How the respiratory system works

The respiratory system allows us to carry out one of the essential functions of living beings: to breathe. Thanks to this set of organs and structures, we are able to take oxygen from the air around us and eliminate gaseous waste compounds (mainly carbon dioxide, but also others).

In this lesson from a TEACHER we will see how the respiratory system works: we will make a brief introduction to the main parts of the respiratory system and we will see in depth both external respiration (or ventilation) and gas exchange.

Index

1. Main organs and structures of respiration
2. Stages of respiration
3. Ventilation
4. Gas exchange in the pulmonary alveoli

To know how the respiratory system works we first have to get an idea of ​​the parts of the respiratory system. Within this system we find organs with different characteristics and functions, which have a direct or indirect relationship with respiration, but the main organs are:

• Nostrils and nostrils. They are the outermost part of the respiratory system and are responsible for communicating the other structures with the outside. In addition, the inner part of the nostrils are lined with small villi and mucus, which retain dust particles and microorganisms. In the nostrils there are folds called turbinates, which slow down the passage of air and favor its humidification and heating.
• Mouth. Some of the air we breathe also enters through the mouth. The mouth is not such an efficient structure for breathing since the air that enters our interior lacks the filtering and heating that occurs in the nose.
• Pharynx. The pharynx is a tube of about 14 cm that allows communication between the nostrils, the oral cavity, the middle ear (through the Eustachian tubes), the larynx and the esophagus.
• Larynx. It is a short tube of about 4 cm in length that contains the vocal cords and that follows the pharynx.
• Windpipe. Tube about 12 cm long and 2 cm in diameter, made up of a series of cartilages shaped like a half-rings (rings cut in half), the rear ends of which are joined by fibers muscular. This prevents friction with the esophagus, which is attached to the back, when food passes through it.
• Bronchi. They are the two tubes in which the trachea bifurcates. Each of them approaches each of the lungs.
• Bronchioles. They are the ramifications of the bronchi. As they approach the lungs, the bronchi divide into smaller tubes such as the bronchioles. The last branches originate the so-called bronchial capillaries that end in pulmonary saccules, which are cavities with numerous globose expansions called pulmonary alveoli, where gas exchange between blood and air takes place.
• Lungs. They are the two main organs in air ventilation. They are shaped like a triangle, and different in size: the right lung is larger and has three lobes and the left, smaller, only two.
• Diaphragm. The diaphragm is a muscular membrane that descends during inspiration allowing the lung dilation (filling with air) and during expiration it rises favoring the emptying of the lungs.
• Pulmonary artery. It contains blood poor in oxygen and rich in carbon dioxide, since it comes from the rest of the body's organs; This blood comes from the heart and is carried to the lungs to be oxygenated.
• Pulmonary vein. It contains blood rich in oxygen and poor in carbon dioxide, which moves from the lungs to the heart to circulate again through the rest of the body.

Breathing is the complete process by which we know the gas exchange between the atmosphere that surrounds us and the blood that bathes the interior of our body. This process can be divided into two very different stages: ventilation or external respiration and the gas exchange proper.

Next we will see each of the phases of respiration separately, naming the main structures and organs.

To know how the respiratory system works we have to know the first of the phases of respiration. Ventilation or external respiration is the process by which air from the external environment enters our lungs and then leaves. It is simply the filling and emptying of the lungs. Ventilation can be divided into two phases:

1. Inspiration. During inspiration, the external intercostal muscles contract and raise the ribs and sternum, and the diaphragm descends. All this increases the capacity of the rib cage, causing the lungs to dilate and enter oxygen-rich air from outside the body through the pharynx and larynx (upper airway) and trachea and bronchi (upper airway) lower). Inspiration is said to be a active process, in which our muscles have to work so that the air penetrates to our lungs.
2. Expiration. During the exhalation phase, the external intercostal muscles relax and the ribs and sternum are lowered and the diaphragm rises. All this decreases the capacity of the rib cage, causing the lungs to contract and, therefore, Therefore, the air contained in our lungs (rich in carbon dioxide, water vapor, etc.). We can say that this stage is the opposite of inspiration: everything that contracts in the Inspiration relaxes on expiration, everything that goes down during inspiration goes up during expiration, etc. Furthermore, expiration is said to be a passive process Since, unlike inspiration, it does not involve an activation of the muscles but rather they simply relax.

Image: Respiratory system

The gas exchange It is the process that occurs in the pulmonary alveoli, in which gases are exchanged between the blood and the air contained in the alveoli, which comes from outside. Specifically, this gas exchange occurs through the thin membrane that lines the blood vessels of the pulmonary alveoli (pulmonary endothelium).

Gas exchange can also be divided into different stages to make it easier for us to study it:

1. Blood from the heart reaches the lungs through the pulmonary artery. The pulmonary artery is dividing, each time into smaller blood vessels until forming the blood capillaries that line the pulmonary alveoli. This blood is loaded with carbon dioxide and contains very little oxygen.
2. Air that is rich in oxygen reaches the pulmonary alveoli from outside. Through all the structures seen in the ventilation, the air from the outside reaches the pulmonary alveoli.
3. Gas exchange occurs. In the alveoli, the distance between the gases contained in their interior and the gases contained within the blood capillaries that line it is very small: only 0.6 microns (0.6µ). In addition, the walls that separate them are permeable to them, so the gases tend to migrate from one side to the other until they equalize the composition on both sides of the walls. Gas exchange is said to be due to gas gradientIn other words, it is a passive process by which the same gases move, to match the composition of the interior of the alveolus with the interior of the capillaries that surround them.
4. Oxygen-rich blood is distributed throughout the rest of the body. The capillaries that line the alveoli unite to form a larger structure: the pulmonary vein. The blood that leaves the blood capillaries that line the pulmonary alveoli joins in the pulmonary vein and goes to the heart, where it is pumped to the rest of the body. This blood is rich in oxygen and very poor in carbon dioxide.

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• Jimeno, A (August 18, 2016) The respiratory system and respiration.
• The human body (s.f) Respiratory System - Functions and Organs