1. The circulatory system is made up of the heart, the bloodand the blood vessels.Blood moving from the heart, delivers oxygen and nutrientsto every part of the body. On the return trip, the bloodpicks up waste products so that your body can get rid ofthem.

2. The heart is about the size of your fist and it islocated a bit to the left in the middle of yourchest. It weighs between 200 and 425 grams.The heart is a muscle. It contracts and relaxesaround 70 times a minute at rest, more if youare exercising.The inside of the heart is divided in fourdifferent chambers. The two chambers ontop are called the atria (atrium if you aretalking about one).The two chambers on the bottom arecalled ventricles. The atriareceive blood returning to the heart fromthe body and lungs. The ventricles sendthe blood to the body and lungs. 3. 1. Oxygen-poor blood (shown inblue) flows from the body intothe right atrium.2. Blood flows through theright atrium into the rightventricle.3. The right ventriclepumps the blood to thelungs, where the bloodreleases waste gasesand picks up oxygen.4. The newly oxygen-richblood (shown inred) returns to theheart and enters theleft atrium.5. Blood flows through the leftatrium into the left ventricle.6. The left ventricle pumps theoxygen-rich blood to all partsof the body.Teachers' Domain, Map of the Human Heart, published September 26, 2003, retrieved on October 13, 2008,http://www.teachersdomain.org/resource/tdc02.sci.life.stru.heartmap/ 4. Your body has about 5 litters ofblood continually travellingthrough it.The heart, the lungs, and theblood vessels work together toform the circle part of thecirculatory system. 5. ArteriesCarry blood away from the heartHave thick muscular wallsHave a pulseDeep under the skinHave no valvesVeinsCarry blood to the heartHave thin wallsDo not have a pulseNear surface of the skinHave valves to stop back-flow ofbloodThe capillaries connect thearteries to veins.THE PULSEEven though your heart is inside you, there is a way to know it's working from theoutside. It's your pulse. You can find your pulse by lightly pressing on the skinanywhere there's a large artery running just beneath your skin. 6. http://texasheart.org/HIC/AnatomyBlood is made mostly of plasma,which is a yellowish liquid that is 90%water. But in addition to the water,plasma contains salts, sugar (glucose),proteins and other substances.There are also 3 main types of blood cells thatcirculate with the plasma:Platelets, which help the blood to clot.Red blood cells, which carry oxygen.White blood cells, which fight infection. 7. What color is blood?Sometimes it is reddish, and sometimes it isbluish.Look at your arm. Can you see the blue veins?Why are they blue?When blood is full of oxygen it is red, but when itis low on oxygen it turns bluish.Why dont you ever see blue blood?Because as it leaves your body, it quickly turnsred, as it takes in oxygen. 8. There are 4 different blood types: A, B, AB, and O.Genes that you inherit from your parents (1 from your mother and 1 fromyour father) determine your blood type.Blood is made by the cells inside your bones, so your body can usuallyreplace any blood lost through small cuts or wounds. But when a lot of bloodis lost we might need a blood transfusion (blood donated by other people).In blood transfusions, the donor andrecipient blood types must becompatible.People with type O blood are calleduniversal donors, because they candonate blood to anyone, but theycan only receive a transfusion fromother people with type O blood.