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Chapter 45.

Endocrine System

Hormones

2004-2005AP Biology

Regulation

� Why are hormones needed?

� chemical messages from one body part to another

� communication needed to coordinate whole body

� homeostasis & regulation

� metabolism

� growth

� development

� maturation

� reproductiongrowth hormones

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Regulation & Communication

� Animals rely on 2 systems for regulation

� endocrine system � ductless gland which secrete

chemical signals directly into blood� chemical travels to target tissue

� slow, long-lasting response

� nervous system� system of neurons, central

nerve system� transmits “electrical” signal to

target tissue

� fast, short-lasting response

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Regulation by chemical messengers

AxonNeurotransmitter

Endocrine gland

Receptor proteins

Hormonecarried by blood

Target cell

� Neurotransmitters released by neurons

� Hormones release by endocrine glands

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Classes of Hormones

� Protein-based hormones

� polypeptides� small proteins: insulin, ADH

� glycoproteins� large proteins + carbohydrate: FSH, LH

� amines� modified amino acids: epinephrine, melatonin

� Lipid-based hormones

� steroids� modified cholesterol: sex hormones,

aldosterone

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How do hormones act on target cells

� Lipid-based hormones

� lipid-soluble

� diffuse across membrane & enter cells

� bind to receptor proteins in cytoplasm & then this hormone-receptor complex moves into nucleus

� bind to receptor proteins in nucleus

� bind to DNA as transcription factors

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Nucleus

Cytoplasm

Steroid hormone (S) passes through plasma membrane.

Inside target cell, the steroid hormone binds to a specific receptor protein in the cytoplasm or nucleus.

Hormone-receptor complex enters nucleus & binds to DNA, causing gene transcription

Protein is produced.

Protein synthesis is induced.

Plasma membrane

DNAmRNA

Protein

Steroidhormone

Blood plasma

Proteincarrier

1

2

2

3

3

5

5 4

4

S

S

S

1

S

Action of steroid (lipid) hormones

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How do hormones act on target cellsSignal molecule

Cell surface receptor

enzyme

G protein

cAMP

Targetprotein

Nucleus

Cytoplasm

ATP

� Protein-based hormones

� hydrophilic & not lipid soluble� can’t diffuse across

membrane

� trigger secondary (2°) messenger pathway� transmit “signal” across

membrane

� “signal transduction”

� usually activates a series of 2°messengers

� multi-step “cascade”

� activate cellular response� enzyme action, uptake or

secretion of molecules, etc.

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Action of protein hormones

3

4

GTPactivatesenzyme

activatesenzyme

activatesenzyme

Receptorprotein

cAMP

Proteinhormone

ATP

1

2

Cytoplasm

Produces an action

proteinmessengercascade

G protein

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adrenal gland

Action of epinephrine (adrenalin)

3

4

GTPactivates

protein kinase-A

activatesphosphorylase

activatesadenylyl cyclase

Receptorprotein cAMP

Epinephrine

ATP

1

2

Cytoplasm

G protein

Liver cell

GlucoseGlycogen

releasedto blood

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Benefits of a 2°messenger system

Amplification!

Signal molecule Receptor protein Activated adenylyl cyclase

Amplification

Amplification

Amplification

Amplification

GTP G protein

2

1

3

4

5

6

7

Enzymatic product

Enzyme

Protein kinase

cAMP

Not yetactivated

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� Ductless glands release

hormones into blood

Endocrine system

Duct glands = exocrine

(tears, salivary)

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Major vertebrate hormones (1)

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Major vertebrate hormones (2)

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Endocrine & Nervous system links

� Hypothalamus = “master control center”

� nervous system

� receives information from nerves around body about internal conditions

� regulates release of hormones from pituitary

� Pituitary gland = “master gland”

� endocrine system

� secretes broad rangeof hormones regulating other glands

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Thyroid gland

Hypothalamus

Anteriorpituitary

Gonadotropichormones:Follicle-stimulatinghormone (FSH) & luteinizinghormone (LH)

Mammaryglandsin mammals

Musclesof uterus

Kidneytubules

Posteriorpituitary

Thyroid-stimulating Hormone(TSH)

Antidiuretichormone(ADH)

Adrenalcortex

Boneand muscle Testis

Ovary

Melanocytein amphibian

Adrenocorticotropic

hormone (ACTH)M

elanocyte-stimulating horm

one(M

SH)

Oxytocin

Pro

lactin(P

RL)

Gro

wth

hor

mon

e (G

H)

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Homology in hormones

prolactin

mammals birds amphibiansfish

milk

production

fat

metabolism

metamorphosis

& maturation

salt &

water

balance

growthhormone

growth

& development

What does this tell you about these hormones?

same gene family

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Hormones & Homeostasis

� Negative feedback

� stimulus triggers control mechanism that inhibits further change

� body temperature

� sugar metabolism

� Positive feedback� stimulus triggers

control mechanism that amplifies effect

� lactation

� labor contractions

Anterior pituitary

Inhibition

–

Inhibition

Target glands

Hypothalamus

Releasing hormones(TRH, CRH, GnRH)

Tropic hormones(TSH, ACTH, FSH, LH)

–

(thyroid, adrenal cortex, gonads)

Hormones

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- triggers

release of glucose by

liver

- stimulates appetite

Regulating blood sugar levels

- triggers uptake of glucose by

body cells- triggers

storage in liver

- depresses appetite

pancreas

pancreas

beta islet cells

alpha islet cells 2004-2005AP Biology

Regulating blood osmolarity

If amount of dissolved

material in blood too

high, need to dilute blood

ADH

Dehydration Lowers blood volume & pressure

Increased waterretention

Increasedvasoconstrictionleading to higherblood pressureReduced

urine volume

Osmotic concentrationof blood increases

ADH synthesized in hypothalamus

ADH released from posterior pituitary into blood

Osmoreceptors NegativefeedbackNegative

feedback

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Regulating metabolism

� Hypothalamus� TRH = TSH-releasing hormone

� Anterior Pituitary� TSH = thyroid stimulating hormone

� Thyroid� produces thyroxine hormones

� metabolism & development

� bone growth

� mental development

� metabolic use of energy

� blood pressure & heart rate

� muscle tone

� digestion

� reproductiontyrosineiodine

thyroxine 2004-2005AP Biology

Goiter

Iodine deficiency causes thyroid to enlarge as it tries to produce thyroxine

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Homology in hormones

Days from emergence of forelimb

TRH rises

TRH TSH Thyroxine

–35 –30 –25 –20 –15 –10 –5 0 +5 +10

Th

yro

xin

e s

ecre

tio

n r

ate

Thyroxine stimulates metamorphosis in amphibians

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Regulating blood calcium levels

Increased blood Ca++

Thyroid

ParathyroidsLow blood Ca++

Parathyroidhormone (PTH)

Increased absorptionof Ca++ from intestine due to PTH activation of Vitamin D

Reabsorption of Ca++ &excretion of PO4

Osteoclasts dissolve CaPO4

crystals in bone, releasing Ca++

–

Negativefeedback

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Hormonal regulation of insect development

Neurosecretory cells

Larval molt Pupal molt Adult molt

ProthoracicglandLow amounts

Brain hormone

Juvenile hormone

Molting hormone

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Any Questions??