You are asking a very important question! The blood circulating in our body is very essential! We could not stay alive without it. When we inhale, oxygen from the air gets absorbed in our lungs and in the lungs transferred into the blood. There are molecules in the blood that grab onto the oxygen atom and carry it with the blood flow to the different organs in our body, which need oxygen to function properly. One of the most important one of those organs is the brain. If the oxygen has been transported - let's say to the brain - the molecules in the blood let go of it and instead take up a carbon dioxide molecule, the waste product in this life sustaining cycle. Now the carbon dioxide gets carried to the lungs with the blood stream and we exhale it through our lungs, while the blood gets new oxygen from the inhalation and the cycle starts over. I have told you, that blood flows in a circle through our body. And this brings me to the first part of your question. Veins and arteries are all muscular blood vessels (the 'tubes' the blood flows through). Veins transport blood towards from the heart and arteries transport blood away the heart. For this reason, in an injury, you have to bind off the artery to stop the blood flow, but you should never bind the vein. Because then the heart gets no fresh blood supplies.
I hope, I have answered your questions. Human biology is a very interesting subject and I am sure, if you want to learn in more detail about the blood system, your teacher can recommend some good books to read.
Thank you for sending us such an important question.
An artery carries blood away from the heart, while a vein carries blood towards the heart.Blood then brings nutrients and oxygen to all your cells and tissues, and when it has given the oxygen to the cells it is carried back through the lungs (to pick up more oxygen) to the heart (via the veins). Cells require oxygen to create energy for them to move and conduct all their life processes (especially muscles and your brain).
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