Mucus

Mucus is a slippery fluid.

It covers many parts of your body. It is found in your nose and ears. It is also in your eyes.

Mucus helps keep you safe. It acts like a trap. It catches dust and tiny germs. This stops them from getting into your lungs.

It also helps your stomach. A thick layer of mucus lines your stomach. This protects your stomach from its own acid.

Some animals use it too. Fish and snails make mucus. It helps them move and stay safe.

Mucus can change color. It might turn yellow or green when you are sick. This shows your body is working hard.

Mucus is a slippery fluid that covers many parts of your body.

It lines your nose, ears, and eyes. It also lines your digestive and breathing systems.

Mucus works like a protective shield. In your breathing tubes, it acts like a trap. It catches dust, pollen, and tiny germs. This keeps them from entering your lungs.

Small hairs called cilia move the mucus. They push it toward your throat so you can swallow it.

In your stomach, mucus has a different job. Your stomach uses strong acid to break down food. This acid could hurt your body. To stop this, a thick layer of mucus lines the stomach wall.

This layer acts as a barrier.

Mucus can also change. When you are sick, it may turn yellow or green. This happens because your white blood cells fight germs. Some people may also cough up thick mucus called phlegm. This helps clear the airways.

Mucus is a slippery, thick fluid that covers many parts of the body. It forms a protective barrier for the surfaces inside and outside of us.

You can find mucus in the eyes, ears, and the systems used for breathing and digestion. It is made of many things, like water, proteins, and salts. Most of the mucus in your body is made in the digestive tract. It helps to trap, destroy, or remove harmful things like bacteria and viruses.

In the respiratory system, mucus works like a clever trap. It is part of a liquid that lines your breathing tubes. This liquid has two layers: a thin layer and a thicker gel layer.

The gel layer is made of large proteins called mucins. These mucins are produced by special cells called goblet cells. As you breathe, the mucus catches dust, pollen, and germs. Tiny hairs called cilia then move the mucus toward your throat. Most of the time, you swallow this mucus without even knowing it.

In the stomach, mucus has a very important job to do. Your stomach uses strong acid to help break down food. This acid is very harsh and could damage the stomach wall. To prevent this, gastric glands produce a thick, basic layer of mucus.

This layer acts as a barrier between the acid and your body. It also helps food move smoothly through your digestive system. In the intestines, mucus helps to reduce inflammation by keeping bacteria away from your cells.

Sometimes, the mucus in your body changes when you are sick. If you have a cold or the flu, your body might make more mucus. This can cause your nose to feel full or run.

When your body fights an infection, the mucus can change color. It might turn yellow or even green. The green color comes from a special enzyme in your white blood cells. This enzyme contains iron and helps your body defend itself. If the mucus becomes very thick, it is called phlegm.

Mucus is also found in other living things. Fish, snails, and slugs produce mucus on their skin for protection. It even helps some animals move more easily. Plants make a similar substance called mucilage. Even in the human reproductive system, mucus changes its thickness. For example, cervical mucus can be clear and runny or thick and sticky. These changes help different parts of the body work the way they should.

Mucus is a viscous colloid that serves as a vital protective barrier for many living things. It is a slippery fluid produced by and covering mucous membranes. These membranes line the internal and external surfaces of the body.

Mucus helps to trap, destroy, or remove harmful particles like fungi, bacteria, and viruses. It is found in the respiratory, digestive, and urogenital systems, as well as in the eyes and ears. Beyond humans, amphibians, fish, snails, and slugs also produce external mucus for protection and movement. Even plants produce a similar substance known as mucilage.

In the human respiratory system, mucus is a key part of the airway surface liquid (ASL). This liquid consists of two distinct layers. The first is the periciliary liquid layer, also called the epithelial lining fluid. This thin layer surrounds the cilia, which are tiny hair-like structures.

Above this sits the mucus layer, which is a thicker gel. This gel layer is a meshwork of cell-tethered mucins and polysaccharides. The mucus blanket protects the lungs by trapping foreign particles, such as dust or allergens, before they can enter deep into the system.

The chemical makeup of mucus is quite complex. It is composed of approximately 95% water. The remaining part includes glycoproteins called mucins, which make up 2–3% of the mixture. Other components include proteoglycans (0.1–0.5%), lipids (0.3–0.5%), proteins, DNA, and inorganic salts. Two major mucins are MUC5AC and MUC5B. MUC5AC is the main gel-forming mucin secreted by goblet cells in the form of threads and thin sheets. MUC5B is a polymeric protein secreted from submucosal glands and some goblet cells in the form of strands. These large polymers give mucus its viscoelastic properties, meaning it can both flow like a liquid and stretch like a solid.

To keep the lungs clean, the body uses a process called mucociliary clearance. The cilia on the respiratory epithelium move in a continuous motion toward the oropharynx. This movement carries the mucus down from the nasal passages and up from the rest of the tract. Most of this mucus is swallowed subconsciously. However, during respiratory illnesses like influenza, mucus production increases. If the mucus becomes thickened with cell debris and bacteria, it is known as phlegm. This thicker substance may be coughed up as sputum to clear the airways.

In the digestive system, mucus performs essential mechanical and chemical roles. It acts as a lubricant to help food move smoothly through the esophagus.

In the stomach, gastric glands produce a thick, alkaline mucus layer. This layer forms the gastric mucosal barrier. It is vital because it protects the stomach wall from the harsh, acidic gastric juice used for digestion. In the colon and small intestine, mucus also helps reduce inflammation. It does this by decreasing the interaction between bacteria and the intestinal epithelial cells.

Mucus can change appearance based on the body's health. While nasal mucus is usually clear and thin, it can turn yellow or green during an infection. A yellow color may result from trapped bacteria, such as Staphylococcus aureus. A green color comes from the heme group in an iron-containing enzyme called myeloperoxidase. This enzyme is secreted by white blood cells during a respiratory burst to act as a cytotoxic defense. In some cases, such as cystic fibrosis, the mucus becomes dehydrated and highly viscous. This is caused by mutations in the CFTR gene, which affects the chloride channel and electrolyte composition. This thick mucus can impair mucociliary clearance and lead to bacterial colonization.

Finally, mucus has unique physical properties like a tunable swelling capacity. This means it can absorb water or dehydrate based on changes in pH. This happens because of the polyelectrolyte effect. Mucins are polyelectrolytes, which are polymers with charged molecules. The charges on mucins come from acidic amino acids like aspartic acid and glutamic acid. When the pH of the environment changes, the number of negative charges on these amino acids changes too. This change in charge attracts counter-ions and creates an osmotic pressure. This pressure drives water to flow into or out of the mucus, allowing it to swell or shrink.