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PowerPoint® Lecture Slides prepared by Barbara Heard, Atlantic Cape Community Ninth Edition College Human Anatomy & Physiology CHAPTER 16 The Endocrine System: Part 1 © Annie Leibovitz/Contact Press Images © 2013 Pearson Education, Inc. Endocrine System: Overview • Acts with nervous system to coordinate and integrate activity of body cells • Influences metabolic activities via hormones transported in blood • Response slower but longer lasting than nervous system • Endocrinology – Study of hormones and endocrine organs 5/24/2017 MDufilho 2 Endocrine System: Overview • Exocrine glands – Nonhormonal substances (sweat, saliva) – Have ducts to carry secretion to membrane surface • Endocrine glands – Produce hormones – Lack ducts 5/24/2017 MDufilho 3 Figure 16.1 Location of selected endocrine organs of the body. Pineal gland Hypothalamus Pituitary gland Thyroid gland Parathyroid glands (on dorsal aspect of thyroid gland) Thymus Adrenal glands Pancreas Gonads • Ovary (female) • Testis (male) 5/24/2017 MDufilho 4 Chemical Messengers • Hormones: long-distance chemical signals; travel in blood or lymph • Autocrines: chemicals that exert effects on same cells that secrete them • Paracrines: locally acting chemicals that affect cells other than those that secrete them • Autocrines and paracrines are local chemical messengers; not considered part of endocrine system 5/24/2017 MDufilho 5 Chemistry of Hormones • Two main classes – Amino acid-based hormones • Amino acid derivatives, peptides, and proteins – Steroids • Synthesized from cholesterol • Gonadal and adrenocortical hormones 5/24/2017 MDufilho 6 Mechanisms of Hormone Action • Though hormones circulate systemically only cells with receptors for that hormone affected • Target cells – Tissues with receptors for specific hormone • Hormones alter target cell activity 5/24/2017 MDufilho 7 Mechanisms of Hormone Action • Hormones act at receptors in one of two ways 1. Water-soluble hormones (all amino acid– based hormones except thyroid hormone) • • • Act on plasma membrane receptors Act via G protein second messengers Cannot enter cell 2. Lipid-soluble hormones (steroid and thyroid hormones) • • 5/24/2017 Act on intracellular receptors that directly activate genes Can enter cell MDufilho 8 Figure 16.2 Cyclic AMP second-messenger mechanism of water-soluble hormones. Slide 1 Recall from Chapter 3 that G protein signaling mechanisms are like a molecular relay race. Hormone Receptor G protein Enzyme 2nd (1st messenger) messenger 1 Hormone (1st messenger) binds receptor. Extracellular fluid Adenylate cyclase G protein (Gs) Receptor 5 cAMP activates protein kinases. cAMP GTP GTP ATP GDP Inactive protein kinase GTP Active protein kinase Triggers responses of target cell (activates enzymes, stimulates cellular secretion, opens ion channel, etc.) Cytoplasm 2 Receptor activates G protein (Gs). 5/24/2017 MDufilho 3 G protein activates adenylate cyclase. 4 Adenylate cyclase converts ATP to cAMP (2nd messenger). 9 Figure 16.3 Direct gene activation mechanism of lipid-soluble hormones. Extracellular fluid Steroid hormone Plasma membrane Cytoplasm Receptor protein Nucleus Slide 1 1 The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor. Receptorhormone complex 2 The receptorhormone complex enters the nucleus. Receptor Binding region DNA mRNA 3 The receptor- hormone complex binds a specific DNA region. 4 Binding initiates transcription of the gene to mRNA. 5 The mRNA directs protein synthesis. New protein 5/24/2017 MDufilho 10 Target Cell Specificity • Target cells must have specific receptors to which hormone binds, for example – ACTH receptors found only on certain cells of adrenal cortex – Thyroxin receptors are found on nearly all cells of body 5/24/2017 MDufilho 11 Target Cell Activation • Target cell activation depends on three factors – Blood levels of hormone – Relative number of receptors on or in target cell – Affinity of binding between receptor and hormone 5/24/2017 MDufilho 12 Target Cell Activation • Hormones influence number of their receptors – 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 5/24/2017 MDufilho 13 Control of Hormone Release • Blood levels of hormones – “Controlled” by negative feedback systems – Vary only within narrow, desirable range • Endocrine gland stimulated to synthesize and release hormones in response to – Humoral stimuli – Neural stimuli – Hormonal stimuli 5/24/2017 MDufilho 14 Figure 16.4a Three types of endocrine gland stimuli. Slide 1 Humoral Stimulus Hormone release caused by altered levels of certain critical ions or nutrients. Capillary (low Ca2+ in blood) Thyroid gland (posterior view) Parathyroid glands Parathyroid glands PTH 5/24/2017 Stimulus: Low concentration of Ca2+ in capillary blood. Response: Parathyroid glands secrete parathyroid hormone (PTH), which increases blood Ca2+. MDufilho 15 Figure 16.4b Three types of endocrine gland stimuli. Slide 1 Neural Stimulus Hormone release