Download CHAPTER 40 (THE VERY LAST ONE!! HOORAY!!!) A disease is any

CHAPTER 40 (THE VERY LAST ONE!! HOORAY!!!)
A disease is any change, other than injury, that disrupts the normal functions of the body. Some are caused by pathogens
(bacteria, viruses, and fungi), some by things in the environment (cigarette smoke), and some are genetic.
Diseases can be spread in many different ways:
1. Physical contact: touching infected person or object, coughing, sneezing. Cover your mouth/nose when you
cough/sneeze. Wash hands thoroughly and often.
2. Contaminated Food/Water: Food poisoning from undercooked food. Water in parts of the world with poor
sanitation/untreated sewage.
3. Infected animals: Animals that spread infectious disease are called vectors. Malaria (mosquitos), Lyme disease (ticks),
rabies (infected mammals).
Antibiotics are the most useful class of infection-fighting drugs. They kill bacteria (NO effect on viruses) without harming
the cells of the host. Over the counter drugs, like cough syrup, ibuprofen, etc.., only treat symptoms- not the disease itself.
The best treatment for most infections is rest, a well balanced diet, and plenty of fluids.
The function of the immune system is to fight infection through the production of cells that inactivate foreign substances or
cells. This process is called immunity.
The immune system has 2 general categories of defense:
1. Non Specific Defenses- Guard against infections by keeping most things out of the body- like a fortress wall.
2. Specific Defenses- Track down and destroy harmful pathogens that break through the non specific defenses. Like the
troops of the castle.
Non Specific Defenses
-First line of defense: The skin. Acts as a barrier. Once broken, then pathogens can enter. Openings to body (mouth/nose)
are lined with mucus to trap pathogens. Cilia sweeps them away. If it makes it to the stomach, acid kills them.
-Second line of defense: The inflammatory response. If pathogens make their way in, the immune system produces
millions of white blood cells to fight infection. Blood vessels near the wound expand, allowing the cells to move into the
tissues. Many of the cells are phagocytes that engulf and destroy bacteria. Tissue may become red, swollen, and painful.
A fever may raise the body temperature to levels that can kill the pathogens.
If a virus enters the body, sometimes the infected cells produce proteins that help other cells resist infection. These
proteins are called interferons, and they help slow down the progress of the infection so the immune system can have
time to respond.
Specific Defenses
Once past the non specific defenses, a pathogen triggers the immune response. A pathogen that triggers this response is
called an antigen. There are two type of lymphocytes that recognize antigens:
1. T cells- provide a defense within living cells. Called cell-mediated immunity.
2. B cells- provide a defense in the body fluids. Called humoral immunity.
-Humoral Immunity: When a pathogen invades, its antigens are recognized by some of the B cells. These B cells grow
rapidly to produce plasma cells and memory B cells. Plasma cells release antibodies- proteins that recognize and bind to
the antigens. Once the infection is over, the plasma cells die.
The memory cells also release antibodies, but they don't die after the infection has ended. They remain in the blood
stream, and if they encounter that same pathogen, they recognize it immediately and begin producing new plasma cells to
help fight the secondary infection.
Antibodies are shaped like the letter Y and has two identical antigen binding sites. The shape of the binding site is specific
to the antigen. A healthy adult can produce about 100 million different antibodies!
Cell-mediated Immunity
When pathogens such as viruses, fungi, or protists enter cells (or the cells become cancerous), antibodies alone cannot
destroy them because they can not reach them. When a pathogen is detected, T cells differentiate into:
-Killer T cells- track down and kill the antigen
-Helper T cells- produce memory T cells (same function as memory B cells)
-Suppressor T cells- release substances to suppress the killer T cells once the infection is under control
The immune system doesn't always know what's good for it! Organs implanted during a transplant are recognized as
foreign and are attacked. Killer T cells must be suppressed with drugs- usually for the rest of the recipient's life- to prevent
rejection. Doctors try to find donors who have cell markers that are nearly identical to the recipient to help prevent
rejection.
Active Immunity- A vaccination is the injection of a weakened form of a pathogen to produce immunity. We currently can
prevent about 20 serious diseases this way. Vaccinations stimulate the immune system to create millions of cells that are
on guard to immediately recognize the specific antigen. This type of immunity is called active immunity and may develop
as a result of natural exposure or a vaccination.
Passive Immunity- When antibodies produced by another animal are injected into the bloodstream. This only lasts a short
while, because eventually the body destroys the foreign antibodies. Useful for when traveling to other countries to prevent
diseases like malaria. Also, antibodies are passed from mother's milk to child.
Immune System Disorders
-Allergies: Overreactions to antigens such as pollen, dust, mold, and bee stings. Allergens enter and are attacked by mast
cells that release histamines. Histamines increase flow of blood and fluids to the area and increase mucus production.
This brings on sneezing, watery eyes, running nose, etc... Take antihistamines to counteract this response.
-Asthma- Chronic respiratory disease caused by some allergic reactions where the air passages become narrower,
making it difficult to breathe. No cure, but if it is caused by an allergy tests can identify the substance. Symptoms can be
relieved with medication.
-Autoimmune Disease: When the immune system makes a mistake and attacks the body's own cells. Type I diabetes
(antibodies attack insulin producing cells in the pancreas). Multiple sclerosis (antibodies attack neuron cells in the brain
and spinal cord).
-AIDS- Results from a viral infection (HIV) that destroys helper T cells. As the number of T cells declines, the normal
immune response breaks down and the person gets infections from unusual diseases and can't fight it.
The HIV virus can be transmitted 4 ways:
1. Sexual intercourse
2. Shared needles
3. Contact with blood
4. Infected mother to child during pregnancy, birth, or breast feeding.
There is currently no cure for AIDS. The HIV virus can be controlled by taking multiple drug/vitamin cocktails. Over 20
million people have died from AIDS.
Cancer
Cancer is a disease in which cells multiply uncontrollably and destroy healthy tissue. Because it's the body's own cells, it
makes it difficult to treat and understand. All forms are caused by gene mutations that damages the DNA- either because
of environmental or genetic reasons.
When the cells grow uncontrollably, it creates a mass of cells called a tumor. But not all tumors are cancerous- some are
benign (non cancerous) and don't spread to other cells. Cancerous tumors are called malignant- which means they can
invade and destroy surrounding tissue.
Environmental causes of cancer are called carcinogens. They are chemicals that cause cell mutations. Include tobacco
smoke and radiation (sunlight, xrays, radon).