Development of Hindgut

Dr. Rania Gabr

Objectives• Enlist the derivatives of hindgut.

• Discuss the development of Hindgut.

• Describe Hindgut abnormalities.

Derivatives of Hindgut• Distal 1/3rd of the transverse colon• Descending colon• Sigmoid colon• Rectum• Upper part of the anal canal• The endoderm of the hindgut also forms the

internal lining of the urinary bladder and urethra.• In 5th week midgut is suspended from the posterior

abdominal wall by a short mesentery.• The Midgut is connected with yolk sac by vitelline

duct or yolk stalk.

Development of Hindgut• The terminal portion of the hindgut enters into

the posterior region of cloaca, the anorectal canal.

• The Developing hindgut is supplied by the inferior mesenteric artery.

• The junction between the segment of transverse colon derived from the midgut and that originated from the hindgut is indicated by the change in blood supply

• The Cloaca is the dilatation of hind gut closed by The cloacal membrane

• The Cloaca receives three openings:

- The Alantois ventrally- 2 Mesonephric ducts one

on each side

Cloaca

Partitioning of the cloaca-Occurs during 4th to 7th weeks- Urorectal septum , which is a mesodermal septum, divides cloaca into:1-Primitive urogenital sinus anteriorly2- Anorectal canal posteriorly

• After division of the cloaca, the anorectal canal becomes continuous with the hindgut to form the Rectum and Anal canal

Formation of primitive urogenital sinus & anorectal

canal

Cloaca• The Primitive urogenital sinus is divided by the the

opening of mesonephric duct into:1. Vesico-uretheral canal2. Definitive urogenital sinus.

• This septum divides also cloacal membrane into ventral urogenital membrane and dorsal anal membrane.

Partitioning of CloacaBy the seventh week, the urorectal septum

has fused with the cloacal membrane

Dividing it into a dorsal anal membrane and a larger ventral urogenital membrane

The area of fusion of the urorectal septum with the cloacal membrane is represented in the adult by the perineal body

Cloacal membrane

urogenital membrane (anteriorly) anal

membrane

(posteriorly)

Urogenital membrane

Anal membrane

Urorectal septum

Rectum and Anal Canal• The Dorsal part of

cloaca (anorectal canal) forms the mucosa of rectum and upper ½ of anal canal.

• While their muscles are develop from the surrounding mesoderm.

• The Lower ½ of anal canal develops from proctodeum (ectodermal depression below anal membrane).

Rectum and Anal Canal

• The Anal membrane ruptures at the 9th week to allow continuity between the 2 parts of anal canal.

• The Upper ½ of the anal mucosa is endodermal while lower ½ is ectodermal.

• The Pectinate line separates between 2 parts in adult.

Congenital Anomalies

• 1- Imperforate Anus:

• Failure of rupture of the anal membrane.

2- Rectovaginal fistula

3- Urorectal fistula

4- Rectoperianeal fistula