Functions of the Respiratory System
The primary function of the respiratory system is the supply of oxygen to the blood so this in turn delivers oxygen to all parts of the body. The respiratory system does this while breathing is taking place. During the process of breathing we inhale oxygen and exhale carbon dioxide. This exchange of gases takes place at the alveoli. The average adult's lungs contain about 600 million of these spongy, air-filled sacs that are surrounded by capillaries. The inhaled oxygen passes into the alveoli and then diffuses through the capillaries into the arterial blood. Meanwhile, the waste-rich blood from the veins releases its carbon dioxide into the alveoli. The carbon dioxide follows the same path out of the lungs when you exhale.
“External respiration is the means by which oxygen from the air passes into the blood stream for transportation to the tissue cells and carbon dioxide is collected and transferred back to the lungs and expelled from the body.” www.pe.edu.net
“Internal respiration involves the vital chemical activities that take place in every living cell requiring oxygen and glycogen to combine and release energy, water and carbon dioxide.” www.brianmac.com/respsyst
Gaseous Exchange
Gaseous exchange occurs primarily by the diffusion between air in the aveoli (tiny sacs) and the blood in the capillaries surrounding the walls. :Adams et al BTEC Sport Level 3
Diffusion occurs when molecules move from an area of high concentration (of that molecule) to an area of low concentration.This occurs during gaseous exchange as the blood in the capillariessurrounding the alveoli which has a lower oxygen concentration of Oxygen than the air in the alveoli which has just been inhaled both the alveoli and capillaries have walls which are only one cell thick and allow gases to diffuse across them.The same happens with Carbon Dioxide (CO2). The blood in the surrounding capillaries has a higher concentration of CO2 than the inspired air due to it being a waste product of energy production. Therefore CO2 diffuses the other way, from the capillaries, into the alveoli where it can then be exhaled.
The concept of partial pressure applies to the diffusion of gases from a gas mixture to a gas in solution and vice versa. Partial pressure is used to describe a mixture of gases. It is defined as the pressure that any one gas would exert on the walls of the veins and arteries if it was the only gas
Dalton’s law states “That the sum of the partial pressures of all of the gases in a mixture will be equal to the total pressure of that mixture.” J.H.Emannuel et al The Body Book (2001)
Partial pressure is also used to describe dissolved gases, particularly in the blood stream, In this case, the partial pressure of a gas dissolved in blood is the partial pressure that the gas would have, if the blood were allowed to “equilibrate” with a volume of gas. The main reason is that when blood is exposed to fresh air in the lungs, it equilibrates completely so that the partial pressure of oxygen in the air spaces in the lungs is equal to the partial pressure of oxygen in the blood. This is demonstrated by the “altitude oxygen calculator”. This says the partial pressure of oxygen in the arteries is slightly less than the partial pressure of oxygen in the lungs; this is because there is always a little bit of blood that passes through the lungs without meeting an air space.
Mechanisms of Breathing
Pulmonary ventilation, which is breathing is the processs in which air is transported throughout the body, into and out of the lungs and is considered to have two separate phases. These phases are inspiration and expiration
Breathing is the main function in what the respiratory system controls and are regulated by the respiratory centres in the brain and the stretch receptors within the air passages and lungs. This requires the thorax in the throat to increase in size so that it can allow air to be taken in, then it will decrease so that air can be forced out.
“The action of breathing in and out is due to changes of pressure within the thorax, in comparison with the outside. When we inhale the intercostal muscles (between the ribs) and diaphragm contract to expand the chest cavity.”www.pe.edu.com
Inspiration
Inspiration is when the intercostal muscles contract to lift the ribs upwards and outwards to allow air into the lug, therefore inflating. the diaphragm is forced downwards and the sternum forwards. This is when there is an expansion in the thorax in every direction which causes a drop in pressure below that of atmospheric pressure, this then encourages air to flood into the lungs, at this point the oxygen is exchanged (see gaseous exchange) for carbon dioxide through the capillary walls.
Expiration
Expiration then comes after inspiration as it is when the intercostal muscles that have contracted to lift the ribs up relax. The diaphragm then extends upwards and the ribs and sternum collapse. This then allows the pressure within the lungs to increase and get forced out. This is when greater amounts of oxygen are required, requiring the intercostal muscles in the stomach and the diaphragm to work a lot harder
Lung Volumes
“Lung volumes and lung capacities refer to the volume of air associated with different phases of the respiratory cycle. Lung volumes are directly measured. Lung capacities are inferred from lung volumes.
The average total lung capacity of an adult human male is about 6 litres of air, but only a small amount of this capacity is used during normal breathing.” www.alevelstudy.co.uk/physicaled/resp
Our Respiratory Rate is the amount of air in which we breathe in over a duration of time, e.g 1 Minute. For an 18-21 year old this is around 12 breaths per minute at rest during this time around 6.5 litres of air passes through our respiratory system, this is significantly increased by exercise to as much as 30-40 breaths per minute.
Tidal Volume
Tidal volume is a term that is used to describe how much we breathe; it measures the air we breathe in and out with each breath. When there are normal conditions, the tidal volume is around 500cm3 of air breathed, inspiration and expiration (inhale and exhale). Tidal volume is defined as the amount of air exchanged in normal breathing. In other words, tidal volume is the differential between air inhaled and exhaled by a particular person. Typically, when calculating tidal volume and other respiratory scientific figures, researchers will calculate tidal volume first. When exercising our Tidal Volume increases because we are breathing at a faster rate and your muscles are using up the oxygen at a quicker rate hence a need for more oxygen therefore our body is increasing the Tidal Volume to allow more oxygen to be consumed and meet the muscles oxygen demands.
Inspiratory Reserve Volume
This is quite simply the amount you breathe when you breathe in deeply; it is possible to breathe in more than the average 350cm3 of air that reaches the alveoli in the lungs. During exercise it is vitally important. The whole reserve volume is the added to the tidal volume that adds up to around 3,000cm3 of air. This is the inspiratory reserve volume.
(Adapted from Adams et al BTEC Sport)
Experiatory Reserve Volume
Expiratory reserve volume (ERV) refers to the extra volume of air that can be exhaled with maximum effort beyond the level reached at the end of a normal, passive exhalation. “This can be up to 1,500 cm3 and it is the amount of the additional air that can be breathed out after normal expiration” Adams et Al BTEC Sport
At the end of normal breath our lungs will contain the residual volume plus the expiratory reserve volume, when we exhale as much as psychically possible, what is left is known as the residual volume.
Vital Capacity
This is the volume that you can actually move out of the lung if you try your hardest after the deepest breath you can take. This is after maximum inspiration which is around 4,800cm3
Residual Volume
This is what is left after all of the air in the lungs in fully expelled of the air, “they are never completely expelled of air as they would collapse” Adams et al BTEC Sport.
The air that is left after the maximum expiration, when you breathe out as hard as we can it is known as residual volume. This is around 1,600cm3 for an average male adult.
Total lung capacity
This is our total lung capacity after we have inhaled as deeply and as much we can . This is improved through endurance exercise.
The respiratory system will become more efficient as a result of strenuous and low intensity long exercise. An affect of exercise is that the respiratory muscles increase in strength. This will result in larger respiratory volumes allowing more oxygen to be diffused into the blood and lungs this will lead to an increase in the efficiency of gaseous exchange.
Control of Breathing
There are many two types of control of breathing these are:
• Neural Control
• Chemical Control
In the human body there are 3 different types of receptors which affect the activity in the respiratory system.
They are the Proprioreceptors which is the type of receptor that controls the muscles, tendons and joints. They inform the control centre that is situated in the brain, hence “Neural Control” that movement has increased which will then mean that our body will need to work harder to get oxygen in and remove carbon dioxide and other waste products.
Chemoreceptor’s detect a decrease in the acidity of the blood due to the build up of lactic acid and CO2 by doing this the chemoreceptor’s need to get all waste products out of the system This will show that rate of gas exchange needs to increase.
The final receptor is called the Baro-receptor. This detects a large increase in partial pressure.
Bibliography
www.brainmac.com
www.alevelstudy.com
www.pe.edu.com
BTEC Sport Adams et al
The Body Book J.H Emmanuel
