Copyright © 2012 American College of Sports Medicine Chapter 6 Endocrine System Responses and Adaptations

Copyright © 2012 American College of Sports Medicine Endocrine System: Overview General Functions –Helps body maintain normal function –Prepares body for exercise –Mediates several adaptations –Is involved in every system Mechanism –Releases chemical messenger (hormone) –Transports hormone to target tissue –Elicits chain of events leading to desired function

Copyright © 2012 American College of Sports Medicine Hormone Actions Autocrine Actions –Hormone acts on cells that produced it Paracrine Actions –Hormone acts on cells adjacent to the ones that produced it Endocrine Actions –Hormone enters general circulation & travels systematically to specific target tissues

Copyright © 2012 American College of Sports Medicine Role of Releasing Hormone Releasing Hormones –Hormones that cause the release of other hormones –Hypothalamus Segment of brain that acts as an endocrine gland Provides link between nervous & endocrine systems Synthesizes & releases neurohormones to the pituitary gland

Copyright © 2012 American College of Sports Medicine Role of Releasing Hormone (cont’d) Hormones Released by the Hypothalamus –Corticotropin-releasing hormone (CRH) –Gonadotropin-releasing hormone (GnRH) –Growth hormone-releasing hormone –Growth hormone-inhibiting hormone –Thyrotropin-releasing hormone (TRH) –Prolactin-inhibiting hormone (PIH)

Copyright © 2012 American College of Sports Medicine Role of Releasing Hormone (cont’d) Hormones Released by the Pituitary in Response to the Release of Hormones from the Hypothalamus –Growth hormone (GH) –Follicle-stimulating hormone (FSH) –Luteinizing hormone (LH) –Adrenocorticotropic hormone (ACTH) –Thyroid-stimulating hormone (TSH) –Prolactin –Beta-endorphins

Copyright © 2012 American College of Sports Medicine Types of Hormones Steroid Hormones –Made of three 6-carbon rings & one 5-carbon ring –Synthesized from cholesterol via synthetic pathways –Actions: Released into circulation Arrive at target tissue Diffuse through cell membrane Bind to specific receptor within cell

Copyright © 2012 American College of Sports Medicine Types of Hormones (cont’d) Common Steroid Hormones –Androgens: testosterone (TE) –Glucocorticoids: cortisone –Progesterone –Prostaglandins –Anabolic steroids: commonly used/abused by athletes

Copyright © 2012 American College of Sports Medicine Types of Hormones (cont’d) Peptide Hormones –Proteins of various sizes Peptides: small chains Polypeptides: large chains –Direct product of: mRNA translation Cleavage from larger parent molecules Other postsynthesis modifications –Circulate & bind to specific receptors on cell membranes of target tissues

Copyright © 2012 American College of Sports Medicine Types of Hormones (cont’d) Common Peptide Hormones –Insulin –Insulin-like growth factor-I (IGF-I) –Superfamily of GH molecules

Copyright © 2012 American College of Sports Medicine Types of Hormones (cont’d) Amine Hormones –Have amine (NH 2 ) group at end of molecule –Derived from amino acids –Classified as protein hormones –Synthesized from: Tyrosine Phenylalanine Tryptophan –Must bind to surface-bound receptor on target tissue –Can act as neurotransmitters in autonomic nervous system

Copyright © 2012 American College of Sports Medicine Types of Hormones (cont’d) Common Amine Hormones (catecholamines) –Epinephrine –Norepinephrine –Dopamine

Copyright © 2012 American College of Sports Medicine Major Endocrine Glands in the Human Body

Copyright © 2012 American College of Sports Medicine Hormone Activity: Production, Release, and Transportation Production & Release –Peptides & amines are synthesized in advance & stored in vesicles until needed –Steroids are synthesized from cholesterol & released (not stored) Transportation –Released into circulation & transported to target tissues –Half-life: time it takes for half of hormone to be degraded –Transport (binding) proteins Protect hormone from metabolism Deliver hormone to its receptor

Copyright © 2012 American College of Sports Medicine Hormone Activity: Production, Release, and Transportation (cont’d) What Determines Hormonal Concentrations in the Blood? –Amount of hormone released –Pattern of release (pulsatility) –Rate of metabolism –Quantity of transport proteins –Time of day (circadian patterns) –Plasma volume shifts (during exercise)

Copyright © 2012 American College of Sports Medicine Hormone Activity: Production, Release, and Transportation (cont’d) Negative Feedback Control –Elevates a hormone when it is low –Reduces a hormone when it is elevated –Example: athlete using anabolic steroids— Reductions in testosterone production lead to Testicular shrinkage due to Negative feedback inhibition of endogenous TE production

Copyright © 2012 American College of Sports Medicine Receptor Interaction Receptor Specificity –Lock-and-key principle: only one hormone will unlock or activate each receptor –Cross-reactivity: allows more than one hormone or molecule to activate a receptor

