Ch13 Endocrine System

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Copyright 2010, John Wiley & Sons, Inc.

Chapter 13

The Endocrine System


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End of Chapter 13

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Comparison: Nervous v. Endocrine

Nervous systemNeurons releaseneurotransmitters atsynapses,neuromuscular orneuroglandular

junctionsEffectors includeother neurons,muscles, glandsRapid responsesfrom effectors

Endocrine systemReleases hormones intointerstitial fluid blood

general circulationEffectors: virtually anytype of body cell so canhave widespread effectson diverse aspects ofmetabolism

Slower, longer-lastingresponses as hormoneslinger in blood


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Comparison: Endocrine v. Exocrine

Endocrine glandsSecretions enterinterstitial fluid and then

bloodstreamStay in the body: endo-Examples: all hormonessuch as growth hormone,insulin, adrenalin,estrogen, testosterone

Exocrine glandsSecrete substances thatenter ductsUltimately exit the body(exo-)Examples: mucus, salivaand other digestivesecretions, sweat, tears


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Endocrine Cells that Make Hormones

In endocrine glandsPituitary, thyroid, parathyroid, adrenal, pineal

In cells within organs that do producehormones but also have other functions

Hypothalamus, thymus, pancreas, ovaries,testes, kidneys, stomach, liver, small intestine,skin, heart, adipose tissue, and placenta



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Location of Endocrine Glands


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Hormone Action

Hormones are carried in blood streamBut only certain cells can be affected byhormones

These target cells have 1000s of receptorsspecific for a particular hormone.Response determined by responding cell: differentcells may respond differently to the samehormone.

Cell may have > 1 type of receptor, so canrespond to more than one hormone


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Hormone ChemistryLipid-soluble

Steroids, such as testosterone, estrogensThyroid hormones: T 3 and T 4 Nitric oxide (NO)

Water-soluble Amino acid derivatives, such as epinephrine,norepinephrinePeptides: antidiuretic hormone (ADH), oxytocin

Proteins: insulin and growth hormoneGeneral action depends on chemistry


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Lipid-Soluble Action

Hormone detaches from carrier in bloodstreamDiffuses through interstitial fluid and cellmembrane into cell

Binds to receptor and activates itReceptor-hormone complex alters geneexpression

If new mRNA protein synthesisNew proteins alter cell activity


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1 Lipid-solublehormonediffuses into cell

Blood capillary

Target cell

Transportprotein

Free hormone


Blood capillary

Activatedreceptor-hormonecomplex altersgene expression

NucleusReceptor

mRNA

DNACytosol

Target cell

Transportprotein

Free hormone

2


Blood capillary

Activatedreceptor-hormonecomplex altersgene expression

NucleusReceptor

mRNANewly formedmRNA directssynthesis of

specific proteinson ribosomes

DNACytosol

Target cell

Transportprotein

Free hormone

Ribosome

2

3

Lipid-SolubleHormone

Action


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Water-Soluble ActionHormone (first messenger) diffuses fromblood and binds to receptor in plasmamembraneStarts reaction inside cell forming second

messengerCyclic AMP is a common oneSecond messenger causes activation ofseveral proteins (enzymes)

Activated proteins produce physiologicalresponsesSecond messenger is inactivated


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Water-solublehormone

Receptor

G protein

Blood capillary

Binding of hormone (first messenger)to its receptor activates G protein,which activates adenylate cyclase

Adenylate cyclase

Target cell

1


Receptor

G protein

cAMP

Second messenger

Activated adenylatecyclase convertsATP to cAMP

Blood capillary


Adenylate cyclase

Target cell

ATP

1

2


Receptor

cAMP serves as asecond messengerto activate proteinkinases

G protein

Protein kinases

cAMP

Second messenger


Blood capillary


Adenylate cyclase

Target cell

ATP

1

2

3 Activatedproteinkinases


Receptor


G protein

Protein kinases

cAMP

Activatedproteinkinases

Second messenger


Activated proteinkinasesphosphorylatecellular proteins

Blood capillary


Adenylate cyclase

Target cell

ATP

1

2

4

3

Protein P

ADP

Protein

ATP


Receptor


G protein

Protein kinases

cAMP


Protein

Second messenger



Millions of phosphorylatedproteins cause reactions thatproduce physiological responses

