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Determinants of GFR

Determinants of GFR. GFR = Capillary filtration coefficient X Net filtration pressure. Increased glomerular Capillary filtration coefficient increases GFR. Probably not a primary mechanism for day-to-day regulation of GFR.

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Determinants of GFR

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  1. Determinants of GFR • GFR = Capillary filtration coefficient X Net filtration pressure. • Increased glomerular Capillary filtration coefficient increases GFR. • Probably not a primary mechanism for day-to-day regulation of GFR. • Glomerular Capillary filtration coefficient is changed in some disease states such as diabetes millitus.

  2. Determinants of GFR • GFR = Capillary filtration coefficient X Net filtration pressure. • Increased hydrostatic pressure in Bowman’s capsule decreases GFR (inverse is also true). • Normally, not a primary mechanism for day-to-day regulation of GFR. • Hydrostatic pressure in Bowman’s capsule can change in some pathologic conditions such as obstruction of the urinary tract. Guyton’s Textbook of Medical Physiology 26-12

  3. Determinants of GFR • GFR = Capillary filtration coefficient X Net filtration pressure. • Increased glomerular capillary colloid osmotic pressure decreases GFR. • Two factors regulate glomerular capillary colloid osmotic pressure: • Arterial plasma colloid osmotic pressure. • Filtration fraction. Guyton’s Textbook of Medical Physiology 26-12 & 13

  4. Determinants of GFR • Increased glomerular capillary colloid osmotic pressure decreases GFR (cont.) • Filtration fraction = GFR/renal blood flow • Such that, a lower rate of blood flow into the glomerulus causes an increase in the filtration fraction • decreased plasma volume with constant filtration volume increasing the protein concentration. • results in an increase in Glomerular colloid osmotic pressure which tends to decrease GFR. • inverse is also true.

  5. Determinants of GFR • GFR = Capillary filtration coefficient X Net filtration pressure. • Increased glomerular capillary hydrostatic pressure increases GFR. • Three variables determine the glomerular hydrostatic pressure. • Arterial pressure. • Afferent arterial resistance. • Efferent arterial resistance. Guyton’s Textbook of Medical Physiology 26-12

  6. Determinants of GFR • Increased arterial pressureincreases glomerular capillary hydrostatic pressure resulting in increased GFR. Sherwood’s Human Physiology 14-10 & 14-11 5th Ed & 14-9 & 14-10 6th Ed

  7. Determinants of GFR • Increased afferent arterial resistancedecreases blood flow to the glomerular capillary resulting in decreased glomerular capillary hydrostatic pressure and reduced GFR. Sherwood’s Human Physiology 14-10 & 14-11 5th Ed & 14-9 & 14-10 6th Ed

  8. Determinants of GFR • Decreased afferent arterial resistance(dilation) _increases_ glomerular capillary hydrostatic pressure and GFR. Sherwood’s Human Physiology 14-10 & 14-11 5th Ed & 14-9 & 14-10 6th Ed

  9. Determinants of GFR • Moderate increases in efferent arterial resistance(constriction) increase glomerular capillary hydrostatic pressure and slightly increases GFR. Guyton’s Textbook of Medical Physiology 26-12

  10. Determinants of GFR • A severe increase in efferent arterial resistance (constriction)increases glomerular capillary hydrostatic pressure, but also increases the colloid osmotic pressure (due to the decreased renal blood flow). This results in a net decrease in GFR. Guyton’s Textbook of Medical Physiology 26-14

  11. Renal blood flow • The Kidneys get ~22% of the cardiac output. • Greater than what is needed to supply kidneys with nutrients and remove waste products. • Great volume is necessary to supply enough plasma for high GFRs. • The renal cortex receives most of the blood. • The renal medulla receives only 1-2% of the blood. • Renal blood flow is determined by the pressure gradient across the renal vasculature divided by the total renal vascular resistance.

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