inspiration

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inspiration

respiratory system

Also known as: inhalation

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Last updated

June 29, 2026

Quick Summary

The human respiratory system is responsible for taking in oxygen and expelling carbon dioxide. This process, known as respiration, involves the lungs, airways, diaphragm, and blood.12

Inspiration

Inspiration, or inhalation, is the process of drawing air into the lungs. This occurs when the diaphragm, the principal muscle of respiration, contracts and flattens. This action increases the volume of the thoracic cavity, lowering the pressure within the lungs and causing air to flow in from the atmosphere. Muscles of the chest and abdomen also play a role in expanding the chest cavity.345

Gas Exchange

Once air reaches the lungs, gas exchange takes place in the alveoli, tiny air sacs with an immense surface area. Oxygen from the inhaled air diffuses across a thin membrane into the blood in the pulmonary capillaries. Simultaneously, carbon dioxide, a waste product from the body's tissues, diffuses from the blood into the alveoli to be exhaled.67

Transport of Gases

Blood transports oxygen and carbon dioxide throughout the body. Most oxygen is carried by hemoglobin in red blood cells, while carbon dioxide is transported in several forms, primarily as bicarbonate ions in the plasma and red blood cells. The circulatory system, including the heart and blood vessels, is essential for this transport.6782

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Respiratory mechanisms
…and synchrony of inhalation (inspiration) and exhalation (expiration). Inspiration and expiration are equally long, equally deep, and transport the same amount of air during the same period of time, approximately half a litre (one pint) of air per breath at rest in most adults. Recordings (made with a device…
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…and synchrony of inhalation (inspiration) and exhalation (expiration). Inspiration and expiration are equally long, equally deep, and transport the same amount of air during the same period of time, approximately half a litre (one pint) of air per breath at rest in most adults. Recordings (made with a device…
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poison
Inhalation
The absorption of inhaled gases and vapors differs from that of aerosols and thus will be discussed separately.
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The absorption of inhaled gases and vapors differs from that of aerosols and thus will be discussed separately.
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human respiratory system
The mechanics of breathing
…air enters the lungs (inspiration), provided the larynx is open; when the air pressure within the alveoli exceeds atmospheric pressure, air is blown from the lungs (expiration). The flow of air is rapid or slow in proportion to the magnitude of the pressure difference. Because atmospheric pressure remains relatively…
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…air enters the lungs (inspiration), provided the larynx is open; when the air pressure within the alveoli exceeds atmospheric pressure, air is blown from the lungs (expiration). The flow of air is rapid or slow in proportion to the magnitude of the pressure difference. Because atmospheric pressure remains relatively…
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human respiratory system
Central organization of respiratory neurons
…neurons that discharge in both inspiration and expiration. It is thought that the respiratory cycle of inspiration and expiration is generated by synaptic interactions within these groups of neurons.
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…neurons that discharge in both inspiration and expiration. It is thought that the respiratory cycle of inspiration and expiration is generated by synaptic interactions within these groups of neurons.
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diaphragm
…its internal pressure and causing inspiration of air. Relaxation of the diaphragm and the natural elasticity of lung tissue and the thoracic cage produce expiration. The diaphragm is also important in expulsive actions—e.g., coughing, sneezing, vomiting, crying, and expelling feces, urine, and, in parturition, the fetus. The diaphragm is pierced…
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…its internal pressure and causing inspiration of air. Relaxation of the diaphragm and the natural elasticity of lung tissue and the thoracic cage produce expiration. The diaphragm is also important in expulsive actions—e.g., coughing, sneezing, vomiting, crying, and expelling feces, urine, and, in parturition, the fetus. The diaphragm is pierced…
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