HUMAN BIOLOGY

the UrInary SyStem 235

the urinary system

The kidneys adjust the chemical

composition of the extracellular

fluid, including blood, in ways that

are essential to the survival of the

body as a whole. They remove

toxic nitrogenous wastes from the

breakdown of proteins. They also

maintain the balance of water,

electrolytes, and acids and bases in

the blood. The bladder, ureters, and

urethra provide for the storage and

elimination of wastes in urine.

in Homeostasis 13.14 Connections: The Nervous System

Skeletal system

The kidneys adjust blood levels of calcium

and phosphate used in building bone.

Respiratory system

Kidney adjustments in acid–base balance

complement shifts in the depth and rate of

breathing that help maintain pH of blood and

tissue fluid.

Digestive system

Kidneys convert vitamin D to a form that aids

absorption of calcium from food.

Nervous system

Kidney management of acid–base balance

helps ensure that nerve cells can function

properly.

Endocrine system

Kidney hormone erythropoietin is part of overall

hormonal controls in the body. Adjustments

that help maintain blood volume assist with

hormone transport in the bloodstream.

Muscular system

Adjustments in elimination of CO 2 help

manage hydrogen ions (H^1 ) in blood and so

help maintain blood pH (acid–base balance).

Cardiovascular system and blood

Kidney adjustments to water content of

urine help maintain blood volume. The

kidney hormone erythropoietin stimulates

the production of red blood cells.

Reproductive system

The male urethra also serves as a channel

for sperm ejaculated during intercourse.

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Immunity and the lymphatic system

Urine washes pathogens out of the urethra.

Adjustments to water and solutes in blood

plasma help assure adequate volume and

chemical composition of lymph.

12.8

ConneCtions

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