Chapter 16 Nutrition and Metabolism

DEFINITIONS Nutrition—food, vitamins, and minerals that are ingested and assimilated into the body Metabolism—process of using food molecules as energy sources and as building blocks for our own molecules Catabolism—breaks food molecules down, releasing their stored energy; oxygen used in catabolism Anabolism—builds food molecules into complex substances

ROLE OF THE LIVER Secretes bile, which breaks down large fat globules Helps maintain normal blood glucose level Helps metabolize carbohydrates, fats, and proteins; synthesizes several kinds of protein compounds Removes toxins from the blood

NUTRIENT METABOLISM Carbohydrates—preferred energy food of the body Three series of chemical reactions in glucose metabolism Glycolysis Changes glucose to pyruvic acid Anaerobic (uses no oxygen) Yields small amount of energy (transferred to ATP) Occurs in cytoplasm Citric acid (Krebs) cycle Changes pyruvic acid to carbon dioxide Aerobic (requires oxygen) Yields large amount of energy (mostly as high energy electrons) Occurs in mitochondria Electron transfer system Transfers energy from high energy electrons (from citric acid cycle) to ATP molecules Located in mitochondria

NUTRIENT METABOLISM Carbohydrates (cont.) Carbohydrates are primarily catabolized for energy (Figure 16-1), but small amounts are anabolized by glycogenesis (a series of chemical reactions that changes glucose to glycogen—occurs mainly in liver cells where glycogen is stored) Adenosine triphosphate (ATP)—molecule in which energy obtained from breakdown of foods is stored; serves as a direct source of energy for cellular work (Figure 16-2) Blood glucose (imprecisely, blood sugar)—normally stays between about 80 and 110 mg per 100 mL of blood during fasting; insulin accelerates the movement of glucose out of the blood into cells, therefore decreases blood glucose and increases glucose catabolism Fats—catabolized to yield energy and anabolized to form adipose tissue (Figure 16-3) Proteins—primarily anabolized and secondarily catabolized

VITAMINS AND MINERALS Vitamins—organic molecules that are needed in small amounts for normal metabolism (Table 16-2) Minerals—inorganic molecules found naturally in the earth, required by the body for normal function (Table 16-3)

METABOLIC RATES Basal metabolic rate (BMR)—rate of metabolism when a person is lying down but awake and not digesting food and when the environment is comfortably warm Total metabolic rate (TMR)—the total amount of energy, expressed in calories, used by the body per day (Figure 16-4)

BODY TEMPERATURE Hypothalamus—regulates the homeostasis of body temperature (thermoregulation) through a variety of processes Skin—can cool the body by losing heat from the blood through four processes: radiation, conduction, convection, evaporation (Figure 16-5)