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63 Cards in this Set
- Front
- Back
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What is the gastric mucosa for?
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Protection (protects normal ulcer formation)
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What are the 2 lines of defense of the gastric mucosa?
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1) Muci-bicarb layer: 1st line of defense. As H+ penetrates, its neutralized by HCO3-. Most H+ won't reach epithelial
2) GMB (gastric mucosal barrier): Main defense, physiological barrier |
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What is reepitheliazation?
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Rapid cell turnover
-> if H+ does penetrate the barrier, hurts the cells .: replace them very quickly |
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What causes ulcers?
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1) weak barrier: some defense is damaged and H+ can pass; can be caused by aspirin or H. pylori
2) excessive HCl output: defense becomes overwhelmed; usually caused by tumours that produce gastrin |
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What are the phases of gastric secretion?
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Cephalic: psychic and gustatory (mediated by vagus)
Gastric: as meal arrives in the stomach Intestinal: when food arrives in stomach |
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Is there neural regulation at the level of the stomach?
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Yes
->Vagus and sympathetic Sympathetic: accompanied by vasoconstriction, inhibition of secretory activity |
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What regulates cephalic secretion?
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**Vagus
sympathetic |
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Does the vagus innervate directly?
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No, sends ACh that acts on nicotinic receptors which release ACh onto muscarinic receptors: cause parietal cells to secrete HCl
Peptic cells to release pepsin Mucous cells to release mucin Aso get Vasodilation (increase blood flow to the mucose) |
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What reflexes are part of the gastric phase of gastric secretion?
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Local reflex
Vago-vagal reflexes |
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What do the local enteric reflexes do?
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Cause Distension
->activates sensory enteric neurons |
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What do the vago-vagal reflexes do?
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Has both sensory and effectors in vagus (vagal trunk)
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What happens if ptns are out in the central region of the stomach?
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Produce a lot of HCl
-> make very little pepsinogen and mucin |
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What are secretagogues?
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Anything that causes secretion
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What do secretagogues do?
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Act on gastrin producing cells in ANTRUM to release gastrin
-> blood -> liver -> system Stimulate secretion of very large volume, of very acidic gastric juice (cuz works mainly on parietal cells) .: a lot of HCl |
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What does the antral region do?
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Stimulation of G-cells, which release hormnes (gastrin) in bloodstream (portal) than systemic
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What is gastrin released in reponse to?
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1) Secretagogues: products of ptn digestion
2) Local enteric reflexes (distension) which can activate exocrine gland. Enteric neurons can stimnulate gastrin producing cells to release the H 3) Vagally-mediated reflexes: results in release of gastrin |
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What does gastrin in the antrum do?
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Acts specifically on parietal cells
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What controls the cephalic phase?
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Neural mechanism (mainly)
Hormonal (secondary) |
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What happens in the cephalic phase?
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Vagally-mediated release of GASTRIN
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How is gastrin self-regulating?
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Negative fdbk mechanism
-G cell sensitive to pH in antrum -if pH<2, then G cell shuts off, gastrin production stops -less stimulation of parietal cells -less acid made -pH in antrum increasess ->G cell released from inhibition, back to Positive fdbk |
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Why is there inhibiton of G cells?
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1) they may have pH receptors
OR 2) Somatostatin (SS) released in low pH inhibits G-cell |
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What is gastrin?
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hormone released by gastric cells, activates parietal cells to secrete HCl-
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What are the physiological roles of gastrin?
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1) HCl secretion
2) Trophic effect: promotes growth of parietal cells |
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What happens to parietal cells in the absence of gastrin?
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Entire mucosa atrophies and parietal cells decrease in number
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What effect does Histamine have?
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Lots of histamine in the gastric mucosa
Adding histamine makes a large volume of gastric juice (with a lot of HCl) ->Histamine has the same effect as gastrin |
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What is the receptor interaction hypothesis?
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SEPARATE receptors for histamin, gastrin, ACh
-> interaction among the 3 receptors (histamine, ACh, gastrin) -Blockade/stimulation of one receptor changes the properties of one or both of the other 2 receptors |
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What is the permissive hypothesis?
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histamine increases sensitivity of parietal cells to gastrin and ACh
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What happens if action of histamine is blocked by H2-antagonists??
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Inhibits acid secretion in response to ACh and Gastrin
according to permissive hypothesis |
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What is the intestinal phase (excitatory or inhibitory)? How?
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Inhibitory
Entry of a meal in the duodenum will send a message to slow down gastric emptying When chyme enters the duodenum, will give rise to inhibition of gastric juice secretion |
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What does the enterogastric reflex do?
