Physiology Flashcards
What is the function of gastric acid?
- Activates pepsin
- Denatures proteins
- Helps kill bacteria and other microorganisms
- Inactivates salivary amylase
What mechanisms control gastric acid secretion?
- Neurocrine - vagus nerve/local reflexes
- Endocrine - gastrin
- Paracrine - histamine
Where is gastrin secreted from?
G cells
Where are G cells found?
Deep within gastric glands
What stimulates the release of gastrin?
- Amino acids
- Peptides
- Distention of stomach
- Neural reflexes
What cells produce histamine?
Enterochromaffin-like cells (ECL)
What cells secrete gastric acid?
Parietal cells
Where are parietal cells found?
Body of the stomach
Draw a diagram of how gastric acid is produced by parietal cells
How do histamine, gastrin, and acetylcholine cause gastric acid secretion?
All cause intracellular reactions which activate protein kinases, leading to acid production
What are the different phases of gastric acid production?
- Cephalic phase
- Gastric phase
- Intestinal phase
How does the sight/smell/taste of food stimulate gastric acid production (cephalic phase)?
Stimulates the vagus nerve, which in turn acts on parietal cells through:
- Direct - ACh
- Indirect - G cells
Gastrin/ACH also acts on ECL cells, which secrete secrete histamine, which acts on parietal cells
What does gastric acid stimulate the release of?
Pepsinogen - converted to pepsin by acid itself
How does the gastric phase lead to Gastric acid production?
- Distention of stomach -> vagal/enteric refelxes -> Parietal cells
- Peptides in lumen -> Gastrin secretion -> Parietal cells
- Gastrin/ACh released -> ECL -> Parietal cells
How is the gastric phase of gastric acid secretion inhibited?
Decreased pH -> decreased gastrin production
What is the net result of the gastric phase?
Digestion of protein, formation of chyme, and controlled entry of chyme into the small intestine
What occurs during the intestinal phase of gastric acid production?
Chyme enters duodenum -> Acid sensed by enterogastric reflex, which causes:
- Secretin release
- Decreased Gastrin production and action on parietal cells
Fat in the duodenum -> GIP release, which decreases:
- Gastrin secretion
- HCl secretion
When is gastric inhibitory peptide released?
In response to carbohydrates
When is secretin released?
In the presence of acidic chyme
When is cholecystokinin released?
In the presence of fats
What is the funciton of CCK?
Slows gastric motility - to promote fat digestion as it takes longer than protein/carb
What is the function of Secretin?
- Inhibits gastric motility
- Stimulate Bicarb release from pancreas -> neutralise acid
What cell is pepsinogen secreted from?
Chief cells
Where is intrinsic factor secreted from?
Parietal cells