Nutrition, Metabolism, and
Body Temperature Regulation
I. Nutrition (pp. 943–956; Figs. 24.1–24.2; Tables 24.1–24.3)
A. A nutrient is a substance in food that is used by the body to promote normal growth,
maintenance, and repair. (pp. 943–944; Fig. 24.1)
1. There are six categories of nutrients: carbohydrates, lipids, proteins, vitamins, minerals,
and water.
2. Essential nutrients are those that cannot be made by the body and must be obtained in the
diet.
B. Carbohydrates (p. 944; Table 24.1)
1. Except for milk sugar (lactose) and small amounts of glycogen found in meats, all the
carbohydrates we ingest are derived from plants.
2. Glucose is the carbohydrate molecule ultimately used by the body as fuel to make ATP.
3. The current recommendation is 125–175 grams of carbohydrates daily with the emphasis
on complex carbohydrates.
C. Lipids (pp. 944–946; Table 24.1)
1. The most common dietary lipids are the neutral fats, triglycerides or triacylglycerols, which
occur as saturated fats and unsaturated fats.
2. Cholesterol is another dietary lipid that is found in egg yolk, meats, and milk products.
3. Dietary fats are essential as the major source of fuel for hepatocytes and skeletal muscle,
for absorption of fat-soluble vitamins, and as components of the myelin sheaths and
cellular membranes of the body.
D. Proteins (pp. 946–947; Fig. 24.2; Table 24.1)
1. Animal products contain the highest-quality proteins, those with the greatest amount and
best ratio of amino acids.
a. Proteins in eggs, milk, and meats are considered to be complete proteins that meet all
the body’s amino acid requirements for tissue maintenance and growth.
b. Legumes, nuts, and cereals are protein-rich but not complete, but when cereal grains
and legumes are ingested together they provide all the essential amino acids.
2. Proteins are important as structural materials of the body, enzymes, and hormones.
a. All amino acids needed to make a particular protein must be present in a cell at the
same time and in sufficient amounts for the protein to be made.
b. For optimal protein synthesis the diet needs sufficient carbohydrate or fat calories for
ATP production.
c. The body is in nitrogen balance when the amount of nitrogen ingested in proteins is
equal to the amount lost in urine and feces.
d. Anabolic hormones accelerate protein synthesis and growth.
3. The amount of protein a person needs reflects his or her age, size, metabolic rate, and
current state of nitrogen balance.
E. Vitamins are potent organic compounds needed in small amounts for growth and good health,
most of which function as coenzymes. (pp. 947–952; Table 24.2)
1. Fat-soluble vitamins (A, D, E, and K) bind to ingested lipids and are absorbed along with
their digestion products.
2. Water-soluble vitamins (B complex vitamins and vitamin C) are absorbed along with water
from the gastrointestinal tract, and excess amounts are excreted from the body in urine.
3. Vitamins A, C, and E are antioxidants that disarm tissue-damaging free radicals.
F. The body requires moderate amounts of seven minerals and trace amounts of about a dozen
others that are used by the body to add strength to structures or to act as ions in the blood and
cells. (pp. 952–956; Table 24.3)
II. Metabolism (pp. 956–981; Figs. 24.3–24.22; Tables 24.4–24.7)
A. Overview of Metabolic Processes (pp. 956–959; Figs. 24.3–24.4; Table 24.4)
1. Anabolism is the general term for all reactions in which larger molecules or structures are
built from smaller ones.
2. Catabolism refers to all processes that break down complex structures to simpler ones.
3. In oxidation-reduction reactions one substance is oxidized and loses energy by losing
electrons, while another substance is reduced and gains energy and electrons that are
transferred from the oxidized substance.
4. Our cells use two mechanisms to capture some of the energy liberated through oxidationreduction reactions to make ATP.
a. Substrate-level phosphorylation occurs when high-energy phosphate groups are
transferred directly from phosphorylated substrates to ADP.
b. Oxidative phosphorylation is carried out by electron transport, which occurs in the cristae
of the mitochondria and couples the movement of substances across membranes to
chemical reactions.
