The Skeleton

Say “skeleton” to children and you probably conjure up in their minds a rickety structure of rigid sticks, or, to the more fanciful child, a clickety-clacketing collection of rattling bones cavorting under a Halloween moon. A look at almost any anatomical drawing of the human skeletal system bears out the child's image: dry sticks of bones, stripped of skin and flesh, muscle and tendon—a grotesque caricature of a living human being.

The Muscles

Some 600 muscles of all sizes and shapes are attached to the framework of the skeletal system. Altogether these muscles make up nearly half of a normal adult's weight.

Skin, Hair, and Nails

Perhaps no other organ of the human body receives so much attention both from its owner and the eyes of others as the skin and its associated structures—hair and nails.

The Nervous System and the Brain

Most of us have heard often enough that the brain, acting as control center for a communication network we call our nervous system, is an incredible computer, weighing a mere three pounds. Its form and functions, however, are often described as being so much more intricate and complex than any existing or imagined computer that thorough knowledge of the brain seems very remote.

The Circulatory System, the Heart, and Blood

When the heart stops beating—that is to say, stops pumping blood—for longer than a couple of minutes, we stop living. But the heart, fortunately, is extremely sturdy.

The Digestive System and the Liver

A physician once remarked that a great many people seem to spend about half their time getting food into their digestive tracts and the other half worrying about how that food is doing on its travels. The physician was exaggerating, but he made his point.

The Respiratory System and the Lungs

The heart, by its construction and shape, tells us a great deal about the lungs and respiration.

The Endocrine Glands

Technically speaking, a gland is any cell or organ in our bodies that secretes some substance. In this broad sense, our liver is a gland, because one of its many functions is to secrete bile.

The Sense Organs

The Urinogenital System and the Kidneys

In large part our good health depends on the quality of the body's internal environment. There is a kind of ecological principle at work within us—if one chain threatens to break, one system becomes polluted, one balance is tilted, then the whole environment is in imminent danger of collapsing.