Health, Disease and Medicine

13.1 There are many causes for diseases

1. Many diseases are caused by micro-organisms such as bacteria and viruses.

2. However there are 6 different causes of diseases
o Genetic: these are diseases caused by genes, like cystic fibrosis and sickle
cell anemia.
o Pathogens: Infectious diseases are caused by other living organisms called
pathogens. E.g. AIDS, syphilis, malaria, gonorrhea.
o Auto-immune diseases: these are caused when a person’s immune system
attacks its own body cells. E.g. muscle dystrophy, some kinds of diabetes
and arthritis.
o Lifestyle: Some diseases are self inflicted as people do things that are not
good for them. E.G. Alcoholism, drug addiction, and lung cancers.
o Deficiency diseases: These are caused due to a lack of a nutrient in the
diet. E.G. Anemia and scurvy.
o Degenerative diseases: are caused due to aging. E.G. Heart disease, and
arthritis.
3. Many diseases are avoidable and treatable.

Genetic disease
13.2 Sickle cell anemia is caused by a recessive allele.

1. Sickle cell anemia is caused by the allele of the gene that is responsible for the
production of hemoglobin.
2. The sickle cell allele is recessive so only a homozygous person for this allele can
have the disease. The sickle cell allele causes the production of abnormal
hemoglobin, which does not carry o2 very well.
3. When the concentration of o2 is low in the blood – during exercise – the sickle
cell hemoglobin forms a precipitate, that pulls the cells into a sickle shape.
4. This sickle celled RBC gets stuck in the capillaries causing a stoppage of the
blood flowing through them.
5. This is very painful and causes anemia, the cells get starved of oxygen.
6. The place that is most hit with this is in Africa.

13.3 A pathogen is an organism which causes disease

1. Many infectious diseases are caused by living organisms called pathogens.

2. They damage our cells by either living in them or feeding on them. Or they
release waste products called toxins which cause symptoms such as high
temperatures and rashes.
3. There are 4 different types of pathogens: Viruses, Bacteria, Protozoa, and Fungi.
13.4 Pathogens get into the body in different ways

1. Through the skin: The skin is usually a very good protective barrier against
pathogens. However there are some bacteria that can get through undamaged skin
like the one that causes warts. Some get through cuts can turn it septic.
2. Through the respiratory passages: The cold and influenza viruses are carried in
the air in tiny droplets of moisture. If someone with these illnesses speaks, coughs
or sneezes, millions of viruses are propelled into the air. If you breathe in the
droplets, you may be affected.
3. In food or water: Some bacteria enter your alimentary canal through your food. If
you eat a large amount of them, then you will get food poisoning. Many
pathogens, including the virus that causes polio and the bacteria that causes
cholera are transmitted through water. If you drink untreated water, you run risk
of catching these diseases.
4. By vectors: In Bio, a vector is an organism that carries a pathogen from one host
to another. E.g. Mosquito is the vector that transmits plasmodium, which causes
malaria.
5. By sexual intercourse: Some bacteria enter the body through sexual intercourse
such as the bacteria causes gonorrhea and syphilis.

13.5 Influenza is caused by a virus

1. Flu is an infectious disease- it can be easily transmitted from one person to

another.
2. The virus which causes it is usually breathed in, in tiny droplets of moisture.
3. Viruses are not considered as living things, because they cannot do anything on
their own that living things can like respire or grow.
4. They are just some protein molecules around some DNA or RNA.
5. But when the get inside another cell, they begin to reproduce.
6. Flu viruses get into the cells lining the respiratory passages and take over these
cells. They use material in the cells to make more flu viruses.
7. So many new viruses are made and the cell is destroyed.
8. Then they burst out of the cell and infect other cells or they get breather out on
tiny droplets of moisture ready to infect someone else’s cells.
9. Naturally you feel rather ill when this happens. But for the first three days – time
you breathed in the viruses – nothing much happens. This is called the incubation
period.
10. The your temperature starts to go up and you get head and muscle aches, a sore
throat and perhaps a cough.
11. If you are relatively fit then your immune system will destroy all the infected cells
and viruses within a week or two.
12. But if you have a weak immune system, then other pathogens take advantage of
the viral infection to get a toehold in the respiratory system. This can cause
secondary infections like bronchitis and pneumonia. These can be fatal.
13. This is why flu causes death in old people.
13.6 Gonorrhea and syphilis are sexually transmitted diseases.

