Blood contains red cells, white cells, serum. The red cells carry oxygen to all the organs within our bodies, back to the heart, where they are re-oxygenated, and then go through their route again and again...they also carry iron and other nutrients to the organs within our bodies. Think of them as "support staff". White cells are always there, fighting or not fighting; think of them as the body's "army" When you have an infection, anything from a cold to just about anything more serious, the white cells kick in from their "resting phase", and multiply into larger and larger numbers to fight the infection. Too many white cells can also be bad; leukemia, or a cancer of the white blood cells, causes them to over-populate the body. Serum carries everything around, and is the clear liquid that comes out of a blister if you pop it.
Blood is necessary for (the life of every part of the body. The first step in understanding this is to realize that the blood contains many different materials and cells. There is a fluid, or liquid, part of the blood which is called "plasma".' It contains many substances dissolved in it. Let's see what some of these are and what they do. Carbohydrates such as sugars are in the blood to give the body energy. Fats are in the fluid for burning or storage. Many salts are also in the blood to meet the body's needs. The blood plasma carries food from the stomach and intestine to the cells, which would starve without it. It also carries waste from the cells to the kidneys and intestine. The secretions of many glands are in the blood and are carried to various parts of the body. The red cells in the blood, which give the blood its colour, contain a substance called "haemoglobin". The body has a-great need for haemoglobin because it combines easily with gases such as oxygen and carbon dioxide. The red cells carry the oxygen in the arteries and capillaries to alt cells of the body. The white cells in the blood called "leukocytes" are very important to the body. They destroy bacteria. Other white cells, called "lymphocytes", are part of the body's process for fighting infections. Still other white blood cells, called "monocytes", take care of dead material and dirt that may get into the body. In addition, the blood contains pieces of cells called "platelets" that help to form clots, so that when a blood vessel is cut you do not lose too much blood.
