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Preksha Dhyana :
fills up the upper left chamber (left aruicle). Then the walls contract. The pressure inside the chamber increases. The blood is forced out from both the auricles. The impure blood from the right auricle rushes first into the right ventricle through the one-way valve and then out of the latter into the pulmonary artery from where it reaches the lungs. Simultaneously, the oxygenated blood from the left auricle rushes first into the left ventricle and then out of the latter into the aorta, from where it is distributed throughout the body through arteries and ultimately into tiny capillaries.
Red blood-cells carrying oxygen squeeze through the tiny capillaries in a single file and deliver the load of oxygen to the cells and get reloaded with carbon dioxide. The flow now reverses its direction and travels towards the heart through the veins and ultimately drains into the upper right chamber by way of two venae cavae. By the time the blood is ready to move towards the heart, the pressure has dropped down to almost zero and the heart is not capable of exerting suction pressure. The flow towards the heart must, therefore, be aided by something outside the system. Such assistance is given by the contraction of muscles which squeeze the veins and push the blood upward while one-way valves prevent the back-flow.
The phase of contraction is called systole, while that of relaxation ts called diastole. When the heart rate is normal i.e. at the rate of 70-72 beats per minute, diastole lasts for .49 seconds and systole for .36 seconds. During heavy physical exertion the heart-rate increases to 170 beats per minute. At this rate, diastole is only .12 seconds while systole lasts for .23 seconds.
It should always be remembered that with every heartbeat, first both auricles and then both ventricles contract sending blood out ; then both sides relax and receive blood from both routes. Nourishment of the Heart
For proper functioning, the heart, like any other organ, must be adequately nourished. In fact, it needs ten times
1. In its retura-journey through veins. blood from the limbs and abdomen must flow against gravity. Three important mechanisms aid in the veinous return : (i) vascomotor action, (ii) muscular pump, and (iii) respiratory pump.
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