Difference Between Inspiration and Expiration

The main difference between inspiration and expiration is that inspiration (inhalation) is the process of taking air into the lungs whereas expiration (exhalation) is the process of liberating air from the lungs. Furthermore, inspiration is important for taking oxygen into the blood through the respiratory membrane while expiration is important for the removal of carbon dioxide to the outside. In addition, inspiration is an active process while expiration is a passive process. 

Inspiration and expiration are the two phases of the process of breathing. Generally, lungs are the primary organs responsible for respiration in most vertebrates. 

Key Areas Covered 

1. What is Inspiration
     – Definition, Process, Importance
2. What is Expiration
     – Definition, Process, Importance
3. What are the Similarities Between Inspiration and Expiration
     – Outline of Common Features
4. What is the Difference Between Inspiration and Expiration
     – Comparison of Key Differences

Key Terms 

Expiration, Inspiration, Lungs, Respiration

What is Inspiration 

Inspiration is the phase of taking air into the lungs during the process of breathing. It is an active process that occurs as a result of muscular contractions. Generally, the two groups of muscles involved in regular inspiration are the diaphragm and the external intercostal muscles. Here, the contraction of the diaphragm moves it inferiorly toward the abdominal, cavity increasing the space of the thoracic cavity.  Meanwhile, the contraction of the external intercostal muscles moves the ribs upward and outward, increasing the volume of the thoracic cavity.

Figure 1: Inspiration and Expiration 

Furthermore, the expansion of the thoracic cavity results in the expanding of the lungs due to their adhesion to the pleural fluid. Subsequently, this expansion decreases in intra-alveolar pressure lower than atmospheric pressure. This pressure gradient makes atmospheric air to enter the lungs. Moreover, inspiration is important for taking oxygen into the blood. 

What is Expiration 

Expiration is the passive phase of liberating air out of the lungs. Generally, pushing air out of the lungs does not require energy. Usually, both diaphragm and the external intercostal muscles relax during expiration, recoiling the lungs. Then, this results in the reduction of the volume of the thoracic cavity, increasing the interpulmonary pressure higher than the atmospheric pressure. Ultimately, the air inside the lungs liberates out of the lungs.  

Similarities Between Inspiration and Expiration 

• Inspiration and expiration are the two phases of the process of breathing. 
• Moreover, they occur in the lungs. 
• They are responsible for the gas exchange by taking oxygen into the body while removing carbon dioxide out of the body. 

Difference Between Inspiration and Expiration 

Definition 

Inspiration refers to the act of drawing air into the lungs while expiration refers to the act of releasing air from the lungs through the nose or mouth. 

Also Known as 

Inhalation is another name for inspiration while exhalation is another name for expiration. 

Active or Passive 

Another difference between inspiration and expiration is that inspiration is an active process while expiration is a passive process. 

Diaphragm 

The diaphragm moves down by contracting and becoming flat during inspiration while the diaphragm moves up by relaxing and becoming dome-shaped during expiration. 

Intercoastal Muscles 

Moreover, the external intercostal muscles contract and internal intercostal muscles relax during inspiration while the external intercostal muscles relax and internal intercostal muscles contract during expiration. 

Intercoastal Muscles Function 

The rib cage moves forward and outward by the action of intercostal muscles during inspiration while the rib cage moves downward and inward by the action of intercostal muscles during expiration. 

The Size of the Chest Cavity 

The size of the chest cavity increases during inspiration while the size of the chest cavity decreases during expiration. 

Air Pressure 

Air pressure inside the lungs decreases due to the increase of volume of the chest cavity during inspiration while air pressure inside the lungs increases due to the decrease of volume in the chest cavity during expiration. 

The Movement of Air 

Air moves into the lungs during inspiration while air moves out of the lungs during expiration. 

Gas Exchange 

Oxygen is taken into the lungs during inspiration while carbon dioxide is removed from the lungs during expiration. 

Chemical Composition of Air 

Inspired air is an oxygen-nitrogen mix while expired air is a carbon dioxide-nitrogen mix.  

Conclusion 

Inspiration or inhalation is one of the two phases of breathing. It is also responsible for taking air into the lungs in response to the decreased pressure inside the chest cavity. This air is rich in oxygen; therefore, red blood cells in the blood take oxygen in through the respiratory membrane. In contrast, expiration or exhalation is the second phase of breathing. However, it is responsible for liberating air out of the lungs in response to the increasing pressure inside the chest cavity. On the other hand, this removes carbon dioxide out of the blood. Meanwhile, inspiration is an active process due to its involvement of the contraction of muscles. Hence, the main difference between inspiration and expiration is the type of process and importance. 

References:

1. “148 22.3 The Process of Breathing.” ANATOMY AND PHYSIOLOGY|BC Campus, Pressbooks. Available Here.

Image Courtesy:

1. “2316 Inspiration and Expiration” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia