Sputum, often called phlegm when coughed up, is thick mucus produced in the lungs. It's not saliva; it's created to keep the delicate lung tissues moist and trap foreign particles, protecting the respiratory system.
The Process of Sputum Formation
The formation of sputum involves several key steps:
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Plasma Filtration: Sputum originates from a plasma filtrate derived from blood capillaries in the lungs. This filtrate is found in small amounts between the layers of the pleura, the membranes surrounding the lungs. [ScienceDirect Topics]
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Mucus Secretion: Specialized cells lining the airways (bronchi and bronchioles), called goblet cells, secrete mucus. This mucus is primarily composed of water, glycoproteins (mucins), lipids, and inorganic salts. [Verywell Health]
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Trapping Foreign Matter: This mucus acts as a sticky trap, catching inhaled particles like dust, pollen, bacteria, and other irritants.
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Ciliary Action: Tiny hair-like structures called cilia, located on the epithelial cells lining the airways, beat rhythmically to move the mucus (with its trapped debris) upwards towards the throat.
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Coughing: When the amount of mucus becomes excessive (due to illness or irritation), or when it contains irritating substances, a cough reflex is triggered, expelling the mucus from the lungs as sputum. [Physiopedia, News-Medical]
In summary, sputum isn't simply produced; it's a complex process involving filtration, secretion, trapping, transport, and expulsion. The body generates it as a natural defense mechanism, but its appearance and consistency can change significantly depending on underlying health conditions. [Medical News Today]
