TLMweb® 10TH CLASS BIOLOGY-HUMAN HEART

10TH CLASS BIOLOGY-HUMAN HEART

10TH CLASS BIOLOGY-HUMAN HEART

One contraction and one relaxation of atria and ventricle! 1. Deoxygenated blood from venacava and oxygenated blood from pulmonary veins enter the right and left atria respectively. Then both the atria contract, forcing the blood to enter the ventricles. When ventricles are filled with blood they start ‘ contracting and atria start relaxing. 2. On ventricular contraction, the blood moves into the aorta and pulmonary artery. The apertures between the atria and ventricles are closed by valves. We can listen to the first sharp sound of the heart ”lub”. When the ventricles start relaxing, the pressure in the ventricles is reduced. The blood which has entered the arteries tries to come back into the ventricles. The valves Which are present in the blood ' vessels are closed to prevent backward flow of ; blood into the ventricles. Then we can listen to a dull sound of the heart ”dub.” The atria are filled up with blood and are ready to pump them into the ventricles. The sequential events in the heart which are cyclically repeated is called cardiac cycle. It includes an active phase systole and a resting phase the 
diastole of atria and ventricles. 
The whole process is completed in approximately 0.8 seconds.

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