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This blood–air barrier is extremely thin (approximately 600 nm-2μm; in some places merely 200 nm) to allow sufficient oxygen diffusion, yet it is extremely strong. This strength comes from the type IV collagen in between the endothelial and epithelial cells. Damage can occur to this barrier at a pressure difference of around 40 millimetres ...
The alveolar membrane is the gas exchange surface, surrounded by a network of capillaries. Oxygen is diffused across the membrane into the capillaries and carbon dioxide is released from the capillaries into the alveoli to be breathed out. [7] [8] Alveoli are particular to mammalian lungs.
Carbon dioxide (CO 2) is transferred from returning blood back into gaseous form in the lungs and exhaled through the lower respiratory tract and then the upper, to complete the process of breathing. Unlike the trachea and bronchi , the upper airway is a collapsible, compliant tube.
The total concentration of carbon dioxide (in the form of bicarbonate ions, dissolved CO 2, and carbamino groups) in arterial blood (i.e. after it has equilibrated with the alveolar air) is about 26 mM (or 58 ml/100 ml), [27] compared to the concentration of oxygen in saturated arterial blood of about 9 mM (or 20 ml/100 ml blood).
Tracheal tubes can be used to ensure the adequate exchange of oxygen and carbon dioxide, to deliver oxygen in higher concentrations than found in air, or to administer other gases such as helium, [27] nitric oxide, [28] nitrous oxide, xenon, [29] or certain volatile anesthetic agents such as desflurane, isoflurane, or sevoflurane.
Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a biological membrane that forms the boundary between an organism and its extracellular environment.
Within the lungs, the ventilation process specifically involves organs like respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. For the perfusion process, the circulatory organs of the cardiovascular system such as the heart, pulmonary arteries, pulmonary veins, and alveolar capillaries are involved.
Dead space reduces the amount of fresh breathing gas which reaches the alveoli during each breath. This reduces the oxygen available for gas exchange, and the amount of carbon dioxide that can be removed. The buildup of carbon dioxide is usually the more noticeable effect unless the breathing gas is hypoxic as occurs at high altitude.