Page 1017 - Fundamentals of anatomy physiology

1004 Unit 5 Environmental Exchange The Nephron

Renal nerves innervate the kidneys and ureters. Most of Recall that the kidneys remove wastes from the blood and help
the nerve fibers involved are sympathetic postganglionic fibers to regulate blood volume and blood pressure, blood ion levels,
from the celiac plexus and the inferior splanchnic nerves. and blood pH. In the kidneys, the functional units—the small-
est structures that can carry out all the functions of a system—
pp. 564, 574 A renal nerve enters each kidney at the hilum are the nephrons (NEF-ronz). Each nephron consists of a renal
and follows the branches of the renal arteries to reach indi- corpuscle and a renal tubule (Figure 26–6). The renal cor-
vidual nephrons. The sympathetic innervation (1) adjusts rates puscle (KOR-pus-ul) is a spherical structure consisting of the
of urine formation by changing blood flow and blood pres- glomerular (Bowman’s) capsule, a cup-shaped chamber approxi-
sure at the nephron; and (2) stimulates the release of renin, mately 200 m in diameter, and a capillary network known as
which u­ ltimately restricts water and salt loss in the urine by
stimulating reabsorption by the nephron. When a substance is
reabsorbed, it is “reclaimed,” eventually reentering the blood.

Figure 26–6 The Functional Anatomy of a Representative Nephron and the Collecting System.

The major functions and characteristic cells of each segment of the nephron (purple) and the collecting system (tan) are
noted. In this representative figure, the nephron has been significantly shortened and some components rearranged.

NEPHRON COLLECTING SYSTEM

Proximal convoluted tubule Distal convoluted tubule
• Reabsorption of water, ions, and
• Secretion of ions, acids, drugs, toxins
all organic nutrients • Variable reabsorption of water, sodium ions,
Cuboidal cells
with abundant and calcium ions (under hormonal control)
microvilli
Mitochondria Cuboidal cells
with few microvilli

Renal corpuscle Renal tubule

• Production of filtrate Descending Ascending Collecting duct
limb of limb of • Variable reabsorption of water and
Squamous cells loop ends
loop begins reabsorption or secretion of sodium,
Efferent arteriole Thick potassium, hydrogen, and
Afferent arteriole ascending bicarbonate ions
limb
Glomerulus Intercalated
Glomerular capsule cell
Principal cell
Capsular space
Papillary duct
26 Nephron loop • Delivery of urine to minor calyx
Squamous cells
Descending limb Columnar cells
Further reabsorption
of water

Ascending limb Thin
Reabsorption of descending
sodium and chloride
ions limb

Low cuboidal cells

KEY Solute reabsorption Minor
Filtrate or secretion calyx

Water reabsorption Variable solute
reabsorption or
Variable water secretion
reabsorption