Transcript Development of the GI tract

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
Bucco-pharyngeal membrane
Midgut
Vitelline duct
Allantois
Cloacal membrane
Hindgut
Foregut
Coeliac artery
Midgut
Sup. mesenteric artery
Hindgut
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
Accessory
pancreatic
duct
Common bile duct
Dorsal bud
Uncinate process
(ventral bud)
Gall bladder
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
Cloacal membrane
Cloaca
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
• Atresia of bile duct: failure
of pyloric sphincter muscles
to recanalize the cystic
diverticulum
Developmental defects - Foregut
• Duplication of gall
• Annular pancreas: mal fusion of
bladder: formation of
ventral & dorsal pancreatic buds
two cystic diverticula
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/ nonreturn 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)