What jobs does blood do?
The blood transports oxygen from the lungs to the cells of the body, where it is needed for metabolism. The carbon dioxide produced during metabolism is carried back to the lungs by the blood, where it is then exhaled (breathed out). Blood also provides the cells with nutrients, transports hormones and removes waste products, which organs such as the liver, the kidneys or the intestine then get rid of.
The blood helps to keep certain things in the body in balance. For instance, it makes sure that the right body temperature is maintained. This is done both through the liquid part of the blood (plasma), which can absorb or give off heat, as well as through the speed at which the blood is flowing: When the blood vessels expand, the blood flows more slowly and this causes heat to be lost. When the temperature outside the body is low, the blood vessels can contract to reduce the amount of heat lost. Even the pH value of the blood is kept at a level ideal for the body. The pH value tells us how acidic or alkaline a liquid is. A constant pH value is very important for things in the body to function properly.
This involves solid parts of the blood such as blood platelets and various substances that are dissolved in the blood plasma. If a blood vessel is damaged, these parts of the blood stick together (clot) very quickly and make sure that a scrape, for instance, stops bleeding. This prevents large amounts of blood loss. White blood cells and certain chemical messengers also play an important role in the immune system.