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A [lung] is one of the two main respiratory organs. It is an organ filled with minute air sacs or alveoli, giving its parenchyma the look and feel of a spongy tissue. Its function is the reoxygenation of blood.
Each lung is located on each side of the thoracic cavity, each one surrounded by a serosa membrane called "pleura". The pleura forms a sac that surrounds the lung and also lines the thoracic wall. The pleura that lines the thoracic wall is called "parietal pleura", while the pleura that lines the lung is called the "visceral pleura". An extension of the visceral pleura inferior to the pulmonary hilum forms the pulmonary ligament.
A lung has three surfaces and an apex. The inferior surface, base, or diaphragmatic surface; the medial surface or mediastinal surface, as if forms the lateral wall of the mediastinum; and the lateral or costal surface.
The lungs are also divided into lobes. The right lung has three lobes: superior, middle, and inferior while the left lung only has two lobes: superior and inferior. Because the heart has a left-sided tilt the left lung is slightly smaller than the right lung.
There are four structures that enter or leave the lung and they are found at the pulmonary hilum in the medial surface of the lung. These structures are: the main or primary bronchus, the pulmonary artery, and two pulmonary veins.
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