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52 Cards in this Set
- Front
- Back
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Is the lumen of the digestive tract part of the internal or external environment?
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External environment
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What kind of process is secretion?
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Active
Energy dependent Blood flow dependent ->results in the releas of a fluid containing ions and a variety of enzymes |
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What are the 2 types of secretions?
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exocrine: released into lumen of GIT (external env)
endocrine: released into internal environment |
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What are the 3 types of enzymes involved in digestion?
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Amylases- digest carbs
Proteases- digest proteins Lipases- digest fats |
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What are the types of regulation of digestion?
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Nervous: most important at the beginning of digestion: mouth, stomach, less important as you go down to the SI
Hormonal (Gut peptides): Most important further down-> large intestine, then less and less as you go to the pancreas and the liver |
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What are the major salivary glands?
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Parotid glands: serous (watery and liquid)
Submandibular gland: mixed Sublingual gland: mucous (viscous) |
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What is special about saliva?
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Only secretion that is hypotonic
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Describe saliva characteristics.
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Volume: 0.5-1.5L/day
Ions: Na+, K+, Cl-. HCO3- pH: 6.5-7 |
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Wha enzymes does the saliva contains?
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Amylase (ptyalin)
Mucin:lubricates bolus |
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What does Ptyalin do?
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Reduces starch polysac to maltose (a disac)
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Is digestion of polysac completed in the mouth?
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NO
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What regulates saliva?
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ANS (exclusively)
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How does the ANS parasympathetically regulate saliva?
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Acts on the gland itself, release ACh which acts on muscarinic receptors to INCREASE secretion
->VASODILATION: increases blood flow so that it can secrete |
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How does the ANS sympathetically regulate saliva?
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May cause very little secretion
->VASOCONSTRICTION decrease in secretion, but some cells secrete a small amount of saliva (this is odd because the symp is doing the same as the parasymp in some salivary cells) |
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What does atropine do?
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Temporarily stops secretion by blocking muscarinic receptors from binding ACh
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What kind of reflexes are involved in the regulation of salivary reflexes?
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Simple Reflexes
Conditioned Reflexes |
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What are conditioned reflexes?
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Eyes, nose
This goes to Higher centres which then goes to Salivary centres in teh medulla |
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What are simple reflexes?
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Come from sensory receptors in the mouth
G through afferent fibers andhe impulses are sent to the salivary center in the medulla |
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What happens once impulses are sent to the salivary center in the medulla, from either the conditional or simple reflexes?
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Efferent output via the parasym, get secretion by the salivary glands
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What are the phases of secretion?
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1) cephalic phase: includes psychic phase (sight of meal, conditioned) and gustatory phase (taste)
2)gastric/intestinal - less important |
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Describe the characteristics of mixed gastric juice.
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Vol: 1.5-2L/day
Isotonic fluid: Na+, K+, Cl-, **H+** **pH: 1-2** very high concentraion of H+ is responsible for the low pH |
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What are the organic substances secreted found in the mixed gastric juice?
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Pepsinogen: inactive precursor of a protease
Intrinsic factor: allows absorption of vitamin B12 Mucin: very effective lubricant, protects against mech. abrasions, contains rough particles |
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What do surface epithelial cells in the stomach secrete?
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Mucous, alkaline fluid
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What secretory cells are present in the gastric glands in the fundus and the corpus?
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Parietal Cells
Chief Cells Mucous neck cells |
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What do parietal cells secrete?
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HCl
Have intracelular channels |
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What do chief cells secrete?
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Pepsinogen (inactive pepsin)
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What do mucus cells secrete?
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Mucin
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What is the structure of the parietal cell?
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Cery active cell .: has a lot of mitochondria
Has lots of microvilli Located in the fundus and corpus Has canaliculus: channels that communicate with lumen and project into cell interior |
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What is the maximum secretion proportional to?
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The number of parietal cells
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What are proton pump inhibitors for?
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For ppl who secrete more acid than normal
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What does nexin do?
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H+/K+ ATPase
Prevents excessive acid secretion |
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What is the H+/K+ ATPase used for?
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Involved in last step, in HCl release
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What happens for every H+ that is secreted in the lumen?
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An HCO3 is secreted in plasma
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What is the concentration of H+ in the plasma?
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4 x 10^-5mEq
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What is HCl in the lumen?
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Isotonic
(150 mEq H+, 150 mEq Cl-) |
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What happens to the urine when the stomach produces a lot of H+?
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NEed to make a lot of HCO3, which increases the alkalinity in urine
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What kind of port is the H+/K+ ATPase?
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Antiporter
pumps H+ outand K+ in (leaves OH- in cell) |
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Describe HCl production
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K+ moves into lumen via diffusion, but is kicked back to parietal cell by H/K pump, which replaces it with H+
The H+ is created by H20=>OH- + H+ OH- is neutralized by H3CO2+OH- => H20 + HCO3- and this bicarb goes into blood vessels of stomach making blood very basic. bicarb out is exchanged for Cl- in. Na/K pumps on basolateral side keep pumping in K+ to maintain this process. |
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hat is the parietal cell secretion?
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Pure HCl fluid
Constant composition, pH= 0.8 Independent of tpe/magnitude of stimulus => pH dependent on number of parietal cells active |
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What does the pH of mixed gastric juice depend on?
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# of parietal cells that are active
(if a lot are active, pH is closer to 1) |
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What are the fcts of HCl?
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1) precipitates soluble proteins - remain longer in the stomach to be acted on by proteases
2) Denatures ptns: exposes more bonds to proteases **3) Activates pepsin and Provides optimal pH for it activity |
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How is pepsin activated?
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Pepsinogen --> pepsin
Need HCl so that pH < 6 Pepsin: autocatalytic positive feedback loop |
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What does pepsin do?
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at pH 2-3:
proteins-> polypeptides |
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Is pepsin required for ptn digestion?
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No, because the pancres producves more powerful proteases
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What is the intrinsic factor?
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Not an Enzyme
Only secretion of the STOMACH that is essential to life -a glycoptn -secreted by parietal ell **required for the absorption in distal small intestine (ileum) of physiological adequate amounts of dietary vit B12 (imp in dev'l of nervous system) |
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What happens if there is a deficiency in intrinsic factor?
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Pernicious anemia
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What produces mucin?
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Surface epithelial cells
Cardiac and pyloric sphincter Mucous neck cells |
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I"s mucin permeable to acid?
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YES
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What does the gastric mucosal barrier (GMB) do?
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Prevents penetration of acid (has apical surfaces and tight junctions)
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What does the muci-bicarb layer do?
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Neutralize the H+ that does penetrate
1st line of defense vs the acid |
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What is the pH of the lumen? Surface epithelial cells? Why?
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lumen: pH 2
Surface epithelial: pH 7 due to muci-bicarb layer |
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What do surface epithelial cells contain to prevent acid?
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Tiht junctions that are relatively impermeable to ions
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