Concepts of Human Anatomy & Physiology   5/e   Van De Graaff/Fox
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I. Nutritional Requirements

Concept: The body's energy requirements must be met by the caloric value of food to prevent catabolism of the body's own fat, carbohydrates, and protein. Additionally, food molecules-particularly the essential amino acids and fatty acids-are needed for replacement of molecules in the body that are continuously degraded. Vitamins and elements do not directly provide energy but instead are required for diverse enzymatic reactions.

II. Regulation of Energy Metabolism

Concept: The blood plasma contains circulating glucose, fatty acids, amino acids, and other molecules that can be used by the body tissues for cell respiration. These circulating molecules may be derived from food or from the breakdown of the body's own glycogen, fat, and protein. The building of the body's energy reserves following a meal and the utilization of these reserves between meals are regulated by the action of a number of hormones that act to promote either anabolism or catabolism.

III. Energy Regulation by the Pancreatic Islets

Concept: Insulin secretion is stimulated by a rise in the blood glucose concentration, and insulin promotes the entry of blood glucose into tissue cells. Insulin thus increases the storage of glycogen and fat while causing the blood glucose concentration to fall. Glucagon secretion is stimulated by a fall in blood glucose, and glucagon acts to raise the blood glucose concentration by promoting glycogenolysis in the liver.

IV. Metabolic Regulation by the Adrenal Hormones, Thyroxine, and Growth Hormone

Concept: Epinephrine, the glucocorticoids, thyroxine, and growth hormone stimulate the catabolism of carbohydrates and lipids. These hormones are thus antagonistic to insulin in their regulation of carbohydrate and lipid metabolism. Thyroxine and growth hormone promote protein synthesis, however, and are needed for body growth and proper development of the central nervous system. The stimulatory effect of these hormones on protein synthesis is complementary to that of insulin.

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