Mechanisms of Hormone Action
Widespread distribution of hormones in
the body permits certain hormones,
such as the growth hormone of the pituitary
gland, to affect most, if not all,
cells during specific stages of cellular differentiation. Other hormones produce
highly specific responses only in
certain target cells and at certain times.
Such specificity is made possible by receptor molecules on or in target
cells. A hormone will engage only those
cells that display the receptor that, by
virtue of its specific molecular shape,
will bind with the hormone molecule.
Other cells are insensitive to the
hormone’s presence because they lack
the specific receptors. Hormones
act through two kinds of receptors: membrane-bound receptors and nuclear receptors.