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endocrine organprimary: main role is the production and secretion of hormonessecondary: production and secretion of hormones is secondary to some other functionConsider: An endocrinegland is one that secretes hormones directly into tissue fluids and the blood without ducts. An exocrinegland secretes its substances thru ducts onto free surfaces.Target cells are those that contain specific receptor proteins for the hormones, and which therefore can respond in a specific fashion to them. Some hormones target only a limited number of cells and other hormones, such as Growth Hormone and Insulin, target almost all cellsin the body.hormone classificationsteroids: lipophilic and hydrophobic; since these molecules can pass directly through the plasma membrane, receptors in cytosol or nucleus,triggers gene activationamino acids, peptides/proteins, amines: lipophobic (except for thyroid hormones which are lipophilic and follow those patterns), receptors onplasma membrane, change cell activity thru channel-gatedreceptors, enzyme linked receptors, or G protein-linked receptors, activates a second messenger(often cAMP) inside the cell; cAMP activates protein kinase that activates other enzymes in the cell in a cascading process.Consider: A hormoneis a chemical signal that affects the behavior or other tissues or glands.Which hormones have receptors on the surface of the target cell and which have receptors? What is a second messenger? What does a second messenger such as cAMP do?Note: Steroid based hormones diffuse intothe cell to cause changes while a.a., peptide/protein, amine based hormones interact with a receptor onthe plasma membrane. hormone activityproduction and release is controlled by the nervous system, other hormones, and other chemical substances; negative feedback mechanisms are primary regulatorWhat controls hormone production and release? Are the mechanisms thru positive or negative feedback?hypothalamusa portion of the brain base that regulates autonomic functions and secretes hormones, most of which regulate secretory activity of the pituitary glandThe hypothalamus has a direct association with what gland?