Inhalation in mammals is a vital process of respiration that facilitates the exchange of gases between the atmosphere and the organisms' bloodstream. The process can be divided into several steps involving various structures of the respiratory system:
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Diaphragm and Intercostal Muscles: Inhalation begins with the contraction of the diaphragm, a dome-shaped muscle located at the base of the thoracic cavity. At the same time, the external intercostal muscles, located between the ribs, contract. This combination of muscle contractions expands the thoracic cavity.
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Expansion of the Thoracic Cavity: As the diaphragm moves downward and the rib cage expands outward, the volume of the thoracic cavity increases. This expansion lowers the air pressure inside the thoracic cavity compared to the atmospheric pressure outside the body.
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Airflow into the Lungs: The pressure difference created allows air to flow into the lungs through the trachea (windpipe), which divides into the left and right bronchi, leading to the bronchioles and eventually into the alveoli (tiny air sacs). The airways are lined with mucous membranes that help filter, warm, and moisten the incoming air.
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Gas Exchange: In the alveoli, oxygen from the inhaled air diffuses across the thin alveolar walls into the surrounding capillaries, where it binds to hemoglobin in red blood cells. Meanwhile, carbon dioxide, a waste product of metabolism in the body, diffuses from the blood into the alveoli to be exhaled.
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End of Inhalation: Inhalation continues until intrathoracic pressure equilibrates with atmospheric pressure. Once this occurs, the diaphragm and intercostal muscles relax, which leads to the next phase of the respiratory cycle: exhalation.
This process is carefully regulated by the respiratory centers in the brain, which respond to levels of carbon dioxide and oxygen in the blood to ensure efficient breathing and gas exchange.
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