COPD stands for Chronic Obstructive Pulmonary Disease.
COPD is a combination of emphysema (destroyed lung tissue) and chronic bronchitis (long-term lung airway inflammation).
COPD is almost always caused by smoking.
Source: El Camino Hospital
Mouth/nose, pharynx, larynx, trachea, bronchi, bronchioles, alveoli
For more information, here is a Khan Academy video reviewing the respiratory system.
Just like balloons, the walls of alveoli are stretchy and elastic so that they can expand when you inhale and then deflate when you exhale. They are gathered together like a bunch of grapes and are surrounded by blood vessels. They have thin walls that allow gas to pass into and out of the bloodstream. This is how you get oxygen (O2) into the body and carbon dioxide (CO2) out.
Source: Lumen Learning
Source: Palo Alto VA
The toxic chemicals in cigarette smoke destroy the alveoli.
Smoking makes the alveoli less stretchy, causing air to get trapped.
Inflammation from the smoke destroys the protein in the alveolus that makes it stretchy and elastic, called “elastin.” Since the alveoli can no longer spring back after being filled with air, air gets trapped in the alveoli. This traps CO2 in your lungs, and when you take your next breath, you can’t bring in as much new oxygen.
Smoking makes the walls of the alveoli thick, so oxygen cannot travel across them well.
Smoking eventually destroys the alveoli so the lung is made up of large holes rather than healthy lung tissue.
Your body produces sticky mucus that can trap invading bacteria or inhaled dust and prevent it from getting deeper into your lung tissue.
It then has to get rid of the mucus. One group of airways, called the bronchi, have little finger-like projections, called “cilia,” that move the mucus up into the trachea so that you can swallow it or cough it up. This system of mucus + cilia is sometimes called the “mucociliary escalator” (see the picture above!)
Smoking destroys the cilia and increases mucus production. This is why one of the symptoms of COPD is coughing with mucus. It’s harder to clear bacteria and easier for them to get into the lungs, which is why patients with COPD have frequent lung infections (pneumonias).
Smoking also decreases the diameter of the bronchi so that it’s harder to get air in. This is a combination of increased mucus inside the bronchi as well as inflammation causing the walls of the bronchi to thicken, so there is less room for air to flow to the alveoli for gas exchange.
Lungs are not able to clear infection as well.
Lungs at baseline are not working well. A person with healthy lungs can have a lot of their lung tissue temporarily not work, but still be able to breathe and maintain a normal oxygen saturation. This is because the rest of their lungs are working well and are able to bring in enough oxygen for the body. A person with unhealthy lungs does not have the reserve to take on this extra challenge, and may need mechanical help to continue breathing.
Age - our immune system is not as strong as we get older.