Copyright 2009, John Wiley & Sons, Inc. Chapter 18: The Endocrine System.

Copyright 2009, John Wiley & Sons, Inc.

Chapter 18: The Endocrine System


Nervous and Endocrine Systems Act together to coordinate functions of all body

systems Nervous system

Nerve impulses/ Neurotransmitters Faster responses, briefer effects, acts on specific target

Endocrine system Hormone – mediator molecule released in 1 part of the

body but regulates activity of cells in other parts Slower responses, effects last longer, broader influence

18_table_01


Endocrine Glands

2 kinds of glands Exocrine – ducted Endocrine – ductless

Secrete products into interstitial fluid, diffuse into blood

Endocrine glands include Pituitary, thyroid, parathyroid, adrenal and pineal glands Hypothalamus, thymus, pancreas, ovaries, testes, kidneys,

stomach, liver, small intestine, skin, heart, adipose tissue, and placenta not exclusively endocrine glands

Functions of Hormones

1. help regulate chemical composition and volume of internal

environment (interstitial fluid) metabolism and energy balance contraction of smooth and cardiac muscle glandular secretions some immune system activities

2. control growth and development3. regulate operation of reproductive systems4. help establish circadian rhythms



Hormone Activity

Hormones affect only specific target tissues with specific receptors

Receptors constantly synthesized and broken down Down-regulation – less sensitive Up-regulation – more sensitive


Circulating and Local Hormones Hormone types

Circulating – circulate in blood throughout body

Local hormones – act locally Paracrine – act on

neighboring cells Autocrine – act on

the same cell that secreted them


Chemical Classes of Hormones

Lipid-soluble – use transport proteins Steroid Thyroid Nitric oxide (NO)

Water-soluble – circulate in “free” form Amine Peptide/ protein Eicosanoid: arachidonic acid

Prostaglandins Leukotrienes

Hormone Transport in the Blood water-soluble hormones circulate “dissolved”

in plasma as “free” form Lipid-soluble hormones require transport

proteins synthesized in liver three functions

water solubility retard filtration in kidney ready reserve

free fraction (0.1-10%) provide active hormone



Mechanisms of Hormone Action Response depends on both hormone and target cell

various target cells respond differently to the same hormone for example, insulin stimulates glycogen synthesis in liver cells

and triglyceride formation in fat cells other hormonal effects besides new molecule production

include: change in permeability of plasma membrane stimulate transport in or out of cell alter rate of specific metabolic reaction contraction of smooth and/or cardiac muscle


Mechanisms of Hormone Action Lipid-soluble hormones bind to receptors inside target

cells Water-soluble hormones bind to receptors on the

plasma membrane Activates second messenger system Amplification of original small signal

Responsiveness of target cell depends on Hormone’s concentration Abundance of target cell receptors Influence exerted by other hormones

Permissive, synergistic and antagonistic effects


Lipid-soluble and Water-soluble Hormones

1 Lipid-solublehormonediffuses into cell

Blood capillary

Target cell

Transportprotein

Free hormone


Blood capillary

Activatedreceptor-hormonecomplex altersgene expression

NucleusReceptor

mRNA

DNA

Cytosol

Target cell

Transportprotein

Free hormone

2


Blood capillary


NucleusReceptor

mRNANewly formedmRNA directssynthesis ofspecific proteinson ribosomes

DNA

Cytosol

Target cell

Transportprotein

Free hormone

Ribosome

2

3


Blood capillary


NucleusReceptor

mRNANewly formedmRNA directssynthesis ofspecific proteinson ribosomes

DNA

Cytosol

Target cell

New proteins altercell's activity

Transportprotein

Free hormone

Ribosome

Newprotein

2

3

4

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


Control of Hormone Secretion Regulated by

Signals from nervous system

Chemical changes in the blood

Other hormones Most hormonal

regulation by negative feedback Few examples of positive

feedback


Negative and Positive Feedback systems Negative Feedback systems

Reverses a change in a controlled condition Regulation of blood pressure (force exerted by blood as

it presses again the walls of the blood vessels) excess thyroid hormone turns off hypothalamus excess cortisol turns off hypothalamus and pituitary

Positive Feedback systems Strengthen or reinforce a change in one of the

body’s controlled conditions Normal child birth


Negative Feedback: Regulation of Blood Pressure

External or internal stimulus increase BP Baroreceptors (pressure

sensitive receptors) Detect higher BP Send nerve impulses to

brain for interpretation Response sent via nerve

impulse sent to heart and blood vessels

BP drops and homeostasis is restored

Drop in BP negates the original stimulus


Positive Feedback Systems: Normal Childbirth Uterine contractions cause

vagina to open Stretch-sensitive receptors in

cervix send impulse to brain Oxytocin is released into the

blood Contractions enhanced and

baby pushes farther down the uterus

Cycle continues to the birth of the baby (no stretching)


