Immune System

Objectives

• Describe the barriers to keep pathogens out of the body
• Explain how inflammatory response and leukocytes fight pathogens
• Distinguish between active and passive immunity
• Explain why allergies occur

Pathogens are disease causing agents such as bacteria and viruses.

Mechanical barriers physically block pathogens from entering the body. The skin is the most important.

Mucus membranes secrete mucus that traps pathogens. They also have cilia to sweep mucus and pathogens out.

Chemical Barriers

• Sweat
• Mucus
• Tears
• Saliva
• Urine

Biological barriers include living organisms that protect the body.

Inflammatory response is the first reaction to tissue damage or infection. It is caused by cytokines and histamines.

Leukocytes

• Nonspecific defense, eg, phagocytosis
• Specific defense

Active Immunity

• Immune response produces memory cells
• Can result from immunization
• Can last a lifetime

Passive Immunity

• Antibodies transferred to person who has never been exposed
• Lasts only as long as antibodies survive
• Acquired by a fetus through mother's blood
• Also obtained by injection of antibodies

An allergy is when the immune system makes an inflammatory response to a harmless antigen (allergen).

Severe allergic reactions may cause anaphylaxis.