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Human heart How our heart and blood works

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How your heart works?
THE HEART IS A HOLLOW MUSCLE in the middle of the chest that pumps blood around the body supplying cells with oxygen and nutrients. A muscular wall, called the septum, divides the heart lengthways into left and right sides. A valve divides each side into two chambers: an upper atrium and lower ventricle. When the heart muscle contracts, it squeezes blood through the atria and then through the ventricles. Oxygenated blood from the lungs flows from the pulmonary veins into the left atrium, through the left ventricle, and then out via the aorta to all parts of the body. Deoxygenated blood returning from the body flows from the vena cava into the right atrium, through the right ventricle, and then out via the pulmonary artery to the lungs for reoxygenation. At rest the heart beats between 60 and 80 times a minute; during exercise or at times of stress or excitement the rate may increase to 200 beats a minute.
Why does your heart beat?
Your heart beats so that it can pump blood around your body. The heart is an organ in your chest, and it is partly made up of muscles. As its muscles contract, or tighten, the heart pushes blood around the blood vessels, or tubes, inside your body. The blood carries digested food and oxygen around the body and takes away waste.
Where does blood go?
Blood goes all around the body and back again. After it leaves the heart, the blood delivers oxygen to the body. By the time the blood returns to the heart, the oxygen has been used up. So, the heart sends the blood to the lungs to collect more oxygen. Then, it passes back to the heart to be pumped around the body again.
Why is blood red?
Blood is red because there are blood cells in it. Red cells contain hemoglobin, a chemical that carries oxygen, and this is what makes them red. Blood contains fluid called plasma, plus red blood cells, white blood cells and platelets. White blood cells fight harmful germs. Platelets stop us from bleeding to death when our skin is cut by clotting (setting) the blood.
How much blood do you have?
As adult has between 4 and 6 liters of blood. When old blood cells wear out, new ones are made inside your bones in the part called the bone marrow. We each have one of eight different types of blood, called blood groups. It people lose blood in an accident, doctors are careful to check which blood group they need giving them new blood
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