CK-12 Life Science
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Roopal Karia. The Why and What of Epilepsy: A Book for Children. and Teens. PublishAmerica, 2008.
Terry Trueman. Stuck in Neutral. HarperTeen, 2001.
http://kidshealth.org/kid/htbw/brain.html
http://kidshealth.org/parent/general/body_basics/brain_nervous_system.html
http://www.mayoclinic.com/health/migraine-headache/DS00120/DSECTION=causes
http://en.wikipedia.org/wiki
Vocabulary
cerebral palsy
Disease caused by injury to the developing brain early in life that affects the control of body movements.
concussion
Bruise on the surface of the brain; the mildest and most common type of brain injury.
depressant drug
Psychoactive drug that slows down the nervous system.
drug
Any chemical substance that affects the body or brain.
drug abuse
Use of a drug without the advice of a doctor or for reasons other than those for which the drug was intended.
drug addiction
Condition in which a drug takes over people’s lives and they cannot stop using the drug even if they want to.
drug overdose
Taking so much of a drug that it causes serious illness or death.
encephalitis
Infection of the brain that is usually caused by viruses.
epilepsy
Disease in which seizures occur.
hallucinogenic drug
Psychoactive drug that can cause strange sensations, perceptions, and thoughts.
meningitis
Viral or bacterial infection of the membranes that cover the brain and spinal cord.
migraine
Severe type of headache that occurs when blood vessels in the head dilate.
paralysis
Inability to feel or move parts of the body.
physical dependence
Condition in which drug abusers need a drug to feel well physically.
psychoactive drug
Drug that affects the brain and influences how a person feels, thinks, or acts.
psychological dependence
Condition in which drug abusers need a drug to feel well emotionally.
Reye’s Syndrome
Rare, potentially fatal condition associated with aspirin use in young people with viral infections.
seizure
Period of lost consciousness that may include violent muscle contractions.
stimulant drug
Psychoactive drug that speeds up the nervous system.
tension headache
Headache that occurs when muscles in shoulders, neck, and head become too tense.
tolerance
Condition in which people need to take more of a drug to feel the same effects as when they first started using the drug.
tumor
Mass of cells that grow out of control; associated with cancer.
withdrawal
Symptoms like vomiting, diarrhea, or depression that can occur when people stop using a drug.
Points to Consider
Although the nervous system controls the body, it doesn’t do it alone. It gets help from another body system, called the endocrine system. This is a system of glands that secrete hormones. Hormones are chemicals released by cells that affect cells in other parts of the body.
Think of how hormones can help control body processes?
Chapter 21: Diseases and the Body's Defenses
Lesson 21.1: Infectious Diseases
Lesson Objectives
List common causes of infectious diseases.
Explain how the virus known as HIV causes AIDS.
State how infectious diseases can be prevented.
Check Your Understanding
What is a bacteria?
What are the components of blood?
Introduction
Has this ever happened to you? A student sitting next to you in class has a cold. The other student is coughing and sneezing, but you feel fine. Two days later, you come down with a cold, too. Diseases like colds are contagious, or “catching.” Contagious diseases are also called infectious diseases. An infectious disease is a disease that spreads from person to person.
Causes of Infectious Diseases
Infectious diseases are caused by pathogens. A pathogen is a living thing or virus that causes disease. Pathogens are commonly called “germs.” They can travel from one person to another. This is why the diseases they cause are “catching.”
Types of Pathogens
Living things that cause human diseases include bacteria, fungi, and protozoa. Most infectious diseases caused by these organisms can be cured with medicines. For example, medicines called antibiotics can cure most diseases caused by bacteria.
Bacteria are one-celled living things without a nucleus. Although most bacteria are harmless, some cause diseases. Worldwide, the most common disease caused by bacteria is tuberculosis (TB). TB is a serious disease of the lungs. Another common disease caused by bacteria is strep throat. You may have had strep throat yourself. Bacteria that cause strep throat are shown in Figure below. Some types of pneumonia and many cases of food borne illnesses are also caused by bacteria.
Figure 21.1
The structures that look like strings of beads are bacteria. They belong to the genus . Bacteria of this genus cause diseases such as strep throat and pneumonia. They are shown here 900 times bigger than their actual size.
Fungi are simple organisms that consist of one or more cells. They include mushrooms and yeasts. Human diseases caused by fungi include ringworm and athlete’s foot. Both are skin diseases that are not usually serious. What a ringworm infection looks like is shown in Figure below. A more serious fungus disease is histoplasmosis. It is a lung infection.
Figure 21.2
Ringworm isnt a worm at all. Its a disease caused by a fungus. The fungus causes a ring-shaped rash on the skin, like the one shown here.
