NURS 230 TRW Lec6a Endocrine System PDF

Topic 6a: The Endocrine System CHAPTER 16 IN TEXTBOOK Important Pages and Topics Chapter 16 1. List the major endocrine organs P 602 2. Define the term endocrine and how it differs from exocrine, paracrine, autocrine P 602-603 3. Describe how hormones are classified into the different major categor...

Topic 6a: The Endocrine System CHAPTER 16 IN TEXTBOOK Important Pages and Topics Chapter 16 1. List the major endocrine organs P 602 2. Define the term endocrine and how it differs from exocrine, paracrine, autocrine P 602-603 3. Describe how hormones are classified into the different major categories: amino acids and steroids P 603 4. Describe how the different types of hormones function in terms of their cellular mechanisms: Plasma membrane receptors/ second-messenger systems and intracellular receptors P 603-606 5. Describe the 3 types of stimuli that cause hormone release: humoral, neural and hormonal P 607-608 6. Explain how hormones have target cell specificity, the factors that activation depends on and how hormones can interact with each other at target cells P 608 7. Compare the differences between lipid-soluble and water soluble hormones in terms of half-life, onset and duration P 608-609 Introduction to Endocrinology Endocrine system acts with nervous system to coordinate and integrate activity of body cells Influences metabolic activities via hormones transported in blood Responses slower but longer lasting than nervous system responses Endocrinology: study of hormones and endocrine organs Comparison of Endocrine and Nervous Systems Introduction to Endocrinology Endocrine system controls and integrates: ◦ Reproduction ◦ Growth and development ◦ Maintenance of electrolyte, water, and nutrient balance of blood ◦ Regulation of cellular metabolism and energy balance ◦ Mobilization of body defenses Introduction to Endocrinology Exocrine glands ◦ Secrete products via ducts ◦ Ducts carry secretion to membrane surface, body surface, into body cavities ◦ Produce nonhormonal substances ◦ Examples: sweat, mucous, saliva, milk Endocrine glands ◦ Ductless glands ◦ Produce hormones ◦ Release hormones into surrounding tissue ◦ Endo – within ◦ Crine – to secrete Figures from Pages 603  Introduction to Endocrinology ◦ Hormones: long-distance chemical signals; travel in blood or lymph ◦ Autocrine: ◦ chemicals that exert effects on same cells that secrete them ◦ Auto = self ◦ Paracrine: ◦ locally acting chemicals that affect cells other than those that secrete them ◦ Endocrine: ◦ Chemicals that enter circulation to affect long http://weallhaveuniquebrains.com/starting_material/cytokines/ distance cells ◦ Autocrines and paracrines are local chemical messengers; not considered part of endocrine system by some scientists (others do)  Introduction to Endocrinology Endocrine glands: ◦ Pituitary ◦ Thyroid ◦ Parathyroid ◦ Adrenal ◦ Pineal Neuroendocrine organ ◦ Hypothalamus Some have exocrine and endocrine functions ◦ Pancreas, gonads, placenta Other tissues and organs that produce hormones ◦ Adipose cells, thymus, and cells in walls of small intestine, stomach, kidneys, and heart Figure 16.1  Hormone Chemical Structure Two main classes of hormones, based on water solubility Amino acid–based hormones Insulin ◦ Most common ◦ Water soluble, cannot cross plasma membrane ◦ Amino acid derivatives, peptides, and proteins Steroids By The original uploader was Takometer at English Wikipedia - Transferred from en.wikipedia to Commons., CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=1531772 ◦ Synthesized from cholesterol ◦ Lipid soluble, can cross plasma membrane ◦ Page 47-48 refresher A possible third class, eicosanoids, is considered a Estrogen hormone by some scientists, but most classify it as a paracrine ◦ Lipid based http://menopausehealthmatters.com/progesterone-deficiency/estrogen-dominance/ Hormone Action Though hormones circulate systemically, only cells with receptors for that hormone are affected Target cells: tissues with receptors for a specific hormone Hormones alter target cell activity Hormones can have different effects in different