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The Endocrine System What is it? Includes all the endocrine cells and tissues of the body Endocrine cells: glandular secretory cells that release secretions into extracellular fluid. The released chemicals may affect only adjacent cells, or cells throughout the body. Organs in the Endocrine System Organs of the endocrine system: Hypothalamus, Pituitary Gland, Thyroid Gland, Thymus, Adrenal Glands, Pineal Gland, Parathyroid Glands, Heart, Kidney, Digestive Tract, Pancreatic Islets, and Gonads. Release hormones, which are chemical messengers that are released in one tissue and transported in the blood stream to reach specific cells in other tissues. Communication Direct Communication: occurs between cells of the same type that are in physical contact Paracrine Communication: The use of chemical messengers to transfer information from cell to cell within a single tissue Endocrine Communication: The use of hormones to coordinate cellular activities in tissues in distant portions of the body Synaptic Communication: Chemical communication used by the nervous system Hormones Hormones can be divided into three groups based on chemical structure: Amino Acid Derivatives Peptide hormones Lipid derivatives Amino Acid Derivatives Structurally similar to Amino Acids Sometimes called biogenic amines Includes epinephrine, norepinephrine, dopamine, thyroid hormones, and melatonin. Peptide hormones Chains of amino acids Usually produced as Prohormones: inactive molecules that are converted to active hormones before or after they are secreted. 2 groups Group 1: All hormones secreted by the hypothalamus, posterior pituitary gland, heart, thymus, digestive tract, pancreas, and most hormones in the anterior pituitary gland. Group 2: Glycoproteins: proteins that are over 200 amino acids long and have carbohydrate side chains. Most of these hormones are secreted by the anterior pituitary gland and other organs Lipid Derivatives 2 classes Steriod Hormones: derived from cholesterol Released by reproductive organs, adrenal glands, and kidneys Bound to specific transport proteins in plasma and remain in circulation longer than peptide hormones Eicosanoids: derived from arachidonic acid, a 20carbon fatty acid Small molecules with a five-carbon ring at one end Coordinate cellular activities that affect enzymatic processes that occur in extracellular fluids Hormone distribution and transport Hormones may circulate freely in the blood or they may be bound to special carrier proteins A freely circulating hormone is only functional for up to one hour, and possibly for only 2 minutes It becomes inactive when it diffuses out of the blood stream, it is absorbed or broken down by cells of the liver or kidneys, or it is broken down by plasma Thyroid and steroid hormones remain in circulation for much longer because they become attached to special transport proteins after being released. Hormone Function Stimulate the synthesis of enzymes or structural proteins by activating appropriate genes in the cell nucleus Turn existing enzymes “on” or “off” by changing shape and structure Increase or decrease the rate of synthesis of a particular enzyme or other protein by changing the rate of transcription or translation Endocrine Reflexes Functional counterparts of neural reflexes Triggered by: Humoral stimuli: changes in composition of extracellular fluid Hormonal stimuli: the arrival or removal of a specific hormone Neural stimuli: arrival of neurotransmitter at neuroglandular junctions Controlled by negative feedback responses A stimulus triggers the production of a hormone whose effects reduce the intensity of the stimulus. http://freenursetutor.com/menuparent-endocrinesystem/millionaire-game-endocrine-system.html