Endocrinology Chapter 20 PDF

Chapter 20 The Endocrine System: Organization and Acute and Chronic Responses to Physical Activity Copyright © 2023 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter Objectives #1 Draw the body’s major endocrine gland locations List the sequence of events to show ho...

Chapter 20 The Endocrine System: Organization and Acute and Chronic Responses to Physical Activity Copyright © 2023 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter Objectives #1 Draw the body’s major endocrine gland locations List the sequence of events to show how hormones affect specific “target cell” functions Explain how hormones affect enzyme activity and enzyme-mediated membrane transport Describe the hormonal, humoral, and neural stimulation influences on endocrine gland activity List the anterior and posterior pituitary gland hormones, their functions, and how both acute and chronic physical activity affect their release Copyright © 2023 Wolters Kluwer All Rights Reserved Chapter Objectives #2 List the thyroid gland hormones, their functions, and how both acute and chronic physical activity affect their release List the adrenal medulla and adrenal cortex hormones, their functions, and how both acute and chronic physical activity affect their release Outline how exercise training affects endocrine functions Describe three resistance training effects on testosterone and growth hormone release Copyright © 2023 Wolters Kluwer All Rights Reserved Endocrine System Overview and Organization Consists of host organ, minute quantities of chemical messengers, and target organ Endocrine glands are ductless and secrete substances directly into extracellular spaces Exocrine glands: contain ducts and carry substances directly to a specific surface Major endocrine organs: – Pituitary, thyroid, parathyroid, adrenal, pineal, thymus – Other organs classified as endocrine and include pancreas, gonads (ovaries and testes), hypothalamus, and adipose tissues Copyright © 2023 Wolters Kluwer All Rights Reserved Hormones Produced by Endocrine System Copyright © 2023 Wolters Kluwer All Rights Reserved Endocrine Gland Hormones Travel in the Bloodstream Copyright © 2023 Wolters Kluwer All Rights Reserved Hormone Types Hormones, chemical substances synthesized by specific host glands, enter the bloodstream for transport throughout the body Categories: – Steroid-derived hormones – Amine and polypeptide hormones (synthesized from amino acids) Half-life: time required to reduce a hormone’s blood concentration by one half; gives indication of how long effect persists Most hormones circulate in blood as messengers that affect tissues a distance from the specific gland; other hormones exert local effects Copyright © 2023 Wolters Kluwer All Rights Reserved Hormone-Target Cell Specificity Hormones alter cellular reactions of specific target cells by: – Modifying rate of intracellular protein synthesis by stimulating nuclear DNA – Changing rate of enzyme activity – Altering plasma membrane transport via a second- messenger system – Inducing secretory activity A target cell’s response to a hormone depends on specific protein receptors that bind the hormone in a complementary way Copyright © 2023 Wolters Kluwer All Rights Reserved Hormone-Receptor Binding Represents first step in initiating hormone action Extent of target cell’s activation by hormone depends on: – Hormone concentration in the blood – Number of target cell receptors for the hormone – Sensitivity or strength of the union between the hormone and its receptor Copyright © 2023 Wolters Kluwer All Rights Reserved 3′5′-Cyclic Adenosine Monophosphate: The Intracellular Messenger Cyclic AMP acts as a second messenger to activate a specific protein kinase which specific target enzyme (adenylate cyclase) to alter the cellular response – Necessary for hormone to bind with its specific receptor Three factors establish the sequence of reactions set into motion by cyclic AMP: – Type of target cell – Specific enzymes contained in target cell – Specific hormones that act as first messenger Copyright © 2023 Wolters Kluwer All Rights Reserved Nonsteroid Hormone Action Copyright © 2023 Wolters Kluwer All Rights Reserved Hormone Effects on Enzymes 1. Major hormone actions include altering enzyme activity and enzyme-mediated membrane transport 2. Hormones increases enzyme activity by: – Stimulating enzyme production – Combining with the enzyme to alter its shape and ability to act, which increases or decreases the enzyme’s catalytic effectiveness – Activating inactive enzyme forms, thereby increasing total quantity of active enzyme Copyright © 2023 Wolters Kluwer All Rights Reserved Factors That Determine Hormone