Let’s talk a little bit about the capillaries
because, of course, that’s where the oxygen
and nutrient and waste product exchange is
So the capillaries are the main exchange blood
vessels. Their structure is that they emerge
from the arterials. They are very small in
diameter and very numerous and very thin-walled.
And they allow exchange of nutrients both
to the cells and also removing waste products
from the cells. This exchange of oxygen, carbon
dioxide, nutrients and waste products occurs
by osmosis, a process of diffusion from a
higher level to a lower level.
So, for example, in the blood oxygen is at
a very high level and in the cells at a lower
level. So oxygen diffuses across the capillary
membrane and is taken up by the cells. There
can be a limit in terms of the amount of blood
that is delivered to the periphery when there
is contraction of the arterioles and, as we
talked about before, the arterioles are the
main resistance vessels. When they contract,
they limit the blood supply going into a particular
tissue. When they relax, they increase the
blood supply going into a specific tissue.
Let’s move on then and talk about the veins.