netter106

Glomerular Filtratinn

RENAL PHYSIOLOGY

Colloid osmotic pressure of plasma

(U_ln)

Urine inulin concentralion

i 50    100    150    200

Arterial blood pressure |mm Hg)

Figurę 6.4 Glomerular Filtration-

n ultrafiltrate of plasma is produced at the glomerulus It is devoid of and viriually all protein. Smali moleculcs and ions are

at concentrations similar to those of plasma. Fhe glomerular kation ratc (GFR) is determined by the surface area and permeabil ot the glomerulus (K,) and the Starling forces across the capillary • jł. Intracapillary hydrostatic pressure promotes filtration, whereas «tra< apsular hydrostatic pressure and capillary colloid osmotic ■fKOtic) pressure generated by the plasma proteins oppose filtration. S GFR is rclativcly constant, despite variations in blood pressure ?. autoregulation). Changes in intracapillary hydrostatic pressure are responsible for physiologic regulation of the GFR. When acti-vated, sympathetic nerves constrict the afferent and efferent artere oles, redut ing intracapillary hydrostatic pressure and thus the GFR. Although not shown, mcreased delivery of NaCI to the matula densa decreases the GFR, whereas detreased dclivery inc/eases the GFR. A number of hormones can also alter the GFR. Angiotensin II, especially at high concentrations. constriets the afferent arteriole and reduces the GFR. Alrial natriuretic peptide and prostaglandin 6_: dilate the afferent arteriole and increase the GrR. The GrR can be measured with inulin.