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49 Cards in this Set
- Front
- Back
What are the functions of saliva?
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initial starch and triglyceride digestion, lubrication, protects mouth via buffering
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What is the ionic composition of saliva, as compared to plasma?
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higher K, HCO3
lower Na, Cl |
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In what ways do the salivary ducts modify the saliva?
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they r/a Na and Cl, and s/c K and HCO3
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Is the final saliva hypertonic or hypotonic? Why?
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hypotonic - more Na/Cl is r/a than K/HCO3 is s/c; and ducts are impermeable to water
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How does the composition of saliva change at low flow rates?
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most dissimilar to plasma; lowest NaCl and highest K
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How does the composition of saliva change at high flow rates?
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most similar to plasma; highest NaCl and lowest K
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How does the salivary HCO3 concentration change as the flow rate varies? Why?
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high flow rate = high HCO3
low flow rate = low HCO3 HCO3 is selectively stimulated when saliva s/c is stimulated |
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What type of cells make up the parotid glands?
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serous cells
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What type of cells make up the submandibular glands?
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serous and mucous cells
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What type of cells make up the sublingual glands?
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mucous cells
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What are two unusual features in the regulation of salivary secretion?
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1. under exclusive control by ANS, w/no hormonal control
2. parasymp AND symp stimulate salivary s/c (parasymp is dominant) |
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What is the mechanism/pathway of parasympathetic salivary regulation?
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CNVII/CNIX -> release ACh -> stim muscarinic receptors -> IP3 2nd mess -> inc saliva
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What is the mechanism/pathway of sympathetic salivary regulation?
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T1-T3 pregang symp nerves -> synapse in superior cervical ganglion -> postgang release NE -> beta-adrenergic receptor -> cAMP -> inc saliva
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What are some factors that increase saliva production?
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conditioning, food, nausea, smell
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What are some factors that decrease saliva production?
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dehydration, fear, sleep, anticholinergic drugs
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What effect would atropine have on salivation?
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is a cholinergic muscarinic antagonist, and blocks direct pathway of vagal stimulation; causes dry mouth
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Where in the stomach are parietal cells located, and what do they secrete?
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body; HCl and intrinsic factor
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Where in the stomach are chief cells located, and what do they secrete?
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body; pepsinogen
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Where in the stomach are G cells located, and what do they secrete?
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antrum; gastrin
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Where in the stomach are mucous cells located, and what do they secrete?
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mostly antrum, some body; mucous, HCO3 (and pepsinogen)
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What major function does parietal cell secretion of HCl serve?
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acidifies lumen, converts pepsinogen to pepsin
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What transporters/channels are located on the apical and basolateral membranes of parietal cells?
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apical: HK ATPase and Cl channel = s/c HCl
basolat: NaK ATPase and Cl/HCO3 exchanger = r/a NaHCO3 |
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What is the "alkaline tide"?
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pH of venous blood increases after a meal b/c of parietal cell r/a of HCO3
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What is the effect of omeprazole on parietal cells?
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inhibits HK ATPase, thus blocks H s/c
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What are the 3 main stimuli for HCl s/c by parietal cells?
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vagus, histamine, gastrin
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In what way does the vagus DIRECTLY stimulate H s/c from parietal cells?
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ACh released from vagus, binds to parietal muscarinic receptors and via IP3/Ca, initiates H s/c
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In what way does the vagus INDIRECTLY stimulate H s/c from parietal cells?
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GRP released from vagus, binds to G cells and stimulates gastrin s/c, which stimulates H s/c
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Atropine blocks the direct pathway of vagal stimulation, but how could one block both the direct and indirect pathways?
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vagotomy
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How does histamine act to stimulate parietal cell H s/c?
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released from gastric mast cells, binds to parietal H2 receptors and via cAMP, stimulates H s/c
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What effect does cimetidine have on parietal cell H s/c?
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inhibits H s/c by blocking parietal H2 receptors
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In what way does gastrin stimulate parietal cell H s/c?
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is released by G cells in response to small peptides, distention, vagal stim -> via endocrine mech stimulates H s/c (via IP3/Ca)
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What are the potentiating effects of ACh, histamine, and gastrin on parietal cell H s/c?
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histamine potentiates the action of ACh and gastrin, and
ACh potentiates the action of histamine and gastrin (gastrin does not potentiate the other 2) |
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How does the phenomenon of potentiation affect the action of cimetidine?
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has a greater effect than expected b/c it blocks direct action of histamine, AND the potentiated effects of ACh and gastrin
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How does the phenomenon of potentiation affect the action of atropine?
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has a greater effect than expected b/c it blocks direct action of ACh, AND the potentiated effects of histamine and gastrin
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What are the negative feedback mechanisms that inhibit gastric H s/c?
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-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) |
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What is the stimulus for s/c of pepsinogen by gastric chief cells?
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vagus (ACh)
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What is the stimulus for s/c of mucous by gastric mucous cells?
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vagus (ACh)
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What are the stimuli for s/c of gastrin by G cells?
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vagus (GRP), small peptides, distention of stomach
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What is the major causative factor in gastric ulcers?
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helicobacter pylori converts urea to NH4, which damages gastric mucosa
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What happens to H s/c in persons with gastric ulcers? How does this affect gastrin levels?
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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
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What is more common, duodenal ulcers or gastric ulcers?
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duodenal
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What causes duodenal ulcers?
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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)
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How are gastrin levels affected by duodenal ulcers?
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normal baseline levels, but secretion in response to meal is increased; b/c H has a reduced ability to inhibit gastrin
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What is an effect of chronically elevated gastrin levels?
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trophic effect on stomach, which increases parietal cell mass
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What causes Zollinger-Ellison syndrome?
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gastrin-secreting tumor of the pancreas (gastrinoma)
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What are the effects of elevated gastrin levels in Zollinger-Ellison syndrome?
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increases H s/c, and excess duodenal H erodes mucosa (ulcer) and causes steatorrhea; also increases parietal cell mass
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Why is steatorrhea one of the symptoms of Zollinger-Ellison syndrome?
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low duodenal pH inactivates pancreatic lipases necessary for fat digestion = fat in stool
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What is the treatment for Zollinger-Ellison syndrome?
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cimetidine (blocks action of histamine at H2 receptors), and omeprazole (blocks parietal cell HK ATPase), and surgical removal of tumor
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What is the only ESSENTIAL secretion of the stomach? What happens if it is absent?
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intrinsic factor; pernicious anemia (require vit B12 injections)
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