Non-infectious Disease and Disorders
What you must understand
Non-infectious diseases are not caused by pathogens and cannot be transmitted between individuals. Know the major categories: genetic diseases (e.g. cystic fibrosis, caused by inherited alleles), nutritional deficiencies (e.g. scurvy from vitamin C deficiency), environmental diseases (e.g. lung cancer from smoking, skin cancer from UV exposure), and autoimmune diseases (the immune system attacks the body's own tissues).
Understand homeostasis and how disruption leads to disease. Negative feedback loops maintain temperature, blood glucose and water balance. Know how diabetes illustrates homeostatic failure: Type 1 involves insufficient insulin production; Type 2 involves reduced insulin sensitivity.
Understand risk factors - genetic, environmental and lifestyle - and how epidemiology identifies associations. Know the difference between correlation and causation, and why controlled studies are needed. Understand prevention and management strategies for non-infectious diseases.
Traps in questions
- Non-infectious diseases cannot be "caught"; they are not transmitted between people.
- A risk factor increases the chance of disease but does not guarantee it.
- Correlation does not prove causation - a common exam trap.
- Type 1 and Type 2 diabetes have different mechanisms; do not treat them as the same.
- Genetic diseases are inherited, but not all inherited conditions are present at birth.
Rule of thumb
For any non-infectious disease, classify the cause as genetic, nutritional, environmental or autoimmune, then link it to the affected body system and the risk factors involved.
Worked example
Lung cancer is a non-infectious, environmental disease. Smoking is a risk factor that increases the probability of mutations in lung cells, but not every smoker develops cancer, showing that risk factors raise probability rather than determine outcome.