Hypothalamus and Pituitary Gland Hypothalamus is a major link between

nervous and endocrine system Pituitary attached to hypothalamus by

infundibulum Anterior pituitary or adenohypophysis Posterior pituitary or neurohypophysis


Hypothalamus and Pituitary Gland


Anterior pituitary

Release of hormones stimulated by releasing and inhibiting hormones from the hypothalamus

Also regulated by negative feedback Hypothalamic hormones made by

neurosecretory cells transported by hypophyseal portal system

Anterior pituitary hormones that act on other endocrine systems called tropic hormones


Hormones of the Anterior Pituitary Human growth hormone (hGH) or somatotropin

Stimulates secretion of insulin-like growth factors (IGFs) or somatomedins that promote growth, protein synthesis

Thyroid-stimulating hormone (TSH) or thyrotropin Stimulates synthesis and secretion of thyroid hormones by

thyroid Follicle-stimulating hormone (FSH)

Ovaries initiates development of oocytes, stimulates sperm production by testes

Luteinizing hormone (LH) Ovaries stimulates ovulation, testes stimulates testosterone

production


Hormones of the Anterior Pituitary Prolactin (PRL)

Promotes milk secretion by mammary glands Adrenocorticotropic hormone (ACTH) or

corticotropin Stimulates glucocorticoid secretion by adrenal

cortex Melanocyte-stimulating Hormone (MSH)

Unknown role in humans

18_table_03


Negative Feedback Regulation


Effects of hGH and IGFs

Low blood glucose(hypoglycemia)stimulates release of

GHRH

1 Low blood glucose(hypoglycemia)stimulates release of

hGH

GHRH stimulatessecretionof hGH bysomatotrophs

GHRH

1

2


hGH


GHRH

hGH and IGFs speedup breakdown of liverglycogen into glucose,which enters the bloodmore rapidly

1

3

2


hGH


GHRH


Blood glucose levelrises to normal(about 90 mg/100 mL)

1

3

4

2


hGH


GHRH



If blood glucosecontinues to increase,hyperglycemia inhibitsrelease of GHRH

1

3

4

5

2

Anteriorpituitary


High blood glucose(hyperglycemia)stimulates release of

hGH


GHIHGHRH




1 6

3

4

5

2

Anteriorpituitary

GHIH inhibitssecretion ofhGH bysomatotrophs



hGH


GHIHGHRH




1 6

7

3

4

5

2 GHIH inhibitssecretion ofhGH bysomatotrophs



Anteriorpituitary

hGH


GHIHGHRH

A low level of hGH andIGFs decreases the rateof glycogen breakdownin the liver and glucoseenters the blood moreslowly




1 6

7

83

4

5




Anteriorpituitary

hGH


GHIHGHRH


Blood glucose levelfalls to normal(about 90 mg/100 mL)




1 6

7

8

9

3

4

5




Anteriorpituitary

hGH


GHIHGHRH


Blood glucose levelfalls to normal(about 90 mg/100 mL)




If blood glucosecontinues to decrease,hypoglycemia inhibitsrelease of GHIH

1 6

7

8

9

10

3

4

5

2

18_table_04


Posterior pituitary

Does not synthesize hormones Stores and releases hormones made by the

hypothalamus Transported along hypothalamohypophyseal tract

Oxytocin (OT) Antidiuretic hormone (ADH) or vasopressin


Hypothalamohypophyseal tract


Oxytocin (OT)

During and after delivery of baby affects uterus and breasts

Enhances smooth muscle contraction in wall of uterus

Stimulates milk ejection from mammary glands


Antidiuretic Hormone (ADH)

Decreases urine production by causing the kidneys to return more water to the blood

Also decreases water lost through sweating and constriction of arterioles which increases blood pressure (vasopressin)

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 waterloss by perspirationfrom the skin

Arterioles constrict,which increasesblood pressure

Kidneys retainmore water,which decreasesurine output

ADH

Target tissues

1

2

3

4

Osmoreceptors


Low blood osmoticpressure inhibitshypothalamicosmoreceptors



Hypothalamus




ADH

Target tissues

1

2

3

4

5

Osmoreceptors


Low blood osmoticpressure inhibitshypothalamicosmoreceptors



Hypothalamus

Inhibition of osmo-receptors reduces orstops ADH secretion




ADH

Target tissues

1

2

3

4

5

6

18_table_05



Thyroid Gland

Located inferior to larynx 2 lobes connected by isthmus Thyroid follicles produce thyroid hormones

