Development of the GI tract Sanjaya Adikari Dept. of Anatomy

Ampulla of Vater

Development of the GUT Starts at 4th week IUL due to flexion of embryo Formed by the endoderm lined yolk sac Epithelium and secretory components of glands derive from endoderm Muscles and connective tissues derive from splanchnic mesoderm Primitive gut consists of four parts -Pharynx -Foregut -Midgut -Hindgut Foregut, midgut and hindgut, each has its own artery

Foregut Hindgut Midgut Bucco-pharyngeal membrane Cloacal membrane Vitelline duct Allantois

Foregut Hindgut Midgut Coeliac artery Sup. mesenteric artery Inf. mesenteric artery

Foregut Supplied by Coeliac artery Extends from the bucco-pharyngeal membrane to a point just distal to hepatic diverticulum Its proximal part extends up to tracheo-bronchial diverticulum Its distal part extends from TB diverticulum to HD Derivatives: Pharynx, Oesophagus, stomach, liver, gall bladder, pancreas and duodenum up to duodenal papilla

Development & rotation of stomach Tube dilates, posterior wall grows rapidly than the anterior wall: Produce lesser & greater curvatures Dorsal mesogastrium lengthens rapidly & forms greater omentum Rotates 90 clock wise: left and right vagus nerves become anterior and posterior

Rotation of stomach 90 rotation

Development of spleen Develops from the dorsal mesogastrium

Development of duodenum Develops from distal foregut & proximal midgut Acquires ‘C’ shape due to stomach rotation and growth of pancreatic buds Dorsal mesentery gets absorbed into posterior abdominal wall: 2nd and 3rd Parts becomes retroperitoneal with pancreas

Development of liver & gall bladder Liver parenchyma develops from liver bud/hepatic diverticulum Connective tissue, Kupffer cells and haemopoietic tissue of liver develop from septum transversum Gall bladder, cystic duct and common bile duct develop from cystic diverticulum

Development of pancreas Exocrine part develops from the ventral & dorsal pancreatic buds Endocrine part (Islets of Langerhans) develop from the neural crest cells

Hepatic diverticulum Cystic diverticulum Ventral pancreatic bud Dorsal pancreatic bud

Uncinate process (ventral bud) Dorsal bud Gall bladder Common bile duct Accessory pancreatic duct Main pancreatic duct

Midgut Supplied by Superior mesenteric artery Extends from the hepatic diverticulum to the junction of proximal 2/3 and distal 1/3 of the transverse colon Connected to the yolk sac by vitelline duct through umbilical cord Undergoes 270 rotation anticlockwise Derivatives: Part of duodenum, small intestine, caecum, ascending colon and prox. 2/3 of transverse colon

Midgut… At 6th week I.U.L, mid gut loop herniates through the umbilical region – Physiological umbilical hernia This is due to rapid increase in length relative to the size of the abdominal cavity At 10th week I.U.L, it returns to the abdominal cavity Rotates 90 when herniates and 180 when returns

Hindgut Supplied by Inferior mesenteric artery Extends from the junction of proximal 2/3 and distal 1/3 of the transverse colon to Cloacal membrane Derivates: Distal 1/3 of TC, descending colon, sigmoid colon, rectum and upper part of anus

Perineum Coccyx Anal triangle subpubic angle Urogenital triangle

Urorectal septum Cloaca Cloacal membrane Urorectal septum divides the cloaca into urogenital part and an anorectal part. This septum also divides the cloacal membrane into urogenital and anal membranes. The septum itself becomes the perineal body.

Developmental defects - Foregut Pyloric stenosis: Hypertrophy of pyloric sphincter muscles Atresia of bile duct: failure to recanalize the cystic diverticulum

Developmental defects - Foregut Duplication of gall bladder: formation of two cystic diverticula Annular pancreas: mal fusion of ventral & dorsal pancreatic buds leading to duodenal stenosis

Developmental defects - Midgut Vitelline fistula: Persistence of vitelline duct Vitelline cyst: Cyst formation with ligament on either side Meckels diverticulum: Persistence of small part of vitelline duct connected to gut

Developmental defects - Midgut Omphalocoele: Persistence of physiological umbilical hernia/ non-return of intestinal loops at 10th week IUL

Developmental defects - Hindgut Imperforate anus: Nonrupture of anal membrane

Developmental defects - Hindgut Urorectal fistula: Persistent connection between urinary tract & rectum due to defective formation of urorectal septum

Developmental defects - Hindgut Congenital megacolon: Absence of parasympathetic ganglia in the bowel wall (aganglionic megacolon or Hirschsprung disease)