The Immune System

by Karthik Gurumurthy

Animals bodies are designed to protect themselves against the millions of tiny bacteria, worms, protozoa and viruses that try to invade them every day. These substances, called pathogens or “germs”, are what cause an animal to get sick. But they have to get through the body’s defenses first. To fight pathogens, an animal uses it immune system. The word immune literally means the “protection again disease.” Disease is a condition in which an animal’s body systems cannot function normally.

The first line of defense against pathogens is the skin. It is the barrier between the inside of an animal and the outside world. Skin is thick, with many layers of cells. The outermost cells are woven together to help keep moisture in and pathogens out. Skin is also acidic, which is toxic to invaders.

Most pathogens die  on the skin’s surface before they can get into the body. Some pathogens, however, make it to the body’s the natural openings- the mouth, eyes, nostrils, and ears. Fluids and chemicals, including saliva, tears and earwax, line the body’s openings and kill many pathogens before they can enter the body’s systems.

When unnatural openings occur in the skin- if it is torn or cut-the body works to close the hole as quickly as possible. Blood, mixed with a substance called fibrin, will collect in the hole and harden as a scab until new skin cells can be made.

Once inside, a pathogen meets a second line of defense. White blood cells circulate through the blood looking to pick a fight with a pathogen. When it finds a suspiciously-looking germ, the white blood cell leaves the blood, and surrounds and attempts to destroy the germ.