Stomach Flashcards
What are the 7 main functions of the stomach?
Store and mix food Dissolve and continue digestion Kill microbes Secrete intrinsic factor Activate proteases Lubrication Mucosal protection
What are the 4 main cell types of the stomach?
Mucous cells
Parietal cells
Chief cells
Enteroendocrine cells
What type of cell produces HCl?
Parietal cells
What triggers the production of HCl? (2)
Cephalic phase = Upon the sight, smell and chewing of food, acetylcholine is released (parasympathetic nervous system) which acts directly on parietal cells.
Gastric Phase = Upon gastric distension and presence of proteins, gastrin is released which triggers the release of histamine which then acts on the parietal cells.
Does gastrin directly cause the production of HCl?
No, it triggers the release of histamine which then acts on the parietal cells (which produce HCl)
What (2) triggers the inhibition of production of HCl?
Gastric Phase = A low luminal pH (very acidic), directly inhibits gastrin release and stimulates somatostatin release. This inhibits the action of parietal cells
Intestinal Phase = Duodenal distension, low luminal pH and hypertonic luminal contents, triggers release of secretin and cholecystokinin (CCK).
What are the 4 methods/adaptation of the gastric mucosa to defend itself from the highly acidic conditions?
Alkaline mucus
Tight junctions between epithelial cells
Replacement of damaged cells
Feedback loops
What are 4 common causes of peptic ulcers?
Helicobacter pylori infection
Drugs e.g. NSAIDS (non-steroidal-anti-inflammatories)
Chemical irritants e.g. alcohol
Gastrinoma
Why do peptic ulcers form?
When the gastric epithelium is damaged leading to decreased gastric mucosal damage.
What types of cells produce pepsinogen?
Chief cells
What encourages the activation (by breakdown) of pepsinogen to pepsin?
HCl and pepsin (self catalyst)
It is also pH dependent - most efficient when pH>2
Importance and role of pepsin…
Not essential but…
accounts for 20% of protein digestion (so accelerated protein digestion)
breaks down collagen so increasing the surface area available for digestion.
What allows the stomach to expand?
receptive relaxation
What causes peristaltic waves?
Pacemaker cells in muscularis propria
What is the key feature of pacemaker cells in muscularis propria which make it ideal for gastric peristalsis?
Undergo slow depolarisation-repolarisation cycles
