Blood is a body fluid that circulates through the body, delivering nutrients and oxygen to the body's cells and carrying away waste products. Blood is pumped by the heart through arteries to all the areas of the body. At the end of the arteries, the blood enters capillaries - thin blood vessels that allow sufficient exchange of nutrients, oxygen, and waste products between the blood and the cells. Blood then returns to the heart through a third type of blood vessel - veins.
Blood is composed of:
- Blood plasma - the yellow liquid that remains when all cells are removed. It is 93% water with proteins, sugars, minerals, oxygen gas, carbon dioxide, and hormones among other things making up the rest.
- Red blood cells - cells that help dissolve more oxygen than water alone would.
- White blood cells