Page 216 - The Miracle of the Blood and Heart

Smooth muscle
over elastic layer
Outer coat membrane Endothelium
basement
From the heart Endothelium
Smooth muscle cell

Arteriole b) Arteriole structure

The arteries divide into
arterioles before leading
Capillary
into capillaries. They
serve as control valves in
the sending of blood to
the capillaries. They
therefore possess very
special features: Thanks
to their strong muscular
walls, they control the
Venule
blood flowing into the
capillaries and prevent
them from being dam-
Endothelium
aged.
To the heart
a) Details of the capillary network

may cause the flow to stop completely, besides regulating its
speed, because they are able to determine to which cells they
will give special treatment. In order to be able to carry out this
delicate determination, the blood leaves the small arteries and
enters the arterioles, just a few millimeters long and 8 to 50
microns in diameter. Each arteriole divides into branches so as
to be able to supply 10 to 100 capillaries. 107
The small red blood cell, having entered an arteriole, then
branches off to the tissue it will subsequently feed. It needs to
enter a capillary in order to supply oxygen and nutrients. It
will pass one of the arterioles—the control valves, in
other words—that will act as a guide for it. The time
has now come for it to do its job.
Harun
Yahya

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