Mucous Glands: Definition, Composition, Function, Associated Conditions and Importance

We are talking about a set of cells responsible for the production of mucus.

The mucous glands, also known as the mucípal glands , are found in different parts of the body and generally stain more lightly than the serous glands during standard histological preparation.

The mucous glands consist of thin superficial layers over a supporting layer of connective tissue. Many contain glands that produce mucus, but some, including those in the urinary tract, produce no or only a small amount of mucus.

Mucus has a reputation as a thick substance and is one that many people would want to avoid.

It is actually a very useful material with important functions. It destroys bacteria and viruses, traps particles such as dirt, prevents water loss, humidifies passages, lubricates material movement, and protects surfaces from damage.

Mucus is a slippery fluid made by mucous membranes. The membranes line the corridors of our bodies that connect to the outside environment. These passages include the nose, mouth, respiratory tract, digestive tract, and reproductive tract.

A mucous membrane is also found on the white of the eye and on the inside of the eyelid.

Composition and state of mucus

Mucus contains water, proteins such as mucins, antibodies, antiseptics, and salts. Mucins are glycoproteins, which are proteins with attached carbohydrates. The carbohydrate coating gives the mucin molecules a great ability to absorb water.

Antibodies help the immune system to attack pathogens (organisms that cause disease), while antiseptics kill pathogens directly.

Although mucus is important in many places in the body, for most of us its presence is most obvious in the nose and respiratory tract.

People may not deliberately look at your nasal mucus or mucus, but may accidentally notice that it occasionally has an unusual appearance. The change is usually temporary and harmless, but sometimes it indicates a problem.

Function of the mucous glands in the respiratory system

We produce between one and two liters of mucus in the respiratory tract every day. If we have a respiratory infection we produce even more.

The role of cilia in the respiratory tract

In the airways of the lungs, mucus traps inhaled particles and humidifies the air. Small hair-like structures called cilia line the airways.

The cilia beat in a coordinated pattern, sweeping the mucus down the back of the throat, where it was swallowed or released into the nose.

Smoking can damage the cilia and cause a buildup of mucus in the respiratory tract. Mucus buildup can make breathing difficult and cause a person to cough frequently in an effort to clear the blockage.

The paranasal sinuses

They are divided into four:

  • Frontal sinus.
  • Ethmoid sinuses or ethmoidal air cells.
  • Sphenoid sinuses.
  • Maxillary sinuses.

The sinuses are hollow spaces in the facial bones. They are lined with a mucous membrane that produces mucus. The function or functions of the breasts are unknown.

They can humidify the air we breathe, protect sensitive areas such as tooth roots from rapid changes in temperature, lighten the skull, act as crumple zones during an impact, or increase the resonance of our voice.

The sinuses are not isolated but are connected to other structures in the face, including the nose. This means that bacteria can travel to a breast and cause an infection.

A sinus infection is called sinusitis. It involves inflammation of the lining of the sinus and excessive mucus production. The mucus can be yellow or green in color and is discharged through the nose or down the throat through post-nasal drip.

Nasal mucus color

The mucus just produced by the respiratory system is colorless. When removed from the nose, it can be gray, white, yellow, green, brown, black, orange, pink, red, or a rust color. Colored mucus sometimes indicates a health problem, but this is not always the case.

Some of the most common reasons for mucus color changes are listed below. However, there are other reasons for some of the changes. A doctor should be consulted if anyone is concerned about the appearance of their nasal mucus.

Gray, white, yellow, or green mucus


The trapped mucus that is removed from the nose is usually gray in color due to the dust and dirt it contains and the fact that it has partially dried. The dry group of mucus is colloquially known as a “booger.”

Cloudy or white

A cloudy appearance suggests that the tissues are inflamed and swollen, causing the mucus to move more slowly, lose moisture, thicken, and become cloudy.

The inflammation may be due to an infection or allergy. Mucus that is white rather than cloudy can indicate an infection such as a cold.

