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CHAPTER
24
Nutrition, Metabolism, and Body
Temperature Regulation
Objectives
Diet and Nutrition
1. Define nutrient, essential nutrient, and calorie.
2. List the six major nutrient categories. Note important sources and main cellular uses.
3. Distinguish between simple and complex carbohydrate sources.
4. Indicate the major uses of carbohydrates in the body.
5. Indicate uses of lipids in the body.
6. Distinguish between saturated, unsaturated, and trans fatty acid sources.
Overview of Metabolic Reactions
14. Define metabolism. Explain how catabolism and anabolism differ.
15. Define oxidation and reduction and indicate the importance of these reactions in
metabolism.
Metabolism of Major Nutrients
18. Summarize important events and products of glycolysis, the Krebs cycle, and electron
transport.
20. Describe the process by which fatty acids are oxidized for energy.
23. Describe the need for protein synthesis in body cells.
Metabolic States of the Body
24. Explain the concept of amino acid or carbohydrate-fat pools, and describe pathways by
which substances in these pools can be interconverted.
The Metabolic Role of the Liver
26. Describe several metabolic functions of the liver.
Energy Balance
28. Explain what is meant by body energy balance.
29. Describe several theories of food intake regulation.
Developmental Aspects of Nutrition and Metabolism
33. Describe the effects of inadequate protein intake on the fetal nervous system.
34. Describe the cause and consequences of the low metabolic rate typical of the elderly.
Suggested Lecture Outline
I. Diet and Nutrition (pp. 907–913; Figs. 24.1–24.2; Tables 24.1–24.3)
A. A nutrient is used by the body to promote normal growth and development.
1. Major nutrients are carbohydrates, lipids, and proteins; vitamins and minerals are
micronutrients (p. 907; Fig. 24.1).
B. Carbohydrates consist of sugars (monosaccharides and disaccharides) from fruits,
sugarcane, sugar beets, honey, and milk; and polysaccharides from grains, fruits, and
vegetables (p. 908; Table 24.1).
2. Polysaccharides, such as insoluble cellulose and other soluble polysaccharides,
provide fiber in the diet.
1. Essential fatty acids linoleic acid and linolenic acid cannot be made by the body, so
these must be consumed in the diet.
3. Lipids help the body absorb fat-soluble vitamins, serve as a cellular fuel, are an
integral component of myelin sheaths and cell membranes, form adipose tissues, and
serve as regulatory molecules.
D. Proteins that have all essential amino acids are complete proteins, and are found in eggs,
milk, fish, and meats; proteins that are low or lacking in one or more of the essential
amino acids are incomplete, and are found in legumes, nuts, and cereals (pp. 910–911;
Fig. 24.2; Table 24.1).
1. Proteins are important structural and functional molecules in the body.
2. The amino acids from proteins may be used for synthesis of new molecules or may be
burned for energy, depending on:
a. The presence of all necessary amino acids needed for a particular protein.
E. Vitamins mostly serve as coenzymes, many of which are not made by the body and must
be consumed (pp. 911–913; Table 24.2).
1. Vitamins A, D, E, and K are fat-soluble and are absorbed when bound to ingested
lipids.
II. Overview of Metabolic Reactions (pp. 913–917; Figs. 24.3–24.5)
A. Metabolic processes are either anabolic, in which larger molecules are synthesized from
smaller ones, or catabolic, in which large molecules are broken down to simpler ones
(pp. 913–914; Fig. 24.3).
1. In cellular respiration, food molecules are broken down in cells, with some of the
energy released used to power ATP synthesis, manufacture of the body’s primary
energy currency.
B. Oxidation-reduction reactions are coupled reactions that involve the transfer of electrons
from one molecule to another, resulting in a transfer of energy between molecules
(pp. 914–916).
1. In the body, oxidation-reduction reactions are enzyme-catalyzed reactions requiring
specific coenzymes that transfer the energy contained in food fuels to other molecules,
ultimately leading to the synthesis of ATP from ADP.
III. Metabolism of Major Nutrients (pp. 917–930; Figs. 24.6–24.16; Table 24.4)
A. Carbohydrate Metabolism (pp. 917–925; Figs. 24.6–24.13; Table 24.4)
1. Glucose enters the cell by facilitated diffusion and is phosphorylated to
glucose-6-phosphate, essentially trapping glucose within the cell.
2. Glucose enters glycolysis, an anaerobic process that occurs in the cytosol.
a. In phase 1 of glycolysis, sugar activation, glucose is phosphorylated in a series of
steps to fructose-6-phosphate to provide the activation energy for events that occur
later in the pathway.
