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PowerPoint® Lecture Slide Presentation by Vince Austin
Human Anatomy & Physiology
FIFTH EDITION
Elaine N. Marieb
Chapter 25
Nutrition, Metabolism,
and Body Temperature
Regulation
Part A
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Nutrition
• Nutrient – a substance that promotes normal growth,
maintenance, and repair
• Major nutrients – carbohydrates, lipids, and proteins
• Other nutrients – vitamins and minerals (and
technically speaking, water)
• Grains, fruits, vegetables, meats and fish, and milk
products
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Nutrition
Figure 25.1
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Carbohydrates
• Complex carbohydrates (starches) are found in
bread, cereal, flour, pasta, nuts, and potatoes
• Simple carbohydrates (sugars) are found in soft
drinks, candy, fruit, and ice cream
• Glucose is the molecule ultimately used by body
cells to make ATP
• Neurons and RBCs rely almost entirely upon glucose
to supply their energy needs
• Excess glucose is converted to glycogen or fat and
stored
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Carbohydrates
• The minimum amount of carbohydrates needed to
maintain adequate blood glucose levels is 100 grams
per day
• Starchy foods and milk have nutrients such as
vitamins and minerals in addition to complex
carbohydrates
• Refined carbohydrate foods (candy and soft drinks)
provide energy sources only and are referred to as
“empty calories”
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Lipids
• The most abundant dietary lipids, triglycerides, are
found in both animal and plant foods
• Essential fatty acids – linoleic and linolenic acid,
found in most vegetables, must be ingested
• Dietary fats:
• Help the body to absorb vitamins
• Are a major energy fuel of hepatocytes and skeletal
muscle
• Are a component of myelin sheaths and all cell
membranes
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Lipids
• Fatty deposits in adipose tissue provide:
• A protective cushion around body organs
• An insulating layer beneath the skin
• An easy-to-store concentrated source of energy
• Prostaglandins function in:
• Smooth muscle contraction
• Control of blood pressure
• Inflammation
• Cholesterol stabilizes membranes and is a precursor
of bile salts and steroid hormones
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Lipids: Dietary Requirements
• Higher for infants and children than for adults
• The American Heart Association suggests that:
• Fats should represent less than 30% of one’s total
caloric intake
• Saturated fats should be limited to 10% or less of
one’s total fat intake
• Daily cholesterol intake should not exceed 200 mg
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Proteins
• Complete proteins that meet all the body’s amino acid
needs are found in eggs, milk, milk products, meat,
and fish
• Incomplete proteins are found in legumes, nuts, seeds,
grains, and vegetables
• Proteins supply:
• Essential amino acids, the building blocks for
nonessential amino acids
• Nitrogen for nonprotein nitrogen-containing
substances
• Daily intake should be approximately 0.8g/kg of body
weight
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Proteins: Synthesis and Hydrolysis
• All-or-none rule
• All amino acids needed must be present at the same
time for protein synthesis to occur
• Adequacy of caloric intake
• Protein will be used as fuel if there is insufficient
carbohydrate or fat available
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Proteins: Synthesis and Hydrolysis
• Nitrogen balance
• The rate of protein synthesis equals the rate of
breakdown and loss
• Positive – synthesis exceeds breakdown (normal in
children and tissue repair)
• Negative – breakdown exceeds synthesis (e.g., stress,
burns, infection, or injury)
• Hormonal control
• Anabolic hormones accelerate protein synthesis
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Vitamins
• Organic compounds needed for growth and good
health
• They are crucial in helping the body use nutrients and
often function as coenzymes
• Only vitamins D, K, and B are synthesized in the
body; all others must be ingested
• Water-soluble vitamins (B-complex and C) are
absorbed in the gastrointestinal tract
• B12 additionally requires gastric intrinsic factor to be
absorbed
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Vitamins
• Fat-soluble vitamins (A, D, E, and K) bind to ingested
lipids and are absorbed with their digestion products
• Vitamins A, C, and E also act in an antioxidant
cascade
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Minerals
• Seven minerals are required in moderate amounts
• Calcium, phosphorus, potassium, sulfur, sodium,
