HK 3810 Package 2 Kidneys.docx

Products move from the lumen of the tubule and into

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Products move from the lumen of the tubule and into the ISS The ISS has volume and pressure Pressure in the PTC is low, but the blood gets concentrated as it moves through the glomerulus, so there is high oncotic pressure in the PTC There is small pressure to move volume from PTC to ISS, but larger drive to move fluid from ISS to PTC Delta P < delta Pi, so always reabsorbing NOTE: In the level of the kidney, we’ve split filtration and reabsorption into 2 capillary beds; filter in glomerulus, reabsorb in PTC Movement of substrates from proximal tubule into ISS (which is important to move it from ISS and into PTC) Only place to get phosphate, glucose, lactate back There are 2 different cell types Two fundamental ways to make a filter: make a membrane that takes out bad stuff or filter everything and take back what is wanted/needed Proximal tubule has symporters for glucose, AA, phosphate, lactate, bicarb to move them from lumen of tubule and into ISS There are also antiporters that help manage bicarb and H+ (acid base balance) CA is an enzyme that can convert CO2 and H2O to carbonic acid to dissociate to H+ and bicarb, then bicarb can move to lumen of tubule or ISS We have the ability to secrete anions (bile salts, cAMP, penicillin) and cations (epi/NE, morphine) from blood space to ISS then from ISS to lumen of tubule using transporters Ions (Na+, Cl-, H2O, K+ Ca2+, urea, CO2) can also be moved through diffusion between tight junctions and through cells Solvent drag is when H2O moves whatever is dissolved in it with it H2O moves by osmosis and through aquaporins (H2O channels) Ionic capture is another system which splits glutamine into bicarb and ammonia, then there are transporters for the ammonia If ammonia is attached to H+, it will become NH4+ then it cannot come back into the cell Regulation of proximal tubule reabsorption Autoregulation o Myogenic response Over a range of pressure, flow will stay constant Volume in the glomerulus will stay constant based on this mechanism Over a range of MAP, GFR will remain constant o Possible problem: increase GFR increase Q tubule decrease equilibration time decrease time to remove solutes in proximal tubule potentially lose solutes through excretion
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HK 3810 Package 2 Kidneys o GFR is a constant over a range of MAP: myogenic response, tubuloglomerular feedback Glomerulotubular balance – intrinsic control at the level of proximal tubule o If GFR increases increase tubular Q increase rate of reabsorption in PT o MECHANISM UNKNOWN Direct SNS innervation (neural) o Increase Na+ reabsorption increase H2O reabsorption Hormonal o EPI increase NA+ reabsorption increase H2O reabsorption o AII, ACTH increase Na+ reabsorption increase H2O reabsorption o ANP may act to decrease Na+ reabsorption decrease H2O reabsorption Loop of Henle Thin descending limb – H2O permeable, Na+ impermeable
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