McKenna's Pharmacology for Nursing, 2e

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P A R T 9  Drugs acting on the renal system

Efferent arteriole

Afferent arteriole

Glomerular (Bowman’s) capsule

Glomerulus

Proximal convoluted tubule Distal convoluted tubule

To renal vein From renal artery

Peritubular capillaries

Ascending limb Descending limb

FIGURE 50.2  The nephron—the functional unit of the kidneys. Secretion and reabsorption of water, electrolytes and other solutes in the various segments of the renal tubule, the loop of Henle, and the collecting duct can be influenced by diuretics, other drugs and endogenous substances, including certain hormones. In the kidneys, the distal convoluted tubule wraps around and is actually next to the afferent arteriole.

Loop of Henle

Collecting duct

Calyx

Blood supply The blood flow to the nephron is unique. The renal arteries come directly off the aorta and enter each kidney. As a renal artery enters each of the kidneys, it divides to form interlobar arteries, which become smaller arcuate (bowed) arteries and then afferent arterioles. The afferent arterioles branch to form the glomeru- lus inside Bowman’s capsule. The glomerulus is like a tuft of blood vessels with a capillary-like endothelium that allows easy passage of fluid and waste products. The efferent arteriole exits from the glomerulus and branches into the peritubular capillary system, which returns fluid and electrolytes that have been reabsorbed from the tubules to the bloodstream. These capillaries flow into the vasa recta, which flows into intralobar veins, which in turn drain into the inferior vena cava. The two arterioles around the glomerulus work together to closely regulate the flow of fluid into the glomerulus,

increasing or decreasing pressure on either side of the glomerulus as needed. Other structures A small group of cells, called the juxtaglomerular apparatus, connects the afferent arteriole to the distal convoluted tubule. This is where erythropoietin and renin are produced. Because of their proximity to the afferent arteriole, these cells are especially sensitive to the volume and quality of blood flow into the glomer- ulus. Surrounding the nephrons is an area called the macula densa, which consists of immune system cells and chemicals that can respond quickly to any cellular damage or injury. Nephron function The nephrons function by using three basic pro- cesses: glomerular filtration (passage of fluid and small