Yellow or green

Yellow or green mucus does not necessarily indicate an infection is present. However, if the colors are persistent, there may be a viral or bacterial infection.

The Cleveland Clinic recommends that people see a doctor after twelve days with green mucus. Harvard Health Publications recommends a doctor visit after ten days. However, if there are other symptoms besides colored mucus, you should visit the doctor much earlier.

The green color is due to the presence of a colored enzyme called green peroxidase, which is released by white blood cells or leukocytes. Some of these cells actively fight pathogens.

Others are involved in the inflammatory response, which often accompanies allergies. Therefore, yellow or green mucus may appear due to allergies or infections.

Medical sources sometimes differ in their ideas about the meaning of mucus color. However, everyone agrees on the following points. If an unusual color persists, or if the change is accompanied by other symptoms such as fever, you should see a doctor.

Brown, black, orange, or red mucus

Brown or black

Brown mucus can be caused by dirt in the nose or by the presence of blood. Black mucus can be caused by a significant fungal infection that requires medical treatment.

Cigarette smoke can stain the mucus in the respiratory system brown or black. Coal miners can also develop black mucus from inhaling coal dust.

Orange, red, or rust-colored

People with pneumonia can produce mucus with a burnt orange color, which is caused by the presence of blood. Anyone with pneumonia should be under the care of a doctor.

Pink, red, or rust-colored mucus also indicates the presence of blood. In these cases, the blood can be produced by a minor wound in the nostrils. However, if the red color persists or if a large amount of blood is released, the advice of a physician should be sought.

The digestive tract is lined with a mucous membrane that produces mucus.

Mucus in the mouth and stomach


The saliva in the mouth contains mucus with a thin consistency. This mucus is an excellent lubricant and facilitates the ingestion of food.


The stomach lining is covered in a protective layer of mucus. The glands in the stomach produce mucus, hydrochloric acid, and an inactive enzyme called pepsinogen.

In the stomach cavity, hydrochloric acid transforms pepsinogen into an active digestive enzyme called pepsin. This enzyme digests proteins. The mucus layer acts as a barrier that prevents the stomach lining from being attacked by pepsin and acid.

If the mucus layer in the stomach thins or is shed, which can occur during an infection with a bacteria called Helicobacter pylori, pepsin and acid can attack the stomach lining. The infection can cause inflammation (gastritis) and sores called ulcers.

This is part of the mucosa that lines the small intestine. The folds are known as villi. They increase the surface area for the absorption of digested food.

The intestine

The glands in the lining of the small intestine and the large intestine also produce mucus. There is often some mucus in the stool, but generally it is not enough to be noticeable.

Notable amounts can show up in intestinal problems such as the predominant form of irritable bowel syndrome (IBS) diarrhea.

The mucus looks like a thin, shiny jelly. In ulcerative colitis, the lining of the large intestine becomes inflamed and ulcers develop. Mucus and blood are often released in the stool in this disorder.

The reproductive tract

The cervix is ​​the lower end of the uterus. The glands in this area produce cervical mucus. The consistency of this mucus changes during a woman’s monthly cycle as reproductive hormone levels change in her body.

Cervical mucus helps prevent infection and supports or inhibits sperm movement.

After menstruation, very little cervical mucus is produced. As the cycle progresses, the amount increases. The mucus is white or cream-colored and sticky.

Around the time of ovulation, when an egg is released from an ovary and the woman is more fertile, the mucus is more abundant and is colorless, thin, and often stretchy.

This is the best texture to allow penetration of the sperm. After ovulation, mucus decreases in quantity, becomes cloudy, and re-develops a sticky texture.

Mucus is important in the eye

The eyes

The conjunctiva is a mucous membrane that covers the white part of the eye (the sclera) and the inside of the eyelid. It produces a thin mucus that lubricates the eye and contributes to the formation of tears.

Tears have three layers:

  1. A layer of internal mucus made by the conjunctiva.
  2. A watery middle layer made by the lacrimal gland.
  3. A fatty outer layer made by the meibomian glands in the eyelids.

