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TheEndocrineSystem

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Theendocrinesystem

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Theendocrinesystem

extracellular fluid meta o sm

biological clock

contraction of cardiac and smooth muscle glandular secretion

some immune functions

reproduction

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Exocrine glands

secrete products into ducts which empty into body cavities or

body surface sweat, oil, mucous, and digestive enzymes

Endocrine glands

pituitary, thyroid, parathyroid, adrenal, pineal

o er organs secre e ormones as a secon ary unc on

hypothalamus, thymus, pancreas, ovaries, testes, kidneys,

s omac , ver, sma n es ne, s n, ear an p acen a

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Hormonereceptors

Hormones only affect target cells with specific receptors

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Circulatin andlocalhormones Circulating hormones

travel in blood

Local hormones

paracrines act on neighboring cells

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The circulation hormones endocrineact on distant targets

travel in blood

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e oca ormones paracr ne an au ocr neparacrines act on neighboring cells

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Hormonesclassification

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Lipidsolublehormones

Steroids

cholesterol

Thyroid hormones

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WatersolubleHormones Amine, peptide and protein

hormones

modified amino acids or

amino acids put together serotonin, melatonin,

histamine, epinephrine

Eicosanoids

acid (fatty acid)

leukotrienes

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Hormonetransportinblood Protein hormones circulate in free form in blood

Steroid and th roid hormones must bind to trans ort

proteins synthesized by liver slow loss of hormone b filtration within kidne

create reserve of hormone

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Hormone binds to cell surface or receptor inside target cells

Cells may then synthesize new molecules

chan e ermeabilit of membrane

alter rates of reactions

Each target cell responds to hormone differently

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adipose---insulin stimulates triglyceride synthesis

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Mechanismofactionoflipophilichormones Hormone diffuses throu h hos holi id bila er and into cell

ormone-recep or comp ex en n s o n e nuc eus(turning on/off specific genes)

Influence cell physiology by altering proteins synthesis.

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1818

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Mechanismofactionoflipophobic hormones Can not diffuse throu h lasma membrane.

.

Receptor protein activates G-protein in membrane

G-proteins activate a membrane bound enzyme.

Results in a cascade of amplification of hormone effects

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Amplificationofhormoneeffects Single molecule of hormone binds to receptor

c va es -pro e ns

Each activates an adenylate cyclase molecule which then

produces 1000 cAMP

,

1000s of substrate molecules

One molecule of epinephrine may result in breakdown of millions

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,

in the blood or by other hormones

Negative feedback control (most common)

ecrease ncrease n oo eve s reverse

Positive feedback control

the chan e roduced b the hormone causes morehormone to be released