Hormones Intro PDF

Hormones Intro  Endocrine System 2 The neuroendocrine system is a communication system.  Nervous system: electrical communication & neurotransmitters  Endocrine system: chemical communication Endocrine system...

Hormones Intro  Endocrine System 2 The neuroendocrine system is a communication system.  Nervous system: electrical communication & neurotransmitters  Endocrine system: chemical communication Endocrine system is slower to respond but longer lasting than the nervous system. hormones: Chemical messengers that are synthesized, stored, and released into the blood by endocrine glands and certain other cells. Endocrine system consists of: (1) host organ, (2) small [concentrations] of chemical messengers, and (3) a target or receptor organ Endocrine vs. Exocrine glands Fig. 4.1. Kenney et al. 2019. Physiology of Sport & Exercise. Hum.Kin.  Endocrine System 3 Hormones are chemical substances synthesized by specific host glands Half‐life: the time required to reduce a hormone’s blood concentration by one half and gives an indication of how long its effect persists Most circulate in the blood as messengers that affect tissues a distance from the specific gland and others exert local effects in their region of synthesis  Many have to be carried by transport proteins (e.g. sex hormone binding globulin)  Effect depends on receptor location  Only “free” hormones are able to interact with their receptors Fig. 20.2. McArdle et al. 2010. Exercise Physiology… LWW  Endocrine System 4 Constantly monitors internal environment Coordinates integration of physiological systems during rest and exercise Maintains homeostasis via hormones  Control and regulate cell and organ activity  Act on target cells Maintains homeostasis during exercise  Controlssubstrate metabolism  Regulates fluid and electrolyte balance Fig. 4.1. Kenney et al. 2019. Physiology of Sport & Exercise. Hum.Kin. Patterns of Hormone Release 5 Most hormones respond to peripheral stimuli on an as‐needed basis Secreted in bursts (pulsatile)  Plasma concentrations fluctuate over minutes/hours.  Concentrations fluctuate over days/weeks.  Regulates Homeostasis Negative feedback (e.g. like a thermostat) Positive feedback or Feed‐forward stimulation (e.g. oxytocin) Some release at regular intervals during a diurnal pattern or cycle of secretion  Some secretory cycles span several weeks while others follow daily (24hr) cycles  Hormone Receptors 6 Hormone binds to receptor to create a hormone– receptor complex (H‐RC). Receptors can be on the cell surface or inside the cell  Hormone affects only tissues with specific receptor.  Hormone exerts effects after binding with receptor.  Typical cell has 2,000 to 10,000 receptors.  Hormone‐Receptor Binding 7 “Lock and Key” mechanism Is the first step in initiating hormone action The extent of a target cell’s activation by a hormone depends on: 1) [Hormone] in the blood 2) Available receptors for the hormone on the target cell Can be upregulated, downregulated, or saturated 3) Affinity or sensitivity of the union between hormone and receptor 4) Other chemical inhibitors (e.g. beta blockers) Fig. 3.3. Baechle et al. 2009. Essentials of Strength… Human Kinetics  Hormone‐Target Cell Reactions 8 Hormones alter cellular reactions of specific target cells by: 1) Changing rate of enzyme activity 2) Modifying the rate of intracellular protein synthesis by stimulating nuclear DNA 3) Activating a second‐messenger system (e.g. G‐proteins, cAMP system, kinase reactions) https://www.youtube.com/watch?v=e6W1086Dcn0 (to 0:37) 4) Inducing secretory activity (e.g. GH & IGFs) Fig. 20.3. McArdle et al. 2010. Exercise Physiology… LWW  Hormone‐Target Cell Reactions 9 The same hormone can have different actions depending on the specific target organ Steroid migration into a target cell by either testosterone in skeletal muscle or dihydrotestosterone in sex‐linked tissues Fig. 3.6. Baechle et al. 2009. Essentials of Strength… Human Kinetics  Figure & Notes References 10 Kenney, Wilmore, Costill. Physiology of Sport and Exercise (7th ed). Human Kinetics, 2018. McCardle, Katch, Katch. Exercise Physiology: Nutrition, Energy, and Human Performance, 8th Edition. Wolters Kluwer Health, 2014. Baechle & Earle. Essentials of Strength & Conditioning, 4th Edition. Human Kinetics, 2016. 10