Task 1
a.
1. Nasal Cavity The nose is the route for entry of air into the respiratory system. When air is drawn in through the nostrils, it enters the nasal cavity. This is a space that is separated into two by the septum, and it is positioned above and separated from the oral cavity by the palate. The nose is lined with mucous which help moisten the passageway. Three structures within the nasal cavity called the turbinates exist to increase surface area of air flowing through and for this air to be warmed. The mucous lining the nasal cavity allows foreign particles to be trapped before the warmed air continues through to the pharynx.
2. Mouth/Oral Cavity The mouth/oral cavity is part of the airway of the respiratory system, and is connected to the pharynx. Air inhaled into the mouth will pass through the oral cavity to the pharynx to the lungs, and air will also be exhaled out of the mouth during expiration. Air that enters the mouth is not warmed like it is in the nasal cavity. The mouth allows more air to enter the body quickly because of its shorter distance and larger diameter.
3. Larynx The larynx is located directly below the pharynx and consists of pieces of cartilage held together with membranes and ligaments. The cartilage of the larynx ensures the structure does not collapse as air passes through to the trachea.
4. Right Lung The lungs are large spongy organs that are protected by the ribcage. The lungs are responsible for bringing oxygen into the body and removing carbon oxide from the body. The inside of the lungs consist of millions of air sacs, known as alveoli at the ends of very fine tubes called bronchioles. The alveoli within the lungs is the location where the exchange of oxygen and carbon dioxide occurs.
5. Right main bronchus The bronchus connects the trachea to the lungs. The trachea divides into two main bronchus – a right and a left. They are composed of a large branching system of passages that reach the alveoli of the lungs where gas exchange occurs.
6. Diaphragm The diaphragm is a skeletal muscle, in a dome shape, that is positioned across the bottom of the chest cavity. The contraction and relaxation of this muscle helps pump carbon dioxide out of the lungs and oxygen in to the lungs. Its dome shape aids this process by its ability to flatten, allowing the enlarging of the chest cavity and oxygen to be pulled into the lungs.
7. Pharynx The pharynx is a funnel like tube that acts as a passageway for air to the lungs. The pharynx is lined with thick mucosal epithelium – it is the thickest in the pharynx than in any other part of the respiratory system. This is for the protection of the tissues from any trauma from food – be this abrasive or chemical.
8. Trachea The trachea is also known as the windpipe. It is a tube that begins at the larynx and ends at just below the sternum. The function of the trachea is for the passage of air through to the lungs for respiration. When it reaches just below the sternum, it divides into two bronchi, which then enter each of the lungs.
9. Left primary bronchus The trachea divides into two smaller tubes called the bronchi – the left main bronchus and the right main bronchus. The branch system from the left bronchus enters the left lung and reaches the alveoli.
10. Bronchi The bronchi is the part of the respiratory system that connects the primary bronchus to the bronchioles and then the alveoli. Bronchi are smaller passageways than bronchus and upon dividing into smaller airways they will be known as bronchioles. Bronchi may also be known as secondary or tertiary bronchi – tertiary being the smallest passages before branching off to bronchioles.
11. Alveoli Alveoli are cup-shaped cavities within the lungs where gas exchange of oxygen and carbon dioxide between the blood and air occurs. Alveoli have a large surface area, a lining one cell thick and a rich blood supply to ensure the efficient exchange of oxygen and carbon dioxide gases by diffusion.
b.
Gas exchange occurs in the lungs in tiny air chambers located at the end of each bronchiole. These chambers contain many cavities which are called alveoli. The alveoli in the lungs are structured so that an efficient exchange of oxygen and carbon dioxide is guaranteed.
The lining of the alveoli cavity is just one cell thick and consists of simple squamous epithelial cells. This lining is permeable, and the thin walls ensure the gases do not have far to travel for efficient exchange and so diffusion can occur much quicker and easier.
The shape of the alveoli is also adapted for its function – a very large surface area is produced by folds in the walls and this increases the amount of exchange that can occur.
The alveoli have a rich blood supply thanks to its location, surrounded by capillaries. A good blood supply is required for efficient gas exchange because a concentration gradient is needed between the air in the alveoli and in the blood. This is because the blood is constantly bringing carbon dioxide in and taking oxygen away – if the blood supply was poor and the maximum concentration gradient was non-existent, this efficient exchange of gases could not occur.
Finally, the alveoli have good ventilation. Waste carbon dioxide is constantly removed and replaced with oxygen and this also assists the maintenance of a maximum concentration gradient between the air in the alveoli and the blood. Therefore, this ensures the gas exchange is efficient.
c.
