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This blood gas barrier is extremely thin (in humans, on average, 2.2 μm thick). It is folded into about 300 million small air sacs called alveoli [23] (each between 75 and 300 μm in diameter) branching off from the respiratory bronchioles in the lungs, thus providing an extremely large surface area (approximately 145 m 2) for gas exchange to ...
The lungs are suspended within the pleural cavity of the thorax. The pleurae are two thin membranes, one cell layer thick, which surround the lungs. The inner (visceral pleura) covers the lungs and the outer (parietal pleura) lines the inner surface of the chest wall. This membrane secretes a small amount of fluid, allowing the lungs to move ...
Small sacs called atria radiate from the walls of the tiny passages; these, like the alveoli in other lungs, are the site of gas exchange by simple diffusion. [108] The blood flow around the parabronchi and their atria forms a cross-current process of gas exchange (see diagram on the right).
The pulmonary arteries carry deoxygenated blood to the lungs, where carbon dioxide is released and oxygen is picked up during respiration. [3] Arteries are further divided into very fine capillaries which are extremely thin-walled. [4] The pulmonary veins return oxygenated blood to the left atrium of the heart. [3]
Arteries branch into small passages called arterioles and then into the capillaries. [19] The capillaries merge to bring blood into the venous system. [ 20 ] The total length of muscle capillaries in a 70 kg human is estimated to be between 9,000 and 19,000 km. [ 21 ]
Lung structure, alveolar organization, and alveolar capillaries contribute to the physiological mechanism of ventilation and perfusion. [ 1 ] Ventilation–perfusion coupling maintains a constant ventilation/perfusion ratio near 0.8 on average, with regional variation within the lungs due to gravity.
A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the innermost layer of an artery or vein), consisting of a thin wall of simple squamous endothelial cells. [2]
Bronchial arteries carry oxygenated blood to the lungs; Pulmonary capillaries, where there is exchange of water, oxygen, carbon dioxide, and many other nutrients and waste chemical substances between blood and the tissues; Bronchial veins drain venous blood from the large main bronchi into the azygous vein, and ultimately the right atrium.