Gut Tube Development. For it s rare that a man thinks of anything so seriously as his dinner!

Transcription

1 For it s rare that a man thinks of anything so seriously as his dinner! Ben Johnson Gut Tube Development This chapter will follow the development of the embryonic gut caudal to the developing pharynx, where the focus will be on the emergence of the digestive system anatomy. Like the pharyngeal wall, the endodermal lining of the foregut, midgut, and hindgut exhibits great developmental potential. As this endodermal epithelium develops, it does so in concert with the surrounding splanchnic mesoderm. In the end, the simple gut tube that arose from the old yolk sac becomes all the anatomy of the digestive tract and its associated organs. You should be familiar with the anatomy of the digestive system and the topographical relationships of the various organs in the peritoneal cavity. Understand which digestive organs arise from the three embryonic parts of the gut fore, mid, and hind. Understand the processes that account for the development of the different digestive organs. Understand how gut tube development accounts for the position and relations of the mesenteries and omenta. 97

2 Anatomy Review Review the basics of the digestive system Topography of the digestive organs Note location of organs Intraperitoneal Retroperitoneal Basic structure of the gut tube Understand the different tunics and their tissues Organs of the digestive system Esophagus Stomach Small intestine Pancreas Liver Large intestine Associated organ Spleen E m b r y o l o g y L e c t u r e M a n u a l b y M a r k N i e l s e n 98

3 G u t T u b e D e v e l o p m e n t Review of Embryonic Folding Lateral folding Cranial caudal folding 99

4 Sections Through Peritoneal Coelom and Gut Tube Transverse sections through embryo at beginning of 5th week Foregut section Dorsal mesentery Ventral mesentery Midgut section Dorsal mesentery Yolk sac Hindgut section Dorsal mesentery Basic anatomy of tube Epithelial lining from endoderm Other layers from splanchnic mesoderm E m b r y o l o g y L e c t u r e M a n u a l b y M a r k N i e l s e n 100

5 G u t T u b e D e v e l o p m e n t Development of the Foregut Terminal esophagus Relation to diaphragm Stomach Differential growth and enlargement Rotation Tilting Mesentery Spleen Relation to stomach s mesentery Mesenchymal condensation 101

6 Duodenum Diverticula of the duodenum Hepatic plate Hepatic diverticulum Liver cords Bile canaliculi Hepatic ducts Cystic diverticulum Gall bladder Cystic duct Common bile duct Dorsal pancreatic bud Head, body, and tail of pancreas Accessory pancreatic duct Ventral pancreatic bud Uncinate process Main pancreatic duct Results Liver Gall bladder Pancreas E m b r y o l o g y L e c t u r e M a n u a l b y M a r k N i e l s e n 102

7 Finalizing the foregut Final positioning of the retroperitoneal and intraperitoneal organs G u t T u b e D e v e l o p m e n t Ventral mesentery Lesser omentum Falciform ligament of the liver Lesser sac (omental bursa) Epiploic foramen Upper recess of lesser sac Lower recess of lesser sac Greater omentum 103

8 Development of the Midgut Umbilical herniation Causes Midgut loop Cranial limb of loop Part of duodenum and all of jejunum and ileum Caudal limb of loop First half of large intestine Cecal diverticulum Rotation of midgut loop Relation to superior mesenteric artery First rotation is counterclockwise around the artery 90 degrees Return of midgut to abdomen Further rotation of midgut Rotates another 180 degrees counterclockwise Fixation of intestines E m b r y o l o g y L e c t u r e M a n u a l b y M a r k N i e l s e n 104

9 G u t T u b e D e v e l o p m e n t 105

10 Formation of cecum and appendix Cecal diverticulum Differential growth and position of appendix Development of the Hindgut Fate of organs and mesenteries Descending colon Sigmoid colon Rectum Partitioning of the cloaca Cloaca Cloacal membrane Allantois Urogenital sinus Urorectal septum Urogenital membrane Proctodeum E m b r y o l o g y L e c t u r e M a n u a l b y M a r k N i e l s e n 106