Your blood has two main kinds of cell – red cells and white cells – plus pieces of cell called platelets (see blood).
Red cells are button-shaped and they contain mainly a red protein called haemoglobin.
Haemoglobin is what allows red blood cells to ferry oxygen around your body.
Red cells also contain enzymes which the body uses to make certain chemical processes happen (see enzymes).
White blood cells are big cells called leucocytes and most types are involved in fighting infections.
Most white cells contain tiny little grains and are called granulocytes.
Most granulocytes are giant white cells called neutrophils. They are the blood’s cleaners, and their task is to eat up invaders.
Eosinophils and basophils are granulocytes that are involved in fighting disease. Some release antibodies that help fight infection (see antibodies).
Lymphocytes are also types of white cells (see lymphocytes and antibodies). Each red blood cell contains more than 200 million molecules of haemoglobin.
Cells are the basic building blocks of your body. Most are so tiny you would need 10,000 to cover a pinhead.
There are over 200 different kinds of cell in your body, including nerve cells, skin cells, blood cells, bone cells, fat cells, muscle cells and many more.
A cell is basically a little parcel of organic (life) chemicals with a thin membrane (casing) of protein and fat. The membrane holds the cell together, but lets nutrients in and waste out.
Inside the cell is a liquid called cytoplasm, and floating in this are various minute structures called organelles.
At the centre of the cell is the nucleus — this is the cell’s control centre and it contains the amazing molecule DNA (see genes). DNA not only has all the instructions the cell needs to function, but also has the pattern for new human life.
Each cell is a dynamic chemical factory, and the cell’s team of organelles is continually busy — ferrying chemicals to and fro, breaking up unwanted chemicals, and putting together new ones.
The biggest cells in the body can be nerve cells. Although the main nucleus of nerve cells is microscopic, the tails of some cells can extend for a metre or more through the body, and be seen even without a microscope.
Among the smallest cells in the body are red blood cells. These are just 0.0075 mm across and have no nucleus, since nearly their only task is ferrying oxygen.
Most body cells live a very short time and are continually being replaced by new ones. The main exceptions are nerve cells — these are long-lived, but rarely replaced.
Mitochondria arc the cell’s power stations, turning chemical fuel supplied by the blood as glucose into energy packs of the chemical ATP (see muscle movement)
The endoplasmic reticulum is the cell’s main chemical factory, where proteins are built under instruction from the nucleus
The Golgi bodies arc the cell’s despatch centre, where chemicals arc bagged up inside tiny membranes to send where they are needed The lysosomes are the cell’s dustbins, breaking up any unwanted material
The ribosomes are the individual chemical assembly lines, where proteins are put together from basic chemicals called amino acids (see diet)
The nucleus is the cell’s control centre, sending out instructions via a chemical called messenger RNA whenever a new chemical is needed
There are 75 trillion cells in your body!
The instructions come from the nucleus in the cell’s control centre, but every kind of organelle has its own task.