Definition: The World Health Organization (WHO) defines lung cancer as tumors arising from the respiratory epithelium (bronchi, bronchioles, and alveoli). OR Lung cancer is a type of cancer caused by uncontrolled cell division of the respiratory epithelium (bronchi, bronchioles, and alveoli). Normal structure and function of the lungs: Lungs are 2 sponge, pyramid-like organs located in the chest. Each lung is divided into sections called lobes. The right lung has three lobes while the left lung has two lobes. The left lung is smaller than the right one because the heart on the left side takes up more room of the chest. When you inhale air through mouth and nose it enters into lungs through trachea (windpipe). The trachea divides into tubes called bronchi, which enter the lungs and divide into smaller branches called bronchioles. At the end of bronchioles there are small tiny sacs called alveoli. These alveoli absorb oxygen from the inhaled air into your blood and
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