Development of Mid/Hindgut Flashcards

1
Q

when does formation of the midgut start

A

during week 5

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2
Q

how does formation of the midgut start

A

rapid elongation to from the primary intestinal loop which communicates with the yolk sac through the vitelline duct

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3
Q

what does the cranial limb form

A

distal duodenum, jejunum and proximal ileum

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4
Q

what does the caudal limb

A

distal ileum caecum appendix ascending colon and proximal 2/3 transverse colon

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5
Q

what happens to the midgut in week 6

A

rapid elongation of the midgut and growth of the liver

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6
Q

what happens if there is not enough room in the abdomen for the midgut to grow

A

primary intestinal loop herniates into the umbilical cord

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7
Q

what does herniation of the midgut cause

A

rotation of the midgut 90 anti-clockwise bring the cranial limb to the right and caudal limp to the left forming the jejunoileal loops

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8
Q

what happens to the midgut in week 10

A

midgut returns to the abdomen and rotates a further 180 degree anticlockwise

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9
Q

what is the vermiform appendix

A

the caecum develops a wormlike diverticulum

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10
Q

when is the villitine duct destroyed

A

in week 10 during the formation of the vermiform appendix

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11
Q

by what day does the midgut return to the abdomen

A

by week 11 and has undergone 270 degrees anti-clockwise rotation in total

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12
Q

describe the decent of the caecum

A

the caecum descends from below the kiver to the right iliac fossa

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13
Q

what does the descent of the caecum stimulate

A

pulls the ascending and transverse colon into place resulting in the final arrangement of the midgut

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14
Q

what happens to the ascending and descending colon during descent of the caecum

A

they shorten and degenerate pulling them against the posterior abdominal wall making them secondarily retroperitoneal

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15
Q

how does the decent of the caecum affect the appendix

A

descent causes appendix to be located in the retrocaecal position in 64% of people

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16
Q

what is meckels/ileal diverticulum

A

remnant of the villitine duct that creates an out pocketing of the ideal wall

17
Q

what is the role of 2’s in meckels/ileal diverticulum

A
affects 2% of population 
2 times more common in male 
2 feet from ileocaecal junction 
2 inches 
symptomatic in 2% of cases
18
Q

what is omphalocele

A

failure of midgut to return to abdomen in week 10

abdominal viscera herniating into base of umbilicus

19
Q

what happens in non-rotation of the midgut

A

gut does initial 90 degrees anticlockwise but then fails the extra 180
results in small intestine on the right side of the large intestine
asymptomatic

20
Q

what happens during reverse rotation of the midgut

A

initial 90 degress anticlockwise then 180 degrees clockwise which results in overall 90 degrees clockwise
means duodenum lies ventral to transverses colon

21
Q

what is volvulus

A

twisting of the midgut
causes acute obstruction of the bowel and bilious vomiting
also can constraint arterial supply to gut causing ischemia and infarction

22
Q

describe the formation of the hindgut

A

distal end of the hangout enters the dorsal part of the cloaca - anorectal canal
ventral part of the cloaca (urogenital sinus) will from the bladder, pelvic urthrea, penile urethra and caudal part of the vagina

23
Q

what happens during week 4-6 of the hindgut

A

layer of mesoderm extends caudally to separate the urogenital sinus and anorectal canal - uroretal septum

24
Q

what happens in week 7 of the hindgut

A

the cloacal membrane ruptures creating the anal opening and a ventral opening for the urogenital sinus
the tip of the urorectal septum lies between them and froms the perineal body

25
describe the formation of the anal canal
The upper 2/3 is derived from hindgut – endoderm The lower 1/3 is derived from proctodeum (anal pit) - ectoderm Become continuous when cloacal (anal) membrane degenerates Junction between endoderm and ectoderm derivatives is marked in adult by the pectinate line Different epithelial linings, lymphatic drainage and blood supply
26
describe congenital rectourethral and rectorviginal fistula
1 in 5000 births abnormal cloaca eg too small or failure of urorectal spetum to extend caudally opening of hindgut is shifted ventrally to the urethra in males and the vagina in females
27
what is an imperforate anus
failure of anal membrane to degenerate - cursed with surgery and good prognosis
28
describe the innervation of the gastrointestinal tract
There are 2 enteric plexi: Myenteric (Auerbach’s) plexus between the circular and longitudinal muscle layers co-ordinates muscle contraction Submucosal (Meissner’s) plexus between the circular muscle and mucosa and regulates secretion The enteric nervous system is derived from neural crest cells (ectoderm origin) that migrate from neural tube to GIT
29
what is hirschsprung disease / congenital aganglionic megacolon
failure of neural crest cells to migrate bowel obstruction as lack of peristalsis dilation of bowel usually rectum or sigmoid colon
30
what genetic condition is associated with hirschsprung disease
trisomy 21