Study Guide Exam II Pet 3322 Anatomy and Physiology I February 21 2013 The Endocrine System An Overview 1 Define an endocrine gland and list the major endocrine glands of the body and their locations Endocrine gland a gland that secretes hormones into interstitial fluid and then the blood a ductless gland Major endocrine glands figure 18 1 on page 682 o Pituititary gland occupying the hypophyseal fossa of the sphenoid bone and attached to the hypothalamus by the infundibulum o Thyroid gland located anterior to the trachea just inferior to the cricoid o Parathyroid gland embedded in the posterior surfaces of the lateral lobes of the thyroid gland o Adrenal gland located superior to each kidney o Pineal gland located in the roof of the third ventricle that secretes cartilage melatonin Hormones 2 Define a hormone and describe the chemical categories of hormones hormone a secretion of endocrine cells that alters the physiological activity of target cells of the body Chemically hormones can be divided into two broad classes lipid soluble hormones and water soluble hormones Lipid soluble bind to receptors in the cytoplasm or nucleus of the cell o Steroid hormones derived from cholestrol o Thyroid hormones T3 T4 synthesized by attaching iodine to the amino acid tyrosine o Nitric oxide NO both a hormone and a neurotransmitter Its syntheiss is catalyzed by the enzyme nitric oxide synthase Water soluble binds to receptors on the surface of the cell o Amine hormones synthesized by decarboxylating and otherwisse modifying certain amino acids Retain an amino group NH3 o Peptide hormones protein hormones amino acid polymers Examples peptide antidiuretic hormone and oxytocin protein human growth hormone and insulin o Eicosanoid hormones derived from arachidonic acid a 20 carbon fatty acid Important local hormones and may act as circulating hormones 3 Explain the relationship of hormones to target cells and the types of changes that result in target cells in response to hormone stimulation Relationship a hormone must first announce its arrival to a target cell by binding to its receptors Various target cells respond differently to the same hormone Types of changes the synthesis of new molecules changing the permeability of the plasma membrane stimulating transport of a substance into or out of the target cells altering the rate of specific metabolic reactions or causing contraction of smooth muscle or cardiac muscle 4 Describe the second messenger systems used by amino acid based hormones A water soluble hormone first messenger diffuses from the blood through interstitial fluid and then binds to its receptor of its target cell G protein is activated which activates adenylate cyclase Adenylate cyclase converts ATP into cyclic AMP Cyclic AMP second messenger activates one or more protein kinases ATP is converted to ADP Activated protein kinases phosphorylaate one or more cellular protens Phosphorylated proteins cause reactions that produce physiologcal responses After a brief period an enzyme called phosphodiesterase inactivates cAMP 5 Explain the mechanism of intracellular activation used by steroid hormones and thyroid hormone a free lipid soluble hormone molecule diffuses from the blood through interstitial fluid nd through the lipid bilayer of the plasma membrane into a cell Hormone binds to and activates receptors located within target cell The activated receptor hormone complex turns specific genes of the nuclear DNA on or off As the DNA is transcribed new messenger RNA forms leaves the nucleus and enters the cytosol The new proteins alter the cell s activity and cause the responses typical of that hormone 6 Examine the factors that determine target cell activation and compare how the cell uses up regulation and down regulation to alter its responsiveness to hormones Factors blood levels of the hormone relative number of receptors on the target cell and the affinity of those receptors for the hormone up regulation when a hormone is deficient the number of receptors may increase this makes a target cell more sensitive to a hormone down regulation when a hormoone is present in excess the number of taarget cell receptors may decrease this makes a target cell less sensitive to a hormone 7 Identify the factors that affect circulating hormone concentration and the differences in the time required for the effects of hormones to be seen in target cells factors affecting concentration rate of release speed of inactivation removal from the body Local hormones are inactivated quickly circulating hormones may linger in the blood and exert their effects for a few minutes or occasionally for a few hours 8 Underscore the three types of hormone interaction on target cells permissive effect when the actions of some hormones on target cells require a simultaneous or recent exposure to a second hormone synergistic effect when the effect of two hormones acting together is greater or more extensive than the effect of each hormone acting alone antagonistic effect when one hormone opposes the actions of another hormone 9 Discuss the three types of stimuli that promote or inhibit the release of hormones and the effect of nervous system modulation Three types of stimuli humoral stimuli secretion of hormones in direct response to changing blood levels of ions and nutrients example concentration o calcium ions in the blood neural stimuli nerve fibers stimulate hormone release hormonal stimuli release of hormones in response to hormones produced by other endocrine organs Effect of nervous system modulation Negative feedback system the hormone output reverses a particular stimulus If blood Ca2 is low there is a stimulus for the parathyroid glands to release more PTH If the level gets too high the body will cease PTH production and secrete calcitonin to lower the Ca2 levels Positive feedback system the hormone output reinforces and encourages the stimulus example during childbirth the hormone oxytocin stimulates contractions of the uterus and uterine contractions in turn stimulate more oxytocin release Major Endocrine Organs 10 List the hormones produced by the major endocrine organs the factors controlling their release and their effects on target cells Liver and other tissues human growth hormone hGH somatotropin stimulates liver muscle cartilage boen and other tissues to synthesize and secrete insulinlike growth factors IGFs promote growth of body cells protein synthesis tissue repair lipolysis and elevation of
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