Lung

The lung is the essential organ of respiration in air-breathing vertebrates.

Mammalian lungs

The lungs of mammals have a spongy texture and are honeycombed with epithelium having a much larger surface area in total than the outer surface area of the lung itself. The lungs of humans are typical of this type of lung. The environment of the lung is very moist, which makes them a hospitable environment for bacteria. Many respiratory illnesses are the result of bacterial or viral infection of the lungs.

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Breathing is largely driven by the diaphragm below, a muscle that by contracting expands the cavity in which the lung is enclosed. The rib cage itself is also able to expand and contract to some degree.

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As a result, air is sucked into and pushed out of the lungs through the trachea and the bronchial tubes or bronchi; these branch out and end in alveoli which are tiny sacs surrounded by capillaries filled with blood. Here oxygen from the air diffuses into the blood, where it is carried by hemoglobin.

Related Topics:
Trachea - Bronchial tubes - Alveoli - Capillaries - Oxygen - Diffuses - Hemoglobin

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The deoxygenated blood from the heart reaches the lungs via the pulmonary artery and, after having been oxygenated, returns via the pulmonary veins.

Related Topics:
Heart - Pulmonary artery - Pulmonary vein

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Anatomy

The lungs are located inside the thoracic cavity, protected by the bony structure of the rib cage and enclosed by a double-walled sac called pleura. The inner layer of the sac (visceral pleura) adheres tightly to the lungs and the outer layer (parietal pleura) is attached to the wall of the chest cavity. The two layers are separated by a thin space called the pleural cavity that is filled with pleural fluid; this allows the inner and outer layers to slide over each other, and prevents them from being separated easily. The left lung is smaller than the right one to give way for the heart.

Related Topics:
Thoracic cavity - Rib cage - Pleura - Visceral pleura - Parietal pleura - Pleural cavity - Pleural fluid

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The lungs attach to the heart and trachea through structures that are called the "roots of the lungs." The roots of the lungs are the bronchi, pulmonary vessels, bronchial vessels, lymphatic vessels, and nerves. These structures enter and leave at the hilus of the lung.

Related Topics:
Heart - Trachea - Bronchi

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The lungs are divided into lobes by the horizontal and oblique fissures. The right lung has three lobes and the left lung has two. A unique feature of the left lung is the cardiac notch, which helps create the lingula (Latin for "tongue") of the left lung.

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The lungs are connected to the upper airway by the trachea and bronchi. The trachea runs down the neck and divides into left and right bronchi behind the sternal angle. The right main bronchus is shorter and runs more vertically than the left. For this reason, it is more common to aspirate foreign objects into the right lung. The bronchi enter the lung and branch out to form the bronchial tree. The bronchi divide into smaller bronchioles, which terminate into alveoli. An alveolus is composed of respiratory tissue and is the site of gas exchange in the lung.

Related Topics:
Bronchus - Bronchioles

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The blood supply to the lungs is from two sources: the pulmonary vessels and the bronchial vessels. The bronchial vessels support the nonrespiratory tissue and the pulmonary vessels provide support to the respiratory tissue.

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The pulmonary arteries carry deoxygenated blood that has returned to the heart from the venous system to the lungs to be reoxygenated. The pulmonary veins carry oxygenated blood back to the heart to go to the arterial system. The right and left pulmonary arteries arise from the pulmonary trunk and carry "venous" blood to their respective lungs. The pulmonary veins, two on each side, carry "arterial" blood to the left atrium of the heart.

Related Topics:
Pulmonary arteries - Pulmonary veins

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The bronchial arteries that supply the nonrespiratory tissue of the lung arise from different sources. The left bronchial arteries come off of the thoracic aorta, however, the right bronchial artery has a variable source.

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