Development of Mid/Hindgut

Question 1

when does formation of the midgut start

Answer 1

during week 5

Question 2

how does formation of the midgut start

Answer 2

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

Question 3

what does the cranial limb form

Answer 3

distal duodenum, jejunum and proximal ileum

Question 4

what does the caudal limb

Answer 4

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

Question 5

what happens to the midgut in week 6

Answer 5

rapid elongation of the midgut and growth of the liver

Question 6

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

Answer 6

primary intestinal loop herniates into the umbilical cord

Question 7

what does herniation of the midgut cause

Answer 7

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

Question 8

what happens to the midgut in week 10

Answer 8

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

Question 9

what is the vermiform appendix

Answer 9

the caecum develops a wormlike diverticulum

Question 10

when is the villitine duct destroyed

Answer 10

in week 10 during the formation of the vermiform appendix

Question 11

by what day does the midgut return to the abdomen

Answer 11

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

Question 12

describe the decent of the caecum

Answer 12

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

Question 13

what does the descent of the caecum stimulate

Answer 13

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

Question 14

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

Answer 14

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

Question 15

how does the decent of the caecum affect the appendix

Answer 15

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

Question 16

what is meckels/ileal diverticulum

Answer 16

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

Question 17

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

Answer 17

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

Question 18

what is omphalocele

Answer 18

failure of midgut to return to abdomen in week 10

abdominal viscera herniating into base of umbilicus

Question 19

what happens in non-rotation of the midgut

Answer 19

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

Question 20

what happens during reverse rotation of the midgut

Answer 20

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

Question 21

what is volvulus

Answer 21

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

Question 22

describe the formation of the hindgut

Answer 22

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

Question 23

what happens during week 4-6 of the hindgut

Answer 23

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

Question 24

what happens in week 7 of the hindgut

Answer 24

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

Question 25

describe the formation of the anal canal

Answer 25

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

Question 26

describe congenital rectourethral and rectorviginal fistula

Answer 26

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

Question 27

what is an imperforate anus

Answer 27

failure of anal membrane to degenerate - cursed with surgery and good prognosis

Question 28

describe the innervation of the gastrointestinal tract

Answer 28

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

Question 29

what is hirschsprung disease / congenital aganglionic megacolon

Answer 29

failure of neural crest cells to migrate
bowel obstruction as lack of peristalsis
dilation of bowel usually rectum or sigmoid colon

Question 30

what genetic condition is associated with hirschsprung disease

Answer 30

trisomy 21