Figure 36.3 The nephron Aflerent Arterioia Collecting Duct Distal Convoluted Tub

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Figure 36.3 The nephron Aflerent Arterioia Collecting Duct Distal Convoluted Tubui Eflerent Arteriole Glomerular Capsule Glomerulus Loop of Henle 10Interiobular Artery interiobular Vein Pertubular Capilaries Proximal Convoluted Tubule Renal Corpuscle upper end of the ureter. The indentation in the kid- Urine Formation ney where renal blood vessels and the ureter are Nephrons form urine by three processes: (1) filtration. joined to the kidney is known as the hilum (label 9). (2) reabsorption, and (3) secretion. In this way, water and essential substances in the blood are conserved The Nephrons The basic functional unit of the kidney is the cluding nitrogenous wastes (urea, uric acid, and nephron. There are about a million kidney. The enlargement in Figure 35.2 shows four mation maintains the normal concentration of sub- nephrons, and Figure 35.3 shows a single nephron in stances in blood plasma. greater detail. About 80% of the nephrons are located in the cortex. These are called cortical nephrons Figure 35.4. Note that the arteries and veins are (label 14 in Figure 35.2). The remaining nephrons, essentially parallel to each other. The renal artery the juxtamedullary nephrons, are located partially branches to form interlobar arteries that extend in the cortex and partially in the medulla. while the concentrations of surplus substances, in- creatinine), are reduced. The process of urine for- The blood supply to the kidney is shown in in each through the renal columns to form arcuate arteries Refer to Figure 35.3 as you study this section. that run along the base of the renal pyramids. The ar- Each nephron consists of two major parts: a renal cuate arteries give off small and numerous branches, corpuscle and a renal tubule. A renal corpuscle con-the interlobular arteries (label 2, Figure 35.3), sists of an inner tuft of capillaries, the glomerulus which permeate the cortex and give off extremely (label 5), and an outer, double-walled glomerular numerous branches, the afferent arterioles. capsule that envelops the glomerulus. A renal tu- afferent arteriole (label 3, Figure 35.3) carries bule consists of three sequential segments: (1) the blood to a glomerulus. An efferent arteriole (label proximal convoluted tubule, which leads from 4, Figure 35.3) carries blood from a glomerulus to the glomerular capsule; (2) the loop of Henle the peritubular capillaries (label 12, Figure 35.3) the downward U-shaped portion; and (3) the distal that enmesh the nephron tubule. From the capillar- convoluted tubule (label 10)-the terminal segment ies, blood drains into an interlobular vein, which that empties into a collecting duct. Several tubules opens into an arcuate vein. Arcuate veins empty empty into a single collecting duct. There are thou- into interlobar veins, which carry blood to the re- sands of collecting ducts in each renal pyramid. nal vein. Their presence produces the faint lines extending from the base to the apex of each pyramid. The efferent arteriole has a smaller diameter than the afferent arteriole. This difference elevates The Urinary Organs 195

Explanation / Answer

1) Interiobular vein

2) Interiobular artery

3) Afferent arteriole

4) Efferent arteriole

5) Glomerulus

6) Glomerular capsule

7) Renal corpuscle

8) Proximal convoluted tubule

9) Collecting duct

10) Distal convoluted tubule

11) Loop of Henle

12) Peritubular capillaries

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