Transcript Oxidation of Fat

chapter
2
Fuel for Exercising
Muscle-metabolism and
hormonal control
Learning Objectives
w Learn how our bodies change the food we
eat into ATP to provide our muscles with
the energy they need to move.
w Examine three systems that generate energy
for muscles.
w Explore how energy production and
availability can limit performance.
(continued)
Learning Objectives
w Learn the role of your endocrine system in
maintaining homeostasis in the body during
rest and during acute physical activity.
Metabolism and bioenergetics
w Three basic energy(Substrate) , glucose, protein and fat.
w Bioenergetics .
w metabolism.
Metabolism and bioenergetics
w Energy in biological systems is measured in calories (cal).
w 1 cal is the amount of heat energy needed to raise 1 g of
water 1°C from 14.5°C to 15.5°C.
w In humans, energy is expressed in kilocalories (kcal),
where 1 kcal equals 1,000 cal.
w People often mistakenly say “calories” when they
mean more accurately kilocalories. When we speak
of someone expending 3,000 cal per day, we really
mean that person is expending 3,000 kcal per day.
Energy for Cellular Activity
w Energy is transferred from food sources to our cells to be
stored as ATP.
w ATP is a high-energy compound stored in our cells and is
the source of all energy used at rest and during exercise.
Energy Sources
w At rest, the body uses carbohydrates and fats for energy.
w Protein provides little energy for cellular activity, but serves
as building blocks for the body's tissues.
w During moderate to severe muscular effort, the body relies
mostly on carbohydrate for fuel.
Carbohydrate
w Readily available (if included in diet) and easily
metabolized by muscles
w Once ingested, it is transported as glucose and taken up
by muscles and liver and converted to glycogen
w Glycogen stored in the liver is converted back to glucose
as needed and transported by the blood to the muscles
where it is used to form ATP
w Glycogen stores are limited, which can affect performance
Fat
w Provides substantial energy at rest and during prolonged,
low-intensity activity
w Body stores of fat are larger than carbohydrate reserves
w Less accessible for metabolism because it must be
reduced to glycerol and free fatty acids (FFA)
w Only FFAs are used to form ATP
w Fat is limited as an energy source by its rate of energy
release
w Fat (9.4kcal/g)
carbohydrate(4.1kcal/g)
Body Stores of Fuels and Energy
g
kcal
110
500
15
451
2,050
62
625
2,563
7,800
161
73,320
1,513
7,961
74,833
Carbohydrates
Liver glycogen
Muscle glycogen
Glucose in body fluids(blood)
Total
Fat
Subcutaneous and visceral
Intramuscular
Total
Note. These estimates are based on an average body weight of 65 kg
(143 lb) with 12% body fat.
Protein
w Can be used as an energy source if converted to
glucose via gluconeogenesis(糖生成作用)
w Can generate FFAs in times of starvation through
lipogenesis(脂質生成作用)
w Only basic units of protein— amino acids—can be
used for energy: ~4.1 kcal of energy per g of protein
Rate of Energy Release (Enzymes)
w Specific protein molecules that control the breakdown of
chemical compounds
w Names are often complex, but always end in “ase”
w Work at different rates and can limit a reaction
w Glycolytic enzymes act in the cytoplasm, while oxidative
enzymes act in the mitochondria
ACTION OF
ENZYMES
(lock and key)
Bioenergetidcs:The Basic Energy Systems
1. ATP-PCr system (phosphagen system)—cytoplasm
2. Glycolytic system—cytoplasm
3. Oxidative system—mitochondria or powerhouses of cell
ATP MOLECULE
ATP-PCr System
w This system can prevent energy depletion by quickly
reforming ATP from ADP and Pi.
w This process is anaerobic—it occurs without oxygen.
w 1 mole of ATP is produced per 1 mole of
phosphocreatine (PCr). PCr is not used for cellular work
but solely for regenerating ATP.
RECREATING ATP WITH PCr
ATP AND PCr DURING SPRINTING
Glycogen Breakdown and Synthesis
Glycolysis—Breakdown of glucose; may be anaerobic or
aerobic(無氧糖解)
Glycogenesis—Process by which glycogen is synthesized
from glucose to be stored in the liver(肝糖生成作用)
Glycogenolysis—Process by which glycogen is broken
into glucose-1-phosphate to be used by muscles(肝糖分解作用)
Figure 03.17
20
21
Glycolytic System
w Requires 12 enzymatic reactions to breakdown glucose
and glycogen into ATP(P52 fig2.5)
w Glycolysis that occurs in glycolytic system is generally
anaerobic (without oxygen)
w The pyruvic acid produced by anaerobic glycolysis
becomes lactic acid
w 1 mole of glycogen produces 3 mole ATP; 1 mole of
glucose produces 2 mole of ATP. The difference is due to
the fact that it takes 1 mole of ATP to convert glucose to
glucose-6-phosphate, where glycogen is converted to
glucose-1-phosphate and then to glucose-6-phosphate
without the loss of 1 ATP. (P52 fig2.5)
Did You Know…?
