Lecture 4.1 - Functions of the Stomach Flashcards
Why must food be stored within the stomach temporarily?
We eat food faster than we digest it
What would happen if the food remained static within the stomach during storage?
Pressure within the stomach would rise, causing reflux
How is reflux avoided during storage of food in the stomach?
- Receptive relaxation: vagally mediated relaxation of the orad region of the stomach
- Rugae distend, increasing stomach volume
How are the stomach contents mixed?
Peristalsis - coordinated movements every 20s or so
Briefly explain how the stomach separates out the larger chunks of food (which need further digestion) from the liquid chyme which is ready to move on to the duodenum
Peristalsis propels food from proximal to distal.
This allows the stomach to act as a funnel, as it is larger proximally than distally –> separates out the liquid chyme from the larger chunks
Is the pyloric sphincter open during peristalsis? Explain
No - only opes when chunks of food are small enough to progress
What is achieved by the acidity of the stomach’s internal environment?
- Unravels proteins
- Activates zymogens such as proteases
- Disinfects stomach contents
What do the parietal cells produce?
HCl and intrinsic factor
Where are the parietal cells found?
Proximal part of stomach - fundus and body only
Why is intrinsic factor important?
Vital for vitamin B12 absorption
Where are the G cells found?
What do they secrete?
Found in antrum
Secrete gastrin
What do enterochromaffin-like cells produce?
Histamine
What do the chief cells secrete?
Pepsinogen
What do the D cells produce?
Somatostatin
List the important cell types found in the stomach
Parietal cells G cells D cells Chief cells Enterochromaffin-like cells Mucous cells
What substances does the stomach secrete?
HCl Intrinsic factor Mucus HCO3- Pepsinogen
Where does secretion take place within the stomach walls?
Secretion occurs from gastric pits which overly gastric glands.
Gastric pits appear as pin-prick like holes in the stomach wall
List the cell types lining the gastric pit and gland, from superficial to deep
Mucous cells - most superficial - line pit
Parietal cells
Chief cells
Enteroendocrine cells - deepest
Briefly outline the mechanisms of stomach acid secretion
1) Water splits into OH- and H+
2) H+ moves into stomach lumen via H+/K+-ATPase –> highly ATP dependent
3) At the same time, Cl- moves into the parietal cell from the ECF in exchange for HCO3-, which is produced from the combination of CO2 and OH-. HCO3- moves into the bloodstream
4) Cl- then moves into the stomach lumen where it combines with H+ to form HCl
Explain the phenomenon known as the “alkaline tide”
Just after eating, there is a transient increase in blood pH.
This is caused by the influx of HCO3- moving into the blood from parietal cells, in exchange for secretion of HCl into the stomach lumen.
What stimulates parietal cells to secrete HCl?
Gastrin
Histamine
ACh
What does histamine bind to on parietal cells to stimulate HCl secretion?
Does histamine have a major role in stimulation of secretion?
H2 receptors
No - fine-tuning only
What sort of receptors does ACh bind to on parietal cells to stimulate acid secretion?
What nerve controls this?
Muscarinic receptors
Vagus nerve
What sort of receptors does gastrin bind to on parietal cells?
CCK receptors
