endocrine system. endocrine system –composed of glands “ductless glands” –secrete chemical...

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  • ENDOCRINE SYSTEM

  • ENDOCRINE SYSTEMEndocrine systemComposed of glandsDuctless glandsSecrete chemical signals into the bloodstream(Exocrine glands secrete substances through ducts to surfaces)Secretory products are hormones

  • HORMONESHormonesChemical signal (ligand)Produced in minute amounts by a collection of cellsSecreted into the interstitial spacesEnters the circulatory systemTransported throughout the bodyInfluences the activity of specific tissuesTarget tissues

  • REGULATIONEndocrine and nervous systems both regulate the activities of structures within the bodyAccomplished in different waysHormones are amplitude-modulated signalsSignals consist mainly of increases or decreases in the concentration of hormones in body fluidsResponse produced within several seconds to hoursAction potentials are frequency-modulated signalsAction potentials vary in frequency but not in amplitudeResponse produced within milliseconds

  • REGULATIONNervous and endocrine systems are intimately relatedThe two systems cannot be completely separated either anatomically or functionallye.g., Some neurons secrete neurohormones into the circulatory systemFunction like hormonese.g., Some neurons directly innervate endocrine glands and influence their secretory activitye.g., Some hormones secreted by endocrine glands affect the nervous system and influence its activity

  • CHEMICAL SIGNALSIntercellular chemical signals allow cells to communicate with each othere.g., Neurotransmitters, neuromodulators, and hormonesThere are various types of intercellular signalsAutocrine chemical signalsParacrine chemical signalsPheromones

  • CHEMICAL SIGNALSAutocrine chemical signalsReleased by cells and have an effect on similar cellse.g., Prostaglandins are released by smooth muscle cells and platelets in response to inflammationCauses aggregation of platelets and relaxation of blood vessel smooth muscle

  • CHEMICAL SIGNALSParacrine chemical signalsReleased by cells and affect other cell types locally without being transported in the bloode.g., The peptide somatostatin is released by cells in the pancreas and functions locally to inhibit the secretion of insulin from other cells of the pancreas

  • CHEMICAL SIGNALSPheromonesSecreted into the environment and modify the behavior and physiology of other individualse.g., Pheromones released in urine of cats and dogs signal fertilitye.g., Pheromones released by women influence the menstrual cycles of other women

  • CHEMICAL SIGNALSMany intercellular chemical signals consistentlyIntercellular signalsMany consistently fit one specific definitionMany do not consistently fit one specific definitione.g., Norepinephrine functions both as a neurotransmitter and a neurohormone

  • HORMONE STRUCTUREThree main classes of hormonesPolymers of amino acidsProteins or polypeptidesGlycoprotein hormones contain carbohydrate componentsDerivatives of single amino acidsLipidsSteroids or derivatives of fatty acids

  • SECRETIONMost hormones are not secreted at a constant rateSecretion increases and decreases dramatically over timeSecretion rate generally controlled by negative feedbackBody activity regulated is maintained within normal rangeHomeostasis is maintainedSecretion is sometimes regulated by positive feedbackLess frequente.g., components of the female reproductive systemEstrogen stimulates LH secretionLH stimulates estrogen secretion

  • SECRETIONThree major patterns of regulationChanges in the extracellular concentration of a non-hormone molecule can affect an endocrine glandNeural control of the endocrine glandControl of hormone secretion by another hormone or neurohormoneRegulation of hormone secretion often involves more than one of these mechanisms

  • SECRETIONChanges in the extracellular concentration of a non-hormone molecule can affect an endocrine glande.g., Blood glucose levels affect insulin secretion from the pancreasInsulin increases glucose movement into cellsInsulin secretion decreases

  • SECRETIONNeural control of the endocrine glandNeurons synapse with hormone-producing cellsNeurotransmitter release stimulates or inhibits hormone releasee.g., Stress or exercise stimulates the adrenal gland to secrete epinephrine and norepinephrine

  • SECRETIONControl of hormone secretion by another hormone or neurohormonee.g., Thyroid-releasing hormone (TRH) from the hypothalamus stimulates the secretion of thyroid-stimulating hormone (TSH) from the anterior pituitary glandTSH stimulates the secretion of thyroid hormones (T3 & T4)etc.

