Difference Between Inhalation and Exhalation

Key Differences Between Inhalation and Exhalation

Both inhalation and exhalation are two significant components of the breathing mechanism. These two processes strictly follow Boyle’s Law that states pressure and volume are inversely proportional; likewise, these two parts of respiration rely on the pressure between the lungs and atmosphere. Along with that thoracic cavity plays a significant role in breathing. 

However, the inhalation and exhalation process are different from each other. Nonetheless, both of them are dependent on each other in completing a full circle of respiration. 

A healthy adult takes typically 12-18 breaths per minute. While an inhalation takes two seconds, an exhalation requires three seconds on an average. 

Meaning of Inhalation

Inhalation definition refers to the process of breathing in air, containing oxygen and transporting it to the lungs. It is the first segment of respiration and is known as an active process. During inhalation, the diaphragm and intercostals muscle contract, which results in the expansion of lung volume. Simultaneously, the thoracic cavity expands and allows air to enter the lungs. 

Once you get an idea of what is inhalation now, it’s time to learn about exhalation. 

Meaning of Exhalation

Similarly, exhalation is the process of releasing air containing carbon dioxide out of lungs. It is the concluding part of respiration and is referred to as passive action. During exhalation, diaphragm relaxes and moves towards the thoracic cavity. In this process, the pressure within thoracic cavity increases and allows the air flow out of lungs. 

The inhalation and exhalation process are spontaneous events that do not require any conscious effort.  

Dissimilarities Between Inhalation and Exhalation

Point of Difference




Drawing air and other gases into lungs.

Expelling carbon dioxide from lungs. 


As muscles contract during the process it is an active event.

As muscles do not actively contract, it is a passive event.

Chest Size



Role of Diaphragm

Moves lower due to contraction. 

Moves back higher due to relaxation and takes up the shape of a dome. 

Lung Volume

Increases and inflated.

Decreases and deflated.

Intercostal Muscle Function


Internal muscles relax and external muscles contract.

Internal muscles contract and external muscles relax.

Intercostal Muscle Effect 

Ribcage moves forward and upward.

Ribcage moves backward and downward. 

Components of Air

Mixture of oxygen and other gases is inhaled.

Mixture of carbon dioxide and nitrogen is exhaled.

Air Pressure




Transporting oxygen to blood cells through lungs.

Expelling carbon dioxide from body via lungs. 

The following table contains the striking differences between inhalation and exhalation process. 

Mechanism of Inhalation and Exhalation 

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Fig1: Inhalation and Exhalation Process Diagram

The lung is the primary organ that actively takes part in respiration. However, several other supporting muscles and organs aid in carrying out the inhalation and exhalation process. 

  • Both Inhalation and Exhalation occur due to Pressure Gradients. 

  • During Inhalation, the lung volume increases. According to Boyle’s law the lung pressure reduces compared to atmospheric pressure. It makes the air to rush into lungs. Afterwards, blood promptly transports the air containing oxygen to every part of body. 

  • In the case of expiration, the lung volume decreases because of the elastic flinch of lung tissues. As a result, the pressure within lungs increases compared to the outside pressure. It allows the air carrying carbon dioxide to push out of body. 

  • The tiny sacs within lungs or alveoli also play a crucial role in respiration. 

  • During inspiration, alveoli help in exchanging oxygen with bloodstreams. On the other hand, during expiration, take out carbon dioxide from blood. 

Fill in the Gap: Aerobic respiratory passage is also known as ____________ pathway. 

Answer: Amphibolic 

Gaseous Components During Inspiration and Expiration 


Percentage of Inhaled 

Percentage of Exhaled





Oxygen helps in retaining cellular activity of an organism.

Carbon dioxide



Carbon dioxide comes out as waste product of breathing process. 




Nitrogen gas does not take part in cellular activities.



On higher side

During exhalation a little amount of water evaporates and gets mixed in air. 

Did You Know?

  • Tennis court and lung size can be the same! It may seem absurd, but if the lungs are cut open, it can cover an entire tennis court!

  • The lungs can float on water. It is the only human organ that is capable of doing so. 

FAQs (Frequently Asked Questions)

1. Which one takes more Time, Inhalation or Exhalation?

Ans. Exhalation consumes more time than inhalation. The air we exhale contains not only carbon dioxide but a mixture of other gases. Moreover, exhalation facilitates exchange of gases better; thus, it requires more time. 

2. Why is Exhaled Air Hotter than Inhaled?

Ans. Exhaled air is warmer than inhaled because our body temperature is higher than surrounding temperature. Also, it contains the maximum amount of carbon dioxide. However, both inhalation and exhalation process take part in gaseous exchange through alveoli.  

3. How much Carbon dioxide we Exhale per day?

Ans. Per day we exhale approximately 500 litres of carbon dioxide. It almost amounts to near about 1 kg in mass. 

4. What is 4-7-8 pattern in Breathing?

Ans. It refers to a particular breathing sequence. Inhale quietly through nose for 4 seconds. Then hold the breath for 7 seconds and finally breathe out forcibly through mouth for 8 seconds. Repeating this process for four times will improve the breathing flow.