1. What has happened when a cut in your skin becomes infected? What could have been done to prevent it?

2.  Your body has a number of defenses against infection.  1 st line of defense against infectious disease includes both chemical and physical defenses. ◦ skin ◦ Mucous membranes ◦ cilia ◦ Saliva and tears ◦ Stomach acid

3.  Your skin serves as both a chemical and a physical barrier against pathogens.  The surface cells are hard and have no gaps between them.  Sweat acts as a chemical barrier because it contains acids that kill many bacteria.  Old skin cells are shed constantly, and the pathogens on these cells are shed, too.

4.  The openings into your body, mouth, eyes, and nose are covered by protective linings called mucous membranes.  The mucous that is secreted traps many pathogens and washes them away.  Mucous also contains chemicals that attack pathogens.

5.  Some of your body’s mucous membranes are lined with tiny hair-like structures called cilia.  Together, cilia and mucus help trap and remove pathogens.  As you inhale dust and pathogens get trapped in the mucus of your air passages.  The cilia flow together and move the mucus towards your mouth and nose.  Coughing, sneezing, or blowing your nose will remove this mucus and the pathogens that were on it.

6.  Can trap pathogens and wash them away.  Like mucus, they contain chemicals that will attack pathogens.

7.  Chemicals in your digestive system, including acids in your stomach, kill many pathogens.  The normal motions of the digestive system not only move food through your system but also move pathogens out.  Bacteria that normally live in your digestive system produce substances that can harm or kill invading bacteria.

8.  The body’s second line of defense after the physical and chemical defenses.  Inflammation is your body’s general response to all kinds of injury, from cuts and scrapes to internal damage.  Inflammation fights infection and promotes the healing process.

9.  Within seconds after your body is injured, the damaged cells release chemicals that cause blood vessels in the injured area to enlarge.  Blood, other fluids, and white blood cells called phagocytes leak out of the enlarged vessels.  The phagocytes engulf and destroy pathogens.

10.  Phagocytes also give off substances that cause healing to begin.  The fluids, phagocytes, and dead cells that accumulate at the injury site often result in the formation of a thick, white liquid called pus.  Eventually, the inflammation process heals the damage, and the inflammation subsides.