Chapter 12

Fighting Disease

Infectious DiseaseHistory:

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 DiseasePathogens: 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 toxinsExample: strep throat

Virus: tiny particles that damage cells by reproducing inside of themExample: colds and fluFungi: eukaryotic heterotrophs that absorb

their food and use spores to reproduceExample: 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 waterExample: Dysentery, cholera

Contaminated objects Example: Cold, flu, tetanus

Infected animalsExample: Rabies, lyme disease, malaria

The Body’s DefensesThe 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 ResponseIn 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 SystemThe 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

LymphocytesLymphocytes: White blood cells that

distinguish between different kinds of pathogens

T Cells: Identify pathogens and distinguish between one kind of pathogen from anotherAntigen: 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 pathogensAntibodies: Chemical produced by B cells that

destroys pathogens

AIDSAcquired 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 DiseaseImmunity: the body’s ability to destroy

pathogens before they can cause disease

Active ImmunityA person acquires active immunity when their

own immune system produces antibodies in response to the presence of a pathogenImmune 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 illnessesFor viral infections:

Take over-the-counter medication to reduce fever, clear your nose, or stop a cough

Get plenty of restDrink plenty of fluid

Passive ImmunityA 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 DiseaseNoninfectious Disease: disease that are

not caused by pathogens in the bodyCannot be transferred from person to

personWhile 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 allergyHistamine: 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

DiabetesDiabetes: disease causing the pancreas to stop

producing enough insulinInsulin: chemical that enables the body to take

in glucose from the blood and use it for energyA 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 EnvironmentLink between soot and cancer (London

doctor Pervicall Pott)Environment may contain carcinogensEnvironmental Protection Agency (EPA) is in

charge of enforcing environment laws

Environmental Carcinogens TodayUltraviolet light (skin cancer)Vinyl Chloride, PVC (liver cancer)Arsenic, pesticides, preservatives (liver,

bladder, kidney, lung cancer)