chloride, and magnesium
• Dozens are required in trace amounts
• Minerals work with nutrients to ensure proper body
functioning
• Calcium, phosphorus, and magnesium salts harden
bone
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Minerals
• Sodium and chloride help maintain normal
osmolarity, water balance, and are essential in nerve
and muscle function
• Uptake and excretion must be balanced to prevent
toxic overload
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Metabolism
• Metabolism – all chemical reactions necessary to
maintain life
• Cellular respiration – food fuels are broken down
within cells and some of the energy is captured to
produce ATP
• Anabolic reactions – synthesis of larger molecules
from smaller ones
• Catabolic reactions – hydrolysis of complex
structures into simpler ones
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Metabolism
• Enzymes shift the high-energy phosphate groups of
ATP to other molecules
• These phosphorylated molecules are activated to
perform cellular functions
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Stages of Metabolism
• Energy-containing nutrients are processed in three
major stages
• Digestion – breakdown of food; nutrients are
transported to tissues
• Anabolism and formation of catabolic intermediates
where nutrients are:
• Built into lipids, proteins, and glycogen
• Broken down by catabolic pathways to pyruvic
acid and acetyl CoA
• Oxidative breakdown – nutrients are catabolized to
carbon dioxide, water, and ATP
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Stages of Metabolism
Figure 25.3
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Oxidation-Reduction Reaction
• Oxidation occurs via the gain of oxygen or the loss of
hydrogen
• Whenever one substance is oxidized, another
substance is reduced
• Oxidized substances lose energy
• Reduced substances gain energy
• Coenzymes act as hydrogen (or electron) acceptors
• Two important coenzymes are nicotinamide adenine
dinucleotide (NAD+) and flavin adenine dinucleotide
(FAD)
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Mechanisms of ATP Synthesis: Substrate-Level
Phosphorylation
• High-energy
phosphate groups are
transferred directly
from phosphorylated
substrates to ADP
• ATP is synthesized
via substrate level
phosphorylation in
glycolysis and the
Krebs cycle
Figure 25.4a
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Mechanisms of ATP Synthesis: Oxidative
Phosphorylation
• Uses the chemiosmotic process whereby the
movement of substances across a membrane is
coupled to chemical reactions
• Is carried out by the electron transport proteins in the
cristae of the mitochondria
• Nutrient energy is used to pump hydrogen ions into
the intermembrane space
• A steep diffusion gradient across the membrane
results
• When hydrogen ions flow back across the membrane
through ATP synthase, energy is captured and
attaches phosphate groups to ADP (to make ATP)
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Mechanisms of ATP Synthesis: Oxidative
Phosphorylation
Figure 25.4b
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Carbohydrate Metabolism
• Since all carbohydrates are transformed into glucose,
it is essentially glucose metabolism
• Oxidation of glucose is shown by the overall
reaction:
C6H12O6 + 6O2  6H2O + 6CO2 + 36ATP + heat
• Occurs in three pathways
• Glycolysis
• Krebs cycle
• The electron transport chain and oxidative
phosphorylation
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Carbohydrate Metabolism
Figure 25.5
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Glycolysis
• A three-phase pathway in which:
• Glucose is oxidized into pyruvic acid
• NAD+ is reduced to NADH + H+
• ATP is synthesized by substrate-level
phosphorylation
• Pyruvic acid:
• Moves on to the Krebs cycle in an aerobic pathway
• Is reduced to lactic acid in an anaerobic environment
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Glycolysis
Figure 25.6
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Glycolysis: Phase 1 and 2
• Sugar activation
• Two ATP molecules activate glucose into
fructose-1,6-diphosphate
• Sugar cleavage
• Fructose-1,6-diphosphate is cleaved into two 3carbon isomers
• Dihydroxyacetone phosphate
• Glyceraldehyde 3-phosphate
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Glycolysis: Phase 3
• Oxidation and ATP formation
• The 3-carbon sugars are oxidized (reducing NAD+)
• Inorganic phosphate groups (Pi) are attached to each
oxidized fragment
• The terminal phosphates are cleaved and captured by
ADP to form four ATP molecules
• The final products are:
• Two pyruvic acid molecules
• Two reduced NAD+ (NADH + H+) molecules
• A net gain of two ATP molecules
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