Gastric Secretions Flashcards
How much liquid does the stomach secrete a day?
2Litres of gastic juices a day due to the cells lining the stomach known as the gastric mucosa
What are the types of mucosa?
Split into two regions
Oxyntic mucosa - in the fundus and body
Pyloric gland area - in the antrum
Where are mucosal gland cells found?
Gastric pits
What do the parietal cells produce? What does this cause?
Hydrogen Chloride at around 160mmol/L
Strong Acid so causes pH to be around 0.8-1.0
Why is the Acid environment crucial?
Aids digestion by:
1) Activates the enzyme pepsin providing an acid medium for optimal pepsin activity
2) Aids the breakdown of connective tissue and muscle fibres
Crucial as a non-specific defence mechanism, killing ingested micro-organisms
Pariental cells also release intrinsic factor that binds to VitB12 to enable it’s absorption
What is the major constituent of gastric secretion?
Pepsinogen
-Produced by the chief cells
What is the Cephalic Phase?
The stimulation of gastric secretion prior to the arrival of food in the stomach
stimulated just by the thought or expectation of food and the sight, taste, chewing or swallowing of food
How much does the cephalic phase contribute to gastric secretion? What is it dependent on?
30-50% of total gastric secretion and is dependent upon the activity of the vagus nerve
How does gastric secretion increase when food reaches the stomach?
1) Local vago-vagal reflexes in response to mechanical stimulation, due to the presence of food in the antrum (no CNS)
2) Stimulation of gastrin release from G-cells by peptide fragments of partially digested proteins (major mechanism)
What percentage of gastric secretion makes up the intestinal phase?
approx. 5% of gastric secretions
may be due to circulating amino acids or gastrin
What amount of Cardiac Output goes to the stomach in both resting and active environments?
Resting stomach = 0.5% CO
Active Stomach = >10% CO
How is gastric secretions reduced?
1) Removal of peptide fragments
2) Removal of food leads to a decrease in pH. At pH less than 2, gastrin release from G-cells is inhibited directly and via somatostatin release
3) Distension of the duodenum, or the presence of acid or food products in chyme lead to a release in hormones that inhibit gastrin release
4) Gastrin secretion can also be influenced by cephalic factors such as fear or depression
How does the stomach prevent itself from self-digestion?
1) Luminal membranes of gastric mucosal cells are impermeable to H+ ions. Cells are interconnected with tight junctions, therefore no H+ movement between cells
2) Negative feedback. pH < 2.0 inhibits G-Cells directly and via somatostatin release from D cells
3) Mucus released from surface epithelial cells
4) Rapid repair of damaged mucosa