Blood capillary


Adenylate cyclase

Target cell

P

ADP

Protein

ATP

ATP

1

2

4

3

5


Receptor


G protein

Protein kinases

cAMP


Protein

Second messenger

Phosphodiesteraseinactivates cAMP



Millions of phosphorylatedproteins cause reactions thatproduce physiological responses

Blood capillary


Adenylate cyclase

Target cell

P

ADP

Protein

ATP

ATP

1

2

6

4

3

5

Water-SolubleHormone

Action


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Control of Hormone Secretions

Release occurs in short burstsRegulated bySignals from nervous system

Example: adrenal medulla release of epinephrine

Chemical changes in bloodExample: blood Ca 2+ affects parathyroid hormone

Other hormonesExample: ACTH from pituitary stimulates release of

cortisol from adrenal cortex


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Hormone RegulationInteractions Animation

Introduction to Hormonal Regulation,Secretion, and Concentration

You must be connected to the internet to run this animation.
http://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_intro_horm_reg/anim_intro_horm_reg/screen0.swfhttp://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_intro_horm_reg/anim_intro_horm_reg/screen0.swfhttp://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_intro_horm_reg/anim_intro_horm_reg/screen0.swfhttp://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_intro_horm_reg/anim_intro_horm_reg/screen0.swf


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Hypothalamus and Pituitary

Serve as major link between nervous andendocrine systemsHypothalamic cells synthesize

Many releasing and inhibiting hormonesTwo hormones (oxytocin and ADH) that are thenstored and released from the posterior pituitary

Anterior pituitary synthesizes 7 hormones

Regulate growth, development, metabolismand homeostasis


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Pituitary

Located in depression in sphenoid bone justinferior to the brainPituitary is attached to hypothalamus by stalk(infundibulum)Pituitary has 2 lobes: anterior and posterior


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Effects of Hypothalamus on Pituitary

Axons of hypothalamic neurons(neurosecretory cells) end near capillaries ofhypothalamusSecrete releasing hormones or inhibiting

hormones portal veinsThese hormones regulate release of anteriorpituitary hormones


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Pituitary Gland Blood Supply


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Seven Anterior Pituitary Hormones

1. Human growth hormone (hGH)2. Thyroid-stimulating hormone (TSH)3. Follicle-stimulating hormone (FSH)

4. Luteinizing hormone (LH)5. Prolactin6. Adrenocorticotropic hormone (ACTH)

7. Melanocyte-stimulating hormone (MSH)


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1. Human Growth Hormone (hGH)hGH promotes synthesis of insulinlike growthfactors (IGFs) = somatomedins

Secreted by liver, muscle, cartilage, bone cells Actions of IGFs much like those of insulin

RegulationBy hypothalamic hormones

Growth hormone-releasing hormone (GHRH)Growth hormone-inhibiting Hormone (GHIH )

By blood glucose levelsLow blood glucose levels release of GHRH


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1. Human Growth Hormone (hGH) Actions of hGH

Stimulates protein synthesisMaintains muscle and bone massPromotes healing of injuries, tissue repair

Makes fuel (ATP) available for growth Causes fat breakdown (baby fat) and release of fattyacids into bloodBreaks down liver glycogen releases glucose intoblood


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2. Thyroid-Stimulating Hormone (TSH)

Stimulates the formation and secretion ofthyroid hormones (T 3, T 4) by thyroid glandRegulation of TSH (negative feedback)

Low blood levels of T3, T

4

Hypothalamus Thyrotropin-releasing hormone(TRH) TRH stimulates release of TSH

TSH stimulates thyroid production of T 3, T 4


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In femalesFSH starts follicle development