Thyroxine or tetraiodothyronine (T4)

Triiodothyronine (T3) Both increase BMR, stimulate protein synthesis, increase use

of glucose and fatty acids for ATP production

Parafollicular cells or C cells produce calcitonin Lowers blood Ca2+ by inhibiting bone resorption


Thyroid Gland


Control of thyroid hormone secretion

Thyrotropin releasing hormone (TRH) from hypothalamus

Thyroid stimulating hormone (TSH) from anterior pituitary

Situations that increase ATP demand also increase secretion of thyroid hormones

18_table_06


Parathyroid Glands

Embedded in lobes of thyroid gland Usually 4 Parathyroid hormone (PTH) or parathormone

Major regulator of calcium, magnesium, and phosphate ions in the blood

Increases number and activity of osteoclasts Elevates bone resorption

Blood calcium level directly controls secretion of both calcitonin and PTH via negative feedback


Parathyroid Glands


Roles of Calcitonin, Parathyroid hormone, Calcitriol in Calcium Homeostasis

1 High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.


CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.

2


Low level of Ca2+ in bloodstimulates parathyroid gland chief cells to release more PTH.


3

2




PARATHYROID HORMONE (PTH)promotes release of Ca2+ frombone extracellular matrix intoblood and slows loss of Ca2+ in urine, thus increasing bloodCa2+ level.

3

4 2

1

PTH also stimulatesthe kidneys to releaseCALCITRIOL.

High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.




3

4 25

1

CALCITRIOL stimulatesincreased absorption ofCa2+ from foods, whichincreases blood Ca2+ level.

PTH also stimulatesthe kidneys to releaseCALCITRIOL.

High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.




3

4 25

6

18_table_07


Adrenal Glands

2 structurally and functionally distinct regions Adrenal cortex

Mineralocorticoids affect mineral homeostasis Glucocorticoids affect glucose homeostasis

cortisol Androgens have masculinzing effects

Dehydroepiandrosterone (DHEA) only important in females Adrenal medulla

Modified sympathetic ganglion of autonomic nervous system

Intensifies sympathetic responses Epinephrine and norepinephrine


Adrenal Glands

Mineralocorticoids

Aldosterone Regulates homeostasis of:

two mineral ions sodium conservation potassium secretion

blood pressure blood volume excretion of H+

Glucocorticoids

Cortisol (hydrocortisone), corticosterone, and cortisone

Following effects:1. protein breakdown

2. glucose formation / gluconeogenesis

3. lipolysis

4. stress resistance

5. anti-inflammatory effects

6. depression of immune responses

Androgens

Dehydroepiandrosterone (DHEA) little effect in adult males since testes take over females

promote libido converted into estrogens after menopause androgen conversion only source of

estrogens androgens stimulate axillary and pubic hair in

pubertal children secretion partially controlled by ACTH

18_table_08


Pancreas


Pancreatic Islets

Both exocrine and endocrine gland Roughly 99% of cells produce digestive enzymes Pancreatic islets or islets of Langerhans

Alpha or A cells secrete glucagon – raises blood sugar Beta or B cells secrete insulin – lowers blood sugar Delta or D cells secrete somatostatin – inhibits both insulin

and glucagon F cells secrete pancreatic polypeptide – inhibits

somatostatin, gallbladder contraction, and secretion of pancreatic digestive enzymes


Negative Feedback Regulation of Glucagon and Insulin

Low blood glucose(hypoglycemia)stimulates alphacells to secrete

1

GLUCAGON

Glucagon acts onhepatocytes(liver cells) to:

• convert glycogen into glucose (glycogenolysis)• form glucose from lactic acid and certain amino acids (gluconeogenesis)


GLUCAGON

1

2 Glucagon acts onhepatocytes(liver cells) to:


Glucose releasedby hepatocytesraises blood glucoselevel to normal


GLUCAGON

1

2

3




If blood glucosecontinues to rise,hyperglycemia inhibitsrelease of glucagon


GLUCAGON

1

2

3

4






High blood glucose(hyperglycemia)stimulates beta cellsto secrete

GLUCAGON

1 5

2

3

4

INSULIN

Insulin acts on variousbody cells to:

• accelerate facilitated diffusion of glucose into cells• speed conversion of glucose into glycogen (glycogenesis)• increase uptake of amino acids and increase protein synthesis• speed synthesis of fatty acids (lipogenesis)• slow glycogenolysis• slow gluconeogenesis







