Systole and Diastole

• Systole & Diastole

  • The cardiac cycle is the cycle of events that occurs as the

  heart contracts.

  • There are two phases of the cardiac cycle.

  • In the diastole phase, the heart ventricles are relaxed and

  the heart fills with blood.

  • In the systole phase, the ventricles contract and pump blood into the arteries.
• Atrial Systole

  • During diastole the return of blood causes the volume of blood in the atria to increase.

  • Eventually the pressure is greater than that of the ventricles and so the AV valves are forced open and the blood moves down into the ventricles.

  • During atrial systole the two atria contract at the same time and send the remainder of the blood into the ventricles through the open AV valve.

  • Atrial systole is followed about 0.1 seconds later by ventricular systole.
• Ventricular Systole

  • This involves the contraction of the ventricles and closure of the AV valves.

  • The pressure on the blood in the ventricles from the cardiac muscle contracting soon exceeds the pressure in the ARTERIES which forces the SL valves open.

  • The blood is pumped into the aorta or the pulmonary artery.
• Diastole

  • This involves the contraction of the ventricles and closure of the AV valves.

  • The pressure on the blood in the ventricles from the cardiac muscle contracting soon exceeds the pressure in the ARTERIES which forces the SL valves open.

  • The blood is pumped into the aorta or the pulmonary artery.
• The cardiac conducting system

  The heart beat originates in the heart itself but is regulated by both nervous and hormonal control.

  The auto-rhythmic cells of the sino-atrial node (SAN) or pacemaker set the rate at which cardiac muscle cells contract. The SAN is located in the wall of the right atrium.