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Teach PE (2010) states "The function of the respiratory system is to transport air into the lungs and facilitate the diffusion of oxygen into the blood stream. It also receives waste carbon dioxide from the blood and exhales it"
Our respiratory system consists of:
Nose: - This is an external structure on the face and also includes the internal structure called the nasal cavity. Both are air passageways. The nose allows air into the respiratory tract via the nostrils. The nose is usually the primary route that air enters the body from the atmosphere.
The nose and nasal cavity are strong structures made of bone and cartilage, and remain open all the time, allowing air carrying vital oxygen to enter the body, and air carrying the waste product carbon dioxide to leave the body. The nose and nasal cavity also warm the air, so the air does not upset the homeostasis of the body.
Mouth: - Although the nose is the primary air passageway, the mouth is also used as an air passageway. The mouth tends to be used for ventilation whilst exercising, during illness and some people’s personal choice. It is a large air passage way. Made of bone cartilage and ligaments; making the structure strong. It is also large to allow optimum ventilation when needed.
Pharynx: - This is predominately made out of muscle but also has cartilage and is funnel shaped. Although this is part of the respiratory tract it also carries food to the oesophagus. Due to its ability to carry food, its muscular walls can constrict and push food to the oesophagus, this movement is commonly referred to as swallowing. This too is a strong, open air passageway that does not close readily, and allows air to flow freely further into the body.
Larynx: - This is a small structure, commonly associated with talking since the larynx contains our vocal chords. It also contains a small cartilage disc, called the epiglottis. The epiglottis prevents foreign bodies entering the respiratory tract; this is the larynx’s main function to protect the respiratory tract. It does this, by covering the trachea (the next part of the respiratory tract) due to muscle contraction when the person is consuming food and drink.
The larynx is made of 5 different types of cartilage, ligaments and muscles, giving a solid structure that will remain open.
Trachea: - Commonly referred to as the windpipe. It is made of hyaline cartilage and fibro-elastic tissue and is about 12 cm long. This means that the trachea is strong, but flexible to a point. The trachea enters deep into our bodies, practically reaching the lungs. When it reaches our lungs the trachea divides into 2 air passage ways known as the bronchus. At the point the trachea divides this is called the carina.
Bronchus: - One that enters each lung. Structurally the bronchi are similar to the trachea, but they also contain muscle fibres that allow them to constrict or dilate when appropriate to do so.
All the above parts of the respiratory system, not only have very similar structures i.e. they all contain cartilage that is strong that allows system to remain open all the time. Containing the cartilage is their form of protection so that they do not collapse.
They also have the same internal lining; cilia (tiny hairs) and goblets cells that secrete mucus. The mucus is essential to help catch foreign bodies and pathogens that have been breathed into our bodies. The cilia to a lesser extent also catches foreign bodies, but their main function is to continuously sweep the mucus away from the lungs, keeping the lungs pathogen free and to allow more mucus to be secreted to catch more foreign bodies and more pathogens.
Lungs: - Humans have 2 lungs. The left lung is slightly smaller than the left due to position of the heart. The right lung is divided into the upper, middle and lower lobe whereas the left lung consists only of the upper and lower lobe. The lungs are not made of cartilage and therefore less solid compared to the rest of the respiratory tract. They are spongy in appearance and since there is no protection internally, protection is provided externally by the rib cage. Pleural membrane surrounds each lung. This membrane keeps the lungs moist which is essential of movement and gaseous exchange the main function of the lungs. This membrane allows some protection and helps keep the lungs shape. The rib cage also has a pleural membrane, and fluid separates these membranes which prevents friction and allows movement which is essential of ventilation to occur.
Bronchioles: - When the bronchus enters the lungs, the air passageway becomes narrower and these are called bronchioles. Bronchioles branch out throughout the lung, and get narrower and narrower. Due to this branching they are often referred to as the ‘bronchial tree’. These bronchioles are structurally different from the rest of the respiratory tract. They contain no cartilage, cilia or mucus cells. However they do contain muscle fibres that allow for changes in their diameter if necessary. The moist environment of the lungs and the muscle fibres help to keep them open at all times.
Alveoli: - As the bronchioles get smaller and smaller they become known as tertiary bronchioles, and it is at this point the air in them enters their final part of the journey. Here the bronchioles enter the alveoli. The alveoli cluster together, and therefore have a grape like appearance. They are tiny hollow sacs, which are one cell thick. It is here in the alveoli that gaseous exchange takes place through the alveoli wall and the capillaries which cover the lungs. Here, is where the much needed oxygen is diffused into the blood supply and carbon dioxide is diffused into the lungs again to be exhaled out into the atmosphere.
Respiratory Muscles: - These are their diaphragm and intercostal muscles. The diaphragm is a dome shaped muscle situated under the rib cage. It separates the thorax from the abdomen. The intercoastal muscles are found between the lungs and the rib cage. Having these large muscles that work together to allow movement within the respiratory tract is essential for sufficient ventilation.
Although air will naturally fill any space, large amounts of air needs to get all the way deep into the body to be useful. This can only be achieved by movement of the lungs that allow air to be sucked into the body inhalation and air to be forced out of the body exhalation. This movement that occurs is due to the respiratory muscles, the dome shaped diaphragm and the intercostal muscles which surround the lungs.
To inhale both the respiratory muscles contract. As this occurs the diaphragm flattens and pushes the rib cage out. As the intercoastal muscles contract, and the rib cage moves up and out. This means that the volume of the lungs increases, and pressure decreases so air readily flows into the body. Air that contains the oxygen that is needed for cellular respiration.
To exhale the respiratory muscles relax. This means the diaphragm becomes domed shaped again, and the intercostal muscles move the rib cage down and inwards. This decreases the volume in the lungs, and the pressure increases forcing air to be expelled out of the body. This air contains carbon dioxide, waste product from cellular respiration.
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