Chapter 12 Fighting Disease

Infectious Disease History: Modern medicine is a new invention. Not too long ago, surgery was very dangerous. Even if the patient survived the procedure, they could die from infection. It wasn’t until the 1860’s that surgeons started washing their hands before operations! We can thank British surgeon Joseph Lister for hypothesizing that micro-organisms cause infection, and it might be a good idea to sterilize!

Understanding Infectious Disease  Pathogens: microscopic organisms that cause disease  Infectious disease: disease caused by the presence of a living thing within the body  Pathogens make you sick by damaging individual cells  Each infectious disease is caused by a specific kind of pathogen

Kinds of Pathogens  Bacteria: one-celled micro-organisms that cause a variety of diseases by producing toxins  Example: strep throat  Virus: tiny particles that damage cells by reproducing inside of them  Example: colds and flu  Fungi: eukaryotic heterotrophs that absorb their food and use spores to reproduce  Example: athlete’s foot, ringworm  Protist: eukaryotes that cannot be classified as animal, plant, or fungi  Example: malaria, dysentery

How Pathogens are Spread  Infected people  Example: Cold, flu  Soil, food, and water  Example: Dysentery, cholera  Contaminated objects  Example: Cold, flu, tetanus  Infected animals  Example: Rabies, lyme disease, malaria

The Body’s Defenses The body’s disease-fighting system is so effective that most people only get sick occasionally By eliminating pathogens that can harm your cells, your body maintains homeostasis

Barriers that keep pathogens out! Skin: Oil and sweat kill many pathogens. Even if they don’t die, many pathogens fall off with dead skin cells. If they manage to stay on the skin, then they must get through the tightly packed dead cells that form on top of living skin cells. Breathing Passages: The nose, pharynx, trachea, and bronchi contain mucus and cilia that remove pathogens that enter the respiratory system. When pathogens do get in, irritation causes you to sneeze or cough them out. Mouth and Stomach: Saliva contains destructive chemicals and the stomach produces acid. Most pathogens swallowed are destroyed by saliva or stomach acid.

The Inflammatory Response In spite of barriers, some pathogens will get into your body and begin to damage cells. When body cells are damaged, they release chemicals that trigger the inflammatory response. In the inflammatory response, fluid and white blood cells leak from blood vessels into nearby tissues. The white blood cells then fight the pathogens.

The Body’s General Defense Phagocyte: White blood cell that engulfs pathogens and destroys them by breaking them down Inflammation: Blood cells widen in the affected area and increase blood flow to the area, delivering more disease- fighting white blood cells to the area Fever: The high temperature kills pathogens

The Immune System The cells of the immune system can distinguish between different kinds of pathogens The immune system cells react to each kind of pathogen with a defense targeted specifically at that pathogen

Lymphocytes Lymphocytes: White blood cells that distinguish between different kinds of pathogens T Cells: Identify pathogens and distinguish between one kind of pathogen from another Antigen: Molecules that the immune system recognizes either as a part of your body or as coming from outside your body B Cells: Produce proteins that help destroy pathogens Antibodies: Chemical produced by B cells that destroys pathogens

AIDS Acquired immunodeficiency syndrome (AIDS) is a disease caused by a virus that attacks the immune system The virus that causes AIDS is called the human immunodeficiency virus (HIV) HIV is the only kind of virus known to attack the human immune system directly and destroy T cells HIV can spread from one person to another only if bodily fluids from an infected person come in contact with those of an uninfected person HIV is not spread through touching an infected person or by using a toilet seat after it has been used by an infected person

Preventing Infectious Disease Immunity: the body’s ability to destroy pathogens before they can cause disease

Active Immunity A person acquires active immunity when their own immune system produces antibodies in response to the presence of a pathogen Immune response is triggered by T and B cells that recognize the pathogens from the last time they were destroyed. The memory cells recognize the antigen and start the immune response so quickly you won’t get sick Vaccinations introduce harmless antigens from dead or weakened pathogens into the body to produce active immunity

When You Do Get Sick Antibiotic: chemical that kills bacteria or slows their growth without harming the body cells There are no medications that are effective against viral illnesses For viral infections: Take over-the-counter medication to reduce fever, clear your nose, or stop a cough Get plenty of rest Drink plenty of fluid

Passive Immunity A person acquires passive immunity when the antibodies that fight the pathogen come from a source other than the person’s body Passive immunity does not last as long as active immunity Example: People are given injections to cure rabies, babies acquire passive immunity from their mother before birth

Noninfectious Disease Noninfectious Disease: disease that are not caused by pathogens in the body Cannot be transferred from person to person While infectious diseases have become less common, noninfectious diseases have grown more common

Allergies Allergy: disorder in which the immune system is overly sensitive to a foreign substance Allergen: any substance that causes an allergy Histamine: chemical that is responsible for the symptoms of an allergy, such as sneezing and watery eyes Antihistamine: drugs that interfere with the action of histamine, used to lessen the allergic reaction Asthma: disorder in which the respiratory passages narrow significantly

Diabetes Diabetes: disease causing the pancreas to stop producing enough insulin Insulin: chemical that enables the body to take in glucose from the blood and use it for energy A person with diabetes has high levels of glucose in the blood, but the body cells do not have enough glucose Effects: weight loss, weakness, excessive hunger and thirstiness, frequent urination, blindness, kidney failure, heart disease Types: I (childhood- needs injections), II (adulthood)

Cancer and the Environment Link between soot and cancer (London doctor Pervicall Pott) Environment may contain carcinogens Environmental Protection Agency (EPA) is in charge of enforcing environment laws

Environmental Carcinogens Today Ultraviolet light (skin cancer) Vinyl Chloride, PVC (liver cancer) Arsenic, pesticides, preservatives (liver, bladder, kidney, lung cancer)