The trachea is also known as the windpipe. It is a tube, around 4 inches in length with a diameter smaller than an inch. The trachea is located directly below the larynx and ends just below the sternum. Here, it splits into two passageways known as bronchi – the right main bronchi and the left main bronchi. The trachea consists of around 20 tough, C-shaped cartilage rings, and the back section of the tube is made up of muscle, along with connective tissue. The inner lining of the trachea is composed of moist mucosa tissue. The main function of the trachea is for the passage of air through to the lungs for respiration. In inspiration, the trachea will slightly widen and lengthen, and then return to its original position during expiration.
The structure of the trachea is such that the integrity of the airway is ensured – the tough cartilage ensures the passageway does not fold in. Because the rings are C-shaped, and not full circles, this allows for flexibility where the trachea needs to widen during inspiration. The muscle and connective tissue at the back of the trachea allow for the contraction of the oesophagus – during swallowing the oesophagus is protected by damage from the cartilage because of the muscle and tissue in its position at the back of the trachea. The mucus lining of the trachea provides protection for the lungs and body – it will trap foreign bodies to ensure the prevention of their entry into the lungs, where they could become harmful. When the mucus has trapped the foreign substance, it expels it upwards where it can either be swallowed or expelled out of the mouth. If foreign substances managed to penetrate into the trachea, the cilia become irritated and the trachea has the ability to induce a cough, to attempt to expel the foreign substance. The trachea is also able to warm and humidify air before it enters the lungs. The trachea is able to ensure the body’s thermoregulation is balanced by being able to adapt to changes in temperature of the air being drawn into the body.
Task 2.
a.
Inspiration Expiration
Diaphragm
During inspiration, the diaphragm contracts and flattens while moving downwards, pushing down the abdominal muscles and organs. This increases the volume in the thoracic cavity.
During expiration, the diaphragm relaxes and returns to its dome shape. It moves upwards which decreases the volume of the thoracic cavity.
External
Intercostal
muscle During inspiration, the external intercostal muscles contract which expands the ribcage. This pulls the ribs up and out, increasing the volume of the thoracic cavity.
During expiration, the external intercostal muscles relax to allow the ribs to return to original position, decreasing the volume of the thoracic cavity.
Ribs
During inspiration, the ribs are pulled upwards and outwards, which increases the volume of the thoracic cavity. Ribs 2-7 are lifted upwards away from the spinal column during inspiration.
During expiration, the rib cage drops inwards and downwards, returning the volume of the thoracic cavity to its original.
Thoracic
cavity During inspiration, the movements of the other respiratory structures create an increase in the volume of the thoracic cavity, which in turn lowers the pressure.
Expiration is usually a passive process that requires with very little individual input of energy. When the diaphragm and ribs return to their original positons, the volume of thorax decreases and the pressure increases in turn.
Lungs
During inspiration, the lungs are pulled downwards which means the volume in the thoracic cavity is increased. The lungs inflate due to the behaviour of the rib cage and diaphragm, and are able to move in their position in the chest due to the lining of pleural membranes and the existence of pleural fluid. This prevents friction and allows smooth movements.
During expiration, the lungs deflate and so return to their original positon. This therefore decreases the volume of the lungs and alveoli.
Pressure in lungs During inspiration, the pressure of air decreases in the lungs and alveoli to below atmospheric pressure. Air will be pulled in to equalize pressure.
During expiration, the pressure of the lungs and the alveoli increases to above atmospheric pressure. Air will be pushed out to equalize this pressure.
b.
Tidal breathing can also be referred to as quiet breathing or eupnea, and it is the concept of inhalation and exhalation that takes place during restful breathing. It does not require the active contraction of the expiratory muscles because the gravity acting on the elevated rib cage along with the elasticity of the lung tissue allows the chest cavity and lungs to return to their relaxed state. Tidal breathing doesn’t require any cognitive thought from the person breathing. The range of tidal breathing is set by the inspiration depth, but also by where the recoil of the ribcage outwards is balanced by the recoil inwards of the lungs – the end point of passive exhalation. Tidal Volume is the measure of tidal breathing – the amount of air that usually enters the during tidal or quiet breathing. The average person’s tidal volume is around 500ml.
