Hindgut Development

Question 1

Hindgut development

Answer 1

1. Gut part found in tail fold extending from transverse colon Left 1/3 till cloacal membrane
2. Gives rise to: transverse colon left 1/3, left colic flexure, descending colon, , sigmoid colon, rectum and anal canal upper part
3. Hindgut part caudal to allantois origin is called cloaca, cloacal membrane forms cloaca ventral boundary

Question 2

Development of rectum and anal canal upper part

Answer 2

Transverse ridge (urorectal septum) arises between allantois and hindgut grows caudally dividing cloaca in:
1. Anterior part (primitive urogenital sinus)
2. Posterior part (rectoanal canal)
It also divides cloacal membrane into:
1. Urogenital membrane (in front)
2. Anal membrane (behind)

Question 3

Development of anal canal lower part

Answer 3

1. Mesoderm around anal membrane proliferates forming anal folds
2. Anal membrane lies at proctodeum (anal pit) bottom then membrane ruptures
3. So anal canal is of double origin:
   - Upper part: Endodermal
   - Lower part: Ectodermal

Question 4

Congenital anomalies

Answer 4

1. Congenital megacolon (Hirschsprung disease):
   due to absence of parasympathetic ganglia in bowel wall
2. Rectourethral or rectovaginal fistulas: may be caused by abnormalities in formation of cloaca and/or urorectal septum
3. Rectoanal atresia: loss of segment of rectum and anus
4. Imperforated anus: due to failure of anal membrane to break down