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

Cloaca 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

Partitioning of the cloaca -Occurs during 4th to 7th weeks - Urorectal septum , which is a mesodermal septum, divides cloaca into: 1-Primitive urogenital sinus anteriorly 2- 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 canal 2. Definitive urogenital sinus. This septum divides also cloacal membrane into ventral urogenital membrane and dorsal anal membrane.

Partitioning of Cloaca By 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 Urorectal septum Anal membrane

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 Dr. Sherif Fahmy

4- Rectoperianeal fistula