The average man has between 10 and 12 pints of blood in his body. The average woman has between 8 and 9 pints. To give you an idea of how much blood that is, 8 pints is equal to 1 gallon (think of a gallon of milk).
Blood is actually a tissue. It is thick because it is made up of a variety of cells, each having a different job. In fact, blood is actually about 80% water and 20% solid.
We know that blood is made mostly of plasma. But there are 3 main types of blood cells that circulate with the plasma:
Platelets, which help the blood to clot. Clotting stops the blood from flowing out of the body when a vein or artery is broken. Platelets are also called thrombocytes.
Red blood cells, which carry oxygen. Of the 3 types of blood cells, red blood cells are the most plentiful. In fact, a healthy adult has about 35 trillion of them. The body creates these cells at a rate of about 2.4 million a second, and they each have a life span of about 120 days. Red blood cells are also called erythrocytes.
White blood cells, which ward off infection. These cells, which come in many shapes and sizes, are vital to the immune system. When the body is fighting off infection, it makes them in ever-increasing numbers. Still, compared to the number of red blood cells in the body, the number of white blood cells is low. Most healthy adults have about 700 times as many red blood cells as white ones. White blood cells are also called leukocytes.
Blood also contains hormones, fats, carbohydrates, proteins, and gases.