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.

Determinants of GFR 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. GFR = Capillary filtration coefficient X Net filtration pressure. Guyton’s Textbook of Medical Physiology 26-12

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

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.

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

Determinants of GFR Increased arterial pressure increases glomerular capillary hydrostatic pressure resulting in increased GFR. Sherwood’s Human Physiology & th Ed & 14-9 & th Ed

Determinants of GFR Increased afferent arterial resistance decreases blood flow to the glomerular capillary resulting in decreased glomerular capillary hydrostatic pressure and reduced GFR. Sherwood’s Human Physiology & th Ed & 14-9 & th Ed

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

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

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

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.