2.06 GI Secretions & Asorption Flashcards
How is the stomach antrum different from the corpus/body in terms of what cells it has?
No parietal cells
Endocrine Cells
What does gastric fluid look like in a low secretion or low gastric acid state?
Resembles plasma electrolyte composition (pH 6-7)
High Na+ and Low H+ b/c non parietal cells
What does gastric fluid look like in a high gastric acid or high secretion state?
Low pH (1-2), H+ secreted by parietal cells (HCL) rather than NaCl , b/c increase in gastrin and Histamine signaling
What does the parietal cells have that allows it to increase its surface are when cell is stimulated?
Tubulovesicular structures (canaliculus when active)
Where do the H+ ions pumped out by the parietal cells come from?
Passive uptake of CO2 and H20 (OH) that gets converted by carbonic anhydride to HCO3- (bicarb/Cl- exchanger) and H+
What helps regulate parietal cell pH levels at the basal state?
Na-H exchanger
What are three things that acts synergistically to release H+ from parietal cells?
Ach
Histamine
Gastrin
Where does Ach come from and bind to directly act on parietal cells?
Ach from vagus binds to M3 receptor
Where does gastrin come from and what does it bind to in order to directly stimulate parietal cells?
Gastrin from G cells to CCK2 receptor
Where does Histamine come from and what does it bind to in order to active parietal cells?
His from ECL cell binds to H2 receptor
What are H2 blockers that act as competitive antagonists to block Histamine?
Cimetidine & Ranitidine
What are indirect ways to activate the parietal cell?
All through the ECL cells
Ach to M3 to release His
Gastrin to CCK2 to release His
Condition that results in gastric hypersecretion that can lead to peptic ulcers and gastrinomas?
Zollinger Ellison Syndrome
How does high gastrin both directly and indirectly acts on pathways?
Direct = CCK2 on parietal
Indirect = ECL stimulation
What is the endocrine cels responsible for relabeling gastrin?
G cells
What is the endocrine cell responsible for the inhibition of gastrin release?
D cell
What are the stimuli for gastrin release?
Food (luminal peptides and amino acids) and Neuronal (direct vagal or D cells)
What is the stimuli for the inhibition of gastrin?
Gastrin activates CCK2 on C cells and stimulated tor release Somatostatin that inhibits G cells & partial cells
What cells works to inhibit the release of gastrin?
D cells
What inhibits the release of somatostatin from D cells?
Ach on M3 receptor (D cells)
What is GRP>
Gastrin releasing peptide activated by vagus and directly stimulates G cell
The D cell in the antrum has what pathway source?
Endocrine
The D cell in the corpus has what pathway source?
Paracrine
What is the stimuli that inhibits gastric acid secretion?
Fat, acid, and hyperosmolar solution in the duodenum!
What is the most potent stimuli to inhibit gastric acid release?
Fat
Where does secretin come from?
S cells from duodenum and jejunum
Where does CCK come from?
I cells from duodenum and jejunum
Where does gastric inhibitory peptide (GIP) come from?
K cells from duodenum and jejunum response to nutrients
Where does peptide YY come from?
L cells in distal intestine
What are the direct effects of secretion?
Down regulate H/K atpase pump from parietal cells and inhibit gastrin release form G cells
What are teh indirect affects of secretin?
Stimulate D cells to release somatostatin that further inhibits acid secretion
What stimulates the release of prostaglandin E2?
Increased luminal acid exposure
What does prostaglandin E2 INdirectly do?
Bind to EP3 on BL membrane to inhibit AC and prevent AMP increase and blocked H2 receptor pathway (not receptor)
Indirect inhib His and gastrin release
What drug activates the EP3 receptor to indirectly inhibit H/K ATPase?
Misoprostol
What does ingesting food do to the gastric acid?
Decreases cause it buffers it, it increases as food leaves the stomach to the standard 1-2.5 pH
What do chief cells do?
Release pepsinogen (inactive)
What converts pepsinogen to pepsin?
HCL
When does pepsin become inactive?
When it reaches duodenum cause of higher pH
What does pepsin do?
Breakdown proteins into AA at stomach
What stimulates chief cells to release pepsinogen?
Ach from vagal, gastrin from G cells, local cholinergic reflex triggered by low pH, secretin from S cells
Where is B12 absorbed?
Ilium
Where is IF secreted?
Parietal cells
Damage to what can contribute to loss of acid secretion and loss of IF?
Parietal cells
Unvaccinated child under <5 years with watery diarrhea and viral origin should hint at?
Rotavirus
