Cardiac output-
volume of blood
pumped by the heart
per minute
cardiac output = stroke volume x heart rate
Heart rate- number of
heartbeats per minute. Can
measure by feeling your pulse
(surges of blood forced through
arteries by heart contracting)
Stroke volume- volume
of blood pumped during
each heartbeat
Cardiac cycle- pumps
blood round body
Ongoing sequence of
contraction/relaxation of
atria and ventricles. Keeps
blood continuously
circulating round body.
Volume of atria and
ventricles change. Pressure
changes also occur due to
changes in chamber volume.
3 stages
Ventricles relax, Atria
contract. This decreases
the volume of the chamber
and increases pressure.
Pushes blood into
ventricles. Slight increase
in ventricular pressure and
chamber volume as they
receive ejected blood.
Ventricles contract, Atria relax.
Decreases volume and increases
pressure. Pressure becomes
higher in ventricles than atria-
forces AV valves shut to prevent
back-flow. Pressure in ventricles
also higher in aorta and pulmonary
artery so forces open SL valves &
blook forced out into arteries.
Ventricles relax, Atria relax.
Higher pressure in pulmonary
artery and aorta closes SL valves
to prevent back-flow into
ventricles. Blood returns to heart
and atria fill again due to higher
pressure in vena cava and
pulmonary vein. Starts to ^
pressure of atria. As ventricles
relax pressure falls below that of
atria so AV valves open. Allo w
blood to flow passively into
ventricles. Atria contract & process
begins again...