Edexcel Biology Gcse - Treating, Curing and Preventing Diseases Part 3

• Hair shaft

• Capillaries

• Epidermis

• Dermis

• Vein

• Artery

• Subcutaneous tissue

• Stomach acid

| - Lysozymes

The hydrochloric acid in our stomachs does not break down food. It is part of the body's non-specific first line of defence. It is hydrochloric acid and while it does us no harm, it is strong enough to kill any pathogens that have been caught in mucus in the airways or consumed in food or water. Stomach acid is a chemical barrier against infection.

To stop eye infections we have evolved chemicals within our tears called lysozymes. These are enzymes that destroy bacterial cells by breaking down their cell walls. Lysozymes are found in saliva, breast milk and mucus, as well as in tears. Lysozymes are chemicals so, like stomach acid, they are a form of chemical defence against infection.

You can catch a communicable disease when you are exposed to a pathogen. There are many ways in which this can happen, but some include touching an infected person, drinking dirty water or breathing in an airborne pathogen.

If pathogens pass the non-specific first line of defence they will cause an infection. However, the body has a second line of defence to stop or minimise this infection. This is called the immune system. As a part of this there are two types of white blood cell called phagocytes and lymphocytes.

Phagocytes are white blood cells. They are attracted to pathogens. They surround them in the blood, bind to them and engulf them.

The phagocytes' membrane surrounds the pathogen and the enzymes found inside the cell, then break down the pathogen in order to destroy it. As phagocytes do this to all pathogens that they encounter, we call them 'non-specific'.

Lymphocytes are another type of white blood cell. They recognise proteins on the surface of pathogens called antigens. Lymphocytes detect that both the proteins and pathogens are foreign, not naturally occurring within your body and produce antibodies. This can take a few days, during which time you may feel ill. The antibodies created by the lymphocytes cause pathogens to stick together, and make it easier for phagocytes to engulf them.

A specific type of lymphocyte called a memory lymphocyte can 'remember' the antigens from an infection by a previous pathogen. A second exposure to it will result in a much faster immune response. Antibodies will be produced much faster, which often stops us becoming ill again. There are hundreds of common colds caused by different viruses. It is very unlikely you will become infected by the same virus because memory lymphocytes exist to fight the infection immediately. This response to a known antigen is called the secondary response and it is much quicker than the response to an antigen for the first time.

During the primary infection the antibodies slowly increase, peak at around ten days and then gradually decrease. A second exposure to the same pathogen causes the white blood cells to respond quickly in order to produce lots of the relevant antibodies, which prevents infection.

Some pathogens produce toxins which make you feel ill. Lymphocytes can also produce antitoxins to neutralise these toxins. Both the antibodies and antitoxins are highly specific to the antigen on the pathogen, thus the lymphocytes that produce them are called 'specific'.

Pathogens are microbes that cause diseases. Immunisations allow an inactive form of the disease causing pathogen to be introduced into the body, which contain a specific antigen. This causes the immune system, specifically the white blood cells, to produce complementary antibodies, which target and attach to the antigen.

1) Syringe injects an altered or weakened form of the pathogen.
2) White blood cells release complementary antibodies to the specific antigen.
3) They attach and clump pathogens together.
4) White blood cells engulf the pathogens. Phagocytosis occurs.

Following an immunisation, a person can become immune to the specific disease. This immunity gives protection against illness in an individual. When the majority of the population are immunised against serious diseases, this means that even those people who have not been immunised will still be protected because they are less likely to come into contact with an infected person. This type of immunity is herd immunity.

1) The majority of the population are not immunised against a specific disease, however, a few people are ill and contagious. This can develop easily into a mass infection because the majority of the population aren't immunised.
2) Most of the population are not immunised against the specific disease but are well, some are immunised and healthy, and a few are not immunised, but ill and contagious. Mass infection can result again, but a small number of immunised individuals remain healthy and some that are not immunised will also be healthy.
3) The majority of the population are immunised and healthy against a specific disease, a few are not immunised but well. A few are not immunised against the disease, and they are ill and contagious. The result is that the majority are protected due to the high level of immunisation. A few individuals will still become ill, but the large number of immunised individuals gives protection.

If the number of people immunised against a specific disease drops in a population, it leaves the rest of the population at risk of mass infection, as they are more likely to come across people who are infected and contagious. This increases the number of infections, as well as the number of people who could die from a specific infectious disease.

Antibiotics are substances that slow down or stop the growth of bacteria. They are commonly prescribed medicines, examples include penicillin and amoxicillin. These can be taken to cure the diseases by killing the pathogens, but only cure bacterial diseases and not viral ones.

Penicillin was the first antibiotic discovered in 1928 by Alexander Fleming. He noticed that some bacteria he had left in a Petri dish had been killed by the naturally occurring Penicilliummould.

Antibiotics damage the bacterial cells by inhibiting their cellular processes, but do not damage the host cells. They have the ability to cure some bacterial diseases that would have previously killed many people. Since their introduction, they have had a large influence on the world's health and death rate.

Different bacteria cause different diseases. One antibiotic may only work against one type of bacteria, or a few types. This means that a range of different antibiotics is needed for the treatment of the whole range of bacterial diseases.

Viral diseases cannot be cured by antibiotics, as they reproduce inside the host cells. It is very difficult to develop antiviral drugs, as they might damage the host cell whist killing the virus. Antiviral drugs only slow down viral development, and viruses change their antigens quickly which means new drugs have to be generated regularly.