The passage describes the mammalian circulatory system.
Complete the passage by writing a suitable word in each blank space.
Mammals possess a closed, ...................................................... circulatory system, meaning blood passes through the heart twice for each complete circuit of the body.
Deoxygenated blood returning from the body enters the right atrium via the major vein known as the ...................................................... .
When the ventricles contract during systole, backflow of blood into the atria is prevented by the closure of the ...................................................... valves.
Blood is then pumped from the right ventricle to the lungs through the ...................................................... artery.
In the lungs, oxygen binds reversibly to the transport protein ...................................................... inside red blood cells.
This oxygenated blood returns to the left atrium of the heart via the ...................................................... vein.
The left ventricle then contracts, pumping blood out of the heart at high pressure into the main systemic artery called the ...................................................... .
To supply the actively respiring cardiac muscle tissue itself with oxygenated blood, branches called the ...................................................... arteries emerge from this main artery.
