Gastric Phys Flashcards
What are the five gastric secretions?
Acid Pepsinogens Mucus IF Water
What does the oxyntic gland secrete?
HCl
What secretes gastrin?
Pyloric mucosa (specific region)
Describe the types of cells in a gastric gland starting most superficial
Surface epithelium
Mucous neck cells
Pareital cells (oxyntic)
Peptic (chief) cells
What is the alkaline tide?
Venous blood leaving stomach has higher pH than arterial because of bicarbonate after meal
Describe the cellular mechanism of acid secretion
CO2 made into HCO3- + H+ by CA. HCO3- diffuses into blood while H is secreted into the blood via a H/K ATPase (K inside).
Cl- is antiported inside when HCO3- leaves, and is then goes through channel into stomach.
Also note the regular Na/K ATPase.
H is secreted __ its electrical gradient and __ its concentration gradient
down electrical gradient
against concentration gradient
Cl is secreted __ its electrical gradient and __ its concentration gradient
against both
What are some substances that disrupt the stomach cell membranes?
ASA
EtOH
How do the concentrations gastric ion secretions change with secretory rate?
Cl and H go up with faster rate
K goes up slightly with increase
Na decreases with faster rate
Patients with chronic vomiting have what kind of ion and acid-base disorders?
hypokalemia and alkalosis
Describe non-meal state stomach secretions?
Low volume production
Isotonic to plasma
Describe acid-secreting state stomach secretions?
HCl and potassium
High volume
Parietal cell activity
What are the three secretogogues of acid secretion?
Gastrin
Histamine
ACh
How does gastrin stimulate acid secretion?
hormone!
CCKB receptor –> Gq/IP3 mechanism that stimulates H/K ATPase
How does ACh stimulate acid secretion?
neurocrine!
M3 receptor –> Gq/IP3 mechanism that stimulates H/K ATPase
How does histamine stimulate acid secretion?
paracrine!
Histamine from ECL cells –> h2 receptor –> Gs/cAMP –> stimulates H/K ATPase
Describe the interaction between gastrin levels and acid levels
Independent
What’s the difference in picking your food vs. not?
More acid secretion when you get to pick
This phase of acid secretion is entirely mediated by the vagal nerve **
Cephalic (30% of secretion) via ACh, even when gastrin is absent
Describe the interdigestive output
Peaks at night (GERD worst then)
unrelated to plasma gastrin
Describe the gastric phase of acid release
peaks 20-40 minutes after meal
lasts 3-4 hours
More acid with high protein
Gastrin elevated ~ 1.5h
How does the CNS affect acid output based on stimuli?
Vagal signals to release ACh and gastrin
This substance can inhibit all gastrin release
somatostatin
What effects on acid secretion does distention have?
Stimulates vagus which causes ACH and GRP release
Also stimulates ‘local reflexes’ to release ACH to act on G cells to release gastrin
What affect does digested protein have on acid secretion?
Stimulates G cells to secrete gastrin
What mechanisms of acid secretion are found in all stages?
Gastrin - ECL - histamine release
ACh - ECL - histamine release
Why does pH rise after a meal?
Food buffers
Why does the pH begin to fall after the stomach digests a meal?
As food is digested the buffer capacity is diminished
How is pepsinogen released? 2 ways
Vagal stimulation of peptic cell
Acid itself triggers cholinergic stimulation of peptic cells
Upon reaching the duodenum, acid causes __ release
secretin
What is the mechanism of secretin?
Acts hormonally to stimulate more pepsinogen release from peptic cells
What is the main difference between peptic and duodenal ulcers?
Duodenal: ulcers in antrum, fewer secretions
Gastric: ulcers all over stomach, high secretions
