Gut tube
Dorsal mesentery (back) from lower oesophagus to cloaca
Ventral mesentery (front) from lower oesophagus to 1st part of duodenum
Transformation
hollow → occluded → recanulization → definitive hollow
Abnormal recanulization can form duplication, stenosis, or atresia
Stomach formation
Differential growth → greater + lesser curve
- 90° clockwise rotation craniocaudally so lesser curvature from ventral → medial, greater curvature dorsal → lateral
- Some rotation ventrodorsal axis. Greater curvature faces slightly caudally and lesser cranially
Midgut
- Undergoes rapid elongation to form primary intestinal loop
- Primary intestinal loop herniates into umbilical cord
- Also rotates 90° anticlockwise
- Week 10 midguts returns to abdo and rotates a further 180° - 270° total
- Vitelline duct also obliterated
Anal canal
- Upper 2/3 hindgut - endoderm
- Lower 1/3 from ectoderm
The function between the two is marked by the pectinate line
Liver & gallbladder
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Liver expands from outpouching
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Becomes too large to be contained within the septum transversum (diaphragm) - protrudes into ventral mesentery
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Rotation of stomach pushes liver up - bare area on liver
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Liver is about 10% of body weight at this stage (5% at birth)
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Main function in foetus is haematopoiesis
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gallbladder outgrowth of bile duct
Pancreas
- Initially develops as 2 endodermal buds that fuse
- As the duodenum rotates 90° (as stomach rotates) the ventral bud is carried dorsally
- Ventral bud forms uncinate process
Spleen
- Unlike rest of abdo organs, not derived from endoderm - mersoderm derivative
- Rotation of stomach brings spleen over to lefthand side (from dorsally)
- Dorsal mesentery becomes ligaments