25.10 : 表面膜屏障

Surface barriers such as the skin and mucous membranes are the body's initial defense against pathogens, offering physical and chemical protection.

The outer layer of the skin, the epidermis, with its densely packed keratinized cells, is a robust physical barrier against microbial entry unless compromised by cuts or burns.

Additionally, sebaceous glands in the skin secrete oily sebum, further inhibiting microbial entry.

Mucous membranes lining body cavities act as immune barriers by secreting mucus, which traps microbes and foreign substances.

For instance, the mucous membranes in the nose have hair, and those in the upper respiratory tract have cilia, both of which are mucus-coated to filter microbes from the inhaled air.

Both mucous membranes and skin secrete antimicrobial peptides like defensins to inhibit microbial growth.

Other body fluids, including tears, saliva, and sweat, contain lysozyme, an enzyme that can break down the cell walls of bacteria.

Furthermore, the low pH of various bodily secretions, such as sweat and vaginal discharge, discourages bacterial growth.