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How Does The Respiratory System Maintain Homeostasis

by Lyndon Langley
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How Does The Respiratory System Maintain Homeostasis

How Does The Respiratory System Maintain Homeostasis

The lungs are a complex organ system with many different jobs to do. One of the most important tasks it performs is respiration – breathing air into the lungs where it mixes with oxygen and then exhaling this mixture back into the atmosphere.
With each breath we take in around 20 million litres of oxygen and expel roughly 1 million litres of carbon dioxide. This process allows our bodies to use the available oxygen for cell metabolism and removes toxins from the body.
The pulmonary circulation transports blood from the heart, through the arteries, capillaries and finally on to the pulmonary veins which lead to the left atrium of the heart. From here, the blood travels via the pulmonary vein to the right side of the heart and then into the superior vena cava (which leads to the right atrium) and ultimately to the lungs.
Once inside the lungs, oxygenated blood enters the bronchial artery which branches off the pulmonary artery. These two vessels form the basis of the pulmonary circulatory system. The lung tissue consists of millions of microscopic structures called alveoli. Each one of these alveoli has an opening leading into the airways or trachea. Here they branch off into smaller ducts known as bronchi which eventually end up forming small tubes called bronchioles. At this point, the airways split into two primary pathways known as the upper and lower lobes which each contain several thousand alveoli.
As blood flows through the alveolar capillary bed, oxygen diffuses across the membrane of red blood cells, entering them, while carbon dioxide exits the cells and leaves the capillaries. In order to maintain this homeostasis, there must be constant movement of fluid between the airspaces within the lungs and the outside environment.
This is accomplished by using the highly efficient pulmonary surfactant systems. Surfactants play an essential role in maintaining normal surface tension levels at the interface between the air-water boundary layer. The best way to understand how surfactants work is to imagine a large number of very tiny bubbles floating on top of water. If you were to put your finger down on the surface of the water, you would feel a slight wetness because of all the tiny bubbles covering the skin. However, if you took your finger away, the bubbles would float upwards due to their buoyancy.
In much the same way, surfactants reduce the surface tension of the liquid lining the inner walls of the airway passages making it easier for the tiny air sacs to inflate and deflate without collapsing. When the lungs are under stress, such as during exercise, surfactants increase their ability to keep surfaces moist and flexible.
Surface tension also plays an important part in regulating the amount of mucus present in the airways. Normal mucous membranes produce copious amounts of sticky mucins which act as lubricants and protectants against infection. However, when excess mucus accumulates in the airways it becomes difficult for the airways to expand fully. This makes it harder to breathe and can cause coughing attacks. Surfactants help prevent excessive production of mucus. They coat the inner wall linings of the airways, reducing surface activity, thus preventing the formation of excessive mucus.
Although surfactants provide a great deal of protection to the lungs, they are not perfect. For example, surfactants cannot repair damaged tissues in the lungs. Lung diseases such as emphysema and asthma attack the lungs’ ability to clear mucus effectively. Other factors such as pollution damage the lung’s natural defences.
Air pollutants such as cigarette smoke irritate the airways resulting in chronic inflammation. Inflammation increases the permeability of the lung tissues to foreign substances including viruses or bacteria. This causes further irritation and swelling of the delicate airway passages. This cycle can become self-perpetuating causing further problems.
Other environmental insults such as dust particles can also trigger asthma symptoms and make existing conditions worse. Excess exposure to ozone and other oxidising chemicals can aggravate symptoms in people who have underlying lung disorders.
Fortunately, there are ways to treat these conditions. The drugs used in treating asthma may include corticosteroids, beta2 agonists, anticholinergics and leukotriene modifiers. Allergic rhinitis patients may benefit from oral antihistamines. Treatments for obstructive sleep apnoea include nasal continuous positive airway pressure, uvulopalatopharyngoplasty (UPPP), surgery and breathing exercises. Chronic bronchitis patients can improve their condition with inhalers containing either ipratropium bromide or salbutamol sulphate. Patients suffering from chronic obstructive pulmonary disease (COPD) may need long term inhaled steroid therapy.
Homeostasis is maintained in the lungs thanks to the efforts of the respiratory system’s numerous components and processes working together. Understanding how the lungs perform their vital function helps us appreciate the complexity behind maintaining life.

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