Levels Hormone secretion usually adjusts rapidly to meet demands of changing bodily conditions Factors that determine plasma concentration of a hormone: – Quantity synthesized in host gland – Catabolism or secretion rate into the blood – Quantity of transport proteins present – Plasma volume changes Copyright © 2023 Wolters Kluwer All Rights Reserved Endocrine Gland Stimulation Copyright © 2023 Wolters Kluwer All Rights Reserved The Pituitary Gland, Its Secretions, and Targets Copyright © 2023 Wolters Kluwer All Rights Reserved Growth Hormone: Direct and Indirect Metabolic Actions Copyright © 2023 Wolters Kluwer All Rights Reserved Growth Hormone (GH) GH promotes cell division and cellular proliferation throughout the body GH facilitates protein synthesis by: – Increasing amino acid transport through plasma membrane – Stimulating RNA formation – Activating cellular ribosomes that increase protein synthesis GH also slows carbohydrate breakdown and initiates mobilization and use of fat for energy Copyright © 2023 Wolters Kluwer All Rights Reserved Growth Hormone, Physical Activity, and Tissue Synthesis #1 Increased physical activity for relatively short durations stimulates a sharp rise in GH pulse amplitude and the amount of hormone secreted per pulse. Benefits muscle, bone, and connective tissue growth and remodeling. Optimizes fuel mixture during physical activity. Net metabolic effect preserves plasma glucose concentration for CNS and muscle functions. Copyright © 2023 Wolters Kluwer All Rights Reserved Growth Hormone, Physical Activity, and Tissue Synthesis #2 Trained and sedentary individuals similarly increase GH concentration with exhaustive exercise. Sedentary individuals maintain higher GH levels for several hours into recovery and have a greater GH response during submaximal exertion than trained. Copyright © 2023 Wolters Kluwer All Rights Reserved Thyrotropin Thyrotropin (thyroid-stimulating hormone or TSH) controls thyroid gland secretion. TSH maintains growth and development of the thyroid gland and increases thyroid cell metabolism. Copyright © 2023 Wolters Kluwer All Rights Reserved Thyroid Hormones Thyroxine (T4) and Triiodothyronine (T3) – T4 secretion raises metabolism except in brain, spleen, testes, uterus, and thyroid gland. – T3 release facilitates neural reflex activity, whereas low T4 levels cause sluggishness. T4 and T3 regulate tissue growth and development, skeletal and nervous system formation, and maturation and reproduction. Play role in maintaining blood pressure by increasing adrenergic receptors in blood vessels. Copyright © 2023 Wolters Kluwer All Rights Reserved Feedback System That Controls Thyroid Hormone Release Copyright © 2023 Wolters Kluwer All Rights Reserved Posterior Pituitary Hormones Stores antidiuretic hormone (ADH; vasopressin) – ADH inhibits water excretion by the kidneys. Increased ADH release, stimulated by sweating, helps to conserve body fluids during hot weather physical activity with accompanying dehydration. Powerful vasoconstrictor Distal convoluted tuble Copyright © 2023 Wolters Kluwer All Rights Reserved Adrenal Gland Hormones & Secretions Copyright © 2023 Wolters Kluwer All Rights Reserved Role of Norepinephrine and Epinephrine in Substrate Mobilization Copyright © 2023 Wolters Kluwer All Rights Reserved Catecholamine Response to Increasing Intensity Cycling Copyright © 2023 Wolters Kluwer All Rights Reserved Adrenocortical Hormones: Mineralocorticoids Major function: regulates mineral balance in extracellular fluids Aldosterone represents 95% of mineralocorticoids – Controls total sodium concentration and extracellular fluid volume – Stimulates sodium ion reabsorption in distal kidney tubules – Helps stabilize serum potassium and pH – Major effects during recovery from physical activity Copyright © 2023 Wolters Kluwer All Rights Reserved Major Factors Control Aldosterone Release Copyright © 2023 Wolters Kluwer All Rights Reserved Glucocorticoids Cortisol affects glucose, protein, and FFA metabolism six ways: – Promotes breakdown of protein to amino acids – Supports action of other hormones – Serves as an insulin antagonist by inhibiting cellular glucose uptake and oxidation – Promotes triacylglycerol breakdown to glycerol and fatty acids in adipose tissue – Suppresses immune system function – Produces negative calcium balance Copyright © 2023 Wolters Kluwer All Rights Reserved Factors That Affect Cortisol Secretions and Its Actions Copyright © 2023 Wolters Kluwer All Rights Reserved Pancreatic Hormones Pancreas consists of two different types of tissues, acini and islets of Langerhans. Islets comprise 20% α- cells that secrete glucagon and 75% β-cells that secrete insulin and amylin