130b/131b - Salivary Gland, Stomach, Pancreas Secretion Flashcards
List 3 mechanism that prevent the stomach from digesting itself
- Mucous barrier is impenetrable by acid
- Any acid that gets neutralized by bicarbonate
- Any acid that is not neutralized is washed away by blood flow
What is the most powerful stimulator of gastrin secretion in the gastric phase?
Stretch
- Stretch
- -> Vagus nerve relesases GRP
- -> G cell stimulation
- -> Gastrin release
- -> Histamine release from ECL cells -> HCl from parietal
- -> HCl from parietal
How does the composition of pancreatic secretion vary with flow rate?
- Low flow
- Low bicarbonate, high Cl-
- High flow
- High bicarbonate, low Cl-
Higher flow = more stuff from stomach = need more HCO3-
Parietal cell receptor and second messenger pathway activated by ACh?
- Receptor:
- 2nd Messenger:
- Receptor: M3 muscarinic
- 2nd Messenger: Ca2+/IP3
Which hormone most strongly stimulates bicarbonate secretion from the pancreas?
Secretin (from S cells);
Released in response to HCl in the duodenum
- ACh from the enteric nervous system also plays a role
What mechanisms convert pepsin to pepsinogen?
Does this vary depending on pH?
- At pH 3.0-5.0: hydrolysis
-
At pH <3.5: Pepsin can cleave pepsinogen to pepsin
- Self-activation
How does gastric secretion vary based on flow rate?
- Low flow rate:
- Surface epithelial cells secrete bicarbonate-enriched fluids
- Less Cl- secreted
- High flow rate:
- Secretion from parietal cells dominates; lots of HCl
Salivary composition varies with secretory rate.
How will saliva compare to plasma at low secretory rates?
High secretory rates?
Saliva will always be hypotonic to plasma
- Low secretory rate = more hypotonic
- High secretory rate = more similar to plasma, but still hypotonic
*Note: secretions from salivary acinar cells are isotonic to plasma, but secretions are modified by ductal cells
(Ductal cells absorb Na+, Cl-, secrete K+, HCO3-)
Which ions are secreted by salivary ductal cells?
Which ions are absorbed?
- Secreted = K+, HCO3-
- Absorbed = Na+, Cl-
List 3 things that stimulate gastric acid secretion from the parietal cell
-
Histamine from ECL cells
- Stimulated by ACh and Gastrin; the indirect pathway
- Gastrin from G cells
- Stimulated by GRP (released from CNX in response to stretch)
- ACh from the vagus nerve
A patient is prescribe vitamin B12 shots for the rest of their life.
Loss of which cells in the GI tract might prompt this treatment?
Loss of parietal cells
Parietal cells secrete gastric acid and Intrinsic Factor (IF)
IF is needed for Vitamin B12 absorption
Possible causes of parietal cell loss:
Gastric bypass surgery, removal of the body and/or fundus of the stomach, chronic autoimmune gastritis
Parietal cell receptor and second messenger pathway activated by histamine?
- Receptor:
- 2nd Messenger:
- Receptor: H2 histamine
- 2nd Messenger: cAMP
What mechanism is responsible for the “alkaline tide” that occurs after a meal?
In response to a meal:
- H+/K+ ATPase is upregulated to pump H+ into the stomach lumen (Cl- follows)
- To maintain pH balance, OH- is sent to the interstitial space via HCO3-/Cl- exchanger
Remember, these gradients are set up by the Na+/K+ ATPase on the basolateral membrane
What are the effects of secretin on:
- Gastric smooth muscle:
- Parietal cells:
- Gastric smooth muscle: relaxation
- Parietal cells: decreased HCl secretion
Remember, secretin is released in response to HCl in the duodenum
Production of secretin is proportional to acid load, not concentration
What are the effects of CCK on the:
- Gallbladder:
- Pancreas:
- Stomach:
- Sphincter of Oddi:
- Gallbladder: Contraction to release bile
- Pancreas: Acinar secretion for digestive enzymes
- Stomach: Reduced emptying so the duodenum isn’t overwhelmed
- Sphincter of Oddi: Relaxation to allow bile and pancreatic secretions into the duodenum
Remember, CCK is released in response to nutrients in the duodenum
Parietal cell receptor and second messenger pathway activated by gastrin?
- Receptor:
- 2nd Messenger:
- Receptor: CCK-B
- 2nd Messenger: Ca2+/IP3