caused by neural input. CNS (spinal cord) Preganglionic sympathetic fibers Medulla of adrenal gland Capillary 5/24/2017 Stimulus: Action potentials in preganglionic sympathetic fibers to adrenal medulla. Response: Adrenal medulla cells secrete epinephrine and norepinephrine. MDufilho 16 Figure 16.4c Three types of endocrine gland stimuli. Slide 1 Hormonal Stimulus Hormone release caused by another hormone (a tropic hormone). Hypothalamus Anterior pituitary gland Thyroid gland 5/24/2017 Adrenal Gonad cortex (Testis) Stimulus: Hormones from hypothalamus. Response: Anterior pituitary gland secretes hormones that stimulate other endocrine glands to secrete hormones. MDufilho 17 Nervous System Modulation • Nervous system modifies stimulation of endocrine glands and their negative feedback mechanisms – Example: under severe stress, hypothalamus and sympathetic nervous system activated • body glucose levels rise • Nervous system can override normal endocrine controls 5/24/2017 MDufilho 18 Hormones in the Blood • Hormones circulate in blood either free or bound – Steroids and thyroid hormone are attached to plasma proteins – All others circulate without carriers • Concentration of circulating hormone reflects – Rate of release – Speed of inactivation and removal from body 5/24/2017 MDufilho 19 Interaction of Hormones at Target Cells • Multiple hormones may act on same target at same time – Permissiveness: one hormone cannot exert its effects without another hormone being present – Synergism: more than one hormone produces same effects on target cell amplification – Antagonism: one or more hormones oppose(s) action of another hormone 5/24/2017 MDufilho 20 Amino Acid based hormones • • • • • 5/24/2017 Water soluble May be stored and release later Most are free – metabolized quickly Shorter half-live Example – Amino acid based hormones except Thyroxin MDufilho 21 Steroid Homones • • • • • • 5/24/2017 Lipid-soluble Cannot be stored Transported by plasma proteins Half life is longer Less fluctuation in blood Example: Estrogen, progesterone, testosterone, aldosterone, corticol MDufilho 22 The Pituitary Gland and Hypothalamus • Pituitary gland (hypophysis) has two major lobes – Posterior pituitary (lobe) • Neural tissue – Anterior pituitary (lobe) (adenohypophysis) • Glandular tissue 5/24/2017 MDufilho 23 Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2). Slide 1 Paraventricular nucleus Hypothalamus Posterior lobe of pituitary Optic chiasma Infundibulum (connecting stalk) Hypothalamichypophyseal tract Supraoptic nucleus Inferior hypophyseal artery Axon terminals 2 Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary. 3 Oxytocin and ADH are stored in axon terminals in the posterior pituitary. Posterior lobe of pituitary Oxytocin ADH 5/24/2017 1 Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH). MDufilho 4 When hypothalamic neurons fire, action potentials arriving at the axon terminals cause oxytocin or ADH to be released into the blood. 24 Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2). Slide 1 Hypothalamus Anterior lobe of pituitary Superior hypophyseal artery 2 Hypothalamic hormones travel through portal veins to the anterior pituitary where they stimulate or inhibit release of hormones made in the anterior pituitary. 3 In response to releasing hormones, the anterior pituitary secretes hormones into the secondary capillary plexus. This in turn empties into the general circulation. GH, TSH, ACTH, FSH, LH, PRL Hypothalamic neurons synthesize GHRH, GHIH, TRH, CRH, GnRH, PIH. 1 When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus. Hypophyseal portal system • Primary capillary plexus • Hypophyseal portal veins • Secondary capillary plexus A portal system is two capillary plexuses (beds) connected by veins. Anterior lobe of pituitary 5/24/2017 MDufilho 25 Posterior Pituitary and Hypothalamic Hormones • Oxytocin and ADH – Each composed of nine amino acids – Almost identical – differ in two amino acids • What are the actions of Oxytocin? • How about ADH? 5/24/2017 MDufilho 26 ADH (Vasopressin) • Inhibits or prevents urine formation • Primary purpose water balance – osmolarity of body fluids – normal 285 – 300 milliosmols • Targets kidney tubules reabsorb more water • Release also triggered by pain, low blood pressure, and drugs • Inhibited by alcohol, diuretics • High concentrations vasoconstriction 5/24/2017 MDufilho 27 Determining Osmolality • Osmolality = concentration based on # solutes/liter • Lab reports do not show osmolality – show electrolyte concentration – need to double Na+ concentration • Hypertonicity = >300 mOsm • Edema = <285 mOsm • Osmoreceptors respond to change in osmolality of plasma 5/24/2017 MDufilho 28 ADH • Diabetes insipidus – ADH deficiency due to hypothalamus or posterior pituitary damage – Must keep well-hydrated • Syndrome of inappropriate ADH secretion (SIADH) – Retention of fluid, headache, disorientation – Fluid restriction; blood sodium level monitoring 5/24/2017 MDufilho 29