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This 6 page Class Notes was uploaded by Jess Graff on Wednesday February 17, 2016. The Class Notes belongs to BMS 508 at University of New Hampshire taught by Mary Katherine Lockwood, PhD in Spring 2016. Since its upload, it has received 47 views. For similar materials see Human Anatomy and Physiology II in Biological Sciences at University of New Hampshire.
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Date Created: 02/17/16
BMS 50803 1292016 Chapter 18 cont Endocrine System cont Hormones Secretion and Distribution of Hormones Thyroid and Steroid Hormones Remain in circulation much longer because most are quotboundquot Enter bloodstream More than 99 become attached to special transport proteins Bloodstream contains substantial reserve of bound hormones Mechanisms of Hormone Action Hormone Receptor Protein molecule to which a particular molecule binds strongly Responds to several different hormones Different tissues have different combinations of receptors Presence or absence of speci c receptor determines hormonal sensitivity Hormones and Plasma Membrane Receptors Catecholamines and Peptide Hormones Not lipid soluble Unable to penetrate plasma membrane Bind to receptor proteins at outer surface of plasma membrane extracellular receptors Eicosanoids Lipid soluble Diffuse across plasma membrane to reach receptor proteins on inner surface of plasma membrane intracellular receptors First and Second Messengers Bind to receptors in plasma membrane Cannot have direct effect on activities inside target cell Use intracellular intermediary to exert effects First Messenger Leads to second messenger May act as enzyme activator inhibitor or cofactor Results in change in rates of metabolic reactions Important Second Messengers CyclicAMP cAMP Derivative of ATP CyclicGMP cGMP Derivative of GTP Calcium ions The Process of Ampli cation The binding of a small number of hormone molecules to membrane receptors Leads to thousands of second messengers in cell Magni es effect of hormone on target cell Downregulation Presence of a hormone triggers decrease in number of hormone receptors When levels of particular hormone are high cells become less sensitive to it Upregulation Absence of a hormone triggers increase in number of hormone receptors When levels of particular hormone are low cells become more sensitive to it G Protein Enzyme complex coupled to membrane receptor Involved in link between rst messenger and second messenger G Proteins and cAMP Adenylate cyclase is activated when hormone binds to receptor at membrane surface and changes concentration of second messenger cyclicAMP cAMP within cell Increased cAMP level accelerates metabolic activity within cell G Proteins and Calcium Ions Activated G proteins trigger Opening of calcium ion channels in membrane Release of calcium ions from intracellular stores G protein activates enzyme phospholipase C PLC Enzyme triggers receptor cascade Production of diacylglycerol DAG and inositol triphosphate IP3 from membrane phospholipids May further activate more calcium ion channels through protein kinase C PKC Calcium ions may activate calmodulin which causes further cellular changes Hormones and Intracellular Receptors Alter rate of DNA transcription in nucleus Change patterns of protein synthesis Directly affect metabolic activity and structure of target cell Include steroids and thyroid hormones Control of Endocrine Activity by Endocrine Re exes Endocrine Re exes Functional counterparts of neural re exes In most cases controlled by negative feedback mechanisms Stimulus triggers production of hormone the direct or indirect effects of the hormone reduce intensity of the stimulus Endocrine Re exes Can be triggered by Humoral stimuli Changes in composition of extracellular uid Hormonal stimuli Arrival or removal of speci c hormone Neural stimuli Arrival of neurotransmitters at neuroglandular junctions Simple Endocrine Re ex lnvolves only one hormone Controls hormone secretion by the heart pancreas parathyroid gland and digestive tract Complex Endocrine Re ex 1 intermediary steps 2 hormones The hypothalamus provides highest level of endocrine control Neuroendocrine Re exes Pathways include both neural and endocrine components Complex Commands Issued by changing Amount of hormone secreted Pattern of hormone release Hypothalamic and pituitary hormones released in sudden bursts Frequency changes response of target cells The Pituitary Gland The Pituitary Gland Also called hypophysis Lies within sella turcica Sellar diaphragm A dural sheet that locks pituitary in position Isolates it from cranial cavity Hangs inferior to hypothalamus Connected by infundibulum Releases nine important peptide hormones Hormones bind to membrane receptors Use cAMP as second messenger The Anterior Lobe of the Pituitary Gland Also called adenohypophysis Hormones quotturn onquot endocrine glands or support other organs Has 3 regions Pars distalis Pars tuberalis Pars intermedia The Hypophyseal Portal System Median eminence Swelling near attachment of infundibulum Where hypothalamic neurons release regulatory factors lnto interstitial uids Through fenestrated capillaries Portal Vessels Blood vessels link two capillary networks Entire complex is portal system Ensures that regulatory factors reach intended target cells before entering general circulation Hypothalamic Control of the Anterior Lobe 2 classes of hypothalamic regulatory hormones Releasing hormones RH Stimulate synthesis and secretion of 1 hormones at anterior lobe Inhibiting hormones IH Prevent synthesis and secretion of hormones from the anterior lobe Rate of secretion is controlled by negative feedback
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