Bài giảng Biology - Chapter 45: Hormones and the Endocrine System

Chapter 45Hormones and theEndocrine SystemOverview: The Body’s Long-Distance RegulatorsAn animal hormoneIs a chemical signal that is secreted into the circulatory system and communicates regulatory messages within the bodyHormones may reach all parts of the bodyBut only certain types of cells, target cells, are equipped to respondInsect metamorphosisIs regulated by hormonesFigure 45.1Concept 45.1: The endocrine system and the nervous system act individually and together in regulating an animal’s physiologyAnimals have two systems of internal communication and regulationThe nervous system and the endocrine systemThe nervous systemConveys high-speed electrical signals along specialized cells called neuronsThe endocrine system, made up of endocrine glandsSecretes hormones that coordinate slower but longer-acting responses to stimuliOverlap Between Endocrine and Nervous RegulationThe endocrine and nervous systemsOften function together in maintaining homeostasis, development, and reproductionSpecialized nerve cells known as neurosecretory cellsRelease neurohormones into the bloodBoth endocrine hormones and neurohormonesFunction as long-distance regulators of many physiological processesControl Pathways and Feedback LoopsThere are three types of hormonal control pathwaysPathway ExampleStimulusLow bloodglucoseReceptorproteinPancreassecretesglucagon ( )EndocrinecellBloodvesselLiverTargeteffectorsResponsePathwayExampleStimulusSucklingSensoryneuronHypothalamus/posterior pituitaryNeurosecretorycellBloodvesselPosterior pituitarysecretes oxytocin( )TargeteffectorsSmooth musclein breastResponseMilk releasePathwayExampleStimulusHypothalamicneurohormonereleased inresponse toneural andhormonalsignalsSensoryneuronHypothalamussecretes prolactin-releasinghormone ( )NeurosecretorycellBloodvesselAnteriorpituitarysecretesprolactin ( )EndocrinecellBloodvesselTargeteffectorsResponseMammary glandsMilk production(c) Simple neuroendocrine pathway(b) Simple neurohormone pathway(a) Simple endocrine pathwayHypothalamusGlycogenbreakdown,glucose releaseinto bloodFigure 45.2a–cA common feature of control pathwaysIs a feedback loop connecting the response to the initial stimulusNegative feedbackRegulates many hormonal pathways involved in homeostasisConcept 45.2: Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responsesHormones convey information via the bloodstreamTo target cells throughout the bodyThree major classes of molecules function as hormones in vertebratesProteins and peptidesAmines derived from amino acidsSteroidsSignaling by any of these molecules involves three key eventsReceptionSignal transductionResponseCell-Surface Receptors for Water-Soluble HormonesThe receptors for most water-soluble hormonesAre embedded in the plasma membrane, projecting outward from the cell surfaceFigure 45.3aSECRETORYCELLHormonemoleculeVIABLOODSignal receptorTARGETCELLSignaltransductionpathwayCytoplasmicresponseNuclearresponseNUCLEUSDNAOR(a) Receptor in plasma membraneBinding of a hormone to its receptorInitiates a signal transduction pathway leading to specific responses in the cytoplasm or a change in gene expressionThe same hormone may have different effects on target cells that haveDifferent receptors for the hormoneDifferent signal transduction pathwaysDifferent proteins for carrying out the responseThe hormone epinephrineHas multiple effects in mediating the body’s response to short-term stressDifferent receptorsdifferent cell responsesEpinephrinea receptorEpinephrineb receptorEpinephrineb receptorVesselconstrictsVesseldilatesGlycogenbreaks downand glucose is releasedfrom cell(a) Intestinal blood vessel(b) Skeletal muscleblood vessel(c) Liver cellDifferent intracellular proteinsdifferent cell responsesGlycogendepositsFigure 