Human Respiratory System: Function and Structure
The Respiratory System
For our cells to get energy from nutrients, they need to undergo a series of oxidation reactions that require oxygen (O2). As a result of these reactions, carbon dioxide (CO2) is produced. CO2 is a toxic gas that enters the blood and must be eliminated.
The respiratory system is responsible for taking oxygen from the outside air, transporting it to the blood, and removing carbon dioxide.
The respiratory system consists of the lungs and airways. The airways are pipes and chambers through which air passes from the outside to the inside of the lungs and vice versa. They consist of: the nostrils, pharynx, larynx, trachea, bronchi, and bronchioles.
Airways and Lungs
Pharynx
A muscular and elastic duct, common to the digestive system, which carries air to the larynx. At the bottom is the epiglottis, which prevents food from penetrating the airway during swallowing.
Larynx
It is a short tube, inside which are the vocal cords that vibrate to produce the voice.
Bronchi
There are two tubes that penetrate the lungs, where they branch into finer tubes called bronchioles. These, in turn, are divided into smaller branches, ending in thin-walled sacs called pulmonary alveoli.
Nostrils
There are two cavities located above the mouth and opening to the outside by the nostrils. Air enters through these cavities, where it is heated and moistened.
Trachea
A tube running through the neck that carries air to the lungs. It descends parallel to the esophagus and in front of it. It is protected by a series of C-shaped cartilages, which prevent it from being crushed.
Lungs
They are two spongy organs protected by the ribs. The interior is where gas exchange with blood occurs. Each lung is surrounded by a double membrane called the pleura, filled with pleural fluid, which allows the lungs to adapt to respiratory movements. The right lung is divided into three lobes and is larger than the left, which has only two.
Gas Exchange
Air, laden with oxygen, enters the respiratory system through the nostrils, which warms, moistens, and cleans it of particles. These particles are retained by the mucus secreted by the airways.
The air continues through the pharynx and larynx into the trachea. It passes from the trachea to the bronchi, and from these to the bronchioles, ending in the alveoli, which are surrounded by many blood capillaries.
The exchange of gases (oxygen and carbon dioxide) between the internal and external environment takes place in the pulmonary alveoli.
In each lung, there are millions of alveoli, providing a large surface area for gas exchange. This exchange takes place through the thin membranes of the capillaries and alveoli by diffusion, moving from the place where its concentration is higher to where it is lower.
When the air reaches the alveoli, the oxygen it contains passes into the blood capillaries, which are loaded with carbon dioxide. This gas passes through the membranes in the reverse direction to oxygen, moving from the blood into the alveoli, where it is expelled.
The blood, carrying oxygen, distributes this gas to the body’s cells and picks up the carbon dioxide produced to take it back to the lungs.