Mucus

# Overview
Mucus is a slippery secretion of the lining of the mucous membranes in the body. It is a viscous colloid containing antiseptic enzymes (such as lysozyme) and immunoglobulins. Mucus is produced by goblet cells in the mucous membranes that cover the surfaces of the membranes. It is made up of mucins and inorganic salts suspended in water.  Phlegm is a type of mucus that is restricted to the respiratory tract, while the term mucus refers to secretions of the nasal passages as well.Mucus can be found in your nose.

# Functions
Mucus serves many different functions within the processes in an animal's body:

## Respiratory system
In the respiratory system, mucus traps particles such as bacteria and dust, helping to prevent them from entering the body; this occurs especially in the nose. Mucus aids in the protection of the lungs by trapping foreign particles that enter the nose during normal breathing.  Additionally, it prevents tissues from drying out.
Increased mucus production in the respiratory tract is a symptom of many common illnesses, such as the common cold. The presence of mucus in the nose and throat is normal, but increased quantities can impede comfortable breathing and must be cleared by blowing the nose or expectorating phlegm from the throat. Among the components of nasal mucus are tears.
Dried nasal mucus (vulgarly or colloquially called "snot", "booger(s)", "boogie(s)" (US) or "bogey" (UK)) is partially solidified mucus from the nose. Dried nasal mucus forms when the mucus traps dust and other particles in the air.  Mucus dries around the particle and hardens, somewhat like a pearl forming in an oyster.  Since catching foreign particles is one of the main functions of nasal mucus, the presence of dried nasal mucus is a good indicator of a properly functioning nose.

### Mucin
Mucus is produced by submucosal cells as well as goblet cells in the respiratory system. It consists of mucin, a highly glycosylated peptide. Upon stimulation, MARPKs (myrastine-alanine rich protein kinases) signal the binding of mucin filled vesicles to the plasma membrane. The fusion of the vesicles causes the release of the mucin, which as it exchanges Ca2+ for Na+ expands up to 600 fold. The result is a viscoelastic product of interwoven molecules called mucus.

## Digestive system
In the digestive system, mucus is used as a lubricant for materials which must pass over membranes, e.g., food passing down the esophagus.  A layer of mucus along the inner walls of the stomach is vital to protect the cell linings of that organ from the highly acidic environment within it.

## Reproductive system
In the female reproductive system, cervical mucus prevents infection and helps the movement of the penis during sexual intercourse. When thin, cervical mucus helps the movement of spermatozoa. The consistency of cervical mucus varies depending on the stage of a woman's menstrual cycle. At ovulation cervical mucus is clear, runny, and conducive to sperm; post-ovulation, mucus becomes thicker and is more likely to block sperm.
In the male reproductive system, the seminal vesicles located behind the bladder contribute up to 60% of the total volume of the semen and contain mucus, amino acids, and fructose as the main energy source for the sperm.

## Nasal mucus
Nasal mucus is mucus produced by the nasal mucosa. It serves to protect the respiratory tract and trap foreign objects such as dust and pollen before they enter the remainder of the respiratory tract. Nasal mucus is produced continually, and most of it is swallowed unconsciously.

# Diseases involving mucus
Generally mucus is clear and thin, serving to filter air during inhalation.  During times of infection, mucus can change color to yellow or green either as a result of trapped bacteria, or due to the body's reaction to viral infection.
In the case of bacterial infection, the bacterium becomes trapped in already clogged sinuses, breeding in the moist, nutrient-rich environment.  In this case, the clogged sinuses are a result of some other condition (such as allergies) and the bacterial infection is secondary to this original cause.  When two different colors of common bacteria become mixed (such as yellow Staphylococcus aureus and blue Pseudomonas aeruginosa) the resulting shade is often green.  Antibiotics may be used fruitfully to treat the secondary infection in these cases, but will generally not help with the original cause.
In the case of a viral infection such as cold or flu, the first stage of infection causes the production of a clear, thin mucus in the nose or back of the throat.  As the body begins to react to the virus (generally one to three days), mucus thickens and may turn yellow or green.  In these cases, antibiotics will not be useful, and are a major source of misuse.  Treatment is generally symptom-based; the only cure is to allow the immune system to fight off the virus over time.

## Cystic fibrosis
Cystic fibrosis is an inherited disease that affects the entire body, but symptoms begin mostly in the lungs with excess production of mucus which is difficult to expel.

# Cold weather and mucus
During cold weather, the cilia which normally sweep mucus away from the nostrils and towards the back of the throat (see respiratory epithelium) become sluggish or completely cease functioning.  This results in mucus running down the nose and dripping (a runny nose).  Mucus also thickens in cold weather; when an individual comes in from the cold, the mucus thaws and begins to run before the cilia begin to work again.

## As a medical symptom
Increased mucus production in the respiratory tract is a symptom of many common diseases, such as the common cold. The presence of mucus in the nose and throat is normal, but increased quantities can hinder comfortable breathing and may be cleared by blowing the nose or expectorating excess mucus from the back of the throat. Nasal mucus may also be removed by using traditional methods of nasal irrigation. Excess mucus, as with a cold or allergies may be treated cautiously with decongestant drugs. Excess mucus in the bronchial tubes, as which occurs in asthma or bronchitis, may be treated with anti-inflammatory drugs to reduce the mucus production.  Thickening of mucus by decongestant drugs may produce problems of drainage and circumstances that promote infection. Mucus with any color other than clear or white is generally an indicator of an infection of the nasal mucosa or the paranasal sinus.

# Dried mucus
Dried mucus forms when the mucus traps dust and other particles in the air and becomes desiccated.  Mucus dries around the particle and  hardens into a solid or semi-solid sticky object, resulting in the particle's eventual expulsion from the body.  Since catching foreign particles is one of the main functions of nasal mucus, the presence of dried mucus formations is a good indicator of a properly functioning nose (as opposed to a "runny nose", which can indicate illness).

## Rhinolith
A rhinolith is sometimes mistaken for dried mucus but is actually a medical condition caused by salt deposition with the nasal cavity.

## Slang terms
A "loogie" is a slang expression used in North America to refer to a mass of sputum that is ejected from the mouth after being expelled from the throat of a person with nasal congestion.  The expression "hocking a loogie" refers to expelling the phlegm in an obviously noisy manner involving violent vibrations of the uvular, producing a low, guttural, rumbling sound.  "Hock" (alternate spelling "hawk") is derived from the archaic word "hough," pronounced the same way, meaning to clear one's throat.  The word "loogie" arose as early as 1970, and appears to be a conjunction of the older slang "lung-er" (meaning an expectoration or a tuberculosis patient) and the word "booger" or "boogie."  This practice may have other names in other countries and within the medical community. In the UK, the mass can be referred to as a 'flob', a portmanteau of the phonetic pronunciation of phlegm and 'gob', a slang term for saliva.
A "snot rocket" is a slang term referencing the act of holding one nostril while forcefully exhaling through the other mucous filled nostril resulting in a "rocket"-like projection of mucus from the nose and sinuses.  This is also known as a "dustman's flick", "air hanky", "farmer's blow", "nose gob" or "farmer's hanky" or more offensively as a "guinea hankerchief" and "dutch hanky."
Dried nasal mucus is often removed by nose-picking. The social taboos regarding nasal mucus have also led to a wide variety of slang terms for nasal mucus. These include "snot", or "snotter" (Scottish), for nasal mucus; and "boogers" (U.S.), "boogies" (U.S.), or "bogies" (UK) for dried nasal mucus.