What are the structures of trachea and bronchus?

The walls of trachea and bronchus have mucosa, submucosa and adventitia from inside to outside.

(1) Mucosal layer: It consists of mucosa epithelium, mucociliary organ and lamina propria.

① Mucosal epithelium: The trachea to bronchioles are pseudostratified ciliated columnar epithelial cells. The middle section from terminal bronchioles to respiratory bronchioles is a single layer of ciliated columnar epithelial cells. The alveolar ducts and alveoli below the respiratory bronchioles are single-layer columnar or single-layer flat 7 epithelial cells without cilia. The cilia of trachea and bronchus are carpet-like, and the terminal bronchioles are isolated clusters. In addition, there are goblet cells scattered between ciliated columnar epithelial cells from trachea to terminal bronchioles. Clara cells are found in the mucosal epithelium of terminal bronchioles and respiratory bronchioles. There are neurocorpuscles from trachea to alveoli; There are basal cells in the epithelial basement from trachea to bronchioles.

② Mucous ciliary apparatus: There is a mucociliary apparatus on the surface from trachea to bronchioles, and its inner layer is thin serous fluid, which is called serous fluid layer, and its outer layer is discontinuous dripping mucus, which is called strong viscous layer. The mucociliary device has a defense function, and the dust and bacteria captured by mucus can be removed by regularly swinging the cilia and pushing them to the throat.

③ lamina propria: The lamina propria is located in the deep mucosa and consists of abundant elastic fibers, collagen fibers, nerve fibers, blood vessels, glandular ducts, lymphoid tissues, smooth muscles, plasma cells and dense connective tissues. Plasma cells can secrete and store antibodies, and elastic fibers and collagen fibers can make respiratory bronchioles elastic and keep the airway in a proper relaxation and contraction range. When the annular smooth muscle of the lung relaxes, the bronchi dilate; When the longitudinal smooth muscle relaxes, the lungs expand.

(2) Submucous layer: It is composed of connective tissue and contains many glands. The catheter is open on the mucosal surface. These glands often secrete mucus, which keeps the mucosal epithelium moist and can adhere to inhaled dust and bacteria, thus coughing them out of the body through ciliary movement of the epithelium. Infection or allergic inflammation, such as asthma attack, excessive secretion of glands and increased sputum volume.

Chronic or repeated inflammation can make submucosal glands proliferate and hypertrophy, and the secretion function is hyperfunction.

(3) adventitia: composed of cartilage and fibers; At the position of trachea, cartilage is C-shaped, and smooth muscle and connective tissue are connected at the cartilage space. The function of cartilage is to support the respiratory tract so that it is not easy to be trapped. Starting from the lower part of the bronchus, with the continuous branching of the bronchial tree, the cartilage in the outer layer becomes irregular cartilage pieces intermittently, and it becomes more and more rare, and the mucosal epithelium becomes thinner and thinner, and more and more smooth muscles appear in the epithelium; The contraction and spasm of these smooth muscles are the important causes of lower respiratory tract obstruction during the attack of bronchial asthma.