Embryology of the Gut and Lungs 212 Functional Anatomy Stuart Bunt

Embryonic Curvature traps part of the yolk sac inside the embryo to form the gut.

Embryology of Gut

Lung Buds from the Gut

Stages of Lung Development

Physiological hernia The large liver takes up abdominal space Intestine lengthens into umbilicus Rotates as it grows out and again as it re-enters abdomen Omphalocele....no re-entry Umbilical hernia, goes back out covered in peritoneum

Complex adult layout due to 270o rotation Foregut, Midgut and Hindgut suspended by the dorsal mesentary, initially straight Ventral mesentary connects stomach and ant. abd. wall, rest of gut free anteriorly Mesentary supplies blood and nerves to gut between layers of peritoneum

Stomach rotates and distends Front Dorsal Mesentary Ventral Mesentary Back Splenic tissue Omentum Epiploic Foramen

Liver and spleen form in mesentary Anterior 1. Falciform ligament 2. Lesser Omentum 3. Dorsal mesentary, divided into:- 4a. Gastrosplenic ligament 4b. Lienorenal ligament 1 Liver 2 Stomach 4a Spleen 3 4b Posterior

Formation of Omentum

90 degrees rotation

180 degrees rotation

Final 90 - 270 degrees in total

Blood Supply of the Gut Foregut Midgut Hindgut Rectum Celiac trunk Superior mesenteric artery Hindgut Inferior mesenteric artery Rectum Internal iliac artery (pudendal and rectal arteries)

Blood Supply to Abdominal Organs Celiac trunk Foregut Midgut Superior mesenteric artery Hindgut Inferior mesenteric artery Rectum Internal iliac artery (pudendal and rectal arteries)

Canalisation of the Gut

Peritoneum Flattened endothelial cells on fibro-elastic connective tissue Parietal and visceral layers Makes gut watertight Suspends gut Contains nerves and blood vessels Omentum contains infection Flattened Endothelial cell

Mesenteries are important:- Paracolic gutters channel fuid Stop herniation due to bipedal posture Supply blood/nerves Sensitive to stretch Contain infection Useful in surgery

Intra and Retroperitoneal To prevent the intestines falling into the pelvis our upright posture has been accompanied by a fusion of parts of the gut tube to the posterior abdominal wall. These parts become retro-peritoneal.

Uro-rectal septum divides the bladder and urogenital sinus from the rectum