In this article we will discuss about the six main factors that maintain circulation in human heart.
Factor # 1. Pumping Action of the Heart:
This is the main motive force of circulation.
Factor # 2. Elastic Recoil of the Arteries:
Ventricles contract during systole and relax during diastole. So during systole certain amount of blood is being led directly into the aorta and thus the vessel is stretched (potential energy is gained). But due to elasticity of blood vessel wall, the aorta recoils during diastole of the ventricle and thus blood moves forward (due to change of potential energy into kinetic energy for flow) towards the periphery as the backward movement is restricted due to presence of semilunar valves.
Factor # 3. Pressure Gradient:
Blood pressure gradually falls from the left to the right side of the heart. In the big arteries the average pressure is 120 mm of Hg; in the arterioles the pressure sharply falls to about 50-60 mm of Hg; in the capillaries the pressure is about 15 mm of Hg; in the veins the pressure falls further, while near the heart the pressure is 0 mm of Hg or even negative. Due to this pressure gradient blood passes from the higher to the lower pressure, i.e., from the left to the right side of the heart.
Factor # 4. Respiration:
During inspiration intrathoracic pressure falls and intra-abdominal pressure rises. Hence, with each inspiration, venous blood is sucked up by the thorax and is pumped out by the abdomen. In this way respiration helps venous return and acts as a great force in maintaining circulation.
Factor # 5. Muscular Exercise:
When muscles contract, they squeeze the capillaries and veins, and thus help venous return. This is aided by the valves of veins, which prevent the passage of blood back towards the capillary bed (Fig. 7.21).
Factor # 6. Effect of Gravity:
Above the level of heart, it helps venous return. But below the level of heart, it works against it.