Abdomen 3 - Small Intestine (jejunum & ileum) Flashcards
transition point between foregut and midgut?
major duodenal papilla
transition point between midgut and hindgut?
2/3 along the transverse colon - near the left colic/splenic flexure
transition point between hindgut and anal canal?
pectinate line - separates hindgut-derived (above) & ectoderm-derived structures (below)
proximal anal canal is part of hindgut - pectinate line separates it from distal anal canal
artery supplying the midgut?
superior mesenteric artery
artery supplying the hindgut?
inferior mesenteric artery
where does the midgut start & end?
starts mid-duodenum (second half of the 2nd part of the duodenum)
ends at distal 2/3 of transverse colon
where does the hindgut start & end?
starts at distal 1/3 of transverse colon
ends at recto-anal junction (proximal anal canal - at the pectinate line)
(CLINICAL) what is omphalocele?
condition where gut contents protrude through the umbilical ring due to malrotation of the midgut during foetal development
(CLINICAL) how are the gut contents protected in omphalocele?
gut contents are covered by the tissue surrounding the umbilical cord
(CLINICAL) what developmental issue is associated with omphalocele?
failure of the rectus abdominis to develop properly - causes ongoing problems
(CLINICAL) what condition is associated with malrotation of the midgut during development? what does this lead to?
omphalocele - leads to protrusion of gut contents through umbilical ring
where does the jejunum begin, following the duodenum?
begins at the duodenojejunal flexure - near the suspensory ligament of the diaphragm
where does the ileum end?
at the ileocecal junction - where it meets the cecum
is there a clear boundary/ distinct structure between the jejunum and ileum?
no - gradual transition
where does the jejunum end & ileum begin?
no clear boundary - gradual transition
how much of the small intestine does the jejunum and ileum make up?
jejunum - approx. 2/5
ileum - approx. 3/5
in what quadrant of the abdomen is the jejunum located?
left upper quadrant
in what quadrant of the abdomen is the ileum located?
right lower quadrant
which part of the small intestine is located in the right lower quadrant?
ileum
what structure covers the jejunum and ileum from the front?
greater omentum
what are the two muscle layers in the wall of the small intestine?
circular (inner) layer
longitudinal (outer) layer
what structural features does the mucosal lining of the jejunum & ileum consist of that helps with absorption?
plicae circularis (circular folds)
villi & microvilli
what are plicae circularis?
circular folds in the mucosal lining - increase surface area for absorption
why does the duodenum have fewer circular folds than the jejunum and ileum?
prevent damage from acidic stomach contents - duodenum receives chyme from the stomach
jejunum & ileum are more focused on nutrient absorption
what does ‘the mesentery (of the small intestine)’ do?
fan-shaped double fold of peritoneum - anchors the jejunum & ileum to the posterior abdominal wall
how long is the root of the mesentery?
approx. 15cm - runs obliquely downward to the right
where does the mesentery extend from and to?
from the duodenojejunal junction (left of L2) to the ileocolic junction (right sacroiliac joint)
what major artery supplies the jejunum and ileum?
superior mesenteric artery - gives off jejunal & ileal branches that run through the mesentery
how does venous drainage from the small intestine occur?
blood drains into superior mesenteric vein - flows into hepatic portal vein
what does the mesentery contain?
superior mesenteric artery - jejunal & ileal branches
superior mesenteric vein - jejunal & ileal tributaries
nerves
lymphatics
which part of the small intestine is redder? why?
jejunum - has a higher vascular supply for increased nutrient absorption
which has a thicker wall - jejunum or ileum?
jejunum - greater nutrient absorption function
which part of the small intestine has a higher blood supply?
jejunum - supports the higher nutrient absorption rate
where is more fat found in the mesentery: jejunum or ileum?
ileum
how do circular folds (plicae circulares) differ between the jejunum and ileum?
