Download 12-3 Cardiac Cycle

12-3 Cardiac Cycle
Jocelyn Sassano & Sarah Miller
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The period between the start of one
heartbeat and the start of the nest is a single
cardiac cycle
Can be divided into two phases:
◦ During contraction, or systole, the chamber
squeezes blood into adjacent chamber
◦ Relaxation, or diastole, follows where the chamber
fills with blood and prepares for the start of the
next cardiac cycle
◦ Fluids move from an area of higher pressure to
lower pressure. An increase in pressure in one
chamber causes blood to flow into another
chamber.
The Cardiac Cycle
1.
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◦
2.
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Atrial Systole:
The atria are filled with blood, and the
ventricles are partially filled with blood, and
the ventricles are partially filled with blood
The atria contract, completely filling the
ventricles with blood
Atrial Diastole and Ventricular Systole:
The AV valves swing shut as pressure in the
ventricles rise
Blood pushes open the semilunar valves and
flows into the aorta and pulmonary trunk
Phases of the Cardiac Cycle
3. Ejection phase of Ventricular systole
◦ Pressure in the ventricles rises higher than
arties
◦ Blood pushes open the semilunar valves and
flows into the aorta and pulmonary trunk
4. Ventricular Diastole
◦ Semilunar valves close as ventricular pressures
decline
◦ As ventricular pressures fall below atrial
pressures, the AV valves open and blood flows
from the atria into the ventricles
Phases of the Cardiac Cycle
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Stethoscopes are used to listen for four heart
sounds
◦ The first heart sound (“lubb”) is produced as the AV
valves close and semilunar valves open
◦ The second heart sound (“dupp”) occurs at the
beginning of the ventricular diastole when the
semilunar valves close
◦ Third and Fourth heart sounds may be audible as
well, but they are very faint and rarely detectable
 Associated with atrial contraction and blood flowing
into the ventricles
Heart Sounds