Fuel for Exercising Muscle-metabolism and hormonal control 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). 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 Carbohydrates Liver glycogen 110 451 Muscle glycogen 500 2,050 Glucose in body fluids(blood) 15 62 Total 625 2,563 Fat Subcutaneous and visceral 7,800 73,320 Intramuscular 161 1,513 Total 7,961 74,833 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

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 high-intensity 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

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 ¯

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

Adenosine triphosphate produced from 1 molecule of palmitic acid棕櫚酸 Energy Production From the Oxidation of Palmitic Acid (C16H32O2) Fatty acid activation 0 –2 -oxidation 0 35 Krebs cycle 8 88 Subtotal 8 121 By oxidative Stage of process Direct phosphorylation Total 129 Adenosine triphosphate produced from 1 molecule of palmitic acid棕櫚酸

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 (continued) 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. (continued) w Angiotensin II increases peripheral arterial resistance, which increases blood pressure and triggers the release of aldosterone.

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.