Skin Structure and Functions of the Skin
摘要
The human skin is composed of three layers: the epidermis, the dermis, and subcutaneous tissue or hypodermis. The epidermis is the most superficial layer and consists of packed epithelial cells. The middle layer, the dermis, is made of connective tissue, blood and lymphatic vessels, hair follicles, and sweat glands. Beneath the dermis lies subcutaneous tissue, which is composed of adipose tissue. In addition to protecting against pathogens (mainly microorganisms), chemicals, physical agents, and ultraviolet radiation, the skin also contains a range of immune cells that contribute to innate and adaptive immune responses.