The primary function of the tracheobronchial tree is processing the air that is breathed into the lungs. The tree’s lining is made up of column-shaped surface cells (columnar epithelium) and glands that produce mucus and a clear plasma known as serous fluid.
Thin hairs known as cilia are attached to the columnar epithelium and assigned the duty of cleansing harmful organisms and foreign bodies from the airways. Healthy lungs self-clean with the assistance of watery mucus that is moved by the cilia. Smoking or other toxic exposures cause defective cilia and other abnormalities in the tissue lining.
Trachiobronchial branches are classified as either segmental bronchi or bronchioles. Segmental bronchi have coverings made of connective tissue and are larger than 1 mm in diameter. Bronchioles do not have the tissue coverings and are less than 1mm in diameter.
Lung cancer, like every other cancer, is the result of malfunctioning cells in the body. In a healthy system, cells divide to produce new cells on an as-needed basis. When a cell deviates from this pattern, the two cells created by the division are also abnormal.
The abnormal cells multiply quickly, upsetting the body’s proper balance of healthy cells by squeezing out others while creating an excess of themselves. This excess forms a mass known as a tumor, which will be either malignant (cancerous) or benign (non-cancerous).
Malignant tumors spread out aggressively and invade the nearby organs and tissues. When they enter into the bloodstream or the lymphatic system (a network associated with the immune system) through the lymph nodes (filters for the lymph fluid), the cancerous cells are transported to other areas of the body and begin the tumor-producing process at those sites.
The secondary sites are known as metastases. Lung cancer tends to metastasize early on and often spreads to the brain, liver, adrenal glands, or bones. The reverse is also true, and cancer of the lung is often a secondary cancer that has, metastasized from another site.
Both primary (initial) and secondary lung cancer can appear first in any part of the lung, but it is believed that over 90% of them have started in the bronchi and the bronchioles. For this reason, lung cancer is also referred to as bronchogenic carcinoma.