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Lung Cancer: Quit Smoking or Quit Breathing? 
 
by Kealoha Wells August 24, 2005

Lung cancer is one the deadliest forms of the disease and one of the easiest to prevent. Over 90% of all lung cancers are caused directly or indirectly by cigarette smoke. Are you at risk?

Lungs

Lungs are the major organs of the body’s respiratory (breathing) system. At birth, they are a pinkish-white color, but over the years they darken to gray or black because of the particles inhaled.

They are in the rib cage, one on either side, and are enveloped in a membrane known as the pleura, or the serous coat (named for the watery fluid called serous that moistens it). The parietal (outer layer) pleura is located on the side of the nearest the rib, the visceral (inner layer) pleura is the layer nearest to the lung.

Lung parenchyma, the main tissue of the lung, consists of clusters of spongy air sacs called lobules. Each lobule is made up of tiny air sacs called alveoli that exchange oxygen for carbon dioxide. Each lung has around 130,000 lobules, and each lobule has about 2200 alveoli in its approximately 3.5 mm diameter.

The lungs are separated from each other by the mediastinum (middle chest) which consists of, among other things, the heart and the windpipe (trachea.) The midline region directly beneath the middle chest is called the hilum or hilus and is made up of blood vessels, nerves, and lymphatic tissues. The bronchial tubes also enter and exit the system here.

Both lungs are divided into upper lobes (the top is called the apex), which extend to the just above the first rib, and the lower lobes (the bottom is called the base), which extend down to the diaphragm. The diaphragm is an important muscle that separates the chest from the abdomen. It contracts and descends with each intake of air (inhalation or inspiration) and relaxes and elevates again when the air is expelled from the lungs (exhalation or expiration).

The larger and heavier right lung also has a middle lobe, a triangular section located in the upper portion. It is possible to remove one lobe without damaging the rest, which will continue to function as normal.

Each lung is connected to the heart and the windpipe by a system known as the root. Each root is made up of a bronchus, a pulmonary vein (the only veins that carry red oxygenated blood), a pulmonary artery (carries blood without oxygen to the lungs), lymphatic vessels (carriers of the clear, watery lymph fluid), nerves (messengers between the brain and various body parts), and bronchial arteries and veins (supply blood and nutrition to the lungs).

Each bronchus is a large airway that connects the trachea to the lungs. The single trachea divides into the two bronchial tubes (also called bronchi). Each bronchus enters a lung and then “branches” out, dividing and subdividing into pairs of smaller and finer tubes, creating what is known as the tracheobronchial tree.

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