Understanding the respiratory system

The anatomical structure of the respiratory system and function of the lungs
Together, the two lungs rank among the biggest organs in the body and they are very important organs in the body. Without the lungs, oxygen will never reach the cells and tissues. Indeed, there is no life in the absence of oxygen.

The anatomy of the respiratory system
The respiratory system is made up of structures that are used in breathing, the nose (and mouth when a lot of oxygen is required to do more work, like in exercising). The nose is lined with a mucous membrane and hair to lubricate the airways and heat up the air respectively. At the back of the nose and mouth are areas referred to as the naso-pharynx and oro-pharynx (behind the nose and mouth respectively), both of them open into the laryngo-pharynx. The laryngo-pharynx connects to the trachea, which runs down to the carina. The trachea is a tube lined by layers of semi-circular cartilage separated by smooth muscles.

There is no cartilage at the back of the trachea. The trachea lies on the eosophagus at the back. At the carina, the trachea divides into two, the right and left bronchi. One bronchus goes into the left lung and the second into the right lung. Inside each of the lungs, the bronchi divide into smaller tubes known as bronchioles. After three or four more divisions, the bronchioles enter into air sacs known as alveoli. The alveoli look like a bunch of grapes, hence the name, which means grapes in Italian. The alveoli are lined with a very thin membrane and supplied with equally tiny blood vessels known as capillaries. It is at this alveolar level that oxygen passes from the alveoli into the blood and carbon dioxide from the blood to the alveoli to be breathed out.

This is the main function of the respiratory system – inhaling of oxygen and exhaling of carbon dioxide. The air we breathe in is loaded with all sorts of particles of pollutants, bacteria, fungi, allergens, chemicals, smoke etc. The respiratory system has certain defence systems by which it protects itself from potential harm and this is very significant because if it fails, different kinds of diseases can occur and such can be fatal.

How the respiratory system protects itself
1. It begins from the nose. The nose is full of hairs that act as filters, filtering the air that we breath in. This filtering process prevents large particles from getting to the deeper reaches of the respiratory system and the lungs. The hairs in the nose also heat up the air that is entering to bring it as close to the body temperature as possible. This prevents cold air from getting into the lungs. The practice of shaving the nasal hair, which is very common in some parts of the country should be discouraged so as to avoid fatal consequences.

Furthermore, the airways are covered by a thin layer of mucus. This mucus layer traps any particle or irritant that passes through the nose. The mucus and whatever is trapped in it, will be swept upwards toward the throat by cilia, tiny hair-like structures that also line the airways. The mucus and its contents pass through the epiglotis and get swallowed. This is happening all the time without you knowing. However, on some occasions, the mucus secreted may be so copious in response to an irritant or an infecting organism. This will lead to the second defence mechanism, which is cough.
2. Cough, this happens as a result of an irritation in the bronchial tree. The cough reflex expels the mucus from the lungs and bronchial tree.
3. Sneezing is a defence mechanism against particles or irritants in the nose and upper portions of the respiratory system.
4. Bronchospasm

In response to irritation to the bronchial tree by irritants or particles, the smooth muscles of the airways may contract to narrow the bronchial tree so as to keep the irritant at bay. This defence mechanism could lead to more serious conditions as asthma or chronic obstructive pulmonary disease (COPD).