Health & Disease: Disease Types (OCR Gateway GCSE Biology: Combined Science)

Defining health

• The World Health Organisation (WHO) defines health as 'a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity'
• This means that health is not just dependent on whether an individual is physically sick or not.
• There are lots of factors that should be considered when assessing the health of an individual which includes mental health as well as the level of social support in place

Communicable diseases

• Communicable diseases are caused by microorganisms called pathogens which can spread between individuals
  • E.g. chickenpox, a common childhood disease, is caused by a viral pathogen called the varicella-zoster virus

Communicable Diseases Table

Non-communicable diseases

• Non-communicable diseases are not caused by pathogens and cannot be passed on between individuals
  • Their effects on health tend to be longer-lasting
  • Examples include: asthma, CHD and most cancers
• The risk of developing non-communicable diseases may be increased by certain factors (including diet, stress and life situations) as these factors may have a profound effect on both physical and mental health
  • Eating a balanced diet that provides the right amount of energy and nutrients helps maintain good health whereas a poor diet can lead to deficiencies, obesity, diabetes and poor mental health
  • Constantly being under stress can lead to cardiovascular issues (such as high blood pressure, increasing the risk of CHD) and poor mental health
  • Where a person lives and their income can have a profound impact on health - this affects the standard of healthcare that is accessible to them (and what they can afford), what food they buy etc.

Risk Factors in Non-Communicable Diseases Table

Susceptibility

• If an individual suffers from one disease, they are likely to be more susceptible to other diseases
• This is because the immune system may be compromised in some way or the different types of disease may interact in ways that affect the health of the individual negatively 
  
  • Defects in the immune system mean that an individual is more likely to suffer from infectious diseases
    • Individuals infected with HIV eventually end up with reduced numbers of lymphocytes (a type of white blood cell) circulating around the blood
    • This reduces the ability of the immune system to tackle opportunistic infections like pneumonia
•  Viruses living in cells can be the trigger for cancers; the HPV virus can infect cells of the cervix in women resulting in cervical cancer developing in some cases, whereas some strains of the hepatitis virus can cause liver cancer
• Immune reactions initially caused by a pathogen can trigger allergies such as skin rashes and asthma - these often develop as a result of an overactive immune response
• Severe physical ill health can lead to depression and other mental illness; both can impact the immune system negatively and affect lifestyle choices made by the individual, further compounding the effects of poor health

The interaction of HIV and AIDS

• Human Immunodeficiency Virus (HIV) destroys white blood cells in the immune system
• Initial symptoms are flu-like
  
  • This includes headaches, high temperature, joint and muscle pains
• If untreated, the virus compromises the immune system leading to the onset of Acquired Immune Deficiency Syndrome (AIDS)
• AIDS is used to refer to several life-threatening illnesses which may result from having a compromised immune system
  
  • The most common of these is pneumonia
• The virus infects a certain type of lymphocyte of the immune system
• Normally lymphocytes seek out and destroy pathogens that enter the body, producing antibodies that attach to pathogens, enhancing phagocytic activity
• However, HIV avoids being recognised and destroyed by lymphocytes by repeatedly changing its protein coat
• It then infects a certain type of lymphocyte and uses the cells’ machinery to multiply
• This reduces the number of lymphocytes of the immune system
  • And therefore the number of antibodies that can be made
• As a result, the body has a reduced ability to tackle infections, eventually leading to AIDS (Acquired immunodeficiency)

How HIV affects lymphocytes

The interaction of HPV and cervical cancer

• Human Papilloma Virus (HPV) can be associated with cervical cancer
  • HPV is sexually transmitted, though is not thought to affect men, who are carriers of the virus
• HPV viruses living in cells can be the trigger for cervical cancer in women
• Girls aged 12-13 are injected with a vaccine for HPV
  • Before they reach the age of sexual activity
• Vaccination triggers an immune response
  • Which reduces the risk of viruses spreading in a subsequent infection
• So in turn, the risk of cervical cancer in those girls/women is reduced