April 8 Lectures

Danielson

kidneys regulate concentration of substances in blood and urine.  Concentration = amount/volume.  Therefore, concentration can change in two ways - changing amount or changing volume

use this to measure volume:  volume = amount/concentration; e.g., 8g/8g/L = 1 L 


Osmolarity - the most important osmolytes (particles that contribute to plasma osmolarity) are sodium, glucose, and BUN.  Sodium dominates because it is the major osmolyte in extracellular fluid.  [Na] x 2 = plasma osmolarity estimate.  Normal = 290 mOsm/L


How is osmolarity regulated?  Osmoreceptors in the hypothalamus detect osmolarity and regulate secretion of ADH.


sea water has osmolarity about 8 times higher than plasma (about 2000 mOsm/L)


practice questions using volume diagrams: 

http://www.boom-outahere.com/boardreview/generalcell.html 



Naik

Important note: afferent and efferent arterioles are sites of resistance and that are in series; i.e., the total resistance is the sum of the two.  Rt = Ra +Re.  Need to Know how changes in Raff and Reff affect capillary P (GFR) and renal plasma flow (RPF).
Good summary figure from First Aid:

JGA line afferent arteriole. secrete renin and serve as baroreceptors.
glomerular caps = high pressure, high surface area, leaky (fenestrated) = high volume of filtration

peritubular caps = low pressure, higher oncotic pressure = high volume of reabsorption.  vasa recta caps maintain osmotic gradient.


myogenic reflex is primarily occurring in afferent arterioles.


macula densa cells in distal convoluted tubule sense salt and water delivery to DCT
feedback control.  inc. GFR = inc. Na delivery = release of adenosine, etc. = constriction of afferent arteriole = dec GFR.


JGA cells, increase stretch = depolarization = inc. Ca = DECREASE in renin release (opposite to neurons)


ANP dilates afferent and constricts efferent arterioles = double increase in GFR; decreases Na reabsorption in collecting duct
BNP from ventricle has longer half life than ANP = more useful as clinical marker.


Prostaglandins (PGI2, PGE2) don't alter renal blood flow under normal conditions but may buffer vasoconstriction effects; e.g., fight or flight sympathetic activation vasoconstricts both afferent and efferent but this is reversed by prostaglandins released by kidney.  also important in settings of volume depletion.  dangerous to use NSAIDS if volume depletion will occur.