Na+ H2O H2O H2O H2O H2O H2O H2O H2O H2O Cl-Cl-K+ K+ K+ H+ H+ H+glomerulus glucose amino acids polypeptides distal convoluted tubule collecting tubule proximal convoluted tubule loop of Henleurea thin descending limb collecting duct MEDULLA CORTEX urea distal straight tubule H2O Na+ organic acids Ca2+ Mg2+ Na+ Na+ Na+ Cl-thin ascending limb proximal straight tubule Active transport Active exchange Active cotransport Passive diffusion ADH-dependent H2O movement Aquaporin-dependent H2O movement (AQP)2 2 2 3 3 H+ bicarbonate anion bicarbonate anion Na+ Na+ K+ 1 1 K+K+ Cl-
FIGURE 20.23 • Diagram showing movement of substances into and out of the nephron and collecting system. The symbols indicate the mode of transport as noted in the key.
Interlobular arteries branch from the arcuate arteries and ascend through the cortex toward the capsule. Although the boundaries between lobules are not distinct, the interlobular arteries, when included in a section cut perpendicular to the vessel, are located midway between adjacent medullary rays, traveling in the cortical labyrinth. As they traverse the cortex toward the capsule, the interlobular arteries give off branches, the afferent arterioles, one to each glomerulus. A single afferent arteriole may spring directly from the interlobular artery, or a common stem from the interlobular artery may branch to form several afferent arterioles. Some interlobular arteries terminate near the periphery of the cortex, whereas others enter the kidney capsule to provide its arterial supply.
Afferent arterioles give rise to the capillaries that form the glomerulus. The glomerular capillaries reunite to form an efferent arteriole that, in turn, gives rise to a second network of capillaries, the peritubular capillaries. The arrangement of these capillaries differs according to whether they originate from cortical or juxtamedullary glomeruli.
 Efferent arterioles from cortical glomeruli lead into a peritubular capillary network that surrounds the local uriniferous tubules (G1 and G2, Fig. 20.24).
 Efferent arterioles from juxtamedullary glomeruli descend into the medulla alongside the loop of Henle; they break up into smaller vessels that continue toward the apex of the pyramid but make hairpin turns at various levels to
FIGURE 20.24 • Schematic diagram of the renal blood supply. The renal artery gives rise to interlobar arteries that branch into arcuate arteries at the border between the medulla and cortex. Interlobular arteries (IL) branch from the arcuate arteries and travel toward the renal capsule, giving off afferent arterioles to the glomeruli (G). Glomeruli in the outer part of the cortex (G1, G2) send efferent arterioles to the peritubular capillaries (PC) that surround the tubules in the cortex; glomeruli near the medulla (G3), the juxtamedullary glomeruli, send efferent arterioles almost entirely into the medullary plexus (MP) of capillaries via the arteriolae rectae spuriae (ARS). Blood returns from the capillaries via veins that enter the arcuate veins. Stellate veins (SV) near the capsule drain both the capsular (CC) and the peritubular capillaries.