peptide. Acini serve an exocrine function and secrete digestive enzymes. Copyright © 2023 Wolters Kluwer All Rights Reserved Insulin Insulin regulates glucose entry into all tissues (primarily muscle and adipose) except brain. Following a meal, insulin-mediated glucose uptake by cells decreases blood glucose levels. With insufficient insulin secretion, blood glucose concentration increases and spills into urine. Insulin’s action also triggers intracellular enzyme activity that facilitates protein synthesis: – Increases amino acid transport – Increases cellular RNA levels – Increases protein formation by ribosomes Copyright © 2023 Wolters Kluwer All Rights Reserved Insulin’s Primary Functions in the Body Copyright © 2023 Wolters Kluwer All Rights Reserved Target Tissues and Specific Metabolic Responses to Insulin Copyright © 2023 Wolters Kluwer All Rights Reserved Transporters to Facilitate Glucose Entry into Cells Cells possess different glucose transport proteins (GLUTs), depending on variations in insulin and glucose concentrations Muscle contains GLUT-1 (primary glucose transporter during rest) and GLUT-4 (primary glucose transporter after a meal or exercise) GLUT receptors migrate to the cell surface to promote glucose uptake Copyright © 2023 Wolters Kluwer All Rights Reserved Glucose-Insulin Interaction Blood glucose levels within pancreas directly control insulin secretion. Elevated blood glucose levels cause insulin release. The interaction between glucose and insulin serves as a feedback loop to maintain blood glucose concentration within narrow limits. Physical activity inhibition of insulin output explains why no excessive insulin release occurs with a concentrated glucose feeding during physical activity. Copyright © 2023 Wolters Kluwer All Rights Reserved Plasma Insulin Levels During Cycle Ergometry Copyright © 2023 Wolters Kluwer All Rights Reserved Insulin Actions and Impaired Glucose Homeostasis A defect anywhere along the pathway for glucose uptake signals diabetes. Seven possible causes: – Destruction of β-cells – Abnormal insulin synthesis – Depressed insulin release – Inactivation of insulin in blood by antibodies or other blocking agents – Altered insulin receptors or decreased number of receptors on peripheral cells – Defective processing of insulin message within target cells – Abnormal glucose metabolism Copyright © 2023 Wolters Kluwer All Rights Reserved Normal Insulin-Glucose Interaction and Insulin Resistance Copyright © 2023 Wolters Kluwer All Rights Reserved Glucagon The α-cells of the islets of Langerhans secrete glucagon, the “insulin antagonist.” Primarily stimulates both glycogenolysis and gluconeogenesis by liver and increases lipid catabolism. Plasma glucose concentration controls pancreatic output of glucagon. Glucagon primarily regulates blood glucose as physical activity progresses and glycogen reserves deplete. Copyright © 2023 Wolters Kluwer All Rights Reserved Glucagon Secretion and Its Actions Copyright © 2023 Wolters Kluwer All Rights Reserved Exercise Training and Endocrine Function Endurance training produces a decline in the magnitude of hormonal response to a standard exercise load. Improved target tissue sensitivity and/or responsiveness to a given amount of hormone accounts for much of this “efficiency” in response. During maximal exercise, trained subjects have an identical or somewhat greater hormonal response than sedentary counterparts. Copyright © 2023 Wolters Kluwer All Rights Reserved Growth Hormone and Exercise GH stimulates lipolysis and inhibits carbohydrate breakdown. Compared with untrained, endurance-trained individuals show less rise in blood GH levels at a given exercise intensity. Attributed to reduced exercise stress as training progresses and fitness improves. Females typically maintain higher GH levels at rest than males, a difference that disappears during prolonged physical activity. Copyright © 2023 Wolters Kluwer All Rights Reserved Thyroid Hormones and Exercise Exercise training produces a coordinated pituitary– thyroid response that reflects increased turnover of thyroid hormones. Increased thyroid turnover often reflects excessive hormonal action that could lead to hyperthyroidism. No evidence indicates a higher incidence of hyperthyroidism in trained individuals. Greater T4 turnover with training occurs through a mechanism that differs from “normal” thyroid hormone dynamics. Copyright © 2023 Wolters Kluwer All Rights Reserved Antidiuretic Hormone (ADH) Intense physical activity to exhaustion or prolonged submaximal activity maintained at the same relative intensity produces no difference in ADH levels between trained and untrained individuals. ADH (vasopressin) concentration