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160 Cards in this Set
- Front
- Back
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function of ICC
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interstitial cells of cajal: pacemaker cells
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GI smooth muscle resting potential?
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between -40 to -80 mV
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background oscillations in resting membrane potential are called
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slow waves or BER (basic electrical rhythm)
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what modulates the amplitude of slow waves?
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nerves and hormones
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PANS affect on slow wave amplitude?
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increases
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SANS affect on slow wave amplitude?
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decreases
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what controls the inherent excitability of pacemaker cells?
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tonic inhibition from inhibitory motor neurons
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what is the function of the cephalic phase of digestion?
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to prepare the GI to receive food
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Results of PANS stimulation during cephalic phase?
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increased salivation, gastric acid, pepsinogen, gastrin, pancreatic juice, bile
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functions of saliva
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Digestion: alpha-amylase, mucin to soften and lubricate food; protection: alkaline pH to neutralize acid, IgA, lysozyme, lactoferrin
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function of lactoferrin:
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binds iron and acts as a bacteriostat
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salivary glands consist of these two cell types:
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acinar cells: secrete saliva into acini; Duct cells: line salivary duct and secrete stuff to modify saliva composition
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two types of salivary acinar cells
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mucous and serous
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mucus acinar cells secrete:
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mucin glycoproteins
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serous acinar cells secrete:
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alpha amylase, water, K, Cl, Na, HCO3
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Innervation of salivary secretion
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PANS --> Ach --> M3 receptor on acinar and duct cells; SANS --> NE --> alpha and beta --> stims salivation
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Which cells are the primary H+ secreters?
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Parietal cells
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what is the alkaline tide?
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secretion of HCO3- into bloodstream by parietal cells as by product of acid secretion
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three direct stimulants of gastric acid secretion
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Ach, Gastrin, Histamine
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which neurons release Ach in enteric system?
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vagal post ganglionic and enteric neurons
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what does Ach bind in the enteric system?
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M3 receptor
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Which cells secrete gastrin?
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G cells
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What does gastrin bind?
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CCKb
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through which pathway do gastrin and Ach act?
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PLC to IP3 and DAG leading to increased intracellular Ca2+
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which cells secrete histamine?
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ECL and mast cells
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through which pathway does histamine act?
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adenylyl cyclase leading to increased cAMP and then PKA
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how do Ca and cAMP increase acid secretion?
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stimulate K+ channels on apical membrane, promote K+ efflux, hyperpolarizes the cell, promotes Cl- secretion into lumen; also increase insertion of Cl- chans and H+/K+ ATPase in apical membrane
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Pathophys of Zollinger-Ellizon Syndrome?
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gastrin producing tumor leading to excess production of gastric acid
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how does indirect gastrin stimulation work?
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gastrin and Ach induce ECL to release more histamine
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What does somatostatin do?
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reduces acid secretion
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How does somatostatin function?
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directly: reduces intracellular cAMP in parietal cells via receptors, indirectly by inhibiting gastrin and histamine secretion
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which D cells have direct contact with the lumen?
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those in the antrum
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what stimulates somatostatin secretion?
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protons in the antrum
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What inhibits somatostatin secretion?
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Ach
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describe stimulation in cephalic phase
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neural Ach directly activates parietal cells, indirectly activates ECL cells, antral vagal stim induces release of GRP, Ach inhibits somatostatin release
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describe stimulation in gastric phase
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distention triggers vagovagal response and release of Ach, partially digested prots in antrum stim release of gastrin
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which cells secrete pepsinogen?
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chief cells
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what stimulates mucus secretion?
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vagal Ach and mucosal irritation
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what is intrinsic factor used for?
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vital for B12 absorption
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describe process of B12 absorption
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B12 binds haptocorrin in stomach, duodenal proteases digest haptocorrin, B12 binds intrinsic factor and absorbed in ileum via receptors
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name two mediators which inhibit stomach contraction
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VIP and NO
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what stimulates Secretin release?
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acid
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what does secretin do?
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inhibits antral contractions and stimulates contraction of pyloric sphincter
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what induces CCK release?
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fat
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what does CCK do?
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stims vagovagal response to decrease gastric emptying, stimulates prot secretion from acinar cells
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function of Sphincter of Oddi?
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at junction between common bile duct at entrance into duodenum
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list pancreatic digestive enzymes (4)
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alpha amylase, lipases, proteases, nucleases
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List pancreatic lipases (4)
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pancreatic lipase, procolipase, phospholipase A2, carboxyl ester hydrolase
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List pancreatic proteases (5)
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trypsin, chymotrypsin, carboxypeptidase A and B, elastase
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which enzyme activates trypsinogen?
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enterokinase
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what is CCK
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hormone from small intestine
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which acinar receptors does CCK bind to?
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CCK-A
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Which hormones affect Acinar cells?
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CCK, Ach, VIP, Secretin
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What does Ach do to acinar cells?
