The lungs are the main components of the human respiratory system, crucial for inhaling oxygen, expelling carbon dioxide, and maintaining normal metabolism. The lungs are located in the thoracic cavity on either side of the heart, divided into the left lung and the right lung. The left lung consists of two lobes, while the right lung has three lobes (upper, middle, and lower). The lungs have a soft, spongy structure that allows them to contract and expand during breathing. Each lobe connects to the trachea via tubes called bronchi.
As the bronchi continue to branch, they gradually become narrower, forming bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, and alveolar ducts. The smallest branches, called alveoli, are sac-like structures.
There are nearly 300 million alveoli in our lungs, surrounded by capillaries. Alveoli are the sites where oxygen and carbon dioxide are exchanged between the body and the external environment. Oxygen passes through the alveolar wall and is absorbed by the blood, which transports it to various parts of the body. Carbon dioxide and other waste gases produced by the body enter the alveoli through the alveolar wall and are ultimately expelled from the body during exhalation.
The total surface area of adult alveoli reaches 80 to 100 square meters. A portion of the alveoli usually remains closed, but during intense physical activity, all alveoli participate in gas exchange.
In healthy individuals, the lungs appear reddish, while smokers show different colors due to the accumulation of tar and toxins, leading to what is termed "colorful lungs." Over time, the color of the lungs darkens with prolonged smoking, and even after quitting, the lungs do not return to their original color.
Lung cancer refers to cancer originating from the bronchial or alveolar epithelium, medically known as primary bronchogenic carcinoma. It is the most common malignant tumor of the lungs, where bronchial epithelial cells or alveolar epithelial cells undergo malignant transformation due to various carcinogenic factors, uncontrollably proliferating and forming solid tumors.
Lung cancer is categorized into central lung cancer and peripheral lung cancer based on its location. Central lung cancer primarily occurs in the trachea, main bronchi, lobar bronchi, and segmental bronchi, growing towards surrounding lung tissue.