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Difference Between Inspiration and Expiration

Main Difference

The main difference between Inspiration and Expiration is that Inspiration (inhalation) is the method of taking air from the outside into the lungs, whereas Expiration (exhalation) is the method of releasing air from the lungs to the outside.

Inspiration vs. Expiration

Inspiration is also known as the inhalation, considered as the process of drawing air inside the lungs. Expiration, also called the exhalation, viewed as the process of releasing air to the outside from the lungs through mouth or nose.

During inspiration and taking air into the lungs, the diaphragm moves towards down by contraction and becomes flat; on the other hand, during expiration, when air moves out from the lungs, the diaphragm moves up by relaxing and change into dome-shaped. Moreover, during the process of inspiration, the outer intercostal muscles contract. On the other hand, the internal intercostal muscles relax; on the flip side, during the process of expiration, the outer intercostal muscles relax while the internal intercostal muscles contract.

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By the action of intercostal muscles, the rib cage moves forward and towards outward during the process of inspiration; on the contrary, through the action of intercostal muscles, the rib cage moves downward and towards inward during the process of expiration. During inspiration or inhalation, the size of the chest cavity increases; on the other hand, during the expiration or exhalation process, the size of the chest cavity decreases.

Due to the increase in the volume of the chest cavity during the act of inspiration, the air pressure inside the lungs decreases; on the flip side, due to the decrease in the volume of the chest cavity during expiration, the air pressure inside the lungs increases. In the course of inspiration, the air moves towards the lungs, while during the expiration, the air moves out of the lungs.

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Comparison Chart

InspirationExpiration
The method of taking air into the lungs is known as inspiration.The act of expulsion of the air out from the lungs is known as the expiration.
Also Known As
Inspiration is also known as the inhalation processExpiration is also known as the exhalation process
Active or Passive
An active processA passive process
Diaphragm
The diaphragm moves towards down by contraction and becomes flatThe diaphragm moves up through relaxing and change into dome-shaped
Intercostal Muscles
The external intercostal muscles contract and on the other hand the internal intercostal muscles relaxThe outer intercostal muscles relax while the internal intercostal muscles contract
Intercostal Muscles Function
The rib cage moves forward and towards outward during the process through the action of intercostal musclesThe rib cage moves downward and towards inward during the process by the action of intercostal muscles
The Size of the Chest Cavity
The size of the chest cavity increasesThe size of the chest cavity decreases
Air Pressure
The air pressure inside the lungs decreases because of the increase in the volume of the chest cavityThe air pressure inside the lungs increases due to the decrease in the volume of the chest cavity
The Movement of Air
Air moves towards the lungsAir moves out of the lungs
Gas Exchange
Oxygen moves inward the lungsCarbon dioxide is taken out from the lungs
Chemical Composition of Air
Inspired air consist of an oxygen-nitrogen mixExpired air consist of carbon dioxide-nitrogen mix
Internal Pressure
The pressure of air in the lungs is less than the atmospheric pressureThe pressure of the air inside the lungs is higher than the atmospheric pressure
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What is Inspiration?

Inspiration is known as the phase of taking air into the lungs during breathing. Inspiration is also known as the inhalation process, and it is an active process because it is the involvement of the contraction of the muscles.

Typically, in the process of regular inspiration, the two groups of muscles involved which are diaphragm and the outer intercostal muscles. In this process, the contractions occur in the diaphragm, moving it downward about the abdomen cavity and increasing the space of the thorax cavity.

In the meantime, the outer intercostals muscle contract and move the ribs outward and upward and expand the volume or quantity of the thoracic cavity. Besides, the enlargement of the thoracic cavity results in the intensifying of the lungs because of their adhesion to the pleural fluid. As a result, this expansion of the thoracic cavity is the decrease in intra-alveolar pressure, which is lower than the atmospheric pressure, and this pressure gradient results in the atmospheric pressure to enter into the lungs.

The process of inspiration is vital for taking oxygen inside the blood. The normal estimated air breathe consists of 21% of oxygen (O2) and 0.04% of carbon dioxide (CO2). The amount of needed oxygen increased when we do exercise, and this automatically increases the uptake of oxygen and makes breathing faster. This increased uptake of oxygen is known as VO2.

What is the Expiration?

Expiration is known as the passive process for taking out the air from the lungs. Normally, the liberating out the air from the lungs does not require any energy. So both the muscles diaphragm and external intercostal muscles become relax during expiration by recoiling the lungs.

The lessening of the diaphragm and intercostal muscles results in a decrease in the volume of the thoracic cavity and an increase in the interpulmonary pressure, which is higher than the atmospheric pressure. As a result, ultimately, the air which is present inside the lungs liberates out of the lungs.

Key Differences

  1. The inspiration is known as the active process, which brings air into the lungs, while the expiration is the passive method that excludes air out of the lungs to the outer environment.
  2. During the inspiration process, the inspired air consist of oxygen-nitrogen mixture; on the other hand, during the expiration process, the expired air consist of the mixture of carbon dioxide and nitrogen.
  3. The method of inspiration is also called as the inhalation process; on the flip side, the act of expiration is also known as the exhalation process.
  4. During inspiration, the mass of the chest cavity increase, whereas during the process of expiration, the mass of the chest cavity decreases.
  5. The intercostal muscles present outside contracts, and the intercostal muscles inside become relaxed during inspiration, while the outside intercostal muscles during expiration relaxed and internal intercostal muscles contract.
  6. The function of intercostal muscles includes forward and outward movement of the rib cage in inspiration; on the other hand, the function of intercostal muscles during expiration is the downward and inward movement of the rib cage.
  7. In the gaseous exchange, oxygen enters into the lungs in the course of inspiration; on the contrary, during expiration, carbon dioxide is removed from the lungs.

Conclusion

The above discussion concludes that inspiration is the active process because of the involvement of muscle contractions. At the same time, expiration is known as the passive process, which is the involvement of muscle relaxation. Inspiration is responsible for taking air into the lungs, whereas expiration is liberating of the air out from the lungs.

Janet White

Janet White is a writer and blogger for Difference Wiki since 2015. She has a master's degree in science and medical journalism from Boston University. Apart from work, she enjoys exercising, reading, and spending time with her friends and family. Connect with her on Twitter @Janet__White