Chief Complaint: 8 year old girl with excessive thirst, frequent urination, and weight lossHistory: History: Cindy Mallon, an 8-year-old girl in previously good health, has noticed that, in the past month, she is increasingly thirsty. She gets up several times a night to urinate, and finds herself gulping down glassfulls of water. At the dinner table, she seems to be eating twice as much as she used to, yet she has lost 5 pounds in the past month. In the past three days, she has become nauseated, vomiting on three occasions, prompting a visit to her pediatrician.

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At the doctor's office, blood and urine samples are taken. The following lab results are noted: blood glucose level = 545 mg/dl (normal 50-170 mg/dl)blood pH level = 7.23 (normally 7.35-7.45)urine = tested positive for glucose and ketone bodies (normally urine is free of glucose and ketone bodies)

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Acts with nervous system to coordinate and integrate activity of body cellsInfluences metabolic activities via hormones transported in blood Response slower but longer lasting than nervous systemEndocrinologyStudy of hormones and endocrine organs

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Controls and integratesReproductionGrowth and developmentMaintenance of electrolyte, water, and nutrient balance of bloodRegulation of cellular metabolism and energy balanceMobilization of body defensesSlide 2

Exocrine glandsNonhormonal substances (sweat, saliva)Have ducts to carry secretion to membrane surfaceEndocrine glandsProduce hormonesLack ductsSlide 3

Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands Hypothalamus is Neuroendocrine organSome have exocrine and endocrine functionsPancreas, gonads, placentaOther tissues and organs that produce hormonesAdipose cells, thymus, and cells in walls of small intestine, stomach, kidneys, and heartSlide 4

Figure 16.1 Location of selected endocrine organs of the body.Pineal glandHypothalamusPituitary glandThyroid glandParathyroid glands(on dorsal aspect of thyroid gland)ThymusAdrenal glandsPancreasGonads Testis (male) Ovary (female)Slide 5

Hormones: long-distance chemical signals; travel in blood or lymphAutocrines: chemicals that exert effects on same cells that secrete themParacrines: locally acting chemicals that affect cells other than those that secrete themAutocrines and paracrines are local chemical messengers; not considered part of endocrine systemSlide 6

Two main classesAmino acid-based hormones Amino acid derivatives, peptides, and proteinsSteroidsSynthesized from cholesterolGonadal and adrenocortical hormones

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Though hormones circulate systemically only cells with receptors for that hormone affectedTarget cellsTissues with receptors for specific hormoneHormones alter target cell activitySlide 8

Hormone action on target cells may be toAlter plasma membrane permeability and/or membrane potential by opening or closing ion channelsStimulate synthesis of enzymes or other proteinsActivate or deactivate enzymesInduce secretory activityStimulate mitosisSlide 9

Hormones act at receptors in one of two ways, depending on their chemical nature and receptor locationWater-soluble hormones (all amino acidbased hormones except thyroid hormone)Act on plasma membrane receptorsAct via G protein second messengersCannot enter cellSlide 10

2.Lipid-soluble hormones (steroid and thyroid hormones)Act on intracellular receptors that directly activate genesCan enter cellSlide 11

cAMP signaling mechanism:Hormone (first messenger) binds to receptorReceptor activates G proteinG protein activates adenylate cyclaseAdenylate cyclase converts ATP to cAMP (second messenger) cAMP activates protein kinases that phosphorylate proteinsSlide 12

cAMP signaling mechanismActivated kinases phosphorylate various proteins, activating some and inactivating otherscAMP is rapidly degraded by enzyme phosphodiesteraseIntracellular enzymatic cascades have huge amplification effectSlide 13

Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.Hormone(1st messenger)ReceptorG proteinEnzyme2ndmessengerAdenylate cyclaseExtracellular fluidG protein (Gs)GDPReceptor Hormone (1st messenger) binds receptor. Receptor activates G protein (Gs). G protein activates adenylate cyclase. Adenylate cyclase convertsATP to cAMP (2nd messenger).InactiveproteinkinaseTriggers responses of target cell (activatesenzymes, stimulatescellular secretion,opens ion channel, etc.)Activeproteinkinase cAMP activates protein kinases.CytoplasmcAMPGTPGTPGTPATP12345Slide 14

Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.Hormone(1st messenger)ReceptorG proteinEnzyme2ndmessenger Hormone (1st messenger) binds receptor.1Extracellular fluidReceptorCytoplasmSlide 15

Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.Hormone(1st messenger)ReceptorG proteinEnzyme2ndmessengerExtracellular fluid Hormone (1st messenger) binds receptor.1G protein (Gs)GDPReceptorGTPGTP Receptor activates G protein (Gs).2CytoplasmSlide 16

Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.Hormone(1st messenger)ReceptorG proteinEnzyme2ndmessengerAdenylate cyclaseExtracellular fluidG protein (Gs)GDPReceptor Hormone (1st messenger) binds receptor. Receptor activates G protein (Gs). G protein activates adenylate cyclase.CytoplasmGTPGTPGTP123Slide 17

Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.Hormone(1st messenger)ReceptorG proteinEnzyme2ndmessengerAdenylate cyclaseExtracellular fluidG protein (Gs)GDPReceptor Hormone (1st messenger) binds receptor. Receptor activates G protein (Gs). G protein activates adenylate cyclase. Adenylate cyclase convertsATP to cAMP (2nd messenger).CytoplasmcAMPGTPGTPGTPATP1234Slide 18

Recall from Chapter 3 thatG protein signaling mechanismsare like a molecular relay race.Hormone(1st messenger)ReceptorG proteinEnzyme2ndmessengerAdenylate cyclaseExtracellular fluidG protein (Gs)GDPReceptor Hormone (1st messenger) binds receptor. Receptor activates G protein (Gs). G protein activates adenylate cyclase. Adenylate cyclase convertsATP to cAMP (2nd messenger).InactiveproteinkinaseTriggers responses of target cell (activatesenzymes, stimulatescellular secretion,opens ion channel, etc.)Activeproteinkinase cAMP activates protein kinases.CytoplasmcAMPGTPGTPGTPATP12345Slide 19

PIP2-calcium signaling mechanismInvolves G protein and membrane-bound effector phospholipase CPhospholipase C splits PIP2 into two second messengers diacylglycerol (DAG) and inositol trisphosphate (IP3)DAG activates protein kinase; IP3 causes Ca2+ releaseCalcium ions act as second messenger

Ca2+ alters enzyme activity and channels, or binds to regulatory protein calmodulin Calcium-bound calmodulin activates enzymes that amplify cellular response

Cyclic guanosine monophosphate (cGMP) is second messenger for some hormonesSome work without second messengersE.g., insulin receptor is tyrosine kinase enzyme that autophosphorylates upon insulin binding docking for relay proteins that trigger cell responses

Steroid hormones and thyroid hormoneDiffuse into target cells and bind with intracellular receptorsReceptor-hormone complex enters nucleus; binds to specific region of DNAPrompts DNA transcription to produce mRNAmRNA directs protein synthesisPromote metabolic activities, or promote synthesis of structural proteins or proteins for export from cell

The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.15 The receptor-hormone complex enters the nucleus. The receptor- hormone complex binds a specific DNA region. Binding initiates transcription of the gene to mRNA. The mRNA directs protein synthesis.New proteinNucleusmRNADNAReceptorBinding regionReceptor-hormonecomplexReceptorproteinSteroidhormonePlasmamembraneExtracellularfluidCytoplasm234

The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.1NucleusReceptorproteinSteroidhormonePlasmamembraneExtracellularfluidCytoplasmReceptor-hormonecomplex

The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.1 The receptor-hormone complex enters the nucleus.NucleusReceptor-hormonecomplexReceptorproteinSteroidhormonePlasmamembraneExtracellularfluidCytoplasm2

The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.1 The receptor-hormone complex enters the nucleus. The receptor- hormone complex binds a specific DNA region.NucleusDNAReceptorBinding regionReceptor-hormonecomplexReceptorproteinSteroidhormonePlasmamembraneExtracellularfluidCytoplasm23

