Inhalation or Inspiration is a part of breathing where the air is taken into the lungs by creating negative pressure by the contraction of respiratory muscles and diaphragm.
- Inhalation is a vital physical process and is autonomous that occurs without concise or control. However, breathing as a process can be controlled or interrupted to certain limits.
- Inhalation is an active process that requires energy.
- It allows the intake of air that carries oxygen into the lungs, which is then diffused into the bloodstream.
- Inhalation results in an increase in the volume of the lungs by the contraction of various respiratory muscles.
- The space between the outer wall and thoracic wall, called pleural space, is filled with pleural fluid that forms a seal of the lungs from the thoracic wall.
- This seal allows the thoracic cavity to expand, ensuring the expansion of lungs.
- In the process of inhalation, two important muscles are at work; diaphragm and external intercostal muscles.
- The diaphragm flattens by contraction, extending the thoracic cavity upwards. At the same time, the external intercostal muscles contract, and the internal intercostal muscles relax to elevate the ribs and sternum, causing the thoracic cavity to move outwards.
- By the contraction of these muscles, the volume of the thoracic cavity increases, and the connection of lungs to the cavity by the pleural sac eventually allows the increase in the volume of lungs.
- With the increase in the volume of lungs, the pressure in the lungs decreases as per Boyle’s Law.
- As a result, the pressure of the lungs becomes smaller than the pressure of the outside environment. This difference in pressure or pressure gradient allows the movement of air into the lungs through the respiratory passage.
- During inhalation, the air is taken in through the nose that passes through the nasal passage, the pharynx, the larynx to reach the respiratory tree.
- The respiratory tree begins with the trachea that is divided into several narrower branches.
- The air thus passes through these branches and finally reaches the alveoli. The exchange of gases takes place in the alveoli where the oxygen is diffused into the blood present in the blood vessels.
- Forced inhalation is a process that occurs during exercise which occurs by the contraction of accessory muscles like scalenes, sternocleidomastoid, pectoralis major and minor, serratus anterior and latissimus dorsi. All of these muscles assist in increasing the volume of lungs.
Exhalation or Expiration is a part of breathing where the air is drawn out of the lungs by the relaxation of respiratory muscles.
- Exhalation is also a vital physical process and is autonomous that occurs without concise or control. However, the process can be controlled or interrupted to certain limits.
- The main purpose of expiration is to get rid of carbon dioxide that is produced in the body by the process of cellular respiration.
- Exhalation results in a decrease in the volume of the lungs by the relaxation of various respiratory muscles.
- The same set of muscles is involved in expiration as in inspiration but the mechanism of exhalation is opposite to that in inhalation.
- The diaphragm relaxes back to its initial position pulling the thoracic cavity downwards to its previous position.
- Meanwhile, the external intercostal muscles relax and internal intercostal muscles contract, causing the ribs and sternum to fall back which pulls the thoracic cavity inwards.
- The relaxation of these muscles causes a decrease in the volume of the thoracic cavity and the lungs.
- The decrease in volume causes pressure within the lungs that is greater than that of the environment.
- As a result, the air in the lungs is drawn out through the respiratory passage.
- The air in the lungs comes from the diffusion of air from the blood vessels into alveoli after exchanging oxygen and carbon dioxide.
- The air then passes through the respiratory tree, the trachea, and the pharynx and finally passes through the nasal passage before moving out of the body.
- Exhalation takes a longer time than inhalation as it allows a better exchange of gases than inspiration.
- Like in inhalation, the air coming out of the lungs is not just carbon dioxide but a mixture of gases with methanol, isoprene, and other alcohols.
- Exhalation is a passive process controlled by the respiratory centers in the medulla oblongata and pons.
- Voluntary exhalation is an active process that occurs during exercise and is controlled by a more complex neurological pathway.
- It is controlled by the same motor cortex in the brain’s cerebral cortex that controls the voluntary muscle movement.
- The signals from the cortex control the accessory muscles that are involved in forced expiration. Some of these muscles include anterolateral abdominal, internal intercostals, and innermost intercostals that assist in the contraction of the lungs.
Key Differences (Inhalation vs Exhalation)
Basis for Comparison
|Definition||Inhalation is a part of breathing where the air is taken into the lungs by creating negative pressure by the contraction of respiratory muscles and diaphragm.||Exhalation is a part of breathing where the air is drawn out of the lungs by the relaxation of respiratory muscles.|
|Also called||Inhalation is also called inspiration.||Exhalation is also called expiration.|
|Process||Inhalation is an active process as it involves the contraction of muscles.||Exhalation is a passive process as it involves the relaxation of muscles.|
|Diaphragm||The diaphragm contracts and flattens during inhalation causing it to move down.||The diaphragm relaxes and becomes dome-shaped causing it to move up.|
|External intercostal muscles||The external intercostal muscles contract during inhalation.||The external intercostal muscles relax during exhalation.|
|Internal intercostal muscle.||The internal intercostal muscles relax during inhalation.||The internal intercostal muscles contract during exhalation.|
|Ribs and sternum||The ribs and sternum move forwards and outward as a result of the contraction of intercostal muscles.||The ribs and sternum move downwards and inward as a result of the relaxation of intercostal muscles.|
|Thoracic cavity||During inhalation, the volume of the thoracic cavity increases.||During exhalation, the volume of the thoracic cavity decreases.|
|Lungs||The size of the lungs increases during inhalation.||The size of the lungs decreases during exhalation.|
|Air composition||The air going into the lungs is composed largely of nitrogen and oxygen.||The air coming out of the lungs is composed largely of carbon dioxide and nitrogen.|
|Air pressure||The pressure of the air inside the lungs is less than that of the external environment.||The pressure of the air inside the lungs is greater than that of the external environment.|
|Air movement||The air moves from the environment into the lungs.||The air is drawn out from the lungs into the environment.|
|Diffusion||Oxygen diffuses from the alveoli into the blood.||Carbon dioxide diffuses out of the blood into the alveoli.|
|Time||The process of inhalation is shorter than exhalation.||The process of exhalation takes longer than inhalation.|
|Accessory muscles involved||The accessory muscles involved during forced inspiration are scalenes, sternocleidomastoid, pectoralis major and minor, serratus anterior, and latissimus dorsi.||The accessory muscles involved during forced exhalation are anterolateral abdominal, internal intercostals, and innermost intercostals.|
References and Sources
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- 1% – https://simple.wikipedia.org/wiki/Intercostal_muscle
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- 1% – https://en.m.wikipedia.org/wiki/Exhalation
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