Why does a cold cause a runny nose and phlegm?

My answer ().

When the cold virus invades the body from the respiratory tract and causes a person to catch a cold, the virus moves through the nasal cavity, causing the nasal mucosa to swell, and the nose secretes more extra water or mucus (secretions) to help us get rid of the dead virus naturally. If the original clear nasal discharge turns into yellow nasal discharge, it means that the nasal cavity has been inflamed by other bacteria or viruses, and the yellow and clear nasal discharge is like pus.

The inner surface of the nasal cavity of healthy people is lined with a complete layer of mucosa, on which there are many goblet cells with secretory function, and there are mucous glands under the mucosa, which usually carry out secretory activities, and the secreted water is used to moisten and inhale air, in addition, the mucus glands often secrete a small amount of mucus, which is evenly distributed on the surface of the mucosa.

It is very viscous and can adsorb dust and microorganisms in the air inhaled. Mucus also contains lysozyme, which has the ability to inhibit and dissolve bacteria. Under normal conditions, relying on the cleansing effect of this mucus, the inhaled air reaches the back half of the nasal cavity with few microorganisms.

Exist. Normally, the fluid secreted by the nasal mucus glands and the fluid that is evaporated are in relative equilibrium. Once pathological changes occur in the nasal cavity, the discharge may increase, resulting in the formation of nasal discharge.

Good sign, it means that your immune system is very strong!

No. Even if the snot can be spit out of the mouth, it is still snot.

Phlegm is a secretion of the respiratory tract. Under normal circumstances, the human respiratory tract secretes a small amount of mucus, which can moisten and warm the air inhaled into the lungs, and can also absorb some dust and harmful substances in the air.

When there is a lesion in the lungs, mucus is secreted abnormally, forming phlegm that we can feel.

Therefore, swallowing this mucus is harmful to the body.

Nasal discharge is not phlegm. The two are not the same thing.

1) Nasal mucus is a normal condition in which the nasal mucosa of some organisms secretes mucus all the time to moisten the nasal membrane, moisten the inhaled air, and stick to the dust, fine dust and microorganisms inhaled from the air.

Most nasal discharge is secreted by the nasal mucosa itself. The nasal mucosa contains a type of goblet cell that produces a lot of mucin, which is released into the outer cell and absorbs a large amount of water, forming nasal mucus for nasal use.

Part of the snot is actually tears. These tears are produced from the lacrimal glands, partially to the lacrimal ducts, and then through the nasolacrimal ducts to the nasal cavity, where they become part of the nasal discharge.

b) Phlegm is a substance made up of many components. Its high fluid content is the result of the transport of ions and water by the epithelium, while its macromolecules are mainly the products of blood leakage or local secretion of cells.

It's not the same. Nasal mucus is formed by nasal mucus secreting mucus, sticking to dust, or other foreign bodies.

On the other hand, phlegm is formed by the airways secreting mucus and sticking to the foreign body of the inhaled air, as well as the original foreign body.

In this case, it can come out of the nose. The mouth and nose are connected. However, when there is phlegm in the mouth, it flows back into the mouth, but it is unlikely that the phlegm will turn into nasal discharge.