Facts on File Encyclopedia of Health and Medicine

PREFACE TO VOLUME 3

Volume 3 of the four-volume The Facts On File
Encyclopedia of Health and Medicine presents the body
systems that support the body through biochemical
functions. From the breakdown of foods into nutri-
ent forms the body can use to the intertwining of
hormones with nearly every other body system,
biochemistry is the basis of cellular function.

The Gastrointestinal System
Leading Volume 3 is “The Gastrointestinal Sys-
tem,” presenting the organs, structures, and func-
tions that deliver nutrients to cells throughout the
body. Complex biochemical processes break down
all consumed foods into their basic molecular
structures, the biochemical forms the body’s cells
can use.
No matter what a food’s original form—apple,
steak, french fries—the gastrointestinal system
reduces it to molecules. The body then uses the
molecules for fuel to maintain cellular activity and
metabolism. Among the nutrients essential to sus-
tain life are vitamins, minerals, carbohydrates,
proteins, and fats.
As efficient as these processes are for distilling
foods into nutrients, there is of course material
the body cannot digest or use. The gastrointestinal
system takes care of that, too, carrying solid waste
from the body.

The Endocrine System

The endocrine system is the body’s network of
glands and hormones. Glands produce hormones,
the chemical messengers that direct myriad activi-
ties within the body. The hormones the endocrine
system produces interact with every other body
system and are responsible for key functions such
as metabolic rate, blood pressure, and the sleep-
wake (circadian) cycle.

Hormones also manage the processes of diges-

tion. Fat molecules (lipids) are essential for the

production of many hormones. Estrogen brings

the process full circle through its role in how the

body breaks down and uses lipids.

The most common association many people

have with hormones is their role to regulate

growth and to initiate and maintain secondary

sexual characteristics and reproductive ability.

Following a person’s unique genetic blueprint,

hormones determine how fast and how tall the

person grows. Hormones also give a man his deep

voice and regulate a woman’s menstrual cycle.

The Urinary System

The urinary system contains the organs and struc-

tures that filter biochemical wastes from the blood

and excrete them from the body. All blood passes

through the kidneys, which filter from it the

wastes of cellular metabolism. If allowed to accu-

mulate in the blood circulation, these wastes rap-

idly become toxic. Through their filtration

functions, the kidneys also maintain the body’s

fluid and electrolyte levels to help regulate blood

pressure. These versatile organs also produce hor-

mones essential for blood pressure regulation.

The kidney was the first organ to be success-

fully transplanted, and today kidney transplanta-

tion is the most commonly performed transplant

operation. Thousands of people receive trans-

planted kidneys every year in the United States;

kidney transplantation is the only successful treat-

ment for end stage renal disease, a common com-

plication of diabetes and hypertension (high blood

pressure).

Some structures of the male urinary system—

the penis, urethra, and prostate gland—do double

duty as organs of the male reproductive system.

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