Copyright © 2012 American College of Sports Medicine Receptor Interaction (cont’d) Steroid and Thyroid Hormones –Steroids, because they are lipophilic: Diffuse through target cell membranes Bind to receptors in cytoplasm or nucleus –Receptors are bound to heat-shock proteins in cytoplasm prior to hormone binding

Copyright © 2012 American College of Sports Medicine Hormones and Exercise Exercise Presents a Potent Stimulus for Hormonal Adaptations Resistance Training (RT) Acute Program Variables –Intensity –Volume –Rest intervals –Exercise selection & sequence –Repetition velocity –Frequency

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Aerobic, Plyometric, Sprint, & Agility Training Variables –Intensity –Volume & duration –Modality –Work:rest ratio –Frequency

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Other Variables Affecting Hormonal Responses –Genetic predisposition –Gender –Fitness level –Nutritional intake –Potential for adaptation

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Classifications of Hormonal Responses and Adaptations –Acute responses during exercise –Chronic changes in resting concentrations –Chronic changes in acute response to exercise –Receptor changes

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Testosterone (testes) –Elevated during & immediately following exercise –Acute TE response weaker in women –Changes in resting TE during RT are inconsistent –Regulated by luteinizing hormone (LH) –Bound to sex hormone-binding globulin (SHBG) –Precursors: dehydroepiandrosterone (DHEA), androstendione, & androstenediol

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Growth Hormone (GH) Superfamily (anterior pituitary-brain) –Secreted by anterior pituitary –Released in pulsatile manner –Under control of GHRH & inhibited by somatostatin –Exercise is a potent stimulus for GH secretion –No apparent change in resting GH with consistent exercise –50% of GH binds to GH-specific binding proteins (GHBPs) that extend its half-life & enhance its effects

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Insulin-Like Growth Factors (IGFs) (liver) –Structurally related to insulin & mediate many actions of GH –Small polypeptide hormones secreted by liver in response to GH stimulation –Increase proliferation & differentiation of satellite cells & protein synthesis –Enhance muscle hypertrophy –IGF-1 response to exercise is unclear –No consistent pattern of change in IGF-1 during exercise

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Insulin (pancreas) –Secreted from Islets of Langerhans (B cells) in pancreas –Secreted in response to glucose intake –Increases muscle protein synthesis when amino acid is adequate –Aerobic & anaerobic training: Improves insulin sensitivity Reduces insulin resistance

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Glucagon (pancreas) –Protein hormone consisting of 29 amino acids –Synthesized in A cells in Islets of Langerhans of pancreas –Inhibited by glucose levels –Stimulates breakdown of glycogen –Increases energy availability –Elevated during exercise as energy demands increase

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Cortisol (adrenal cortex; perimeter of adrenal gland top of kidney) –Catabolic glucocorticoid released from adrenal cortex in response to stress under the control of CRH & ACTH –Stimulates lipolysis in adipose cells –Increases protein degradation in muscle cells –Decreases protein synthesis in muscle cells –Elevated during aerobic exercise, with greater response occurring with greater intensity –Increased during RT –Resting concentrations reflect a long-term stress & are transient

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Catecholamines (adrenal medulla; adrenal gland-top kidney) –Secreted by adrenal medulla –Secreted in response to stress (physical, heat, hypoxia, hypoglycemia) –Increased during both aerobic & anaerobic exercise –Magnitude of increase depends on: Muscle mass involved Posture Intensity Duration

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) β-Endorphins (anterior pituitary-brain) –31-amino acid peptide cleaved in anterior pituitary from parent –Act as neurotransmitters in nervous system & as analgesics –Increase relaxation –Enhance immune function –Increased with exercise, with response depending on intensity & duration

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Thyroid Hormones (thyroid gland-neck) –Thyroxine (T4) & triiodothyronine (T3) released into circulation –Travel mostly bound to transport proteins –Increase basal metabolic rate –Increase protein synthesis –Augment actions of catecholamines –Response to exercise not clear

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Fluid-Regulatory Hormones –Fluid homeostasis is critical to exercise performance –Elevations in AVP, atrial peptide, renin, aldosterone, & angiotensin II during exercise –Magnitude of increase dependent on intensity, duration, fitness level, & hydration status

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Leptin (adipose tissue) –Product of ob gene in adipose tissue –Relays satiety signal to hypothalamus to regulate energy balance & appetite –Higher levels in obese individuals (4 times greater) & women –Crosses blood-brain barrier to act with receptors –Concentrations influenced by insulin, glucocorticoids, catecholamines, thyroid hormones, TE, GH, & stimulants –Not affected by exercise, independent of % body fat

Copyright © 2012 American College of Sports Medicine Hormones and Exercise (cont’d) Estrogens (Ovaries) –Include estradiol, estriol, & estrone –Have long half-lives –Synthesized & secreted primarily by ovaries in women, under control of LH & FSH –Produced from conversion of androgens in men –Response to exercise unclear