Abdomen 3 - Small Intestine (jejunum & ileum)

Question 1

transition point between foregut and midgut?

Answer 1

major duodenal papilla

Question 2

transition point between midgut and hindgut?

Answer 2

2/3 along the transverse colon - near the left colic/splenic flexure

Question 3

transition point between hindgut and anal canal?

Answer 3

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

Question 4

artery supplying the midgut?

Answer 4

superior mesenteric artery

Question 5

artery supplying the hindgut?

Answer 5

inferior mesenteric artery

Question 6

where does the midgut start & end?

Answer 6

starts mid-duodenum (second half of the 2nd part of the duodenum)

ends at distal 2/3 of transverse colon

Question 7

where does the hindgut start & end?

Answer 7

starts at distal 1/3 of transverse colon

ends at recto-anal junction (proximal anal canal - at the pectinate line)

Question 8

(CLINICAL) what is omphalocele?

Answer 8

condition where gut contents protrude through the umbilical ring due to malrotation of the midgut during foetal development

Question 9

(CLINICAL) how are the gut contents protected in omphalocele?

Answer 9

gut contents are covered by the tissue surrounding the umbilical cord

Question 10

(CLINICAL) what developmental issue is associated with omphalocele?

Answer 10

failure of the rectus abdominis to develop properly - causes ongoing problems

Question 11

(CLINICAL) what condition is associated with malrotation of the midgut during development? what does this lead to?

Answer 11

omphalocele - leads to protrusion of gut contents through umbilical ring

Question 12

where does the jejunum begin, following the duodenum?

Answer 12

begins at the duodenojejunal flexure - near the suspensory ligament of the diaphragm

Question 13

where does the ileum end?

Answer 13

at the ileocecal junction - where it meets the cecum

Question 14

is there a clear boundary/ distinct structure between the jejunum and ileum?

Answer 14

no - gradual transition

Question 15

where does the jejunum end & ileum begin?

Answer 15

no clear boundary - gradual transition

Question 16

how much of the small intestine does the jejunum and ileum make up?

Answer 16

jejunum - approx. 2/5
ileum - approx. 3/5

Question 17

in what quadrant of the abdomen is the jejunum located?

Answer 17

left upper quadrant

Question 18

in what quadrant of the abdomen is the ileum located?

Answer 18

right lower quadrant

Question 19

which part of the small intestine is located in the right lower quadrant?

Answer 19

ileum

Question 20

what structure covers the jejunum and ileum from the front?

Answer 20

greater omentum

Question 21

what are the two muscle layers in the wall of the small intestine?

Answer 21

circular (inner) layer
longitudinal (outer) layer

Question 22

what structural features does the mucosal lining of the jejunum & ileum consist of that helps with absorption?

Answer 22

plicae circularis (circular folds)
villi & microvilli

Question 23

what are plicae circularis?

Answer 23

circular folds in the mucosal lining - increase surface area for absorption

Question 24

why does the duodenum have fewer circular folds than the jejunum and ileum?

Answer 24

prevent damage from acidic stomach contents - duodenum receives chyme from the stomach

jejunum & ileum are more focused on nutrient absorption

Question 25

what does 'the mesentery (of the small intestine)' do?

Answer 25

fan-shaped double fold of peritoneum - anchors the jejunum & ileum to the posterior abdominal wall

Question 26

how long is the root of the mesentery?

Answer 26

approx. 15cm - runs obliquely downward to the right

Question 27

where does the mesentery extend from and to?

Answer 27

from the duodenojejunal junction (left of L2) to the ileocolic junction (right sacroiliac joint)

Question 28

what major artery supplies the jejunum and ileum?

Answer 28

superior mesenteric artery - gives off jejunal & ileal branches that run through the mesentery

Question 29

how does venous drainage from the small intestine occur?

Answer 29

blood drains into superior mesenteric vein - flows into hepatic portal vein

Question 30

what does the mesentery contain?

