The Human Body

The study of the human body. Many years ago people explained some processes in the human body by saying that a "vital spirit" within the body controlled some body functions. They used this term to explain processes that they could not understand. They believed that this vital spirit could not be explained by the physical laws of science.

Today, scientists know that the human body functions according to the laws of nature. There is no mysterious vital spirit within the body that causes the heart to beat or the brain to operate. Scientists now explain the working of the body by discovering the physical principles behind its operation.

A physiologist is a modem scientist who studies the body and the ways Its parts function. He seeks scientific explanations for the ways the parts of the body operate. He is interested in the ways the parts of the human body work together to help a human to live.

The body is the most complicated organism known. Its many parts interact in so many ways that physiologists must simplify the organisation for purposes of study. In order to understand the functions of the major organs and tissues of the body, physiologists usually divide them into six major systems. These are the skeletal-muscular system, which controls the basic shape and movement of the body; the gastrointestinal system, which controls the progress of foods within the body; the respiratory system, which controls the oxidation of food in the body; the circulatory system, which is the blood circulating mechanism; the nervous system, which is the voluntary and involuntary control center for the body; and the endocrine system, which is a chemical control system for the other systems.

These systems are linked in many ways. For example, the blood in the circulatory system carries the oxygen from the respiratory system to the muscles in the skeletal-muscular system.

The organs. Each of these six systems is composed of organs, such as the heart, liver, stomach, and brain. Most of the important organs of the body are included in one of the six systems. Each of the organs carries out a special function, but it is so related to many other organs in the body that it often depends on them to help in the process.

Thus, the lungs cannot act without the brain, because the brain sends the impulses which regulate breathing. The stomach is worth nothing without the blood to carry the food it digests to the tissues. Virtually every organ depends on other organs to help it carry out its function.

Tissues and cells. The tissues that make up the organs are likewise dependent on other tissues and organs in the body. Tissues are made of cells, the smallest bits of living matter in a human body. The cells need nourishment and a way to cast off their wastes. This nourishment is provided by various organs of the body.

The tissues of the body, like the organs and the systems, are specialized. Each of the four kinds of tissue looks different from the others, and each makes up different organs. For instance, the epithelial cells in your skin are similar to the epithelial cells in your lungs. The muscle cells in your arm are similar to the muscle cells in your stomach. Look at the illustration to see the four shapes of tissue cells. These cells make up the tissues of the body.

When you read about each of the six systems of the body, you should keep one point in mind. The explanations of the six systems are simplifications. The systems are so complicated and so interrelated that they cannot be described in a few pages. In fact, doctors are still searching for functions of many parts of the six systems of the body.

 

Think for Yourself

What systems have structures that are dependent on the skin? You may find that there is more than one system.