✅ EMBRIOLOGÍA del APARATO DIGESTIVO 🍔💩

Embryology of the Digestive System

In this session, Franco discusses the embryological development of the digestive system, starting from the 14th day of gestation when the embryo takes on a disc shape.

Formation of Intestinal Structures

• The primitive intestine is formed through cephalocaudal and lateral folding of the embryo, incorporating a portion of the yolk sac to form the primitive intestine.

• The primitive intestine is divided into foregut, midgut, and hindgut. Mesenteries suspend the intestinal tube from the body wall, with intraperitoneal organs connected to the body wall by mesenteries.

Development of Mesenteries

• Dorsal and ventral mesenteries form during the fifth week. The dorsal mesentery extends from the esophagus to the cloacal region, while the ventral mesentery gives rise to lesser omentum and falciform ligament.

• Differentiation continues with specific regions named based on their location along different parts of the gastrointestinal tract.

Organogenesis in Early Weeks

• The anterior intestine develops into structures like esophagus, stomach, liver, gallbladder, and pancreas. Notably, a respiratory diverticulum emerges in week four.

• Significant changes occur in organ positioning and morphology during subsequent weeks as rotation processes shape structures like stomach and duodenum.

Liver and Pancreas Formation

• The liver and gallbladder begin forming around halfway through week three. Hepatic prominence appears at the distal end of the anterior intestine.

• Pancreas development involves dorsal and ventral pancreatic buds originating from endodermal linings. These buds undergo intricate movements as surrounding structures evolve.

Midgut Development

Development of the Middle Intestine

This section discusses the rapid elongation of the middle intestine and its mesentery, leading to the formation of the primitive intestine. It also explores the herniation and subsequent return of intestinal loops into the abdominal cavity during development.

Development Process

• The middle intestine undergoes rapid elongation, forming the primitive intestine.

• Two branches emerge from the primitive gut tube: a cranial branch and a caudal branch.

• Growth and expansion of the liver cause temporary overcrowding in the abdominal cavity.

• Intestinal loops herniate into the extraembryonic cavity through the umbilical cord, known as physiological umbilical hernia.

Rotation and Return

• The primitive gut tube rotates around an axis formed by the superior mesenteric artery.

• By week ten, herniated intestinal loops start returning to the abdominal cavity.

• The jejunum is among the first parts to return on the left side, followed by other loops shifting towards right.

• The last part to return is a small conical projection at the caudal end of the primary intestinal loop.

Formation of Posterior Intestine

This segment delves into how posterior intestine gives rise to various structures like colon, rectum, and anal canal during embryonic development.

Differentiation Process

• The posterior intestine contributes to forming different segments including colo-transverse, colo-descending, colo-sigmoid, rectum, and upper anal canal.

• It enters into cloaca's posterior region becoming primitive anorectal canal while allantois forms urogenital sinus anteriorly.

Cloacal Development

• Cloaca is lined with endoderm; its ventral border covered by superficial ectoderm.

• A mesodermal structure called urorectal septum separates allantois from posterior intestine.

• As folding continues in embryo growth, urorectal septum approaches cloacal membrane by seventh week.