Gastric physiology Flashcards
What are invaginations of the parietal cells called which act to increase their surface area?
Canaliculi
What are the functions of the stomach?
The functions of the stomach:
Store & mix food
Regulate emptying into the duodenum
Secrete and activate proteases
Mucosal protection
Lubrication
Kill microbes
Secrete intrinsic factor for Vitamin B12 absorption in the ilium
Which of the following is not secreted by the body of the stomach:
a) HCl
b) Gastrin
c) Pepsinogen
d) Mucus
The body of the stomach secretes mucus, HCl and pepsinogen (not gastrin)
Which of the following is not secreted by the antrum of the stomach:
a) HCl
b) Gastrin
c) Pepsinogen
d) Mucus
The antrum of the stomach secretes mucus, HCl and gastrin (not pepsinogen)
Antrum = gAstrin
Which cells secrete somatostatin?
a) Enteroendocrine
b) D cells
c) Chief cells
d) Enterochromaffin like cells
Somatostatin is secreted by D Cells
Which cells secrete pepsinogen?
a) Enteroendocrine
b) D cells
c) Chief cells
d) Enterochromaffin like cells
Pepsinogen is secreted chief cells
Which cells secrete Histamine?
a) Enteroendocrine
b) D cells
c) Chief cells
d) Enterochromaffin like cells
Histamine is secreted by enterochromaffin cells
Which cells secrete gastrin?
a) Enteroendocrine
b) D cells
c) Chief cells
d) Enterochromaffin like cells
Gastrin is secreted by enteroendocrine cells
Which nervous system and neurotransmitter are involved in the cephalic phase of turning on gastrin acid secretion?
Turning it on (Cephalic phase):
Parasympathetic nervous system
- Stimulated by sight, smell, taste of food, and chewing
Acetylcholine release
ACh acts directly on parietal cells
ACh triggers release of gastrin and histamine (both act to increase HCl)
Net effect = increased acid production
What triggers the gastric phase when turning on gastric acid production?
Turning it on (Gastric phase):
Gastric distension, presence of peptides and amino acids
Stimulates: Gastrin release
Gastrin acts directly on parietal cells & triggers release of histamine
Histamine acts directly on parietal cells
Net effect = increased acid production
Why is histamine important in gastric acid production?
- Histamine is involved in the upkeep of proton pumps
- Histamine is the main way to turn of parietal cells
- Mediates the affects of gastrin and ACh
Explain how gastric acid production can be stopped/reduced in the gastric phase?
High [H+]
- inhibits gastrin secretion & indirectly inhibits histamine (as less gastrin)
- Increases somatostatin production
Somatostatin inhibits parietal cells = less HCl
In the duodenum, what changes turn off gastric acid secretion?
Turning it off (Intestinal phase) In the duodenum:
- Duodenal distension
- Low luminal pH
- Hypertonic luminal contents
- Presence of amino acids and fatty acids
During the intestinal phase of turning of gastric acid production, name the 2 enterogasterones that are produced.
Intestinal phases, triggers release of enterogastrones:
Secretin (inhibits gastrin release, promotes somatostatin release)
Cholecystokinin (CCK)
Note: short and long neural pathways reduce the ACh released
What is an ulcer?
A breach in a mucosal surface
What are the 4 main causes of peptic ulcers?
Helicobacter pylori infection
Drugs – NSAIDS
Chemical irritants – alcohol, bile salts, ? Dietary factors
Gastrinoma
How does the gastric mucosa defend itself?
Alkaline mucus
Tight junctions between epithelial cells
Replacement of damaged cells
-ve feedback loops to turn off acid production
Which of the following causes peptic ulcers by: Secreting urease, which increases the amount of ammonium in the gastic lumen. Ammonium damaged the epithelium and causes an inflammatory response.
a) Helicobacter pylori
b) NASIDS
c) Cemical irritants
Helicobacter pylori
NSAIDs inhibit cyclo-oxygenase 1. Cyclo-oxygenase 1 needed for prostaglandin synthesis. Mucus secretion is stimulated by prostaglandins = Reduced mucosal defence
Which of the following is responsible for converting pepsinogen to the active form pepsin?
a) Somatostatin
b) Histamine
c) Gastrin
d) HCl
HCl
Pepsinogen secretion = HCl secretion
Most efficient at pH 2
+ve feedback - pepsin also catalyses the reaction
What percentage of protein digestion is pepsin responsible for?
a) 10%
b) 20%
c) 60%
d) 80%
Normally accounts for ~20% of total protein digestion
Breaks down collagen in meat – helps shred meat into smaller pieces with greater surface area for digestion
Accelerates digestion
What is receptive relaxation and what is it mediated by?
Receptive relaxation = relaxation of smooth muscle in body and fundus of stomach to increase volume without increasing pressure.
Mediated by: Parasympathetic nerves in enteric plexus (release NO & serotonin), coordination by afferent via vagus and swallowing centres in the brain.
Describe Peristalsis
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)
What increases the strength of peristaltic contraction?
Gastrin
Gastric distension (medicated by mechanoreceptors)
What decreased the strength of peristaltic contractions?
Strength of peristaltic contractions decreased by:
Duodenal distension
Increased: Duodenal luminal fat
Duodenal osmolarity
Sympathetic NS action
Decreased: Duodenal luminal pH
Parasympathetic NS action
(turned on by brain and stomach and off by the duodenum)
