Exam 2 Study Guide 2 2 12 The Endocrine System The nervous and endocrine systems coordinate all of the body systems Nervous through the action of neurons and NTs neurotransmitters they secrete Endocrine uses hormones produced by glandular structures to produce their effects o Hormones mediator molecules have effects on cells in the local environment or in distant part of body Autocrine hormones local hormones that are secreted and bid to the same cell Paracrine hormones local hormones that are secreted into interstitial fluid and act on nearby cells Endocrine hormones secreted into interstitial fluid and then absorbed into bloodstream to be carried systemically to any cell that displays the appropriate type of receptor Types of Hormones Amino acid based Amines thyroxin peptide protein hormones Steroids gonadal and adrenocortical hormones Eicosanoids leukotrienes and prostaglandins Alter target cell activity by 2 ways the precise response depends on type of target cell 1 Second Messengers a Regulatory G proteins b Amino acid based hormones 2 Direct Gene Activation a Steroid hormones Solubility hormones can be divided into broad chemical classes Lipid soluble bind to receptors in cytoplasm or nucleus of cell o Consist of steroid hormones thyroid hormones and gas nitric oxide Steroid h are derived from cholesterol Interaction prompts DNA transcription to produce mRNA Thyroid h T3 and T4 synthesized by attaching iodine to amino acid tyrosine Nitric oxide NO is both a hormone and a neurotransmitter Its synthesis is catalyzed by the enzyme nitric oxide synthase o Require carrier protein for transport in blood o At destination able to freely pass through plasma membrane to bind to receptors located in the cytoplasm of the nucleus of the target cell Water soluble bind to receptors on surface of cell o Include peptide and protein hormones and others with amine group and a group of local hormones derived from the arachidonic acid on our cell membranes called eicosanoids Peptide hormones and protein hormones are amino acid polymers Easy to transport in blood Plasma membrane is impermeable to them Exert their efforts by binding to receptors exposed on surface of target cells The hormone binding to its receptor acts as the first messenger in a cascade of signal transduction First messenger then causes production of second messenger inside cell where specific hormone stimulated response takes place o Cyclic AMP cAMP o Steps Hormone FM binds to receptor which binds to a G protein G protein is activated as it binds to GTP displacing GDP Activated G protein activates the effector enzyme adenylate cyclase Adenylate Cyclase generates cAMP second messenger from ATP cAMP activates protein kinases which then cause cellular effects Mechanism of Hormone Action H produce one or more of the following cell changes in target cells o Alter plasma membrane perm o o Activate deactivate enzyme systems Stimulate protein synthesis o o Induce secretory systems Stimulate mitosis Effects of Hormones Prostaglandins PGs and leukotrienes are eicosanoid hormones with local control They are synthesized from membrane lipids and have widespread effects Mediate pain platelet aggregation fever and inflammation Aspirin is a drug that works by inhibiting an enzyme necessary for synthesis of certain PGs the ones that facilitate pain and Regulated smooth muscle contraction gastric secretion and airway size inflammatory response Endocrine hormones control a variety of physiological processes Balance composition and volume of body fluids Regulate metabolism and energy production Direct the rate and timing of growth and development Exert emergency control during physical mental stress Oversee reproduction mechanisms 2 Types of Glands Endocrine System Glands secrete endocrine hormones into the bloodstream Exocrine System Glands secrete their products into ducts Target Cell Specificity Hormones circulate to all tissues but only activate cells referred to as target cells Target cells must have specific receptors to which the hormone binds These receptors may be intracellular or located on the plasma membrane Examples of Hormone Activity ACTH receptors are only found on certain cells of the adrenal cortex Thyroxin receptors are found on nearly all cells of the body Target Cell Activation Depends on 3 factors o Blood levels of hormone o Relative number of receptors of target cell o Affinity of those receptors for the hormone Receptors can be modified Hormones circulate blood in 2 forms free or bound Steroid hormones and thyroid hormones are attached to plasma proteins All others are unencumbered move freely Concentration of circulating hormone reflect rate of release speed of inactivation and removal from body removed from the blood by degrading enzymes the kidneys liver enzyme systems 3 types of hormone interaction Permissiveness one hormone cannot exert its effects without another hormone present o Up regulation target cells form more receptors in response to the hormone o Down regulation target cells lose receptors in response to the hormone for example insulin receptors and obesity Synergism more than one hormone produces the same effects on a target cell Antagonism one or more hormone opposes the action of another hormone i e PTH and calcitonin Hormones are synthesized and released in response to humoral stimuli neural stimuli hormonal stimuli Secretion of hormones in direct response to changing blood levels of ions and nutrients Example concentration of calcium ions in blood Nerve fibers stimulate hormone release Preganglionic sympathetic systems SNS fibers stimulate the adrenal medulla to secrete catecholamines Release of hormones in response to hormones produced by other endocrine organs o Hypothalamic hormones stimulate anterior pituitary Control of Hormone Release primarily controlled by negative feedback systems see PTH and calcitonin diagram above few by positive feedback example oxytocin in childbirth see diagram to right vary only within a narrow desirable range hormones normally are released in frequent bursts Hypothalamus The major link between the nervous system and endocrine system Receives input from several regions in brain Mainly controls the pituitary gland o Side note hypothalamus is connected to anterior adenohypophysis glandular tissue and posterior neurohypophysis neural tissue pituitary gland by the infundibulum o Anterior accounts for about 75 of total weight of gland o Pituitary gland two lobed organ that
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