An Introduction to the Endocrine System
An Introduction to the Endocrine System
An Introduction to the Endocrine System
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Modulation of Target Cell Sensitivity<br />
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.<br />
Hormone<br />
Recep<strong>to</strong>r<br />
Low recep<strong>to</strong>r density<br />
Weak response<br />
(a ) Up-regulation<br />
High recep<strong>to</strong>r density<br />
Strong response<br />
(b ) Down-regulation<br />
Increased recep<strong>to</strong>r density<br />
Increased sensitivity<br />
Reduced recep<strong>to</strong>r density<br />
Reduced sensitivity<br />
Response<br />
Stronger response<br />
Response<br />
Diminished response<br />
• target cell sensitivity<br />
adjusted by changing <strong>the</strong><br />
number of recep<strong>to</strong>rs<br />
• up-regulation means<br />
number of recep<strong>to</strong>rs is<br />
increased<br />
– sensitivity is increased<br />
• down-regulation reduces<br />
number of recep<strong>to</strong>rs<br />
– cell less sensitive <strong>to</strong> hormone<br />
– happens with long-term<br />
exposure <strong>to</strong> high hormone<br />
concentrations<br />
• bind <strong>to</strong> o<strong>the</strong>r recep<strong>to</strong>rs<br />
• converted <strong>to</strong> different hormone
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