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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 A © 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 © 2013 Pearson Education, Inc. Endocrine System: Overview • 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 © 2013 Pearson Education, Inc. Endocrine System: Overview • Exocrine glands – Nonhormonal substances (sweat, saliva) – Have ducts to carry secretion to membrane surface • Endocrine glands – Produce hormones – Lack ducts © 2013 Pearson Education, Inc. Endocrine System: Overview • Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands • Hypothalamus is Neuroendocrine organ • 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 © 2013 Pearson Education, Inc. 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) © 2013 Pearson Education, Inc. 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 © 2013 Pearson Education, Inc. Chemistry of Hormones • Two main classes – Amino acid-based hormones • Amino acid derivatives, peptides, and proteins – Steroids • Synthesized from cholesterol • Gonadal and adrenocortical hormones © 2013 Pearson Education, Inc. 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 © 2013 Pearson Education, Inc. Mechanisms of 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 © 2013 Pearson Education, Inc. Mechanisms of Hormone Action • Hormones act at receptors in one of two ways, depending on their chemical nature and receptor location 1. Water-soluble hormones (all amino acid– based hormones except thyroid hormone) • • • © 2013 Pearson Education, Inc. Act on plasma membrane receptors Act via G protein second messengers Cannot enter cell Mechanisms of Hormone Action 2. Lipid-soluble hormones (steroid and thyroid hormones) • • © 2013 Pearson Education, Inc. Act on intracellular receptors that directly activate genes Can enter cell 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 © 2013 Pearson Education, Inc. 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 © 2013 Pearson Education, Inc. 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 © 2013 Pearson Education, Inc. 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 © 2013 Pearson Education, Inc. 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 © 2013 Pearson Education, Inc. Neural Stimuli • Nerve fibers stimulate hormone release – Sympathetic nervous system fibers stimulate adrenal medulla to secrete catecholamines © 2013 Pearson Education, Inc. 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 Stimulus: Action potentials in preganglionic sympathetic fibers to adrenal medulla. Response: Adrenal medulla cells secrete epinephrine and norepinephrine. © 2013 Pearson Education, Inc. Figure 16.4b Three types of endocrine gland stimuli. Slide 2 Neural Stimulus Hormone release caused by neural input. CNS (spinal cord) Preganglionic sympathetic fibers Medulla of adrenal gland Capillary © 2013 Pearson Education, Inc. Figure 16.4b Three types of endocrine gland stimuli. Slide 3 Neural Stimulus Hormone release caused by neural input. CNS (spinal cord) Preganglionic sympathetic fibers Medulla of adrenal gland Capillary Stimulus: Action potentials in preganglionic sympathetic fibers to adrenal medulla. Response: Adrenal medulla cells secrete epinephrine and norepinephrine. © 2013 Pearson Education, Inc. 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 © 2013 Pearson Education, Inc. Figure 16.4c Three types of endocrine gland stimuli. Hormonal Stimulus Hormone release caused by another hormone (a tropic hormone). Hypothalamus Anterior pituitary gland Thyroid gland Adrenal Gonad cortex (Testis) Stimulus: Hormones from hypothalamus. Response: Anterior pituitary gland secretes hormones that stimulate other endocrine glands to secrete hormones. © 2013 Pearson Education, Inc. Slide 1 Figure 16.4c Three types of endocrine gland stimuli. Hormonal Stimulus Hormone release caused by another hormone (a tropic hormone). Hypothalamus Anterior pituitary gland Thyroid gland © 2013 Pearson Education, Inc. Adrenal Gonad cortex (Testis) Slide 2 Figure 16.4c Three types of endocrine gland stimuli. Hormonal Stimulus Hormone release caused by another hormone (a tropic hormone). Hypothalamus Anterior pituitary gland Thyroid gland © 2013 Pearson Education, Inc. Adrenal Gonad cortex (Testis) Slide 3 Figure 16.4c Three types of endocrine gland stimuli. Hormonal Stimulus Hormone release caused by another hormone (a tropic hormone). Hypothalamus Anterior pituitary gland Thyroid gland Adrenal Gonad cortex (Testis) Stimulus: Hormones from hypothalamus. Response: Anterior pituitary gland secretes hormones that stimulate other endocrine glands to secrete hormones. © 2013 Pearson Education, Inc. Slide 4 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 © 2013 Pearson Education, Inc. 