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The effect of exercise on gas exchange and breathing

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Practical Four The effect of exercise on gas exchange and breathing Authors Greg Deane, Mike Doree, Emily Gibbs, Holly Franklin, Leah Frisby, Rhian Jones, Emma Kirk, Charlotte Hall Aim * To investigate the gas composition air expired at rest and during exercise. * To find out how moderate exercise for 3 minutes affects the percentages of oxygen and carbon dioxide in expired air, tidal volume, respiratory rate and respiratory minute volume. Introduction The respiratory system can be divided into to sections: the upper and lower respiratory system. The upper respiratory system consists of the nasal and oral cavities and the pharynx. The upper respiratory system warms and moistens the air before it reaches the lungs. The lower respiratory system consists of the trachea, the lungs and the diaphragm. The trachea, bronchi and bronchioles are the conducting zone and do not have a gas exchange role. The alveoli are the respiratory zone and gas exchange solely occurs here. The lungs are divided into lobes; the right lung divided into three lobes (superior, middle and inferior) whilst the left lung is only divided into two lobes (superior and inferior). The primary functions of the respiratory system are: * Exchange of oxygen from the atmosphere to the blood and of carbon dioxide from the blood to the atmosphere. * Providing protection from inhaled pathogens and irritants * Regulation of plasma pH through the CO2/HCO3 system * Allowing vocalization Air passes from the upper respiratory system into the lower via the trachea. The trachea is a flexible but strong structure made up of rings of cartilage separated by smooth muscle. The inside of the trachea is lined with a layer of epithelial cells, which are ciliated. There are also mucus producing goblet cells in the layer. These act as a filter as dust particles, bacteria and other irritants, which may damage the lung stick to the mucus. ...read more.


Dopamine is a neurotransmitter and stimulates the sensory nerves, increasing the frequency of impulses sent to respiratory centres and therefore increases ventilation. This reflex doesn't appear to play a vital role in day-to-day ventilation as the arterial PO2 has to be significantly reduced. However it is important when PO2 falls below 60mmHg for example when at high altitudes or during hypoventilation. During exercise a noticeable change in PCO2 and PO2 would be expected however this is not the case, as their levels remain nearly constant. This is due to ventilation keeping pace with metabolism and removing CO2 as fast as its produced and supplying O2 as fast as its consumed. As stated before the respiratory system is divided in the conducting and respiratory zones. As the conducting zone does not perform gas exchange it is referred to as the anatomical dead space and has a volume of around 150ml. The volume of air, which leaves the alveoli to be exhaled, is 500ml but only 350ml reaches the atmosphere as 150ml remains in the airways or dead space. Each time air is inhaled only 350ml out of the 500ml tidal volume is fresh air, the other 150ml is stale air from the last exhalation. Alveolar ventilation is a more accurate way to look at efficiency of ventilation, as pulmonary ventilation doesn't take into consideration the volume of the anatomical dead space. Alveolar ventilation = (tidal volume - dead space) x breaths per min Pulmonary ventilation or respiratory minute volume = tidal volume x breaths/min Therefore an individual with a small tidal volume but high number of breaths per minute may have the same respiratory minute volume as an individual with a large tidal volume but lower number of breaths per minute or ventilation rate. However the individual with the small tidal volume would have much lower alveolar ventilation and would be breathing less efficiently as they use a lot of effort in moving the air back and forth in the dead space. ...read more.


So when exercise was under taken the proprioceptors may have been partly responsible for the increase in respiratory rate during exercise. There were variations in the results for the group; this could be due to a numbers of factors. These factors are: * Age * Fitness * Whether the individual was a smoker or former smoker * Whether the individual had a cold or other illness which may reduce their ability to breath normally * Height or size * Gender The during exercise respiratory rate had the most variation and the factors above would tend to affect this, as taller people tend to have a larger tidal volume compared to shorter people and so breath more deeply rather than more quickly. The same is true for fitness as the fitter people tend to have a larger tidal volume compared to less fit people. The pace or intensity at which exercise was taken would have had an effect on the during exercise results. Not all the may have been group following the same pace of exercise, to improve this I would use a treadmill as a form of exercise as the pace can be determined and the group must stick to the pace to avoid falling over. Another problem is that breathing is controlled by automatic and voluntary systems. Therefore an individual could in theory slow or quicken their breathing voluntarily by looking at the screen. To prevent this the individuals would either face the opposite direction or wear a blindfold. A problem found with the stepping exercise was that the breathing pattern during exercise had a stepping rhythm as shown in the trace below. This meant it was difficult to calculate the number of breaths and also the person may have expired more than they inspired, which could be a reason why the volume of oxygen expired per minute increased during exercise. Control During exercise The during exercise trace doesn't have peak as the results go out of range as the equipment needs to be adjusted. ...read more.

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