The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.1 The receptor-hormone complex enters the nucleus. The receptor- hormone complex binds a specific DNA region. Binding initiates transcription of the gene to mRNA.NucleusmRNADNAReceptorBinding regionReceptor-hormonecomplexReceptorproteinSteroidhormonePlasmamembraneExtracellularfluidCytoplasm234

The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.15 The receptor-hormone complex enters the nucleus. The receptor- hormone complex binds a specific DNA region. Binding initiates transcription of the gene to mRNA. The mRNA directs protein synthesis.New proteinNucleusmRNADNAReceptorBinding regionReceptor-hormonecomplexReceptorproteinSteroidhormonePlasmamembraneExtracellularfluidCytoplasm234

Target cells must have specific receptors to which hormone binds, for exampleACTH receptors found only on certain cells of adrenal cortexThyroxin receptors are found on nearly all cells of body

Target cell activation depends on three factorsBlood levels of hormoneRelative number of receptors on or in target cellAffinity of binding between receptor and hormone

Hormones influence number of their receptorsUp-regulationtarget cells form more receptors in response to low hormone levelsDown-regulationtarget cells lose receptors in response to high hormone levels

Blood levels of hormonesControlled by negative feedback systemsVary only within narrow, desirable rangeEndocrine gland stimulated to synthesize and release hormones in response toHumoral stimuliNeural stimuliHormonal stimuli

Changing blood levels of ions and nutrients directly stimulate secretion of hormones Example: Ca2+ in bloodDeclining blood Ca2+ concentration stimulates parathyroid glands to secrete PTH (parathyroid hormone)PTH causes Ca2+ concentrations to rise and stimulus is removed

Figure 16.4a Three types of endocrine gland stimuli.Humoral StimulusHormone release caused by alteredlevels of certain critical ions ornutrients.Stimulus: Low concentration of Ca2+ incapillary blood.ParathyroidglandsParathyroidglandsCapillary (low Ca2+in blood)Thyroid gland(posterior view)PTHResponse: Parathyroid glands secreteparathyroid hormone (PTH), whichincreases blood Ca2+.

Figure 16.4a Three types of endocrine gland stimuli.Humoral StimulusHormone release caused by alteredlevels of certain critical ions ornutrients.ParathyroidglandsParathyroidglandsCapillary (low Ca2+in blood)Thyroid gland(posterior view)

Figure 16.4a Three types of endocrine gland stimuli.Humoral StimulusHormone release caused by alteredlevels of certain critical ions ornutrients.Stimulus: Low concentration of Ca2+ incapillary blood.ParathyroidglandsParathyroidglandsCapillary (low Ca2+in blood)Thyroid gland(posterior view)PTHResponse: Parathyroid glands secreteparathyroid hormone (PTH), whichincreases blood Ca2+.

Hormones stimulate other endocrine organs to release their hormones Hypothalamic hormones stimulate release of most anterior pituitary hormonesAnterior pituitary hormones stimulate targets to secrete still more hormonesHypothalamic-pituitary-target endocrine organ feedback loop: hormones from final target organs inhibit release of anterior pituitary hormones

Figure 16.4c Three types of endocrine gland stimuli.Hormonal StimulusHormone release caused by anotherhormone (a tropic hormone).Stimulus: Hormones from hypothalamus.AnteriorpituitaryglandThyroidglandAdrenalcortexGonad(Testis)HypothalamusResponse: Anterior pituitary gland secreteshormones that stimulate other endocrine glands to secrete hormones.

Figure 16.4c Three types of endocrine gland stimuli.Hormonal StimulusHormone release caused by anotherhormone (a tropic hormone).AnteriorpituitaryglandThyroidglandAdrenalcortexGonad(Testis)Hypothalamus

Figure 16.4c Three types of endocrine gland stimuli.Hormonal StimulusHormone release caused by anotherhormone (a tropic hormone).AnteriorpituitaryglandThyroidglandAdrenalcortexGonad(Testis)Hypothalamus

Figure 16.4c Three types of endocrine gland stimuli.Hormonal StimulusHormone release caused by anotherhormone (a tropic hormone).Stimulus: Hormones from hypothalamus.AnteriorpituitaryglandThyroidglandAdrenalcortexGonad(Testis)HypothalamusResponse: Anterior pituitary gland secreteshormones that stimulate other endocrine glands to secrete hormones.