Starts egg productionStarts estrogen production from follicle cells

LH stimulates formation of corpus luteumCompletion of egg and its ovulationSecretion of progesterone + estrogen

In malesFSH sperm production in testesLH release of testosterone from testes

3, 4. Follicle Stimulating Hormone (FSH)and Luteinizing Hormone (LH)


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Regulation (feedback mechanisms)Gonadotrophin-releasing hormone (GnRH) fromhypothalamus release of FSH or LH from

anterior pituitaryFSH increases estrogen in femalesLH increases estrogen (E) and progesterone(P) in females and testosterone (T) in males

High levels of these ovarian or testicularhormones (E, P, and T) suppress production ofGnRH

3, 4. Follicle Stimulating Hormone (FSH)and Luteinizing Hormone (LH)


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5. Prolactin (PRL)Initiates and maintains milk production bymammary glands

Ejection of milk depends on oxytocin

RegulationProlactin inhibiting hormone (PIH) suppressesprolactin releaseHigh levels of estrogens PRH prolactin

releaseUnknown function in males

Hypersecretion erectile dysfunction


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6. Adrenocorticotropic Hormone(ACTH)

Controls production and secretion ofglucocorticoids from adrenal cortexRegulation of ACTH

Corticotrophin releasing hormone (CRH) fromhypothalamus stimulates secretion of ACTHStress-related stimuli can also stimulate ACTHrelease

Glucocorticoids inhibit CRH and ACTH release


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7. Melanocyte Stimulating Hormone(MSH)

Small amounts in bloodstreamExcess amounts causes skin darkening


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Posterior PituitaryHormones made in hypothalamus passdown axons to posterior pituitary

Nerve impulses there cause release of hormones

Two hormones released

Oxytocin causesSmooth muscle contraction of uterus during childbirthCauses letdown of milk from glands to ducts Some sexual pleasure during sexual activity


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Posterior Pituitary Antidiuretic Hormone (ADH) = vasopressin

Causes kidneys to retain more waterCauses vasoconstriction increases blood pressureDehydration, pain, stress increase ADH secretion


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Posterior Pituitary

High blood osmotic1

High blood osmotic1

High blood osmotic1

High blood osmotic1

High blood osmotic Low blood osmotic1 5

High blood osmotic Low blood osmotic1 5


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Osmoreceptors

High blood osmoticpressure stimulateshypothalamicosmoreceptors

1

Osmoreceptors


Osmoreceptorsactivate theneurosecretory cellsthat synthesize andrelease ADH

Hypothalamus

1

2Osmoreceptors


Nerve impulsesliberate ADH fromaxon terminals inthe posteriorpituitary intothe bloodstream


Hypothalamus

ADH

1

2

3

Osmoreceptors




Hypothalamus

Sudoriferous(sweat) glandsdecrease water

loss by perspirationfrom the skin

Arterioles constrict,which increasesblood pressure

Kidneys retainmore water,which decreases

urine output

ADH

Target tissues

1

2

3

4

Osmoreceptors


Low blood osmoticpressure inhibitshypothalamicosmoreceptors



Hypothalamus





urine output

ADH

Target tissues

1

2

3

4

5

Osmoreceptors


Low blood osmoticpressure inhibitshypothalamicosmoreceptors



Hypothalamus

Inhibition of osmo-receptors reduces orstops ADH secretion





urine output

ADH

Target tissues

1

2

3

4

5

6

ADHRegulation


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Thyroid GlandLocation: inferior to larynx: two lobesStructure and function

Follicular cells produce hormones and storethem in follicles

Thyroxin (T 4)Triiodothyronine (T 3)Parafollicular cells (C-cells) produce

Calcitonin (CT)


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Thyroid Gland


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ThyroidGland


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Low blood levels of T 3d T l t b li

1


1


1


1


1


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and T 3 or low metabolicrate stimulate release of

HypothalamusTRH

Actions of Thyroid Hormones:

Increase basal metabolic rate

Stimulate synthesis of Na + /K + ATPase

Increase body temperature (calorigenic effect)

