What is the origin of mucus?

From the Guidelines

Mucus is primarily produced by specialized cells called goblet cells and mucous glands located in the epithelial lining of the respiratory and digestive tracts. These cells continuously produce mucus, a thick, slippery substance composed of water, mucin proteins, electrolytes, and antimicrobial enzymes 1. In the respiratory system, mucus is produced by the nasal passages, sinuses, throat, and lungs, serving to trap inhaled particles, bacteria, and viruses. The presence of a gel-like mucus in the airways of healthy people is essential for normal mucociliary clearance, with the mucus being eliminated by the action of mucociliary clearance to the hypopharynx, where it is swallowed and rarely noticed 1.

Some key points about mucus production include:

• The body typically produces about 500 mL of sputum daily, which is usually not noticed 1
• Smokers with chronic bronchitis produce larger amounts of sputum each day, as much as 100 mL/d more than normal, resulting in cough and sputum production 1
• The excess mucus in chronic bronchitis occurs as a result of an increase in the size and number of the submucosal glands and an increase in the number of goblet cells on the surface epithelium 1
• Mucous gland enlargement and hyperplasia of the goblet cells are the pathologic hallmark of chronic bronchitis, with goblet cells normally absent in the small airways, and their presence there (often referred to as mucous metaplasia) being important to the development of COPD 1.

Overall, the production of mucus is a critical component of the body's defense mechanism, and its increased production during illness or irritation helps to trap and remove irritants or pathogens from the body 1.

From the Research

Origin of Mucus

• Mucus is a highly specialized secretory fluid produced by goblet or mucous-producing cells that line the epithelial surfaces of all organs exposed to the external world 2.
• The major structural and functional component of mucus is mucin, a complex glycoprotein coded by about 20 mucin genes 2.
• Mucin is synthesized in the endoplasmic reticulum and further modified via glycosylation in the cis and medial Golgi, before being packaged into mucin granules and released from the cells through exocytosis 2.

Production and Composition of Mucus

• Mucus is composed of water, ions, and various kinds of macromolecules, including mucin, which is responsible for its viscoelastic property 3.
• There are at least eight mucin genes identified in the human airways, which can generate various kinds of mucin molecules 3.
• The defensive role of airway surface liquid (ASL) is determined not only by individual components but also by a combination of these components, including mucins and other macromolecules 3.

Mucus Production in Different Organs

• Mucus is produced in various organs, including the lungs, intestine, and respiratory tract, where it plays a crucial role in protecting the body against foreign particles and pathogens 4, 5, 6.
• In the lungs, mucus is cleared by cilia and airflow, and its transport rates are heavily dependent on mucus concentration 5.
• In the intestine, mucus is attached to the epithelium and plays a crucial role in protecting the body against bacteria and other pathogens 6.