chapter 19 nutrition and metabolismcf.linnbenton.edu/mathsci/bio/klockj/upload/chapter18...
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Chapter 18
Nutrition and Metabolism
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Objectives
• Define and contrast catabolism and
anabolism
• Describe the metabolic roles of
carbohydrates, fats, proteins, vitamins,
and minerals
• Define basic metabolic rate and list
some factors that affect it
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Objectives
• Describe three disorders associated
with eating or metabolism
• Discuss the physiological mechanisms
that regulate body temperature
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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
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Definitions
• Catabolism—process that breaks food
molecules down, releasing their stored
energy; oxygen used in catabolism
• Anabolism—process that builds food
molecules into complex chemical
compounds
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Metabolic Function of the Liver
• Processes blood immediately after it
leaves the gastrointestinal tract
– Helps maintain normal blood glucose level
– Site of protein and fat metabolism
– Removes toxins from the blood
– Synthesizes several kinds of protein
compounds
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Nutrient Metabolism
• Carbohydrate metabolism – Carbohydrates are the preferred energy food of
the body
– Three series of chemical reactions that occur in a precise sequence make up the process of glucose metabolism
• Glycolysis—occurs in cytoplasm of the cell
– Anaerobic process (uses no oxygen)
– Changes glucose to pyruvic acid, which is then converted into acetyl CoA
– Yields small amount of energy (transferred to ATP)
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Nutrient Metabolism
• Citric acid (Krebs) cycle—occurs in the
mitochondria
– Aerobic process (requires oxygen)
– Changes acetyl CoA to carbon dioxide
– Yields small amount of energy
– Most energy leaving the citric acid cycle is in the form of
high-energy electrons)
• Electron transport system—occurs in the
mitochondria
– Transfers energy from high-energy electrons (from citric
acid cycle) to ATP molecules
– ATP serves as direct source of energy for cells
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Nutrient Metabolism
• Carbohydrate metabolism (cont’d)
– Energy transferred to ATP differs from energy in
food molecules
• Not stored; released almost instantly
• Can be used directly to do cellular work
– Carbohydrates primarily catabolized for energy,
but small amounts anabolized by glycogenesis
(series of chemical reactions that changes glucose
to glycogen—occurs mainly in liver cells where
glycogen is stored)
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Nutrient Metabolism
• Carbohydrate metabolism (cont’d)
– Blood glucose (imprecisely, blood sugar)—
amount of glucose in blood
• 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
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Nutrient Metabolism
• Fat metabolism
– Fats are primarily an energy food
– Converted to glucose by catabolism
– Excess fat is anabolized to form adipose tissue
• Protein metabolism
– Proteins are catabolized for energy only after
carbohydrate and fat stores are depleted
– Gluconeogenesis breaks apart amino acids to
convert them to glucose
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Vitamins and Minerals
• Vitamins—organic molecules that are
needed in small amounts for normal
metabolism (Table 18-2)
– Avitaminosis—deficiency of a vitamin
• Can lead to severe metabolic problems
• Avitaminosis C can lead to scurvy
– Hypervitaminosis—excess of a vitamin
• Can be just as serious as avitaminosis
• May be chronic or acute
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Vitamins and Minerals
• Minerals—inorganic molecules found
naturally in the earth
– Required by the body for normal function,
including nerve conduction (Table 18-3)
– Can attach to enzymes to facilitate their
work
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Metabolic Rates
• Basal metabolic rate (BMR)—rate of
metabolism when a person is lying
down, is awake, is not digesting food,
and the environment is comfortably
warm
• Total metabolic rate (TMR)—the total
amounts of energy, expressed in
calories, used by the body per day
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Metabolic and Eating Disorders
• Disruption or imbalance of metabolism
caused by several different factors
– Inborn errors of metabolism—genetic
conditions involving deficient or abnormal
metabolic enzymes
– Some metabolic disorders are
complications of other conditions
• Hormonal imbalances
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Metabolic and Eating Disorders
• Eating disorders
– Anorexia nervosa—characterized by chronic refusal
to eat
– Bulimia—an alternating pattern of craving of food
followed by a period of self-denial; in bulimarexia, the
self-denial triggers self-induced vomiting
– Obesity—abnormally high proportion of fat in the
body; may be a symptom of an eating disorder
– Protein-calorie malnutrition (PCM)—results from a
deficiency of calories in general and proteins in
particular
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Metabolic and Eating Disorders
– Protein-calorie malnutrition (PCM)—results
from a deficiency of calories in general and
proteins in particular • May be a complication of a preexisting condition
• Marasmus—type of advanced PCM caused by an overall
lack of calories and protein, characterized by tissue
wasting and fluid and electrolyte imbalances
• Kwashiorkor—type of advanced PCM caused by a lack
of protein in the presence of sufficient calories; similar to
marasmus but distinguished by ascites and flaking
dermatitis
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Body Temperature
• Hypothalamus—regulates the
homeostasis of body temperature
through a variety of processes
– Blood flow to the skin increases when body
is overheated
– Heat is lost through the skin by radiation,
conduction, convection, evaporation
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Body Temperature
• Abnormal body temperature can have serious
physiological consequences
– Fever (febrile state)—unusually high body
temperature associated with systemic
inflammation response
– Malignant hyperthermia (MH)—inherited condition
that causes increased body temperature
(hyperthermia) and muscle rigidity when exposed
to certain anesthetics
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Body Temperature
– Heat exhaustion—results from loss of fluid
as the body tries to cool itself; may be
accompanied by heat cramps
– Heat stroke (sunstroke)—overheating of
body resulting from failure of
thermoregulatory mechanisms in a warm
environment
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Body Temperature
– Hypothermia—reduced body temperature
resulting from failure of thermoregulatory
mechanisms in a cold environment
– Frostbite—local tissue damage caused by
extreme cold; may result in necrosis or
gangrene