overview of the GI tract II Flashcards
what is the small intestine made of?
duodenum, jejunum, ileum
what does the GI tract absorb?
- 80% ingested water
- electrolytes
- vitamins
- minerals
- carbs — acitve/facilities transport
- proteins
- lipids
what does the GI tract secrete?
digestive enzymes
- peptidases
- sucrases
- maltase
- lactase
- saccharidases
- lipase
- nucleases
what does bicarbonate secretion by the pancreas into the duodenum have to equal?
the production of HCl in the stomach — brings us to a more normal pH in the SI
intestinal absorptive efficiency decreases with age. how is the SI adapted to this?
the SI has lots of functional residual reserve capacity
what is the only part of the SI with Brunner’s glands?
duodenum
describe Brunner’s glands
located in the submucosa of the duodenum. They secrete an alkaline fluid containing mucin, which protects the mucosa from the acidic stomach contents entering the duodenum.
the duodenum cups around the head of what?
the pancreas
what is the smallest section of the SI?
duodenum
where are plicae circulares found?
lower part of duodenum and jejunum
where is iron absorbed?
absorbed quickly at start of duodenum
where are carbs absorbed?
most absorbed in duodenum and into jejunum, but get consistent rate of absorption into ileum
where are protein, lipids, sodium, and water absorbed?
vast majority absorbed early on in SI
what is another name for vitamin B12
cobalamin
where is cobalamin absorbed?
ileum
where are bile acids absorbed?
at end towards ileum
what in the SI is rapidly turned over? relevance?
the epithelium is rapidly turned over
chemo killing specifically dividing cells — get GI side effects of treatment
loss of cells at villi tips causes what?
release of enzymes into the lumen
what do crypt cells secrete?
2-3 litres isotonic fluid / day
how does the SI have a huge SA for absorption?
folded mucosa — folds have villi — specialised absorptive cells with microvilli consisting of some actin and myosin filaments
describe glucose uptake in the SI
- coupled transport process
- NaK ATPase pumps Na out of the basolateral membrane
- this in turn drives the Na-glucose symporter in the apical membrane
Na+ transport coupled with glucose transport
where are bile salts produced and stored?
produced by liver and stored in gall bladder (gall bladder contracts and empties its contents into the SI)
describe fat absorption in the SI
- large fat globules are emulsified by bile salts in the duodenum (large fat globules are broken down into smaller droplets and then coated by the bile salts)
- digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides, which then form micelles
- fatty acids and monoglycerides leave micelles and enter epithelial cells by diffusion
- chylomicrons containing fatty substances are transported put of the epithelial cells and into lacteals (in villi), where they are carried away from the intestine by lymph
what are micelles made up of?
fatty acids, monoglycerides and bile salts
