Endocrine System PDF

18 The Endocrine System An Introduction to the Endocrine System The Endocrine System Regulates long-term processes Growth Development Reproduction Uses chemical messengers to relay information and instructions between cells Figure 18-1 Organs an...

18 The Endocrine System An Introduction to the Endocrine System The Endocrine System Regulates long-term processes Growth Development Reproduction Uses chemical messengers to relay information and instructions between cells Figure 18-1 Organs and Tissues of the Endocrine System Hypothalamus Pineal Gland Production of ADH, oxytocin, and Melatonin regulatory hormones Parathyroid Glands (located on the posterior surface of Pituitary Gland the thyroid gland) Anterior lobe: Parathyroid hormone (PTH) ACTH, TSH, GH, PRL, FSH, LH, and MSH Posterior lobe: Release of oxytocin and ADH Figure 18-1 Organs and Tissues of the Endocrine System Organs with Secondary Endocrine Functions Heart: Secretes natriuretic peptides. See Atrial natriuretic peptide (ANP) Chapter Brain natriuretic peptide (BNP) 21 Thyroid Gland Thymus: (Undergoes atrophy See Thyroxine (T4) during adulthood) Chapter Triiodothyronine (T3) Secretes thymosins 22 Calcitonin (CT) Adipose Tissue: Secretes Leptin Adrenal Glands Digestive Tract: Secretes See Adrenal medulla: numerous hormones involved in the Chapter Epinephrine (E) coordination of system functions, 25 Norepinephrine (NE) glucose metabolism, and appetite Adrenal cortex: Kidneys: Secrete See Cortisol, corticosterone, Erythropoietin (EPO) Chapters aldosterone, androgens Calcitriol 19 and 26 Pancreas (Pancreatic Islets) Gonads: See Testis Testes (male): Chapters Androgens (especially testosterone), 28 and 29 Insulin inhibin Glucagon Ovaries (female): Estrogens, progestins, inhibin Ovary 18-1 Homeostasis and Intercellular Communication Direct Communication Exchange of ions and molecules between adjacent cells across gap junctions Occurs between two cells of same type Highly specialized and relatively rare Paracrine Communication Uses chemical signals to transfer information from cell to cell within single tissue Most common form of intercellular communication 18-1 Homeostasis and Intercellular Communication Endocrine Communication Endocrine cells release chemicals (hormones) into bloodstream Alters metabolic activities of many tissues and organs simultaneously 18-1 Homeostasis and Intercellular Communication Target Cells Are specific cells that possess receptors needed to bind and “read” hormonal messages Hormones Stimulate synthesis of enzymes or structural proteins Increase or decrease rate of synthesis Turn existing enzyme or membrane channel “on” or “off” 18-1 Homeostasis and Intercellular Communication Synaptic Communication Ideal for crisis management Occurs across synaptic clefts Chemical message is “neurotransmitter” Limited to a very specific area Table 18-1 Mechanisms of Intercellular Communication 18-2 Hormones Classes of Hormones Hormones can be divided into three groups 1. Amino acid derivatives 2. Peptide hormones 3. Lipid derivatives Secretion and Distribution of Hormones Hormones circulate freely or travel bound to special carrier proteins 18-2 Hormones Amino Acid Derivatives Are small molecules structurally related to amino acids Derivatives of Tyrosine: Thyroid hormones Catecholamines Epinephrine, norepinephrine Derivatives of Tryptophan: Dopamine, serotonin, melatonin 18-2 Hormones Peptide Hormones Are chains of amino acids Most are synthesized as prohormones Inactive molecules converted to active hormones before or after they are secreted Glycoproteins Proteins are more than 200 amino acids long and have carbohydrate side chains Thyroid-stimulating hormone (TSH) Luteinizing hormone (LH) Follicle-stimulating hormone (FSH) 18-2 Hormones Peptide Hormones Short Polypeptides/Small Proteins Short chain polypeptides Antidiuretic hormone (ADH) and oxytocin (OXT) (each 9 amino acids long) Small proteins Growth hormone (GH; 191 amino acids) and prolactin (PRL; 198 amino acids) Includes all hormones secreted by: Hypothalamus, heart, thymus, digestive tract, pancreas, and posterior lobe of the pituitary gland, as well as several hormones produced in other organs 18-2 Hormones Lipid Derivatives Eicosanoids - derived from arachidonic acid, a 20- carbon fatty acid Paracrine factors that coordinate cellular activities and affect enzymatic processes (such as blood clotting) in extracellular fluids Some eicosanoids (such as leukotrienes) have secondary roles as hormones A second group of eicosanoids - prostaglandins - involved primarily in coordinating local cellular activities In some tissues, prostaglandins are converted to thromboxanes and prostacyclins, which also have strong paracrine effects 18-2 Hormones Lipid Derivatives Steroid hormones - derived from cholesterol Released by: The reproductive organs (androgens by the testes in males, estrogens and progestins by the ovaries in females) The cortex of the adrenal glands (corticosteroids) The kidneys (calcitriol) Because circulating steroid hormones are bound to specific transport proteins in the plasma: They remain in circulation longer than secreted peptide hormones 18-2 Hormones Secretion and Distribution of Hormones Free Hormones Remain functional for less than 1 hour 1. Diffuse out of bloodstream and bind to receptors on target cells 2. Are broken down and absorbed by cells of liver or kidneys 3. Are broken down by enzymes in plasma or interstitial fluids 18-2 Hormones Secretion and Distribution of Hormones Thyroid and Steroid Hormones Remain in circulation much longer because most are “bound” Enter bloodstream More than 99% become attached to special transport proteins Bloodstream contains substantial reserve of bound hormones 18-2 Hormones Mechanisms of Hormone Action Hormone Receptor Is a protein molecule to which a particular molecule binds strongly Responds to several different hormones Different tissues have different combinations of receptors Presence or absence of specific receptor determines hormonal sensitivity 18-2 Hormones Hormones and Plasma Membrane Receptors Catecholamines and Peptide Hormones Are not lipid soluble Unable to penetrate plasma membrane Bind to receptor proteins at outer surface of plasma membrane (extracellular receptors) Eicosanoids Are lipid soluble Diffuse across plasma membrane to reach receptor proteins on inner surface of plasma membrane (intracellular receptors) 18-3 The Pituitary Gland The Pituitary Gland Also called hypophysis Lies within sella turcica Sellar diaphragm A dural sheet that locks pituitary in position Isolates it from cranial cavity Hangs inferior to hypothalamus Connected by infundibulum 18-3 The Pituitary Gland The Pituitary Gland Releases nine important peptide hormones Hormones bind to membrane receptors Use cAMP as second messenger Figure 18-6a The Anatomy and Orientation of the Pituitary Gland Third Median Mamillary ventricle eminence body HYPOTHALAMUS Optic chiasm Infundibulum Sellar diaphragm Anterior lobe Pars tuberalis Pars distalis Posterior pituitary Pars intermedia lobe Sphenoid (sella turcica) Relationship of the pituitary gland to the hypothalamus Figure 18-6b The Anatomy and Orientation of the Pituitary Gland Anterior lobe Posterior lobe Pars Pars distalis intermedia Secretes other Secretes Releases pituitary MSH ADH and hormones oxytocin Pituitary gland LM  77 Histological organization of pituitary gland showing the anterior and posterior lobes of the pituitary gland 18-3 The Pituitary Gland The Anterior Lobe of the Pituitary Gland Also called adenohypophysis Hormones “turn on” endocrine glands or support other organs Has three regions 1. Pars distalis 2. Pars tuberalis 3. Pars intermedia