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post in: Video Date:25 Oct 2017, 08:35 views:2939
Morton Lippmann, the respiratory system extends from the breathing zone just outside of the nose and mouth through the conductive airways in the head and thorax to the alveoli, where respiratory gas exchange takes place between the alveoli and the capillary blood flowing around them.
Its prime function is to deliver allergy oxygen (O2) to the gas-exchange region of the lung, where it can diffuse to and through the walls of the alveoli to oxygenate the blood passing through the alveolar capillaries as needed over a wide range of work. In addition, the system must also: (1) remove an equal volume of carbon dioxide entering the lungs from the alveolar capillaries; (2) maintain body temperature and water vapour saturation within the lung airways (in order to maintain the viability and functional capacities of the surface.
It must accomplish all of these demanding tasks continuously over a lifetime, and do so with high efficiency in terms of performance and energy utilization.
The system can be abused and overwhelmed by severe insults such as high concentrations of cigarette smoke and industrial dust, or by low concentrations of specific pathogens which attack or destroy its defence mechanisms, or cause them to malfunction. Its ability to overcome or compensate for such insults as competently as it usually does is a testament to its elegant combination asthma of structure and function. Mass Transfer, the complex structure and numerous functions of the human respiratory tract have been summarized concisely by a Task Group of the International Commission on Radiological Protection (icrp 1994 as shown in figure.1.
The conductive airways, also known as the respiratory dead space, occupy about.2 litres. They condition the inhaled air and distribute it, by convective asthma (bulk) flow, to the approximately 65,000 respiratory acini leading off the terminal bronchioles.
As tidal volumes increase, convective flow dominates gas exchange deeper into the respiratory bronchioles.
In any case, within the respiratory acinus, the distance from the convective tidal front to alveolar surfaces is short enough so that efficient CO2-O2 exchange takes place by molecular diffusion. By contrast, airborne particles, with diffusion coefficients smaller by orders of magnitude than those for gases, tend to remain suspended in the tidal air, and can be exhaled without deposition. Figure.1 Morphometry, cytology, histology, function and structure of the respiratory tract and regions used in the 1994 icrp dosimetry model.