Endocrine System PDF

Response Systems 2 long-distance systems for responding to changes: nervous system rapid response short duration endocrine system slower response longer duration generally: these two systems are the integrating centers most other body systems are the effector systems 3 Endocrinology = The Study of H...

Response Systems 2 long-distance systems for responding to changes: nervous system rapid response short duration endocrine system slower response longer duration generally: these two systems are the integrating centers most other body systems are the effector systems 3 Endocrinology = The Study of Hormones Responsible for long-term, ongoing functions of the body Metabolism Regulation of the internal environment Reproduction Growth Development Act in 3 basic ways 1. Rates of enzymatic reactions 2. Transport of ions or molecules across cell membranes 3. Gene expression and protein synthesis 5 Properties of Hormones There are a number of types of chemical signals that cells use to communicate. What is unique about hormones? A hormone is a chemical signal that: is secreted by a cell or group of cells is secreted into the blood Secretion from a cell to ECF or external environment is transported to a distant target Transported by blood Growth factors act at short distance exerts its effect at very low concentrations 6 Hormone Receptors Determine whether a cell or tissue is a target for a particular hormone Initiate the response within the target cell Must be terminated most circulating hormones are degraded by enzymes in liver and/or kidneys measurable half-life (t1/2) other hormones eliminated/metabolized by target cells or enzymes in plasma 7 Half-life (t1/2) 8 Chemical Classification of Hormones Classification by tissue source (figure 7.2) Classification by chemical class (table 7.1): peptide minimum of 1 peptide bond steroid all derived from cholesterol amino-acid derivatives (amine hormones) modified tryptophan or tyrosine 10 Peptide Hormones Majority of hormones From 3 to hundreds of amino acids 11 Post-Translational Modification Preprohormone large, inactive precursor signal sequence Prohormone prepro minus the signal sequence still inactive 12 Preprohormone Prohormone Active hormone peptide fragments cleaved into active forms stored in vesicle requires signal to be released 13 Peptide Hormones Transported in the blood Half-life of peptide hormones Relatively short half-life To extend effect, must be secreted continually 14 Cellular Mechanism of Action of Peptide Hormones Bind surface membrane receptors Cellular response through one of several signal transduction systems: Second messenger system (p. 173-4) receptor activates G-protein which… opens ion channel, or activates amplifier enzyme (adenylyl cyclase) enzyme catalyzes formation of second messenger (ATP conversion to cAMP) cAMP activates an enzyme (protein kinase) that phosphorylates cytoplasmic protein 15 Cellular Mechanism of Action of Peptide Hormones Bind surface membrane receptors Cellular response through one of several signal transduction systems: Receptor-enzymes (p. 174-5) receptor has enzyme (tyrosine kinase) on cytoplasmic surface TK can directly phosphorylate proteins to activate them 16 Steroid Hormones All derived from cholesterol Made only in a few organs Adrenal cortex of adrenal gland gonads Steroid hormone synthesis and release Made as needed, not stored Release by simple diffusion 17 Steroid Hormones Transport in the blood Bind carrier proteins in blood Half-life of steroid hormones Longer half-life example: cortisol = 69-90 minutes in blood Cellular mechanism of action of steroid hormones Cytoplasmic or nuclear receptors stimulate genomic effects Cell membrane receptors stimulate nongenomic repsonses 18 Single AA Derivatives Derived from tryptophan Melatonin from pineal gland Derived from tyrosine Single tyrosine give rise to catecholamines Epinephrine, norepinephrine, and dopamine Behave like peptide hormones Two tyrosine molecules give rise to thyroid hormones Behave like steroid hormones 19 20 Some Simple, Others Complex Reflex pathways have similar components Stimulus, sensor, input signal, integration, output signal, one or more targets, & response The endocrine cell is the sensor in simple endocrine reflexes Parathyroid hormone (PTH) Insulin Many endocrine reflexes involve the nervous system Neurohormones are secreted into the blood by neurons 22 The Pituitary: Both Simple and Complex The posterior pituitary stores and releases two neurohormones Neural tissue Stores hormones produced in the hypothalamus The anterior pituitary secretes six hormones Epithelial origin, thus true endocrine gland 23 Posterior Pituitary When hypothalamus is stimulated, posterior pituitary secretes two neurohormones: vasopressin (antidiuretic hormone (ADH)) and oxytocin 24 Anterior Pituitary Regulated by hypothalamic hormones hypophyseal portal system Prolactin (PRL) Growth hormone (GH) Somatostatin (SS) = growth hormone-inhibiting hormone Trophic hormones stimulate secretion of other hormones Thyrotropin (aka, thyroid stimulating hormone, TSH) adrenocorticotropin (ACTH) follicle-stimulating hormone (FSH) luteinizing hormone (LH) 25 26 Hormone Interactions In synergism, the effect of interacting hormones is more than additive A permissive hormone allows another hormone to exert its full effect Permissiveness Antagonistic hormones have opposing effects One substance opposes the action of another Competitive inhibitors vs. functional antagonists glucagon and insulin are an example of functional antagonists 28 Too Much or Too Little? Hypersecretion exaggerates a hormone’s effect Often caused by tumors or exogenous iatrogenic treatment Negative feedback may lead to atrophy of gland Hyposecretion diminishes or eliminates a hormone’s effect Caused by decreased synthesis materials or atrophy Absence of negative feedback leads to overproduction of trophic hormones 30 Receptor Problems Down-regulation of receptors target cell attempting to diminish its responsiveness to excess hormone e.g., hyperinsulinemia (Type II diabetes mellitus) 31 Diagnosis is Complicated, Too 33 Diagnosis is Complicated, Too 34 Diagnosis is Complicated, Too 35