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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 an organ.

  • 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 3 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 amount of blood flowing through the kidneys is huge relative to their size. Renal blood flow (RBF) is about 1 L/min. This constitutes 20% of the resting cardiac output through tissue that constitutes less than 0.5% of the body mass! Considering that the volume of each kidney is less than 150 mL, this means that each kidney is perfused with over 3 times its total volume every minute. All of this blood is delivered to the cortex. About 10% of the cortical blood flow is then directed to the medulla.

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, cortical radial arteries project upward toward the kidney surface and give off a series of afferent arterioles (AAs), each of which leads to a glomerulus within Bowman's capsule (Figure 2–1). These arteries and glomeruli are found only in the cortex, never in the medulla. 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 (EAs). The vast majority of the EAs soon subdivide into a second set of capillaries called peritubular capillaries. These capillaries are profusely distributed throughout the cortex intermingled with the tubular segments. The peritubular capillaries then rejoin to form the veins by which blood ultimately leaves the kidney.

Figure 2–1.

The renal microcirculation. Arcuate arteries run just above the corticomedullary border, parallel to the surface, and give rise ...

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