WORKING OF HEART

Our heart beats regularly and rhythmically and pumps a certain amount of blood (called cardiac output) to different parts of the body. The contraction of the heart is SYSTOLE whereas relaxation is DIASTOLE. One contraction and relaxation forms a heart beat. Each cardiac cycle lasts for about 0.8 second.

HEART WORKING



1.)The cardiac cycle begins with the initiation of the artial systole by the electrochemical stimulus tramsmitted through the sino-artial (SA) node (i.e. natural pacemaker). The stimulus is transmitted through atrio-ventricular (AV) node to the Bundle of His which spreads and forms the Purkinje fibre on the ventricle.

During this artial contraction blood from auricles is forced into the sides of the ventricles. Bicuspid and tricuspid valves prevent the reverse flow of blood.



2.)The ventricles now undergo a powerful contraction (ventricular systole). The ventricular blood pressure increases and the blood enters the Aorta and pulmonary arteries through the semilunar valves.

3.) The ventricles relax when the blood enters the arteries and the pressure (diastolic pressure) in them falls. Simultaneously the artia relax and blood rushes in from the vena cava and pulmonary veins. Now the ventricles are ready to receive blood again.

This way the cardiac cycle continues.

Sounds

Simultanous closure of the atrio-ventricular valves makes the first sound LUB which is heard during contraction. The second sound DUB (which is higher-pitched, shorter and sharper) is produced due to simultaous closure of aortic and pulmonary valves.

Extra sounds

Extra sounds (murmur or hiss) occur due to leakage of blood from artery back to the ventricle. This maybe due to defect in the valves. The sound heard can be Lub-hiss-dub or lub-dub-hiss.