HUMAN BIOLOGY

Studying the urinary system will tap your knowledge of

pH and buffer systems (2.7) and of osmosis and transport

mechanisms (3.10, 3.11).

You will also use what you have learned about blood

circulation (7.1) and the movement of substances into

and out of blood capillaries (7.7).

Key ConCepts

LinKs to earLier ConCepts

Ed Kashi/VII/Documentary/Corbis

Maintaining the

extracellular Fluid

The body must eliminate chemi-

cal wastes from extracellular fluid,

including the blood, and manage

the levels of water and solutes in

it. The urinary system performs this

task. S e c t i o n 12.1

Light or dark? Clear or cloudy? A lot or a little?

Like blood, urine can tell a lot about a person’s health. Acidic

urine can signal metabolic problems, while alkaline urine may be a

sign of a bacterial infection. Too much protein in urine might mean

the kidneys are not functioning properly. Specialized urine tests

can detect chemicals produced by certain cancers. Do-it-yourself

urine tests are popular for monitoring hormones that indicate a

woman’s fertile period or early signs she may be pregnant. Urine

can also tell the tale if you use any of a variety of illegal drugs.

That urine can be such a trusty indicator of health, the

presence of hormones, and drug use is a tribute to the urinary

system. As you will discover in this chapter, the kidneys are the

urinary system’s all-important blood filters.

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tHe urinary system

12 The Urinary System

The urinary system consists of the

kidneys, ureters, bladder, and ure-

thra. In the kidneys, structures called

nephrons filter substances from the

blood, eliminating unneeded ones in

urine. Section 12.2

How the Kidneys Form Urine

The kidneys form urine in steps

called filtration, reabsorption, and

secretion. Hormones and a thirst

mechanism adjust the chemical

makeup of urine. Sections

12.3 –12.5

Disorders of the Urinary

System Sections 12.6 –12.7

coNNecTioNS:

The Urinary System in

Homeostasis Section 12.8

Homeostasis preview

Blood filtering by the kidneys rids the body of excess water and

excess or harmful substances in the blood and other body fluids.

223

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