3. The two pyruvic acid molecules can follow two distinct pathways, depending on the
availability of oxygen.
a. If adequate oxygen is present in the cell, glycolysis continues, and NADH delivers
4. In aerobic pathways, pyruvic acid is transported into the mitochondrion, where it
enters the Krebs cycle.
a. Pyruvic acid is first converted to acetyl CoA by removing a carbon, oxidizing the
5. The electron transport chain is the oxygen-requiring process of aerobic respiration
involving the pickup of hydrogens removed from food fuels during oxidation by O2,
resulting in the formation of water, a process called oxidative phosphorylation.
a. In the electron transport chain, hydrogens from NADH and FADH2 are shuttled
6. The net energy gain from one glucose molecule is 30 ATP.
7. Because the cell cannot store large amounts of ATP, other processes are used to
handle glucose in excess of what can be used in ATP synthetic pathways.
a. Glycogenesis is a process that forms glycogen from glucose when high cellular
ATP begins to inhibit glycolysis; this process occurs mostly in the liver and skeletal
muscle.
B. Lipid Metabolism (pp. 926–928; Figs. 24.14–24.15; Table 24.4)
1. Lipids are the body’s most concentrated source of energy, producing approximately
twice the energy of either carbohydrates or proteins.
2. Catabolism of triglycerides involves the splitting of the molecule into glycerol and
fatty acids: the glycerol portion is converted to glyceraldehyde phosphate, which
C. Protein Metabolism (pp. 928–930; Table 24.4)
1. Before amino acids can be oxidized for energy, they must have the amine group
removed, a process called deamination.
structural and functional proteins of the body.
IV. Metabolic States of the Body (pp. 930–935; Figs. 24.17–24.20; Table 24.5)
A. Catabolic-Anabolic Steady State of the Body (pp. 930–932; Fig. 24.17; Table 24.5)
1. There is a dynamic catabolic-anabolic state of the body as molecules are broken down
and rebuilt.
2. The body draws molecules to meet these needs from various nutrient pools: amino
acid, carbohydrate, and fat stores.
B. During the absorptive state, anabolism exceeds catabolism (pp. 931–933; Figs. 24.18–
24.19; Table 24.5).
1. All absorbed monosaccharides are made into glucose by the liver and released to the
blood or converted to glycogen or fat.
3. Insulin is the hormone that directs all events of the absorptive state:
a. Increases glucose uptake by body cells
b. Enhances glucose oxidation in tissue cells
f. Inhibits gluconeogenesis
C. In the postabsorptive state, net synthesis of fat, glycogen, and proteins ends, and the body
shifts to catabolism of these molecules (pp. 933–935; Figs. 24.20–24.21; Table 24.5).
2. If the body experiences prolonged fasting, it will enter glucose sparing, which is aimed
at conservation of blood glucose by promoting increased use of noncarbohydrate fuel
3. Hormonal and neural controls of the postabsorptive state:
a. Insulin-promoted processes are inhibited as insulin levels fall.
b. Declining blood glucose levels promote the release of glucagon, which targets the
liver, causing enhanced glycogenolysis, lipolysis, and gluconeogenesis, in order to
keep blood energy sources available to body cells.
V. The Metabolic Role of the Liver (pp. 935–938; Fig. 24.22; Table 24.6)
A. Cholesterol Metabolism and Regulation of Blood Cholesterol Levels (pp. 935–938; Fig.
24.22; Table 24.6)
2. Lipoprotein complexes vary in the percentage of lipid they contain, but all contain tri-
glycerides, phospholipids, and cholesterol, in addition to protein.
4. High levels of HDL are considered beneficial, as the cholesterol they contain is bound
for removal, but high levels of LDL are considered a risk, because the cholesterol they
contain may be laid down on vessel walls, forming plaques.
5. Blood levels of cholesterol are partly regulated through negative feedback, and a high
intake of cholesterol will somewhat inhibit cholesterol synthesis by the liver.
VI. Energy Balance (pp. 938–948; Figs. 24.23–24.26)
A. There is a balance between the body’s energy intake, defined as the energy produced
during food oxidation, and energy output, which includes energy lost as heat, used to do
work, or stored as fat or glycogen (pp. 938–939).
1. When energy intake and energy output are balanced, body weight remains stable, but
when they are not, weight is gained or lost.
C. Regulation of Food Intake (pp. 939–941; Fig. 24.23)
1. The hypothalamus produces several peptides controlling feeding behavior, which
ultimately reflect two sets of neurons: one set promoting hunger and the other set
promoting satiety.
3. Long-term regulation of food intake relies on the hormone leptin, secreted by adipose
cells.
4. Other factors that may affect food-seeking behaviors are changes in ambient tempera-
ture, stress, other psychological factors, infections, sleep deprivation, or composition
of gut bacteria.
