Introduction to the Small Intestine

Question 1

what secretes mucus in the small intestine

Answer 1

Brunners glands

Question 2

list hormones secreted by the small intestine

Answer 2

secretin, CCK, motilin, vasoactive intestinal peptide (VIP), gastric inhibitory peptide (GIP)

Question 3

what is the function of motilin

Answer 3

stimulates migrating motor complexes (waves of electrical activity that pass through intestines during fasting, ultimately trigger peristalsis) via both enteric and autonomic nervous systems

Question 4

Function of vasoactive intestinal peptide

Answer 4

increases blood flow to the GI tract

Question 5

function of GIP (2)

Answer 5

inhibits gastric secretion

stimulates insulin secretion

Question 6

cholecystokinin function

Answer 6

inhibits gastric secretion and motility.
stimulates release of pancreatic enzymes
contraction of the gall bladder

Question 7

function of secretin

Answer 7

controls pancreatic HCO3- secretion and bile production in the liver

Question 8

secretions of exocrine pancreas (7)

Answer 8

alkali (HCO3-), trypsin, chymotrypsin, carboxypeptidase, pancreatic amylase, lipases, other enzymes e.g. phospholipase, cholesterol esterase etc.

Question 9

what cell type secretes pancreatic enzymes

Answer 9

acinar cells

Question 10

what cell type secretes pancreatic HCO3-

Answer 10

duct cells

Question 11

what converts trypsinogen to trypsin, what is trypsin function

Answer 11

membrane bound enterokinase

trypsin converts zymogens to active enzymes.

Question 12

mechanism of pancreatic HCO3- secretion

Answer 12

essentially reverse of stomach acid secretion. HCO3- secreted into duct lumen, H+ secreted into blood

Question 13

Pancreatic enzyme secretion is mediated by

Answer 13

CCK and ACh

Question 14

Pancreatic alkali secretion controlled by

Answer 14

secretin, potentiated by CCK and ACh

Question 15

Fats digested by what, making what

Answer 15

lipase, monoglyceride and fatty acids

Question 16

starch is digested by which pancreatic enzyme

Answer 16

pancreatic amylase

Question 17

proteins are broken down by which pancreatic enzyme

Answer 17

trypsin and chymotrypsin = proteins –> peptide fragments
carboxypeptidase (pancreas) and aminopeptidase (s.intestine epithelial cells) = peptide fragments –> individual amino acids

Question 18

4 steps of fat digestion and absorption

Answer 18

1. emulsification by bile salts and phospholipids
2. fats digested by pancreatic lipase, products held in micelles combined with bile salts and phospholipids
3. micelles move into unstirred layer by brush border, fatty acids and monoglycerides diffuse into cell membrane
4. monogllycerides reassembled into fats

Question 19

what are triglyceride molecules packaged into

Answer 19

chylomicrons

Question 20

what happens to fat in chylomicrons

Answer 20

exported across basolateral membrane and leave intestinal villus via lymph

Question 21

what stimulates absorption of Ca2+

Answer 21

Vitamin D

Question 22

describe processing of Fe in s.intestine

Answer 22

Fe3+ (inabsorbable) reduced to Fe2+ in stomach
Fe2+ crosses luminal membrane on carrier protein
Much of this binds ferritin, Fe2+ that does not is transported across basolateral membrane by a second carrier protein

Question 23

Vitamin B processing in the small intestine

Answer 23

in stomach vitamin B12 binds R protein
in duodenum and jejunum, B12 binds to intrinsic factor
in the terminal ileum, B12-IF complex is absorbed by receptor mediated endocytosis

Question 24

coeliac disease, site of pathology and defect caused

Answer 24

duodenum and jejunum (damage to mucosa)

fat absorption, lactose hydrolysis

Question 25

pancreatitis effect on GI tract

Answer 25

deficiency of enzyme secretion. | Impairs digestion, particularly fat

Question 26

implication of surgical resection of ileum/chrons disease on digestion

Answer 26

vitamin b12 and bile salt/acid absorption

Question 27

lactase deficiency

Answer 27

affects small intestine - lactase hydrolysis

Question 28

symptoms of malabsorption (6)

Answer 28

``` weight loss abdominal distension diarrhoea steatorrhoea pernicious anaemia hypochromic anaemia ```

Question 29

effect of excessive vomiting on acid-base balance

Answer 29

large loss of acid, potentially resulting in metabolic alkalosis

Question 30

effect of diarrhoea on the acid-base balance

Answer 30

excessive loss of fluid (and hence HCO3-) in faeces may result in metabolic acidosis

Question 31

products of gastric digestion and low pH trigger release of

Answer 31

``` hormones alkali digestive enzymes water mucus ```