THE ENDOCRINE SYSTEM Chapter 15. HOMEOSTASIS, HORMONES & THE ENDOCRINE SYSTEM Topic 15.1.
The Endocrine System
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Transcript of The Endocrine System
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The Endocrine System
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The Endocrine SystemSecond-messenger system of the bodyUses chemical messengers (hormones) that
are released into the bloodHormones control several major processes
ReproductionGrowth and developmentMobilization of body defensesMaintenance of much of homeostasisRegulation of metabolism
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Hormone OverviewHormones are produced by specialized cellsCells secrete hormones into extracellular
fluidsBlood transfers hormones to target sitesThese hormones regulate the activity of
other cells
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The Chemistry of HormonesHormones are classified chemically as
Amino acid–based, which includesProteinsPeptidesAmines
Steroids—made from cholesterolProstaglandins—made from highly active
lipids
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Mechanisms of Hormone ActionHormones affect only certain tissues or
organs (target cells or target organs)Target cells must have specific protein
receptorsHormone-binding alters cellular activity
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Effects Caused by HormonesChanges in plasma membrane permeability
or electrical stateSynthesis of proteins, such as enzymesActivation or inactivation of enzymesStimulation of mitosisPromotion of secretory activity
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The Chemistry of HormonesTwo mechanisms in which hormones act
Direct gene activationSecond-messenger system
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Direct Gene Activation (Steroid Hormone Action)Diffuse through the plasma membrane of
target cellsEnter the nucleusBind to a specific protein within the nucleusBind to specific sites on the cell’s DNAActivate genes that result in synthesis of
new proteins
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Figure 9.1a
NucleusCytoplasmSteroidhormone Receptor
protein
Hormone-receptorcomplex
DNA
mRNANewprotein
Plasmamembraneof targetcell
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Second-Messenger System (Nonsteroid Hormone Action)Hormone binds to a membrane receptorHormone does not enter the cellSets off a series of reactions that activates
an enzymeCatalyzes a reaction that produces a
second-messenger moleculeOversees additional intracellular changes
to promote a specific response
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Figure 9.1b
CytoplasmNonsteroidhormone (firstmessenger)
Enzyme
Receptorprotein
Secondmessenger
Effect on cellular function,such as glycogenbreakdown Plasma
membraneof target cell
ATP
cAMP
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Control of Hormone ReleaseHormone levels in the blood are mostly
maintained by negative feedbackA stimulus or low hormone levels in the
blood triggers the release of more hormoneHormone release stops once an appropriate
level in the blood is reached
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Hormonal Stimuli of Endocrine GlandsMost common stimuliEndocrine glands are activated by other
hormonesExamples:
Anterior pituitary hormones
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Hormonal Stimuli of Endocrine Glands
Figure 9.2a
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Humoral Stimuli of Endocrine GlandsChanging blood levels of certain ions
stimulate hormone releaseHumoral indicates various body fluids such
as blood and bileExamples:
Parathyroid hormoneCalcitoninInsulin
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Humoral Stimuli of Endocrine Glands
Figure 9.2b
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Neural Stimuli of Endocrine GlandsNerve impulses stimulate hormone releaseMost are under the control of the
sympathetic nervous systemExamples include the release of
norepinephrine and epinephrine by the adrenal medulla
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Figure 9.2c
Neural Stimuli of Endocrine Glands
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Major Endocrine OrgansPituitary glandThyroid glandParathyroid glandsAdrenal glandsPineal glandThymus glandPancreasGonads (Ovaries and Testes)Hypothalamus
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Location of Major Endrocrine Organs
Figure 9.3
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Pituitary GlandSize of a peaHangs by a stalk from the hypothalamus in
the brainProtected by the sphenoid boneHas two functional lobes
Anterior pituitary—glandular tissuePosterior pituitary—nervous tissue
Often called the “master endocrine gland”
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Hormones of the Anterior PituitarySix anterior pituitary hormones
Two affect non-endocrine targetsGrowth hormoneProlactin
Four stimulate other endocrine glands (tropic hormones)Thyroid-stimulating hormone (thyrotropic hormone)Adrenocorticotropic hormoneTwo gonadotropic hormones
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Hormones of the Anterior PituitaryCharacteristics of all anterior pituitary
hormonesProteins (or peptides)Act through second-messenger systemsRegulated by hormonal stimuli, mostly
negative feedback
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Hormones of the Anterior Pituitary
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Hormones of the Anterior PituitaryGrowth hormone
General metabolic hormoneMajor effects are directed to growth of
skeletal muscles and long bonesPlays a role in determining final body sizeCauses amino acids to be built into proteinsCauses fats to be broken down for a source
of energy
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Hormones of the Anterior PituitaryGrowth hormone (GH) disorders
Pituitary dwarfism results from hyposecretion of GH during childhood
Gigantism results from hypersecretion of GH during childhood
Acromegaly results from hypersecretion of GH during adulthood
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Hormones of the Anterior PituitaryGigantism
Figure 9.5a
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Hormones of the Anterior PituitaryDwarfism
Figure 9.5b
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Hormones of the Anterior PituitaryProlactin (PRL)
Stimulates and maintains milk production following childbirth
Function in males is unknownAdrenocorticotropic hormone (ACTH)
Regulates endocrine activity of the adrenal cortex
Thyroid-stimulating hormone (TSH)Influences growth and activity of the thyroid
gland
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Hormones of the Anterior PituitaryGonadotropic hormones
Regulate hormonal activity of the gonadsFollicle-stimulating hormone (FSH)
Stimulates follicle development in ovariesStimulates sperm development in testes
Luteinizing hormone (LH)Triggers ovulation of an egg in femalesStimulates testosterone production in males
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Pituitary–Hypothalamus RelationshipHormonal release is regulated by releasing
and inhibiting hormones produced by the hypothalamus
Hypothalamus produces two hormonesThese hormones are transported to
neurosecretory cells of the posterior pituitaryOxytocinAntidiuretic hormone
The posterior pituitary is not strictly an endocrine gland, but does release hormones
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Hormones of the Posterior PituitaryOxytocin
Stimulates contractions of the uterus during labor, sexual relations, and breastfeeding
Causes milk ejection in a nursing woman
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Hormones of the Posterior PituitaryAntidiuretic hormone (ADH)
Inhibits urine production by promoting water reabsorption by the kidneys
In large amounts, causes vasoconstriction leading to increased blood pressure
Also known as vasopressin
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Hormones of the Posterior Pituitary
Figure 9.6