D. Metabolic Rate and Heat Production (pp. 941–944)
1. The body’s rate of energy output is called the metabolic rate.
2. The basal metabolic rate reflects the amount of energy required for performance of
only the essential activities of the body and is expressed as kilocalories per square
meter of body surface area.
E. Regulation of Body Temperature (pp. 944–948; Figs. 24.24–24.26)
1. Body temperature averages 37°C and is usually maintained between 35.8–38.2°C.
2. Temperature homeostasis keeps body temperature at a value that is optimal for
enzymatic activity within the body.
from the lungs, oral mucosa, and the skin.
5. The hypothalamus contains the heat-loss and heat-promoting centers that aid in the
regulation of behavioral and physiological mechanisms to maintain normal body
temperature.
6. Heat-promoting mechanisms maintain or increase body core temperature and include
constriction of cutaneous blood vessels, shivering, increase in metabolic rate, and
increased release of thyroxine.
VII. Developmental Aspects of Nutrition and Metabolism (pp. 948–949)
A. Inadequate nutrition during pregnancy and in the first three years of life seriously
compromises brain growth and development, as well as muscle and bone development
(p. 948).
Cross References
Additional information on topics covered in Chapter 24 can be found in the chapters listed below.
1. Chapter 2: Chemical bonding; carbohydrates; lipids; proteins; water; ATP;
2. Chapter 3: Membrane transport; cytoplasm; mitochondria
3. Chapter 12: Hypothalamus
4. Chapter 13: Receptors
Lecture Hints
1. In order to fully understand the metabolic pathways, students should review the basic
concepts of chemistry in Chapter 2 and cellular structure in Chapter 3. Refer the class to
specific sections related to the lecture topic being discussed.
6. One of the most effective methods for presenting the biochemical pathways of
ATP synthesis is to start with a quick review of cell structure related to the process
(membranes, cytoplasm, mitochondria, etc.). Then give the overall outcome of each step
(glycolysis, Krebs cycle, electron transport), followed by a more detailed examination of
each step. It is essential that students see the “overall picture” in order to understand the
significance of the metabolic pathways.
10. Mention possible alternate terms for the Krebs cycle: citric acid cycle (citrate is the first
substrate in the cycle), tricarboxylic acid cycle (several intermediates have three carboxyl
groups).
11. A diagram of the chemiosmotic mechanism of ATP synthesis is very helpful in present-
ing electron transport. Construct a diagram of the phospholipid bilayer, fill in electron
carriers and the ATP synthase complex, and trace the pathway of electron flow. It is
helpful for the instructor to physically draw the diagram during class, especially if the
students are required to draw and/or analyze diagrams on the exam.
Activities/Demonstrations
1. Audiovisual materials are listed in the Multimedia in the Classroom and Lab section of
this Instructor Guide (p. 387).
2. Using the Dubois Body Surface Chart, students can make rough estimations of basal
metabolic rate by calculating respiratory rate and body surface area.
Critical Thinking/Discussion Topics
1. Discuss the need for a balanced diet.
3. Examine the differences between the fat- and water-soluble vitamins and why care
should be taken when using vitamins as a food supplement.
Library Research Topics
1. Investigate the pros and cons of vitamin and mineral supplements. What issues/concerns
exist surrounding dosages of high-potency supplements?
2. Study the effects of the inability to sweat.
List of Figures and Tables
All of the figures in the main text are available in JPEG format, PPT, and labeled & unlabeled
format on the Instructor Resource DVD. All of the figures and tables will also be available in
Transparency Acetate format. For more information, go to www.pearsonhighered.com/educator.
Figure 24.1 Two visual food guides.
Figure 24.2 Essential amino acids.
Figure 24.6 The three major phases of glycolysis.
Figure 24.7 Simplified version of the Krebs (citric acid) cycle.
Figure 24.8 Oxidative Phosphorylation.
Figure 24.9 Electronic energy gradient in the electron transport chain.
Figure 24.11 Structure and function of ATP synthase.
Figure 24.12 Energy yield during cellular respiration.
Figure 24.13 Glycogenesis and glycogenolysis.
Figure 24.14 Initial phase of lipid oxidation.
Figure 24.19 Insulin directs nearly all events of the absorptive state.
Figure 24.20 Major events and principal metabolic pathways of the postabsorptive
state.
Figure 24.21 Glucagon is a hyperglycemic hormone that stimulates a rise in blood
glucose levels.
Figure 24.25 Mechanisms of heat exchange.
Figure 24.26 Mechanisms of body temperature regulation.
Table 24.1 Summary of Carbohydrate, Lipid, and Protein Nutrients
Table 24.2 Vitamin Requirements of Humans
Answers to End-of-Chapter Questions
Multiple-Choice and Matching Question answers appear in Appendix H of the main text.