Nerve fibers stimulate hormone releaseSympathetic nervous system fibers stimulate adrenal medulla to secrete catecholamines

Figure 16.4b Three types of endocrine gland stimuli.Neural StimulusHormone release caused by neural input.Stimulus: Action potentials in preganglionicsympathetic fibers to adrenal medulla.CNS (spinal cord)PreganglionicsympatheticfibersMedulla ofadrenal glandCapillary Response: Adrenal medulla cells secreteepinephrine and norepinephrine.

Figure 16.4b Three types of endocrine gland stimuli.Neural StimulusHormone release caused by neural input.CNS (spinal cord)PreganglionicsympatheticfibersMedulla ofadrenal glandCapillary

Figure 16.4b Three types of endocrine gland stimuli.Neural StimulusHormone release caused by neural input.Stimulus: Action potentials in preganglionicsympathetic fibers to adrenal medulla.CNS (spinal cord)PreganglionicsympatheticfibersMedulla ofadrenal glandCapillary Response: Adrenal medulla cells secreteepinephrine and norepinephrine.

Nervous system modifies stimulation of endocrine glands and their negative feedback mechanisms Example: under severe stress, hypothalamus and sympathetic nervous system activated body glucose levels rise Nervous system can override normal endocrine controls

Hormones circulate in blood either free or boundSteroids and thyroid hormone are attached to plasma proteinsAll others circulate without carriersConcentration of circulating hormone reflects Rate of releaseSpeed of inactivation and removal from body

Hormones removed from blood byDegrading enzymesKidneysLiver Half-lifetime required for hormone's blood level to decrease by halfVaries from fraction of minute to a week

Some responses ~ immediateSome, especially steroid, hours to daysSome must be activated in target cells

LimitedRanges from 10 seconds to several hoursEffects may disappear as blood levels dropSome persist at low blood levels

Multiple hormones may act on same target at same timePermissiveness: one hormone cannot exert its effects without another hormone being presentSynergism: more than one hormone produces same effects on target cell amplificationAntagonism: one or more hormones oppose(s) action of another hormone

Pituitary gland (hypophysis) has two major lobesPosterior pituitary (lobe)Neural tissueAnterior pituitary (lobe) (adenohypophysis)Glandular tissue

Posterior pituitary (lobe)Downgrowth of hypothalamic neural tissueNeural connection to hypothalamus (hypothalamic-hypophyseal tract)Nuclei of hypothalamus synthesize neurohormones oxytocin and antidiuretic hormone (ADH)Neurohormones are transported to and stored in posterior pituitary

Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2). Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH). Oxytocin and ADH are stored in axon terminals in the posterior pituitary. When hypothalamic neurons fire, action potentials arriving at the axon terminals cause oxytocin or ADH to be released into the blood.1234OxytocinADHPosterior lobeof pituitaryOpticchiasmaInfundibulum(connecting stalk)Hypothalamic-hypophysealtractAxon terminalsPosterior lobeof pituitaryParaventricular nucleusHypothalamusSupraopticnucleusInferiorhypophysealartery Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary.

Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2). Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH).1Posterior lobeof pituitaryOpticchiasmaInfundibulum(connecting stalk)Axon terminalsParaventricular nucleusHypothalamusSupraopticnucleusInferiorhypophysealarteryHypothalamic-hypophysealtractPosterior lobeof pituitary

Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2). Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH).12Posterior lobeof pituitaryOpticchiasmaInfundibulum(connecting stalk)Axon terminalsParaventricular nucleusHypothalamusSupraopticnucleusInferiorhypophysealartery Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary.Hypothalamic-hypophysealtractPosterior lobeof pituitary

Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2). Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH). Oxytocin and ADH are stored in axon terminals in the posterior pituitary.123Posterior lobeof pituitaryOpticchiasmaInfundibulum(connecting stalk)Axon terminalsParaventricular nucleusHypothalamusSupraopticnucleusInferiorhypophysealartery Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary.Hypothalamic-hypophysealtractPosterior lobeof pituitary

Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2). Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH). Oxytocin and ADH are stored in axon terminals in the posterior pituitary. When hypothalamic neurons fire, action potentials arriving at the axon terminals cause oxytocin or ADH to be released into the blood.1234OxytocinADHPosterior lobeof pituitaryOpticchiasmaInfundibulum(connecting stalk)Axon terminalsParaventricular nucleusHypothalamusSupraopticnucleusInferiorhypophysealartery Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary.Hypothalamic-hypophysealtractPosterior lobeof pituitary

Anterior Lobe:Originates as out-pocketing of oral mucosaVascular connection to hypothalamusHypophyseal portal systemPrimary capillary plexusHypophyseal portal veinsSecondary capillary plexus Carries releasing and inhibiting hormones to anterior pituitary to regulate hormone secretion

Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2). Hypothalamic hormones travel through portal veins to the anterior pituitary where they stimulate or inhibit release of hormones made in the anterior pituitary. In response to releasing hormones, the anterior pituitary secretes hormones into the secondary capillary plexus. This in turn empties into the general circulation.GH, TSH, ACTH,FSH, LH, PRLAnterior lobeof pituitary When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus.Hypophysealportal system Primary capillary plexus Hypophyseal portal veins Secondary capillary plexusSuperiorhypophysealarteryAnterior lobeof pituitaryHypothalamusHypothalamicneurons synthesizeGHRH, GHIH, TRH,CRH, GnRH, PIH.A portal system is two capillary plexuses (beds) connected by veins.123

Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2). GH, TSH, ACTH,FSH, LH, PRLAnterior lobeof pituitary When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus.Hypophysealportal system Primary capillary plexus Hypophyseal portal veins Secondary capillary plexusSuperiorhypophysealarteryAnterior lobeof pituitaryHypothalamusHypothalamicneurons synthesizeGHRH, GHIH, TRH,CRH, GnRH, PIH.A portal system is two capillary plexuses (beds) connected by veins.1

Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2). Hypothalamic hormones travel through portal veins to the anterior pituitary where they stimulate or inhibit release of hormones made in the anterior pituitary.GH, TSH, ACTH,FSH, LH, PRLAnterior lobeof pituitary When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus.Hypophysealportal system Primary capillary plexus Hypophyseal portal veins Secondary capillary plexusSuperiorhypophysealarteryAnterior lobeof pituitaryHypothalamusHypothalamicneurons synthesizeGHRH, GHIH, TRH,CRH, GnRH, PIH.A portal system is two capillary plexuses (beds) connected by veins.12

Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2). Hypothalamic hormones travel through portal veins to the anterior pituitary where they stimulate or inhibit release of hormones made in the anterior pituitary. In response to releasing hormones, the anterior pituitary secretes hormones into the secondary capillary plexus. This in turn empties into the general circulation.GH, TSH, ACTH,FSH, LH, PRLAnterior lobeof pituitary When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus.Hypophysealportal system Primary capillary plexus Hypophyseal portal veins Secondary capillary plexusSuperiorhypophysealarteryAnterior lobeof pituitaryHypothalamusHypothalamicneurons synthesizeGHRH, GHIH, TRH,CRH, GnRH, PIH.A portal system is two capillary plexuses (beds) connected by veins.123

Oxytocin and ADHEach composed of nine amino acidsAlmost identical differ in two amino acids

Strong stimulant of uterine contractionReleased during childbirthHormonal trigger for milk ejectionActs as neurotransmitter in brain

Inhibits or prevents urine formationRegulates water balanceTargets kidney tubules reabsorb more waterRelease also triggered by pain, low blood pressure, and drugsInhibited by alcohol, diureticsHigh concentrations vasoconstriction

