Gastric Secretion

Question 1

Fundus function

Answer 1

Storage

Question 2

Body of stomach function

Answer 2

Storage, mucus, HCl, Pepsinogen, Intrinsic factor

Question 3

Antrum function

Answer 3

mixing/grinding, gastrin

Question 4

HCl function in stomach

Answer 4

marinating

Question 5

What is pepsinogen the inactive form of

Answer 5

pepsin - a proteolytic enzyme

Question 6

why is pepsin stored in its inactive form

Answer 6

so as to not erode the stomach

Question 7

chyme definition

Answer 7

mixed food as it leaves the antrum

Question 8

gastrin definition

Answer 8

hormone released in antrum from G-cells and secreted into the circulation - acts on cells of body

Question 9

what is the cellular composition of a gastric gland

Answer 9

Gastric Pit -
1.surface mucous cells

Gastric Gland -

1. mucous neck cells
2. parietal cells
3. chief cells

Question 10

Mucous neck cells secrete

Answer 10

mucus

Question 11

parietal cells secrete

Answer 11

HCl, intrinsic factor

Question 12

chief cells secrete

Answer 12

pepsinogens

Question 13

Why are the junctions between cells very tight

Answer 13

to stop stomach acid entering

Question 14

How is HCl made in the stomach

THIS IS A VERY LONG ANSWER

Answer 14

1. CO2 into cell – combines with water – makes carbonic acid – made faster by carbonic anhydrase – H2CO3 doesn’t last long – immediately dissociates to form H ions and bicarbonate
2. H ions pumped out (need ATP) – works similar to NaK pump – one H out, one K in
   HCO3 – pumped out on exchange protein – HCO3 out, – HCO3 out causes temporary alkalisation
3. Cl in (through cell and out the other side-joins with the other H and water to make the HCl in the stomach)

Question 15

when is the only time HCl is produced in the stomach

Answer 15

when eating

Question 16

What three molecules control acid production

Answer 16

1. Gastrin
2. Histamine
3. Acetylcholine

Question 17

What controls the switch off mechanism for acid production

Answer 17

prostaglandins

Question 18

how does gastrin work

Answer 18

Binds to its receptor – g-protein coupled receptor – causes a rise in Ca – acts through protein kinase C to increase turn around of K/H proton pump

Question 19

how does histamine work

Answer 19

stomach has a unique histamine receptor – H2 receptor – coupled with Gs

Question 20

how does acetylcholine work

Answer 20

neurotransmitter – acts on muscarinic cholinergic receptros (M3) – g protein coupled – rise in Ca – rise in turn around of H/K

Question 21

How do prostaglandins inhibit acid production

Answer 21

Gi – inhibitor protein – coupled with that prevents reaction taking place – take away stimulus – turn pump off

Question 22

what three mechanisms is gastric acid section controlled by

Answer 22

1. Neurocrine - (vagus/local reflexes)
2. Endocrine (gastrin)
3. Paracrine (histamine)

Question 23

What are the two phases of acid secretion

Answer 23

1. cephalic - anticipation of food

2. gastric - food reaching stomach

Question 24

What is the only essential (non-compensated) function of the stomach

Answer 24

the production of intrinsic factor

Question 25

where is intrinsic factor produced

Answer 25

parietal cells

Question 26

intrinsic factor function

Answer 26

vitamin B12 absorption - intrinsic factor/B12 complex is absorbed from the ileum

Question 27

what does a defect in the production of intrinsic factor cause

Answer 27

pernicious anaemia (failure of erythrocyte maturation)

Question 28

what is the role of gastric mucus

Answer 28

CYTOPROTECTIVE role 1. protects mucosal surface from mechanical injury 2. neutral pH (HCO3) - protects against gastric acid corrosion and pepsin digestion

Question 29

How does the gastric mucus protect against corrosion

Answer 29

High bicarbonate content – protects – makes pH around 7 at cell surface Acid buffered and neutralised by bicarbonate as it enters mucus layer

Question 30

what is interesting about when acid is neutralised in the stomach

Answer 30

only neutralised on the way IN to the stomach - not on the way out

Question 31

Describe the processes that occur during the cephalic stage of acid production

Answer 31

1. anticipation of food stimulates vagus nerve = release of ACh 2. vagus nerve stimulation casues stimulation of G-cells = release of Gastrin 3. With both Gastrin and ACh present ECL cells are stimulated = release of histamine 4. With ACh, gastrin and histamine all present -Parietal cells are activated

Question 32

Describe the processes that occur during the gastric phase of acid production

Answer 32

1. arrival of food in stomach takes over for stimulating vagus nerve = release of ACh 2. Peptides present in lumen take over for stimulation of G-cells = release of gastrin 3. With both Gastrin and ACh present ECL cells continue to be stimulated = release of histamine 4. With ACh, gastrin and histamine all present -Parietal cells are activated

Question 33

what are the two indicators that stop acid production

Answer 33

1. acid in the duodenum | 2. fat in the duodenum

Question 34

how does acid in the duodenum stop acid production

Answer 34

1. stimulates enterogastric (splanchnic) reflex 2. stimulates secretin release 3. both of these processes lead to a decease in gastrin secretion which causes a decease in the stimulation of parietal cells

Question 35

how does fat in the duodenum stop acid production

Answer 35

1. causes release of GIP | 2. leads to a decrease in gastrin secretion which leads to a decrease in HCl secretion from parietal cells

Question 36

what are enterogastrones

Answer 36

hormones released from gland cells in duodenal mucosa - act collectively to prevent further acid build up

Question 37

name the three enterogastrones

Answer 37

1. secretin 2. cholecystokinin (CCK) 3. GIP (Gastro-inhibitory peptide)

Question 38

when are enterogastrones released

Answer 38

in response to acid or hypertonic solutions (mainly secretin) and fatty acids or monoglycerides (mainly GIP) in the duodenum

Question 39

what are the two strategies by which enterogastrones work

Answer 39

1. inhibit gastric acid secretion | 2. reduce gastric emptying (inhibit motility/contract pyloric sphincter)

Question 40

what is the name of the inactive form of an enzyme precursor (eg pepsinogen)

Answer 40

zymogen

Question 41

where is pepsinogen secreted

Answer 41

chief cells

Question 42

what determines secretion of pepsinogen

Answer 42

low pH (<3) - causes secretion of pepsinogen which is then converted to pepsin

Question 43

what kind of feedback mechanism does pepsin production use

Answer 43

positive feedback - i.e. presence of pepsin makes more pepsin

Question 44

how is the pepsin reaction stopped

Answer 44

by raising the pH - inactivated at neutral pH