Mucus

Mucus is a slippery fluid that our bodies make to keep us safe. It is found in many places, like our noses, throats, stomachs, eyes, and ears. This special fluid helps trap and remove tiny germs, such as bacteria and viruses, that could make us sick.

Our bodies produce mucus in special cells called mucous glands. It contains important substances that fight off infections and help protect our cells. Most of the mucus in our bodies is made in our digestive system.

Even animals like fish, snails, and slugs make mucus. For them, it helps protect against germs, aid in movement, and line the gills of fish. Plants also make something similar called mucilage, which is used by some tiny living things too.

Respiratory system

Further information: Mucociliary clearance

In your body, the respiratory system makes mucus to help keep your lungs safe. Mucus is part of a special liquid that lines your airways. It traps tiny particles like dust, germs, and allergens before they can get into your lungs. The mucus helps move these particles out of your body when you cough or swallow.

Mucus is made mostly of water and special proteins. It is produced by cells in your airways and helps keep the air moist. When you have a cold or allergies, you might make more mucus, which can make your nose runny or feel stuffy. Your body also makes extra mucus when the air is dry. This helps keep your nose and airways from drying out.

Digestive system

In the human digestive system, mucus helps things like food move smoothly down the esophagus. It is very important in the gastrointestinal tract, where it forms a protective layer in the colon and small intestine. This layer helps keep the gut calm by keeping bacteria away from the cells that line the intestines.

The gastric glands in the gastric mucosa make gastric juice that contains enzymes and gastric acid, which can hurt the stomach. To protect the stomach wall, some glands make a thick layer of mucus. This mucus lines the stomach and creates a barrier that keeps the stomach safe.

Reproductive system

In the human female reproductive system, cervical mucus helps keep things clean and provides lubrication. The texture of this mucus changes during a woman's monthly cycle. Around the time she can become pregnant, the mucus becomes clear and runny to help sperm move. After this time, the mucus gets thicker and can block sperm. Some people watch these changes in mucus to help plan for or avoid becoming pregnant.

Clinical significance

Nasal mucus is usually clear and thin, helping to clean the air we breathe. When we get sick, like with a cold or flu, the mucus can change to yellow or green. This happens because of germs or the body’s way of fighting them off.

Sometimes, mucus can get stuck in our sinuses, leading to a condition called sinusitis. This can make us feel very congested. Most sinusitis cases are caused by viruses and get better on their own without medicine. If bacteria are involved, antibiotics might help. There are also special breathing exercises that can help keep our airways clear and healthy.

Properties of mucus

Mucus can change its size by soaking up or losing water, depending on the surrounding pH. This ability comes from the special structure of molecules called mucin in mucus. These molecules have parts that attract water, allowing mucus to swell or shrink as needed.

Mucus also controls what can pass through it by acting like a filter. It lets some tiny particles pass while blocking others, which helps protect the body. This filtering ability depends on the electrical charge of the particles and can change depending on the state of the mucus.

Other animals

Mucus is made by many animals besides humans. Fish are covered in mucus from glands on their bodies. Snails and slugs produce mucus, often called snail slime, which helps them move and keeps them from drying out. This mucus also helps protect their eggs during reproduction. In some snails, the mucus is used in special mating rituals where the slugs lower themselves on a mucus thread. Hagfish use mucus as a way to scare away animals that might want to eat them. Some sea animals and baby lampreys also make mucus to help them eat by filtering food from the water.