The combined actions of the ATP-PCr and glycolytic
systems allow muscles to generate force in the absence
of oxygen; thus these two energy systems are the major
energy contributors during the early minutes of highintensity exercise.
Oxidative System
w Relies on oxygen to breakdown fuels for energy
w Produces ATP in mitochondria of cells
w Can yield much more energy (ATP) than anaerobic
systems
w Is the primary method of energy production during
endurance events
Oxidative Production of ATP
1. Aerobic glycolysis—cytoplasm
2. Krebs cycle—mitochondria
3. Electron transport chain—mitochondria(ETC)
Aerobic respiration
26
AEROBIC GLYCOLYSIS AND THE
ELECTRON TRANSPORT CHAIN
KREBS
CYCLE
Oxidation of Carbohydrate
1. Pyruvic acid from glycolysis is converted to acetyl
coenzyme A (acetyl CoA).
2. Acetyl CoA enters the Krebs cycle and forms 2 ATP,
carbon dioxide, and hydrogen.
3. Hydrogen in the cell combines with two coenzymes that
carry it to the electron transport chain.(NADH)
4. Electron transport chain recombines hydrogen atoms to
produce ATP and water.
5. One molecule of glycogen can generate up to 39
molecules of ATP.
OXIDATIVE PHOSPHORYLATION
¯
31
Oxidation of Fat
w Lypolysis—breakdown of triglycerides into glycerol and
free fatty acids (FFAs).
w FFAs travel via blood to muscle fibers and are broken
down by enzymes in the mitochondria into acetic acid乙酸
which is converted to acetyl CoA.
w Aceytl CoA enters the Krebs cycle and the electron
transport chain.
w Fat oxidation requires more oxygen and generates more
energy(129ATP) than carbohydrate oxidation.
METABOLISM OF FAT , carbohydrate and protein
The overall pathways for the metabolism of
food
34
Energy Production From the Oxidation
of Palmitic Acid (C16H32O2)
Adenosine triphosphate
produced from 1 molecule
of palmitic acid棕櫚酸
Stage of process
Direct
By oxidative
phosphorylation
Fatty acid activation
0
–2
-oxidation
0
35
Krebs cycle
8
88
Subtotal
8
121
Total
129
Oxidation of Protein
w Body uses little protein during rest and exercise
(less than 5% to 10%).
w Some amino acids that form proteins can be converted
into glucose.
Interaction of the three energy system
Oxidative Capacity of Muscle
w Oxidative enzyme activity within the muscle
w Fiber-type composition and number of mitochondria
w Endurance training
w Oxygen availability and uptake in the lungs
OXIDATIVE ENZYME ACTIVITY
AND OXIDATIVE CAPACITY
HORMONAL CONTROL
Hormonal control
w The endocrine and nervous system work to initiate and
control movement and all physiology process
w The nervous system function quickly, short-lived, localized
effects
w The endocrine system responds more slowly but has
longer-lasting effects
ENDOCRINE
ORGANS
Hormones
w Chemical messengers from endocrine glands that travel in
the blood placing them in direct contact with all cells
w Hormones travel in the blood to their specific target
cell
w Receptors are specific to hormones such that only the
correct hormone will “fit” the correct receptor—each cell
has 2,000 to 10,000 specific receptors
Chemical classification of hormones
Steroid Hormones
w Lipid soluble
w Diffuse easily through cell membranes; receptors
located within cell
w Chemical structure is derived from or is similar to
cholesterol
w Secreted by adrenal cortex (e.g., cortisol), ovaries (e.g.,
estrogen), testes (e.g., testosterone), placenta (e.g.,
estrogen)
Nonsteroid Hormones
w Nonlipid soluble
w Cannot easily diffuse through cell membranes;
receptors located on cell membrane
w Two types: amino acid derivatives (e.g., epinephrine腎
上腺素) and protein or peptide hormones縮氨酸
(e.g., insulin)
ACTION OF A STEROID HORMONE
Hormone Actions
w Hormone-receptor complex enters nucleus, binds to parts
of cell’s DNA, actives certain genes—direct gene
activation
w Activation mRNA within nucleus, mRNA enters
cytoplasm and promotes proteins synthesis.
w These protein may be, enzyme, structural protein and
regulatory protein.
w Nonsteroid hormones mechanism as fig 2.13
ACTION OF A NONSTEROID HORMONE
w cAMP produce specific physiological response,
including: activation of cellular enzyme, change
membrane permeability, promotion protein synthesis,
change cellular metabolism, stimulation cellular
secretion. Adenylate cyclase腺苷酸環化酶
Hormone receptors
w Plasma levels of specific hormones fluctuate.
w Secretion is regulated by a negative feedback system.
w Cells can also alter their number of hormone
receptors via down- or up-regulation.
