Chapter 24 – Nutrition, Metabolism and Thermoregulation G.R. Pitts, J.R. Schiller, and James F....
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![Page 1: Chapter 24 – Nutrition, Metabolism and Thermoregulation G.R. Pitts, J.R. Schiller, and James F. Thompson, Ph.D. Use the video clip, CH 24 Nutrition for.](https://reader035.fdocuments.us/reader035/viewer/2022062217/5697bf8f1a28abf838c8d362/html5/thumbnails/1.jpg)
Chapter 24 – Nutrition, Metabolism and Thermoregulation
G.R. Pitts, J.R. Schiller, and James F. Thompson, Ph.D.
Use the video clip, CH 24 Nutrition for a review of general nutrition
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Nutrition
We eat, we digest, we absorb, then what?
3 fates for food = nutrients
1) Most are used to supply energy for life2) Some are used to synthesize structural or
functional molecules3) The rest are stored for future use – love
handles!
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Nutrition for College Students
Four Groups:
Grease
Salt
Sugar
Alcohol
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Weight ManagementIf energy consumption (food
intake) equals energy utilized (activity), then body weight will remain constant
Activity and consumption levels vary day to day, but individuals keep relatively constant weight for long periods of time
Many individuals in affluent nations have an imbalance between intake and use obesity
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Regulation of Food Intake Hypothalamus - complex
integrating center receiving sensory information from all parts of the body
Two hypothalamic centers control eating• Feeding (hunger) center
located in lateral hypothalamus
when stimulated, it initiates feeding, even if one is “full”
• Satiety center ventromedial nucleiwhen stimulated, they cause
cessation of eating, even if one has been starved for days
Controls for their set points are unknown!
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Regulation of Food Intake (cont.)
Feeding center is always active; but the satiety center can inhibit it• May be driven by changes in blood
compositionglucostatic theory – blood glucose levels varylipostatic theory - blood lipid levels vary; fat
released from adipose tissue between meals
• Other influencesblood amino acid levelstemperature - high temp decreases appetiteGI tract distension (a slow and variable reflex)social and psychological factorshormones (CCK), neurotransmitters, ions (Zn+)
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MetabolismAll biochemical reactions in the bodyBalance between synthesis (anabolic) and breakdown (catabolic) reactions
• Anabolism chemical reactions that combine simple, smaller molecules into more complex molecules uses energyprotein formation from amino acidscarbohydrate formation from simple sugarsetc.
• Catabolismchemical reactions that break down complex organic molecules into simpler onesreleases energyproteins are broken down by various proteasesetc.
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Relationship of Catabolism to Anabolism
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ATP is the link between anabolism and catabolism
ATP energy is the “currency” used in most cellular energy exchanges
catabolic reactions provide the ATP energy that most anabolic reactions require
only about 10-30% of the energy released by catabolic reactions can be used• most chemical energy is lost as “waste heat”• “waste heat” is not wasted; it is essential in maintaining a
constant body temperature
Adenosine Tri-Phosphate
3 Phosphates
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ATP MetabolismAllows for transfer of small but useful amounts
of energy from one molecule to anotherCell's entire amount of ATP is recycled
approximately every minuteATP is NOT for long term energy storage
• too reactive in the cell• other molecules available for energy storage (neutral
fats, glycogen, creatine phosphate, etc.)
