1, basal layer: basal cell layer, which is the lowest layer of epidermis. The basal layer is the cell layer with the strongest ability of division and proliferation in epidermis. Every day, 30%~50% of basal cells undergo nuclear division, and the division cycle is about 19 days. The new cells produced move upward into the spinous layer, so the basal layer is also called mucus layer. The proliferative cells in the basal layer continue to move to the epidermal layer and gradually differentiate into other layers. In the process of skin wound healing, basal cells play an important role in regeneration and repair.
2. Spine layer: located in the basal layer, it consists of 4- 10 layers of polygonal cells with large volume, and also has the ability of division and proliferation, but it is limited to cells near the basal layer in the deep layer. The cells in the deep layer of spinous layer are polygonal, and the shallower they are, the flatter they are.
3. Granular layer: located in the shallow layer of spinous cells, it is common in the epidermis of palms and soles, and the cell thickness can reach 10 layer. Because it transits between normal epidermal cells and dead keratinocytes, it is also called transition zone. The "membrane particles" in the cells above the granular layer release phospholipids into the intercellular space, making it difficult for adjacent cells to separate and become waterproof barriers, making it difficult for body surface water to penetrate and preventing body water from oozing out.
4. transparent layer: it is the anterior stratum corneum, which consists of 2~3 layers of flat cells. It has no nucleus and is only found in the epidermis of palms and soles. HE staining is eosinophilic, and the section is wavy and banded, so it is named transparent layer. It has barrier function to prevent water, electrolyte and chemicals from passing through. In static electricity, the granular cell layer is a negative charge belt, and the transparent layer is a positive charge belt, which constitutes an important defense barrier of the epidermis.
5. Cuticle: It is the outermost layer of epidermis, consisting of multiple layers of keratinocytes and keratin lipids. The stratum corneum is mainly composed of 5 ~ 10 layers of flat dead cells without nuclei, while the palmoplantar can reach 40 ~ 50 layers. When these cells fall off, the cells located in the basal layer will be pushed upward to form a new stratum corneum. This layer can prevent water loss caused by the formation of sebum film. The normal moisture content of stratum corneum is 20%-25%. When the moisture content of cuticle is lower than 10% when skin is dry, it will dry and peel off; When it is less than 5%, it will be red, swollen, hot, painful and itchy.
Extended data:
Skin is divided into epidermis and dermis. Epidermis is on the skin surface and can be divided into stratum corneum and mucus layer. Keratinized cells form the stratum corneum, which falls off and becomes dander. Mucous layer cells divide constantly, which can replenish the exfoliated stratum corneum. There are melanocytes in the mucus layer, which can prevent ultraviolet rays from damaging internal tissues. Epidermis is a stratified epithelium, while dermis is a dense connective tissue with many elastic fibers and collagen fibers, so it has elasticity and toughness. The dermis is thicker than the epidermis and is rich in blood vessels and nerves. There is subcutaneous tissue under the skin, which belongs to loose connective tissue and has a large number of fat cells. Skin also has many appendages, such as hair, sweat glands, sebaceous glands and nails.
References:
Baidu encyclopedia-skin