Hormone Transport in the Blood
Most water-soluble hormones circulate in the watery blood plasma in “free” form (not attached to other molecules) but most lipid-soluble hormones are bound to Transport Proteins which are synthesized by the liver.
They have 3 functions :
They make lipid-soluble hormones temporarily water-soluble increasing their solubility in blood. They slow the passage of small hormone molecules through the filtering process of the kidneys, therefore slowing the rate of hormone loss in the urine. They provide a ready reserve of hormone already present in the bloodstream.
Hormone Interaction
The responsiveness of a target cell to a hormone depends on:
Hormone concentration: a target cell responds well when the level of a hormone rises. The abundance of the target cell’s receptors: a target cell responds well when it has more receptors (up-regulation). Influences exerted by other hormones: actions of some hormones on target cells require simultaneous or recent exposure to a second hormone.
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