Endocrine System Chapter 16 - Part I PDF

10 Endocrine System Chapter 16 - Part I Topics: Endocrine system (overview) Hormones (types, chemistry, control) Target cell action Signaling mechanisms Target cell properties (specificity, receptors) Target cell activation ...

10 Endocrine System Chapter 16 - Part I Topics: Endocrine system (overview) Hormones (types, chemistry, control) Target cell action Signaling mechanisms Target cell properties (specificity, receptors) Target cell activation  9 Endocrine System: Overview ▪ Endocrine system - integrated system of small organs exerting large effects on cell metabolic activity - controls cell activity by hormonal means ▪ Hormones - bloodborne chemical substances functioning as signaling (messenger) molecules, regulates cell activity - effects are seen far away from hormone-releasing organ - either stimulates or inhibits target tissue’s growth and/or function - effects can last from seconds to days ▪ Hypothalamus - neuroendocrine organ, produces/releases several hormones - major endocrine controller (“The Boss”)* * Also controls ANS response  8 Endocrine System: Overview ▪ Local-acting hormones - produced by several other tissues - adipose cells, small intestine, stomach, kidneys, heart - not “true hormones” since action occurs close to site produced 1. autocrines - exerts effects on same cells secreting them, receptors on autocrine cells example: prostaglandin release by smooth muscle cells in blood vessel walls causes them to rapidly contract (vasoconstriction) 2. paracrines - exert effects on nearby cells close to those secreting them, receptors on paracrine cells example: pancreatic somatostatin inhibits release of both insulin & glucagon* * Secreted by pancreatic beta () & alpha () cells, respectively http://4.bp.blogspot.com/_tWtCNvW2zi0/Sw3q3iWq2OI/AAAAAAAAAng/41HzipeDVmU/s1600/paracrine.JPG  7 Hormone Control & Glands ▪ Most body cells are hormone targets in regulating growth, maintenance and/or repair mechanisms Controlled processes include reproduction, growth/development, electrolyte balance, H2O regulation, cell metabolism, blood nutrients, energy production, immune response ▪ Gland types: 1. exocrine - sweat glands, salivary glands, digestive organs moved through excretory ducts directly into adjoining areas where they exert their action 2. endocrine - pituitary, thyroid, parathyroid, adrenal, pineal released into local interstitial fluid, transported through bloodstream, binds to target organ receptors 3. mixed (exocrine/endocrine) - pancreas, gonads, placenta Na+ H+/K+ pancreatic insulin (endocrine) v. digestive enzymes (exocrine) Electrolyte balance  6 Hormones ▪ General characteristics: - regulate metabolic activity of other cells - most exhibit lag (delay) times (secs → hrs) - most have prolonged (lasting) effects ▪ Classification: Hypothalmic regulation 1. amino acid-based - most hormones are protein hormones amines, short chain peptides, long polypeptides 2. steroids - cholesterol-based hormones (e.g., corticosteroids) 3. eicosanoids - biologically active lipids with local “hormone- like” activity released by nearly all cell membranes leukotrienes, prostaglandins http://wikis.lib.ncsu.edu/images/0/06/Hormones.jpg Dopamine Cholesterol  5 Hormone Chemistry ▪ Membrane interaction: 1. amino acid-based hormones - water soluble so they cannot pass through cell membranes, except for thyroid hormone* relays an external signal to an internal messenger system Protein hormones stay outside target cells 2. steroid hormones - lipid soluble so they can readily pass directly through target cell membranes hydrophobic cholesterol base molecule enables steroid hormones to pass through hydrophobic region of phospholipid bilayer ▪ Exact hormone cellular response depends on target cell type & expressed receptors - hormones specifically alter target cell activity * Poorly soluble in water so it can act like a steroid hormone http://www.visualphotos.com/SAPhotos/157/4/2/6/1/Medres/13740.jpg Hand-off to 2nd messenger  4 Hormone Action On Target Cells ▪ Hormones signal a change in cellular action - causes shifts in protein production, intracellular enzyme activation, ion channel opening/closing, cellular secretion ▪ Target cell effects: 1. alters plasma membrane permeability (insulin) 2. stimulates protein synthesis (promote anabolic reactions) 3. activates or deactivates enzyme systems (turns it on or off) 4. induces secretory activity (causes substance release) 5. stimulates mitosis (supports maintenance, growth, &/or repair) https://ib.bioninja.com.au/_Media/mitosis-3_med.jpeg  3 Hormones Signaling: Steroid v. Peptide ▪ Peptide/steroid hormone target cell activation mechanism differs due to membrane permeability/receptor location 1. steroid hormone enters cell → binds to a chaperone protein → complex migrates to nucleus → binds to an internal receptor (DNA recognition site) direct mechanism, changes cell activity by stimulating transcription 2. peptide hormone binds to an extracellular (primary messenger) receptor → signal (hormone recognition site) transduction occurs → generates(secondary cAMP → activates enzymes messenger ) indirect mechanism, changes cell activity via triggered response Adenylate cyclase (Ac) activity Pi + E Pi + E ATP → ADP → AMP → cAMP Steroid hormones Peptide hormones  2 Peptide Hormones: Target Cell Properties ▪ Hormones circulate through bloodstream to most body tissues excluded from brain by blood-brain barrier (targets) (tight junctions) ▪ Hormone specificity: - hormones activate target cells expressing their specific receptor a single cell can express several different hormone receptor type receptor-binding of hormone turns on a “pre-programmed” function ▪ Receptor location: - amount/types of external receptors vary between target cells ACTH receptors are only found on adrenal cortex cells thyroid hormone receptors are found on nearly all body cells, including adrenal cortex http://www.jonbarron.org/sites/default/files/images/nl/target-cells.jpg  1 Peptide Hormones: Target Cell Activation ▪ Controlling factors: 1. hormone blood levels (concentration) 2. relative number of target cell receptors (how many) 3. hormone-receptor affinity (attractive force/binding strength) ▪ Regulation: ▪ control of target cell peptide receptor numbers is dynamic 1. up-regulation - persistently low hormone levels cause an increase () in membrane receptor numbers 2. down-regulation - continuously high hormone levels cause a decrease () in receptor numbers Down-regulation prevents “over responsiveness” by desensitizing target cells. They respond less vigorously to the hormone that is still present http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/basics/targets.gif