About 8kg (17 lb) of ATP is produced every hour in an average male
Total amount of ATP present in the body at any time is only about 50g
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ATP Metabolism (cont.) energy is released by
breaking the third phosphate group’s bond
• ATP ADP + Pi
a reversible reactionthe energy released is enough
to drive anabolic reactions
• ATP ADP + CrP creatine provides energy
storage in skeletal muscleallows for more ATP to be
formed when O2 is less readily available during skeletal muscle contraction
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Energy ProductionEnergy is stored in chemical bonds Oxidation-Reduction (Redox) reactions:
• Oxidation component:also known as dehydrogenation reactionsremove electrons from molecules
o decreases the energy remaining in the oxidized moleculeo generally, 2e- (and 2H+) are removed simultaneously
Can also be the gain of oxygen
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Energy Production (cont.)Oxidation-Reduction
reactions (cont.)• Reduction
component:addition of electrons to
a moleculeincreases the energy of
the reduced molecule
These 2 component reactions are always coupled: oxidation-reduction reactions
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Energy Production (cont.) ATP Generation
• Addition of phosphate to a chemical compound is phosphorylation
• 3 mechanisms for this:(1) substrate-level
phosphorylation – a high-energy phosphate group is transferred directly from a molecule to ADP to make ATP
For example, when the energy stored on a high-energy phosphate group on creatine phosphate is transferred to ADP to make ATP in skeletal muscles
CK transfers its high energy phosphate to ADP
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Energy Production (cont.) ATP Generation
• Adding a phosphate ion to a molecule is phosphorylation
• 3 mechanisms:(2) oxidative
phosphorylation o electrons (H+)
removed from molecules
o enzymes combine H+ with O2 releasing enough energy for ATP formation
(3) photo-phosphorylation - photosynthesis
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Carbohydrate MetabolismGeneral
• 80% of carbohydrates ingested contain glucose; remainder: fructose, galactose
• glucose is the body's preferred carbohydrate energy source
Fate of carbohydrates -- depends on needs of body cells• ATP production• Amino acid synthesis• Glycogenesis • Lipogenesis • Excretion in urine (minimal)
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Carbohydrate Metabolism (cont.)
Glucose anabolism• Glucose storage:
glycogenesisglycogen formation is
stimulated by insulinglucose not needed
immediately is stored in the liver (25%) and in skeletal muscle (75%)
• Glucose release: glycogenolysis
converts glycogen to glucose
occurs between meals, stimulated by glucagon and epinephrine
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Carbohydrate Metabolism (cont.)
Glucose anabolism (cont.)• Formation of glucose from proteins, fats:
gluconeogenesis
when blood glucose level is low, you eat; if glucose remains low, body catabolizes some proteins and fats
stimulated by cortisol and thyroid hormoneo cortisol (glucocorticoids) mobilizes proteins, making AA's
availableo thyroid hormone mobilizes proteins (AA's) and may mobilize
lipids
epinephrine, glucagon, hGH also stimulate
These five hormones are often referred to as the “insulin antagonists.”
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Glucose Metabolism
Glucose Catabolism• glucose oxidation is known as cellular
respirationcomplete catabolism of each molecule of
glucose to CO2, H2O maximum yield of 36 ATP molecules/glucose
o 38% of the energy present in a glucoseo excellent efficiency for a biological systemo the rest of the energy is “waste heat”
2 linked enzymatic pathways are involved in glucose catabolism
o glycolysiso Kreb’s cycle
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Glucose Metabolism (cont.)Glycolysis - OverviewOccurs in cytosol1 glucose 2
pyruvates (pyruvic acid)
net gain 2 ATP’s• 2 ATP’s used• 4 ATP’s made
net gain 2 NADH + 2H+ (aerobic conditions)
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Glucose Metabolism (cont.)Fate of pyruvate (pyruvic acid) - depends on
availability of O2
• without O2: NADH + H+ + pyruvate lactic acid
• with O2 available to the cellpyruvate converted to acetyl coenzyme A (acetyl CoA)this reaction couples glycolysis to the Krebs cycle
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Glucose Metabolism (cont.) Pyruvic acid - formation of acetyl coenzyme A (Acetyl
CoA) + CO2 • lose one carbon from pyruvate to form CO2 (waste)
• the remaining two carbons, the acetyl group, join with CoA, to generate NADH + H+ (1 from each pyruvate = 2 NADH + 2H+ total from one glucose)
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Glucose Metabolism (cont.)Krebs cycle (Citric
Acid Cycle or Tricarboxylic Acid Cycle (TCA)• oxidation of acetyl
Coenzyme A• reduction of
coenzymes (NAD+, FAD+)
Oxidative phosphorylation• uses NADH2‘s and
FADH2‘s to make additional ATPs
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Glucose Metabolism (cont.)
