Difference Between Inhalation and Exhalation

Main Difference – Inhalation vs Exhalation

Inhalation and exhalation are the two process that in the lungs. The main difference between inhalation and exhalation is that inhalation is taking air into the lungs whereas exhalation is the liberating air from lungs. The lungs are situated inside the chest cavity, resting on the diaphragm. The diaphragm is a large, muscular sheet which forms the floor of the chest cavity. It plays a major role in and exhalation by changing the volume of the chest cavity. The external and internal intercostal muscles in the rib cage are also involved in the change of the volume of the chest cavity. During inhalation, the diaphragm moves down and the rib cage moves outwards, increasing the volume of the chest cavity. In contrast, the volume of the chest cavity decreases during the exhalation as the diaphragm moves upwards and the rib cage moves inwards.

Key Areas Covered

1. What is Inhalation
      – Definition, Process, Role
2. What is Exhalation
      – Definition, Process, Role
3. What is the difference between Inhalation and Exhalation
      – Comparison of Key Differences

Key Terms: Inhalation, Exhalation, Breathing, Respiration, Lungs, Diaphragm, Chest Cavity, Oxygen, Carbon Dioxide, Air, Lung Muscles

What is Inhalation

Inhalation is the act of inhaling, which brings air or other vapors into the lungs. It is also called ‘breathing in’. During inhalation, the volume of the lungs is increased by the action of three sets of muscles in the body. They are the diaphragm, the intercostal muscles, and the accessory muscles. The diaphragm contracts and moves downwards, pushing the abdomen out. As the volume of the chest cavity increases, the air pressure inside the lungs decreases, sucking air into the lungs from the external environment. Phrenic nerves, which originate at the C-3, C-4, and C-5 cervical levels of the spinal cord, stimulate the contraction of the diaphragm. Two types of intercostal muscles are attached to the rib cage. They are external intercostal muscles and internal intercostal muscles. The external intercostal muscles contract and internal intercostal muscles relax during inhalation. The intercostal muscles are stimulated by intercostal nerves, which are originated at T-1 to T-11 thoracic levels of the spinal cord. The accessory muscles which are located in the neck are stimulated by the nerves at C-1 to C-3 cervical levels, assisting deep respiration.

What is Exhalation

Exhalation is the act of exhaling, i.e., the act of liberating the air inside the lungs. It is also called ‘breathing out’. During exhalation, the lungs recoil, forcing the air out of the lungs. The nerve signals coming to the diaphragm and intercostal muscles from the respective nerves stop when the walls of the lungs and chest are being stretched due to the inflation by the inhaled air. Thus, the diaphragm and intercostal muscles relax and come to their original positions. The elasticity of the lungs and chest wall cause them to return to a resting shape, expelling the air out of the lungs. Since no muscular contractions are involved in exhalation, it is considered as a passive process. But during coughing, the air blows forcefully out of the lungs. The abdominal muscles, which originate at T-6 to L-1 thoracic, and lumbar levels of the spinal cord contract, forcing the diaphragm upwards during coughing.

Difference Between Inhalation and Exhalation

Definition

Inhalation: The action of inhaling or ‘breathing in’ refers to the inhalation.

Exhalation: The action of exhaling or ‘breathing out’ refers to the exhalation.

Diaphragm

Inhalation: The diaphragm contracts and flattens by moving down during inhalation.

Exhalation: The diaphragm relaxes and becomes dome-shaped by moving up during exhalation.

Intercostal Muscles

Inhalation: The external intercostal muscles contract and internal intercostal muscles relax during inhalation.

Exhalation: The external intercostal muscles relax and internal intercostal muscles contract during exhalation.

Effect of the Intercostal Muscles

Inhalation: The rib cage moves forward and outward due to the effect of intercostal muscles.

Exhalation: The rib cage moves downward and inward due to the effect of intercostal muscles.

Chest Cavity

Inhalation: The size of the chest cavity increases during inhalation.

Exhalation: The size of the chest cavity decreases during exhalation.

Air Pressure

Inhalation: Air pressure inside the lungs is reduced due to the increase of volume in the chest cavity.

Exhalation: Air pressure inside the lungs is increased due to the decrease of volume in the chest cavity.

Air

Inhalation: During inhalation, air from the outside rushes into the lungs.

Exhalation: During exhalation, air goes out of the lungs.

Lungs

Inhalation: The lungs are inflated during inhalation.

Exhalation: The lungs are deflated during exhalation.

Active/Passive Process

Inhalation: Since muscular contractions are involved in the process of inhalation, it is an active process.

Exhalation: Since no muscular contractions are involved in the process of exhalation, it is considered as a passive process.

Respiratory Gas Exchange

Inhalation: During inhalation, oxygen is taken into the blood.

Exhalation: During exhalation, carbon dioxide is taken off from the blood.

Chemical Composition of the Air

Inhalation: Inhaled air is composed of an oxygen-nitrogen mix.

Exhalation: Exhaled air is composed of a carbon dioxide-nitrogen mix.

Conclusion

Inhalation and exhalation are the two opposite actions involved in breathing. Inhalation is an active process in which the oxygenated air rushes into the lungs. Oxygen gas from the air is dissolved in the alveoli and diffuses into the blood. It is required for cellular respiration, which produces energy inside the cell. Carbon dioxide is produced as a metabolic waste during cellular respiration. It dissolves in the blood and diffuses into the alveoli. Carbon dioxide is removed from the body during exhalation. Exhalation is a passive process in which the air is expelled from the lungs. The main difference between inhalation and exhalation is in their mechanisms and their functions in the body.

Reference:
“The Mechanics of Human Breathing.” Boundless. N.p., 08 Aug. 2016. Web. Available here. 31 May 2017.

Image Courtesy:
“Inhalation and exhalation, diaphragm movement” by Siyavula Education (CC BY 2.0) via Flickr