Gastric Secretions Flashcards
What is the vago-vagal response?
Refers to signals involving the vagal nerve and gut stimuli.
What does swallowing food do to the oesophageal sphincter and the stomach?
Swallowing relaxes the oesophageal sphincter
On entry of food bolus, the vago-vagal response results in relaxation of the stomach.
What steps are involved in mixing and grinding of bolus?
Closure of pyloric sphincter
Antral peristalsis that grinds bolus.
What are the two inputs that control gastric emptying?
Partly CNS input - PNS increases, SNS decreases (ANS).
MOSTLY, endocrine feedback from duodenum: Secretes cholecystokinin and secretin that prevents gastric emptying to prevent duodenal overfilling.
What do mucous cells secrete, and what is the stimulus for its release?
Mucous cells secrete mucous, and bicarbonate in the mucus as a buffer to prevent gastric acid from damaging the epithelium.
Mucous functions as a physical barrier between lumen and epithelium.
Mucous is secreted tonically, and also in response to irritation of mucosa.
What do parietal cells secrete, and what is the stimulus for its release?
Parietal cells secrete gastric acid (HCl) and instrinsic factor (complexes with B12 to enable absorption).
Release of both is stimulated by acetylcholine, gastrin and histamine.
What do enterochromaffin like cells secrete, what is it’s role and what triggers its secretion?
Secrete histamine.
Triggered by acetylcholine and gastrin to stimulate gastric acid secretion.
What do chief cells secrete, what purpose do they serve and what triggers its release?
Chief cells secrete pepsin, pepsinogen and gastric lipase. THey function ot digest proteins and fats.
Release is stimulated by acetylcholine, acid and secretin.
What do D cells secrete, what is it’s purpose and what triggers its release?
D cell secrete somatostatin in response to acid in the stomach. Somatostatin acts to inhibit gastric acid secretion.
What do G cells secrete, what is its purpose and what triggers its release?
G cells secrete gastrin - stimulates gastric acid secretion.
Triggered by acetylcholine, peptides and amino acids in stomach.
Describe the mechanism of acid secretion in the stomach.
Maximal [H+] in the gut is 3,000,000x plasma [H+].
This is facilitated by the H+/K+ ATPase proton pump.
Describe the regulation of proton pumps.
Parietal cells ahve a resting state and an activate state for secretion.
Resting state - proton pumps are stored in vesicles.
Active state - acetylcholine, histamine and gastrin (*main one) causes exocytosis and activation of proton pumps.
What stimulates gastrin release from G cells?
Release is stimulated by:
- Vagal stimulation (e.g. sight or smell of food)
- SMall proteins and digestion products in stomach
- Antral distension (via vago-vagal reflex)
What stimulates somatostatin release in the antrum?
D cells sense drops in pH, and release somatostatin to stop gastrin production.
Describe the feedback cycle of the stomach’s acid production.
Gastrin is released from G cells via vagal stimulation, small proteins and digestion products and antral distension.
Gastrin activates proton pumps to secrete acid into the stomach.
When pH decreases too much, D cells in the antrum release somatostatin to inhibit gastrin production.
