Naziha Sultan Ahmed, BVMS, MSc Scientific degree (Prof. Assis.), Department of Anatomy College of Veterinary Medicine, University of Mosul, Mosul, Iraq https://orcid.org/0000-0002-2856-8277 https://www.researchgate.net/profile/Naziha_Ahmed Anatomy | Part II | 2nd year 2019

Digestive System The embryonic development of the digestive system

The head and tail folds with the lateral folds formed through the 4thweek of embryonic development. These folds makes the dorsal part of the yolk sac included within the embryo as a primitive gut which represent the primordium of the digestive system.

The endoderm of primitive gut give rise to the epithelium of the digestive system and parenchyma of the accessory glands (liver & pancreas).

Epithelium of the proctodeum (caudal end of anal canal) and the stomodium (cranial end of mouth) which originate from the ectoderm & endoderm (without mesoderm).

The primitive gut divided into 3 parts: forgut, midgut, hindgut.

Derivatives of the forgut:

Pharynx, lower respiratory system, esophagus, stomach, cranial duodenum, liver, pancreas and biliary system.

The primitive pharynx derived from the branchial arches. The remaining of the primitive pharynx after formation of the tongue, palate, respiratory system called the pharynx.

Esophagus derived from the foregut between the pharynx and septum transversum (primordium of the diaphragm).

The simple stomach derived from a tubular segment of the foregut caudally to the septum transversum as a fusiform dilation suspended to the dorsal wall of abdominal cavity via a dorsal mesogastrium.

CouAnatomy | Digestive system | Prof. Assis. Naziha Sultan Ahmed Page | 1

Cecum

The midgut derivatives:

Small intestine, cecum, vermiform appendix, ascending colon, most of transverse colon.

Intestine derived from midgut loop (ventral loop), projects into the umbilical cord, where it elongates and rotates then return to abdominal cavity.

The hindgut derivatives:

Left part of the transverse colon, descending colon, sigmoid colon, rectum, epithelium of urinary bladder, most of urethra and upper part of anal canal.

Liver arise as hepatic diverticulum from the region of the foregut that will become the descending duodenum within the ventral mesogastrium.

CouAnatomy | Digestive system | Prof. Assis. Naziha Sultan Ahmed Page | 2 The pancreas develop as two separate endodermal diverticulae:

-One arises ventrally as a bud of hepatic diverticulum,

-The other one arises dorsally from the duodenum.

CouAnatomy | Digestive system | Prof. Assis. Naziha Sultan Ahmed Page | 3