CBSE Class 7 Answered

Hi Nila,

Capillaries are present at the junction of arterioles and venules, i.e they are the link between arteries and veins.

The oxygenated blood mixes with the deoxygenated blood when it is out of the capillaries and in the organs or muscles, but due to the pressure under which the blood flows in the arteries, the mixed blood does not move back into the arterial system. Also the presence of valves in the veins prevents the back flow of blood into the organs and muscles.

As more blood is brought into the organs or muscles by the arteries, more blood accumulates in them, thus the deoxygenated blood moves out into the veins and is carried back to the heart and lungs.