45.4a–cIntracellular Receptors for Lipid-Soluble HormonesSteroids, thyroid hormones, and the hormonal form of vitamin DEnter target cells and bind to specific protein receptors in the cytoplasm or nucleusThe protein-receptor complexesThen act as transcription factors in the nucleus, regulating transcription of specific genesSECRETORYCELLHormonemoleculeVIABLOODTARGETCELLSignalreceptorSignaltransductionand responseDNAmRNANUCLEUSSynthesis ofspecific proteins(b) Receptor in cell nucleusFigure 45.3bParacrine Signaling by Local RegulatorsIn a process called paracrine signalingVarious types of chemical signals elicit responses in nearby target cellsLocal regulators have various functions and includeNeurotransmittersCytokines and growth factorsNitric oxideProstaglandinsProstaglandins help regulate the aggregation of plateletsAn early step in the formation of blood clotsFigure 45.5Concept 45.3: The hypothalamus and pituitary integrate many functions of the vertebrate endocrine systemThe hypothalamus and the pituitary glandControl much of the endocrine systemThe major human endocrine glandsHypothalamusPineal glandPituitary glandThyroid glandParathyroid glandsAdrenal glandsPancreasOvary(female)Testis(male)Figure 45.6Major human endocrine glands and some of their hormonesTable 45.1Table 45.1Relation Between the Hypothalamus and Pituitary GlandThe hypothalamus, a region of the lower brainContains different sets of neurosecretory cellsSome of these cells produce direct-acting hormonesThat are stored in and released from the posterior pituitary, or neurohypophysisFigure 45.7HypothalamusNeurosecretorycells of thehypothalamusAxonAnteriorpituitaryPosteriorpituitaryHORMONEADHOxytocinTARGETKidney tubulesMammary glands,uterine musclesOther hypothalamic cells produce tropic hormonesThat are secreted into the blood and transported to the anterior pituitary or adenohypophysisTropic Effects OnlyFSH, follicle-stimulating hormoneLH, luteinizing hormoneTSH, thyroid-stimulating hormoneACTH, adrenocorticotropic hormoneNontropic Effects OnlyProlactinMSH, melanocyte-stimulating hormoneEndorphinNontropic and Tropic EffectsGrowth hormoneNeurosecretory cellsof the hypothalamusPortal vesselsEndocrine cells of theanterior pituitaryHypothalamicreleasinghormones(red dots)HORMONEFSH and LHTSHACTHProlactinMSHEndorphinGrowth hormoneTARGETTestes orovariesThyroidAdrenalcortexMammaryglandsMelanocytesPain receptorsin the brainLiverBonesPituitary hormones(blue dots)Figure 45.8The anterior pituitaryIs a true-endocrine glandThe tropic hormones of the hypothalamusControl release of hormones from the anterior pituitaryPosterior Pituitary HormonesThe two hormones released from the posterior pituitaryAct directly on nonendocrine tissuesOxytocinInduces uterine contractions and milk ejectionAntidiuretic hormone (ADH)Enhances water reabsorption in the kidneysAnterior Pituitary HormonesThe anterior pituitaryProduces both tropic and nontropic hormonesTropic HormonesThe four strictly tropic hormones areFollicle-stimulating hormone (FSH)Luteinizing hormone (LH)Thyroid-stimulating hormone (TSH)Adrenocorticotropic hormone (ACTH)Each tropic hormone acts on its target endocrine tissueTo stimulate release of hormone(s) with direct metabolic or developmental effectsNontropic HormonesThe nontropic hormones produced by the anterior pituitary includeProlactinMelanocyte-stimulating hormone (MSH)-endorphinProlactin stimulates lactation in mammalsBut has diverse effects in different vertebratesMSH influences skin pigmentation in some vertebratesAnd fat metabolism in mammalsEndorphinsInhibit the sensation of painGrowth HormoneGrowth hormone (GH)Promotes growth directly and has diverse metabolic effectsStimulates the production of growth factors by other tissuesConcept 45.4: Nonpituitary hormones help regulate metabolism, homeostasis, development, and