Gi physiology

Question 1

what do chief cells do

Answer 1

Release inactive pepsinogen -> pepsin which breaks down protein

Question 2

what do parietal cells do

Answer 2

Intrinsic factor – for absorption of B12

HCl – denatures proteins and kills microorganisms

Question 3

what increases stomach emptying

Answer 3

• Increased volume of chyme [increased distension]
• Decreased viscosity of chyme [thinner]

Question 4

what decreases gastric emptying

Answer 4

Fat decreases gastric emptying as more time required for digestion.

Question 5

what stimulates and is the action of Gastrin

Answer 5

• peptides/ amino acids in stomach
• increases secretion and promotes intestinal contraction

Question 6

what stimulates and is the action of Ghrelin

Answer 6

fasting state
- stimulates hunger and satiety

Question 7

what stimulates and is the action of histamine

Answer 7

food in stomach
- Stimulates parietal cells H+/K+ATPase to release HCl

Question 8

what stimulates and is the action of serotonin

Answer 8

food in stomach
- decreases secretions and gastric movement

Question 9

what stimulates and is the action of somatostatin

Answer 9

food in stomach
- decreases secretions and reduces intestinal absorption

Question 10

what stimulates secretions

Answer 10

Ach

Question 11

what inhibits secretions

Answer 11

somatostatin

Question 12

what does prostaglandin E do (PGE2)

Answer 12

reduces histamine and increases mucus / bicarbonate secretion

Question 13

where are gastrin and somatostatin secreted

Answer 13

at the pyloric antrum

Question 14

describe the mucosal barrier to the stomach

Answer 14

1. Stomach wall coated by thick wall of bicarbonate-rich mucus
2. Epithelial cells meet at tight junctions preventing gastric juice from penetrating
   underlying tissue layers
3. Stem cells replace damaged epithelial mucosal cells (completely replaced every 3-6
   days)

Question 15

what does the presence of chyme in the duodenum do

Answer 15

activates receptors that inhibit gastric secretion

Question 16

adapted for absorption as increase in surface area due to:

Answer 16

• Circular folds
• Villi – lymphatic vessels [lacteals]
• Microvilli – brush border

Question 17

what does the duodenum mucosa have

Answer 17

Brunner’s glands

Question 18

Extrinsic innervation of the small intestine:

Answer 18

• Parasympathetic nerve fibres from vagus nerve
• Sympathetic nerve fibres from thoracic splanchnic nerve

Question 19

describe gastrin

Answer 19

released by G cells
- stimulates secretion of bile and pancreatic enzymes

Question 20

describe CCK

Answer 20

released by I cells
- stimulates release of pancreatic juices and bile

Question 21

describe secretin

Answer 21

released by S cells
- stimulates bicarbonate release from pancreas in response to H+ in duodenum

Question 22

describe motilin

Answer 22

released by M cells
- inhibits gastric secretion, stimulates insulin secretion

Question 23

what do CCK and secretin do

Answer 23

decrease parietal cell secretion of HCL

Question 24

describe cholecystokinin

Answer 24

secreted by I cells
- promotes the contraction of the gallbladder, increasing the secretion of the bile into the duodenum at the ampulla of vater

Question 25

describe Leptin

Answer 25

a hormone secreted by adipose tissue that promotes satiety - genetic defect in leptin signalling may cause monogenic obesity

Question 26

what is somatostatin secreted by

Answer 26

D cells

Question 27

what does secretin do

Answer 27

decrease gastric acid secretion

Question 28

what are acinar cells

Answer 28

digestive enzymes

Question 29

what does trypsin do

Answer 29

activate all other protein enzymes

Question 30

what is the haustra

Answer 30

tonic contractions of taenia coli bunch up into pouches called haustra

Question 31

what does stomach distension do

Answer 31

promotes gastrocolic reflex increasing motility in colon

Question 32

what must carbohydrates be converted into for absorption

Answer 32

monosaccarides

Question 33

what does amylase do

Answer 33

break down a-1,4 linkages as long as they are not terminal

Question 34

what does HCL do

Answer 34

denature proteins

Question 35

what does pepsin do

Answer 35

cleaves proteins into peptides

Question 36

what do pancreatic enzymes do eg (trypsin, chymotrypsin, elastase)

Answer 36

breakdown proteins into oligopeptides

Question 37

what do Peptidases at brush border do

Answer 37

hydrolyse oligopeptides to amino acids

Question 38

what stabilises the emulsions and how

Answer 38

Amphiphilic molecules stabilise the emulsions by forming a surface layer on droplets of fatty acids, biliary phospholipids, cholesterol, bile salts.

Question 39

what are bile salts

Answer 39

Bile salts are amphipathic – hydrophilic and hydrophobic. They are released from gall bladder in response to CCK and aid in emulsifying lipid droplets.