jejunum = denser & taller folds
ileum = sparser & shorter folds - disappear in the terminal ileum
folds get shorter and sparser going form jejunum & ileum
why does the jejunum have a greater surface area & vascular supply for absorption than the ileum?
jejunum absorbs most nutrients as it processes freshly digested food - needs more circular folds, villi, microvilli & vascular supply
ileum absorbs remaining nutrients & specific vitamins (e.g. vitB12) the jejunum didn’t - doesn’t need such a great surface area or vascular supply
how do arterial arcades & vasa recta differ in the jejunum and ileum?
jejunum has fewer arterial arcades & long thick vasa recta
ileum has more arterial arcades & smaller vasa recta
describe the arterial arcades & vasa recta supplying the jejunum
few arterial arcades (1-2 loops)
long, thick vasa recta
how do the loops of arterial arcades differ in the jejunum and ileum?
jejunum - fewer (1-2 loops)
ileum - many loops
how do vasa recta differ in the jejunum and ileum?
jejunum - long & thick
ileum - small & thin
why is blood flow slower in the ileum compared to the jejunum?
ileum has many arterial arcade loops & smaller vasa recta
has a higher cross-sectional area of blood vessels = lowers blood pressure = slows absorption for leftover vitamins/nutrients
why does the jejunum require a faster blood flow than the ileum?
jejunum absorbs most nutrients - needs quick blood circulation to transport them efficiently
a patient has an obstruction in a vasa recta supplying the jejunum. would this have a greater or lesser impact compared to the same obstruction in the ileum? why?
greater impact in the jejunum
- jejunum has fewer vasa recta & it needs a greater vascular supply to absorb more nutrients (has a higher absorption rate)
ileum has many smaller vasa recta & its function isn’t as dependent on an efficient blood supply for nutrient absorption
function of Peyer’s patches? which has more - jejunum or ileum?
Peyer’s patches are aggregated patches of lymphoid tissue - help with immune surveillance
ileum has more
why are plicae circulares more developed in the jejunum than the ileum?
jejunum absorbs the majority of nutrients = needs a larger SA
ileum has a lower absorption rate & mainly absorbs bile salts & B12 = doesn’t need a higher SA; has shorter and fewer folds
a surgeon is differentiating between the jejunum and ileum during surgery. What 3 structural features could they use to tell them apart?
colour/ vascular supply: jejunum is redder; ileum is pinker (more vs less vascular supply)
mesentery fat: jejunum has less fat; ileum has more
plicae circularis: jejunum has denser & taller folds; ileum has sparse, short folds which become absent in the terminal ileum
why does blood flow more slowly in the ileum compared to the jejunum?
ileum has more arterial arcades (loops) = higher cross-sectional area of blood vessels = lowers blood pressure & slows blood flow
if a disease reduced the blood supply to the ileum, what specific deficiencies would you expect to see?
vitamin B12 deficiency
bile salt malabsorption
(CLINICAL) what is the embryological cause of an ileal diverticulum?
failure of the vitelline duct to degenerate - leaves an outpouching of the ileum (ileal diverticulum)
what are the two types of ectopic cells that may be found in an ileal diverticulum? what complications do they cause?
gastric cells - secrete acid, leads to ulceration and pain
pancreatic cells - secrete pancreatic juices with enzymes (e.g. proteases), leads to self-digestion and inflammation
why can an ileal diverticulum be mistaken for appendicitis?
both cause pain in the right lower quadrant - but an appendix will appear normal in the case of an ileal diverticulum
four potential complications of an ileal diverticulum?
- diverticulitis (inflammation of diverticulum)
- ulceration & bleeding (from ectopic gastric cells)
- intestinal obstruction/perforation
- fistula formation (abnormal connections to other organs)
why might an ileal diverticulum lead to bleeding?
if gastric cells are present - produce acid, leads to ulceration - erodes blood vessels, leads to bleeding
what is the most severe consequence of an untreated, inflamed ileal diverticulum?
peritonitis - perforation of the diverticulum causing an infection of the peritoneal cavity