behaviorMany nonpituitary hormonesRegulate various functions in the bodyThyroid HormonesThe thyroid glandConsists of two lobes located on the ventral surface of the tracheaProduces two iodine-containing hormones, triiodothyronine (T3) and thyroxine (T4)The hypothalamus and anterior pituitaryControl the secretion of thyroid hormones through two negative feedback loopsHypothalamusAnteriorpituitaryTSHThyroidT3T4+Figure 45.9The thyroid hormonesPlay crucial roles in stimulating metabolism and influencing development and maturationHyperthyroidism, excessive secretion of thyroid hormonesCan cause Graves’ disease in humansFigure 45.10The thyroid gland also produces calcitoninWhich functions in calcium homeostasisParathyroid Hormone and Calcitonin: Control of Blood CalciumTwo antagonistic hormones, parathyroid hormone (PTH) and calcitoninPlay the major role in calcium (Ca2+) homeostasis in mammalsCalcitoninThyroid glandreleasescalcitonin.StimulatesCa2+ depositionin bonesReducesCa2+ uptakein kidneysSTIMULUS:Rising bloodCa2+ levelBlood Ca2+level declinesto set pointHomeostasis:Blood Ca2+ level(about 10 mg/100 mL)Blood Ca2+level risesto set pointSTIMULUS:Falling bloodCa2+ levelStimulatesCa2+ releasefrom bonesParathyroidglandIncreasesCa2+ uptakein intestinesActivevitamin DStimulates Ca2+ uptake in kidneysPTHFigure 45.11Calcitonin, secreted by the thyroid glandStimulates Ca2+ deposition in the bones and secretion by the kidneys, thus lowering blood Ca2+ levelsPTH, secreted by the parathyroid glandsHas the opposite effects on the bones and kidneys, and therefore raises Ca2+ levelsAlso has an indirect effect, stimulating the kidneys to activate vitamin D, which promotes intestinal uptake of Ca2+ from foodInsulin and Glucagon: Control of Blood GlucoseTwo types of cells in the pancreasSecrete insulin and glucagon, antagonistic hormones that help maintain glucose homeostasis and are found in clusters in the islets of LangerhansGlucagonIs produced by alpha cellsInsulinIs produced by beta cellsMaintenance of glucose homeostasisBeta cells ofpancreas are stimulatedto release insulininto the blood.InsulinLiver takesup glucoseand stores itas glycogen.Body cellstake up moreglucose.Blood glucose leveldeclines to set point;stimulus for insulinrelease diminishes.STIMULUS:Rising blood glucoselevel (for instance, aftereating a carbohydrate-rich meal)Homeostasis:Blood glucose level(about 90 mg/100 mL)Blood glucose levelrises to set point;stimulus for glucagonrelease diminishes.STIMULUS:Dropping blood glucoselevel (for instance, afterskipping a meal)Alpha cells of pancreasare stimulated to releaseglucagon into the blood.Liver breaksdown glycogenand releasesglucose intoblood.GlucagonFigure 45.12Target Tissues for Insulin and GlucagonInsulin reduces blood glucose levels byPromoting the cellular uptake of glucoseSlowing glycogen breakdown in the liverPromoting fat storageGlucagon increases blood glucose levels by Stimulating the conversion of glycogen to glucose in the liverStimulating the breakdown of fat and protein into glucoseDiabetes MellitusDiabetes mellitus, perhaps the best-known endocrine disorderIs caused by a deficiency of insulin or a decreased response to insulin in target tissuesIs marked by elevated blood glucose levelsType I diabetes mellitus (insulin-dependent diabetes)Is an autoimmune disorder in which the immune system destroys the beta cells of the pancreasType II diabetes mellitus (non-insulin-dependent diabetes)Is characterized either by a deficiency of insulin or, more commonly, by reduced responsiveness of target cells due to some change in insulin receptorsAdrenal Hormones: Response to StressThe adrenal glandsAre adjacent to the kidneysAre actually made up of two glands: the adrenal medulla and the adrenal cortexCatecholamines from the Adrenal MedullaThe