Development of midgut and hindgut Flashcards
What does the midgut develop into?
Duodenum, distal to bile duct Ileum Jejunum Caecum, appendix Ascending colon Transverse colon, proximal 2/3
What is the blood supply of the midgut?
Superior mesenteric artery
How does the midgut develop?
Elongates a lot
Forms a loop
Herniates into umbilical cord
Rotates
Enters abdominal cavity again
Caecal bud descends
Why does the midgut form a loop?
Because as it elongates, it runs out of space
What is the structure of the midgut loop?
Cranial end and caudal end
Superior mesenteric artery at its axis
What is the name of the midgut loop?
Primary intestinal loop
Why does the midgut herniate?
Because as it elongates and forms a loop
it runs out of space
How does the midgut loop rotate?
270degrees anti-clockwise
What is the arrangement of the midgut loop after rotation?
Cranial end is to the left
Caudal end is to the right
What is the effect of the rotation of the midgut loop?
Means that cranial end of midgut loop returns to abdominal cavity first
moving to left side
And that caudal end lies anterior over cranial end
Where is the caecal bud initially located?
To the right
at the level of the duodenum
Where does the caecum descend to?
To the level of the inferior ileum
What is recanalisation?
Cell death in walls of primitive gut tube to increase the lumen of the primitive gut tube
Why does the lumen of the primitive gut tube need to be increased by recanalisation?
Because cell growth in walls of primitive gut tube
can be so rapid
that the lumen becomes narrow, closed up
What structures commonly require recanalisation?
Oesophagus
Bile duct
Duodenum, ileum, jejunum
What does the hindgut develop into?
Transverse colon, distal 1/3 Descending colon Sidmoid colon Rectum Anal canal, superior part Epithelium of urinary bladder
What is the blood supply of the hindgut?
Inferior mesenteric artery
Where does the inferior mesenteric artery arise from?
Abdominal aorta
What forms the superior part of the anal canal?
Hindgut
What forms the inferior part of the anal canal?
Proctodeum
What is the proctodeum?
Depression in the ectoderm that lines the cloaca
What is the cloacal membrane made up of?
Endoderm lining primitive gut tube
Ectoderm lining proctodeum
What is the line that marks the division of the superior and inferior parts of the anal canal?
Pectinate line
What is the difference between the epithelial lining of the superior and inferior parts of the anal canal?
Superior part is lined by simple columnar epithelium
Inferior part is lined by stratified squamous epithelium
What is the difference between the blood supply of the superior and inferior parts of the anal canal?
Superior part is supplied by inferior mesenteric artery
Inferior part is supplied by pedundal artery
What is the difference between the innervation of the superior and inferior parts of the anal canal?
Superior part of anal canal is innervated by sympathetic least splanchnic nerve, parasympathetic pelvic splanchnic nerves
Inferior part of anal canal is innervated by pudendal nerve
What is the difference between the sensory functions of the superior and inferior parts of the anal canal?
Superior part of anal canal can only detect stretch
Inferior part of anal canal can detect temperature, pressure, pain
What are the openings of the primitive gut tube?
Foregut and hindgut have no openings
Midgut has an opening to the yolk sac at the umbilicus
How is the midgut related to the yolk sac?
Midgut is connected to yolk sac
What connects the midgut to the yolk sac?
Vitelline duct