Alteration in Number of Receptors
Down-regulation—Decrease in number of cell receptors;
less hormone can bind to the cell and higher concentrations
of the hormone remain in the blood plasma
Up-regulation—Increase in number of cell receptors; more
hormone can bind to the cell and lower concentrations of
the hormone remain in the blood plasma
Hormones of the anterior and posterior
pituitary, table 2.4
HORMONES OF THE PITUITARY GLAND
Thyroid gland
Hormones of the Thyroid Gland
Triiodothyronine (T3) and Thyroxine (T4)
w Increase the rate cellular metabolism, contracting heart
w Increase size and number of mitochondria in cells
w Promote rapid cellular uptake of glucose
w Enhance glycolysis and glycogenesis
w Increase FFA availability for oxidation
Calcitonin
w Decreases plasma calcium concentration
w Acts primarily on bones and kidneys
Did You Know…?
The parathyroid gland produces parathyroid hormone
(PTH), which regulates plasma calcium and plasma
phosphate concentrations by targeting the bones,
intestines, and kidneys.
Adrenal medulla
Hormones of the Adrenal Medulla
w Catecholamines—epinephrine and norepinephrine
w Stimulated by sympathetic nervous system to prepare
you for immediate action
w Increase rate and force of heart contraction, blood
pressure, and respiration
w Increase metabolic rate, glycogenolysis, and release of
glucose and FFA into blood
w Allow more blood to go to the skeletal muscles through
vasodilation and vasoconstriction of specific vessels
Adrenal cortex
Hormones of the Adrenal Cortex
Mineralocorticoids
w Maintain electrolyte balance in extracellular fluids
w Include aldosterone
Glucocorticoids
w Maintain consistent plasma glucose levels between meals
w Include cortisol
Gonadocorticoids
w Released in addition to those released by reproductive
organs but in lesser amounts
w Include androgens, estrogens, and progesterones黃體酮
Pancreas
Hormones of the Pancreas
Insulin—secreted when plasma glucose levels are elevated
(hyperglycemia)
Glucagon—secreted when plasma glucose concentrations
are below normal (hypoglycemia)
Regulation of metabolism during exercise
Regulation of plasma glucose concentration
Regulation of plasma glucose concentration
w Glucagon
w Epinephrine
w Norepinephrine
w Cortisol
PLASMA LEVELS OF HORMONES
.
DURING CYCLING AT 65% VO2MAX
Glucose uptake by muscle
Increased sensitivity to insulin during
prolonged effort
Regulation of Fat Metabolism during exercise
w Cortisol
w Epinephrine
w Norepinephrine
w Growth hormone
w Decreased insulin
PLASMA LEVELS OF FFA AND
CORTISOL DURING
. CYCLING
AT 65% TO 75% VO2MAX
PLASMA LEVELS OF EPINEPHRINE,
NOREPINEPHRINE, GH, AND FFA
DURING
CYCLING AT 65% TO 75%
.
VO2MAX
Did You Know…?
When carbohydrate reserves are low, the hormones
accelerate the oxidation of fats to ensure your muscles
get the energy they need. The rate of fat breakdown into
FFA and glycerol may partly determine the rate at which
muscles use fat as a fuel source during exercise.(β
oxidation)
Hormonal regulation of fluid and electrolyte
balance during exercise
Posterior pituitary(ADH)
HOW ADH CONSERVES BODY WATER
Adrenal cortex (Aldosterone)
RENIN-ANGIOTENSIN MECHANISM
PLASMA VOLUME AND ALDOSTERONE
DURING CYCLING
Hormones and Fluid and Electrolyte Balance
Anitdiuretic hormone (ADH)—Released by the posterior
pituitary in response to increased blood osmolarity;
promotes water conservation by increasing plasma volume.
Aldosterone—Released by the adrenal cortex in response
to decreased blood pressure; promotes sodium and H2O
reabsorption in kidneys and increases plasma volume.
Did You Know…?
Following the initial drop, plasma volume remains relatively
constant throughout exercise due to
1. The actions of Aldosterone and ADH,
2. Water returning from the exercising muscles to the blood,
and
3. The increase in amount of water produced by metabolic
oxidation within muscles.(p54 fig2.6)
Postexercise Fluid Balance
Fluid loss from the blood results in hemoconcentration—a
concentration of the particles of the blood. Hemodilution,
on the other hand, is a dilution of the constituents of the
blood caused by gains in fluid to the blood.
PLASMA VOLUME CHANGES
Key Points
Hormones and Fluid Balance
w Aldosterone and ADH are the two primary
hormones involved in regulating fluid
balance.
w When plasma volume or blood pressure
decrease, the kidneys produce renin that
eventually converts to angiotensin II.
w Angiotensin II increases peripheral arterial
resistance, which increases blood pressure
and triggers the release of aldosterone.
(continued)
Key Points
Hormones and Fluid Balance
w Aldosterone promotes sodium
reabsorption in the kidneys, which in turn
causes water retention, thus increasing the
plasma volume.
w ADH is released in response to increased
plasma osmolarity and acts on the kidneys
to promote water conservation.
w Plasma volume increases, which results in
dilution of the plasma solutes and blood
osmolarity decreases.