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Chapter 5 Hormonal Responses to Exercise Objectives • Describe the hormone-receptor interaction • Identify 4 factors that influence the contraction of a hormone in the blood • Describe how steroid hormones act on cell • Describe “second messenger” hormone action • Describe the role of hypothalamus-releasing factors in the control of hormone secretion from the anterior and posterior pituitary Objectives • Identify the site of release, stimulus for release, & the predominate action of the following hormones: epinephrine, norepinephrine, glucagon, insulin, cortisol, aldosterone, thyroxine & growth hormone • Discuss the use of anabolic steroid & growth hormone on muscle growth and their potential side effects 1 Objectives • Contrast the role of plasma catecholamines w/ intracellular factors in the mobilization of muscle glycogen during exercise • Graphically describe the chagnes in the following hormones during graded and prolonged exercise & discuss how those changes influence the 4 mechanisms used to maintain the blood glucose concentration: insulin, glucagon, cortisol, growth hormone, epinephrine, and norepinephrine Objectives • Describe the effect of changing hormone & substrate levels in the bld on the mobilization of free fatty acids from adipose tissue Neuroendocrinology • Endocrine glands release hormones directly into the bld • Hormones alter the activity of tissues that possess receptors to which the hormone can bind • The plasma hormone concentration determines the magnitude of the effect at the tissue level 2 Bld Hormone Concentration Determined by: • Rate of secretion of hormone from endocrine gland • Rate of metabolism or excretion of hormone • Quantity of transport pro • ∆s in plasma volume Control of Hormone Secretion • Rate of insulin secretion from the pancreas is dependent on: – Magnitude of input – Stimulatory vs. inhibitory Factors That Influence the Secretion of Hormones 3 Hormone-Receptor Interactions • Trigger events at the cell • Magnitude of effect dependent on: – Concentration of the hormone – Number of receptors on the cell – Affinity of the receptor for the hormone Hormone-Receptor Interactions • Hormones bring about effects by: – Altering membrane transport – Stimulating DNA to increase protein synthesis – Activating second messengers • • • • Cyclic AMP Ca++ Inositol triphosphate Diacylglycerol Steroid Hormones Mechanism 4 Non-Steroid Hormone Mechanism Cyclic AMP “Second Messenger” Mechanism Hormones: Regulation & Action • Hormones are secreted from endocrine glands – Hypothalamus & pituitary glands – Thyroid & parathyroid glands – Adrenal glands – Pancreas Hypothalamus • Controls activity of the anterior & posterior pituitary glands • Influenced by (+) & (-) input 5 Positive & Negative Input to the Hypothalamus Anterior Pituitary Gland Growth Hormone • Secreted from the anterior pituitary gland • Essential for normal growth – Stimulates protein synthesis & long bone growth • ↑s during exercise 6 Growth Hormone Posterior Pituitary Gland • Secretes antidiuretic hormone (ADH) • Reduces water loss from the body to maintain plasma volume • Stimulated by: ∆ in the Plasma ADH Concentration During Exercise 7 Thyroid Gland • Triiodothyronine (T3) & thyroxine (T4) – Important in maintaining metabolic rate & allowing full effect of other hormones • Calcitonin – Regulation of plasma Ca++ • Parathyroid Hormone – Also involved in plasma Ca++ regulation Adrenal Gland • Adrenal medulla – Secretes catecholamines • Epinephrine and norepinephrine – ↑s Î HR, Glycogenolysis, Lypolysis, • Adrenal cortex – Secretes steroid hormones • Mineralcorticoids, glucocorticoids & sex steroids Adrenal Medulla • Part of the