Net Filtration Pressure (NFP) = GBHP – CHP – BCOP
Therefore, normal
NFP = 55 – 15 – 30
NFP = 10 mmHg .
Therefore, a pressure of only 10 mmHg causes a normal amount of blood plasma (minus plasma proteins) to filter from the glomerulus into the capsular space.
Glomerular Filtration Rate (GFR)
GFR: the amount of filtrate formed in all renal corpuscles of both kidneys each minute. In horses, GFR averages 2 mL/min/kg or about 1L/ min for a 500kg horse. Homeostasis of body fluids requires the kidneys maintain a relatively constant GFR. If GFR is too high, needed substances may pass so quickly through the renal tubules that some are not reabsorbed and are lost in the urine. If GFR is too low, nearly all the filtrate may be reabsorbed, and certain waste products may not be adequately excreted. GFR is directly related to pressures that determine NFP; any changes in NFP will alter GFR. Filtration ceases if GBHP drops to 45 mmHg because the opposing pressures add up to 45 mmHg (CHP + BCOP). NFP would now equal 0mmhg.
Mechanisms that regulate GFR operate in 2 main ways:
1. adjusting blood flow into and out of the glomerulus
2. altering the glomerular capillary surface area available for filtration.
Coordinated control of both afferent and efferent arteriole diameter regulates glomerular blood flow.
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