Page 1018 - Fundamentals of anatomy physiology

the glomerulus. The renal tubule begins at the renal corpuscle. Chapter 26 The Urinary System 1005
It is a long tubular passageway that may be 50 mm (1.97 in.)
in length. renal tubule. The renal tubule has three crucial functions:
(1) reabsorbing all the useful organic nutrients in the filtrate;
Blood arrives at the renal corpuscle by way of an afferent (2) reabsorbing more than 90 percent of the water in the fil-
arteriole. This arteriole delivers blood to the glomerulus (glo- trate; and (3) secreting into the tubule lumen any wastes that
MER-u. -lus; plural, glomeruli), which consists of about 50 inter- did not pass into the filtrate at the glomerulus.
twined capillaries. The glomerulus projects into the glomerular
capsule much as the heart projects into the pericardial cavity. The renal tubule has two convoluted (coiled or twisted)
Blood leaves the glomerulus in an efferent arteriole. It flows segments—the proximal convoluted tubule (PCT) and the dis-
into a network of capillaries called the peritubular capillaries, tal convoluted tubule (DCT). They are separated by a simple
which surround the renal tubule. These capillaries in turn drain U-shaped tube, the nephron loop, also called the loop of Henle
into small venules that return the blood to the venous system (HEN-le. ). The convoluted segments lie in the cortex of the
(Figure 26–7b,c). kidney, and the nephron loop dips at least partially into
the medulla. For clarity, the nephron shown in Figure 26–6
The process of filtration takes place in the renal corpuscle. has been shortened and straightened.
In this process, blood pressure forces water and dissolved sol-
utes out of the glomerular capillaries and into a chamber—the The regions of the nephron vary by structure and function.
capsular space—that is continuous with the lumen of the renal As the filtrate travels along the renal tubule, it is now called
tubule (Figure 26–6). Filtration produces an essentially protein- tubular fluid, and it gradually changes in composition. The
free solution, known as a filtrate, that is otherwise similar changes that take place and the characteristics of the urine that
to blood plasma. From the renal corpuscle, filtrate enters the result are due to the activities under way in each segment of
the nephron. Figure 26–6 and Table 26–1 survey the regional
specializations.

Figure 26–7 The Locations and Structures of Cortical and Juxtamedullary Nephrons.

Cortical
nephron

Juxtamedullary Cortex Peritubular Distal
nephron capillaries convoluted
Proximal tubule (DCT)
convoluted
Peritubular capillaries Distal tubule (PCT)
convoluted Renal
Efferent corpuscle
arteriole tubule
Afferent
arteriole 26

Medulla Renal Collecting
corpuscle duct

Collecting Collecting Vasa recta
duct duct

Papillary Peritubular
duct capillaries

Renal Nephron Nephron
papilla loop loop

Minor calyx c The circulation to a
juxtamedullary nephron
a The general appearance and location b The circulation to a
of nephrons in the kidneys cortical nephron