Forced exhalation is a type of breathing can occur in two ways; during exercise or during actions that require breathing to be actively manipulated and can also be known as hypernea. During forced exhalation, abdomen muscles contract, including the obliques, and this forces the abdominal organs upwards where they push against the diaphragm. This is turn pushes the diaphragm further into the thoracic cavity where air is forced out due to the reduction in volume. The internal intercostal muscles also aid this during forced exhalation, as they compress the rib cage again reducing the thoracic cavity volume. Forced exhalation can be measured and this measure is known as Expiratory reserve volume or ERV. This is defined as the amount of air that can be forcefully exhaled past tidal expiration. The average person’s ERV is around 1200ml.
Task 3
1. Calculate the following measures of lung function for the subject:
• tidal volume
Scale of above graph: 1dm3 = 1.9cm
Tidal Volume difference = 1.4cm
Converted into dm3: 1.4/1.9 = 0.74dm3
• inspiratory reserve volume
Inspiratory reserve volume difference = 2.7cm
Converted into dm3: 2.7/1.9 = 1.42dm3
• expiratory reserve volume
Expiratory reserve volume = 2.5cm
Converted into dm3: 2.5/1.9 = 1.32dm3
• vital capacity
Vital capacity = 7.8cm
Converted into dm3: 7.8/1.9 = 4.11dm3
2. a) Explain how breathing rate is regulated at rest.
The rate of breathing is said to be involuntary – no specific conscious thought has to be made to breathe in or out and so breathing rate is able to be adapted to the requirements of the body. The Respiratory Centre – located in the medulla oblongata – controls breathing. Regular nerve impulses are sent down the outgoing nerves from the respiratory centre in the brain to the external intercostal muscles and the diaphragm. These muscles are then caused to contract, which begins the process of inhalation. When air enters the lungs, it is detected by stretch receptors which send impulses back to the brain to inform the brain of the progress of inhalation and the response of the lungs. Faster impulses are sent to the brain depending on the rate of the lungs inflating, and once the lungs are inflated sufficiently, the regular nerve impulses from the respiratory centre stop for a short period of time, and then exhalation will follow automatically. Exhalation is usually passive in that the elastic recoil of the diaphragm along with gravity aids the respiratory structures to return to their original positions.
b) Exercise leads to an increase in the rate of breathing. Explain how.
Because breathing rate and its control is involuntary, our bodies are able to detect changes in physical and chemical variations that may occur as the result of undertaking different activities. Levels of oxygen in the arteries vary very insignificantly during exercise but it is extremely important for homeostasis that the body has a constant supply of oxygen. To ensure breathing rate is changed to meet the demands of the body, carbon dioxide levels is used as an indicator as carbon dioxide levels vary proportionally to the intensity of exercise. The more intense the exercise, the higher the carbon dioxide concentration in the blood. This, along with an increase in lactate levels in the blood will lower the pH of the blood. This decrease in pH will be detected by chemoreceptors that can be found in three locations in the body: In the medulla oblongata in the brain, Central receptors detect the differences in carbon dioxide levels in the blood that flows through the brain. In the Carotid artery, carotid bodies are found in the walls can detect changes in carbon dioxide and pH in the blood flowing to the brain, and finally, in the aortic arch there are aortic bodies that detect the same changes in the blood as it flows to the rest of the body. During exercise and once these chemoreceptors have detected a change in the blood, nerve impulses are sent to the respiratory centre in the medulla oblongata. The respiratory centre will then respond by increasing the frequency of the regular nerve impulses that are sent to the external intercostal muscles and the diaphragm. These muscles will then contract more frequently, causing more frequent inhalation and causing the breathing rate to become faster and harder. Along with the increase in breathing rate, heart rate and ventilation rate also increase, meaning that oxygen delivery to the tissues and muscles that need it and removal of carbon dioxide is increased at the same time.
Task 4
Write an essay on how oxygen is transported around the body. You should include descriptions and explanations of:
The Respiratory System is a series of organs and structures that are responsible for the taking in of oxygen and the removal of carbon dioxide. This process is known as gas exchange and it takes places in the lungs. The Respiratory System comprises of many structures including the lungs and within them; bronchus, bronchi, bronchioles and alveoli, but also muscles such as the diaphragm and intercostal muscles. The brain also houses a respiratory centre and blood is an extremely important part of the respiratory system and the process of gas exchange.
Oxygen can be transported through the body by simple diffusion – where oxygen in the air around our bodies would move from the high concentration of the air across the skin into the body to regions of low concentration. However, if simple diffusion was the only oxygen transport system we had, oxygen may only reach the first three layers of cells below the skin before it ran out, and so it would never reach the muscles, organs and tissue that need it the most. The skin of the human body would not provide a big enough surface area for simple diffusion to be relied on as the only oxygen transport process, therefore the respiratory system is needed to ensure the efficient transport of oxygen throughout the body.
