Development of the GI tract

Sanjaya AdikariDept. 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

MidgutBucco-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

Urogenital triangle

Anal triangle

Coccyx

subpubic angle

Perineum

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.

Urorectal septum

CloacaCloacal membrane

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

• Congenital megacolon: Absence of parasympathetic ganglia in the

bowel wall (aganglionic megacolon or Hirschsprung disease)

Developmental defects - Hindgut