts as an extrinsic sphincter preventing reflux. The lower oesophageal sphincter (LOS) is physiological (no anatomical sphincter). Achalasia: failure of LOS relaxation due to degeneration of myenteric ganglia → progressive dysphagia to solids and liquids.

Stomach

The stomach lies in the left hypochondrium and epigastrium. Parts: cardia, fundus (most superior, contacts left diaphragm), body (largest), pyloric antrum + pyloric canal + pylorus (connects to duodenum). The lesser curvature faces right (hepatogastric ligament); the greater curvature faces left (gastrosplenic + gastrocolic ligaments). The angular incisure (incisura angularis) marks the junction of body and antrum. Relations: anterior — left lobe liver, diaphragm, anterior abdominal wall; posterior — omental bursa (lesser sac), then pancreas, left kidney, spleen, transverse mesocolon.