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83 Cards in this Set
- Front
- Back
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in which part of the SI does a large amt of digestion occur?
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duodenum, jejunum
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what are fold of kerckring?
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longitudinal folds of SI; villi project from the folds with microvilli on each intestinal cell
allows for massive incr in absorptive SA |
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what are cypts?
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projection down into the surface at the base of the villi (3 per villi)
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what are the 3 cells of the SI?
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enterocytes, goblet cells, crypt cells
replaced every 3-6 days |
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enterocytes of SI
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columnar epithelial cells that make up the villi
have microvilli from apical border digest, absorb, secrete |
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which enterocytes on a villi are best able to absorb and digest?
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the ones near the tip of the villi
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goblet cells and crypt cells of SI
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goblet-mucus
crypt-at base of villus; proliferative cells of intestine; form both enterocytes and goblet cells; secrete fluid, electrolytes |
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fxn of SI: (5)
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mix chyme with digestive juice, bile
reduce size of chyme particles to incr solubility bring chyme into contact with absorptive surface propel chyme into colon 2-4hrs to go length of SI |
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what are the 3 types of contractions in the SI?
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segmentation, peristaltic, migrating motility complex
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describe segmentation
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most common
contraction of one segment of circular smooth mm moves chyme in both directions-> mixes net movement towards colon b/c more contractions in proximal SI |
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fxn of peristalsis
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propel chyme
only covers short distances |
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describe the migrating motility complex (MMC)
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every 90 min
clears remaining chyme in SI (~ migrating myoelectric complex in stomach) |
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what must occur for contraction in SI?
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spike potentials must be present on top of slow waves (vs. stomach)
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what det the strength of the contraction?
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proportional to freq of spike potentials generated by amplitude of the slow wave
(grter amplitude of slow wave-> more spike potentials-> greater strength of contraction) |
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how does the freq of contractions change along the length of the SI?
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freq decr distally
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is SI motility affected by nervous system?
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yes
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what is the peristaltic reflex/rush?
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moves intestinal contents along SI
initiated by chyme that distends or irritates mucosa can also be caused by infectious diarrhea |
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what is the intestinointestinal reflex?
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overdistention of one segment of SI prevents contraction in rest of SI
prevents movement of material into already distended bowel |
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what is the gastroileal reflex?
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gastric empyting incr peristalsis in ileum and relaxes ileocecal sphincter to allow movement into colon
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what are the 2 types of cells of the pancreas rel to GI physio?
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acinar cells and ductal cells
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fxn of acinar cells of pancreas
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prod enzymes for digestion: peptidases, lipases, amylases
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fxn of ductule cells of pancreas
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rel pancreatic juice with high bicarb
neutralize acidic pH to allow max digestion by enzymes |
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what is the aqueous component of pancreatic secretion?
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isotonic with plasma at ALL rates of secretion
composed primarily of Na and Cl at slow rates; contains Na and HCO3 at high rates HCO3 higher than plasma but Cl lower than plasma; Na, K stay the same at all flow rates |
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initial pancreatic juice
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Na and Cl from acinus
modified by ductule and centroacinar cells which secrete HCO3 and absord Cl |
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transport across ductal cells of pancreas
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Na/H antiporter on basolateral surface (Na into cell, H into blood)
H in blood combines with HCO3 to form more CO2 that diffuses back into cell-> forms more HCO3 in the cell that is secreted into duct lumen in exchange for Cl Na/K ATPase on BL mbr keeps intracell Na low for Na/H exchange |
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how does venous blood from an actively secreting pancreas differ from nonactive?
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with active pancreas, more H is being transported into blood-> more acidic venous blood
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what det the rate of secretion of HCO3 into the duct lumen?
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the presence of Cl in the duct lumen; the presence Cl in the duct lumen dep on a fxning Cl channel in the apical mbr that moves Cl from cell into lumen (CF channel)
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what follows HCO3 into pancreatic lumen to keep neutral?
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Na
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how does water flow across ductule cell of pancreas?
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permeable to water; osmosis
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what comprises the enzymatic component of pancreatic secretion?
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active lipase and amylase
inactive proteases: typisin and chymotrypsin (activated in SI) trypsin inhibitor to prevent autodigestion |
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regulation of pancreatic secretion: cephalic and gastric phases
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ACh acts on acinar and ductule cells
vasovagal reflex stim by stomach distention-> secretion |
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when does most pancreatic secretion take place?
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intestinal phase (70%)
stim by acid, fat and protein in duodenum |
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how does acid in the duodenum activate pancreatic secretion?
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acid rel secretin from S cells of duodenum
Secretin acts on ductule cells to incr HCO3 secretion |
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how do fat and protein contribute to pancreatic secretion?
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stim rel of CCK from I cells of duodenum
CCK stim acinar cells to rel enzymes |
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describe the potentiation of pancreatic secretions?
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CCK and ACh potentiate actions of secretin on ductal cells
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how does pancreatic secretion resp to a meal?
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what is digested det what is secreted
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how does a high protein, low carb diet affect pancreas secretion?
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incr proteases, decr amylases
CCK incr expression of protease genes secretin and GIP in expression of lipase genes |
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pancreatitis: causes and forms
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due to gallstones or chronic alcoholism
acute and chronic forms |
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sx of acute pancreatitis
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severe abdominal pain
nausea and vomiting, diarrhea fever |
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what enzymes are elevated in pancreatitis?
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serum amylase and lipase
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chronic pancreatitis usually due to:
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recurring acute pancreatitis due to chronic alcholism
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CF:
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red secretion of aqueous and enzymatic components of pancreatic secretion: less aqueous-> concentrated pancreatic juice-> blocks secretion of enzymatic
sx: malabsorption and steatorrhea |
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what is bile req for?
