Gastric Secretion

Question 1

What is the role of the fundus, body, antrum of the stomach

Answer 1

Fundus (top part) = storage
Body (main part) = storage, secretion (mucus, HCl, Pepsinogen, intrinsic factor)
Antrum (bottom part) = mixing/grinding, gastrin secretion

Question 2

What is intrinsic factor used for

Answer 2

Absorption of B12

Question 3

What cells release gastrin

Answer 3

G-cells

Question 4

How is HCl produced

Answer 4

Hydrogen + chloride in stomach lumen creates osmotic gradient —> water coming into stomach lumen

Question 5

Which hormones increase activity of the hydrogen potassium pump, therefore increasing HCl production (3)

Answer 5

Gastrin
Histamine
Acetylcholine (parasympathetic nervous system)

Question 6

What inhibits the hydrogen potassium pump

Answer 6

Prostaglandins

Question 7

What is the cephalic phase of gastric acid secretion

Answer 7

Cephalic = in head (before any food has made it to the gut)

Vagus nerve innervates the G cells producing gastrin —> HCl production

Question 8

Why is the cephalic mechanism important for gut health

Answer 8

Before swallowing stomach produces acid in advance which is a protective preemptive mechanism for things entering stomach

Question 9

How does distension of stomach (arrival of food), peptides (protein) in lumen and gastrin/Ach stimulate parietal cells to produce HCl

Answer 9

Distension of stomach (by food) = vagal/enteric reflexes —> ACh acting on parietal cells
Peptides in lumen = G cells —> gastrin acting on parietal cells
Gastrin/ACh = ECL cells —> histamine acting on parietal cells

Question 10

How does the cephalic phase inhibit gastric acid secretion

Answer 10

Stopping eating —> decreased vagal activity

Question 11

How does the gastric phase inhibit gastric acid secretion

Answer 11

Decreasing stomach pH (due to increased HCl) —> decreased gastrin (negative feedback system)

Question 12

How does the intestinal phase inhibit gastric acid secretion (which reflex is this and what is released)

Answer 12

(Intestinal phase = stomach starts to empty its contents)
Acid from stomach enters duodenum triggering splanchnic reflex + release of secretin
Both cause reduction in gastrin secretion and reduce stimulation of parietal cells in gastrin

Question 13

How does fat/CHO in duodenum inhibit gastric acid secretion

Answer 13

Releases gastric inhibitory peptide (GIP)
Causes reduction in gastrin secretion + reduction in parietal HCl secretion

Question 14

What are enterogastrones

Answer 14

Hormones released from gland cells in duodenal mucosa
(Secretin, cholecystokinin, GIP) that inhibit the forward motion (analward) of chyme

Question 15

What stimulates enterogastrones release (4)

Answer 15

Acid
hypertonic solutions
fatty acids
monoglycerides in duodenum

Question 16

What do enterogastrones do

Answer 16

Prevent further acid build up in duodenum:
- inhibit gastric acid secretion
- reduce gastric emptying (inhibit motility/contract pyloric sphincter)

Question 17

Why is stomach acid build up in duodenum bad

Answer 17

Damaging to pancreatic enzymes and duodenum itself

Question 18

What is pepsinogen

Answer 18

Active precursor of pepsin

Question 19

Why is pepsin stored as pepsinogen

Answer 19

Prevents pepsin from digesting the cells containing it

Question 20

In what pH conditions is pepsinogen turned into active pepsin

Answer 20

Acidic solution (pH < 3)
Only operates in very low pH environments

Question 21

What is the role of gastric mucus

Answer 21

Cytoprotective (protects the cells)
- mechanical injury: makes surface slippery so abrasive materials glide off surface
- protection against corrosion (gastric acid - mucus has VERY high bicarbonate concentration) and digestion (pepsin)

Question 22

What is the role of intrinsic factor (produced by what cells, what does it do, once in complex where is it absorbed)

Answer 22

Produced: parietal cells
Required for vitamin B12 absorption
The intrinsic factors/B12 complex absorbed from ileum

Question 23

What condition arrises from intrinsic factor defect

Answer 23

Pernicious anaemia

Question 24

What does somatostatin do

Answer 24

Reduce gastric secretions by limiting release of gastrointestinal hormones (including secretin and gastrin)

Reduces gut motility