Catch 24 II/2 [antikvár]

A INTERMEDIATE I. READING COMPREHEN8ION MAN AND HIS BODY, HOW IT WORKS The humaa bódy caa be divided iato a number of separate sys-tems, each with a special job. The skeletoa (boay system) provides a supporting framework and protects delicate organs such as the brain and heart. It also works together with the tnuscular system to provide a means of moving about. The breathing, circulatory and digestive sys-tems co-operate to set free the energy and provide the materials needed for growth and repair of the body. The urinary system disposes of some of the waste produced by the chemical activities of the body. The re-productive system enables babies to be conceived, fed and protected be-fore birth. The endocrine system is a number of glands, such as the thyroid, sex and adrenal glands that secrete chemicals called hormones into the blood. These hormones control growth, sexual activities, some aspects of food digestion and many other body functions. The nervaus system keeps all the other systems under control and enables human beings to think, reason and make decisions. The separate systems all work together for the proper fanctioning of the body. Each system has its own organs. The lungs, for instance, are organs in the breathing system, the heart is an organ in the circulatory system and the liver is an organ in the digestive system. The organs in the human body are similar to those in other mammals; they serve the same sort of systems and they are arranged in a similar way. Every organ is made up of several different kinds of tissues. Epi-thelial tissue, which includës the skin, forms a covering over organs, and connective tissue includes bone and cartilage. Other types of tissues are muscle, nerve and blood. Every piece of tissue is made up of units called cells, and each different type of tissue is composed of similar cells. Most cells are so small that they have to be measured in thousandths of a millimetre and can only be seen through a microscope. There are more than 50 million millioa cells in a human body. The largest is the human egg, which is about as big as the head of a pin. Each cell is covered by a thin membrane enclosing a nucleus and a jel-