Page 1020 - Fundamentals of anatomy physiology

are cortical nephrons, located almost entirely within the su- Chapter 26 The Urinary System 1007
perficial cortex of the kidney (Figure 26–7a,b). In a cortical
nephron, the nephron loop is relatively short, and the efferent Next let’s examine the structure of each segment of a rep-
arteriole delivers blood to a network of peritubular capillaries, resentative nephron.
which surround the entire renal tubule. These capillaries drain
into small venules that carry blood to the cortical radiate veins The Renal Corpuscle
(Figure 26–5c).
Each renal corpuscle is 150–250 m in diameter (Figure 26–8).
The remaining 15 percent of nephrons, termed juxta- It includes both the glomerular capsule and the capillary net-
medullary (juks-tuh-MED-u-la. r-e. ; juxta, near) nephrons, work known as the glomerulus (Figure 26–8a). The glomerular
have long nephron loops that extend deep into the medulla capsule is connected to the initial segment of the renal tubule
(Figure 26–7a,c). In juxtamedullary nephrons, the peritubular and forms the outer wall of the renal corpuscle. It encapsulates
capillaries are connected to the vasa recta (vasa, vessel + the glomerular capillaries.
recta, straight)—long, straight capillaries that parallel the
­nephron loop. The outer wall of the capsule is lined by a simple squamous
capsular epithelium (Figure 26–8a). This layer is continuous
Cortical nephrons do most of the reabsorption and se- with the visceral epithelium, which covers the glomerular cap-
cretion in the kidneys because they are more numerous than illaries. The capsular space separates the capsular and visceral
juxtamedullary nephrons. However, as you will see later in the epithelia. The two epithelial layers are continuous where the
chapter, it is the juxtamedullary nephrons that enable the kid- glomerular capillaries are connected to the afferent arteriole
neys to produce concentrated urine. and efferent arteriole.

The visceral epithelium consists of large cells with complex
processes, or “feet,” that wrap around the specialized dense layer

Figure 26–8 The Renal Corpuscle.

Glomerular capsule Podocyte Filtration
nucleus membrane
Capsular Glomerular Capsular Visceral
space capillary epithelium epithelium Fenestrated
(podocyte) endothelium

Efferent arteriole Proximal Mesangial Dense layer 26
convoluted cell
Distal convoluted Filtration
tubule tubule slits

Juxtaglomerular Capillary
complex endothelial
cell
Macula densa
Juxtaglomerular Pores

cells RBC

Pedicels
Podocyte

Capsular space

Afferent arteriole Capsular
epithelium

a Important structural features of a renal corpuscle. b This cross section through a portion of the
glomerulus shows the components of the
filtration membrane of the nephron.