  • SECRETIONSome hormones are in the circulatory system at relatively constant levelse.g., Thyroid hormonesLevels of some hormones change suddenly in response to certain stimulie.g., Epinephrine is released in response to stress or exerciseLevels of some hormones change in relatively constant cyclese.g., Reproductive hormones cycle in women during their reproductive years

  • SECRETIONSome hormones are in the circulatory system at relatively constant levelse.g., Thyroid hormones

  • SECRETIONLevels of some hormones change suddenly in response to certain stimulie.g., Epinephrine is released in response to stress or exercise

  • SECRETIONLevels of some hormones change in relatively constant cyclese.g., Reproductive hormones cycle in women during their reproductive years

  • HORMONE TRANSPORTHormones are dissolved in blood plasmaTransported in two fashionsFree formBound to plasma proteins

  • HORMONE TRANSPORTFree hormones diffuse readily into interstitial spacesConcentration of hormone in the blood affects the amount of hormone diffusing into interstitial spaces

  • HORMONE TRANSPORTMany hormones bind only to certain types of plasma proteinse.g., The type of plasma protein binding to thyroid hormones differs from the type of plasma protein binding to testosterone

  • HORMONE TRANSPORTHormones that bind to plasma proteins do so reversiblyH + BP HBPThis equilibrium is importantOnly free hormone can diffuse into the interstitial spaceHormones bound to plasma proteins tend to remain at a relatively constant level in the blood for long periods of timeDecrease in plasma protein concentration reduces half-life of hormone

  • HORMONE TRANSPORTA decrease in plasma protein concentration reduces the half-life of hormoneEliminated in either the kidneys of the liver

  • HORMONE TRANSPORTThe circulatory system quickly distributes hormones throughout the bodyDiffuse through capillary endotheliumRate varies between hormonesLipid-soluble hormones readily diffuse through the walls of all capillariesWater-soluble hormones pass through pores (fenestrae) in the capillary endotheliumCapillary endothelia of organs regulated by protein hormones have large poresEndocrine glands secreting these hormones also have large pores

  • METABOLISM & EXCRETIONHormone destruction and elimination limit the time in which they are activeWater-soluble hormones have relatively short half-livesRapidly degraded by enzymesPresent in circulatory system or organsNormally have concentrations that increase and decrease rapidlyGenerally regulate activities that have a rapid onset and a short duration

  • METABOLISM & EXCRETIONHormone destruction and elimination limit the time in which they are activeLipid-soluble hormones have relatively long half-livesCommonly circulate in the blood bound to plasma proteinsReduces rate of elimination Reduces rate at which they diffuse through capillary endotheliumNormally maintained at relatively constant levels

  • METABOLISM & EXCRETIONFour main modes of hormone removal from the bloodExcretionMetabolismActive transportConjugation

  • METABOLISM & EXCRETIONFour main modes of hormone removal from the bloodExcretionKidneys excrete hormones into the urineLiver excretes hormones into the bile

  • METABOLISM & EXCRETIONFour main modes of hormone removal from the bloodMetabolismHormones metabolized or chemically modifiedEnzymes in blood or tissuese.g., Liver, kidneys, lungs, etc.End products may be excreted in urine or bileEnd products may be taken up by cellse.g., Epinephrine is modified, then excretede.g., Protein hormones are broken down into amino acidsAmino acids are then taken up by cells

  • METABOLISM & EXCRETIONFour main modes of hormone removal from the bloodActive transportActively transported into cellsHormones are recyclede.g., Epinephrine and norepinephrine are actively transported into cellsThese hormones can be secreted again

  • METABOLISM & EXCRETIONFour main modes of hormone removal from the bloodConjugationAttachment of water-soluble molecules to hormonesTypically sulfate or glucuronic acidIncreases rate of excretion by kidneys or liver

  • INTERACTION WITH TARGET TISSUESIntercellular chemical signalsLigandsBind to proteins and change their functionsVarious classesHormonesNeurotransmittersChemical mediators of inflammation

  • INTERACTION WITH TARGET TISSUESLigands bind to proteins at their binding siteReceptor site if protein is a receptorLock-and-key fitSpecificitye.g., Insulin binds to insulin receptorse.g., Insulin does not bind to growth hormone receptorsMultiple types of receptors exist for some hormonese.g., There are multiple types of epinephrine receptors

  • INTERACTION WITH TARGET TISSUESHormones are distributed throughout the body by the circulatory systemTarget cells respond to a given hormonePossess receptors to which the hormone bindsCells lacking receptors do not respond

  • INTERACTION WITH TARGET TISSUESDrugs with structures similar to a particular chemical signal may compete with that molecule fo

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