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A pulmonary alveolus (pl. alveoli; from Latin alveolus 'little cavity'), also called an air sac or air space, is one of millions of hollow, distensible cup-shaped cavities in the lungs where pulmonary gas exchange takes place. [1] Oxygen is exchanged for carbon dioxide at the blood–air barrier between the alveolar air and the pulmonary ...
Intraalveolar blood vessels (pulmonary capillaries) are thin walled vessels adjacent to alveoli which are subject to the pressure changes described by zones 1-3. Flow in zone 4 is governed by the arteriointerstitial pressure difference (Pa − Pi). This is because as Pi rises, the arterial caliber is reduced, thereby increasing resistance to flow.
The most notable shared characteristic is the presence of cortical (near the surface) alveoli (sacs). These are flattened vesicles (sacs) arranged as a layer just under the membrane and supporting it, typically contributing to a flexible pellicle (thin skin). In armored dinoflagellates they may contain stiff plates.
The rest of the difference is due to the continual uptake of oxygen by the pulmonary capillaries, and the continual diffusion of CO 2 out of the capillaries into the alveoli. The alveolar pO 2 is not routinely measured but is calculated from blood gas measurements by the alveolar gas equation.
Alveoli and their capillary networks 3D medical illustration showing different terminating ends of bronchioles. Alveoli consist of two types of alveolar cell and an alveolar macrophage. The two types of cell are known as type I and type II cells [32] (also known as pneumocytes). [3] Types I and II make up the walls and alveolar septa.
The alveoli are tiny air sacs in the lungs where gas exchange takes place. The mean number of alveoli in a human lung is 480 million. [11] When the diaphragm contracts, a negative pressure is generated in the thorax and air rushes in to fill the cavity. When that happens, these sacs fill with air, making the lung expand.
Transpulmonary pressure is the difference between the alveolar pressure and the intrapleural pressure in the pleural cavity. During human ventilation, air flows because of pressure gradients. P tp = P alv – P ip. Where P tp is transpulmonary pressure, P alv is alveolar pressure, and P ip is intrapleural pressure.
Ventilation–perfusion coupling is the relationship between ventilation and perfusion in the respiratory and cardiovascular systems. [1] Ventilation is the movement of air in and out of the lungs during breathing. [2] Perfusion is the process of pulmonary blood circulation, which reoxygenates blood, allowing it to transport oxygen to body tissues.