Protozoa are one-celled eukaryotes (with a nucleus). They cause diseases such as malaria. Malaria is a serious disease that is common in warm climates; the protozoa is transferred to people by a mosquito. More than a million people die of malaria each year. Other protozoa cause diarrhea. An example is Giardia lamblia, which is shown in Figure below.
Figure 21.3
This picture shows a one-celled organism called . It is a protozoan that causes diarrhea.
Viruses are nonliving particles that take over living cells in order to multiply. Viruses cause many common diseases. For example, viruses cause colds and flu. Cold sores are caused by the virus Herpes simplex. This virus is shown in Figure below. Antibiotics do not affect viruses. However, medicines called antiviral drugs can treat many diseases caused by viruses.
Figure 21.4
The virus, which is shown here, causes cold sores on the lips. Viruses are extremely small particles. This one is greatly magnified.
How Pathogens Spread
Different pathogens spread in different ways. Some pathogens spread through food. They cause food borne illnesses. These illnesses were discussed in the Food and Digestive System chapter. Some pathogens spread through water. Giardia lamblia is one example. Water can be boiled or purified in other ways to kill Giardia and most other pathogens. Several pathogens spread through sexual contact. HIV is one example. It is a virus you will read about below. Other pathogens that spread through sexual contact are discussed in the Reproductive Systems and Life Stages chapter.
Many pathogens that cause respiratory diseases spread by droplets in the air. Droplets are released when a person sneezes or coughs. Thousands of tiny droplets are released when a person sneezes is shown in Figure below. Each droplet can contain thousands of pathogens. Examples of pathogens spread in this way are the viruses that cause colds and flu. You may get sick if you breathe in the pathogens.
Figure 21.5
As this picture shows, thousands of tiny droplets are released into the a
ir when a person sneezes. Each droplet may carry thousands of pathogens. You cant normally see the droplets from a sneeze because they are so small. However, you can breathe them in, along with any pathogens they carry. This is how many diseases of the respiratory system are spread.
Other pathogens spread when they get on objects or surfaces. A fungus may spread in this way. For example, you can pick up the fungus that causes athlete’s foot by wearing shoes an infected person has worn. You can also pick up this fungus from the floor of a public shower. After acne, athlete’s foot is the most common skin disease in the United States. Therefore, the chance of coming in contact with the fungus in one of these ways is fairly high. Bacteria that cause the skin disease impetigo can spread when people share towels or clothes. The bacteria can also spread through direct skin contact in sports like wrestling.
Still other pathogens are spread by vectors. A vector is an organism that carries pathogens from one person or animal to another. Most vectors are insects, such as ticks and mosquitoes. When an insect bites an infected person or animal, it picks up the pathogen. Then it transfers the pathogen to the next person or animal it bites. Ticks carry the bacteria that cause Lyme disease. Mosquitoes, like the one in Figure below, carry West Nile virus. Both pathogens cause fever, headache, and tiredness. If the diseases are not treated, more serious symptoms may develop.
Figure 21.6
Some diseases are spread by insects. The type of mosquito shown here can spread West Nile virus. The virus doesnt make the mosquito sick. The mosquito just carries the virus from one person or animal to another.
The first case of West Nile virus in North America occurred in 1999. Within just a few years, the virus had spread throughout most of the United States. Birds as well as humans can be infected with the virus. Birds often fly long distances. This is one reason why West Nile virus spread so quickly.
HIV Infection and AIDS
HIV, or human immunodeficiency virus, causes AIDS. AIDS stands for acquired immune deficiency syndrome. It is a fatal condition with no known cure. AIDS usually develops 10 to 15 years after a person is first infected with HIV.
How HIV Spreads
HIV spreads through direct contact of mucous membranes or the bloodstream with an infected person’s body fluids. Body fluids that may contain HIV include blood, semen, vaginal fluid, and breast milk. The virus can spread through sexual contact or shared drug needles. It can also spread from an infected mother to her baby during childbirth or breastfeeding.
Some people think they can become infected with HIV by donating blood or receiving donated blood. This is not true. The needles used to draw blood for donations are always new. Therefore, they cannot spread the virus. Donated blood is also tested to make sure it is free of HIV.
HIV and the Immune System
How does an HIV infection develop into AIDS? HIV destroys white blood cells called helper T cells. The cells are produced by the immune system. This is the body system that fights infections and other diseases. You will read more about the immune system in Lesson 4. HIV invades helper T cells and uses them to reproduce. This is shown in Figure below. Then the virus kills the helper T cells. As the number of viruses in the blood rises, the number of helper T cells falls. Without helper T cells, the immune system is unable to protect the body. As a result, the infected person cannot fight infections and other diseases.
