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  • Define renal blood flow, renal plasma flow, glomerular filtration rate, and filtration fraction, and give normal values.

  • State the formula relating flow, pressure, and resistance in any vascular bed.

  • Identify the successive vessels through which blood flows after leaving the renal artery.

  • State the relative resistances of the afferent arterioles and efferent arterioles.

  • Describe how changes in afferent and efferent arteriolar resistances affect renal blood flow.

  • Describe the three layers of the glomerular filtration barrier and define podocyte, foot process, and slit diaphragm.

  • Describe how molecular size and electrical charge determine filterability of plasma solutes; state how protein binding of a low-molecular-weight substance influences its filterability.

  • State the formula for the determinants of glomerular filtration rate, and state, in qualitative terms, why the net filtration pressure is positive.

  • State the reason glomerular filtration rate is so large relative to filtration across other capillaries in the body.

  • Describe how arterial pressure, afferent arteriolar resistance, and efferent arteriolar resistance influence glomerular capillary pressure.

  • Describe how changes in renal plasma flow influence average glomerular capillary oncotic pressure.

  • Define autoregulation of renal blood flow and glomerular filtration rate.


image The volume of blood flowing through the kidneys is huge relative to their size or metabolic need. Renal blood flow (RBF) is 1 L/min, representing 20% of the resting cardiac output. This is through a tissue that constitutes less than 0.5% of the body mass! Considering that the volume of each kidney is less than 150 cc, this means that each kidney is perfused with over three times its total volume every minute. All of this blood is delivered to the cortex. About 5% to 10% of the cortical blood flow is then directed to the medulla before returning to the general circulation. When discussing RBF it is important to keep in mind the unique arrangement of the renal vasculature. This organization is critical for renal function, over and above the necessity of providing oxygen and nutrients.

Blood enters each kidney at the hilum via a renal artery. After several divisions into smaller arteries blood reaches arcuate arteries that course across the tops of the pyramids between the medulla and cortex. From these, interlobular arteries (also called cortical radial arteries) project upward toward the kidney surface. These arteries give off numerous arterioles, each of which leads to an individual Bowman’s capsule and the glomerulus within (see Figure 2–1). These arteries and glomeruli are found only in the cortex, never in the medulla. The arterioles leading to glomeruli are called afferent arterioles and have important functional characteristics discussed later. In most organs, capillaries recombine to form the beginnings of the venous system, but the glomerular capillaries instead recombine to form another set of arterioles, the efferent arterioles. The vast majority of the efferent arterioles soon subdivide into a second set of capillaries called peritubular capillaries. These capillaries are widely distributed throughout ...

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