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Mechanism of Breathing

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All living beings need oxygen to live. The process of breaking down food particles into energy also requires an oxygen supply. Saying this, breathing is a respiratory process of taking in oxygen and exhaling carbon dioxide. This is also called ventilation. In short, the out and in movements of air into the lungs is called breathing or external ventilation.


Plants benefit from  human’s expiration by making use of carbon dioxide for their photosynthesis. Regardless of whether it is a plant, animal, bird or human being, the entire breathing process is continuous throughout one’s living. The pace of breathing, however, will vary according to the species. It is also influenced by factors such as health conditions, environment, present activity levels, temperature, etc. For example, a person will breathe more when involved in sports or exercising. On the other hand, one’s breathing rate would be calm or less, when in a relaxed state.  


Inhalation is the term used to define the taking-in process of oxygen. Exhalation is referred to as exhaling on flushing out carbon dioxide out of the body. The terms inspiration and expiration are also used often to refer to the breathing process.  Following is a detailed explanation for the same.


Mechanism of Breathing

As noted, the breathing rate varies from person to person, ranging from 15-18 times per minute. When it comes to understanding the mechanism of respiration,  the pressure of air plays a major role. The alveolar spaces of the lungs take in air by the active process of inspiration;  when the pressure inside the lungs exceeds the pressure of the atmosphere, the oxygen comes out as carbon dioxide during expiration. 


Important Pointers About the ‘Inspiration’ Process:

  • Muscles contract.

  • The ribs pull outside.

  • Diaphragm contracts.

  • The above steps result in the expansion of the chest cavity.

  • A minimal amount of air is sucked into the lungs and gets filled into the expanded alveoli region. 

  • Inside the lungs, the pressure of air and the atmosphere is quite similar. 

  • Yet, when the lungs expand, the pressure of air will decrease inside the lungs.


This is the common mechanism of breathing in human beings, irrespective of age, gender and any other physical factors. Note that the inspiration of air takes place only when the thoracic cavity increases in volume.


Important Pointers About the ‘Expiration’ Process:

On the contrary, expiration is a process of exchanging gaseous matter inside the lungs, to expel the air outside.

  • Rib muscles contract.

  • Air pressure increases outside of the thoracic region.

  • Internal intercostal muscles contract whereas the external intercostal muscles relax.

  • The size of the thoracic cavity is reduced, hence ribs pull inwards.

  • Abdominal muscles will contract in shape.

  • Lungs will compress due to the relaxation of the diaphragm.

  • Henceforth, due to an increase in pressure, the air is pushed outside.


To understand and describe the mechanism of breathing in human beings, it is important to learn about the mechanism of oxygen and gas transportation. 


Mechanism of Respiration

Respiration, in short, is breathing + gaseous matter exchange. All gases exchange between the surface of the alveolus and are influenced by external factors such as tissues, blood, etc. When the alveolar region diffuses, the gases exchange inside the lungs. There are over 600 million alveoli in the human body.


The lungs can achieve high compliance due to their power of low surface tension and high elasticity.


Exchange of Gases

Oxyhaemoglobin is one of the chemical components formed during the transportation of oxygen. As the name says, oxyhaemoglobin is nothing but haemoglobin and oxygen together. This occurs when the oxygen concentration is higher in the blood. The 2nd form is the same solution of oxyhaemoglobin formed inside the blood plasma region. 


Now, the carbon dioxide gets transported from the human tissue into the lungs in 3 different mechanisms:

  1. Carbonic Acid (CH2O3) is formed in the process of CO2 dissolving with the plasma’s water.

  2. Carbonic Acid dissociates atoms through a chemical process termed ionization, thus producing bicarbonate ions.  Carbonic anhydrase will catalyze these H2 ions.

  3. CO2 combines with haemoglobin to form carbaminohemoglobin. 


All the gaseous content formed is delivered out of the body through the process of expiration. 


Key Points on the Mechanism of Breathing

As a takeaway, the following points are to be kept in mind to explain the mechanism of breathing in human beings

  • Inhaling oxygen (O2) into the lungs and exhaling carbon dioxide (CO2) out of the body is breathing. 

  • The breathing mechanism of human beings is similar to that of animals. Plants process breathing vice-versa.

  • Breathing rate differs across species.

  • During inspiration, the diaphragm gets contracted. During expiration, the diaphragm gets relaxed. The diaphragm has 75% responsibility in the process of breathing.

  • Humans lose some amount of water content from their bodies while breathing out.

  • To accommodate the heart, the left lung is smaller than the right.

  • Air is pushed outside when the lung pressure increases.

  • The relaxation and contraction of muscles with the alveolar region change the volume of the lungs.

Last updated date: 23rd Sep 2023
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FAQs on Mechanism of Breathing

1. Explain the mechanism of breathing.

The physical process of taking oxygen into the lungs and leaving out carbon dioxide from the body is breathing. Breathing rate is usually 15-18 times per minute. The breathing mechanism consists of two simple processes that are inspiration and expiration. Inspiration is a process in which air moves into the lungs and during this process contraction of muscles attached to ribs take place and on the outer side, ribs are pulled out. This results in the expansion of the chest cavity, and this expansion of the chest cavity produces a partial vacuum that helps to suck the air into the lungs and expand the alveoli. Whereas expiration is the process of giving air out of the lungs. 

Once the gaseous exchange is done in the lungs, the air is expelled out and during the expiration process, the muscles attached to ribs are contracted then muscles of the diaphragm and abdomen relax further leading to the decrease in volume of the chest cavity. 

2. What is the difference between breathing and respiration?

Breathing involves exhalation of CO2 and inhalation of O2 inside the lungs. Whereas, respiration involves breaking down glucose molecules to form energy to facilitate basic cell functions.

3. Where does the oxygen go during breathing?

The oxygen which is inhaled by the lungs will enter several blood vessels of the body. These blood vessels are called capillaries and surround the alveoli, also called the bronchioles (the balloon-like air sacs).

4. What are the natural ways to get oxygen?

The body needs oxygen for the working of various life processes. Regular exercising, developing aroma inside rooms, growing indoor plants, practising mindfulness, green dieting, mediation are some of the practical ways to get oxygen from the natural environment. 

5. How do plants breathe?

Just like humans, plants do need oxygen for respiration. But unlike animals plants do not have any specialised structure or process for gaseous matter exchange. Plants have stomata that are present in the leaves and lenticel present in the stems. These two are involved in the exchange of gases. The oxygen released from these plants is useful to the process of human breathing. 

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