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44 Cards in this Set

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What makes lipids soluble so that they can be digested?
bile added to the intestine in the duodenum acts as a detergent
What is bile made up of?
-bile acids (60%)
-water and electrolytes
-cholesterol
-phospholipids
-proteins
-wastes (bilirubin, drug metabolites)
Where are bile acids made?
the liver
What is the functional unit of the liver?
the liver lobule
What is the significance of having fenestrated sinusoids in the liver?
they allow direct contact and exchange between the blood and the hepatocyte -- hepatocyte can remove large amts of material from the blood
What is bile made from?
cholesterol
Are bile salts coming into the liver in the hepatic vein reused or discarded?
they are reused by being imported into hepatocyte via Na+ dependent transport, then go out into bile canniliculi
Which hormone stimulates secretion of HCO3- in the duct cells of the bile duct?
secretin
Where does bile empty into the duodenum?
sphincter of oddi via the common bile duct (it is combined with pancreatic juices from the pancreatic duct here)
How much does the gall bladder concentrate bile?
10-20x
What reflexes control the contraction of the gall bladder and relaxation of the sphincter of oddi after a fatty meal?
1) neural (local and vagal)
2) hormonal (CCK)
Whare are bile salts reabsorbed in the intestine?
the terminal ileum

(actively via Na linked carrier mechanisms and passively due to lipid solubility)
How often is the bile salt pool recirculated (enterohepatic circulation)?
2x during a normal meal
How much bile salts are made daily?
about 20% to match amount lost in feces daily
Name 2 examples of primary bile acids (synthesized de novo by hepatocytes from cholesterol).
1) cholic acid
2) chenodeoxycholic acid
What is the difference between primary and secondary bile acids?
secondary bile acids are modified by bacteria in the intestine which dehydroxylate them
Name some examples of secondary bile acids.
1) deoxycholic acid
(from cholic acid)
2) lithocholic acid
(from chenodeoxycholic acid)
Which is better at digesting fats, primary or secondary bile acids?
primary bile acids

- because as lose OH-, less able to digest fats (secondary bile acids have been dehydrated)
What are bile acids conjugated to and what is the result of the conjugation?
- conjugated to taurine or glycine
- makes more hydrophilic thus better at solubilizing fats
What is Critical Micelle Concentration?
a defined concentration of bile salts above which bile salts spontaneously form micelles
(it is specific to each bile salt)
How much do micelles increase the solubility of a FA?
1000x

(get digestion where lipase can contact lipid)
What stabilizes lipid droplets to a greater extent, an emulsion or micelles?
micelles
What is the main form of ingested lipids?
TGs
What molecule must pancreatic lipase work with to act at oil/water interface to begin hydrolyzing ester linkages?
Co-lipase
Explain the cycle of a micelle.
- pancreatic lipase/co-lipase bkdn lipids into 2FFAs and 1 2-MG - these + chol, PL etc form micelles - move to gut wall - release contents to cross gut wall - return to lumen
Where in the small intestine does most of the absorption of lipolytic products occur?
in the jejunum

(take as while to "get going")
What 2 things does the movement of Na+ in the gut depend on?
1) region of the gut
2) state of the gut (postprandial or interdigestive)
What kind of Na+ absorption predominates in the postprandial state?
nutrient-coupled (apical)


(Na/K ATPase (basolateral))
What kind of Na+ absorption predominates in the interdigestive state?
electroneutral NaCl absorption (apical)

(Na/K ATPase (basolateral))
How does most water enter enterocytes in the intestine?
thru the paracellular route due to "leaky" tight junctions

(less water absorption due to tight juctions when you move distally)
What 3 ways can change the "leakiness" of tight junctions in enterocytes?
1) NTs
2) hormones
3) nutrients (ex. glucose)
Is water and sodium absorption in the intestine energy-dependent?
yes - need ATP to move Na+ out of cells at basolateral surface via Na/K ATPase
Is K+ passively or actively absorbed in the small intestine?
passively when concentrations increase in ECF
Does the colon secrete or absorb K+?
secretes at luminal conc <25mM
absorbs at luminal conc 25+
List the state of Cl- and HCO3- in the small intestine and colon (in terms of secretion or absorption).
proximal duodenum - secretion of HCO3-
jejunum - net absorption of both HCO3- and Cl-
ileum and colon - chloride absorbed, HCO3- secreted
What 2 things increase the absorption of Ca?
1) PTH
2) Vitamin D
What distinguishes absorbed Ca (via intestine) and Ca for an AP?
absorbed Ca binds to a brush border membrane carrier protein, then a cytosolic Ca binding protein in the cell
What 2 things promote iron absorption?
1) acidic pH in stomach
2) Vitamin C
What form of Fe is most soluble?
Fe2+
What is the carrier protein associated with iron in the intestinal lumen?
transferrin
What is a Mucosal Block in reference to iron?
iron is stored in cells and is lost when cell is desquamated, chich prevents excess iron from entering blood (which would be toxic)
Which water soluble vitamins are NOT passively absorbed?
1) Vit C
2) Biotin
3) Vit B1
4) Vit B12
Can Vit B12 be absorbed normally?
No -- it must have intrinsic factor (which is secreted by oxyntic cells of stomac)
Are fat soluble vitamins solubilized in micelles and chylomicrons like lipids are?
Yes