Short Answer Essay Questions
16. Cellular respiration is a group of reactions that break down (oxidize) glucose, fatty acids,
17. Glycolysis occurs in the cytoplasm of cells. It may be separated into three major events:
(1) sugar activation, (2) sugar cleavage, and (3) oxidation and ATP formation. During
sugar activation, glucose is phosphorylated, converted to fructose, and phosphorylated
again to yield fructose-1,6-biphosphate, consuming two molecules of ATP. These
reactions provide the activation energy for the later events of glycolysis. During sugar
18. Pyruvic acid is converted to acetyl CoA, which enters the Krebs cycle. For pyruvic acid
19. Glycogenesis is the process by which glucose molecules are combined in long chains to
form glycogen. Gluconeogenesis is the formation of new sugar from noncarbohydrate
molecules. Lipogenesis is the term for triglyceride synthesis.
a. Glycogenesis (and perhaps lipogenesis) is likely to occur after a carbohydrate-rich
21.
neutral fats glycerol
+
glucose
glyceraldehyde-3-phosphate
pyruvic acid
fatty acids
22. HDLs function to transport cholesterol from the peripheral tissues to the liver. LDLs
transport cholesterol to the peripheral tissues. (p. 936)
23. Factors influencing plasma cholesterol levels include diet (through intake of cholesterol
and/or saturated fatty acids), smoking, drinking, and stress. Sources of cholesterol in the
24. “Body energy balance” refers to the balance between energy intake and total energy
output. If energy intake exceeds energy output, weight is gained. Weight is lost if energy
output is greater than energy intake. (pp. 938–939)
25. Metabolic rate is increased with increased production of thyroxine. Eating increases
metabolic rate, an effect called chemical thermogenesis. A higher ratio of body surface
26. The body’s core includes organs within the skull and the thoracic and abdominal cavities.
27. Heat-promoting mechanisms to maintain or increase body temperature include vasocon-
striction in the shell, which inhibits heat loss via radiation; conduction and convection;
increase in metabolic rate due to epinephrine release; and shivering. Heat-loss mecha-
Critical Thinking and Clinical Application Questions
1. The number of ATP molecules resulting from the complete oxidation of a particular fatty
acid can be calculated easily by counting the number of carbon atoms in the fatty acid and
dividing by two to determine the number of acetyl CoA molecules produced. For our ex-
2. Hypothermia is abnormally depressed body temperature. It kills by dropping the body
temperature below the relatively narrow range in which biochemical reactions can take
3. With a diagnosis of high cholesterol and severe arteriosclerosis, he should avoid foods
containing saturated fatty acids and avoid eating eggs and large amounts of red meat.
He should substitute foods containing unsaturated fatty acids and add fish to his diet. He
should also stop smoking, cut down on his coffee, avoid stressful situations when possi-
ble, and increase his amount of aerobic exercise. (p. 938)
4. The chemiosmotic machinery concerns the operation of the electron transport chain and
5. Simon is exhibiting signs of vitamin C deficiency, otherwise known as scurvy. Although
he has rich sources of many nutrients on his island, his diet is lacking fruits and green
leafy vegetables as sources of vitamin C. (p. 912)
Suggested Readings
Bolnick, D. A., et al. “Nondestructive Sampling of Human Skeletal Remains Yields Ancient
Nuclear and Mitochondrial DNA.” American Journal of Physical Anthropology 147 (2)
(Feb. 2012): 293–300.
Christensen, Damaris. “Fatty Findings.” Science News 159 (15) (April 2001): 238–239.
Dallongeville, J., et al. “The Association of Metabolic Disorders with the Metabolic
Syndrome Is Different in Men and Women.” Annals of Nutrition & Metabolism 48 (1)
(Jan./Feb. 2004): 43–50.
Dulloo, Abdul G. “A Sympathetic Defense Against Obesity.” Science 297 (5582)
(Aug. 2002): 780–781.
Flier, Jeffrey S. “The Missing Link with Obesity?” Nature 409 (6818) (Jan. 2001): 292–293.
Pradhan, Aruna. “Obesity, Metabolic Syndrome, and Type 2 Diabetes: Inflammatory Basis
of Glucose Metabolic Disorders.” Nutrition Reviews 65 (3) (Dec. 2007): S152–S156.
Rader, Daniel J. “A New Feature on the Cholesterol-Lowering Landscape.” Nature Medicine
7 (12) (Dec. 2001): 1282–1284.
Seppa, N. “Weak Appetite in Elderly Ties to Hormone.” Science News 160 (Dec. 2001): 390.
Stubbins, R. E., et al. “Oestrogen Alters Adipocyte Biology and Protects Female Mice from
Adipocyte Inflammation and Insulin Resistance.” Diabetes, Obesity and Metabolism
14 (1) (Jan. 2012): 58–66.