Answer 30

superior mesenteric artery - jejunal & ileal branches superior mesenteric vein - jejunal & ileal tributaries nerves lymphatics

Question 31

which part of the small intestine is redder? why?

Answer 31

jejunum - has a higher vascular supply for increased nutrient absorption

Question 32

which has a thicker wall - jejunum or ileum?

Answer 32

jejunum - greater nutrient absorption function

Question 33

which part of the small intestine has a higher blood supply?

Answer 33

jejunum - supports the higher nutrient absorption rate

Question 34

where is more fat found in the mesentery: jejunum or ileum?

Answer 34

ileum

Question 35

how do circular folds (plicae circulares) differ between the jejunum and ileum?

Answer 35

jejunum = denser & taller folds ileum = sparser & shorter folds - disappear in the terminal ileum folds get shorter and sparser going form jejunum & ileum

Question 36

why does the jejunum have a greater surface area & vascular supply for absorption than the ileum?

Answer 36

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

Question 37

how do arterial arcades & vasa recta differ in the jejunum and ileum?

Answer 37

jejunum has fewer arterial arcades & long thick vasa recta ileum has more arterial arcades & smaller vasa recta

Question 38

describe the arterial arcades & vasa recta supplying the jejunum

Answer 38

few arterial arcades (1-2 loops) long, thick vasa recta

Question 39

how do the loops of arterial arcades differ in the jejunum and ileum?

Answer 39

jejunum - fewer (1-2 loops) ileum - many loops

Question 40

how do vasa recta differ in the jejunum and ileum?

Answer 40

jejunum - long & thick ileum - small & thin

Question 41

why is blood flow slower in the ileum compared to the jejunum?

Answer 41

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

Question 42

why does the jejunum require a faster blood flow than the ileum?

Answer 42

jejunum absorbs most nutrients - needs quick blood circulation to transport them efficiently

Question 43

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?

Answer 43

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

Question 44

function of Peyer's patches? which has more - jejunum or ileum?

Answer 44

Peyer's patches are aggregated patches of lymphoid tissue - help with immune surveillance ileum has more

Question 45

why are plicae circulares more developed in the jejunum than the ileum?

Answer 45

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

Question 46

a surgeon is differentiating between the jejunum and ileum during surgery. What 3 structural features could they use to tell them apart?

Answer 46

*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

Question 47

why does blood flow more slowly in the ileum compared to the jejunum?

Answer 47

ileum has more arterial arcades (loops) = higher cross-sectional area of blood vessels = lowers blood pressure & slows blood flow

Question 48

if a disease reduced the blood supply to the ileum, what specific deficiencies would you expect to see?

Answer 48

vitamin B12 deficiency bile salt malabsorption

Question 49

(CLINICAL) what is the embryological cause of an ileal diverticulum?

Answer 49

failure of the vitelline duct to degenerate - leaves an outpouching of the ileum (ileal diverticulum)

Question 50

what are the two types of ectopic cells that may be found in an ileal diverticulum? what complications do they cause?

Answer 50

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

Question 51

why can an ileal diverticulum be mistaken for appendicitis?

Answer 51

both cause pain in the right lower quadrant - but an appendix will appear normal in the case of an ileal diverticulum

Question 52

four potential complications of an ileal diverticulum?

Answer 52

1. diverticulitis (inflammation of diverticulum) 2. ulceration & bleeding (from ectopic gastric cells) 3. intestinal obstruction/perforation 4. fistula formation (abnormal connections to other organs)

Question 53

why might an ileal diverticulum lead to bleeding?

Answer 53

if gastric cells are present - produce acid, leads to ulceration - erodes blood vessels, leads to bleeding

Question 54

what is the most severe consequence of an untreated, inflamed ileal diverticulum?

Answer 54

peritonitis - perforation of the diverticulum causing an infection of the peritoneal cavity