An Introduction to the Endocrine System
An Introduction to the Endocrine System
An Introduction to the Endocrine System
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Hormone Mode of Action<br />
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.<br />
Transport<br />
protein<br />
Free<br />
hormones<br />
Bound<br />
hormone<br />
Blood<br />
Hydrophilic<br />
hormone<br />
Recep<strong>to</strong>r in<br />
plasma<br />
membrane<br />
Secondmessenger<br />
activation<br />
Hydrophobic<br />
hormone<br />
Recep<strong>to</strong>r in<br />
Tissue fluid<br />
nucleus<br />
Target<br />
cell<br />
• hydrophobic hormones<br />
– penetrate plasma<br />
membrane and enter<br />
nucleus<br />
– act directly on <strong>the</strong> genes<br />
changing target cell<br />
physiology<br />
– estrogen, progesterone,<br />
thyroid hormone act on<br />
nuclear recep<strong>to</strong>rs<br />
– take several hours <strong>to</strong> days<br />
<strong>to</strong> show effect due <strong>to</strong> lag<br />
for protein syn<strong>the</strong>sis<br />
• hydrophilic hormones<br />
– cannot penetrate in<strong>to</strong><br />
target cell<br />
– must stimulate<br />
physiology indirectly
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