Once air has been inhaled into the body via the oral or nasal airways, it travels the respiratory system from the pharynx, the larynx and trachea to the bronchi, bronchioles and the alveoli within the lungs. The alveoli are the main site for gas exchange and whereas the skin of the human body is not sufficient surface area for simple diffusion, the millions of alveoli in the lungs ensure around forty times the surface area for oxygen absorption. The alveoli are surrounded by a very good blood supply in a vast network of capillaries – small fine blood vessels with walls just one cell thick for efficient diffusion of gases and other substances.
The blood in the network of capillaries that surround the alveoli becomes oxygenated in order to transport oxygen around the body. The alveoli have a moist layer lining to allow oxygen to dissolve within it. This creates a concentration gradient – the moist lining of the alveoli is saturated with oxygen and so is at a high concentration, whereas the blood in the surrounding capillaries is at a low concentration. By diffusion, oxygen from the alveoli can then pass across the cell membrane and into the blood of the capillaries. It then enters red blood cells and binds to a protein called haemoglobin. This then takes the oxygen out of the blood solution ensuring that the low concentration and the gradient between two mediums is maintained so that the process of gas exchange is constant. Oxygen can then be transported around the body.
Red Blood Cells are a cellular structure of the blood and are found in their millions. They carry oxygen from the lungs to the other organs, tissues and muscles of the body and transport carbon dioxide back to the lungs to be expelled. Red blood cells are small, round and biconcave in shape and are flexible to ensure passage through the smallest of blood vessels. Red blood cells have no nucleus, therefore they need very little oxygen themselves to carry out their function and so most of the oxygen they do carry can be passed to the tissues. The ability of a red blood cell to absorb oxygen into the cell maintains the concentration gradient between the blood solution and the lining of the alveoli. This ensures the rate of gas exchange is maintained at a constant. The biconcave shape, shown in Figure 1 below, of red blood cells also creates a bigger surface area for oxygen to enter.
Figure 1:
Within red blood cells, a protein called haemoglobin exists that is able to carry four molecules of oxygen. This can be seen below in Figure 2. Haemoglobin is small and is found in red blood cells to ensure it does not pass out of the blood at the kidneys. Haemoglobin is structured with four polypeptide chains with each of these chains containing a haem group. Each haem group is able to collect one molecule of oxygen. The function of haemoglobin is to collect oxygen in the red blood cells at the capillaries in the lungs and transport it around the body, releasing it to muscles, tissues and organs that require it.
Figure 2:
When the first molecule of oxygen combines with the haemoglobin, its shape becomes distorted. The second and third molecules of oxygen are able to bind much easier after the distortion, with the fourth less easy as the haemoglobin becomes saturated. This process of oxygen molecules binding to the haemoglobin is known as loading. Oxygen diffuses across the cell membrane of the alveoli, into the blood plasma, enters the red blood cells and four molecules can be loaded to the haem groups in one haemoglobin protein. Once the molecules of oxygen are loaded onto the haemoglobin, it is called Oxyhaemoglobin and it is this that gives blood its red colour. Oxyhaemoglobin will travel from the capillaries in the lungs to the heart via the pulmonary veins where it will then be transported around the body via the arteries. Whereas loading the binding of oxygen to haemoglobin, unloading is the removal of the oxygen from the oxyhaemoglobin in the tissues. Both loading and unloading of oxygen are dependent on the concentration gradients between the alveoli and the blood, and the blood and the muscle tissues.
Partial pressure is the measure of the concentration of oxygen. The air in the alveoli has a partial pressure (written as pO2) of around 14kPa. Resting tissues have a pO2 of around 5.3kPa and active tissues pO2 is approximately 2.7kPa. The deoxygenated blood arriving at the lungs has a pO2 of 5.3kPa. Because blood arriving at the lungs has a lower partial pressure than that of the lungs, there is a concentration gradient and so the oxygen will move from the alveoli into the blood. The concentration gradient is maintained by the constant taking in of oxygen when we breathe – oxygen is always coming into the body and so although oxygen is moving across the concentration gradient, the supply of oxygen into the alveoli is constant. The maximum concentration gradient for oxygen is maintained also by the blood supply that surrounds the alveoli. The blood is always circulating – deoxygenated blood is always arriving at the lungs and oxygenated blood is always leaving the lungs. This means that the pO2 is the alveoli will always be higher than that of the blood and so oxygen will always move across this concentration gradient.
