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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 ...
An increase in Pi causes extraalveolar blood vessels to reduce in caliber, in turn causing blood flow to decrease (extraalveolar blood vessels are those blood vessels outside alveoli). Intraalveolar blood vessels (pulmonary capillaries) are thin walled vessels adjacent to alveoli which are subject to the pressure changes described by zones 1-3.
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 ...
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).
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.
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.
Exchange of gases in the lung occurs by ventilation and perfusion. [1] Ventilation refers to the in-and-out movement of air of the lungs and perfusion is the circulation of blood in the pulmonary capillaries. [1] In mammals, physiological respiration involves respiratory cycles of inhaled and exhaled breaths.
A pulmonary contusion is a bruise of the lung tissue caused by trauma. [35] Damaged capillaries from a contusion can cause blood and other fluids to accumulate in the tissue of the lung, impairing gas exchange. Pulmonary edema is the buildup of fluid in the parenchyma and alveoli. An edema is usually caused by left ventricular heart failure, or ...