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digestion and absorption of fats
excretion of water insoluble cholesterol and bilirubin |
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where is bile prod, stored, and what triggers its rel?
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prod cont by hepatocytes
stored in gallbladder rel when chyme triggers CCK rel which stim contraction of gallbladder and relaxation of sphincter of oddi |
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composition of bile
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bile acids
phospholipids cholesterol bile pigments electrolytes |
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where are bile acids prod? what do they eventually form?
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primary bile acids prod in liver from cholesterol
conjugated w/ glycine/taurine and Na in liver to form bile salts that are more water soluble |
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what is the fxn of bile salts?
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form micelles in which FFA,MAG, cholesterol and fat-soluble vitamins can be transported
bile salts amphipathic |
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what are the main phospholipids of bile? what is their fxn?
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lecithin
solubiized by bile salt micelles micelles able to solubilize other lipids better when they contain phospholipids |
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how is cholesterol incorporated into bile?
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solubilized by micelles and excreted in bile
bile is main excretory path for cholesterol via bile acids |
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what happens if more cholesterol is in diet than can be solubilized?
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crystal forms in bile and may seed gallstone formation
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what is the main component of bile pigments?
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bilirubin- breakdown prod of hemoglobin
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how is bilirubin made soluble? how is it excreted?
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conjugated to glucuronic acid in liver
excreted as soluble salt bilirubin glucuronide NOT part of micelles |
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what is the electrolyte composition of bile?
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Na, Cl, HCO3 (similar to pancreatic juice)
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what is enterohepatic circulation?
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circulation of bile salts at least 2X per meal (gallbladder, SI, portal circ, liver)
involved in bile secretion |
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what happens to bile salts when they are rel into the duodenum?
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most are ACTIVELY reabsorbed in terminal ileum
transported in portal circulation bound to plasma proteins |
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how are the bile acids-Na reabsorbed in the liver? electrolytes and water?
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bile acids reabsorbed via 2ndary active transport linked to Na reabsorption
req Na/K ATPase to keep intracell Na low electrolytes and water move along osmotic gradient to be added to bile in liver |
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what det the rate of bile sale syn in the liver?
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det by rate of return to liver
bile salts lost in feces replaced by syn in liver |
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what is the bile independent fraction of biliary secretion?
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dep on vol of water and electrolytes secretion due to presence of secretin
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what is the bile dependent fraction of biliary secretion?
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dep on amt of bile salts secreted by liver
amt secreted proportional to amt reabsorbed by liver |
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what is choleretics?
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bile salts and bile acids are potent stim of bile secretion
(they also inhibit new bile acid syn) |
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what are the 2 fxns of the gallbladder?
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store bile in interdigestive periods
concentrates bile by actively reabsorbing Na, Cl and HCO3; water follows |
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what are the 2 stim for gallbladder contraction?
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CCK and vagal activity
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when is CCK rel and what are its actions on the gallbladder?
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rel due to fatty acid and peptides in duodenum
stim gallbladder contraction and relaxation of sphincter of oddi |
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what are the 2 types of gallstones?
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cholesterol and pigment stones
cholesterol 70-80% in W. societies |
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how do cholesterol stones form?
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XS cholesterol cant be solubilized -> crystallizes
seed stone formation |
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how do pigment stones form?
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composed of Ca-bilirubinate
unconjugated blirubin formed in gallbladder; not soluble in bile precipitates with Ca-> seeds stone formation |
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how are gallstones treated?
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cholecystectomy- remove gallbladder
normal digestion and absorption unaffected; should avoid high fat foods bile empties slowly but continuously in SI |
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haustra of LI
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present when colon empty
sac-like |
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ileocecal sphincter
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relaxes when ileum distended
contracts when colon distended |
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segmentation contractions of LI
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majority of contractions in prox colon and distal colon
mix contents contribute to appearance of haustra |
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peristaltic contractions of LI
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moves chyme slowly down length of colon
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mass movements of LI
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peristaltic wave 1-3 times/day
moves contents long distances propels contents into rectum |
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contents of rectum
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usually empty
freq of segmental contractions greater in rectum than sigmoid colon-> moves material into sigmoid colon (allows for absorption of suppositories) |
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what is the rectosphincteric reflex?
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when fecal material moves into rectum, rectum contracts and internal anal sphincter relaxes
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when is the urge to defecate produced?
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when rectum filled 25%
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what prevents defecation?
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external anal sphincter (skeletal mm.)
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what happens if defecation doesnt occur after urge is produced?
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internal anal sphincter contracts and rectum relaxes to move feces back into rectum and urge to defecate subsides
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contents of feces
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inorganic material
undigested plant fibers bacteria and water contents rel unaffected by diet b/c lg amt of feces of nondietary origin ex: even if starving will defecate |
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hirschsprungs disease
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megacolon
absent enteric NS from segment of colon (normally inhibitory/regulates contractions) loss-> tonic contraction and contents accumulate proximal to segment severe constipation tx by removing segment |
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constipation
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MORE segmentation contractions
incr time through colon |
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what are some things that can lead to constipation?
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ignoring urge to defecate
lack of exercise meds-narcotics, antidepressants old age longterm use of laxatives |
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divertilulosis/ diverticulitis
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small finger-shaped pouches through weak colon wall
can be inflamed local pain can perforate wall may be due to longterm lack of fiber in diet many are asx |
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crohns disease
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breakdown of wall/transmural inflammation (primarily in SI)
tx with removal |
