CHAPTER 40 THE IMMUNE SYSTEM AND DISEASE 40-1 Infectious Disease • Some diseases are inherited and others are caused by materials in the environment (cigarette smoke) • There are even more that are caused by agents such as bacteria, viruses, and fungi • Disease-causing agents such as bacteria are known as pathogens and cause infectious diseases because they infect the body of the person who gets sick

Agents of Disease • The human body provides just the right environment for growth; the right temperature, a watery environment, and many nutrients • Many bacteria produce toxins which are poisons that produce illness by upsetting the body’s functions • Some organisms act as parasites and live off of their host taking needed nutrients from them

intestinal roundworms tapeworm

How Diseases are Spread • Some infections are spread from one person to another by coughing, sneezing, or physical contact • Other infectious diseases are spread through contaminated food or water • There are others that are spread by infected animals • Animals that carry disease-causing organisms from person to person are called vectors

Fighting Infectious Disease • Drugs are often used in the prevention of disease the most important of which is antibiotics • Antibiotics kill bacteria without harming the cells of the infected person • Antibiotics have no effect on viruses but we now have some antiviral drugs that are quite effective by inhibiting the ability of the virus to multiply inside of cells

40-2 THE IMMUNE SYSTEM • The immune system is the body’s primary defense against pathogens • The body’s first line of defense is to keep pathogens out and this is the job of the skin • If pathogens get in through the mouth and nose, they get trapped in mucus • The second line of defense is the body’s inflammatory response which is important if pathogens do manage to get in • When this happens the area gets red, swollen, and pus forms where bacteria are being engulfed by white blood cells; sometimes this is accompanied by fever

• If pathogens manage to get past the first and second lines of defense then the body reacts with a series of specific defenses called the immune response • The substance that triggers this response is an antigen • The body responds by forming a specific antibody to the antigen which will destroy it

Developing Immunity • Once the body has been exposed to a pathogen, millions of memory cells remain behind which can respond by making antibodies if there is another exposure to the same pathogen • The response is stronger and quicker the second time • There are two types of immunity; active and passive • The immunity produced by a vaccination (deliberate exposure to the pathogen) is called active immunity because the individual has the ability to produce an immediate active response against the pathogen • Passive immunity is also called maternal immunity because it occurs when antibodies pass from mother to fetus through the placenta or to the infant from the mother’s milk • Passive immunity protects the child for only the first few months of life or longer if the child is breast-fed