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49 Cards in this Set

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What are the functions of saliva?
initial starch and triglyceride digestion, lubrication, protects mouth via buffering
What is the ionic composition of saliva, as compared to plasma?
higher K, HCO3
lower Na, Cl
In what ways do the salivary ducts modify the saliva?
they r/a Na and Cl, and s/c K and HCO3
Is the final saliva hypertonic or hypotonic? Why?
hypotonic - more Na/Cl is r/a than K/HCO3 is s/c; and ducts are impermeable to water
How does the composition of saliva change at low flow rates?
most dissimilar to plasma; lowest NaCl and highest K
How does the composition of saliva change at high flow rates?
most similar to plasma; highest NaCl and lowest K
How does the salivary HCO3 concentration change as the flow rate varies? Why?
high flow rate = high HCO3
low flow rate = low HCO3

HCO3 is selectively stimulated when saliva s/c is stimulated
What type of cells make up the parotid glands?
serous cells
What type of cells make up the submandibular glands?
serous and mucous cells
What type of cells make up the sublingual glands?
mucous cells
What are two unusual features in the regulation of salivary secretion?
1. under exclusive control by ANS, w/no hormonal control
2. parasymp AND symp stimulate salivary s/c (parasymp is dominant)
What is the mechanism/pathway of parasympathetic salivary regulation?
CNVII/CNIX -> release ACh -> stim muscarinic receptors -> IP3 2nd mess -> inc saliva
What is the mechanism/pathway of sympathetic salivary regulation?
T1-T3 pregang symp nerves -> synapse in superior cervical ganglion -> postgang release NE -> beta-adrenergic receptor -> cAMP -> inc saliva
What are some factors that increase saliva production?
conditioning, food, nausea, smell
What are some factors that decrease saliva production?
dehydration, fear, sleep, anticholinergic drugs
What effect would atropine have on salivation?
is a cholinergic muscarinic antagonist, and blocks direct pathway of vagal stimulation; causes dry mouth
Where in the stomach are parietal cells located, and what do they secrete?
body; HCl and intrinsic factor
Where in the stomach are chief cells located, and what do they secrete?
body; pepsinogen
Where in the stomach are G cells located, and what do they secrete?
antrum; gastrin
Where in the stomach are mucous cells located, and what do they secrete?
mostly antrum, some body; mucous, HCO3 (and pepsinogen)
What major function does parietal cell secretion of HCl serve?
acidifies lumen, converts pepsinogen to pepsin
What transporters/channels are located on the apical and basolateral membranes of parietal cells?
apical: HK ATPase and Cl channel = s/c HCl
basolat: NaK ATPase and Cl/HCO3 exchanger = r/a NaHCO3
What is the "alkaline tide"?
pH of venous blood increases after a meal b/c of parietal cell r/a of HCO3
What is the effect of omeprazole on parietal cells?
inhibits HK ATPase, thus blocks H s/c
What are the 3 main stimuli for HCl s/c by parietal cells?
vagus, histamine, gastrin
In what way does the vagus DIRECTLY stimulate H s/c from parietal cells?
ACh released from vagus, binds to parietal muscarinic receptors and via IP3/Ca, initiates H s/c
In what way does the vagus INDIRECTLY stimulate H s/c from parietal cells?
GRP released from vagus, binds to G cells and stimulates gastrin s/c, which stimulates H s/c
Atropine blocks the direct pathway of vagal stimulation, but how could one block both the direct and indirect pathways?
vagotomy
How does histamine act to stimulate parietal cell H s/c?
released from gastric mast cells, binds to parietal H2 receptors and via cAMP, stimulates H s/c
What effect does cimetidine have on parietal cell H s/c?
inhibits H s/c by blocking parietal H2 receptors
In what way does gastrin stimulate parietal cell H s/c?
is released by G cells in response to small peptides, distention, vagal stim -> via endocrine mech stimulates H s/c (via IP3/Ca)
What are the potentiating effects of ACh, histamine, and gastrin on parietal cell H s/c?
histamine potentiates the action of ACh and gastrin, and
ACh potentiates the action of histamine and gastrin

(gastrin does not potentiate the other 2)
How does the phenomenon of potentiation affect the action of cimetidine?
has a greater effect than expected b/c it blocks direct action of histamine, AND the potentiated effects of ACh and gastrin
How does the phenomenon of potentiation affect the action of atropine?
has a greater effect than expected b/c it blocks direct action of ACh, AND the potentiated effects of histamine and gastrin
What are the negative feedback mechanisms that inhibit gastric H s/c?
-low pH in stomach, via somatostatin release (food moves to duod and no longer buffers gastric H, pH drops below 3)
-chyme in duodenum (via GIP and secretin)
What is the stimulus for s/c of pepsinogen by gastric chief cells?
vagus (ACh)
What is the stimulus for s/c of mucous by gastric mucous cells?
vagus (ACh)
What are the stimuli for s/c of gastrin by G cells?
vagus (GRP), small peptides, distention of stomach
What is the major causative factor in gastric ulcers?
helicobacter pylori converts urea to NH4, which damages gastric mucosa
What happens to H s/c in persons with gastric ulcers? How does this affect gastrin levels?
H s/c decreases b/c some of the H that is s/c leaks into damaged mucosa; gastrin levels are increased in response to low H
What is more common, duodenal ulcers or gastric ulcers?
duodenal
What causes duodenal ulcers?
occurs when H secretory rates are higher than normal, overwhelming buffering capacity of HCO3; H acts with pepsin to damage mucosa (h. pylori is causative factor)
How are gastrin levels affected by duodenal ulcers?
normal baseline levels, but secretion in response to meal is increased; b/c H has a reduced ability to inhibit gastrin
What is an effect of chronically elevated gastrin levels?
trophic effect on stomach, which increases parietal cell mass
What causes Zollinger-Ellison syndrome?
gastrin-secreting tumor of the pancreas (gastrinoma)
What are the effects of elevated gastrin levels in Zollinger-Ellison syndrome?
increases H s/c, and excess duodenal H erodes mucosa (ulcer) and causes steatorrhea; also increases parietal cell mass
Why is steatorrhea one of the symptoms of Zollinger-Ellison syndrome?
low duodenal pH inactivates pancreatic lipases necessary for fat digestion = fat in stool
What is the treatment for Zollinger-Ellison syndrome?
cimetidine (blocks action of histamine at H2 receptors), and omeprazole (blocks parietal cell HK ATPase), and surgical removal of tumor
What is the only ESSENTIAL secretion of the stomach? What happens if it is absent?
intrinsic factor; pernicious anemia (require vit B12 injections)