The oxygenated blood is then taken around the body to the muscles and tissues where it is needed. In active muscle tissues, the cells are constantly respiring, and so oxygen is being used quickly. The partial pressure of the active muscles will therefore be low, and the pO2 of the blood arriving at the muscles will be higher, again creating a concentration gradient. The haemoglobin will unload the oxygen which will then be used for respiration. Where the concentration gradient is maintained in the lungs by the constant supply of both deoxygenated blood and oxygen to the lungs, the concentration gradient in the muscle tissues is maintained by the constant supply of oxygenated blood to the tissues, and the constant need for oxygen to be unloaded at the tissues because of the cells that are respiring. Therefore, the pO2 of the active muscle tissues will always be lower than that of the oxygenated blood arriving.
The transport of carbon dioxide and its removal out of the body follows the concentration gradient as for oxygen but in the reverse direction. At the active muscle tissues, carbon dioxide that is produced by respiration will diffuse into the red blood cells where it will form carbonic acid. Some carbon dioxide binds to haemoglobin to form carbaminohaemoglobin. The CO2 concentration exists and is maintained by the constant production of CO2 during respiration at the muscle tissues, and by the low level of CO2 that exists in the oxygenated blood that arrives at the tissues. Therefore, carbon dioxide will move from the muscle tissues and into the blood, where it will be taken back to the heart and then on to the lungs. At the lungs, the concentration gradient exists between the deoxygenated blood arriving and the air in the alveoli. The partial pressure of carbon dioxide, written as pCO2 in the deoxygenated blood (that has come from the respiring muscle tissues and the heart) will be high and the pCO2 in the air in the alveoli will be low, and so the carbon dioxide will move across from the blood into the alveoli to be expelled out of the body. The gradient at the lungs for carbon dioxide transport is maintained by the constant supply of deoxygenated blood to the lungs, and by the constant exhalation of the CO2 when we breathe.
The respiratory system and the transport of oxygen is unequivocally important to the human body. Although oxygen and carbon dioxide can travel via simple diffusion, the ability of the body to exchange gases as it does means that waste products and carbon dioxide can be removed from the body quickly and oxygen can be transported around the body to where it is needed extremely efficiently.
Task 5
For each of the headings below, draw an additional line on the graph to show how the dissociation curve will be changed. Explain why this change takes place and highlight the significance of these changes.
Foetal Haemoglobin
Fetal haemoglobin has a greater affinity for oxygen than the haemoglobin of an adult – this means that the haemoglobin of a foetus will be able to bind to oxygen mush easier than that of an adult. This enables the foetus to take oxygen from the Mother’s haemoglobin in the placenta. Although foetus’s have lungs from around ten/eleven weeks, they do not use them until they are born. Therefore the foetus must obtain oxygen from the placenta – and this is done by the onloading of oxygen at the same oxygen tension as the Mother’s haemoglobin is offloading it. This means the foetal oxygen dissociation curve will show a steeper and quicker saturation of haemoglobin.
Myoglobin
Myoglobin is a respiratory pigment found in skeletal muscle. It is very similar to haemoglobin as it holds oxygen within the muscle for when it is required – acting like an oxygen store. The oxygen dissociation curve for myoglobin is steeper than that of haemoglobin due to the fact that it loads oxygen at the same oxygen tension of the haemoglobin that is releasing it.
Increased partial pressure of carbon dioxide
An increase in partial pressure of carbon dioxide would affect the saturation of haemoglobin. This increase would cause an increase in carbon dioxide dissolving to form carbonic acid. The production of carbonic acid stimulates the release of oxygen from the haemoglobin, and so more carbon dioxide producing more carbonic acid would mean more oxygen being released from the haemoglobin. This can therefore be shown on the graph in a flatter curve where there is a lower saturation of the haemoglobin.
Low pH
pH affects the quantity of oxygen carried by the haemoglobin. If the environment is acidic, oxygen will dissociate from haemoglobin easily, and conversely in an alkaline environment, the binding between oxygen and haemoglobin is much stronger. So for a lower pH, the haemoglobin would be less saturated as some of the oxygen will have been released to tissues. This is known as the Bohr Effect, where an increase in pH will cause a higher saturation of haemoglobin, and a decrease in pH will cause a lower saturation of haemoglobin but an increase of oxygen release to the tissues. Because of the lowering of carbon dioxide tension in the alveoli, the environment is less acidic and so this increases the uptake of oxygen.
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