1. The Bacteria that causes gonorrhea and syphilis is transmitted from person to
person by sexual intercourse.
2. The bacteria that causes gonorrhea is a small and round cell.
3. It can only survive in moist places, like the tissues of the tubes lining the
reproductive systems.
4. If the gonorrhea bacteria is present in a woman’s vagina, or a mans urethra, the
infection can be passed from one person to another through sexual intercourse.
5. The first symptoms vary in men and women. 2-7 days after infection.
a. In men the bacteria reproduce inside the urethra and this produces an
unpleasant discharge and pain when urinating.
b. In a woman, the bacteria reproduce in the cervix, and this produces a
discharge. But woman don’t notice it and they don’t suffer as much pain as
men.
6. Therefore men know that they have it and woman don’t!
7. The bacteria that causes syphilis is spiral shaped and it is transferred from person
to person just in the same way as gonorrhea.
8. The first symptoms usually occur about one or two weeks after the infection, in
the form of a painless ulcer at the place where the bacteria were introduced into
the body.
9. This disappears after 2 months and therefore people think there is nothing wrong.
10. But in reality the bacteria now spread all over the body and after a while they
suffer from sore throat, headache or fever, followed by a skin rash.
11. but these also go away, and people think they are alright, and some of them may
not be affected.
12. However, many in people the bacteria continue to live for several years. They
start to destroy their organs like the brain or heart.
13. Both gonorrhea and syphilis can be treated with antibiotics like penicillin and this
is very effective.
14. But the best thing is to avoid these diseases in the first place by
a. Remaining sexually inactive
b. Using contraceptives
c. Having only one sexual partner
d. Tracing, warning and treating all possible sexual contacts of person who is
diagnosed with syphilis.

13.7 Malaria is transmitted by a vector.

1. The pathogen that causes malaria is a protoctist called plasmodium.

2. You get malaria if you get bitten by the female mosquito of the genus anopheles if
she is carrying plasmodium in her saliva.
3. The mosquito has a long proboscis, which she pushes through the skin into the
blood vessel.
 4. Then she sucks the blood through the proboscis. She injects some saliva to stop
clotting of the blood and her saliva contains plasmodium, then it injects that as
well.
5. The mosquito is a vector for the disease. That’s why malaria is present where
anopheles mosquitoes are present.
6. The plasmodium organisms get into your liver cells. Here they breed for a few
days and then they leave the liver and enter your RBC. This is when you first feel
ill, feeling a bit as though you have the flu.
7. The organisms breed even faster when they are in the RBC. When a RBC is full
of young organisms it bursts and they get released into your blood so they infect
other blood cells.
8. This happens at set intervals- every two days. Every time a RBC bursts your
temperature rises and you feel ill. 40 degrees. Many people die at this high
temperature.
9. The burst blood cells block the capillaries and cut of o2 to many parts of the body.

13.8 Malaria is difficult to control

1. Malaria is very difficult to control. The best way to stop it is to kill the vectors
involved.
2. Insecticides: Adult mosquitoes are active at night and rest during the day.
Insecticides including DDT have been used to spray their resting places. This is
very effective in some places but in many places the mosquitoes have become
resistant to the insecticides.
3. Dealing with ponds: Mosquitoes lay their eggs in stagnant water and their larvae
grown into adults in the water. They come up to the surface to get o2 from the air.
In some places swamps and other open water sources have been drained to reduce
the amount of water available for mosquitoes to breed. People also take care not
to leave containers of water or even puddles near the house where they can breed.
Oil can be sprayed on top so that the larvae can not come to the top to get o2.
These methods are successful, but they are expensive and affect other organisms.
4. Avoiding mosquitoes: Malaria can only be transmitted by anopheles mosquitoes.
So by sleeping under a net prevents mosquitoes from coming near you. Insect
repellant creams can also be used. And wearing clothes that completely cover you
prevents you from being bitten.
5. Drugs: Drugs can be used to kill the plasmodium virus in an infected person’s
body. There also drugs that prevent plasmodium from infecting you even if your
are bitten. However plasmodium appears to be able to quickly become resistant to
them and so new drugs have to be discovered all the time.
6. Until recently there was no vaccine for malaria. But in 1994 one was discovered.

