The cardiac cycle and conduction system

The cardiac cycle and conduction system

• The Sino-atrial node located in the right atrial wall generates the electrical impulse and fires it through the atria walls causing them to contract. The SA node is he pacemaker and the firing rate will determine heart rate.
• When the atria walls contract it forces the remaining blood from the atria from diastole into the ventricles. (Atrial systole.)

The cardiac cycle and conduction system

• The Atrio-ventricular node collects the impulse and delays it for 0.1 seconds approx. to allow the atria to finish contracting. it the releases the impulse to the Bundle of His.
• The Bundle of His ,located in the septum, splits the impulse in two, ready to be distributed through each separate ventricle.
• The bundle branches carry the impulse to the base of each ventricle.
• The Purkinje fibres then distribute the impulse through the ventricle walls causing them to contract.
• The ventricles contract increasing the pressure closing the atrio-ventricular valves to prevent back flow into the atria.
• The semi-lunar valves are forced open as blood is ejected from the ventricles into the aorta and pulmonary artery.
• (Ventricular systole)

The cardiac cycle and conduction system.

• Once the impulse' journey is complete, the atria and ventricles relax and the heart re-fills with blood. This process signifies one heartbeat.
• As the atria and the ventricles relax, they expand drawing blood into the atria. The pressure in the atria increases opening the Atrio-ventricular valves causing blood to passively enter the ventricles. The semi -lunar valves are closed to prevent blood from leaving the heart.
• (Diastole)