Fighting germs

 Your body is under constant attack. Tiny organisms are continually trying to get inside you and multiply, which can make you ill. Fortunately, your body has a powerful immune system to repel the Invaders. 

The first line of defence against germs is your body's surface, which acts as a barrier. The surface includes not only your skin but also the surface of your eyes and the soft tissues lining your mouth, nose, throat, and stomach. If germs find a break in any part of your body - such as a cut - the damaged tissue reacts immediately by becoming inflamed: it swells and fills with germ-destroying blood cells. Many parts of the immune system work to block all kinds of germs, but others are more specific. Your adaptive immune system identifies new germs and then targets them specifically. It also remembers them for the future, giving you immunity to the diseases they cause. 

Filtering germs

Germs that break through the body's barriers and invade internal tissues do not usually survive for long. The human body contains a network of tiny vessels that collect fluid from every organ and carefully filter it for germs, which are swiftly destroyed. This network of vessels is called the lymphatic system. Dotted along it's vessels are small filtering units called lymph nodes, which are packed with germ-destroying cells. 

Tears

With every blink, watery tears wash dirt and bacteria off the surface of your eyes. Tears also contain lysozyme,a chemical that destroys the cell walls of bacteria. 

Saliva

Continually produced by glands in your cheeks and under your tongue, saliva flushes germs out of your mouth and into your stomach, where acid destroys them. Saliva also contains a range of antibacterial chemicals that germs. 

Tonsils

These soft red areas at the back of the month are packed with white blood cells that destroys germs from food or the air. When you have a sore throat caused by viruses or bacteria, your tonsils swell up as they help fight the germs. 

Skin

Your skin forms a thick, protective barrier that germs cannot cross, unless the skin gets cut. Glands in the skin secrete sweat and an oily fluid called sebum, both of which contain chemicals that repel germs. 

Stomach acid

The lining of the stomach makes powerful hydrochloric acid, which destroys germs in food. It also kills the germs in mucus from the throat, which we swallow regularly to help keep the airways clean. 

Lymph node

As body fluids flow through the vessels of the lymphatic system, they are filtered through swellings called lymph nodes, which vary from the size of a full stop to the size of a grape. They are packed with white blood cells that s screen the passing fluid for germs and destroy them. 

An allergy

occurs when the

immune system

attacks something

harmless, like pollen

or household dust. 

Germs

Whenever you touch something or breathe in, you pick up tiny organisms too small to see. Most do no harm, but some try to invade your body and feed on you. Harmful microorganisms are called germs. The most common types are viruses and bacteria. Viruses cause colds, warts, and many diseases. Bacteria make wounds swell up and can also cause various diseases. 

Bacteria

Bacteria are single-celled organisms. They are so tiny that hundreds could fit on the point of needle. 

Defence force

The human body contains about 50 billion white blood cells. These are the body's defenders. They seek out germs and kill them, using a variety of different methods. White blood cells called macrophages kill by swallowing germs whole and digesting them. 

How antibodies work

Antibodies are chemicals that stick to specific kinds of germs, flagging them for destruction. There are millions of different germs, but the human body can manufacture 10 billion different antibodies, ensuring there's one for any germ you encounter. Once an antibody cell has been activated by meeting a matching germ, it makes copies of itself and makes the body immune. 

1. Infect

A new germ invades the body and multiplies. It gets carried by body fluids to a lymph node, where many different white blood cells examine it. 

2. Detect

Antibody cells touch the germ to see if it matches molecules on their surface. Eventually, an antibody cell with matching molecules sticks to the germ. 

3. Activate

Now activated, the matching cell makes an army of clones. It also makes memory cells, which will stay in the body for years in case the germ returns. 

4. Seek

The clones make antibodies and release them into the blood. When they find germs, they stick to them. 

5. Destroy

The antibodies act as signposts to cells called macrophages, which swallow and destroy the germs. 

A vaccine

triggers your body

into producing

antibodies, making

you immune to a

 disease without

having to suffer it.