Hormonal Regulation - CHAPTER 21 PDF

CHAPTER 21: MECHANISMS OF HORMONAL REGULATION Mechanisms of Hormonal Regulation Functions of the endocrine system o Di2erentiation of the reproductive and central nervous systems in the developing fetus o Stimulation of sequential growth and development during chil...

CHAPTER 21: MECHANISMS OF HORMONAL REGULATION Mechanisms of Hormonal Regulation Functions of the endocrine system o Di2erentiation of the reproductive and central nervous systems in the developing fetus o Stimulation of sequential growth and development during childhood and adolescence o Coordination of the male and female reproductive systems o Maintenance of an optimal internal environment o Initiation of corrective and adaptive responses when emergency demands occur Chemical messengers that are released by glands o General characteristics o Specific rates and rhythms of secretion o Diurnal or circadian, pulsatile and cyclic, and patterns, depending on circulating substrates o Operate within feedback systems o A2ect only cells with appropriate receptors o Are inactivated by the liver or directly excreted by the kidneys Regulation of Hormone Release Hormones are released o In response to an alteration in the cellular environment o To maintain a regulated level of certain substances or other hormones Chemical, endocrine, or neural factors: regulate hormones Negative feedback: most common Positive feedback Hormone Transport Hormones are released into the circulatory system by endocrine glands and distributed throughout the body. o Water-soluble hormones circulate in free, unbound forms. o Lipid-soluble hormones are primarily transported bound to a carrier or transport protein. Hormone Receptors Target cells o Recognize and bind with a high a2inity to hormones o Initiate a signal o The more receptors, the more sensitive the cell Up-regulation: Low concentrations of hormones increase the number of receptors per cell. Down-regulation: High concentrations of hormones decrease the number of receptors. Are located in or on the plasma membrane or in the intracellular compartment of the target cell Water-soluble hormones: Have a high molecular weight, cannot di2use across the plasma membrane  Lipid-soluble hormones: Easily di2use across the plasma membrane and bind to cytosolic or nuclear receptors First messenger: Hormone that carries the message to the target cell Signal transduction: Process by which this message is communicated into the target cell o Steps § Receptor activation or binding of a hormone to its receptor § Activation of a G protein (transducer) and membrane-associated enzyme (e2ector enzyme) § Production of a second messenger § Activation of an intracellular enzyme, such as protein kinase A or C § Alterations in gene transcription and the resulting target cell response to the hormone Second messengers o Are the initial link between the first signal (hormone) and the inside of the cell o Examples § Cyclic adenosine monophosphate (cAMP): must activate adenylyl cyclase § Cyclic guanosine monophosphate (cGMP): is activated by the enzyme guanylyl cyclase § Calcium (Ca++): binds with calmodulin, a regulatory protein o Associates with inositol trisphosphate (IP3) and diacylglycerols (DAG) to produce physiologic e2ects Lipid-Soluble Hormone Receptors Lipid-soluble hormones are synthesized from cholesterol Examples: Androgens, estrogens, progestins, glucocorticoids, mineralocorticoids, vitamin D, retinoid Di2use across the plasma membrane and bind to cytoplasmic or nuclear receptors. Activate o Ribonucleic acid (RNA) polymerase o Deoxyribonucleic acid (DNA) transcription Hormone E