Once the tears and mucus have spread over the surface of the eye, they drain into the nose through small openings in the inner corner of the eye.

Each opening is called a lacrimal point. Some people wake up in the morning with dried mucus particles in the corner of the eye due to improper drainage while asleep and do not blink.

Cystic fibrosis or CF.

Cystic fibrosis is a genetic disorder in which the body produces mucus that is much thicker and stickier than normal. Thick material cannot move very easily and collects in passages in the body.

Mucus in the breathing tubes makes breathing difficult and often leads to bacterial infections. Also, mucus often blocks the tube that carries digestive enzymes from the pancreas to the small intestine.

This results in a reduction in the digestion of food, especially carbohydrates and fats, and therefore reduces the absorption of nutrients.

People with cystic fibrosis generally have a shorter life. However, the good news is that the average lifespan of patients is increasing rapidly in many countries due to improved treatments.

The goal of the research is to give patients a normal lifespan and a better quality of life.

A significant part of each day in the life of a CF patient is spent on treatments to clear the lungs. They take many pills a day.

They periodically use oxygen inhalers and wear a vibrating vest to break up the mucus in the lungs. Also, digestive enzymes are taken with all meals and snacks to get enough nutrients from food.

Cystic fibrosis results from a mutation in both copies of the gene for a protein called cystic fibrosis transmembrane conductance regulator, or CFTR.

Health problems associated with cystic fibrosis


Asthma is another problem that involves the production of more mucus than normal. People with this disorder have airways that are sensitive to specific allergens or irritants.

Irritants include dust mites, cold air, cigarette smoke, certain components of food, or exercise. During an asthma attack, the airways become inflamed and inflamed, restricting the passage of air.

The airways produce extra mucus, which further blocks the passage of air. Also, the muscles surrounding the airways contract, contracting the air passages. A hissing or whistling sound is often heard when the person breathes.

Asthma can be treated and controlled, but it cannot be cured. Many asthmatics find that with their doctor’s guidance they can reduce, weaken, and even eliminate asthma attacks. However, sometimes asthma is more difficult to manage, and occasionally it can be a medical emergency.


Bronchitis involves inflammation of the airways and excessive mucus production. Acute bronchitis lasts for a short time and is usually caused by a viral infection. Chronic bronchitis lasts a long time and is usually permanent. It usually results from smoking or chronic inhalation of certain chemicals or pollutants.

People with acute bronchitis can produce colored mucus in their airways. This mucus may be white at first and then turn yellow or green.

The color may indicate the presence of white blood cells associated with inflammation rather than a bacterial infection. As always, if symptoms persist or worsen, a visit to a doctor is in order.

Mucus that is expelled from the respiratory system is sometimes called phlegm. Sputum is phlegm mixed with saliva.

COPD causes an excessive accumulation of mucus and severe lung damage.

Chronic obstructive pulmonary disease

Chronic bronchitis and emphysema are the two most common diseases classified as chronic obstructive pulmonary disease or COPD.

Both are mainly caused by smoking, but can be made worse by breathing in polluted air. Symptoms include wheezing, shortness of breath, and coughing up mucus.

Unfortunately, the trigger that causes the disease damages the lungs and the disorder is progressive. The earlier the disease is diagnosed and the trigger avoided, the better the outcome.

People with COPD can have chronic bronchitis or emphysema, but they often have both conditions. The alveoli are small air sacs in the lungs where oxygen is absorbed into the blood. In emphysema, the walls of the alveoli rupture, making exhalation difficult.

Mucus: friend and foe

Mucus is an essential substance in the human body and is generally a friend, despite its distasteful reputation.

However, sometimes, or in certain people, too much mucus is produced and the mucus is transformed from useful material into a dangerous enemy. This is especially sad in diseases that affect the quality of life.

Hopefully, medical research will continue to discover improved ways to treat excess mucus and its consequences.