Energy Balance, Metabolism, & Nutrition

The endocrine system, like the nervous system, adjusts and correlates the activities of the various body systems, making them appropriate to the changing demands of the external and internal environment. Endocrine integration is brought about by ductless glands and transported in the circulation to target cells. Other types of chemical messengers are discussed. Some of the hormones are amines, and others are amino acids, polypeptides, proteins, or steroids.

The hormones regulate metabolic processes. The term metabolism, meaning literally "change," is used to refer to all the chemical and energy transformations that occur in the body.

The animal organism oxidizes carbohydrates, proteins, and fats, producing principally CO₂, H₂O, and the energy necessary for life processes. CO₂, H₂O, and energy are also produced when food is burned outside the body. However, in the body, oxidation is not a one-step, semiexplosive reaction but a complex, slow, stepwise process called catabolism, which liberates energy in small, usable amounts. Energy can be stored in the body in the form of special energy-rich phosphate compounds and in the form of proteins, fats, and complex carbohydrates synthesized from simpler molecules. Formation of these substances by processes that take up rather than liberate energy is called anabolism. This chapter sets the stage for consideration of endocrine function by providing a brief summary of the production and utilization of energy and the metabolism of carbohydrates, proteins, and fats.