Short notes on the functioning of the human heart


Functioning of the heart:

Working of heart can be studied under the following heads:

Heart beat:


The heart muscles contract and expand (relax) in a regular rhythmic fashion. The phase of contraction is known as systole and the phase of relaxation is called diastole. One diastole and one systole to­gether constitute a heartbeat. The contraction and relaxation of the au­ricles and ventricles take place in a definite order. The auricles and ven­tricles do not contract simultaneously.

The functioning of the heart may be divided into three phases.

I phase:

The auricle contracts and the blood is pumped into the ventricle which is relaxing. The auricle is said to be in systolic stage while the ventricle is said to be in diastolic stage.


II phase:

In this phase the ventricles contract while the auricles are relax­ing. The blood is forced into the arteries.

III phase:

In this stage, both auricles and ventricles are relaxing and the blood enters into the auricles.


Cardiac Cycle:

The heart contracts rhythmically throughout life. Each heart beat consists of a systole and a diastole. The total duration is about 0.8 seconds. The total heart action involving all the three phases men­tioned above is called the cardiac cycle.

The volume of blood that is ejected during a single heart beat is called the stroke volume (SV). The cardiac output (CO) is the total volume ejected over 9ne minute and is therefore the product of the stroke volume and the heart rate (the heart beats about 70 times per minute in a healthy man and it is known as the heart rate). The cardiac output may be calculated as follows.



Where CO = Cardiac output, SV = Stroke volume and HR= Heart rate. Each heart beat is accompanied by 2 heart sounds which are called the first heart sound and the second heart sound. This usually sound like lub and dup. The first heart sound results from the closure of the atrioven­tricular valves while the second heart sound is due to closure of the exit valves of the heart in the roots of the aortic and pulmonary arteries.

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