Lec30: Embryology, Midgut and Hindgut

Question 1

midgut: adult derivatives

Answer 1

duodenum distal to common bile duct, jejunum, ileum, cecum, appendix, ascending colon, proximal TV colon

Question 2

midgut and foregut relative to yolk sac during folding

Answer 2

midgut: in front of yolk sac
foregut: behind yolk sac

Question 3

what suspends the midgut as it loops

Answer 3

dorsal mesogastrium

Question 4

primary vasculature to midgut

Answer 4

SMA

Question 5

when’s / how’s physiological midgut herniation

Answer 5

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

Question 6

temporary cnxn between yolk sac, midgut

Answer 6

yolk stalk / vitelline duct / omphaomesenteric duct

week 6

Question 7

loop of midgut that grows faster

Answer 7

cranial

Question 8

rotation of midgut

Answer 8

week 6, counterclockwise around SMA axis, mostly cranial loop, while within umbilicus; week 10, back in abdominal cavity, caudal loop rotates 180 degrees

Question 9

caudal loop of midgut =

Answer 9

large intestine

Question 10

what ends up in lower right quadrant, why

Answer 10

cecum, appendix

270 degree rotation of midgut

Question 11

small intestine re: SMA after rotation

Answer 11

posterior to SMA

Question 12

fixation of intestines in abdominal cavity

Answer 12

small intestine- ventral mesentery, mesogastrium

ascending colon- fused to posterior abdominal wall, then that disappears

Question 13

line of attachment of small intestine that persists

Answer 13

line from duodenojejunal junction, ileocecal junction

Question 14

how cecum forms

Answer 14

week 6, diverticulum of caudal limb of midgut loop

Question 15

appendix formation

Answer 15

cecum enlarges, folds; forms vermaform appendix, enters cecum medially

Question 16

meckel’s diverticulum

Answer 16

omphalomesenteric gut connects yolk stalk-midgut loop, usually obliterated
if not, gut remains around umbilicus, abdominal wall-gut communicate

Question 17

hindgut derivatives

Answer 17

left TV colon, descending colon, sigmoid colon, rectum, superior portion of anus, epithelial lining urinary bladder, urethra

Question 18

midgut-hindgut anatomical difference

Answer 18

SMA branches leave off - IMA branches pick up vascularization

Question 19

hindgut blood supply

Answer 19

IMA

Question 20

cloaca def’n, lining, membrane

Answer 20

expanded distal hindgut

lining: endoderm
outside: ectoderm of protodeum (anal pit)

Question 21

what empties into cloaca

Answer 21

allantois

Question 22

clocal membrane formed by

Answer 22

urorectal septum growing toward distal part of embryo, joins w/ ectoderm

Question 23

urorectal septum

Answer 23

infoldings of lateral cloacal walls partition cloaca into ventral urogenital sinus, dorsal rectum
divides CLOACAL SPHINCTER

Question 24

cloaca partitioning

Answer 24

week 7

distal urorectal septum fuses w/ cloacal membrane > anal membrane, urogenital membrane, perineal body

Question 25

cloacal sphincter regions

Answer 25

ventral: becomes pelvic floor muscles
dorsal: anal sphincter (continence!)

Question 26

anal membrane

Answer 26

disappears, end of week 8

then rectum communicate w/ amniotic cavity

Question 27

anal canal parts

Answer 27

upper 2/3: hindgut
lower 1/3: proctodeum
junction: pectinate line, anal membrane

Question 28

pectinate line- cell change

Answer 28

columnar cells of hindgut > cuboidal, cutaneous cells of proctodeum > anus

Question 29

anal sphincter formed

Answer 29

splanchnic mesoderm, caused by hox genes

Question 30

arterial supply to anal canal

Answer 30

upper 2/3: superior rectal artery (of IMA)

lower 1/3: inferior rectal artery (of internal pudendal a. of iliac a.)

Question 31

lymphatic drainage, anal canal

Answer 31

upper 2/3: inferior mesenteric lymph nodes

lower 1/3: superficial inguinal lymph nodes

Question 32

innervation of anal canal

Answer 32

upper 2/3: ANS, T1-L1, S2-4, involuntary

lower 1/3: inferior rectal nerve, branch of pudendal nerve S2,3,4, voluntary control

Question 33

imperforate anus

Answer 33

failure of apoptosis so solid endodermal tissue, no anal sphincter/opening to outside