A3 - Respiratory System

• The respiratory system is responsible for getting oxygen into the body and getting carbon dioxide out of the body
• The oxygen in used to help produce energy which is used while we take part in sporting activities
• The process of creating energy also produces a waste produce called carbon dioxide which needs to be removed the body
• Breathing rate is controlled by both neural and chemical mechanisms
• The neural control id from the respiratory centre in the brain which is loacted in the medulla oblongata
• During exercise, when the body needs to produce more energy, the amount of carbon dioxide increases and dissolves in the blood stream to produce a weak acid
• As levels of carbon dioxide in the blood rise, this increases the acidity of the blood
• The increase acidity of the blood is sensed by chemoreceptors which are specialised cells within the arteries that detect chemical changes in the blood
• As the body does not like the acidity of the blood, the chemoreceptors signal the medulla oblongata
• The medulla oblongata then sends signals to the diaphragm and intercostal muscles by the phrenic nerves to increase the breathing rate to get rid of the excess carbon dioxide
• During exercise, breathing rate increases because carbon dioxide levels rise rather than the cells demanding more oxygen
• The diaphragm and internal and external intercostal muscles are the main respiratory muscles
• The diaphragm is a large dome-shaped muscle which covers the bottom of the ribcage
• The intercostal muscles are located between the ribs
• During rest, the diaphragm contracts and flattens and pushes the two sides of the ribcage away from each other, which results in an increase in the size of the thoracic cavity, forcing air into the lungs
• The external intercostal muscles also contract during inspiration to push the ribs upwards and outwards to increase the size of the chest cavity, drawing more air in than just the diaphragm contracting alone
• During expiration at rest, the process does not require any contraction of muscles
• During sport and exercise, additional skeletal muscles aid with the process of breathing
• During expiration, the internal intercostal muscles, rectus abdominis, transverse abdominis and the oblique muscles all contract to force air more quickly and more fully out of the lungs, ready for the next inspiration of air
• During inspiration, the sternocleidomastoid muscle aids the process by contracting to raise the upper half of the chest
• Minute Volume can be worked out using the following equation:

  VE = Frequency x Tidal Volume

  Frequency is the number of breaths per minute

  Tidal volume is the volume of air breathed in and out during one breath
• The amount of air we breathe in and out per minute is called the Minute Volume and is given the symbol VE
• Minute Volume can be worked out using the following equation:

  VE = Frequency x Tidal Volume

  Frequency is the number of breaths per minute

  Tidal volume is the volume of air breathed in an out during one breath
• To calculate VE at rest:

  The average breathing rate is around 12 breaths per minute. The average tidal volume is 0.5 L.

  Therefore, the Minute Volume at rest is:

  VE = 12 x 0.5 = 6 Litres
• When you start to exercise, you need to take more oxygen into your body in order for it to be used to help produce energy
• At the start of exercise, the increased oxygen demand occurs by breathing in more air and breathing out more air during each breath. This means tidal volume increases
• The majority of oxygen is transported in blood by haemoglobin with just 1.5% carried in the plasma
• Oxygen reacts with haemoglobin to make oxyhaemoglobin
• The reaction of oxygen with haemoglobin is temporary and completely reversible, which means that oxygen can be unloaded from haemoglobin
• The binding of oxygen to haemoglobin is dependent in the partial pressure of oxygen
• Oxygen combines with haemoglobin in oxygen-rich situations, such as in the lungs
• Oxygen is released by haemoglobin in places where there is little oxygen, such as in exercising muscle
• The oxygen dissociation curve is an S-shaped curve that represents the ease with which haemoglobin will release oxygen when it is exposed to tissues of different concentrations of oxygen. This means that when there is a small rise in the partial pressure of oxygen, haemoglobin will pick up and bin it oxygen to it easily
• Changes in blood carbon dioxide level and hydrogen ion concentration (pH) cause shifts in the oxygen dissociation curve. These shifts enhance oxygen release in tissues and increase oxygen uptake in the lungs. This is known as the Bohr Effect
• During exercise, the blood becomes more acidic because of the increased production of carbon dioxide
• This increase in carbon dioxide and decrease in pH shifts the dissociation curve to the right for a given partial pressure of oxygen, releasing more oxygen to the tissues
• In the lungs there is a low partial pressure of carbon dioxide and low hydrogen ion concentration which shifts the dissociation curve to the left for a given partial pressure of oxygen, and therefore enhances oxygen uptake
• As muscles exercise, they also increase in temperature. This has the effect of shifting the curve to the right, which means oxygen is released much more readily. Conversely, a decreased temperature will shift the curve to the left, which increases oxygen uptake