Regulation and Disorders of Gastric Secretion Flashcards
Describe the stomach anatomically.
- Made up of a fundus, body, antrum, and pylorus
- Cardiac area is where the contents of the oesophagus enter the stomach
What does the fundus secrete?
- Pepsinogen and mucus
What do the cardiac and pyloric areas secrete?
- Mucus
What does the body of the stomach contain?
- Chief cells (pepsinogen-secreting)
- Parietal cells (intrinsic factor-secreting)
What does the antrum secrete?
- Mucus, pepsinogen and gastrin
How is gastric acid made in the stomach lumen? PART 1
- HCO3- is exchanged for Cl- in the blood
- This decreases the acidity of the venous blood from the stomach
How is gastric acid made in the stomach lumen? PART 2
- Excess Cl- diffuses into the stomach through chloride channels
- H+ is pumped into the stomach lumen (K+/H+ ATPase pumps H+ out of the stomach lumen).
How is gastric acid made in the stomach lumen? PART 3
- Net effect of PART 1 and 2 is net flow of H+ and Cl- out of the parietal cells and into the stomach lumen.
List some gastric secretions.
- Mucus
- Rennin
- Lipase
- Intrinsic Factor
- HCl
Describe mucus
- Alkaline
- Forms a water-insoluble gel on epithelial surfaces, protecting against H+ secretion
Describe rennin
- Curdles milk into casein clots
Describe lipase
- Hydrolyses triglycerides into fatty acids and glycerol
Describe Intrinsic Factor
- Aids in Vitamin B12 absorption
- Prevents pernicious anaemia
Describe HCl
- Kills bacteria
- Acid denaturation of digested food
- Activates pepsinogen (for protein digestion)
What is the direct way in which we can control HCl secretion?
- ACh, gastrin and histamine stimulate the parietal cell directly
- Triggers secretion of H+ into the lumen.
What is the indirect way in which H+ secretion can be controlled?
- ACh and gastrin also stimulate the ECL cells, resulting in histamine secretion.
- Histamine then acts on the parietal cell.
What are the three phases of digestion?
Cephalic
Gastric
Intestinal
Describe acid secretion regulation during the cephalic phase.
- Smell, sight, taste, chewing, etc. stimulate ACh release.
- ACh stimulates histamine release from ECL cells.
- ACh also acts directly on the parietal cells, stimulating HCl secretion.
Acid secretion decreases as the acidity of the lumen increase.
Explain how.
- HCl-stimulating somatostatin-releasing cells (D cells).
- Somatostatin inhibits ECL and G-cells to curtail the hypersecretion of acid.
Describe acid secretion regulation during the gastric phase. PART 1
- Increased distention of the stomach increases peptide concentration
- Increases the acidity of the stomach.
Describe acid secretion regulation during the gastric phase. PART 2
- Combination of H+ and proteins decreases the [H+].
- By acting as a buffer, the proteins remove the inhibitory powers of HCl on gastric secretion.
- Increases gastrin-mediated acid secretion.
Describe acid secretion regulation during the intestinal phase.
- High acidity of the duodenal contents inhibits acid secretion
- Increased acidity would inhibit the activity of digestive enzymes, bicarbonate and bile salts
What inhibits acid secretion during the intestinal phase?
- Distention of the duodenum
- Hypertonic solution (indicating that the food has already been digested)
- Amino acids, fatty acids, and monosaccharides
What does inhibition of acid secretion in the small intestine depend on?
- Composition and volume of chyme