Text A. The blood vessels, large and small

The raw material's¹ for the energy that powers man's every thought and action are transported in the blood. The enriched² blood id carried in a network of small vessels, capillaries, to each cell. These capillaries are so small that 60 long ones or 120 short ones would stretch only the length of this line of type. There are so many capillaries in the body that, laid end to end, they would ring the equator³ more than twice.

Blood coming into the capillaries from the arteries has been enriched with oxygen in the lungs or with food from the digestive system. The walls of the capillaries are only one cell thick; so thin that oxygenated blood is able, to pass its oxygen and food to the body's cells and to receive from the cells their waste. The spent blood then flows from the capillaries into the veins, which direct it back to the heart. In the heart the blood enters the arteries and is carried by them to the lungs and digestive system, to be oxygenated and enriched again before returning to the capillaries.

The body's largest blood vessels, the aorta and the pulmonary artery, are about an inch in diameter. Arteries have thick elastic walls, the pulsations, of which assist the heart in pumping. Vein walls are more rigid. Many of them, particulary in the lower part of the body, have valves which prevent a backflow ofblood.

Notes:

1. raw materials — сырые продукты

2. to enrich — обогащать

3. would ring the eqnator — опоясали бы экватор...