Development of Mid/Hindgut Flashcards
when does formation of the midgut start
during week 5
how does formation of the midgut start
rapid elongation to from the primary intestinal loop which communicates with the yolk sac through the vitelline duct
what does the cranial limb form
distal duodenum, jejunum and proximal ileum
what does the caudal limb
distal ileum caecum appendix ascending colon and proximal 2/3 transverse colon
what happens to the midgut in week 6
rapid elongation of the midgut and growth of the liver
what happens if there is not enough room in the abdomen for the midgut to grow
primary intestinal loop herniates into the umbilical cord
what does herniation of the midgut cause
rotation of the midgut 90 anti-clockwise bring the cranial limb to the right and caudal limp to the left forming the jejunoileal loops
what happens to the midgut in week 10
midgut returns to the abdomen and rotates a further 180 degree anticlockwise
what is the vermiform appendix
the caecum develops a wormlike diverticulum
when is the villitine duct destroyed
in week 10 during the formation of the vermiform appendix
by what day does the midgut return to the abdomen
by week 11 and has undergone 270 degrees anti-clockwise rotation in total
describe the decent of the caecum
the caecum descends from below the kiver to the right iliac fossa
what does the descent of the caecum stimulate
pulls the ascending and transverse colon into place resulting in the final arrangement of the midgut
what happens to the ascending and descending colon during descent of the caecum
they shorten and degenerate pulling them against the posterior abdominal wall making them secondarily retroperitoneal
how does the decent of the caecum affect the appendix
descent causes appendix to be located in the retrocaecal position in 64% of people
what is meckels/ileal diverticulum
remnant of the villitine duct that creates an out pocketing of the ideal wall
what is the role of 2’s in meckels/ileal diverticulum
affects 2% of population 2 times more common in male 2 feet from ileocaecal junction 2 inches symptomatic in 2% of cases
what is omphalocele
failure of midgut to return to abdomen in week 10
abdominal viscera herniating into base of umbilicus
what happens in non-rotation of the midgut
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
what happens during reverse rotation of the midgut
initial 90 degress anticlockwise then 180 degrees clockwise which results in overall 90 degrees clockwise
means duodenum lies ventral to transverses colon
what is volvulus
twisting of the midgut
causes acute obstruction of the bowel and bilious vomiting
also can constraint arterial supply to gut causing ischemia and infarction
describe the formation of the hindgut
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
what happens during week 4-6 of the hindgut
layer of mesoderm extends caudally to separate the urogenital sinus and anorectal canal - uroretal septum
what happens in week 7 of the hindgut
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
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
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
what is an imperforate anus
failure of anal membrane to degenerate - cursed with surgery and good prognosis
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
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
what genetic condition is associated with hirschsprung disease
trisomy 21