adrenal medulla secretes epinephrine and norepinephrineHormones which are members of a class of compounds called catecholaminesThese hormonesAre secreted in response to stress-activated impulses from the nervous systemMediate various fight-or-flight responsesStress Hormones from the Adrenal CortexHormones from the adrenal cortexAlso function in the body’s response to stressFall into three classes of steroid hormonesGlucocorticoids, such as cortisolInfluence glucose metabolism and the immune systemMineralocorticoids, such as aldosteroneAffect salt and water balanceSex hormonesAre produced in small amountsStress and the adrenal glandSpinal cord(cross section)NervesignalsNervecellReleasinghormoneStressHypothalamusAnterior pituitaryBlood vesselACTHAdrenalglandKidneyAdrenal medullasecretes epinephrineand norepinephrine.Adrenal cortexsecretesmineralocorticoidsand glucocorticoids.Effects of epinephrine and norepinephrine:1. Glycogen broken down to glucose; increasedblood glucose2. Increased blood pressure3. Increased breathing rate4. Increased metabolic rate5. Change in blood flow patterns, leading to increased alertness and decreased digestive and kidney activityEffects ofmineralocorticoids:1. Retention of sodiumions and water bykidneys2. Increased bloodvolume and bloodpressureEffects ofglucocorticoids:1. Proteins and fatsbroken down andconverted to glucose,leading to increasedblood glucose2. Immune system may be suppressed(b) Long-term stress response(a) Short-term stress responseNerve cellFigure 45.13a,bGonadal Sex HormonesThe gonads—testes and ovariesProduce most of the body’s sex hormones: androgens, estrogens, and progestinsThe testes primarily synthesize androgens, the main one being testosteroneWhich stimulate the development and maintenance of the male reproductive systemTestosterone causes an increase in muscle and bone massAnd is often taken as a supplement to cause muscle growth, which carries many health risksFigure 45.14Estrogens, the most important of which is estradiolAre responsible for the maintenance of the female reproductive system and the development of female secondary sex characteristicsIn mammals, progestins, which include progesteroneAre primarily involved in preparing and maintaining the uterusMelatonin and BiorhythmsThe pineal gland, located within the brainSecretes melatoninRelease of melatoninIs controlled by light/dark cyclesThe primary functions of melatoninAppear to be related to biological rhythms associated with reproductionConcept 45.5: Invertebrate regulatory systems also involve endocrine and nervous system interactionsDiverse hormonesRegulate different aspects of homeostasis in invertebratesIn insectsMolting and development are controlled by three main hormonesBrainNeurosecretory cellsCorpus cardiacumCorpus allatumEARLYLARVALATERLARVAPUPAADULTProthoracicglandEcdysoneBrainhormone (BH)Juvenilehormone(JH)LowJHNeurosecretory cells in the brain produce brain hormone (BH), which is stored in the corpora cardiaca (singular, corpus cardiacum) until release.1BH signals its main targetorgan, the prothoracicgland, to produce thehormone ecdysone.2Ecdysone secretionfrom the prothoracicgland is episodic, witheach release stimulatinga molt.3Juvenile hormone (JH), secreted by the corpora allata,determines the result of the molt. At relatively high concen-trations of JH, ecdysone-stimulated molting producesanother larval stage. JH suppresses metamorphosis.But when levels of JH fall below a certain concentration, a pupa forms at the next ecdysone-induced molt. The adultinsect emerges from the pupa.4Figure 45.15Brain hormoneIs produced by neurosecretory cellsStimulates the release of ecdysone from the prothoracic glandsEcdysonePromotes molting and the development of adult characteristicsJuvenile hormonePromotes the retention of larval characteristics