B. Carbohydrate Metabolism (pp. 959–967; Figs. 24.5–24.12)
1. Oxidation of glucose
a. Glycolysis is a series of ten steps where glucose is converted into two pyruvic acid
molecules in the cytosol of cells.
b. Krebs cycle occurs in the matrix of the mitochondria where the pyruvic acid is passed
through a series of reactions that generate reduced electron carrier molecules, NADH +
H+ and FADH2.
c. Electron transport chain passes electrons through a series of oxidative phosphorylation
reactions that generate 28 ATP molecules.
2. Glycogenesis is the formation of glycogen, the animal storage form of glucose, that occurs
when excess glucose is ingested.
3. Glycogenolysis is the breakdown of glycogen into individual glucose molecules that occurs
when the blood sugar levels drop.
4. Gluconeogenesis is the process of forming new glucose from noncarbohydrate molecules
that occurs in the liver using glycerol and amino acids.
C. Lipid Metabolism (pp. 967–970; Figs. 24.13–24.14)
1. Most body cells easily convert glycerol to glyceraldehyde phosphate, a glycolysis
intermediate that enters the Krebs cycle.
2. Beta oxidation is the first phase of fatty acid metabolism where fatty acid chains are split
into two carbon acetic acid fragments and coenzymes are reduced.
3. Lipogenesis is the reformation of triglycerides from unused glycerol and fatty acid chains
for storage in the body.
4. Lipolysis is the breakdown of stored fats into glycerol and fatty acids to be used by the
body for fuel.
D. Protein metabolism occurs whenever proteins have reached the end of their life span and
must be broken down to replace the “aged” proteins. (pp. 970–971; Fig. 24.15)
1. Oxidation of Amino Acids
a. Transamination is the process of transferring an amine group to alpha-ketoglutaric acid
to make glutamic acid.
b. Oxidative deamination occurs in the liver and removes the amine group of glutamic acid
as ammonia and regenerates alpha-ketoglutaric acid.
c. Keto acid modification is used to produce molecules that can be oxidized in the Krebs
cycle or converted to glucose from keto acids produced through transamination.
E. The body exists in a dynamic catabolic-anabolic state, where substances are continually being
broken down and rebuilt. (pp. 971–973; Figs. 24.16–24.17)
F. Absorptive and Postabsorptive States (pp. 973–978; Figs. 24.8–24.21; Tables 24.5–24.6)
1. Absorptive state is the time during and shortly after eating when nutrients are moving into
the blood from the GI tract.
a. Absorbed monosaccharides are delivered directly to the liver where they are converted
into glucose and either used by the cells of the body, stored as glycogen, or converted
into fats to be stored.
b. Triglycerides are either used for anabolic purposes or stored in adipose tissue.
c. Amino acids are delivered to the liver, which deaminates some and uses others to make
plasma proteins, but most remain in the blood to be distributed to body cells.
d. Insulin directs all events of the absorptive state.
2. Postabsorptive state is the period when the GI tract is empty and energy resources are
supplied by the body reserves.
a. Sources of blood glucose include glycogen in the liver, skeletal muscle cells, adipose
tissues, and cellular proteins.
b. Glucose sparing is the increased use of noncarbohydrate fuel molecules for energy to
save glucose during times of fasting.
c. The sympathetic nervous system and several hormones interact to control the
postabsorptive state.
G. The Metabolic Role of the Liver (pp. 978–981; Fig. 24.22; Table 24.7)
1. The hepatocytes carry out over 500 metabolic functions.
2. Cholesterol serves as the structural basis for bile salts, steroid hormones, vitamin D; as a
component of the plasma membrane; and as a signaling molecule in embryonic
development.
3. About 85% of cholesterol is made in the liver and other body cells, and is lost from the
body in bile salts in feces.