decreases with training. Copyright © 2023 Wolters Kluwer All Rights Reserved Adrenal Hormones and Exercise Adrenal hormone production increase from the stress of both aerobic and resistance exercise. Training adaptations that appear sensitive to adrenal hormone effects include increased muscle mass, fatigue resistance, increased fatty acid oxidation, increased systemic glucose disposal, and resynchronization of skeletal muscles’ circadian rhythm. Copyright © 2023 Wolters Kluwer All Rights Reserved Epinephrine and Norepinephrine and Exercise Sympathoadrenal activity to submaximal exercise remains lower in trained individuals compared to untrained. Greater catecholamine output at the same relative exercise intensity following training reflects three factors requiring greater sympathetic nervous system activation: – Greater absolute demand for substrate use via glycogenolysis and lipolysis – Increased cardiovascular response – Larger muscle mass activation Copyright © 2023 Wolters Kluwer All Rights Reserved Aldosterone, Cortisol, and Pancreatic Hormones and Exercise Training does not affect resting levels for renin- angiotensin-aldosterone system nor their normal response to physical activity. Plasma cortisol levels increase less in trained subjects than in sedentary subjects who perform the same absolute level of submaximal exercise. Endurance training maintains blood levels of insulin and glucagon closer to resting levels during physical activity. The trained state requires less insulin from rest through light to moderately intense physical activity. Copyright © 2023 Wolters Kluwer All Rights Reserved Pre-Post Aerobic Training Differences in Glucagon and Insulin Copyright © 2023 Wolters Kluwer All Rights Reserved Resistance Training and Endocrine Function Hormonal factors responsible for exercise-induced changes in muscle size and function include: – Changes in hepatic and extrahepatic hormone clearance rates – Differential rates of hormone secretion – Altered receptor-site activation via neurohumoral control Testosterone and GH are two primary hormones that affect adaptations to resistance training. Copyright © 2023 Wolters Kluwer All Rights Reserved Heavy Resistance Training Enhances Maximal Power and Strength Copyright © 2023 Wolters Kluwer All Rights Reserved Physical Activity and Immune Function Physical activity, stress, and illness interact, each exerting its separate effect on immunity. Physical activity can positively or negatively modulate the stress response. Each factor—stress, illness, and short- and long-term exercise—exerts an independent effect on immune status, immune function, and resistance to disease. Copyright © 2023 Wolters Kluwer All Rights Reserved Theoretical Interrelationships Among Stress, Physical Activity, Illness, and the Immune System Copyright © 2023 Wolters Kluwer All Rights Reserved Upper Respiratory Tract Infections (UTRI) Light to moderate physical activity offers more protection against URTI than a sedentary lifestyle. Moderate physical activity does not exacerbate the severity and duration of illness when an infection occurs; can boost natural immune functions and hosts defenses for up to several hours. Prolonged exhaustive physical activity or increased training severely depress the body’s first line of defense against infection. Copyright © 2023 Wolters Kluwer All Rights Reserved Relationship Between Physical Activity Intensity and URTI Copyright © 2023 Wolters Kluwer All Rights Reserved Long-Term Exercise Effects on Immune System Function Aerobic training positively affects natural immune functions in young and old individuals and obese persons during weight loss. Areas of improvement include enhanced functional capacity of natural cytotoxic immune mechanisms and diminished age-related decrease in T-cell function and associated cytokine production. The open window hypothesis maintains that an inordinate increase in training or competition exposes highly conditioned athletes to abnormal stress that transiently but severely depresses immune cell function. Copyright © 2023 Wolters Kluwer All Rights Reserved Optimizing Immune Function A lifestyle that emphasizes regular physical activity, maintaining a well-balanced diet, reducing stress, and obtaining adequate sleep optimizes immune function. With prolonged intense activity, ingesting 1 L·hr−1 of a carbohydrate-rich drink reduces negative changes in immune function from the stress of physical activity and carbohydrate depletion. Endurance athletes who consume carbohydrate during a race experience a lower disruption in hormonal and immune measures than athletes who do not consume carbohydrate. Copyright © 2023 Wolters Kluwer All Rights Reserved