Stimulate protein synthesis

Increase the use of glucose and fatty acids for ATP production

Stimulate lipolysis

Enhance some actions of catecholaminesRegulate development and growth of nervous tissue and bones

Anteriorpituitary

TRH, carriedby hypophyseal

portal veins toanterior pituitary,stimulatesrelease of TSHby thyrotrophs


Hypothalamus

TSH

TRH







Stimulate lipolysis


2

Anteriorpituitary



TSH released into

blood stimulatesthyroid follicular cells

Thyroidfollicle


Hypothalamus

Anteriorpituitary

TSH

TRH







Stimulate lipolysis


2

3

T3 and T 4 released intoblood byfollicular cells



TSH released into


Thyroidfollicle


Hypothalamus

Anteriorpituitary

TSH

TRH







Stimulate lipolysis


2

3

4 T3 and T 4 released intoblood byfollicular cells

ElevatedT3inhibitsrelease ofTRH andTSH(negativefeedback)



TSH released into


Thyroidfollicle


Hypothalamus

Anteriorpituitary

TSH

TRH







Stimulate lipolysis


2

3

5

4

Thyroid HormoneRegulation


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Parathyroid GlandsSmall round masses in posterior of thyroidglandRelease parathyroid hormone (PTH)

Increases blood Ca 2+ in 3 ways

Increases number and activity of osteoclasts that breakdown boneSlows loss of Ca 2+ and Mg 2+ in urinePromotes production of calcitriol (vitamin D) increases rate of Ca 2+ , Mg 2+ and HPO 42- absorption in

GI tract increase blood Ca2+

Decreases blood HPO42- by decreasing loss ofHPO 42- in urine


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Parathyroid Glands

Calcium Regulation


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1 High level of Ca 2+ in bloodstimulates thyroid glandparafollicular cells torelease more CT.


CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca 2+ level.

2


Low level of Ca 2+ in bloodstimulates parathyroidgland chief cells to releasemore PTH.


3

2




PARATHYROID HORMONE (PTH)promotes release of Ca 2+ frombone extracellular matrix intoblood and slows loss of Ca 2+ in urine, thus increasing bloodCa 2+ level.

3

4 2

1

PTH also stimulatesthe kidneys to releaseCALCITRIOL.

High level of Ca 2+ in bloodstimulates thyroid glandparafollicular cells torelease more CT.




3

4 25

1

CALCITRIOL stimulatesincreased absorption ofCa 2+ from foods, whichincreases blood Ca 2+ level.

PTH also stimulatesthe kidneys to releaseCALCITRIOL.

High level of Ca 2+ in bloodstimulates thyroid glandparafollicular cells torelease more CT.




3

4 25

6

Calcium Regulation


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PancreasFlattened organ in curve of duodenumMostly an exocrine organ that secretesdigestive enzymesEndocrine cells in pancreatic islets (ofLangerhans)Several cell types

Alpha cells glucagon

Beta cells insulin


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Pancreas


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Pancreas


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Actions of Insulin and GlucagonLow blood glucose stimulates glucagonrelease

Glucagon stimulates liver to release glucose increased blood glucose

High glucose levels stimulate insulin releaseInsulin increases glucose transport into skeletalmuscle and adipose cells decreased bloodglucoseInsulin promotes amino acid uptake, proteinsynthesis, and lipid storage

ANS also modulates hormone release

Low blood glucose(hypoglycemia)

1


1


1


1


High blood glucose(hyperglycemia)

1 5



1 5



1 5



1 5


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(hypoglycemia)stimulates alphacells to secrete

GLUCAGON

Glucagon acts onhepatocytes(liver cells) to:

convert glycogen into glucose(glycogenolysis)

form glucose from lactic acid andcertain amino acids(gluconeogenesis)


