overview of the GI tract II

Question 1

what is the small intestine made of?

Answer 1

duodenum, jejunum, ileum

Question 2

what does the GI tract absorb?

Answer 2

• 80% ingested water
• electrolytes
• vitamins
• minerals
• carbs — acitve/facilities transport
• proteins
• lipids

Question 3

what does the GI tract secrete?

Answer 3

digestive enzymes

• peptidases
• sucrases
• maltase
• lactase
• saccharidases
• lipase
• nucleases

Question 4

what does bicarbonate secretion by the pancreas into the duodenum have to equal?

Answer 4

the production of HCl in the stomach — brings us to a more normal pH in the SI

Question 5

intestinal absorptive efficiency decreases with age. how is the SI adapted to this?

Answer 5

the SI has lots of functional residual reserve capacity

Question 6

what is the only part of the SI with Brunner’s glands?

Answer 6

duodenum

Question 7

describe Brunner’s glands

Answer 7

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.

Question 8

the duodenum cups around the head of what?

Answer 8

the pancreas

Question 9

what is the smallest section of the SI?

Answer 9

duodenum

Question 10

where are plicae circulares found?

Answer 10

lower part of duodenum and jejunum

Question 11

where is iron absorbed?

Answer 11

absorbed quickly at start of duodenum

Question 12

where are carbs absorbed?

Answer 12

most absorbed in duodenum and into jejunum, but get consistent rate of absorption into ileum

Question 13

where are protein, lipids, sodium, and water absorbed?

Answer 13

vast majority absorbed early on in SI

Question 14

what is another name for vitamin B12

Answer 14

cobalamin

Question 15

where is cobalamin absorbed?

Answer 15

ileum

Question 16

where are bile acids absorbed?

Answer 16

at end towards ileum

Question 17

what in the SI is rapidly turned over? relevance?

Answer 17

the epithelium is rapidly turned over

chemo killing specifically dividing cells — get GI side effects of treatment

Question 18

loss of cells at villi tips causes what?

Answer 18

release of enzymes into the lumen

Question 19

what do crypt cells secrete?

Answer 19

2-3 litres isotonic fluid / day

Question 20

how does the SI have a huge SA for absorption?

Answer 20

folded mucosa — folds have villi — specialised absorptive cells with microvilli consisting of some actin and myosin filaments

Question 21

describe glucose uptake in the SI

Answer 21

• 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

Question 22

where are bile salts produced and stored?

Answer 22

produced by liver and stored in gall bladder (gall bladder contracts and empties its contents into the SI)

Question 23

describe fat absorption in the SI

Answer 23

1. 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)
2. digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides, which then form micelles
3. fatty acids and monoglycerides leave micelles and enter epithelial cells by diffusion
4. 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

Question 24

what are micelles made up of?

Answer 24

fatty acids, monoglycerides and bile salts

Question 25

what does a low fat diet encourage?

Answer 25

burning of fat stores

Question 26

what does a low carb diet try to achieve?

Answer 26

trying to get body to switch its preferred source of energy (carbs) to start metabolising and mobilising its fat stores

Question 27

what can a low carb diet can put lots of stress on?

Answer 27

kidneys and metabolism

Question 28

what is orlistat?

Answer 28

a medication that inhibits pancreatic lipase enzyme to significantly reduce fat absorption

Alli is a low dose orlistat preparation available over the counter/online in the UK

Question 29

what does response to orlistat depend on?

Answer 29

patient’s diet

Question 30

what are some undesired effects of orlistat?

Answer 30

increase in the number and nature of bowel movements., abdominal discomfort, oily stools, flatulence (passing gas from back passage), and oily spotting in underwear

Question 31

what is the normal length of the SI?

Answer 31

600cm

Question 32

most carb, protein and fat are absorbed in the first __-__cm of the jejunum

Answer 32

100-150 cm

Question 33

short bowel syndrome results in what state?

Answer 33

malabsorptive state (since problems occur at less than 200cm of functional SI)

can result in fluid and electrolyte imbalances as well as poor nutritional status

Question 34

what is short bowel syndrome due to?

Answer 34

• insufficient absorptive surface area
• may be congenital, as a result of surgical resection, or changes in blood supply to the SI

Question 35

prognosis of short bowel syndrome improves with what?

Answer 35

increasing length of remaining intestine

Question 36

short bowel syndrome treatment?

Answer 36

parenteral nutritional and increasingly intestinal transplant

Question 37

describe bariatric surgery

Answer 37

• for SEVERE obesity — BMI > 40kg/m2
• failure to maintain weight loss by none surgical means over a period of months/years
• techniques include:

1. gastric banding
2. gastric bypass - smaller stomach pouch, and shortening of intestine — without removal of intestine
3. biliopancreatic diversion — removal of portion of stomach, and diversion of bile and pancreatic juices

all aim to functionally shorten the intestine or reduce the capacity of the stomach — absorb fewer nutrients, eat smaller meals