The structure and function of epidermis, skin is the largest organ of our human body, and there is no one. The biggest function of skin is to protect the body and maintain the stability of our environment. The skin will be in direct contact with the outside world. The outermost layer of skin is epidermis, and the structure and function of epidermis are below.
Structure and function of epidermal layer 1 Epidermis is the outermost layer of skin, with a general thickness of 0.035-0.15 mm. According to the differentiation and characteristics of keratinocytes, the epidermis is divided into five layers from outside to inside, namely stratum corneum, transparent layer (only in the palm and sole), granular layer, spinous layer and basal layer, and the basal layer is connected with dermis through basement membrane (Figure 2
1, base
The basal layer is located in the lowest layer of epidermis, and it is only a columnar or cubic basal cell with a size of about 10- 14 micron. The nuclei are large and deeply stained, usually arranged in a fence, and its long axis is perpendicular to the dividing line between epidermis and dermis.
The basal layer and spinous layer, also known as mucus layer, have the ability to divide and proliferate, and their division is active, constantly producing new cells and moving to the superficial layer to supplement the aged and exfoliated keratinocytes, which is related to skin self-repair, wound repair and scar formation.
In the process of basal cell division, one of the two new cells is pushed upward, and finally keratinocytes are formed through the spinous layer and granular layer, which lose their vitality and gradually fall off. The process from the basal layer to the top layer of granular layer and then to the top layer of stratum corneum is called the passage time of epidermis, which is about 28-56 days, while the division cycle of basal layer cells is about 13- 19 days, so the renewal time of epidermis is 4 1-75 days.
2, spinous layer
The spinous layer is located on the basal layer and consists of 4-8 layers of polygonal cells. The cell is large, with many spinous processes and a round nucleus. The intercellular bridge is obvious and prickly, so it is called spinous cell. The bottom spinous cells also have the function of division, and the more they move to the surface, the flatter the cell morphology.
Spine cells and granular layer cells contain lamellar particles wrapped by oval bilayer membrane, which are called Audland corpuscles, also known as lamellar particles and lamellar corpuscles. Lamellar particles first appear in the spinous layer, which is a lipid mixture composed of phospholipids, ceramides, free fatty acids and cholesterol. With the differentiation of epidermis, phospholipids decreased, ceramide, free fatty acids and cholesterol increased.
When the cells on the top layer of granular layer transform into keratinocytes, lamellar particles release lipid contents into intercellular spaces of stratum corneum through exocytosis, forming intercellular lipids.
3. Granular layer
The granular layer consists of 1-3 layers of flat or spindle cells, which are located above the spinous layer and contain transparent keratin granules in their cytoplasm. The closer to the stratum corneum, the bigger and more particles. Transparent keratin particles are mainly composed of electron dense protein, front filament and keratin intermediate filament.
The granular layer of normal skin is directly proportional to the thickness of the stratum corneum. The thin stratum corneum has only 1-3 layers, and the thick stratum corneum, such as the palm toe, has as many as 10 layers.
4. Toumian
The transparent layer consists of 2-3 layers of flat seedless cells, which only exist in the thick epidermis of palms and toes. Under the light microscope, this layer of cells is easy to be stained by eosin, with homogeneous cytoplasm and strong refraction, hence the name transparent layer. The shape and outline of the cell can be recognized under the electron microscope. The nucleus and organelles have degenerated, and the cytoplasm is full of keratin filaments. Its ultrastructure is similar to that of the stratum corneum, which has the functions of waterproof and electrolyte barrier.
5, stratum corneum
The stratum corneum is the outermost layer of epidermis, which consists of 5- 15 layers of keratinocytes and intercellular lipids, and the nucleus and organelles are missing. In 1970s, Professor Peter Elias vividly called the stratum corneum structure "brick wall structure".