GLUCAGON

2 Glucagon acts onhepatocytes(liver cells) to:



Glucose releasedby hepatocytesraises blood glucoselevel to normal


GLUCAGON

2

3





If blood glucosecontinues to rise,

hyperglycemia inhibitsrelease of glucagon


GLUCAGON

2

3

4








(hyperglycemia)stimulates beta cellsto secrete

GLUCAGON

2

3

4

INSULIN

Insulin acts on variousbody cells to:

accelerate facilitated diffusion of glucoseinto cells

speed conversion of glucose into glycogen(glycogenesis)

increase uptake of amino acids and increaseprotein synthesis

speed synthesis of fatty acids (lipogenesis) slow glycogenolysis slow gluconeogenesis









INSULINGLUCAGON

2

3

4

6 Insulin acts on variousbody cells to:





Blood glucose level falls









INSULINGLUCAGON

2

3

4

6

7

Insulin acts on variousbody cells to:





If blood glucose continuesto fall, hypoglycemia

inhibits release ofinsulin

Blood glucose level falls









INSULINGLUCAGON

2

3

4

6

7

8

Glucose/Insulin

Regulation


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Adrenal GlandsLocation: on top of kidneysTwo separate gland structures

Adrenal cortex: 3 zones make steroidsOuter zone mineralocorticoids (aldosterone)

Middle zone glucocorticoids (cortisol)Inner Zone androgens (testosterone)

Adrenl medulla: produces epinephrine (adrenalin)and norepinephrine


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Adrenal Glands


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Adrenal Glands


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Mineralocorticoids


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Glucocorticoid (Cortisol) ActionsIncreases rate of protein breakdownStimulates liver formation of glucoseBreaks down triglycerides in adipose

Anti-inflammatory effectsInhibit white blood cells

Depresses immune systemRegulated by negative feedback: CRH and

ACTH


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AndrogensSmall amount secreted from adrenal cortex inboth females and males

At puberty, in both genders, androgensStimulate axillary and pubic hair growth

Contribute to adolescent growth spurtIn females, androgens

Contribute to libido Are converted to estrogens by other body tissues


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Adrenal MedullaInner portion of adrenal glandsPart of sympathetic nervous system

Consists of sympathetic postganglionic cellsStimulated by preganglionic sympatheticneuronsReleases epinephrine and norepinephrine

Actions mimic sympathetic nerves in stress

Increases heart rate and blood pressureIncreases blood glucose, dilates airways


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Gonads: Ovaries and TestesProduce gametes: sperm and oocytesProduce hormones

Testosterone in malesEstrogen and progesterone in females

Inhibin that inhibits FSH releaseRelaxin during pregnancy: facilitates birth

Regulated byGnRH from hypothalamusFSH + LH from anterior pituitary


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Pineal Gland

Small gland attached to roof of third ventricleof brainProduces melatoninSets bodys biological clock

More released in darkness, less in sunlight


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Other HormonesThymus: thymosinGI tract

GastrinGlucose-dependent insulinotropic peptide (GIP)

SecretinCholecystokinin (CCK)

Kidney: erythropoietin (EPO)

Heart: atrial natriuretic peptide (ANP)


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Other Hormones Adipose tissue: leptinPlacenta: human chorionic gonadotropin(hCG)Prostaglandins (PG) and leukotrienes (LT)Derived from fatty acids

Act locally in most tissues and released frommost body cells


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Other HormonesLTs stimulate white blood cells and mediateinflammationPGs affect many visceral functions, modulateinflammation, promote fever, and intensify

pain


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Stress ResponsesResponse to stressorsWhen successful leads to extra physiologicalcapacity and long term adaptationThree stages1. Initial fight -or- flight response

Nerve mediated response-sympathetic Aldosterone: to raise blood pressure

2. Resistance (slower) 3. Exhaustion (may occur eventually)


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Slower and longer than initial responseHypothalamus increased CRH, GHRH,TRH

CRH ACTH cortisol mobilizes metabolites

(amino acids, glucose and fat)GHRH hGH mobilizes fats and glucose forenergy and promote tissue growth and repairTRH TSH thyroid hormones increasedmetabolic capacity

Stress Responses


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Ch13 Endocrine System