During ventilation what is the direction of the convection current ?
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Convection is the movement of air (or another fluid) in respond to differetial densities, differential pressures, and similar "setups" that might drive mass movement. Convection can be forced or natural, and this makes answering this question much more difficult. That said, consider the instance of natural convection during ventilation.
In a ventilation lineup powered by natural convection, we'd see hoter, less dense air rising, and cooler, more dense air slipping in underneath it. That's the general way a convection cycle begins. The location of a heat source will help determine what's happening. If an oven is on and hot, it will heat air in its vicinity. This hot air will rise and be displaced by cooler air. The heated air will cool in the area higher up and sink, and the cooler air that moved in near the oven will be heated and rise. A "circle" or cycle of convection will have been set up.
There are countless other convection scenarios that can be scripted for a given ventilation situation. But with natural convection, there will be rising air (which is less dense) near the heat source, and cooler (more dense) air will slide in to replace it. The cooler air will have to come from somewhere, and as the hot air will eventually cool, it will sink to "complete the circle" of convection. With something like a simple diagram and a bit of thought based on what has been set down here, an investigator could summarize a convection cycle for ventilation using natural convection.
How does the body know to increase ventilation rate during exercise?
The truth is that nobody really knows what causes the increase of ventilaion in exercise and keeps it close to metabolic rate. CO2 is a powerful stimulator of breathing and an increase of CO2 is produced by the body in exercise. This increase however is only found in the venous circulation where there are no chemoreceptors to detect it. All of the know chemoreceptors (aortic, carotid and central chemoreceptors) are found in the arterial side where there is relativly no fluctuation in the partial pressure of CO2. Furthermore, when the chemoreceptors are denervated breathing can still increase as normal. Other possible candidates that are involved in increasing breathing are, muscle chemoreceptors, efferencekopie, proprioreceptors, catecholamines, potassium levels...but all are either unlikley to be a cause or are impossible to measure (e.g. efferencekopie). So the textbooks will tell you that ventilation remains close to metabolic rate, but they dont say (beacuse they dont know) how it is kept close to metabolic rate. For further information on this look at works by Mike Parkes (university of Birmingham, united kingdom).
In a ventilation lineup powered by natural convection, we'd see hoter, less dense air rising, and cooler, more dense air slipping in underneath it. That's the general way a convection cycle begins. The location of a heat source will help determine what's happening. If an oven is on and hot, it will heat air in its vicinity. This hot air will rise and be displaced by cooler air. The heated air will cool in the area higher up and sink, and the cooler air that moved in near the oven will be heated and rise. A "circle" or cycle of convection will have been set up.
There are countless other convection scenarios that can be scripted for a given ventilation situation. But with natural convection, there will be rising air (which is less dense) near the heat source, and cooler (more dense) air will slide in to replace it. The cooler air will have to come from somewhere, and as the hot air will eventually cool, it will sink to "complete the circle" of convection. With something like a simple diagram and a bit of thought based on what has been set down here, an investigator could summarize a convection cycle for ventilation using natural convection.
How does the body know to increase ventilation rate during exercise?
The truth is that nobody really knows what causes the increase of ventilaion in exercise and keeps it close to metabolic rate. CO2 is a powerful stimulator of breathing and an increase of CO2 is produced by the body in exercise. This increase however is only found in the venous circulation where there are no chemoreceptors to detect it. All of the know chemoreceptors (aortic, carotid and central chemoreceptors) are found in the arterial side where there is relativly no fluctuation in the partial pressure of CO2. Furthermore, when the chemoreceptors are denervated breathing can still increase as normal. Other possible candidates that are involved in increasing breathing are, muscle chemoreceptors, efferencekopie, proprioreceptors, catecholamines, potassium levels...but all are either unlikley to be a cause or are impossible to measure (e.g. efferencekopie). So the textbooks will tell you that ventilation remains close to metabolic rate, but they dont say (beacuse they dont know) how it is kept close to metabolic rate. For further information on this look at works by Mike Parkes (university of Birmingham, united kingdom).
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