The phases of respiration, and how they occur in the human body.

A summary of the phases of respiration, according to various criteria to classify them.

Breathing is a process that we carry out at all times, either consciously or unconsciously. Everyone knows that stopping breathing means death by asphyxiation.

What not everyone knows are the phases that comprise this physiological process, and what are its particularities as well as the existing criteria when applying them.

In this article we are going to see all the phases of respiration and which parts of the organism are involved. and which parts of the organism are involved in each one of them.

What is breathing?

Before going into more detail about the phases of breathing, it is necessary to give a brief description of this process and introduce what are its main phases.

Respiration is a physical process by which an organism exchanges gases with the environment.. The purpose of this is to introduce oxygen into the organism so that it can reach the cells, which will carry out their metabolic functions. Once these metabolic functions have been carried out, these cells will produce another gas as a residue, carbon dioxide, which will be expelled to the outside environment.

In the case of human respiration, this is divided into two main phases: inspiration or inhalation, which involves the entry of oxygen into the lungs, and the other, expiration or exhalation, which involves the expulsion of carbon dioxide. These two phases are made possible by the action of multiple muscles which, by contracting and relaxing, make it possible to modify the volumetric capacity of the thoracic cage and the lungs.

The human respiratory rate varies depending on the age and physical characteristics of the person. characteristics of the individual. On average, an adult person in normal health breathes in and out between 10 and 16 times per minute, while children breathe more frequently, between 15 and 20 times per minute. Newborns and people who frequently practice sports can breathe almost 60 times per minute.

Phases of breathing

We will now look at the phases of respiration, but under two criteria. The first, more traditional, refers to the anatomical characteristics of the process, i.e., which muscles are involved during this phase, which is the degree of physical effort of the organism and also which muscles are involved.

The second case is a classification of the phases of respiration from a more organic perspective, i.e., taking into account the biochemical processes involved in the entry and exit of oxygen and carbon dioxide into and out of the organism, respectively. and carbon dioxide into and out of the organism, respectively.

Traditional phases

These phases are defined on the basis of whether or not the thoracic muscles are exerting any kind of force to move air in or out of the lungs.

1. Inspiration

During inspiration, or inhalation the air involved, especially oxygen, is drawn into the body, reaching the lungs.reaching the lungs.

This process is active, and occurs through the contraction of the intercostal muscles and the descent of the diaphragm. The lungs expand, and the pressure inside these organs is negative compared to that of the atmosphere.

The lungs distend, guided by the pleura and pleural fluid.. Intrapulmonary pressure drops, below the level of atmospheric pressure. To balance both pressures, the lungs are filled with air from the outside. The volumetric capacity of the rib cage increases. Thus, air enters the lungs and oxygen enrichment of the Blood takes place.

During the inspiration phase, the main muscles involved in this process are: diaphragm are: diaphragm, serratus anterior, external intercostals, dorsals, scalenes, supracostal, sternocleidomastoid and pectoral muscles.

2. Exhalation

Exhalation, also called exhalation, is the phase of breathing in which carbon dioxide is eliminated from the body. carbon dioxide is eliminated from the body.. It occurs when the diaphragm rises and the intercostal muscles relax, causing an increase in pressure in the lungs.

The volume in the rib cage and lungs is reduced.This causes an increase in intrapulmonary pressure, which becomes higher than atmospheric pressure. Thus, gases are released from the lungs to the outside.

This process is passive, since it implies that the muscles involved in the previous phase, i.e., inhalation, relax, releasing the air, waste product, which is inside the lungs. During this phase, the following muscles are involved: internal intercostal, oblique, abdominal, transverse and pectoralis major.

Exhalation can be controlled and voluntary or passive and involuntary.. We speak of voluntary expiration when the gases in the lungs are retained in a consciously controlled manner. This can be due to different reasons, such as talking, singing, playing sports or simply because you want to control your breathing, such as when you are diving.

In the case of involuntary expiration, which is totally passive, is due to the metabolic functions of the organism.. It is the one that occurs during sleep or while doing any activity that does not require direct control over the entry and exit of air from the body.

Organic phases

First of all, it is necessary to make a distinction between external respiration and internal respiration.

External respiration occurs outside the cells but inside the organism.It consists essentially of the exchange of gases in the lungs and their transport through the bloodstream.

Internal respiration is the process of introducing oxygen into the cells of the organism. of the organism.

External respiration

External respiration refers to the exchange of gases between the body and the external environment.This type of respiration, particularly the obtaining of oxygen from the outside and the elimination of carbon dioxide from the inside.

This type of respiration is also called ventilation, and is the process in which the pulmonary alveoli transfer oxygen to the red blood cells.

Within external respiration, three subphases can be mentioned:

First, pulmonary ventilation occurs.This is when gases flow in and out of the pulmonary alveoli, allowing gas exchange.

Then comes the pulmonary diffusion or gas exchange, which occurs when the alveoli of the lungs are filled with gas.which occurs when the alveoli absorb the oxygen coming from the external environment that has managed to reach the lungs and carbon dioxide is expelled to the outside.

Y finally, gas transport occurswhich consists of blood with oxygen traveling to the cells that require this gas to function and collecting the residual carbon dioxide produced by their metabolic activities.

2. Internal respiration

Internal respiration is understood as the process in which the red blood cells, which have obtained oxygen from the pulmonary alveoli, transfer this same gas to the cells so that they can carry out their metabolic processes.

In turn, the cells give to the red blood cells the residual carbon dioxidewhich has been obtained after the physicochemical reactions within the cells have been carried out.

This process occurs thanks to the processes of osmosis and diffusion. The pressure of oxygen is higher in the blood than in the tissues, causing this gas to be absorbed by the cells that make up these tissues through the capillaries.

In turn, carbon dioxide, which has a higher pressure in the tissue than in the blood, goes into the bloodstream, traveling through the hemoglobin, and the carbon dioxide is pumped back to the lungs to be pumped to the lungs..

The blood with carbon dioxide travels to the heart, being pumped back to the lungs to perform the exchange again, obtaining oxygen and repeating the cycle again.

Bibliographic references:

• Hall, J. (2011). Guyton and Hall textbook of medical physiology (12th ed.). Philadelphia, Pa.: Saunders/Elsevier.
• Koen, C- L.; Koeslag, J. H. (1995). "On the stability of subatmospheric intrapleural and intracranial pressures". News in Physiological Sciences. 10: 176-178.
• West, J. B. (1985). Respiratory physiology: the essentials. Baltimore: Williams & Wilkins. pp. 21-30, 84-84, 98-101.