Aetioogy and classification of disease

This lecture was basically an overview of what pathology is, so it's not too content-heavy.

Define pathology, aetiology and pathogenesis

• Pathology- The study of disease and its underlying causes.
• Aetiology- The cause or set of causes for a disease.
• Pathogenesis- The mechanism that leads to the development of a disease.

Note that while aetiology and pathogenesis seem quite similar, they aren't the same. Pathogenesis refers more to the steps that take place to cause someone to get sick. For instance, in a pulmonary embolus, a person gets a clot somewhere in the body (usually the leg), which then breaks off and lodges in the smaller blood vessels of the lung. This process is the pathogenesis of the pulmonary embolus. The aetiology, on the other hand, is the cause or set of causes that caused the clot to form in the first place. This could be a range of factors, such as inactivity or heart failure.

Understand how knowledge of pathology, pathogenesis and aetiology of disease can be utilised in patient care

Most importantly, if we know what made someone sick, we can help by (hopefully) treating the cause. Furthermore, knowing a cause might help inspire research into treating the cause, leading to the development of better treatments over time.

Understanding the pathogenesis can also help in telling patients the prognosis of their disease. If you know how the disease progresses, you can tell patients if they are likely to be well again soon, or if they will need long-term treatment.

Describe ways that disease can be classified

Diseases are defined using consistent and reproducible criteria. This is important as it helps doctors and scientists to use the same terminology in communicating with each other.

There are many ways to classify diseases. Often, diseases are classified by process, underlying cause, or time course. Note that the terms "acute" and "chronic" in medicine refer to the time course and onset of the disease, rather than the severity (as the term is often used in casual conversation): in medicine, "acute" refers to sudden and/or short-term illnesses, whereas "chronic" refers to longer-term illnesses.

The "pathological sieve" or the "surgical sieve" is a useful way to think about various causes of disease. It even comes with a nice little acronym: VITAMIN C:

• Vascular (problems with blood flow or blood vessels)
• Inflammatory/Infective (appropriate activation of the immune system, may be caused by an infectious microorganism)
• Trauma (caused by physical damage, like a broken bone)
• Autoimmune (due to the immune system being inappropriately activated)
• Metabolic (related to metabolism or biochemistry)
• Iatrogenic (don't know what caused it) or Idiopathic (caused by medical interventions)
• Neoplastic (new growth, i.e. tumours)
• Congenital (born with) or Genetic (due to a mutation, either inherited or acquired)

Aside from these causes, you also need to consider degenerative diseases (such as Alzheimer's), environmental conditions (such as asbestos-related mesothelioma), and psychological and neurological conditions (such as schizophrenia).