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Inhibits gastric motility and secretion (don't want to get too acidic)
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How is the intestinal phase inhibitory (through which systems)?
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Via ENS and ANS: inhibit gastric juice production in fundus/corpus
Enterogasric reflex: inhibits gastric emptying .: stay longer in the stomach) |
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What causes optimal secretory activity?
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Interplay betweenneural and hormonal mechanisms
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What mediates the cephalic phase?
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Vagus
Vagally-released gastrin |
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What mediates the gastric phase?
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Local enteric reflexes
Vago-vagal reflexes Inhibition of/Gastrin release |
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What mediates the intestinal phase?
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Excitatory and inhibitory aspects via enterogastric reflexes and enterogastrone hormonal complex release
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What does salivary amylase do?
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Polysac --> Disacc (in the mouth)
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What does gastric pepsin do?
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Some ptns --> polypeptides
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What happens to lipids before they reach the intstine?
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Not much changes
Lipids---> Di-, monoglycerides, FA |
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What happens in the upper intestine?
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Neutralization: has to take place cuz the intestinal tract doesn't havr a protective barrier
Osmotic Equilibration: isotonic by the time it leaves duodenum (permeable to H2O) Digestion continues Absorption begins (no absorption before this) |
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What are the 2 functions of the pancreas?
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Endocrine (glucose levels)
Exocrine (digestive system) |
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What are the characteristics of pancreatic juice?
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Vol: 0.5-1.5 L/day
Isotonic: 300mOsm Main electrolytes: Na+, K+, Cl-. HCO3- pH:7.2-8.2 |
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What are the enzymes in the pancreas?
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Amylases
Proteases Lipases (3g% protein: very large amount of ptn/100mL) -> mostly enzymes |
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What does pancreatic amylase do?
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at pH 7
Polysac ---> Disac |
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What must happen to polysac before they are absorbed?
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Disacs must firt be converted to monosac
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Why are proteases secreted in the pancreas as proenz?
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Don't want to break down ptn in the pancreas cuz can end up killing the pancreas
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Where is trysinogen made?
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Pancreas
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What activates trypsin?
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Enterokinase
Trypsinogen --> Trypsin -Trypsin: + fdbk: activates trysinogen |
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Why is the activation of trypsin critical?
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Activates a bunch of other inactive proteases
Chymotrypsinogen --> chymotrypsin Proelastase --> Elastase Procarboxypeptidase --> Carboxypeptidase |
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What does the trypsin inhibitor do?
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Inactivates trypsin
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What secretes the trypsin inhibitor?
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The same cells that secrete proteases of the pancreas
->trypsin inhib prevents activation of trypsin, in the secretory cells and in the ducts of the pancreas ->since trypsin activates many of the other proteases, inhibiting trypsin inhibits activation of them too |
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What does lipase do?
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breaks down mono- and diglycerides into fatty acids, needs to be bound to co-lipase to be effective
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What do bile salts do?
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form water soluble complexes with fat molecules to assist in absorption of fat soluble molecules like vitamins; form micelles.
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Which organ secretes bile? How much?
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liver: .5-1L/day
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Does bile have digestive enz?
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No
but is required for fat digestion |
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What does the sphincter of Oddi do?
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diects bile from liver to gallbladder
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Does the gall bladder synthesize bile?
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No (just stores it)
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Describe liver bile composition.
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Volume: 0.5-1L/day
Isotonic fluid: Na+, K+, Cl-. **HCO3- pH: 7.8-8.2 |
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What are the solids in liver bile composition?
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~3g%
Bile acids (salts) Bile pigments Cholesterol Phospholipids |
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How is bile secreted?
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Continuously *total vol of 0.5-1L/day)
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How does bile enter the duodenum? Why?
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Intermittently
Why: during interdigestive period, sphincter of oddi is closed .: bile goes through cystic duct -> gall bladder, where it is stored |
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What volume of can the gallbladder store?
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50 mL
-> a lot of water and ions in the galls bladder will have been reabsorbed, making [solids] much higher -> 10-20% |
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What are the fcts on the gallbladder?
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1) Concentrates solids:
hepatic bile 3% **gall bladder bile 10-20% (because fluid is reabsorbed) 2) Reduces pH: hepatic bile: 7.8-8.2 *Gallbladder bile: 7.0-7.5 3) Increases viscosity: also because mucin is excreted |
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What happens if the gall bladder is removed (cholesystectomy)?
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Even when removed, there is enough bile salts to digest fat in the diluted bile
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