Page 196 - The Miracle of Hormones

THE MIRACLE OF HORMONES

Until ten years ago, scientists suspected that
some very complex operations occurred in the blood
vessels, but they were unable to answer the questions
posed above. Research has revealed the existence of a
chemical messenger—the nitric oxide molecule. It is
this molecule that gives instructions for the blood
vessels to dilate.
Now, let us examine more closely the wonderful
installations deep in our blood vessels that produce
nitric oxide.
With an electron microscope, the blood vessels
appear to be huge in reverse proportion to their
smallness. For example, ten capillary vessels
arranged side by side are only the size of a human
hair. The inner walls of these tiny blood vessels are
covered with a tissue that is made up of the smooth
muscle cells; the dilation and contraction of the blood
vessels happens as a result of the movement of this
tissue. The muscle cells do not make direct contact
with the blood because a membranous layer exists
between the blood and the muscle cells—the endo-
thelium.
By aligning themselves side by side like the links
of a chain, endothelium cells form the endothelial
layer. Until the 1980's, it was believed that these cells
had no function worthy of attention other than facili-
The fact that blood
tating blood flow in the vessels. We now understand
vessels determine
that they will need that one of the many responsibilities of the endotheli-
an increasing sup-
um cells is the production of the nitric oxide messen-
ply of blood during
exercise is the re- ger.
sult of the flawless
The endothelium cells are factories that produce
design of the body.
nitric oxide molecules. These factories in the blood
vessels are just one millionth of a meter in size. The

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