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 © 2013 Pearson Education, Inc. Hormones in the Blood • Hormones removed from blood by – Degrading enzymes – Kidneys – Liver • Half-life—time required for hormone's blood level to decrease by half – Varies from fraction of minute to a week © 2013 Pearson Education, Inc. Onset of Hormone Activity • Some responses ~ immediate • Some, especially steroid, hours to days • Some must be activated in target cells © 2013 Pearson Education, Inc. The Pituitary Gland and Hypothalamus • Pituitary gland (hypophysis) has two major lobes – Posterior pituitary (lobe) • Neural tissue – Anterior pituitary (lobe) (adenohypophysis) • Glandular tissue © 2013 Pearson Education, Inc. Pituitary-hypothalamic Relationships • Posterior pituitary (lobe) – Downgrowth of hypothalamic neural tissue – Neural connection to hypothalamus (hypothalamic-hypophyseal tract) – Nuclei of hypothalamus synthesize neurohormones oxytocin and antidiuretic hormone (ADH) – Neurohormones are transported to and stored in posterior pituitary © 2013 Pearson Education, Inc. Posterior Pituitary and Hypothalamic Hormones • Oxytocin and ADH – Each composed of nine amino acids – Almost identical – differ in two amino acids © 2013 Pearson Education, Inc. Oxytocin • • • • Strong stimulant of uterine contraction Released during childbirth Hormonal trigger for milk ejection Acts as neurotransmitter in brain © 2013 Pearson Education, Inc. ADH (Vasopressin) • Inhibits or prevents urine formation • Regulates water balance • Targets kidney tubules reabsorb more water • Release also triggered by pain, low blood pressure, and drugs • Inhibited by alcohol, diuretics • High concentrations vasoconstriction © 2013 Pearson Education, Inc. 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 © 2013 Pearson Education, Inc. Anterior Pituitary Hormones • Growth hormone (GH) • Thyroid-stimulating hormone (TSH) or thyrotropin • Adrenocorticotropic hormone (ACTH) • Follicle-stimulating hormone (FSH) • Luteinizing hormone (LH) • Prolactin (PRL) © 2013 Pearson Education, Inc. Anterior Pituitary Hormones • All are proteins • All except GH activate cyclic AMP secondmessenger systems at their targets • TSH, ACTH, FSH, and LH are all tropic hormones (regulate secretory action of other endocrine glands) © 2013 Pearson Education, Inc. Growth Hormone (GH, or Somatotropin) • Produced by somatotropic cells • Direct actions on metabolism – Increases blood levels of fatty acids; encourages use of fatty acids for fuel; protein synthesis – Decreases rate of glucose uptake and metabolism – conserving glucose – Glycogen breakdown and glucose release to blood (anti-insulin effect) © 2013 Pearson Education, Inc. Growth Hormone (GH) • GH release chiefly regulated by hypothalamic hormones – Growth hormone–releasing hormone (GHRH) • Stimulates release – Growth hormone–inhibiting hormone (GHIH) (somatostatin) • Inhibits release • Ghrelin (hunger hormone) also stimulates release © 2013 Pearson Education, Inc. Homeostatic Imbalances of Growth Hormone • Hypersecretion – In children results in gigantism – In adults results in acromegaly • Hyposecretion – In children results in pituitary dwarfism © 2013 Pearson Education, Inc. Figure 16.7 Disorders of pituitary growth hormone. © 2013 Pearson Education, Inc. Adrenocorticotropic Hormone (Corticotropin) • Regulation of ACTH release – Triggered by hypothalamic corticotropinreleasing hormone (CRH) in daily rhythm – Internal and external factors such as fever, hypoglycemia, and stressors can alter release of CRH © 2013 Pearson Education, Inc. Gonadotropins • Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) • Secreted by gonadotrophs of anterior pituitary • FSH stimulates gamete (egg or sperm) production • LH promotes production of gonadal hormones • Absent from the blood in prepubertal boys and girls © 2013 Pearson Education, Inc. Prolactin (PRL) • Secreted by prolactin cells of anterior pituitary • Stimulates milk production • Role in males not well understood © 2013 Pearson Education, Inc. Prolactin (PRL) • Regulation of PRL release – Primarily controlled by prolactin-inhibiting hormone (PIH) (dopamine) • Blood levels rise toward end of pregnancy • Suckling stimulates PRL release and promotes continued milk production • Hypersecretion causes inappropriate lactation, lack of menses, infertility in females, and impotence in males © 2013 Pearson Education, Inc.