Every cell in your body needs oxygen to survive here. You can see red blood cells giving oxygen to a cell to keep it healthy. Red blood cells get the oxygen from your lungs. So it is very important to keep your lungs healthy. When you breathe in oxygen travels down tubes called bronchitis and then into small SACS called alveoli. These SACS have thin walls so that the oxygen can easily pass into the red blood cells. When harmful substances enter the airways, they can damage the lining of the airways.
This is what happens with smoking with each drag of a cigarette smoke enters the lungs through the bronchitis air tubes. There are many poisonous chemicals in smoke and these attack the lining of the air tubes causing the cells to change and grow in an abnormal way. The damaged cells can turn into cancer cells, which clump together to form tumors.
These tumors can then spread throughout the lungs. Smoking is the number one cause of lung cancer. Lung cancer may not cause any symptoms at first, but as the tumor grows, it can start to affect the surrounding lung tissue. The damage to the airway walls can cause you to cough. Parts of the tumor can break off and bleed so that your phlegm may be bloodstained. The cancer can also cause chest pain. If the tumor grows larger, it may block the airways flow of air, making it difficult to breathe.
You have to breathe harder and faster to take in more oxygen as the cancer develops and may cause severe shortness of breath, a hoarse voice, and trouble swallowing. You may feel very tired and lose weight. The cancer cells may spread to other parts of the body such as the liver brain and bone.