INSULINGLUCAGON

1 5

2

3

4

6 Insulin acts on variousbody cells to:


Blood glucose level falls







INSULINGLUCAGON

1 5

2

3

4

6

7

Insulin acts on variousbody cells to:


If blood glucose continuesto fall, hypoglycemiainhibits release ofinsulin

Blood glucose level falls







INSULINGLUCAGON

1 5

2

3

4

6

7

8

18_table_09


Ovaries and Testes

Gonads – produce gametes and hormones Ovaries produce 2 estrogens (estradiol and estrone)

and progesterone With FSH and LH regulate menstrual cycle, maintain

pregnancy, prepare mammary glands for lactation, maintain female secondary sex characteristics

Inhibin inhibits FSH Relaxin produced during pregnancy

Testes produce testosterone – regulates sperm production and maintains male secondary sex characteristics Inhibin inhibits FSH


Hormonal control of testes

At puberty, secretion of gonadotropin-releasing hormone (GnRH) increases

Stimulates anterior pituitary to increase secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH)

LH stimulates Leydig cells to secrete testosterone Synthesized from cholesterol mainly in testes Suppresses secretion of LH and GnRH via negative feedback Enzyme 5 alpha-reductase converts testosterone into

dihydrotestosterone (DHT) in external genitals and prostate FSH acts indirectly on spermatogenesis

FSH and testosterone act on Sertoli cells to stimulate secretion of androgen-binding protein (ABP)

ABP binds testosterone keeping concentration high Testosterone stimulates spermatogenesis Sertoli cells release inhibin which inhibits FSH


Hormonal control of spermatogenesis


Androgens (testosterone and DHT)

Prenatal development Testosterone stimulates male pattern of development or

reproductive system ducts and descent of testes DHT stimulates development of external genitalia

Development of male sexual characteristics At puberty, they bring about development of male sex organs

and development of male secondary sexual characteristics Development of sexual function

Androgens contribute to male sexual behavior, spermatogenesis and sex drive (libido)

Stimulation of anabolism Stimulate protein synthesis – heavier muscle and bone mass

in men


Negative feedback regulates testosterone production


The Female Reproductive Cycle Encompasses ovarian and uterine cycle,

hormonal changes that regulate them, and related changes in breast and cervix

Ovarian cycle – series of events in ovaries that occur during and after maturation of oocyte

Uterine (menstrual) cycle – concurrent series of changes in uterine endometrium preparing it for arrival of fertilized ovum


Hormonal regulation

Gonadotropin-releasing hormone (GnRH) Secreted by hypothalamus controls ovarian and uterine cycle Stimulates release of follicle-stimulating hormone (FSH) and

luteinizing hormone (LH) from anterior pituitary FSH

Initiate follicular growth Stimulate ovarian follicles to secrete estrogens

LH Stimulates further development of ovarian follicles Stimulate ovarian follicles to secrete estrogens Stimulates thecal cells of developing follicle to produce androgens to

be converted into estrogens Triggers ovulation Promotes formation of corpus luteum – produces estrogens,

progesterone, relaxin and inhibin


Hormonal regulation

Estrogens secreted by ovarian follicles Promote development and maintenance of female

reproductive structures and secondary sex characteristics Increases protein anabolism including building strong bones Lowers blood cholesterol Inhibit release of GnRH, LH and FSH

Progesterone Secreted mainly by corpus luteum Works with estrogens to prepare and maintain endometrium

for implantation and mammary glands for milk production Inhibits secretion of GnRH and LH


Hormonal regulation

Relaxin Produced by corpus luteum Relaxes uterus by inhibiting contraction of myometrium At end of pregnancy, increases flexibility of pubic

symphysis and dilates uterine cervix Inhibin

Secreted by granulosa cells of growing follicles and by corpus luteum

Inhibits secretion of FSH and LH


Secretion and physiological effects of hormones in the female reproductive cycle


4 Phases

Typical duration 24-35 days Assume a duration of 28 days

1. Menstrual phase

2. Preovulatory phase

3. Ovulation

4. Postovulatory phase


The female reproductive cycle


Menstrual phase or menstruation

Roughly first 5 days of cycle First day of menstruation is day 1 of new cycle Events in ovaries

Under FSH influence, several primordial follicles develop into primary follicles and then into secondary follicles Takes several months Follicle that begins to develop in one cycle may not mature for

several cycles later Events in uterus

Menstrual discharge occurs because declining levels of estrogens and progesterone stimulate release of prostaglandins causing uterine spiral arterioles to constrict

