When the trachea, bronchi and lungs are stimulated by harmful factors or infected by pathogenic bacteria, the respiratory mucosa is congested and edematous, a large number of inflammatory cells infiltrate, blood vessels expand and ooze more, and goblet cells and submucosal glands in the mucosa proliferate and hypertrophy;

If mucus secretion is excessive, it will increase the burden of ciliated columnar epithelium, which is not conducive to mucus discharge. Under the action of bacteria and their toxins, some degenerated and necrotic tissue cells will remain in the bronchus, and mucus and these degenerated and necrotic tissue cells will also form sputum.

Meaning of phlegm:

The inner wall of trachea and bronchus is covered with a layer of mucosa, which consists of ciliated columnar epithelium and goblet cells. There are many mucous glands and serous glands in the submucosa, and the glandular ducts open on the mucosal surface. Under normal circumstances, goblet cells and glands secrete a small amount of mucus to cover the mucosal surface, protect the mucosa and keep the tracheal mucosa moist;

So as to adhere dust particles and bacteria inhaled into trachea and bronchus and prevent them from entering the depths of lung tissue; Then, with the help of cilia of ciliated columnar epithelium, it is discharged to the larynx at the upper end of trachea and spit out through the mouth, that is, sputum.

Extended data:

Phlegm is a substance composed of many components. Its high liquid content is the result of ion and water transport by epithelial cells, and its macromolecules mainly come from the products of blood leakage or local secretory cells.

Viscosity of sputum:

1, the increase of sputum viscosity is mainly related to the increase of acidic glycoprotein content in sputum, because glycoprotein molecules are crosslinked by different bonds (such as disulfide bonds, hydrogen bonds, etc.). ) to form a gel network.

2. Sputum contains electrolytes, among which Ca2+ content is high, which can increase the viscosity. During respiratory tract infection, the DNA produced due to the nuclear destruction of a large number of inflammatory cells also significantly improves the viscosity of sputum, forming so-called purulent sputum, which is not easy to discharge.

3. The pH of sputum will also affect its viscosity. The viscosity of sputum increases in acidic liquid, but decreases in alkaline liquid.

The role of phlegm:

1, cough, phlegm, asthma and inflammation are the common main symptoms of lower respiratory tract infection. Lower respiratory tract infection can be divided into acute and chronic. Acute infection is mainly acute tracheobronchitis, which is the most common disease of respiratory system, mostly caused by infection, physical and chemical stimulation or allergy. It is an acute inflammation of tracheal-bronchial mucosa, which is common in cold seasons.

2. When inflammatory lesions appear in the respiratory tract, the composition of the respiratory fluid will change to form sputum. Sputum contains mucus, foreign bodies, pathogenic microorganisms, various inflammatory cells and necrotic mucosal epithelial cells.

3. The liquid in sputum is mainly secreted by mucous glands and goblet cells in bronchial mucosa epithelium. Gland secretion is controlled by vagus nerve, and stimulating vagus nerve can promote gland secretion. Besides being controlled by vagus nerve, goblet cells also secrete more after being directly stimulated by inhaling dry air and irritating gas.

4. In chronic tracheitis and other diseases, glands in trachea and bronchus are enlarged, goblet cells are increased, secretion is significantly increased, and its viscosity is also greatly increased, while the cilia movement of tracheal mucosa is weakened, which leads to the obstruction of expectoration and the difficulty of mucus discharge.

Reference: Baidu Encyclopedia-Phlegm