Lec30: Embryology, Midgut and Hindgut Flashcards
midgut: adult derivatives
duodenum distal to common bile duct, jejunum, ileum, cecum, appendix, ascending colon, proximal TV colon
midgut and foregut relative to yolk sac during folding
midgut: in front of yolk sac
foregut: behind yolk sac
what suspends the midgut as it loops
dorsal mesogastrium
primary vasculature to midgut
SMA
when’s / how’s physiological midgut herniation
beginning of week 6 - herniates into umbilical stump
cranial and caudal portions of midgut loop, communicate w/ yolk sac
loop returns into abdomen week 10
temporary cnxn between yolk sac, midgut
yolk stalk / vitelline duct / omphaomesenteric duct
week 6
loop of midgut that grows faster
cranial
rotation of midgut
week 6, counterclockwise around SMA axis, mostly cranial loop, while within umbilicus; week 10, back in abdominal cavity, caudal loop rotates 180 degrees
caudal loop of midgut =
large intestine
what ends up in lower right quadrant, why
cecum, appendix
270 degree rotation of midgut
small intestine re: SMA after rotation
posterior to SMA
fixation of intestines in abdominal cavity
small intestine- ventral mesentery, mesogastrium
ascending colon- fused to posterior abdominal wall, then that disappears
line of attachment of small intestine that persists
line from duodenojejunal junction, ileocecal junction
how cecum forms
week 6, diverticulum of caudal limb of midgut loop
appendix formation
cecum enlarges, folds; forms vermaform appendix, enters cecum medially
meckel’s diverticulum
omphalomesenteric gut connects yolk stalk-midgut loop, usually obliterated
if not, gut remains around umbilicus, abdominal wall-gut communicate
hindgut derivatives
left TV colon, descending colon, sigmoid colon, rectum, superior portion of anus, epithelial lining urinary bladder, urethra
midgut-hindgut anatomical difference
SMA branches leave off - IMA branches pick up vascularization
hindgut blood supply
IMA
cloaca def’n, lining, membrane
expanded distal hindgut
lining: endoderm
outside: ectoderm of protodeum (anal pit)
what empties into cloaca
allantois
clocal membrane formed by
urorectal septum growing toward distal part of embryo, joins w/ ectoderm
urorectal septum
infoldings of lateral cloacal walls partition cloaca into ventral urogenital sinus, dorsal rectum
divides CLOACAL SPHINCTER
cloaca partitioning
week 7
distal urorectal septum fuses w/ cloacal membrane > anal membrane, urogenital membrane, perineal body
cloacal sphincter regions
ventral: becomes pelvic floor muscles
dorsal: anal sphincter (continence!)
anal membrane
disappears, end of week 8
then rectum communicate w/ amniotic cavity
anal canal parts
upper 2/3: hindgut
lower 1/3: proctodeum
junction: pectinate line, anal membrane
pectinate line- cell change
columnar cells of hindgut > cuboidal, cutaneous cells of proctodeum > anus
anal sphincter formed
splanchnic mesoderm, caused by hox genes
arterial supply to anal canal
upper 2/3: superior rectal artery (of IMA)
lower 1/3: inferior rectal artery (of internal pudendal a. of iliac a.)
lymphatic drainage, anal canal
upper 2/3: inferior mesenteric lymph nodes
lower 1/3: superficial inguinal lymph nodes
innervation of anal canal
upper 2/3: ANS, T1-L1, S2-4, involuntary
lower 1/3: inferior rectal nerve, branch of pudendal nerve S2,3,4, voluntary control
imperforate anus
failure of apoptosis so solid endodermal tissue, no anal sphincter/opening to outside