target cells https://www.sciencelearn.org.nz/images/2269-hormone-action Hormone Action Hormone action on target cells may be to: ◦ Alter plasma membrane permeability and/or membrane potential by opening or closing ion channels ◦ Stimulate synthesis of enzymes or other proteins ◦ Activate or deactivate enzymes ◦ Induce secretory activity ◦ Stimulate mitosis Hormone Action Hormones act in one of two ways, depending Insulin (water soluble) on their chemical nature and receptor location Water-soluble hormones (all amino acid–based hormones except thyroid hormone) ◦ Act on plasma membrane receptors ◦ Act via G protein second messengers ◦ Cannot cross plasma membrane Estrogen (steroid, lipid soluble) Lipid-soluble hormones (steroid and thyroid hormones) ◦ Act on intracellular receptors that directly activate genes ◦ Can enter cross plasma membrane and enter cell http://menopausehealthmatters.com/wp-cont ent/uploads/2015/08/estrogen-molecule.png\ Quick Review Questions What is the difference between and endocrine and exocrine gland? Compare and contrast endocrines, autocrines, paracrines Where are the receptors for water soluble and lipid soluble hormones found? Plasma Membrane Receptors and Second-Messenger Systems Amino acid–based hormones, except thyroid hormone, exert effects through second-messenger systems Two main second-messenger systems: ◦ Cyclic AMP (in detail) ◦ PIP2-calcium https://en.wikipedia.org/wiki/Second_messenger_system  Plasma Membrane Receptors and Second-Messenger Systems Cyclic AMP (cAMP) signaling mechanism steps: 1. Hormone (first messenger) binds to receptor on plasma membrane Figure 16.2 Cyclic AMP (cAMP) signaling mechanism steps 2. Receptor activates a G protein Figure 16.2 Cyclic AMP (cAMP) signaling mechanism steps 3. G protein activates (or inhibits) effector enzyme adenylate cyclase Figure 16.2  Cyclic AMP (cAMP) signaling mechanism steps 4. Adenylate cyclase then converts ATP to cAMP (second messenger) ◦ Remember: “cyclase” creates cyclic AMP Figure 16.2  Cyclic AMP (cAMP) signaling mechanism steps 5. cAMP activates protein kinases that phosphorylate (add a phosphate) other proteins ◦ Phosphorylated proteins are then either activated or inactivated – affect a variety of cellular processes ◦ cAMP is rapidly degraded by enzyme phosphodiesterase, stopping cascade ◦ Cascades have huge amplification effect Figure 16.2 cAMP Summary Video https://www.youtube.com/watch?v=e6W1086Dcn0 Plasma Membrane Receptors and Second-Messenger Systems Other second messenger-signaling mechanisms: https://web.squ.edu.om/m ◦ cGMP (cyclic guanosine ed-lib/med_cd/e_cds/Elect ronic%20Study%20Guide% monophosphate) 20of%20Biochemistry/mol ex/cgmp.htm ◦ PIP2: (Phosphatidyl Inositol Bisphosphate) a type of phospholipid Other hormones work without second messenger system: ◦ Example: insulin receptor is a tyrosine kinase enzyme that autophosphorylates receptor upon insulin binding ◦ Activated tyrosine kinases trigger cell responses http://usmle.biochemistryformedics.com/mechanism-of-action-of-insulin/ Intracellular Receptors and Direct Gene Activation Lipid-soluble steroid hormones and thyroid hormone can diffuse into target cells and bind with intracellular receptors ◦ Some found in cytoplasm, some directly within nucleus ◦ Eg. Thyroid hormone receptor, peroxisome proliferator-activated receptor, estrogen receptor, androgen receptor, progesterone receptor, etc. Receptor-hormone complex enters nucleus and binds to specific region of DNA Figure 16.3 Intracellular Receptors and Direct Gene Activation Helps initiate DNA transcription to produce mRNA mRNA is then translated into specific protein ◦ Proteins synthesized have various functions ◦ Examples: metabolic activities, structural purposes, or exported from cell Figure 16.3 Hormone Release Blood levels of hormones ◦ Controlled by negative feedback systems ◦ Increased hormone effects on target organs can inhibit further hormone release ◦ Levels vary only within narrow, desirable range Endocrine glands are stimulated to synthesize and release hormones in response to one of three stimuli: ◦ Humoral stimuli ◦ Neural stimuli ◦ Hormonal stimuli