Epidermis is the protective film of cortex and medulla.
Skin can be divided into three layers: epidermis, dermis and subcutaneous tissue. The outermost layer is epidermis, only 0.2 mm thick, which can prevent foreign bodies from invading, filter ultraviolet rays, absorb ultraviolet rays, lock water, divide and proliferate cells and so on.
The subcutaneous layer occupying most of the structure is dermis, which is about 0.2 cm thick and can be divided into three layers, namely papillary layer, papillary layer and reticular layer. Most of them are composed of protein, this part of protein is composed of collagen and elastin, and others are composed of nerves, capillaries, sweat glands, sebaceous glands, lymphatic vessels and hair roots.
Extended data
The importance of skin is that it is the interface between the body and the external environment and the first line of defense against external influences. For example, skin plays an important role in protecting the body from pathogens and avoiding excessive water loss. Other functions of the skin include heat insulation, temperature regulation, sensation and vitamin D production.
Seriously injured skin will form scars when it heals, and sometimes the color of the skin will change. The thickness of animal skin will vary with different parts. For example, the skin under people's eyes and the skin around eyelids are the thinnest, with a thickness of about 0.5 mm For the first time, crow's feet or other wrinkles appear. The skin of the palm and sole is the thickest, about 4 mm thick.
Fur refers to the skin with thick hair. Some skin will have thick hair, which can insulate heat on the one hand, and is also a secondary sexual characteristic or used as camouflage on the other. Some animals have thick and hard skins, which can be made into leather after treatment.
Reptiles, fish have hard scales to protect the skin, and birds also have hard feathers, which are composed of hard β-keratin. The skin of amphibians can't prevent chemicals from passing through, so chemicals can easily penetrate into the body from the skin. For example, frogs exposed to anesthetics will fall asleep quickly. The skin of amphibians is very important for their daily survival and their ability to live in different habitats and ecosystems.
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