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binds M3, stimulates protein secretion
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what is the mechanism of CCK and Ach in acinar cells?
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via IP3 to increase Ca2+
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which cells make secretin?
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intestinal endocrine cells
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which cells make VIP?
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pancreatic neurons
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what is the mechanism of Secretin and VIP?
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increase intracellular cAMP
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which hormones regulate duct cell secretion?
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Secretin and Ach stimulate it
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what stimulates CCK release?
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fatty acids and 8+ carbon monoglycerides, peptides and amino acids to a lesser extent
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functions of CCK (5)
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stim of pancreatic enzyme secretion, stim of gall bladder contraction, relaxation of Oddi, inhibits gastric emptying by pylorus constriction, appetite suppression
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most important function of secretin?
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increase bicarbonate secretion
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where are S cells found most?
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duodenum and proximal jejunum
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what is the composition of bile?
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bile acids, phospholipids, cholesterol, bilirubin pigments, inorganic ions
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whats the key acid for bile acid synthesis?
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7alpha-hydroxylase
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describe bile synthesis negative feedback?
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reabsorbed bile acids inhibit 7a-hydroxylase, reducing the use of cholesterol for new bile acids
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whats the starting substance for bile acids?
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cholesterol
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MMC associated with cycling levels of which peptide hormone?
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motilin
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diff between MMC and Phasic contractions?
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MMC: infrequent, long, entire intestine; Phasic: more freq, short, local
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two types of intestinal contraction
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segmented contractions and peristalsis
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two excitatory neurotransmitters that activate circular muscle to contract
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Ach on muscarinic receptors and substance P on neurokinin receptors
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two inhibitory neurotransmitters that act on circular muscle
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VIP and NO
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two forms of dietary starch:
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amylase (linear glucose polymer), amylopectin (large branched glucose polymer)
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sucrose is?
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glu-fru
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lactose is?
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glu-gal
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maltose is?
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glu-glu
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dietary fiber composed of?
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cellulose and pectin
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two stages of dietary carb digestion
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alpha amylase cleaving interior 1,4 linkages, then cell surface oligosaccharidases
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name groups of oligosaccharidases
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lactase and alpha-glucosidases
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what are the end products of disaccharide digestion?
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glucose, galactose, fructose
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Glucose and galactose enter apical membrane via?
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cotransport w/ Na through SGLT1
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fructose enters apical membrane via?
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facilitated diffusion through GLUT5
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monosaccharides leave cell on basolateral side via?
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GLUT2, Na+ independent
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what is responsible for peptide digestion in the stomach?
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pepsin and acid
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where does most peptide digestion occur?
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duodenum and jejunum by pancreatic proteases
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how are peptides absorbed?
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di/tri peptides absorbed by H+/oligopeptide cotransporter PepT1
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what generates the proton gradient for PepT1?
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Na/H transporter
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how are amino acids absorbed?
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via Na+/amino acid cotransport
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which enzymes responsible for early fat digestion?
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lingual lipase from saliva and gastric lipase from chief cells
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what do lingial and gastric lipases do?
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release fatty acids from triglyc, leaving diglyc
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where does most lipid digestion occur?
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duodenum and jejunum by pancreatic lipase
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pancreatic lipase requires this for full activity
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alkaline pH and colipase
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fatty acids absorption enhanced by?
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acidic pH: get protonated (neutral now) and diffuse into cell
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what do fatty acid binding proteins do?
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bind and transport newly absorbed fatty acid to ER
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where are most water soluble vitamins absorbed?
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jejunum
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where are B12 and vit. C absorbed?
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Ileum
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describe B12 absorption
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binds R proteins in saliva and gastric fluid, R cleaved in duodenum, B12 binds intrinsic factor, binds receptors in ileum, shows up in blood bound to transcobalmin II
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what are the fat soluble vitamins?
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A, D, E, K
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which of the fat soluble vitamins require energy for absorption?
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K, needs transporter
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Describe Vitamin A absorption
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absorbed as beta carotene, cleaved into 2 retinol molecules, transported in blood via retinol binding proteins
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describe mass peristaltic movements
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strong prolonged contractions that occur 3-4 times a day
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what is colonocolonic reflex?
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contraction of one part of colon leads to relaxation in other parts
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what mediates colonocolonic reflex?
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enteric reflexes and sympathetic nerves
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what is the gastrocolic reflex?
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when food enters stomach, colon motility increases
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what modulates gastrocolic reflex?
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gastrin and CCK
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what is Hirschsprung's disease?
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absence of enteric neurons from parts of colon due to failure of neural crest cell migration, lose colonocolonic reflex
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what does Hirschsprung's disease cause?
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constipation and megacolon
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how to treat hirschsprung's disease?
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surgical excision of affected colon
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mechanisms of water transport across intestinal cells
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paracellular and transcellular via aquaporins
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list 4 mechanisms of Na+ absorption
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cotransport w/ organics, Na+/H+ antiporter, help of Cl-/HCO3- transporter, and ENaC
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mechanism of potassium transport?