sympathetic nervous system – Secrete catecholamines • Epinephrine (E) & norepinephrine (NE) – Bind to receptors on effector organs • Alpha (α) & beta (β) receptors – Bring about ∆s in cellular activity via second messengers 8 Response to Catecholamines: Role of Receptor Type Receptor Type Effect of E/NE Membrane-bound enzyme Intracellular mediator β1 E=NE Adenylate cyclase ↑ cAMP ↑ Heart rate ↑ Glycogenolysis ↑ Lipolysis Effects on Various Tissues β2 E>>>NE Adenylate cyclase ↑ cAMP ↑ Bronchodilation ↑ Vasodilation α1 E≥NE Phospholipase C ↑ Ca++ ↑ Phosphodiesterase ↑ Vasoconstriction α2 E≥NE Adenylate cyclase ↓cAMP Opposes action of β1 & β2 receptors Adrenal Cortex • Mineralcorticoids (aldosterone) – Involved in maintaining plasma Na+ & K+ – Part of the renin-angiotensin-aldosterone system of bld pressure regulation ∆ in Mineralcorticoids During Exercise 9 Adrenal Cortex • Glucocorticoids (Cortisol) Control of Cortisol Secretion Pancreas • Secretes digestive enzymes & HCO3- into small intestine • Releases insulin & glucagon 10 Insulin • Secreted by the β cells of the islets of Langerhans • Promotes the storage of glu, amino acids & fats • Diabetes mellitus is characterized as a lack of insulin (Type 1) or a lack of insulin receptors (Type 2) Glucagon Glucagon • Released from the α cells of the islets of Langerhans • Promotes the mobilization of fatty acids & glu Muscle Glycogen Utilization • Breakdown of muscle glycogen is under dual control – Epinephrine-cyclic AMP – Ca++-calmodulin 11 Control of Glycogenolysis Muscle Glycogen Utilization • Glycogen breakdown is related to exercise intensity Glycogen Depletion During Exercise 12 Plasma EPI Concentration During Exercise Maintenance of Plasma Glu During Exercise • Mobilization of glu from liver glycogen stores • Mobilization of FFA from adipose tissue – Spares bld glu • Gluconeogenesis from AA, lactic acid & glycerol • Blocking the entry of glu into cells – Forces use of FFA as a fuel Bld Glu Homeostasis During Exercise • Permissive & slow-acting hormones – Thyroxine – Cortisol – Growth hormone • Act in a permissive manner to support actions of other hormones 13 Cortisol • Stimulates FFA mobilization from adipose tissue • Mobilizes AA for gluconeogenesis • Blocks entry of glu into cells Role of Cortisol in the Maintenance of Bld Glu Plasma Cortisol During Exercise • At lo intensity • At hi intensity 14 ∆s in Plasma Cortisol During Exercise Growth Hormone • Important in the maintenance of plasma glu Role of Growth Hormone in the Maintenance of Plasma Glu 15 Growth Hormone During Exercise: Effect of Intensity Growth Hormone During Exercise: Trained vs. Untrained Bld Glu Homeostasis During Exercise • Fast-acting hormones • Maintain plasma glu 16 Role of Catecholamines in Substrate Mobilization Epinephrine & Norepinephrine During Exercise • ↑ linearly during exercise • Favor the mobilization of FFA & maintenance of plasma glu ∆ in Plasma Catecholamines During Exercise 17 Epinephrine & Norepinephrine Following Training • ↓d plasma levels in response to exercise bout • Parallels reduction in glu mobilization Plasma Catecholamines During Exercise Following Training Effect of Insulin and Glucagon on FFA Uptake & Oxidation 18 Insulin During Exercise • Plasma insulin decreases during exercise ∆s in Plasma Insulin During Exercise Effect of Training on Plasma Insulin During Exercise 19 Effect of Training on Plasma Glucagon During Exercise Control of Insulin & Glucagon Secretion During Exercise Effect of SNS on Substrate Mobilization 20 Hormonal Responses to Exercise Free Fatty Acid Mobilization During Exercise • FFA mobilization ↓s during heavy exercise • Could be due to hi levels of lactic acid Effect of Lactic Acid on FFA Mobilization 21