The dermis refers to one of the three layers of skin, which is between the epidermis and the subcutaneous tissue. From the outer side of epidermis to the inner side, there are five layers: stratum corneum, transparent layer, granular layer, spiny layer and basal layer.

the epidermis is the protective film of cortex and medulla.

The skin can be divided into three layers: epidermis, dermis and subcutaneous tissue. The outermost layer is epidermis, only .2 mm thick, which can prevent the invasion of foreign bodies, filter ultraviolet rays, absorb ultraviolet rays, lock water, divide and proliferate cells and so on.

The subcutaneous layer, which occupies most of the structure, is the dermis, with a thickness of about .2 cm, and can be divided into three layers, namely, papillary layer, papillary layer and reticular layer. Most of them are composed of protein, and this part of protein is composed of collagen and elastin, while others are composed of nerves, capillaries, sweat glands, sebaceous glands, lymphatic vessels and hairy roots.

Extended information

The importance of skin is that it is the interface between the body and the external environment, and it is 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.

when severely injured skin heals, it will form scars, and sometimes the color of the skin will change. The thickness of animal skin will vary with different parts. For example, the skin under human eyes and the skin around eyelids are the thinnest, with a thickness of about .5 mm, and it is the first time to appear like "crow's feet" or other wrinkles. 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 skin, which can be used as leather after treatment.

Reptiles have hard scales to protect the skin, while birds also have hard feathers, which are all composed of hard β-keratin. The skin of amphibians cannot prevent chemicals from passing through, so chemicals can easily penetrate into the body from the skin. For example, frogs exposed to anesthetics will quickly fall asleep. 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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