COPD & smoking

Why does smoking causes COPD?

- In a smoker's lung, there are basically two things that take place:

1. the lung reacts to smoke particles (e.g. nicotine, tar) => know as indirect injury
2. the smoke particles react to the lung => known as direct injury

- Indirect injury:

• In smokers, there is an accumulation of immune cells (immune cells protecting the body are liken to the policemen & soldiers that protect a country) within the alveoli. (remember the tree analogy? These are the leaves)
• It is believed that the immune cells (neutrophils and macrophages) are attracted to the lung alveoli by the smoke particles, nicotine. (as an action of local immune cells.)
• Of the 2 immune cells, 1 of them (neutrophils) release a variety of protein substances (e.g.neutrophil elastase, proteinase 3 & cathepsin G) finally resulting in lung alveolar damage.
• The other immune cell (macrophage) also releases a protein substance calledmetalloproteinase which causes additional damage to the lung alveoli. (It's just like a war occuring within a country's gates. When bullets are fired, innocent people get hurt too.)

- Direct injury:

• Smoking plays a role in causing direct injury to the lungs by producing harmful products known as reactive oxygen species / "free radicals".
• Free radicals cause lung alveolar damage by destroying the 'guys' that maintain the well-being of the alveoli (known as alpha 1 anti-trypsin)

- All these insults results in the loss of alveolar attachments (supporting structure) & thus acollapse of brochial wall upon breathing. (this is what happens in emphysema)

- The continuous insult in the alveoli causes deposits of hardening tissue (fibrosis) hence thenarrowing of airflow and airway limitation. (this is chronic bronchitis)