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1.
Diastole
As the heart muscle
relaxes, blood is pulled into the right atrium
from the body through the vena
cava and into the left atrium from the lungs. The blood
flows directly into the ventricles because of suction
created by the muscles relaxing.
2.
Atrial systole
The atria contract,
pushing the last bit of blood into the ventricles
3.
Ventricular systole
The
ventricles
contractexplosively,
pumping blood out to the lungs and body
4.
Valves42.5
Q. Why isn't the blood
from being forced backwards into the atria when the
ventricles contract?
-
atrioventricular
valvesare pushed shut
by the pressure
This is
the first sound that you hear with a stethoscope
("lub"); you cannot
hearthe atria
contracting.
FYI:
the right AV valve is known as the
tricuspidvalve because
it is made of three flaps or "cusps". The left AV valve is
called the bicuspid or
mitralvalve (I don't
know why). - see handout
As the
ventricles begin to relax after the contraction, they pull
back on a second set of valves (the semilunar
valves) to block backflow from the
pulminary artery and the
aorta.
This is
the second sound that you hear ("dub").
C.
Cardiac output (CO)
The Cardiac
Outputis the
volume of blood put out by the left
ventricle each
minute.
As with
any pump, output is influencd by both the
rateof pumping
and the
amountof fluid
moved each time it pumps.
For the heart,
CO
= heart rate (HR) + stroke volume (SV)
In
general, humans pump close to their entire blood
volumeper
minute.
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