Body defenses against infectious diseases

13.9 The body has many defenses against infection
 1. The human Body has many ways in which it prevents pathogens getting into it:

Method of entry Example Natural defenses

Through the skin Staphylococcus • The epidermis is a barrier between pathogens
bacterium and body
• When skin is damaged, blood clots seal
wounds and prevent entry of pathogens
• Tears contain lysozyme, which helps to
prevent eye infections
Into respiratory Influenza virus • Cilia and mucus in the respiratory passages
system trap dust particles which carry pathogens, and
sweep them upwards
• Phagocytes petrol the surfaces of the alveoli
and destroy any pathogens they find.
In food or water Salmonella • Distaste for food that looks or smells bad
into the alimentary • Hydrochloric acid in the stomach kills many
canal bacteria
Injection into Plasmodium None
body by a vector
By sexual HIV None
intercourse

2. If pathogens get past these natural defenses, the white blood cells come into
action to destroy them.
3. There are many different types of WBC, but they all have the function of
destroying pathogens.
4. Phagocytes move around the body and engulf and destroy bacteria. They also
destroy your own cells which have been damaged or worn out. They have a large
lobbed nucleus. If your skin gets damaged, then phagocytes collect at the site and
destroy any micro-organisms that come in.
5. Lymphocytes produce chemicals called antibodies, which travel through the blood
and tissue fluid to all parts of the body and kill pathogens.

13.10Antibodies are specific

1. In your body, there are thousands of different kinds of lymphocytes. Each kind of
lymphocytes is capable of producing a different kind of antibody.
2. Antibodies are proteins with a particular shape.
3. To destroy a pathogen, the antibody molecules must be made which is exactly the
right shape to fit the molecules outside the pathogen. These molecules are called
antigens.
4. When an antibody locks on to an antigen, the pathogen is destroyed.
5. There are several ways in which they do this. One simple way is to simply alert
phagocytes to the presence of pathogens to destroy them.
6. Or, they may set of a series of reactions in the blood which produce enzymes to
digest the pathogens.

13.11Lymphocytes multiply when their pathogen is present.

1. Most of the time lymphocytes do not produce antibodies because they that
would be a waste of energy and materials.
2. They wait for a signal that a pathogen which be destroyed by its antibody is
present in the body.
3. If a pathogen enters the body, it is likely to meet a large number of
lymphocytes. One of these may recognize the pathogen as the one its antibody
can destroy.
4. This lymphocyte, divides itself by mitosis rapidly so that a large number of
lymphocytes, that are able to produce that antibody is made.
5. Then they all secrete their antibody to destroy the pathogen.
6. This takes time. It make take some time for the right lymphocyte to recognize
the pathogen. Then it takes a few days so that a large enough clones to be able
to destroy it.
7. In the mean time, the pathogen breeds and you feel ill.
8. Eventually, the lymphocytes gain the upper hand.
1. The types of lymphocytes that produce antibodies are called B lymphocytes.
2. There is also another type that attaches itself to the pathogen or the body cells
infected by the pathogen and destroys it. These are called T Lymphocytes.
3. This means that these are particular good at killing viruses, because viruses
live and breed in body cells.
4. Lymphocytes are very important part of your immune system.
5. The way in which lymphocytes respond to pathogens, either by producing
antibodies, or by attacking them directly is called immune response.

1. Memory cell make you immune

1. The first time a pathogen enter the body; it takes a little while for the immune
system to swing into action. This gives time for the pathogen to breed and make
you ill.
2. When the lymphocytes multiply to produce clones, not all the cells in the clone
take on the responsibility of making antibodies. Some of them remain inactive.
These inactive cells are called memory cells.
3. They can stay inside the blood for a very long time.
4. If the same pathogen returns to the body, then it is likely to be recognized by a
memory cell straight way. The immune response to the pathogen is immediate,
killing it before it has any chance to breed.
5. You are now immune for that pathogen. That’s why chicken pox can only be
caught once.

13.13 Cold Viruses keep Changing

1. For many diseases, immunity lasts all your life. For example if you only the
mumps or measles once.
2. However, this is no the case with the cold virus.
3. The special feature of the cold virus that enables it to win the battle against our
immune system is that it is capable of changing the proteins in their outer coat.
4. Because of this, each cold virus is slightly different and therefore you don’t have
any memory cells for the new type.
5. Therefore you get the cold and produce memory cells for the new type, which
might be useless.

