CHAPTER 3 - The Nature of the Vital Processes

Abstract

This chapter focuses on the processes of nutrition, respiration, and excretion in humans. The processes of nutrition, respiration, and excretion in humans are the three basic characteristics of life. Each of them is dependent on the circulation of the blood and the consequent exchange of substances between the capillaries and tissues for efficient functioning. The body's principal nutritive needs are for energy-producing substances and tissue-building materials. The principal soluble source of energy utilized by the body is glucose, which is derived from the breakdown of more complex carbohydrates such as starch. Energy is also derived from fats in the form of soluble fatty acids and, indirectly, from protein. The growth and repair of tissues are dependent on supplies of soluble amino acids, which are derived from the breakdown of proteins. The constant supply of oxygen to the tissues, the release of energy, and the removal of carbon dioxide and water are termed internal respiration. The exchange of gases in the lungs is the external phase of respiration of breathing, the transport of gases between the lungs and the tissues being a function of the blood. However, carbon dioxide, removed by breathing, is only one of the waste products. Other more complex waste products also have to be removed, and to bring this about, the formation of urine is necessary. The skin also has an important excretory function, which it carries out by expelling water, in which salts are dissolved on to its surface.