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Chapter 7 Endocrine

Chapter 7 Endocrine - Hormones(classification& control...

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Unformatted text preview: Hormones (classification & control of) Endocrine Pathologies Running Problem: Grave’s Disease The endocrine system The endocrine system A. releases chemicals into the bloodstream for distribution throughout the body. B. releases hormones that alter the metabolic activities of many different tissues and organs simultaneously. C. produces effects that can last for hours, days and even longer. D. Both A and B are correct. E. A, B and C are correct Endocrinology ► = The study of hormones, their receptors, the intracellular signaling pathways they invoke, and the diseases and conditions associated with them. ► What are hormones? Where do they come from? ► Fig 7-2 Major endocrine glands? ► Physiological processes controlled by hormones? Hormones: Hormones: ► Known since ancient times ► Secreted by cells into the blood Not always a gland Pheromones? ► Transported to distant targets ► Effective at very low concentration ► Bind to receptors (differing effects on some tissues) ► Hormone action must be of limited duration ► Some are stored, others are manufactured as needed. Chemical Classification of Chemical Classification of Hormones 4 main types: 1. Peptides and proteins 2. 3. 4. 1. Most common Steroids Amines Eicosanoids Differ on basis of synthesis, storage, release, transport and cellular mechanism of action (review Table 7­1) 1. Peptide (Protein) Hormones 1. Peptide (Protein) Hormones ► Synthesis as preprohormone → post­translational modification to prohormone → then hormone ► Storage – release? ► Short half­life (mins.) ► Most common type Fig 7-3 Peptide Hormone Processing Peptide Hormone Processing Fig 7-4 Cellular Mechanism of Action for Cellular Mechanism of Action for Peptide Hormones ► Peptides are lipophobic ⇒ how does message get into cell? ► Usually rapid cellular response because existing proteins are modified ► cAMP 2nd messenger system most common 2. Steroid Hormones 2. Steroid Hormones ► ► Only gonads, adrenals, placenta Derived from cholesterol (lipophilic) Cross membranes (no storage) ► ► SER, on­demand synthesis Usually Bound to Carrier proteins May extend t½ May block entry to target cell ► Activity is intracellular Next slide Steroid Hormone Mechanism of Steroid Hormone Mechanism of Action Lipophilic when unbound Cross membranes New DNA Replication De novo synthesis or response 3. Amine Hormones 3. Amine Hormones ► Derived from tyrosine or tryptophan ► 3 groups Tryptophan ⇒ Melatonin Tyrosine ⇒ Catecholamines behave like peptide hormones Tyrosine ⇒ Thyroid hormones behave like steroid hormones Fig 7-8 Melatonin Melatonin Read focus on Pineal Gland in textbook Fig. 7-22 Tyrosine and Hormone Derivatives I I I I I I I Fig 7-8 Mechanism of Action of Amine Mechanism of Action of Amine Hormones Like peptide hormones: E; NE; dopamine Like steroid hormones: Thyroid hormones 4. Eicosanoids (Fig 6­16) 4. Eicosanoids ► Derivatives of arachidonic acid Unsaturated FA ► ► Produced by MANY cells Unclear if hormone is the proper term May be autocrine/paracrine, too ► Produced by COX in response to cell damage Mediators of inflammation ► NSAIDS are COX inhibitors Many other activities Control of Hormone Release (p Control of Hormone Release 222) All endocrine reflex pathways have similar components Similar to PNS/CNS reflex pathway ► Stimulus / input signal ► Integration (where?) May be all in one cell! ► Output signal (hormone / neurohormone) Physiological action Negative feedback – turns off reflex One Hormone may follow > 1 reflex pathway pattern Fig 7-9 Fig 7-9 Note: 2 different Note: reflex patterns! (multiple stimuli for release) Simple Endocrine Reflex Simple Endocrine Reflex Endocrine cell acts as sensor AND integrating center ⇒ no afferent pathway ⇒ responds by secreting hormone Example: PTH → increases [Ca2+] in plasma Fig 7-10 Neurohormone Neurohormone Reflex NH release by modified neurons upon NS signal ► 3 