Chapter 6

This chapter tells readers the human body and how it works. This book regards human as the first wonder of the universe. Even the most sophisticated man-made machines are primitive compared to the human body.

The human body is built of structural units called cells. Similar cells are organized into tissues for efficient performance of their job. Groups of different tissues cooperate in organs that perform the major work of the body. The body has a number of automatic mechanisms that maintain a constantly favorable internal environment. The digestive system prepares food for the use of the body. It is composed essentially of a long tube together with digestive glands that secrete chemicals that act on food in the tube. Some of the members belonging to digestive system are mouth, salivary glands, gullet, stomach, small intestine, and large intestine. The respiratory system supplies oxygen and gets rid of carbon dioxide. When people inhale air, air passes through nostril and finally arrives air sacs. The air sacs have very thin walls richly supplied with capillaries. The oxygen passes through the thin walls of the air sacs and capillaries into the bloodstream and eventually is carried to every cell in the body. In the circulatory system, blood moves around body in a closed circuit of arteries, veins and capillaries, with the heart serving as a pump. Skin, kidneys, and the lungs play important roles in the excretory system. They rid body of both liquid and gaseous wastes. The headquarters of the nervous system is brain. The spinal cord connects directly with brain and transmits nerve purses to motor nerve cells; thus, make muscles react.

How the human body works is interesting and mysterious. Anthropologists have unraveled some of the mysteries such as the development from the fertilized eggs to the embryos to the babies; however, there is still a long way to go to understand every exact mechanism of the human body.