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The blood–air barrier or air–blood barrier, (alveolar–capillary barrier or membrane) exists in the gas exchanging region of the lungs. It exists to prevent air bubbles from forming in the blood , and from blood entering the alveoli .
Perfusion is the delivery of oxygen-rich blood to the body tissues through the lymphatic system or circulatory system. [6] The primary function of perfusion is the efficient removal of cellular waste and nutrition supply during gas exchange. Perfusion occurs during heart contraction when the oxygenated blood is pumped into the arteries.
Perfusion is the mass flow of blood through the tissues. Dissolved materials are transported in the blood much faster than they would be distributed by diffusion alone (order of minutes compared to hours). [18] The dissolved gas in the alveolar blood is transported to the body tissues by the blood circulation.
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.
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.
Diffusing capacity of the lung (D L) (also known as transfer factor) measures the transfer of gas from air in the lung, to the red blood cells in lung blood vessels. It is part of a comprehensive series of pulmonary function tests to determine the overall ability of the lung to transport gas into and out of the blood.
The blood flow through the bird lung is at right angles to the flow of air through the parabronchi, forming a cross-current flow exchange system (Fig. 19). [ 44 ] [ 46 ] [ 49 ] The partial pressure of oxygen in the parabronchi declines along their lengths as O 2 diffuses into the blood.
The term capillary exchange refers to all exchanges at microcirculatory level, most of which occurs in the capillaries. Sites where material exchange occurs between the blood and tissues are the capillaries, which branch out to increase the swap area, minimize the diffusion distance as well as maximize the surface area and the exchange time. [4]