Nutrition

Objectives

When you have completed this section, you should be able to

• describe the mechanisms of hunger and satiety;
• define nutrient and list the six major categories of nutrients;
• state the function of each class of macronutrients, the approximate amounts required in the diet, and some major dietary sources of each;
• name the serum lipoproteins, state their functions, and describe how they differ from each other; and
• name the major vitamins and minerals required by the body and the general functions they serve.

Think About It

Suppose CCK could be economically produced and packaged as tablets to be taken orally. Would this be an effective diet drug? Why or why not?

Think About It

Glucose concentration is about 15 to 30 mg/dL higher in arterial blood than in venous blood. Explain why.

Think About It

Would you expect a person recovering from a long infectious disease to be in a state of positive or negative nitrogen balance? Why?

Key Point Review

1. What regions of the hypothalamus regulate hunger and satiety? Why would it be wrong to say these are the sole controls over appetite?

2. Explain the following statement: Cellulose is an important part of a healthy diet but it is not a nutrient.

3. What class of nutrients provides most of the calories in the diet? What class of nutrients provides the body's major reserves of stored energy?

4. Contrast the functions of VLDLs, LDLs, and HDLs. Explain how this is related to the fact that a high blood HDL level is desirable, but a high VLDL-LDL level is undesirable?

5. Why do some proteins have more nutritional value than others?

Carbohydrate Metabolism

Objectives

When you have completed this section, you should be able to

• describe the principal reactants and products at each major step of glucose oxidation;
• contrast the purposes and products of anaerobic fermentation and aerobic respiration;
• explain where and how cells produce ATP; and
• describe the production, function, and use of glycogen.

Think About It

Does lactic acid have more free energy than pyruvic acid or less? Why?

Key Point Review

6. Identify the reaction steps in figures 26.3 and 26.5 at which vitamins are essential to glucose catabolism.

7. In the laboratory, glucose can be oxidized in a single step to CO₂ and H₂O. Why is it done in so many little steps in cells?

8. Explain the origin of the word glycolysis and why this is an appropriate name for the purpose of that reaction pathway.

9. What are two advantages of aerobic respiration over anaerobic fermentation?

10. What important enzyme is found in the inner mitochondrial membrane other than those of the electron-transport chain? Explain how its function depends on the electron-transport chain.

11. Describe how the liver responds to (a)an excess and (b)a deficiency of blood glucose.

Lipid and Protein Metabolism

Objectives

When you have completed this section, you should be able to

• discuss some advantages of lipids over carbohydrates for energy storage and fuel;
• describe the processes of lipid catabolism and anabolism;
• describe the processes of protein catabolism and anabolism; and
• explain the metabolic source of ammonia and how the body disposes of it.

Key Point Review

12. Which of the processes in table 26.6 is most comparable to lipogenesis? Which is most comparable to lipolysis? Explain.

13. When fats are converted to glucose, only the glycerol component is used in this way, not the fatty acid. Explain why and what happens to the fatty acids.

14. What metabolic process produces ammonia? How does the body dispose of ammonia?

Metabolic States and Metabolic Rate

Objectives

When you have completed this section, you should be able to

• define the absorptive and postabsorptive states;
• explain what happens to carbohydrates, fats, and proteins in each of these states;
• describe the hormonal and nervous regulation of each state;
• define metabolic rate and basal metabolic rate; and
• describe some factors that alter the metabolic rate.

Key Point Review

15. Define the absorptive and postabsorptive states. In which state is the body storing excess fuel? In which state is it drawing from these stored fuel reserves?

16. What hormone primarily regulates the absorptive state, and what are the major effects of this hormone?

17. Explain why triglycerides have a glucose-sparing effect.

18. List a variety of factors and conditions that raise a person's total metabolic rate above basal metabolic rate.

Body Heat and Thermoregulation

Objectives

When you have completed this section, you should be able to

• identify the principal sources of body heat;
• describe variations in body temperature with age, sex, method and time of measurement, and state of activity;
• define and contrast radiation, conduction, and evaporative cooling and their relative importance to total heat loss;
• describe how the hypothalamus monitors and controls body temperature; and
• state the terms for excessively high and low body temperatures, and describe the consequences of these conditions.

Key Point Review

19. What is the primary source of body heat? What are some lesser sources?

20. What mechanisms of heat loss are aided by convection?

21. Describe the major heat-promoting and heat-losing mechanisms of the body.

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