HORMONES: AN OVERVIEW

• Hormones are produced by most plants and

animals.

• Animal hormones

– are made and secreted mainly by endocrine glands,

– are usually carried by the circulatory system, and

– communicate regulatory messages to specific sites in the body.

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• The endocrine system

– consists of all hormone-secreting cells and

– is the body’s main system for internal chemical regulation.

HORMONES: AN OVERVIEW

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• Endocrine cells secrete into the bloodstream

hormones that

– can affect many cells in many different body organs but

– only affect target cells, cells that have receptors for that specific hormone.

HORMONES: AN OVERVIEW

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Blast Animation: Signaling: EndocrineRight click slide / select “Play”

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Figure 25.1

Endocrine

cell

Blood

vessel

Membrane-enclosedsacs

Hormone

molecules

Receptor

protein

Target cell

Adrenal glands(type of endocrine

gland), which sitatop the kidneys

6 Figure 25.1a

Endocrinecell

Bloodvessel

Membrane-enclosedsacs

Hormonemolecules

Receptorprotein

Target cell

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• There are two general mechanisms by which

hormones trigger changes in target cells:

1. Water-soluble hormones trigger responses without ever entering their target cells.

HORMONES: AN OVERVIEW

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Animation: Water-Soluble HormoneRight click slide / select “Play”

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Figure 25.2-1

Water-solublehormone Receptor

protein

Target

cell Plasma

membrane

Nucleus

1

10 Figure 25.2-2

Water-solublehormone Receptor

protein

Target

cell Plasma

membrane

Relay

molecules

Signaltransduction

pathway

Nucleus

1

2

11

Figure 25.2-3

Water-solublehormone Receptor

protein

Target

cell Plasma

membrane

Relay

molecules

Signaltransduction

pathway

Cytoplasmic

responseor

Gene regulationNucleus

1

2

3

12

2. Lipid-soluble hormones trigger responses after entering the target cell.

HORMONES: AN OVERVIEW

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Blast Animation: Signaling via Steroid HormonesRight click slide / select “Play”

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Animation: Lipid-Soluble HormoneRight click slide / select “Play”

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Figure 25.3-1

Lipid-solublehormone

Target

cellPlasma

membrane

1

Nucleus

16 Figure 25.3-2

Lipid-solublehormone

Receptorprotein

Target

cellPlasma

membrane

2

1

Nucleus

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Figure 25.3-3

Lipid-solublehormone

Receptorprotein

Target

cellPlasma

membrane

Hormone-receptorcomplex

Nucleus

2

1

3

18 Figure 25.3-4

Lipid-solublehormone

Receptorprotein

Target

cellPlasma

membrane

Hormone-receptorcomplex

Gene regulation

Nucleus

2

1

3

4

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