Effects Of Exercise On Heart Rate Physical Education Essay

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Paula has just completed a marathon. Explain the mechanisms responsible for regulating and controlling her heart rate and breathing rate during the race and explain the changes, which occurred in the distribution of blood in her body during exercise:

Regulation and control of heart rate during exercise:

Cardiac Output:

When Paula is running, her cardiac output will increase. Cardiac output is the measure of the volume of blood that is pumped out of the heart each minute. The calculation of the cardiac output is dependent on the stroke volume and the heart rate. Stroke volume is the volume of blood that is pumped out by the heart in one beat. The heart rate is the amount of times the ventricles contract within each minute. (Biology Mad, 2004)The formulae to calculate the cardiac output is as follows:

Cardiac output = stroke volume x heart rate

The reason cardiac output increases when Paula is running, is because it allows oxygen and glucose to get to the muscles faster ,but it also means carbon dioxide, lactic acid and heat can be removed quicker. Running is predominantly an aerobic form of exercise meaning that it uses a lot of oxygen combined with glucose, to make both carbon dioxide, ATP (energy) and water (in the form of sweat). At times during Paula's race, she may be running anaerobically. This may occur when she is sprinting, for example. Here glucose is used, but both lactic acid and ATP will be formed.

The cardiovascular centre in the brain:

The cardiovascular centre in the brain controls Paula's heart rate. The cardiovascular centre is located in the medulla, and from here, it receives information from receptors located around Paula's body. Pressure receptors and chemoreceptors are located in the aortic and carotid bodies which are able to detect the pressure of the blood which is leaving Paula's heart and how oxygenated or deoxygenated the blood it is. The muscles also have receptors, which detect how much the muscles are stretching and the body temperature. The information given by these receptors to the cardiovascular centre is then sent by nerve impulses down the sympathetic nerve (increases heart rate) and parasympathetic (vagus) nerve (slows heart rate) to the Sino atrial node (SAN), which is located in the wall of the right atrium in the heart. http://click4biology.info/c4b/h/images/h5/Cardiac_centre.gif

Click 4 Biology (2011) The control of heart rate [online] Available from: http://click4biology.info [Accessed: January 21st 2013

Changes in the blood during exercise:

Many changes happen to Paula's blood when she exercises one of these being the secretion of nitrogen oxide. Nitrogen oxide is released in order for cardiac output to increase and occurs when oxygen levels in the blood decrease through exercise. Nitric oxide makes the smooth muscle in the arterioles relax which means the lumen of the arteriole gets wider (vasodilation.) This of course, allows more blood to flow through the arteriole and at a quicker rate. Because of this, the heart rate then increases along with the rate at which blood can flow through the body and then back to the heart. (M Jones, 2005)

Due to the greater volume of blood flowing through the heart, the muscles of the heart are stretched. This in turn, makes the heart contract more forcefully meaning that the stroke volume then increases. The stretching of the heart muscles also stimulates the SAN, which causes the heart to beat faster during exercise. (The Open University, 2004)

The other chemical changes within the blood during exercise are picked up by the chemoreceptors in the body. The main chemoreceptors are found:

In the walls of the aorta which detects changes in the blood as it leaves the heart

In the walls of the carotid artery which detects changes in the blood going to the brain

In the medulla which detects and monitors changes in the tissue fluid


ECC book (n.d) Regulation: Oxygen [online] Available from: http://ecc-book.com/html/respir_regulation.html [Accessed January 21st 2013]

The main changes in the blood, which take place during exercise, include:

increased carbon dioxide concentration

decreased oxygen concentration

increase in both body and blood temperature

decrease in blood pH due to carbon dioxide dissolving in the blood to form carbonic acid

Again, all these changes in the blood, which indicate exercise is taking place, are picked up by the chemoreceptors, and sent to the cardiovascular centre in the medulla. The medulla then sends nerve impulses to the SAN, which increases heart rate.

Regulation of ventilation during exercise

When Paula is running the rate (speed), at which she breathes and how deep she breathes (the volume of breath) will increase. When these two things are combined, you get something called the ventilation rate: which is the volume of air that is breathed into the lungs per minute. (Biology Mad, 2004)

The formula for the calculation of ventilation rate is as follows:

Breathing rate x tidal volume= ventilation rate

Tidal volume is the amount of air which is both inhaled and the exhaled during one respiratory cycle. (The Free Medical Dictionary, 2013)

The respiratory centre in the brain:

Both the breathing rate and the tidal volume are controlled in the medulla by the respiratory centre. The reason the ventilation rate increases during exercise is so that oxygen can diffuse into the blood faster to aid respiration and so toxins like carbon dioxide can diffuse out of the blood faster into the outside air. The ventilation rate is increased in the same way the heart rate is increased during exercise. The chemoreceptors in the carotid and aortic bodies detect that there is an increase in respiration, and that the concentration of carbon dioxide in the blood is higher, which subsequently means the pH of the blood has decreased. Nerve impulses from the respiratory centre in the brain make the intercostal muscles in the lungs and the diaphragm contract and relax faster thus increasing the ventilation rate. Before the carbon dioxide levels in the blood get too high stretch receptors in the muscles are able to send out impulses to make the ventilation rate increase. So in fact, Paula's ventilation rate would have increased anyway before carbon dioxide concentration became too high. (Biology Mad, 2004)

Redistribution of blood during exercise:

During Paula's marathon, greater amount of oxygenated blood will be needed in her working muscles. Of course, Paula's body will not gain any blood during exercise to allow greater blood flow to get to her muscles, so other parts of her body will have a greater reduction of blood going to it. The digestive system can easily cope with having less blood going to it during exercise, so during exercise the digestive blood vessels will undergo vasoconstriction. This allows the blood that is normally stored there to circulate around the body and to go to areas that need it most. However, her heart, brain and kidneys still need optimum amount of blood going to them to keep those organs functioning and to keep Paula alive. Vasodilatation of the blood vessels for these organs and the skeletal muscles allows greater blood flow. When the blood reaches the muscles, the maximum amount of oxygen will be unloaded by the blood, this amount also increases the higher the temperature of the blood. The amount of oxygen able to be taken up by the muscles also increases the higher the workload is. (Kent, 2000) During the marathon, waste products will start to build up in Paula's body if they are not taken away via the blood vessels. Sphincters are present at the capillary beds, which are sensitive to the concentration of carbon dioxide and lactic acid. These waste products help relax the capillaries in the muscles to allow more blood to flow through so they can be taken away efficiently. Once the concentration of waste products has returned to normal the sphincter at the capillary bed will contract again.

During the marathon, Paula's body will generate a lot of heat due to the respiration of her muscles. To ensure that her body does not over heat the capillaries close to her skin will dilate which will allow heated blood to the skin's surface. (Pickering, 2002)


Bodo Blog (2012) Vasodilation [online] Available from: http://bodo.web12.hubspot.com/blog/ [Accessed: January 21st 2013]