Your Body’s Immunity Section 11 – Science 24

Your body’s physical defences We are surrounded by billions of bacteria and viruses. To many of them, a human being is like a walking smorgasbord, offering nearly limitless resources that they can use for energy and reproduction. Luckily for us, getting into the human body is not an easy task! From the point of view of these tiny organisms, a human is a bit like a fortress

The skin is thick and very hard to penetrate The skin is thick and very hard to penetrate. In addition, the skin also produces a variety of substances that are harmful to invaders. Openings such as the eyes, nose, and mouth are protected by fluids or sticky mucus that capture harmful attackers. The respiratory tract also has mechanical defenses in the form of cilia, tiny hairs that remove particles. Intruders that get as far as the stomach are up against a sea of stomach acid that kills most of them. BODY’S DEFENCES

Inflammatory Response If pathogens get past the physical barrier created by the skin, the blood vessels surrounding the injury swell and the area becomes red and warm as more blood arrives The body will send white blood cells (macrophages) to repel the invader

Your body’s physical defences and the inflammatory responses are called… GENERAL DEFENCES …because the body reacts in the same way regardless of what kind of pathogen is invading Your third line of defence is the formation of antibodies in the immune system. This line of defense targets specific pathogens as you will see..

Immunity – How does it work? Your body recognizes antigens that are not part of itself Antigens are specifically structures that are attached to pathogens. All living tissues such as viruses, bacteria, fungi, transfused blood, transplanted organs and cancer cells contain antigens.

How does your immune system respond to the antigens it encounters? White blood cells make and release Y-shaped protein compounds called antibodies Antibodies bind to specific antigens making it easier for white blood cells to destroy them

Each antibody has a shape that matches a specific antigen Each antibody has a shape that matches a specific antigen. This means that an antibody produced against a cold virus, for example, would not fit with an HIV antigen. So how do we have immunity from things like chicken pox? When you first contracted chicken pox your body didn’t have antibodies against the chicken pox antigen. But your body immediately started producing them. Now, if you contract it again, your body does have the antibodies so your immune system will recognize and destroy the antigen whenever it shows up again.

Immune System Response 1) When bacteria enter the body, an inflammatory response occurs. Macrophages surround and destroy some of the bacteria.

2) Antigens from the dead bacteria protrude from the macrophages that engulfed the bacteria 3) White blood cells called “Helper T Cells” identify the antigens on the macrophages. Once activated, helper T cells start to divide and to produce proteins that activate B and T cells.

The B cell makes 2 types of cells: 4) White blood cells called B cells are the ones responsible for making and releasing antibodies. But they wait until they are activated by a Helper T cell – to inform them that there is a current invasion The B cell makes 2 types of cells: 1) Plasma cell 2) Memory cell

5) The plasma cell makes antibodies which attach to the antigens on the bacteria 6) This makes them more noticeable to macrophages so they come and eat them. 7) Memory cells store information about the antigen of the invader, making it easier to destroy if it shows up again.

IMMUNE SYSTEM GAME http://nobelprize.org/educational_games/medicine/immunity/index.html

During your computer class tomorrow, you will be training to become a Macrophage Commander.

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