Development of midgut and hindgut

Midgut

Origin: Endodermal

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  1. Cranial limb – forms jejunum and ileum
  2. Caudal limb – forms ascending colon and 2/3 of transverse colon
  3. Cecal swelling – forms cecum, appendix and part of ascending colon
  • Intestinal loop elongates rapidly and leaves the small abdominal cavity and enters umbilical cord – physiological umbilical hernia (6th to 10th week)
  • The elongating loop rotates 270 degrees anticlockwise around axis of superior mesenteric artery (seen in the diagram)
  • Therefore upper part of small intestine lies behind colon
  • 10th week, abdominal cavity enlarges and :
  1. Jejunum reenters to left side
  2. Ileum reenters to right side
  3. Cecal swelling reenters below liver
  • Cecal swelling elongates downwards to right iliac fossa – forms right colic flexure and ascending colon
  • Vitellointestinal duct obliterated

 

Congenital anomalies:

  1. Remnant of vitelline duct:
  • Meckel’s diverticulum – proximal part near ileum remains patent
  • Vitelline fistula – whole vitelline duct remains open
  • Vitelline cyst – Middle part remains open

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2. Omphalocele/ Congenital umbilical hernia – Failure of reduction of physiological hernia due to defect in abdominal wall muscles development

3. Gastroschisis

Image result for omphalocele vs gastroschisis

4. Atresia/ stenosis of any part of primitive intestinal loop – bowel obstruction

5. Abdominal rotation of intestinal loop  – 90 degrees only or clockwise rotation


 

Hindgut

Origin: Endodermal

Derivatives: Left 1/3 transverse colon, descending colon, sigmoid colon, rectum, upper 1/2 anal canal (Lower 1/2 anal canal, proctodeum – ectodermal)

  • Lower end of hindgut dilates to form cloaca
  • And then continues as allantois to umbilicus
  • Below cloaca is cloacal membrane
  • Which is bilaminar: outer ectoderm, inner endoderm
  • Between hindgut and allantois is a urorectal septum, which grows caudally and divides the cloaca and cloacal membrane  into:
  1. Primitive urogenital sinus (ventrally) – Urogenital membrane
  2. Rectoanal canal (dorsally) – anal membrane
  • Opposite rectoanal canal, ectodermal depression called proctodeum forms
  • Anal membrane ruptures:
  1. Proctodeum – lower 1/2 anal canal
  2. Rectoanal canal – rectum and upper 1/2 anal canal

 

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Congenital anomalies:

  1. Imperforate anus – anal membrane fails to rupture
  2. Atresia of rectum – Proctodeum fails to develop
  3. Stenosis of rectum – incomplete canalization
  4. Recto – vaginal fistula, recto – urinary fistula, recto – urethral fistula – incomplete division of cloaca
  5. Anal atresia, anal stenosis
  6. Ectopic anus
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