0313 - Embryology of the Gut Flashcards
From which embryonic tissue layer does the gut derive?
Endoderm
What does Gastrulation mean?
Formation of the gut. Used in a looser sense to mean formation of the trilaminar embryo.
What is the foregut?
Runs from oesophagus to duodenum (1st part). Liver and spleen develop in ventral and dorsal mesenteries respectively, with pancreas in both. Blood supply is coeliac axis, but oesophagus has extra).
How can tracheo-oesophageal fistula form?
Airways arise from branches of the foregut. An abnormal notochord may occlude the foregut, preventing normal separation and leaving a TOF.
What is the notochord?
A transient, embryonic neural structure that is more primitive than a spinal cord and involved in gastrulation. Abnormalities in notochord signalling may give rise to VACTERL abnormalities.
What does VACTERL stand for?
Vertebral anomalies, Anal atresia, Cardiac defects,Tracheoesophageal fistula and/or Esophageal atresia, Renal & Radial anomalies and Limb defects
How does the stomach develop?
Has both dorsal and ventral mesenteries (mesogastria), giving rise to liver, pancreas, and spleen. Enlarges in foregut and rotates to the left, with posterior surface becoming greater curve, and what was the left size becomes anterior. As this happens, duodenum rotates to the right and becomes retroperitoneal.
What are the two parts of pancreatic development
Body and neck (most of it) develop in dorsal mesogastrium), head and uncinate process develop in ventral mesogastrium, and are carried by rotation and growth of duodenum.
Clinically - ventral part may retain a separate duct if it doesn’t fuse with main pancreatic (dorsal) duct.
How does the liver develop?
Endoderm in ventral mesogastrium thickens. Bile duct buds from duodenum (endoderm) grow into ventral mesogastrium (septum transversum - mesoderm), dividing. Thus, it is a network of endodermal cells in a mesodermal vascular sponge.
Briefly outline the midgut.
Runs from second part of duodenum to left transverse colon near splenic flexure. Supplied by superior mesenteric artery.
How does the midgut form its shape?
Physiological hernia resolves in the third month. Gut is attached to abdominal wall (posterior) at ceacum and duodenum, and freely rotates (jejunum, ileum) between those attachments. Both duodenum and hindgut rotate as well.
What is the hindgut?
Splenic flexure to anus, mostly supplied by IMA.
How does the hindgut separate from the urogenital sinus?
The uro-rectal septum (in-growing fold) grows from cranial-caudal to reach the cloacal membrane, which then breaks down, allowing for an opening.
How does the ENS form?
Neuroblasts from rostral neural crest migrate into proximal gut, then aborally to reach anus by week 12. They mature into the enteric ganglia, including VA, SY nerve input)