Humoral stimuli ◦ Changing blood levels of ions and nutrients directly stimulate secretion of hormones ◦ Example: Ca2+ in blood ◦ Declining blood Ca2+ concentration stimulates parathyroid glands to secrete PTH (parathyroid hormone) ◦ PTH causes Ca2+ concentrations to rise, and stimulus is removed ◦ Where do you think the Calcium comes from? ◦ Insulin (glucose) and aldosterone (Na+, K+) are other examples Figure 16.4 Neural stimuli ◦ Nerve fibers stimulate hormone release ◦ Sympathetic nervous system fibers stimulate adrenal medulla to secrete catecholamines ◦ Ie) norepinephrine and epinephrine Figure 16.4 Hormonal stimuli ◦ Hormones stimulate other endocrine organs to release their hormones ◦ Hypothalamic hormones stimulate release of most anterior pituitary hormones ◦ Anterior pituitary hormones stimulate targets to secrete still more hormones ◦ Hypothalamic–pituitary–target endocrine organ feedback loop ◦ Hormones from final target organs inhibit release of anterior pituitary hormones Figure 16.4  Nervous System Modulation Nervous system can make adjustments to hormone levels when needed ◦ Can modify stimulation or inhibition of endocrine glands Nervous system can override normal endocrine controls ◦ Example: under severe stress, hypothalamus and sympathetic nervous system override insulin to allow blood glucose levels to increase https://www.techly.com.au/2016/12/02/fight-flight-response-up-to-you/ ◦ Prepare body for “fight or flight” Target Cell Specificity Target cells must have specific receptors to which hormone binds ◦ Eg. ACTH receptors are found only on certain cells of adrenal cortex, but thyroxin receptors are found on nearly all cells of body Target cell activation depends on three factors: 1. Blood levels of hormone 2. Relative number of receptors on/in target cell 3. Affinity (strength) of binding between receptor and hormone Target Cell Specificity Amount of hormone can influence number of receptors for that hormone ◦ Up-regulation: target cells form more receptors in response to low hormone levels ◦ Down-regulation: target cells lose receptors in response to high hormone levels ◦ Desensitizes the target cells to prevent them from overreacting to persistently high levels of hormone https://basicmedicalkey.com/mechanisms-of-hormonal-regulation/ Half-Life, Onset, and Duration of Hormone Activity Hormones circulate in blood Albumin, a carrier protein either free or bound ◦ Steroids and thyroid hormone are attached to plasma proteins ◦ Not water soluble, need plasma proteins as carriers ◦ All others circulate without carriers Concentration of circulating http://vitroscient.com/rawmaterials/bovine-serum-albumin/ hormone reflects: 1. Rate of release 2. Speed at which it is inactivated and removed from body Half-Life, Onset, and Duration of Hormone Activity Hormones have different response times: ◦ Some responses are immediate ◦ Some, especially steroid, can take hours to days ◦ Some are inactive until they enter target cells The duration of response is usually limited ◦ Ranges from seconds to several hours ◦ Effects may disappear rapidly as blood levels drop, but some may persist for hours at low blood levels Half-Life, Onset, and Duration of Hormone Activity Half-life, onset, and duration of hormone activity are dependent on whether the hormone is water or lipid soluble Interaction of Hormones at Target Cells Multiple hormones may act on same Example of Synergism target at same time ◦ Permissiveness: one hormone cannot exert its effects without another hormone being present ◦ Example: reproductive hormones need thyroid hormone to have effect ◦ Synergism: more than one hormone produces same effects on target cell, causing amplification ◦ Example: glucagon and epinephrine both cause liver to release glucose ◦ Antagonism: one or more hormones oppose(s) action of another hormone http://slideplayer.com/slide/7682537/ ◦ Example: insulin and glucagon Review Questions What is second messenger? Give an example and explain how this mechanism works What are the three types of stimuli that control hormone release? Compare and contrast synergism and antagonism in endocrinology