Stomach physiology Flashcards
What are the functions of the stomach? [9]
Store and mix food
Dissolve and continue digestion
Regulate emptying into the duodenum
Kills microbes
Secretes proteases
Secrete intrinsic factor
Activate proteases
Lubrication
Mucosal protection
What is the purpose of the intrinsic factor secreted by the stomach?
Binds to vitamin B12 to aid absorption of it in the terminal ileum.
What are the main types of cells and their purpose in the stomach? [4]
Mucous cells - lubrication and protection
Parietal cells - in pits - gastric acid and intrinsic factor
Chief cells - pepsinogen
Enteroendocrine cells - hormones e.g. gastrin
Also mast cells and X
How much gastric acid is produced on average per day? What concentration? How is production regulated?
2L
[H+] >150mM
Neurohormonal secretion
Describe movement of ions across the membranes of the parietal cells to produce gastric acid
Apical membrane:
K+ and Cl- each flow down their own concentration gradient, into the lumen.
Antiporter actively transports K+ into cells, H+ into lumen.
Blood side:
Cl- ions pumped in, HCO3- out
What is one way the HCO3- ions and the H+ ions are produced in parietal cells?
CO2 + H2O –carbonic anhydrase–> H2CO3
H2CO3 -> HCO3- + H+
H2O -> OH- + H+
Describe the cephalic stage of gastric secretion [4]
Activated by sight/smell/taste of food and chewing
Parasympathetic nervous system - CN X - release of ACh
ACh acts directly on parietal cells
Also stimulates mast cells to release histamine, neuroendocrine cells to release gastrin
Net effect is to increase acid production.
How are cells in the stomach stimulated by the parasympathetic nervous system?
Release of ACh…
Acts directly on parietal cells to increase acid production.
Neuroendocrine cells release gastrin, stimulates parietal cells.
Mast cells release histamine, also acts directly on parietal cells
Describe the gastric phase of activation of secretion of gastric acid [5]
Gastric distension, presence of peptides and amino acids
Gastrin secretion
Acts directly on parietal cells
Triggers release of histamine (acts directly on parietal cells)
Net effect - inc gastric acid production
Where is gastrin released from?
How does gastrin act?
Released from neuroendocrine cells.
Acts directly on parietal cells
Triggers release of histamines that acts on parietal cells
How does histamine act in the stomach?
Acts directly on parietal cells
Also mediates effects of gastrin and ACh
How do proteins cause an increase in acid production?
Direct stimulus for gastrin release
In the lumen, they act as a buffer mopping up H+
Rise in pH SO
- decreased somatostatin secretion
- more parietal cell activity (dec somatostatin means less inhibition of parietal cells)
