Well, as I mentioned earlier, the heart has
got the valve in it. And those valves stop
the backflow of blood during contraction of
the ventricles, and also contraction of
the atrial components when blood passes from
the atrium into the ventricle, and then the ventricle
into blood vessels. When you look at the histology
of the heart valve, it’s a little bit confusing
unless you know the sorts of sides, the surfaces
on which this heart valve are associated with.
Heart valves either separate the atria from
the ventricle or the ventricle from blood
vessels like the aorta or the pulmonary trunk.
So sometimes, on the surface of the heart
valve, you might have an atrial surface and
a ventricular surface, if you’re looking
at the valve between the atrium and the ventricle.
Sometimes, there could be a blood vessel surface
and a ventricular surface depending on whether
or not you’re looking at a heart valve that
separates the blood vessel from the ventricle.
So bearing that in mind, when you look at
the heart valve, you can identify some histological
components, all be it, they’re rather distorted
here because the heart valves are often very hard
to fix properly and examine under a microscope.
But there is a central core to the heart valve.
That central core is called the fibrosa.
It’s the strong component of the heart valve that
joins on with the fibrous skeleton component
of the heart that I've mentioned earlier. And
then on top, on the surface, that’s adjacent
to either the atrium or either the blood vessel,
you have a thin layer called the spongiosum.
The spongiosum or spongiosa, as it’s often
referred to, is a very thin layer. It’s
elastic, and that helps to dampen the force
of vibrations on the heart valve caused by
the continual closing of the heart valve during
the heartbeat. And finally, the layer below is
called the ventricularis. This is the layer
of tissue that’s adjacent to the ventricle
space. And that’s dense connective tissue
as well, and it becomes continuous with the
chordae tendineae, structures that extend from
the heart valves between the atria and ventricles
that attach to little papillary muscles inside
the ventricle and stop the valves from opening
in the wrong direction during contraction
of the ventricle.