The proper functioning of a human body is dependent on the individual and collective performance of the different bodily systems, which are vital for our survival. The respiratory system is a major body system that is responsible for respiration. It is through this process that the cells of the body receive oxygen for their metabolic reactions. Here is a brief overview about the functions of the human respiratory system.

In simple words, the respiratory system can be explained as a group of organs that help us breathe. Breathing involves inhalation of oxygen and exhalation of carbon dioxide. Even though, the process of breathing appears to be very simple, it involves proper functioning of various parts of the respiratory system. This body system can be divided into two sections - the upper and the lower respiratory tract. The upper section comprises the nasal cavity, sinuses, oral cavity, pharynx, and larynx. The lower respiratory tract is composed of the trachea, bronchi, and the lungs. Inside the lungs, each bronchus branches into bronchioles that end in alveoli. Even the diaphragm that lies beneath the lungs play a key role in respiration. As we all know, gaseous exchange is the most important human respiratory system function. It is through this process, that the cells in our body get the required oxygen for their functioning.

labeled diagram of the respiratory system

The Main Function - Gaseous Exchange

Oxygen is required by the body cells for their normal functioning, and this requirement is fulfilled by the respiratory system. This is achieved through the process of respiration, which involves inhalation and exhalation. The air we take in through the nose and mouth travels to the lungs, wherein the exchange of gases takes place. When we inhale, oxygen is taken in, and when we exhale, carbon dioxide is expelled. Given below is a brief explanation of the procedure, along with the roles played by the different parts of the respiratory system.

Nasal Cavity: Air from the external environment is inhaled through the nose and the mouth. Apart from providing a passageway for the inhaled air, the nasal cavity contains mucus and tiny hair that filter the air. The air is also moistened and warmed inside the nasal cavity. The air travels further to the pharynx, from where it reaches the larynx.

Larynx: It is the larynx that houses the vocal cords - the structures that are mainly involved in producing sounds for speaking, talking, and singing. When food is swallowed, another structure called epiglottis closes the opening of the larynx. This prevents the food particles from entering the windpipe. Even if some food particles enter the larynx, they are expelled through gag reflex.

Trachea: From the larynx, the air passes to the trachea, a tube-like structure that enters the thoracic cavity. Otherwise known as windpipe, the trachea produces mucus that traps foreign particles in the inhaled air. This mucus may come out of the body as phlegm or get swallowed into the stomach. As the trachea enters the chest cavity, it divides into two branches, called bronchi. While the left bronchus enters the left lung, the right bronchus enters the right lung.

Bronchi and Alveoli: Inside the lungs, the bronchi further divides into small tubules called bronchioles that end in tiny air sacs called alveoli. There are millions of alveoli in human lungs. Each one has a thin lining made of a single layer of cells, and is surrounded by lots of blood capillaries. This tiny air sac called alveolus is the actual site of gas exchange.
alveoli covered with blood vessels
exchange of gases inside an alveolus
1. The image shows the alveoli covered with blood capillaries.
2. A cross section of an alveolus and a blood capillary around it. Oxygen (red arrows) is absorbed from the inhaled air inside the alveolus, and carbon dioxide (blue arrows) is released from the blood into the alveolus.

Inside the alveoli, the oxygen in the inhaled air diffuses into the blood in the capillaries. The oxygen gets attached to the hemoglobin molecules in the blood. This oxygenated blood travels to the heart, from where it is pumped to different parts of the body. The cells in the tissues and organs absorb the oxygen in the blood and releases carbon dioxide. The blood that carries carbon dioxide, travels to the lungs. The carbon dioxide is absorbed by the alveoli, and is expelled through exhalation.

Diaphragm: Even the diaphragm and intercostal muscles (found in between the ribs) are involved in the functions of the respiratory system. The diaphragm is a dome-shaped muscular structure that lies beneath the thoracic cavity. During inhalation, the diaphragm flattens, so as to facilitate expansion of the lungs to fill in the air. Even the intercostal muscles contract to expand the ribcage. During exhalation, both the diaphragm as well as the intercostal muscles relax and move back to their earlier position.

movements of diaphragm during respiration

1. The image shows the downward movement of the diaphragm during inhalation. The intercostal muscles (in between the ribs) allow expansion of the ribcage.
2. During exhalation, the diaphragm relaxes and moves upward. The ribcage too contracts.

Even the nervous system is involved in the functions of the respiratory system. The process of breathing is controlled by the nervous system. The circulatory system is closely associated with breathing and resultant gaseous exchange.

Apart from gaseous exchange, the respiratory system has some auxiliary functions too. The epithelial cells of the airways produce certain antimicrobial secretions that can prevent infections of the airways. Along with the kidneys, the lungs too play a key role in maintaining the blood pH. The vocal cords in the larynx is responsible for production of sound. Even the lungs play a major role by maintaining the air pressure and rate of air flow that affects sound production. As we discussed earlier, the respiratory system performs the functions of filtering, warming and moistening the air we inhale. It is also well equipped to expel the foreign particles that get trapped in the airways. In short, the respiratory system has to perform some of the vital functions of the human body.