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paracellular and transcellular via aquaporins
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mechanism of intestinal secretion
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water secretion dependent on Cl-, from Na+/K+/2Cl- on basolat and CFTR on apical
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mechanisms of transport regulation
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hormonal: corticosteroids, mineralicorticoids, angiotensin, epinephrine stimulate absorption; neuronal: VIP and Ach stim secretion; immune: mast cells release histamine which stims secretion
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liver receives blood from these two sources:
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portal vein and hepatic artery
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percentage of liver blood flow from portal vein and hepatic artery
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portal vein: 70%, hepatic artery: 30%
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what is hepatic arterial buffer response?
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balance between blood from from hepatic artery and portal vein to maintain constant flow
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what mediates arterial buffer response?
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adenosine
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portal hypertension accurs beyond what blood pressure?
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>5 mm Hg within the liver
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what is budd-chiari syndrome?
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thrombotic occlusion of the hepatic veins at their opening into the IVC
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mediator of vasoconstriction in the liver
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endothelins
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mediator of vasodilation in the liver
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NO
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functions of liver?
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synth of plasma proteins, blood protection/clearance, bile, solubilization/transport/storage, energy generation/substrate conversion
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which plasma proteins does the liver produce?
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albumin, vitakim K dependent clotting factors, substrate binding proteins, hormones (angiotensinogen, IGF-1)
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protective functions of liver
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phagocytic/endocytic effects of kupffer cells, ammonia metabolism, glutathione synthesis, drug detox
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role ammonia metabilism in liver
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convert toxic ammonia (product of protein metabolism) into urea for excretion
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what is glutathione?
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major cytoplasmic reducing agent, crucial for preventing oxidative damage to proteins
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function of Phase I drug detox reactions
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redox rxns, add oxygen containing group to drug
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function of Phase II drug detox reactions
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covalent attachment t owater soluble carrier molecule (glucuronic acid or glutathione)
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which enzyme is responsible for phase I reactions?
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Cyp450
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what are Phase III drug detox reactions?
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energy dependent pathways for excretion of drugs
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downside of phase I rxns?
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generally convert substances into more toxic intermediates
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which hormone controls gallbladder secretions?
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CCK
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bile acids synthesized by liver are called?
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primary bile acids
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two major primary bile acids are:
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cholic acid and chenodeoxycholic acid
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what are secondary bile acids?
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primary bile acids which have been metabolized by bacteria
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two major secondary bile acids?
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deoxycholic acid and lithocholic acid
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what prevents bile acids from destroying hepatocyte cell membrane?
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cytosolic bile acids bound to bile-acid binding proteins
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what is the key phospholipid in bile?
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lecithins
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what happens to porphyrin from hemoglobin?
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converted to bilirubin
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what is indirect bilirubin?
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bilirubin bound to albumin
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what is direct bilirubin?
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bilirubin after it has been conjugated to two glucuronic acids, water soluble
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what excretes phospholipids?
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MDR2
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where is transferrin synthesized?
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liver
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role of liver and vitamins?
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serves as storage site and actively participates in metabolism
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where is Vitamin A stored?
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liver
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describe vitamin A metabolism
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absorbed, esterified to retinyl esters into chylomicrons, metabolized to retinol, bound to Retinol Binding Protein, transferred to stellate cell, stored in lipid droplets
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describe vitamin D metabolism
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VitD synth from preVitamin D in skin or absorbed in intestine, hydroxylated, hydroxylated again in kidney to 1,25 dihydroxy vitamin D
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what does vitamin E do?
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potent antioxidant, protects membrane structures against free radicals and lipid peroxidation
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describe vitamin E metabolism
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some trnasferred to HDL and LDL, some to liver, packaged into VLDL for distribution
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role of liver in B12 absorption?
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produces transcobalamin II, plasma protein, which binds B12 and takes it to liver
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understand Zonal Gradients
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outer zone (1): most oxygenated, high glucose, inner zone (3) least oxygenated
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what does Zone I do?
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oxidative metab olism, beta oxidation, gluconeogenesis, amino acid metabolism, cholesterol synth, bile formation
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what does Zone III do?
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xenobiotic metabilism, glycolysis, liponeogensis, glucose utilization
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how to control liver function?
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via substrates, hormones, receptors, gene expression changes
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acetominophen intermediate after Phase I?
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NAPQI - very toxic
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how is liver function controlled by substrates?
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glucose enters via GLUT2, phosphorylated: prevents glucose from leaving cell and maintains gradient
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effects of glucagon and epinephrine on liver?
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stimulate glycogen breakdown into glucose
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describe apotransferrin receptor function in liver
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in normal pH low affinity for apotransferrin but high affinity for transferrin, in low vesicle pH, increased affinity for apotransferrin and low affinity for transferrin…this induces iron release
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what is apotransferrin?
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transferrin without iron bound
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hormones critical for hepatocyte regeneration?
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EGF, TGF-a, HGF
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