Biology section 5

• Health


  A state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity
• The World Health Organisation (the WHO) defines health
• Even if someone is very physically fit, they still might be unhealthy if they have mental health issues or are socially isolated
• Communicable diseases


  Diseases that can be spread between individuals
• Non-communicable diseases


  Diseases that can't be transmitted between individuals, e.g. cancer and heart disease
• If you are affected by one disease, it could make you more susceptible to others
• Pathogens


  Organisms such as viruses, bacteria, fungi and protists that cause communicable diseases
• Communicable diseases


  • Cholera
  • Tuberculosis
  • Malaria
  • Chalara ash dieback
• STIs


  Sexually Transmitted Infections, infections that are spread through sexual contact
• HIV


  The Human Immunodeficiency Virus, which infects and kills white blood cells
• HIV infection eventually leads to AIDS (Acquired Immune Deficiency Syndrome)
• Chlamydia


  A sexually transmitted bacterial infection that can result in infertility
• Ways to reduce the spread of Chlamydia

  1. Wearing a condom when having sex

  2. Screening individuals so they can be treated

  3. Avoiding sexual contact
• Physical and chemical barriers that stop pathogens entering the body

  • Skin acts as a barrier
  • Hairs and mucus in nose trap particles
  • Cells in trachea and bronchi produce mucus and have cilia
  • Stomach produces hydrochloric acid
  • Eyes produce lysozyme
• White blood cells


  The most important part of the immune system, they travel around and patrol for pathogens
• Specific immune response


  1. Pathogens have unique antigens

  2. B-lymphocytes produce antibodies specific to the antigen

  3. Antibodies bind to and help destroy the pathogen

  4. Memory lymphocytes are also produced
• First exposure to an antigen

  Slow immune response, symptoms may appear
• Second exposure to the same antigen

  Faster and stronger immune response, often no symptoms
• Immunisation


  Injecting dead or inactive pathogens to trigger an immune response and produce memory lymphocytes
• Antibiotics work by inhibiting processes in bacterial cells, but not in the host organism
• Antibiotics don't destroy viruses, as viruses reproduce using the body's cells
• Stages in developing new drugs

  1. Discovery

  2. Preclinical testing on cells, tissues, animals

  3. Clinical testing on healthy volunteers, then patients
• Placebo effect is when the patient expects the treatment to work and so feels better
• Drug testing


  1. Test on whole animal

  2. Test on live animals to check for effect and toxicity

  3. Clinical trial on healthy volunteers

  4. Clinical trial on patients with illness

  5. Patients randomly given drug or placebo

  6. Clinical trials are blind and double-blind
• Drugs need to be approved by a medical agency before they can be used to treat patients
• Non-communicable diseases


  Diseases not caused by pathogens, but have risk factors associated with them
• Lifestyle factors that may increase risk of non-communicable disease

  • Smoking
  • Diet with too many or too few nutrients
  • Lack of exercise
  • Diet high in fat and sugar
  • Drinking too much alcohol
• Risk factors


  Things linked to an increase in likelihood of developing a disease, but don't guarantee someone will get the disease
• Risk factors can be unavoidable (e.g. age, gender) or lifestyle factors that people can change
• Many non-communicable diseases are caused by several different risk factors interacting, rather than one factor alone
• Non-communicable diseases can have knock-on effects on local areas, the national health system, and a country's economy
• Body Mass Index (BMI)

  A guide to determine if someone is underweight, normal weight, overweight or obese
• Calculating BMI


  BMI = mass (kg) / (height (m))^2
• BMI classifications


  • Below 18.5 - underweight
  • 18.5-24.9 - normal
  • 25-29.9 - overweight
  • 30-40 - moderately obese
  • Above 40 - severely obese
• BMI isn't always a reliable measure of obesity, as athletes with lots of muscle can have a high BMI
• Waist-to-hip ratio


  A measure of abdominal obesity, calculated as waist circumference / hip circumference
• A ratio above 1.0 for males and 0.85 for females indicates too much weight around the middle, which increases health risks
• Cardiovascular disease (CVD)


  • Any disease associated with the heart and blood vessels
  • Caused by fatty deposits restricting blood flow
• How fatty deposits form in arteries

  1. Cholesterol builds up

  2. Damages artery walls

  3. Triggers blood clots to form
• Blocked arteries supplying the heart


  Causes a heart attack