An Introduction to the Endocrine System
An Introduction to the Endocrine System
An Introduction to the Endocrine System
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Thyroid Hormone<br />
TBG<br />
• thyroid hormone enters target<br />
cell by diffusion – mostly as T 4<br />
with little metabolic effect<br />
Various<br />
metabolic effects<br />
• within target cell, T 4<br />
is<br />
converted <strong>to</strong> more potent T 3<br />
Protein<br />
syn<strong>the</strong>sis<br />
mRNA<br />
• T 3<br />
enters target cells and binds<br />
<strong>to</strong> recep<strong>to</strong>rs in chromatin<br />
T 3<br />
T 4<br />
T 4<br />
T 3<br />
I<br />
DNA<br />
• activates genes<br />
– make a muscle protein<br />
(myosin) enhancing cardiac<br />
muscle response <strong>to</strong><br />
sympa<strong>the</strong>tic stimulation<br />
– streng<strong>the</strong>ning heartbeat<br />
Blood<br />
Tissue fluid<br />
Target cell
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