Cells deprived of oxygen begin to die Only stratum basalis remains


Preovulatory phase

More variable in length Lasts from days 6-13 in a 28 day cycle Events in ovaries

Some of secondary follicles begin to secrete estrogens and inhibin

Dominant follicle – one follicle outgrows all others Estrogens and inhibin of dominant follicle decrease FSH

causing other follicles to stop growing Fraternal (non-identical) twins result when 2 or 3 secondary

follicles become codominant and are ovulated and fertilized at the same time


Preovulatory phase

Normally, one dominant follicle becomes the mature (graafian) follicle

In ovarian cycle, menstrual and preovulatory phases are termed follicular phase because follicles are growing

Events in uterus Estrogens stimulate repair of endometrium Cells of stratum basalis undergo mitosis to form new

stratum functionalis Thickness of endometrium doubles In uterine cycle, preovulatory phase is the proliferative

phase because endometrium is proliferating


Ovulation

Rupture of mature (graffian) follicle and release of secondary oocyte

Day 14 of 28 day cycle High levels of estrogens exert a positive

feedback effect on cells secreting LH and GnRH

High levels ofestrogens fromalmost maturefollicle stimulaterelease of moreGnRH and LH

Hypothalamus

Anterior pituitary

Ovary

Corpus hemorrhagicum(ruptured follicle)

Almost mature(graafian) follicle

LH

GnRH

1 High levels ofestrogens fromalmost maturefollicle stimulaterelease of moreGnRH and LH

Hypothalamus

Anterior pituitary

GnRH promotesrelease of FSHand more LH

Ovary



LH

GnRH

1

2

High levels ofestrogens fromalmost maturefollicle stimulaterelease of moreGnRH and LH

LH surgebrings aboutovulation

Ovulatedsecondaryoocyte

Hypothalamus

Anterior pituitary

GnRH promotesrelease of FSHand more LH

Ovary



LH

GnRH

1

2

3


Postovulatory phase

Duration most constant of phases Lasts for 14 days in 28 day cycle (day 15-28) Events in one ovary

After ovulation, mature follicle collapses to form corpus luteum under the influence of LH

Secretes progesterone, estrogen, relaxin and inhibin In the ovarian cycle, this is the luteal phase


Corpus luteum

If oocyte not fertilized, corpus luteum lasts 2 weeks Degenerates in corpus albicans As levels of progesterone, estrogens and inhibin decrease,

release of GnRH, FSH, and LH rise due to loss of negative feedback

Follicular growth resume as new ovarian cycle begins If oocyte is fertilized, corpus luteum lasts more than 2

weeks Human chorionic gonadotropin (hCG) produced by chorion

of embryo about 8 days after fertilization stimulates corpus luteum


Events in uterus

Progesterone and estrogens produced by corpus luteum promote growth of endometrium

Because of secretory activity of endometrial glands, this is the secretory phase of uterine cycle

Changes peak about 1 week after ovulation when a fertilized ovum might arrive in uterus

If fertilization does not occur, levels of progesterone and estrogens decline due to degeneration of corpus luteum

Withdrawal of estrogens and progesterone causes menstruation


Hormonal interactions in the ovarian and uterine cycles


Pineal Gland

Attached to roof of 3rd ventricle of brain at midline

Masses of neuroglia and pinealocytes Melatonin – amine hormone derived from

serotonin Appears to contribute to setting biological

clock More melatonin liberated during darkness

than light

Eicosanoids

Two families prostaglandins leukotrienes

found in all body cells except red blood cells act as local hormones (paracrine and/or

autocrine) in response to mechanical and chemical stimuli

synthesized by clipping 20 carbon arachidonic acid from membrane phospholipids

Eicosanoids

thromboxane is modified PG that constricts blood vessels and activates platelets

rapid, short acting bind receptors on target cells stimulate or inhibit second messenger LTs stimulate chemotaxis and mediate

inflammation

Eicosanoids

PGs alter: smooth muscle contraction glandular secretion blood flow reproductive processes platelet function respiration nerve impulses lipid metabolism immune response

Eicosanoids

PGs promote: inflammation fever pain intensity


The Stress Response

Eustress in helpful stress / Distress is harmful Body’s homeostatic mechanisms attempt to

counteract stress Stressful conditions can result in stress response or

general adaptation syndrome (GAS) 3 stages – initial flight-or-fight, slower resistance reaction,

eventually exhaustion Prolonged exposure to cortisol can result in wasting of

muscles, suppression of immune system, ulceration of GI tract, and failure of pancreatic beta cells


Stress Response


End of Chapter 18

Copyright 2009 John Wiley & Sons, Inc.All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.

Copyright 2009, John Wiley & Sons, Inc. Chapter 18: The Endocrine System.

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Transcript of Copyright 2009, John Wiley & Sons, Inc. Chapter 18: The Endocrine System.