major groups of Neurohormones: Catecholamines from adrenal medulla Hypothalamic neurohormones from posterior pituitary Hypothalamic neurohormones acting on anterior pituitary Neurohormones of Posterior Pituitary Neurohormones of Posterior Pituitary ► Other name of gland? ► 2 neurohormones ► Both are peptides (9 aa) transported in secretory vesicles via axonal transport Fig 7-12 Anterior Pituitary Anterior Pituitary ► Secretes 6 Hormones (names?) ► A Trophic (tropic) hormone controls the secretion of another hormone ► Hypothalamic trophic hormones and the hypothalamic­ hypophyseal portal system Fig 7-13 Examples: Thyroxin, cortisol, testosterone etc Hypothalamus IC1 Ant. pituitary IC2 Endocrine gland IC3 Target tissue Example: Thyrotropin RH Examples: Also inhibiting hormones (IH) TSH Gonadotropins (FSH & LH) Adrenocorticotrop(h)ic hormone Somatotropin Negative Feedback Loops in the Negative Hypothalamic-anterior pituitary axis Hypothalamic-anterior Hypothalamus IC1 Ant. pituitary IC2 Endocrine gland IC3 Target tissue Hormones serve as negative feedback signals: Short-loop vs. long-loop negative feedback. Feedback patterns important in diagnosis of ES pathologies Hormone Interactions Hormone Interactions Multiple hormones can affect a single target simultaneously Three types of hormone interactions: 1. 2. 3. Synergism Permissiveness Antagonism 1. Synergism 1. Synergism ► Combined action of hormones is more than just additive! ► Example: Blood glucose levels & synergistic effects of glucagon, cortisol and epinephrine Fig 7-18 2. Permissiveness 2. Permissiveness ► One hormone allows another hormone to have its full effect Especially during growth 3. Antagonism Antagonistic hormones have opposing physiological actions – Hormone B diminishes the effect of hormone A Hormone Antagonists and Cancer: Tamoxifen blocks estrogen receptors Endocrine Pathologies Endocrine Pathologies “Unbalance leads to disease” Due to: 1. Hypersecretion (excess) 1. 2. 2. Hyposecretion (deficiency) 1. 3. See Running Problem Iatrogenic 1° vs. 2° Abnormal target tissue response 1. Receptor anomaly Hyperadrenocorticism or Cushing’s disease 1. Hypersecretion: 1. Hypersecretion: ► Due to ? Iatrogenic (could lead to gland atrophy) Tumor ► Symptoms: Exaggerated Effects Examples: ► Graves disease ► ► Gigantism in child (acromegaly in adult) Cushing’s Syndrome Example: Hyperthyroidism Example: (Review Running Problem) Most common cause: Graves' disease Autoantibodies (TSI) bind to TSH receptor and stimulate thyroid hormone production This activation by TSI is not subject to the normal negative feedback loop. exophthalmo 2. Hyposecretion: 2. Hyposecretion: ► Due to ? ► Symptoms: Normal effects of hormone diminished or absent Examples: ► Hypothyroidism ► Dwarfism ► Addison’s disease ► DM Example: Hypothyroidism Example: Most common cause in US: chronic autoimmune thyroiditis (Hashimoto's thyroiditis = Chronic thyroiditis ) Other causes ► surgical removal of the thyroid gland ► radioactive iodine treatment ► external radiation (Chernobyl) ► a deficiency in dietary iodide consumption (=endemic or primary goiter) Hypothyroidism cont. Symptoms: Symptoms: During childhood: stunted growth retardation lethargy low body temp. In adulthood: Bradycardia weight gain lethargy low body temp. 3. Abnormal Tissue 3. Abnormal Tissue Responsiveness Hormone levels normal, target unresponsive. Usually inherited Due to: Abnormal hormone / receptor interaction Abnormal signal transduction Diagnosis of Endocrine Pathologies Diagnosis of Endocrine Pathologies ► Primary Pathology Defect arises in last integration center in the reflex, i.e. the secretory cells. Examples? ► Secondary Pathology Defect arises in one of the trophic integration centers, i.e., where the trophic hormones are secreted Examples? ► Sometimes the pathology is not simply an excess or a deficiency Inability to respond to a stimulus Specialized tests are necessary Dx of Hyperadrenocorticism (Cushing’s) Dx of Hyperadrenocorticism (Cushing’s) Fig 7­20 Graves’ disease ...
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