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THE HEART AND BLOOD CIRCULATION The heart is a four chambered muscular pump around the size of a fist. It beats about 100,000 times a day pumping around 2,000 gallons of blood through about 100,000 miles of organic tubing. The heart is a big muscle with four valves connected together to make a two-stage pump. The heart gets its energy by oxidizing blood sugars. This released energy, contracts the heart's many muscle cells, and the four chambers squeeze blood out into the arteries. The arteries are thick walled muscular tubes which carry blood away from the heart. The heart has two sides - the left ventricle and the right ventricle. ...read more.


The venae cavae collects oxygen depleted blood from the body and routes the blood to the right atrium in the heart. When the right atrium squeezes, it pushes blood through the tricuspid valve into the right ventricle. Like the other three heart valves this is a one way valve (blood can only flow in one direction). When the right ventricle contracts, it pushes blood through the pulmonary valve and on into the lungs. Because it does not take much pressure to get blood to the lungs and back, the right side is smaller than the left. The left side has to work harder pumping blood to the rest of the body. ...read more.


The white blood cells fight disease by making antibodies and fighting germs. Blood transports these vital materials around the body. Blood plasma contains nutrients, hormones and waste products. Oxygen is carried as oxyhaemoglobin in red blood cells. Platelets and fibrinogen are needed for blood clotting. From our arteries blood travels into tiny blood vessels called capillaries. These carry blood through our tissues exchanging materials. Capillary walls are only one cell thick. Blood plasma is the liquid part of the blood and it contains glucose, amino acids, minerals, vitamins and hormones, as well as waste materials like urea. Most of these useful things come from our food and are carried to our tissues to keep us healthy, give us energy, or for growth and repair. Hormones carry chemical messages around the body. Waste materials like urea are carried in the blood to our excretory organs. ...read more.

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