13.14 AIDS is caused by a virus which attacks lymphocytes

1. The disease AIDS or acquired immunodeficiency syndrome is caused by HIV or

Human immunodeficiency virus.
2. HIV infects lymphocytes, in particular T cells. Over a long period of time, HIV
slowly destroys the T cells.
3. Several years after infection with virus, the level of certain kinds of T cells is so
low that they are unable to fight against other pathogens effectively.
4. Because the HIV virus destroys the very cells that kill virus, it is very difficult for
someone’s own immune system to protect them against HIV.
5. About ten years after the initial infection, the symptoms of AIDS develop.
6. The person is vulnerable to other infections, such as pneumonia.
7. They may develop cancer, because one of the jobs of the immune system is to
destroy cells beginning to produce cancers. Brain cells are also quite often
damaged by HIV.
8. A person with AIDS dies for a collection of diseases.
9. There are no drugs for the cure of AIDS.

13.16 HIV is transmitted in body fluids

1. The virus that causes AIDS cannot live outside the human body.
2. In fact it is an especially fragile virus, much less tough than the common cold
virus.
3. You can only get infected by Aids, through direct contact with your body fluids
with those of someone with the virus.
Through Sexual intercourse
4. HIV can live in the fluid of the vagina, the rectum and the urethra.
5. During sexual intercourse, fluids from partner come into contact with the fluids of
the other. It is very easy for the virus to be passed this way.
6. The more partners a person has the more chance of getting infected.
7. In parts of the world where men have many sexual partners, AIDS is very
common.
8. The best way of avoiding AIDS is to have only one sexual partner. This would
stop the disease from spreading.
9. Using protection also reduces the risk, but does not rule it out.
Through blood contact
10. Many cases of AIDS have been caused by the transfer of HIV through blood
transfusion.
11. This happened especially before they knew what was causing AIDS in the 1970s
and 1980s.
12. Nowadays, blood used for transfusion is checked for AIDS before it is donated.
13. Blood can also be transferred by using hypodermic needles. This most common
happened with drug users.
14. People who deal with accidents use protective clothing, just in case a bleeding
victim is infected with AIDS.
15. However, there is no general risk of being in contact of someone with AIDS. You
quite easily talk to them, shake hands, drink from cups they have used and so on.
16. In fact they are in more danger from you because they are so vulnerable to
bacterium or virus they might catch from you.

13.17 The immune system can reject transplants

1. People suffering from a serious disease that affects a particular organ can be given
transplants.
2. Many organs can be transplanted, but the most common ones are kidneys, bone
marrows, and hearts.
3. The person who is receiving the organ is called the recipient and the person from
whose body the organ comes from is called the donor.
4. Most donors are people who died in accidents.
5. Organs for transplant have to be removed from the body and have to be kept cold to
prevent degenerating.
6. Sometimes a donor maybe alive. A person may donate a kidney to a brother or sister,
who needs one urgently.
7. You can live perfectly well with one kidney.
8. Transplant operations are usually very successful, however it after the operation that
the big problem comes.
9. The immune system of the recipient recognizes the new organ as foreign and attacks
it. This is called rejection.
10. The receipt is given drugs called immunosuppressant which stop the white bloods
working efficiently, to decrease the chance of rejection.
11. However, the problem with immunosuppressant is that it prevents the immune system
from doings it job, and so the person is likely to suffer from a whole range of
infectious diseases. Also these drugs have to be taken throughout the patients life.
12. The chances of rejection are reduced if the donor is a close relative of the recipient.
This can only be considered if the organ for donation can be given by a living person.
13. Close relatives are likely to have cells with similar antigens and therefore the
recipients immune system is less likely to react to the donated organ as foreign.
14. If a relative cannot donate an organ, then the search can be made world wide for a
potential donor with similar antigens.
 13.18 Antibiotics can kill bacteria in the body

1. Sometimes a persons body needs help in its fight against bacterial infection
2. Antibiotics are substances that kill bacteria but do not damage other living cells. They
have made tremendous improvements in health care.
3. They are usually made by fungi. It is thought that fungi use antibiotics to kill bacteria
near them
4. Both fungi and bacteria are saprophytes, so they might need to compete for food.
5. The first antibiotic to be discovered was penicillin produced by the fungi penicillium;
you might have seen this growing on decaying fruit.
6. Penicillin kills bacteria by stopping them making their cell walls. Since the
introduction of penicillin many new antibiotics have been discovered.
7. We have to go discovering more and more antibiotics because bacteria prove to be
able evolve to become resistant to it.
8. The more we use it, the more selection pressure we apply on bacteria to evolve
resistance.
9. The people who discovered didn’t know this, and it was used for treating the wrong
type diseases caused by viruses.
10. Now doctors are very careful about the amount of antibiotics which they prescribe.
11. We should only use antibiotics when we really need them, and then there is more
chance that they work, when we need them to.