The body produces mucus because the substance exhibits characteristics that help it prevent and fight infection. The body also uses it as a catalyst for certain reproductive functions and as a lubricant. The water-based liquid contains carbohydrates, salts, and protein, all needed by multiple organ systems. The primary proteins are encapsulated in a sugar substance that allows them to absorb large amounts of water, which produce the hydrating properties of mucus on which the body depends for homeostasis. Some proteins are antibodies that kick start the body’s immune system when a foreign invader is detected. Other proteins are antiseptic enzymes that kill the invader as soon as it comes into contact with phlegm.
The average body produces over 4 cups (1 liter) of mucus every day. The majority of it is produced by the respiratory system, where it serves several purposes. As air enters the nasal passageways, mucus traps larger particles that would clog the narrow airways. If any of the particles that gets trapped in the phlegm are pathogenic, the antiseptic and antibiotic properties work to kill the bacteria, virus, or fungi. It also aids in moisturizing the inhaled air, which keeps membranes within the body from drying out due to respiration.
Mucus also functions as the body’s most abundant lubricant. After particles are trapped during respiration, the body propels the lubricated substance, by way of small moving hairs called cilia, toward the stomach. In the stomach, acid can complete the process of killing any pathogens that may infect healthy cells. Cells within the digestive system also produce a large amount of mucus that is used as a lubricant to help propel food through the esophagus. The lining of the stomach also requires a lubricant layer, because while acid is useful in killing infectious particles, it will also eat away at the cells that form the lining if it is not adequately protected.
The female reproductive system relies on mucus to help regulate its cycle. During ovulation, the produced substance is clear and runny. The watery lubricant is conducive to sperm reception and fertilization. Post ovulation, it becomes thicker, and this substance, which also contains more antibiotic proteins, may prevent sperm from traveling any farther than the vagina, preventing fertilization. The male reproductive system produces it in conjunction with semen by way of the seminal vesicles, and this mucus contains carbohydrates and sugars that nourish the sperm during its life cycle.