Renal Physiology. Dr. Mohammad K. Khan. Vascular (Renal Blood Flow and Glomerular Filtration Rate). Renal Blood Flow Renal blood flow (RBF) is regulated by changes in vascular resistance of all the arteries which is regulated by a variety of neurohormonal signals.
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Dr. Mohammad K. Khan
1.Transglomerular (hydraulic) pressure (TGP)—the most significant determinant of GFR. the glomerular capillary is unique in that it can regulate intraglomerular capillary pressure (IGP) independent of systemic pressures through changes in afferent and efferent arteriolar tone.
the pressure within Bowman's space is essentially zero
2.Renal plasma flow—is 20% but an increase in RPF leads to an increase in absolute GFR.
3.Glomerular permeability—an increase in permeability does not lead to an increase in GFR. It may, lead to increased filtration of larger molecules not normally filtered, such as albumin.
Reductions in permeability or in glomerular surface area can lead to reductions in GFR.
4.Oncotic pressure—Under normal circumstances, plasma proteins are not filtered across the glomerular membrane
1.Inulin. Inulin is a fructose polysaccharide, inulin clearance is the best measure of GFR. it is not clinically useful as it is difficult to administer and difficult to measure.
2.Radiolabeled compounds. These include iothalamate and diethylenetriaminepentaacetic acid (DTPA). These clearances are also very accurate but are limited in clinical use by their cost and availability
1. Plasma creatinine (PCr), the most widely used
2. Plasma urea
3. Plasma cystatin C
1.Cockcroft-Gault, originally developed from data collected from individuals with normal renal function, is a simple formula to estimate CrCl (not GFR) that corrects for age, sex, and body mass. The formula is
2. modification of diet in renal disease (MDRD) formulas. more accurate than the Cockcroft-Gault formula.:
-ionized-complexed with ions-protein bound
1,25-hydroxycholecalciferolincrease absorption of Ca + Ph in the gut
Dr. Mohammad K. Khan