--- module: 078-02 language: en chapter: 78 title: "Abdominal Anatomy, Peritoneum, Viscera, and Portal Circulation" module_title: "Oesophagus, stomach, small intestine, colon, rectum, and anorectal anatomy" source_sha256: cff71a4bbd650e67a6cf40df46f15da66a31e440c546b02496a0e49913ba9d15 --- # Gastrointestinal tract anatomy ## Abdominal oesophagus and junction ### Passes hiatus, joins stomach near T11 ### Left vagus anterior, right posterior after rotation ### Junction support without a discrete ring #### Smooth-muscle tone, crura, angle of His #### Phrenooesophageal membrane, abdominal pressure ### Sliding hernia: junction moves upward ### Paraoesophageal hernia: stomach beside fixed junction ### Veins to left gastric and azygos #### Portosystemic site ### Lymph to mediastinum and left gastric nodes #### Longitudinal tumour spread ## Stomach ### Cardia, fundus, body, pyloric part ### Shape varies with filling, posture, body form ### Stomach bed behind lesser sac #### Pancreas, spleen, left kidney, adrenal #### Posterior ulcer can involve pancreas or splenic vessels ### Rich arterial anastomoses along both curvatures #### Short gastric branches supply fundus ### Lymph follows arteries toward coeliac nodes ### Vagus promotes motility and secretion ### Sympathetics via greater splanchnic, coeliac plexus ### Visceral pain refers to epigastrium ## Duodenum ### Four parts curving around pancreatic head ### Proximal intraperitoneal, rest secondarily retroperitoneal ### Superior part ulcer erodes gastroduodenal artery ### Descending part: major papilla #### Bile duct and main pancreatic duct enter #### Minor papilla for accessory duct ### Third part between superior mesenteric artery and aorta #### Compression can obstruct it ### Pancreaticoduodenal arcade marks foregut-midgut junction ## Jejunum and ileum ### Jejunum upper left, ileum lower right and pelvis ### Jejunum: thicker wall, longer vasa recta ### Ileum: more arcades, more mesenteric fat ### Mesenteric border receives vessels ### Ischaemia patterns differ by cause #### Embolus, thrombosis, low flow, venous, strangulation ### Lacteals carry chylomicrons into lymph #### Long-chain lipids bypass portal transport ### Terminal ileum rich in lymphoid aggregates ### Ileocaecal valve limits reflux incompletely ### Mobility permits volvulus, internal herniation ## Caecum, appendix, and colon ### Appendix at convergence of three taeniae #### Position varies, altering symptoms and examination ### Appendicular artery is an end artery ### Ascending and descending colon retroperitoneal ### Transverse and sigmoid colon mobile on mesocolon ### Taeniae, haustra, appendices epiploicae identify colon ### Superior mesenteric: caecum to proximal transverse ### Inferior mesenteric: distal transverse to upper rectum ### Marginal artery and Riolan arc connect systems #### Watersheds at splenic flexure and rectosigmoid ## Rectum and anal canal ### Rectum begins near S3 ### Peritoneal cover decreases by thirds ### Superior rectal vein to portal system ### Middle and inferior rectal veins to systemic #### Portal-systemic communication ### Pectinate line: embryological junction #### Above: columnar, visceral, internal iliac lymph #### Below: squamous, somatic, superficial inguinal lymph ## Sphincters and haemorrhoids ### Internal sphincter: smooth, involuntary tone ### External sphincter: skeletal, three parts ### Puborectalis sling maintains anorectal angle #### Relaxation and floor descent permit defecation ### Haemorrhoidal cushions aid continence ### Internal haemorrhoids less pain-sensitive ### External thrombosis below line is painful ## Enteric and extrinsic innervation ### Myenteric plexus coordinates motility ### Submucosal plexus regulates secretion and blood flow ### Vagus to foregut and midgut ### Pelvic splanchnic S2 to S4 to hindgut ### Sympathetics reduce motility, constrict vessels ### Pain afferents travel with sympathetics ### Pudendal pathways below pectinate line