Stephen & Matti

The second line of defence comes into play when either the first line of defence fails to destroy all pathogens entering the body or when the skin is breached via a cut and the pathogens are then introduced into the body.

Phagocytes are white blood cells. Come from a multipotent cell in the bone marrow Two of the main types of phagocytes are made in the cells of the bone marrow, these two phagocytes are neutrophils and monocytes. The phagocytes release enzymes, when bacterium is trapped, to kill it.

Monocytes become macrophages when, they leave the bloodstreams. They are particularly active against micro-organisms that live inside the cells of the person they infect This is only found in humans

There are some white blood cells that kill virus-infected cells, these are called Natural Killer Cells.

There are about 20 different types of complement proteins Complement proteins are made in the liver and circulate through the blood in an inactive state The ways complement proteins assist in the second line of defence: 1.Some complement proteins stick to invading micro-organisms that then become identifiable as foreign to the phagocytes 2.Some make phagocytes more active 3.Whilst others attract phagocytes to the infection site 4.Another Complement proteins destroys the membranes of invading micro-organism

Interferons are proteins, they are secreted by some cells when they are infected by virus particles. They then move to other cells making them more resistant to the virus. Interferons are particularly important when the virus has spread that far

Cytokinens are the messengers of the immune cells, they are made of proteins They are made by nearly all the immune systems cells

Inflammation is the result of a reaction in which the arterioles in the area around a cut dilate this causes increased blood flow to the area. Pathogens enter tissue Mast cells Basophils Platelets Produce histamine and serotonin Capillaries become permeable and leaky Blood vessels dilate Increased blood flow to region Complement proteins attract phagocytes Phagocytes move to the area Increased phagocytosis Redness Heat Edema Pus

Nature of Biology (third edition) – Judith Kinnear, Marjory Martin, pg