Gastric physiology

Question 1

What do mucous cells secrete?

Answer 1

Mucus

Question 2

What do parietal cells secrete?

Answer 2

HCl
Intrinsic factor (needed for B12 absorption)

Question 3

What do chief cells secrete?

Answer 3

Pepsinogen

in places of low Ph, eg stomach, turns into pepsin where it accelerates protein digestion by 20%

Question 4

What do entero endocrine cells secrete? (or G cells)

Answer 4

Secretes gastin (stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility)

Question 5

What are peptic ulcers?

Answer 5

-Peptic ulcers are a breach in mucosal surface
causes
*helicobacterpylori infection
*drugs
- NSAIDs painkillers (eg ibuprofen, aspirin)
*chemical irritants
-alcohol, bile salts
*gastrinoma (a tumour in the pancreas or duodenum - secretes excess of gastrin (stimulates Hcl secretion into duodenum) leading to ulceration in the duodenum, stomach and the small intestine.

Question 6

Describe mucosa defence of the stomach

Answer 6

1. Alkaline mucus
2. Tight junctions between epithelial cells
3. Replacement of damaged cells
4. Feedback loop
   (bicarbonate ions neutalise acids)

Question 7

Name the stages of gastric acid secretion

Answer 7

1. Cephalic phase
2. Gastric phase (turning on)
3. Gastric phase (turning off)
4. Intestinal phase (turning off)

Question 8

What happens in the cephalic phase?

Answer 8

• Parasympathetic stimulation, sight, smell, chewing, taste of food
• Acetylcholine release, this acts directly on parietal cells
• Ach triggers release of gastrin (stimulates hcl) and histamine

Question 9

What happens in the gastric phase (turning on)?

Answer 9

-Gastric distension due to presence of peptides and amino acids
-Gastrin release - stimulates hcl and histamine
-histamine (basophils and mast cells)
-histamine also acts directly on parietal cells
-parietal cells release Hcl
=increased acid production (and therefore digestion)

Question 10

What happens in the gastric phase (turning off)?

Answer 10

• The low ph inhibits gastrin secretion
• this inhibits histamine release
• stimulates somatostatin release inhibiting parietal cell activity

Question 11

What happens in the intestinal phase?

Answer 11

1. Due to Duodenal distension, low pH and hypertonic contents of aminoacids and fatty acids
2. Ach release is decreased - stops hcl release
3. Secretin and Cholecystokinin are released
   a) secretin inhibits gastrin release (therefore hcl from parietal and histamine) and promotes somatostatin release
   b) cholecystokinin (inhibits gastrin acid secretion and causes gall bladder to release bile into duodenum)

Question 12

Peristalsis

Answer 12

1. Waves begin in gastric body
   weak contractions = little mixing
   pyloric sphincter closes as the wave reaches it
2. More powerful waves
   pylorus closes as the wave reaches it
3. A little chyme enters the duodenum
   antral contents are forced towards the body - mixing

When the acidity reaches the duodenum, an increase in fats and amino acids promotes the secretion of enterogastrones and neural receptors

Question 13

What are zymogens?

Answer 13

Enzymes that are synthesized and stored in inactive forms (this protects the cells from damage)
-eg pesinogen

Question 14

What is the basic electrical rhythm? What determines it?

Answer 14

about 3/min

• determined by pacemaker cells in the muscularis propria
  1. The pacemaker cells undergo slow depolarization/repolarisation cycles
  2. the depolarisation waves are transmitted through gap junctions
  3. There is no significant contraction in an empty stomach

Question 15

What affects the strength of contractions?

Answer 15

• An increase in gastin increases contractions
• mechanoreceptors activated due to gastric distension
• parasym
• decreased duodenal distension decreases contractions
• symp activity
• decrease in duodenal pH (when duodenal decreases due to HCl acid)
• Increased duodenal osmolarity and luminal fat - this prevents overspilling

Question 16

What is gastroparesis?

Answer 16

• delayed gastric emptying

- this causes nausea, early satiety, vomiting of digested food, GORD, abdo pain, anorexia

Question 17

Gastric motility - 3 stages

Answer 17

Peristaltic waves begin in gastric body. Weak contraction in body (little mixing).

More powerful contraction in gastric antrum. Pylorus closes as peristaltic wave reaches it.

Little chyme enters duodenum. Antral contents forced back towards body (mixing).

Question 18

What decreases the strength of peristaltic contractions in gastric motility?

Answer 18

Duodenal distension
Increased duodenal luminal fat
Increased duodenal osmolarity
Decreased duodenal luminal pH
Increased sympathetic action
Decreased parasympathetic action