Glycolysis and Krebs Cycle combined total:
6 CO2 (waste) + 6 H2O10 NADH2 + 2 FADH2 +4 ATP (energy harvest)
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Electron Transport
Animal Physiology, Hill et al., 2004
Electrons Source: NADH2/FADH2 from glycolysis and Krebs cycle
High‑energy electrons enter the system, and low‑energy electrons leave
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Electron Transport System
• Oxidative phosphorylation O2 is the final electron
acceptor for low‑energy electrons from last of the carrier molecules
NADH2 3 ATPFADH2 2 ATP
• Enzyme cytochrome oxidase splits apart O2 moleculesCombines each O atom
with 2 H+ ions to makes H2O = water
Animal Physiology, Hill et al., 2004
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Glucose MetabolismOverview
C6H12O6 + 6 O2
6 CO2 (waste) + 12 H2O + 36 ATP (useful energy)
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LipidsBeta oxidation breaks down fatty acids to form acetyl Coenzyme A.
Lipids are more reduced (have fewer oxygens); therefore, they have more potential chemical energy and can be more fully oxidized as an energy fuel.
Therefore, we gain more energy, gram for gram, from fats than from carbohydrates.
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Protein Metabolism
Amino acids may be deaminated and the resulting “carbon skeletons” of whatever composition, can be entered into the glycolytic or Krebs cycle pathways to yield an energy harvest of ATPS. The amino groups will be joined with CO2 molecules to form the nitrogenous waste urea.
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Nutrient Catabolism Pathways Are All Interconnected
Ketone bodies result from excessive lipolysis and fat catabolism; a symptom of diabetes mellitus
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The Daily Metabolic Cycle
The body shifts back and forth physiologically between the absorptive state and the postabsorptive state.
The absorptive state occurs for approximately 4 hours after each regular meal.
The postabsorptive state takes over until the next meal can be absorbed.
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The Absorptive State
InsulinDominates
theAbsorptive
State
All Cells Rely on Glucose from the Meal for Energy
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The Post-Absorptive State
Glucagon dominates the post-absorptive state and is assisted by the “insulin antagonists (glucocorticoids, thyroid hormones, epinephrine, and hGH).
Only Brain and Spinal Cord Cells Rely on Glucose for Energy; Most Other Body Cells Rely on Fatty Acids for Energy.
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The Post-Absorptive State
Glycogenolysis provides glucose fuel for skeletal muscle.
Glycogenolysis and gluconeogenesis in the liver provide plasma glucose for nervous tissue.
Lipolysis supplies lipids to fuel all other cells.
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Lipid Transport by Lipoproteins
Lipoproteins transport hydrophobic lipids in a droplet which is emulsified by an external layer of phospholipids and proteins which make the surface water soluble.
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Lipid Transport by Lipoproteins Chylomicrons carry
absorbed fat from the meal to adipose tissue via lymph
VLDL and LDL carry cholesterol synthesized in the liver and fat stored in the liver to body tissues
HDL carries excess cholesterol back to the liver for catabolism and excretion
Increased total cholesterol and increased LDL are linked to vessel and heart disease
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Thermogenesis
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Heat Loss to the Environmentradiation away of infrared radiationconvection and conduction of heat to air
or water surrounding the bodyevaporation from sweating and from
ventilating respiratory membranesvasodilation of cutaneous capillary bedsdecreased hormonal activity leading to
decreased basal metabolic rate (BMR)behavioral: stop exercising; move to the
shade, take off clothes, turn on a/c, etc.
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Heat Production/Conservationincreased hormone activity (thyroxine,
epinephrine) leading to increased (BMR)increased sympathetic ANS activity
leading to increased (BMR)shivering of skeletal musclesvasoconstriction of dermal capillary
bedsbehavioral: start exercising, huddle
together, use clothing and shelter, use fire or other means of heating the surroundings
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Thermogenesis (cont.) A complex regulation involving negative feedback
control through endocrine and autonomic pathways:
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Pathology of Temperature Control
fever
heat cramps, heat exhaustion, heat stroke
heat-induced dehydration
burns
hypothermia
alcohol-induced hypothermia
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End Chapter 24