Lung Cancer Symptom
As cigarette smoking is a major cause of lung
cancer, it is important to appreciate how smoking
affects and harms the lungs. This is because smoke
inhalation damages the normal cleaning process by which
the lung protects itself from injury.
The bronchi which conduct inhaled air to the lung
tissues are lined with a single coating of cells on
which lies a defensive coating of mucus. The hair-like
cilia on these cells beat in a regular rhythm to advance
mucus upwards continually from the lung removing any
inhaled particles which may have become trapped in the
process. The effectiveness of
this cleaning mechanism is damaged very quickly by smoke
inhalation. The cilia disappear and the coating they lie
in thickens in an attempt to protect the fine underlying
tissues from further damage. Once this has occurred, the
lung can no longer keep itself clean.
As a consequence, the cancer-causing agents in cigarette
smoke remain trapped in the mucus on the surface lining
of the airway. They then pass into the cells before
being removed by coughing which is the only cleansing
mechanism remaining. Once
they are entered the body, these chemicals alter the
very nature of the cells in the lungs gradually and
increasingly until eventually cancer develops.
Most lung cancers start in the lining of the bronchi,
though some cancers also begin in the trachea,
bronchioles, or alveoli. Lung cancer is thought to
develop over a period of years. To start with there is
probably areas of pre-cancerous changes in the lung, but
these changes don't usually form a mass or tumor.
Unfortunately they can't be detected on an x-ray and
they don't cause any obvious symptoms. As the cancer
develops, it continues to grow and forms a tumor which
is then large enough to become visible on x-rays. These
pre-cancerous changes can be exposed by analyzing cells
in the lining of the airways of smoke-damaged lungs.
Molecular abnormalities considered to be pre-cancerous
have also been recognized in cells from people who are
at high risk of developing lung cancer. These
pre-cancerous changes usually progress to true cancer.
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