4. Cholesterol is insoluble in water and must be transported in the body bound to small lipidprotein complexes called lipoproteins.
5. Factors Regulating Plasma Cholesterol Levels
a. Severe restriction of dietary cholesterol does not lead to a steep reduction in plasma
cholesterol levels.
b. Saturated fatty acids stimulate liver synthesis of cholesterol and inhibit its excretion from
the body.
c. Unsaturated fatty acids enhance excretion of cholesterol from the body.
d. Trans fatty acids cause a greater increase in LDL levels and a greater reduction in HDL
levels than saturated fatty acids.
e. Smoking, coffee drinking, and stress increase LDL levels; regular aerobic exercise
appears to reduce LDL levels and increase HDL levels.
III. Energy Balance (pp. 981–989; Figs. 24.23–24.26)
A. A dynamic exists within the body between the energy intake and energy output. (pp. 981–982)
1. Energy intake is the energy liberated during food oxidation.
2. Energy output includes energy lost as heat, energy used to do work, and energy that is
stored as fat or glycogen.
B. Regulation of Food Intake (pp. 982–984; Fig. 24.23)
1. When energy intake and energy output are balanced weight remains stable; when not
balanced weight is either lost or gained.
2. Factors that control eating include: neural signals from the digestive system, bloodborne
signals related to body energy stores, hormones, body temperature, and psychological
factors.
C. The body’s rate of energy output is called the metabolic rate, which is the total heat produced
by all the chemical reactions and mechanical work of the body. (pp. 984–985)
1. The basal metabolic rate (BMR) reflects the energy the body needs to perform only its
most essential activities.
2. Factors influencing BMR include body surface area, age, gender, stress, and hormones.
3. The total metabolic rate (TMR) is the rate of kilocalorie consumption needed to fuel all
ongoing activities both involuntary and voluntary.
D. Body temperature regulation represents a balance between heat production and heat loss.
(pp. 985–989; Figs. 24.24–24.26)
1. The body’s core (organs within the skull, thoracic and abdominal cavities) has the highest
temperature and its shell (the skin) has the lowest temperature in most circumstances.
2. Mechanisms of Heat Exchange
a. Radiation is the loss of heat in the form of infrared waves (thermal energy).
b. Conduction is the transfer of heat from a warmer object to a cooler one when the two are
in direct contact with each other.
c. Convection occurs when the warm air surrounding the body expands and rises and is
replaced by cooler air molecules.
d. Evaporation removes large amounts of body heat when water absorbs heat before
vaporizing.
3. The hypothalamus is the brain’s main integrating center for thermoregulation, containing
the heat-loss center and the heat-promoting center.
4. Heat-promoting mechanisms are triggered when the external temperature is low, or blood
temperature falls and the heat-promoting center is activated.
a. Vasoconstriction of cutaneous blood vessels
b. Increase in metabolic rate
c. Shivering
d. Enhanced thyroxine release
e. Behavioral modifications
5. Heat-loss mechanisms protect the body from excessively high temperatures.
a. Vasodilation of cutaneous blood vessels allows the body to lose heat through radiation,
conduction, and convection.
b. Enhanced sweating is used if the environment becomes so hot it cannot be lost by other
means than evaporation.
6. Fever is controlled hyperthermia, usually resulting from an infection somewhere in the
body.
IV. Developmental Aspects of Nutrition and Metabolism (pp. 989–992)
A. Embryological
1. Good nutrition is essential in utero for the growth of fetal tissues and brain.
2. Inadequate calories during the first three years of life, a time of brain growth, will lead to
mental deficits or learning disorders.
3. Proteins are needed for muscle and bone growth, and calcium is required for strong bones.
B. Aging
1. By middle age and old age non-insulin-dependent diabetes mellitus becomes a problem,
especially in the obese.
2. Metabolic rate declines as we age.
3. Muscle and bones deteriorate, and the efficiency of the endocrine system decreases.