Health and disease

• A communicable is a disease which can be passed on from one organism to another.
• A non-communicable disease is a disease which cannot be passed on from one organism to another.
• Health is defined as being free from communicable disease. If we are healthy and free from disease.
• Being sick can impact those around us and society in a number of ways:

  • It costs the NHS money to treat us whether it is antibiotics or hospitalisation.
  • It costs businesses as they have to pay sick pay, pay for temporary staff and can reduce productivity.
  • It can cost families as if someone is out of work for a long time. This can reduce the household income.
• Communicable diseases come in 3 forms:

  • Person to person
  • Mother to baby
  • Animal to person
• The body has some natural defences that are used as barriers to the entrance of microbes.

  These include:

  • Skin - is acidic to try and kill bacteria.
  • Mucosa membranes - in the respiratory system, they trap microbes.
  • Blood clotting - closes wounds quickly to form a barrier that stops microorganisms gaining entry to the body.
• All microbes have proteins on their surface that the body recognises as self or non self.
• These proteins are called antigens.
• Antigens cause White blood cells called lymphocytes to produce antibodies and another type of white blood cell called phagocytes to come and break it down.
• Lymphocytes produce antibodies that are complimentary to the antigen on the surface of the microbe.
• When the antibody binds, it can bind to multiple microbes at the same time, causing clumping (agglutination).
• This makes phagocytosis easier, prevents the spread of disease further and can reduce symptoms.
• Phagocytosis

  • phagocyte will engulf the clumped microbes.
  • The phagocytes will continue to engulf the microbes.
  • The phagocytes digested the microbes.
• Lymphocytes

  • Microbes have chemical markers called antigens.
  • Lymphocytes produce antibodies which are complementary in shape to the antigen.
  • They fit together (lock and key) and the antibodies clump together.
  • Antibodies can remain in the body for many years.
• The reaction which takes place the first time an antigen enters the body is called the primary response.
• The reaction which takes place the second time an antigen enters the body is called the secondary response.
• If you are protected from a disease you are said to be immune. This means that your antibody level is high enough that you can combat any microbe.
• There are two types of immunity:

  • Active immunity - is where the body produces the antibodies used to combat the infectious microorganism. This type of immunity is slower acting but usually lasts for a very long time.
  • Passive immunity - is when antibodies from another source (such as those produced by pharmaceutical companies) are injected into the body. These are fast acting but only last for a short period of time.
• Vaccinations involve the use of dead or modified pathogens (microorganisms which cause diseases) that are injected into the body.
• The dead or modified microorganisms still have the antigens on their surfaces that cause the body to produce antibodies at a high enough level to prevent the individual becoming ill later. As a result, memory lymphocytes will remain in the blood in case of secondary exposure.
• How do vaccinations work?

  • Small amounts of dead or inactive pathogens are put into the body. Usually by injections.
  • The pathogens in the vaccine stimulate your white blood cells into making antibodies.
  • The antibodies stick to the antigens on the surface of the pathogen and cause them to clump together. Another white blood cell antibody destroys the pathogen.
  • Memory cells are then retained which means you are now immune to future infections by the pathogen. This is because your body can produce a fast and bigger response the 2nd time and will stop the pathogen before it makes you feel ill.
• Sometimes we need more than one vaccination to make sure that we remain immune for a reasonable period of time. This is known as a follow-up booster vaccination.
• Plants also have defences against disease. They can be physical or chemical.
• • The physical defence is the waxy cuticles which prevent microorganisms from entering the leaf.
  • The chemical defence is the plants producing chemicals that are harmful to infectious microorganisms.
• Chemicals in mint have been shown to have antimicrobial properties that will kill or restrict the growth of bacteria. This can be demonstrated by adding an aqueous mint extract to a Petri dish containing bacteria.

  Similar effects have been demonstrated by digitalis, which is extracted from foxgloves. The digitalis is poisonous to insects, slugs and other animals that would otherwise feed on it.
• Producing penicillin commercially

  • penicillin and other drugs are made In very carefully controlled conditions that maximise productivity.
  • The microbes that make the penicillin are grown in large biodigesters or fermenters that create the perfect conditions for fungal growth.