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VALENCIA BSC 2093C - Lecture Outline

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CHAPTER 18LECTURE OUTLINEI. COMPARISON of CONTROL by the NERVOUS and ENDOCRINE SYSTEMA. Together the nervous and endocrine systems coordinate functions of all body systems.1. The nervous system controls body actions through nerve impulses and neurotransmitters.2. The endocrine system controls body activities by releasing mediator molecules calledhormones.3. The nervous and endocrine systems act as a coordinated interlocking supersystem, the neuroendocrine system.4. Parts of the nervous system stimulate or inhibit the release of hormones.5. Hormones may promote or inhibit the generation of nerve impulses.B. The nervous system causes muscles to contract or glands to secrete. The endocrine system affects virtually all body tissues by altering metabolism, regulating growth and development, and influencing reproductive processes.1. Table 18.1 compares the characteristics of the nervous and endocrine systems.II. ENDOCRINE GLANDSA. The body contains two kinds of glands: exocrine and endocrine.1. Exocrine glands secrete their products into ducts, and the ducts carry the secretions tothe target site.2. Endocrine glands secrete their products (hormones) into the interstitial fluid surrounding the secretory cells from which they diffuse into capillaries to be carried away by blood.a. Endocrine glands constitute the endocrine system and include the pituitary, thyroid, parathyroid, adrenal, pancreas, kidneys, gastrointestinal organs, and pineal glands (Figure 18.1).III. HORMONE ACTIVITYA. The Role of Hormone Receptors1. Although hormones travel in blood throughout the body, they affect only specific target cells.a. Target cells have specific protein or glycoprotein receptors to which hormones bind.2. Receptors are constantly being synthesized and broken down.a. When a hormone is present in excess, down-regulation, the decrease in the number of receptors, may occur.b. When a hormone is deficient, up-regulation, an increase in the number of receptors, may occur.1. Clinical Connection: Synthetic hormones that block the receptors for particular naturally occurring hormones are available as drugs. B. Circulating and Local Hormones1. Hormones that travel in blood and act on distant target cells are called circulating hormones or endocrines.2. Hormones that act locally without first entering the blood stream are called local hormones.a. Those that act on neighboring cells are called paracrines.b. Those that act on the same cell that secreted them are termed autocrines.c. Figure 18.2 compares the site of action of circulating and local hormones.C. Chemical Classes of Hormones1. Table 18.2 provides a summary of the hormones.a. Lipid-soluble hormones include the steroids, thyroid hormones, and nitric oxide, which acts as a local hormone in several tissues.b. Water-soluble hormones include the amines; peptides, proteins, and glycoproteins; and eicosanoids.D. Hormone Transport in Blood1. Most water-soluble hormones circulate in plasma in a free, unattached form.2. Most lipid-soluble hormones bind to transport proteins to be carried in blood.a. The transport proteins improve the transportability of lipid-soluble hormones by making them temporarily water-soluble, retard passage of the small hormone molecules through the kidney filter thus slowing the rate of hormone loss in urine, and provide a ready reserve of hormone already present in blood.3. Clinical Connection: Protein and peptide hormones, such as insulin, will be destroyedby digestive enzymes and, therefore, must be given by injection.IV. MECHANISMS OF HORMONE ACTION A. The response to a hormone depends on both the hormone and the target cell; various target cells respond differently to different hormones.B. Action of Lipid-Soluble Hormone1. Lipid-soluble hormones bind to and activate receptors within cells.2. The activated receptors then alter gene expression which results in the formation of new proteins.3. The new proteins alter the cells activity and result in the physiological responses of those hormones.4. Figure 18.3 shows this mechanism of action.C. Action of Water-Soluble Hormones1. Water-soluble hormones alter cell functions by activating plasma membrane receptors,2. The water-soluble hormone (first messenger) binds to the cell membrane receptor, which set off a cascade of events inside the cell (Figure 18.4).3. A second messenger is released inside the cell where hormone stimulated response takes place.4. A typical mechanism of action of a water-soluble hormone using cyclic AMP as the second messenger is seen in Figure 18.4.a. The hormone binds to the membrane receptor.b. The activated receptor activates a membrane G-protein which turns on adenylate cyclase.c. Adenylate cyclase converts ATP into cyclic AMP which activates protein kinases.d. Protein kinases phosphorylate enzymes which catalyze reactions that producethe physiological response.e. Phosphodiesterase inactivates cAMP5. Since hormones that bond to plasma membrane receptors initiate a cascade of events,they can induce their effects at very low concentrations.D. Hormonal Interactions1. The responsiveness of a target cell to a hormone depends on the hormone’s concentration, the abundance of the target cell’s hormone receptors, and influences exerted by other hormones.2. Three hormonal interactions are the permissive effect, the synergistic effect, and the antagonist effect.V. CONTROL OF HORMONE SECRETIONSA. Most hormones are released in short bursts, with little or no release between bursts. Regulation of hormone secretion normally maintains homeostasis and prevents overproduction or underproduction of a particular hormone; when these regulating mechanisms do not operate properly, disorders result.B. Hormone secretion is controlled by stimuli that are:1. signals from the nervous system2. chemical changes in the blood3. other hormones.4. Most often, negative feedback systems regulate hormonal secretions (Figure 1.3)VI. HYPOTHALAMUS AND PITUITARY GLANDA. The hypothalamus is the major integrating link between the nervous and endocrine systems.B. The hypothalamus and the pituitary gland (hypophysis) regulate virtually all aspects of growth, development, metabolism, and homeostasis.C. The pituitary gland is located in the sella turcica of the sphenoid bone and is differentiated into the anterior pituitary (adenohypophysis), the posterior pituitary (neurohypophysis), and pars intermediaD. Anterior Pituitary Gland (Adenohypophysis)1. The blood supply to the anterior pituitary is


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