Gastric secretion Flashcards
What is secreted in the body of the stomach
Mucous
HCL
Pepsinogen
Intrinsic factor
What secretes Mucous in the stomach
Foveolar cells, found in the necks of the gastric pits (Mucous neck cells)
Mucus-secreting cells are the most abundant cell type in the stomach, giving indications of how important mucus is to the functioning stomach.
What cell secretes HCL
Parietal cells
What cell secretes pepsinogen
Chief cells
What cell secretes intrinsic factor
Parietal cells
What cell secretes Gastrin
G cells
What cells lie in the gastric pit
Surface mucous cells
What cells lie in the Gastric gland
Mucous necks cells
Parietal cells
Chief cells
What is the pH of the stomach
2
What is the pH of blood
7.4
How is HCL made in the stomach
Process involving carbonic anhydrase and carbonic acid
What pumps H ions out of the apical membrane of the gut cells
A hydrogen/potassium pump (uses lots of ATP)
How does bicarbonate exit the enterocyte
Through the baso-lateral membrane via a HCo3 / Chlorine pump.
What happens when Hco3 is dumped in blood after meal
Post prandial alkalosis
What controls the amount of HCL created by parietal cells (x4)
Gastrin
Histamine
Acetylcholine
Prostaglandins
What organs secrete gastrin
Stomach (antrum)
Pancreas
Duodenum
What increases the amount of gastrin secretion
peptides, amino acids and gastric distension
vagal stimulation by gastrin releasing peptide
epinephrine and calcium
What does gastrin act on?
CCKB gastrin receptors on the basolateral membrane of parietal cells
What happens when CCKB gastrin receptors on the basolateral membrane of parietal cells bind gastrin
Calcium is released into the cell which activates protein kinase C and increases activity of the Hydrogen/potassium pump.
What causes the release of histamine in the stomach
Gastrin and acetylcholine
What releases histamine
Enterochromaffin-likecells
What are Enterochromaffin-likecells
A type of neuroendocrinecellfound in thegastricglands of thegastricmucosa beneath the epithelium, in particular in the vicinity of parietalcells, that aid in the production ofgastricacid via the release of histamine.
What does histamine act on
The H2 receptors in the stomach
What happens when histamine binds to the H2 receptors in the stomach
It activates g protein adenylate cyclase which acts on protein kinase C. This increases action of the H/Cl pump - increases Hydrogen
What causes the release of acetylcholine involved in HCL secretion during the cephalic phase
Thinking, seeing, smelling, tasting FOOD
What receptor does acetylcholine act on in the stomach to increase acid production?
The M3 receptor on the stomach (via long and short reflexes)
What happens when acetylcholine acts on the M3 receptors of the stomach
Increases intracellular calcium which activates protein kinase C - this increases H/CL pump
What effect do prostaglandins have on Hydrogen secretion
they inhibit it
What receptor does prostaglandins act on
E3 receptors
What happens when prostaglandins act on E3 receptors
It activates G inhibitory protein which turns off adenyl cyclase and reduces activity of the h/cl pump
Where are prostaglandins found in the stomach
Prostaglandins are found in high concentration in the gastric mucosa and gastric juice.
What 3 stimuli cause increased Hydrogen increase during the gastric phase
Distension of Stomach
peptides in the lumen
Gastrin + Acetylcholine
How does distension of stomach increase acid production
It initiates a vagal/enteric reflex, releasing acetyl choline. This causes the parietal cells to release H ions
How do peptides in the lumen increase acid production
They activate G cells which releases Gastrin which act on parietal cells
How does gastrin and acetyl choline increase acid production together?
They both act on enterochromaffin cells causing them to release histamine which acts on parietal cells
What Inhibits gastric acid secretion in the cephalic phase
When you stop eating it decreases vagal activity so Ach and H+ stops getting produced
What Inhibits gastric acid secretion in the gastric phase
When the Ph gets reduced to a certain level due to an abundance of stomach acid, gastrin secretion gets reduced from G cells
What stimulus reduces gastric acid secretion in the intestinal phase (x2)
Acid in duodenum
Fat/CHO in duodenum
How does acid in duodenum inhibit gastric secretion
It triggers the enterogastric reflex and the release of secretin from S cells. The secretin produces bicarbonate, decreases gastrin secretion and stimulation of parietal cells.
How does fat/CHO in the duodenum inhibit gastric secretion
It triggers the releases of Gastroinhibitory peptide (GIP)
This decreases gastrin secretion and hence decreases gastrin stimulation of parietal cells
What is the collective term for an inactive precursor enzyme
Zymogen
What activates pepsinogen
Low pH (<3)
What lines the stomach surface
Gastric Mucous
What produces gastric mucous in the stomach (x2)
Surface cells
Mucous neck cells
What are 2 functions of gastric mucous
Protects against gastric acid corrosion
Protects from mechanical injury
