Gastric Motility and Secretion Flashcards Preview

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Flashcards in Gastric Motility and Secretion Deck (25)
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1
Q

Outline the functions of the stomach

A
  • Store Food
  • Minimise ingestion of bacteria
  • Dissolve + partially digest macromolecules
  • Regulate emptying
  • Secrete intrinsic factor
2
Q

What are the layers of the GI tract? (From Lower Oesophagus to anal canal)

A
  1. Mucosa
  2. Submucosa
  3. Muscularis
    Inner - circular
    Outer - longitudinal
  4. Serosa
    Inner oblique in muscularis of stomach
3
Q

Outline receptive relaxation of the stomach

A

When food is swallowed, the smooth muscle in the wall of the orad region of the stomach relaxes. Stomach increases volume from 50ml to 1.5L.

4
Q

How is receptive relaxation of the stomach mediated?

A

Vagus nerve -> Enteric plexus

  • Enteric neurons release NO and serotonin to relax muscles.
  • Coordinate with swallowing centre
5
Q

Outline mixing in the stomach

A

1) Contractions start in body and move toward antrum (Peristalsis)
2) When wave reaches antrum pyloric sphincter closes
3) Food is forced backwards into body (Retropulsion)

6
Q

Define peristalsis

A

Waves of alternating contractions and relaxations of smooth muscle layers that mix and squeeze the contents through hollow tubes.

Move a bolus along the length of the GI tract.

7
Q

How are GI peristaltic waves generated?

A

Coordinated contractions of smooth muscle: Slow Waves and Action Potentials

8
Q

What are Slow waves?

A

Pacemaker zone in stomach generate membrane potentials which spreads across smooth muscle cells. 3 slow waves/min.

Slow waves don’t elicit contractions, they bring the threshold potential high enough for an action potential to initiate.

9
Q

What is the pyloric sphincter?

A

Ring of smooth muscle and connective tissue between the gastric antrum and the duodenum.

10
Q

What are the functions of the pyloric sphincter?

A

1) Regulated emptying of gastric contents

2) Prevents regurgitation of duodenal content.

11
Q

What decreases the rate of gastric emptying?

A
  • High fat food
  • Highly acidic food
  • Very hypertonic food
12
Q

What are the components of gastric secretions?

A
  • enzymes: pepsinogens, gastric lipase
  • intrinsic factor
  • HCl
  • mucus
13
Q

In which parts of the stomach are parietal cells and G cells mainly found?

A

Proximal 80 % of the stomach (“oxyntic gland area”)

G-cells are found typically in the antrum (“pyloric gland area”).

14
Q

Where is Gastrin produced and what does it do?

A
G cells
Increases:
- Acid, mucus and pepsinogen
- Gastric motility (but Inhibits gastric emptying)
- Insulin and HCO3- release
- Intestinal motility
15
Q

Where is Histamine produced and what does it do?

A

Enterochromaffin-like (ECL) cells

Stimulates acid secretion and blood flow to stomach

16
Q

Where is Somatostatin produced and what does it do?

A

D cells of antrum

Inhibit acid secretion and gastrin release.

17
Q

What do chief cells secrete?

A

Pepsinogen (converted to pepsin in low pH)

18
Q

What do parietal cells secrete?

A

HCl

Intrinsic factor - Binds VitB12 for absorption

19
Q

How is the parietal cell specialised?

A
  • Pyramidal shape
  • Canaliculi lined with H+/K+ATPases
  • High mitochondria
20
Q

What stimulates and inhibits gastric acid secretion (Give 3 for each).

A

Stimulated by:
gastrin
acetylcholine
histamine

Inhibited by:
somatostatin
prostaglandins E2 and I2
intestinal hormones

21
Q

What are prostaglandins?

A

A group of lipids derived from arachidonic acid.

Involved in the healing;
Control inflammation and blood flow.

Synthesis is catalysed by a cyclooxygenase enzyme.

22
Q

Where is mucus produced in the stomach? And what does it do?

A

Surface epithelial and neck cells. Forms gel that protects stomach lining against acid (Mucosal Barrier)

23
Q

How is the stomach protected from autodigestion?

A

Prostaglandins increase production of mucus and HCO3- and inhibit acid secretion.

Surface epithelial cells secrete HCO3-

Stomach has high cell turnover rate

24
Q

What are the consequences of failure of gastric mucus protection?

A

Gastritis

Gastric Ulcers

25
Q

Overuse of which drug can cause gastric ulcer formation?

A

NSAIDs