GI Secretions Flashcards
Which cells secrete gastric acid in the body
Parietal cells of the stomach
What glands are the parietal cells found
Gastric glands
What are some stimuli for acid secretion from the parietal cells
Gastrin
Vagus nerve
What cells produce gastrin
G cells
What receptor does gastrin bind to on parietal cells to cause acid secretion
CCKb receptor
What is the indirect method gastrin uses to secrete acid
Gastrin binds to (enterochromaffin-like cells) ECL cells which releases histamine which then stimulates the parietal cells to secrete HCl
How does the vagal nerve cause acid secretion
The vagus nerve can release ACh which can bind to the M3 receptors on parietal cells and stimulate them to secrete acid
Can activate G cells to secrete gastrin using gastrin releasing peptide this time not ACh
Blocking ACh does not block vagal nerve function because GRP will continue to function and stimulate acid secretion
Vagotomy could lead to a decreased acid production
True or false
True
Atropine is a muscarinic blocker and could block acid secretion but it’s not as potent. Why
It can block acid secretion by blunting parietal stimulation by ACh but does not block stimulation by the vagus -> gastrin -> HCl
Intrinsic factor is produced by ……. along with H+
Parietal cells
How does vomiting cause a metabolic alkalosis
Vomiting leads to a decrease in HCl which causes the parietal cells to secrete more HCl causing an increase in bicarbonate production thus causing a metabolic alkalosis. Patients also lose chloride in the HCl thus urinary chloride will be relatively low
When a patient has a metabolic alkalosis of an unknown cause what electrolyte could be a useful measurement
Urinary chloride
What could cause a high urinary chloride >20
When patient is taking a diuretic (diuretics block NaCl resorption)
What could cause a low urinary chloride <10-20
Vomiting
Mention two naturally occurring substances that could inhibit secretion of HCl by parietal cells
Somatostatin and prostaglandins
Which acid secretion stimulating hormones work by Gq proteins with IP3/Ca
ACh and gastrin
Gq proteins activate PLC which converts PIP2 to IP3. IP3 will then stimulate calcium release and the calcium will activate proton pumping
Which acid secretion stimulating or inhibitory hormones work by Gs/i and CAMP
Histamine (increases cAMP), somatostatin and PGs (inhibit cAMP)
What PGE1 analog blunts acid secretion
Misoprostol
Which layer in the stomach are chief cells found
Mostly in deeper layers
Dark colored (basophilic)
Which cells secrete pepsin
Chief cells
Which pH works best for pepsin
pH 1 to 3
What is the stimulus for the release of pepsin
Vagus nerve
Which layer of the stomach are parietal cells found
More in the upper layers
Mucosal layer
Pink colored (eosinophilic)
How do parietal cells secrete HCl
There are separate pumps in the membranes of the parietal cells that secrete H+ and Cl- for HCl. There is an ATPase pump which pumps out hydrogen ions in exchange for potassium and there is a separate channel by which chloride is secreted into the lumen of the stomach. The H+ ions that are pumped out into the lumen of the stomach are formed by carbonic anhydrase (takes molecules of water and CO2 and converts them into molecules of bicarbonate and H+). The H+ gets pumped out of the lumen of the stomach via the hydrogen potassium ATPase pump. The bicarbonate then goes out into the serum via a bicarbonate-Cl antiporter (alkaline tide)