Figure 21.7
In this picture, the large structure on the left is a helper T cell. It is infected with HIV. The many small circles on the right are new HIV viruses being shed by the T cell.
Medications can slow down the increase of viruses in the blood. However, the medications cannot rid the body of all the viruses. At present, there is no cure for HIV infection.
AIDS
AIDS is not really a single disease. It is a set of symptoms and other diseases. It results from years of damage to the immune system by HIV. AIDS occurs when helper T cells fall to a very low level and the person develops infections or cancers that people with a healthy immune system can easily resist. These diseases are usually the cause of death of people with AIDS.
The first known cases of AIDS occurred in 1981. Since then, AIDS has led to the deaths of more than 25 million people worldwide. Many of them were children. The greatest number of deaths occurred in Africa. This is probably where HIV first arose. It is also where medications to control HIV are least available. There are currently more people infected with HIV in Africa than any other part of the world.
Preventing Infectious Diseases
What can you do to avoid infectious diseases? Eating right and getting plenty of sleep are a good start. These habits will help keep your immune system healthy. With a healthy immune system, you will be able to fight off many pathogens.
You can also take steps to avoid pathogens in the first place. The single most important way to avoid pathogens is to wash your hands often. You should wash your hands after using the bathroom or handling raw meat or fish. You should also wash your hands before eating or preparing food. In addition, you should wash your hands after being around sick people. The correct way to wash your hands is demonstrated in Figure below. If soap and water aren’t available, use a hand sanitizer. A hand sanitizer that contains at least 60 percent alcohol will kill most germs on your hands.
Figure 21.8
This picture shows the proper way to wash your hands. Frequent hand washing helps prevent the spread of pathogens.
The best way to prevent diseases spread by vectors is to avoid contact with the vectors. For example, you can wear long sleeves and long pants to avoid tick and mosquito bites. Using insect repellent can also reduce your risk of insect bites.
Many infectious diseases can be prevented with vaccinations. You will read more about vaccinations in Lesson 4. Vaccinations can help prevent measles, mumps, chicken pox, and several other diseases.
If you do develop an infectious disease, try to avoid infecting others. Stay home from school until you are well. Also, take steps to keep your germs to yourself. Cover your mouth and nose with a tissue when you sneeze or cough, and wash your hands often to avoid spreading pathogens to other people.
Lesson Summary
Infectious diseases are caused by living things or viruses that can travel from one person to another.
HIV causes AIDS by destroying disease-fighting cells produced by the immune system.
A healthy lifestyle and frequent hand washing can help reduce your risk of infectious diseases.
Review Questions
Name two examples of infectious diseases.
What is a pathogen?
List three ways that pathogens can spread.
What is HIV?
What is the single most important way to avoid pathogens?
Why do antibiotics not cure the common cold?
Explain why covering your mouth when you cough helps prevent the spread of germs.
What role do vectors play in the spread of infectious diseases?
How does an HIV infection develop into AIDS?
Why might using insect repellent reduce your risk of Lyme disease?
Further Reading / Supplemental Links
Jenna Bush. Ana’s Story: A Journey of Hope. Harper Collins, 2007.
Scientific American. Germ Wars: Battling Killer Bacteria and Microbes. Rosen Publishing Group, 2008.
http://www.cdc.gov/ncidod/dvbid/westnile/index.htm
http://www.mayoclinic.com/health/germs/ID00002
http://www.mayoclinic.com/health/infectious-disease/ID00004
[http://www.merck.com/mmhe/sec17/ch188/ch188a.html http://www.merck.com/mmhe/sec17/ch188/ch188a.html
http://www.niaid.nih.gov/healthscience/healthtopics/microbes/PDF/microbesbook.pdf
http://www.nlm.nih.gov/medlineplus/infectiousdiseases.html
http://www.who.int/mediacentre/factsheets/fs094/en/index.html
http://www.nlm.nih.gov/medlineplus/infectiousdiseases.html
http://www.who.int/mediacentre/facts
heets/fs094/en/index.html
http://en.wikipedia.org/wiki/West_nile_virus
Vocabulary
AIDS
Acquired immune deficiency syndrome, which is a fatal condition caused by HIV.
HIV
The human immunodeficiency virus, which causes AIDS.
infectious disease
A disease that spreads from person to person.
pathogen
A living organism or virus that causes disease.
vector
An organism that carries pathogens from one person or animal to another.
Points to Consider
What do you think causes allergies?
Do you know of other diseases that are not caused by pathogens?
Do you think these diseases are contagious?
Lesson 21.2: Noninfectious Diseases
Lesson Objectives
List causes of noninfectious diseases.
Describe causes and treatments of cancer.
Explain why diabetes occurs.
Describe autoimmune diseases and allergies.