Diabetes insipidusADH deficiency due to hypothalamus or posterior pituitary damageMust keep well-hydratedSyndrome of inappropriate ADH secretion (SIADH)Retention of fluid, headache, disorientationFluid restriction; blood sodium level monitoring

Growth hormone (GH)Thyroid-stimulating hormone (TSH) or thyrotropinAdrenocorticotropic hormone (ACTH)Follicle-stimulating hormone (FSH)Luteinizing hormone (LH)Prolactin (PRL)

All are proteinsAll except GH activate cyclic AMP second-messenger systems at their targetsTSH, ACTH, FSH, and LH are all tropic hormones (regulate secretory action of other endocrine glands)

Produced by somatotropic cellsDirect actions on metabolismIncreases blood levels of fatty acids; encourages use of fatty acids for fuel; protein synthesisDecreases rate of glucose uptake and metabolism conserving glucose Glycogen breakdown and glucose release to blood (anti-insulin effect)

Indirect actions on growthMediates growth via growth-promoting proteins insulin-like growth factors (IGFs)IGFs stimulateUptake of nutrients DNA and proteinsFormation of collagen and deposition of bone matrixMajor targetsbone and skeletal muscle

GH release chiefly regulated by hypothalamic hormonesGrowth hormonereleasing hormone (GHRH)Stimulates release Growth hormoneinhibiting hormone (GHIH) (somatostatin)Inhibits releaseGhrelin (hunger hormone) also stimulates release

HypersecretionIn children results in gigantismIn adults results in acromegalyHyposecretionIn children results in pituitary dwarfism

Figure 16.6 Growth-promoting and metabolic actions of growth hormone (GH).Hypothalamussecretes growthhormonereleasinghormone (GHRH), andGHIH (somatostatin)AnteriorpituitaryInhibits GHRH releaseStimulates GHIH releaseInhibits GH synthesisand releaseFeedbackIndirect actions(growth-promoting)Liver andother tissuesInsulin-like growthfactors (IGFs)ProduceEffectsSkeletalExtraskeletalFatmetabolismCarbohydratemetabolismDirect actions(metabolic,anti-insulin)EffectsGrowth hormone (GH)Increased cartilageformation andskeletal growthIncreased proteinsynthesis, andcell growth andproliferationIncreasedfat breakdownand releaseIncreased bloodglucose and otheranti-insulin effectsIncreases, stimulatesInitial stimulusReduces, inhibitsPhysiological responseResult

Figure 16.7 Disorders of pituitary growth hormone.

Produced by thyrotropic cells of anterior pituitaryStimulates normal development and secretory activity of thyroidRelease triggered by thyrotropin-releasing hormone from hypothalamusInhibited by rising blood levels of thyroid hormones that act on pituitary and hypothalamus

HypothalamusTRHAnterior pituitaryTSHThyroid glandThyroidhormonesTarget cellsStimulatesFigure 16.8 Regulation of thyroid hormone secretion.Inhibits

Secreted by corticotropic cells of anterior pituitaryStimulates adrenal cortex to release corticosteroids

Regulation of ACTH releaseTriggered by hypothalamic corticotropin-releasing hormone (CRH) in daily rhythmInternal and external factors such as fever, hypoglycemia, and stressors can alter release of CRH

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH)Secreted by gonadotrophs of anterior pituitaryFSH stimulates gamete (egg or sperm) productionLH promotes production of gonadal hormonesAbsent from the blood in prepubertal boys and girls

Regulation of gonadotropin releaseTriggered by gonadotropin-releasing hormone (GnRH) during and after pubertySuppressed by gonadal hormones (feedback)

Secreted by prolactin cells of anterior pituitaryStimulates milk productionRole in males not well understood

Regulation of PRL releasePrimarily controlled by prolactin-inhibiting hormone (PIH) (dopamine)Blood levels rise toward end of pregnancySuckling stimulates PRL release and promotes continued milk productionHypersecretion causes inappropriate lactation, lack of menses, infertility in females, and impotence in males

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