The atrioventricular valves are two of the four valves
within the heart - the other two valves being the semilunar
valves.
The atrioventricular valves are located between the the atria and the
ventricles of the heart.
The atrioventricular valve between the left
atrium and the left
ventricle is called the bicuspid
valve (also known
as the mitral
valve), and the atrioventricular valve between the right
atrium and the right
ventricle is called the tricuspid
valve.
In each case, as the atrium of the heart contracts it pushes a quantity
of blood into
the corresponding ventricle. The atrioventricular valve
consists of dense connective tissue covered by endothelium and acts to
prevent blood from flowing backward from the ventricle to the atrium: This is important as the next action in the sequence is the contaction
of the ventricle to push the blood out
of the heart
into
an artery
for transport
to the next organ around the body.
The opening and closing of the atrioventricular
valves is controlled by the differences in pressure across them:
When blood passes from an atrium to a ventricle, the atrioventricular
valve is pushed open (and the papillary muscles relax
and the chordae
tendineae lose
their tension, becoming slack). At the next stage in the sequence the ventricle
contracts.
This forces blood out from the ventricle into the artery via which it leaves
the heart. This contraction of the ventricle and the corresponding increase
in blood pressure within that ventricle also presses the cusps of
the atrioventricular valve together until their edges
meet,
closing
the
valve.
At the same time, the papillary muscles contract and the chordae tendineae
tighten - both of which also help to prevent the cusps from enabling the
atrioventricular valves to open.
When in the next stage of the sequence the ventricle relaxes and the
atrium contracts, the blood pressure situation is reversed, the relaxation/tension
of the papillary muscles and the chordae tendineae also reverses, and
the
atrioventricular valve allows blood to pass from the atrium to the ventricle
again. |