The stratum corneum is most closely related to skin water locking. Under normal circumstances, the water content of stratum corneum is 10%-20%. Below 10%, the skin will be dry and peeling. Under normal circumstances, the amount of water loss of cuticle through epidermis is kept at 2-5g/(h cm), and when cuticle is damaged, TEWL will increase.
Structure and function of epidermal layer 2 Epidermal layer is divided into five layers, whose function is to block all dust and pollution from the outside and protect subcutaneous tissue from damage. Strengthen and consolidate subcutaneous tissue and own cells.
The epidermis is divided into five layers, consisting of stratum corneum, transparent layer, granular layer, spinous layer and basal layer.
1, stratum corneum is the most superficial cortex of skin, which consists of several to dozens of flat seedless keratinocytes. Cytoplasm is full of eosinophilic keratin, which has strong resistance to acid, alkali and friction. The stratum corneum is often dander produced during a period of time or washing, and it is also used to block all dust and pollution from the outside world.
2. The transparent layer is below the stratum corneum, on the shallow side of the granular layer, and consists of 2-3 layers of flat cells without nuclei. The cytoplasm contains eosinophilic hyaline keratin, which is denatured by granular cells and exists only in palms and soles.
3. The third layer is granular layer, which consists of 2-3 layers of spindle cells. There are hyaline keratin particles of different sizes in the cytoplasm. Ordinary staining is strongly basophilic, with small nucleus and shallow staining. Mucopolysaccharides, phospholipids and other contents are continuously discharged from membrane particles and enter intercellular spaces, forming a part of intercellular substances, which makes the binding force between surface cells stronger and prevents foreign bodies from invading.
4. The cells in spinous layer and basal layer are the same, but their shapes are slightly different. The basal layer is in the deepest layer of epidermis, connected with the deep layer of dermis, and between many linear fibers in spinous layer, many liquids containing nutrients flow. The basal layer replicates through division and then passes through other layers, becoming the source of other epidermal components.
Structure and function of epidermal layer 3 Epidermis: the outermost tissue of skin, mainly composed of keratinocytes, which can be divided into five layers according to the morphology of keratinocytes: stratum corneum, transparent layer, granular layer, spinous layer and basal layer.
① stratum corneum
The stratum corneum is the outermost part of the epidermis, which evolved from keratinocytes and overlapped to form a tough and elastic layered structure. The cells in the stratum corneum are full of keratin white fibers, and keratin has strong water absorption ability. The stratum corneum can not only prevent the water in the body from emitting, but also obtain a certain amount of water from the external environment. Generally, the fat content of stratum corneum cells is about 7%, and the moisture content is 15%-25%, which keeps the skin soft and moist.
If the moisture drops below 10%, the skin will be dry and wrinkled, with visible cracks and even scales. The stratum corneum is the most important protective layer of skin, which can withstand certain physical, mechanical and chemical injuries, absorb a certain amount of ultraviolet rays and protect internal tissues.
② transparent layer
The transparent layer has a slight honeycomb structure, but the boundary is not obvious. Seedless, colorless and transparent (after the cuticle of the foot is torn off, the red layer is the transparent layer, and blood vessels can be seen). The transparent layer is more obvious in the epidermis of palms and feet. The transparent layer contains keratin and phospholipids, which can prevent moisture and electrolyte from penetrating through the skin and play a physiological barrier role.
③ granular layer
It consists of 2-4 layers of flat, spindle-shaped or rhombic cells. Granular layer is a transitional cell layer from the inner layer of epidermis to the stratum corneum of epidermis. Because it contains keratin, it will produce fat, which can inhibit the loss of water in the body and prevent external water from infiltrating into the body, which has an important impact on the storage of water, usually keeping the water content at 10%-20%.
④ spinous layer
The spinous layer consists of 5- 10 layers of polygonal cells with spinous processes, also known as spinous cell layer. Spinal cells are connected by bridges, and lymph passes between bridges, providing nutrition for cells. It is the thickest layer of epidermis, and the spinous cells under it have the function of division, participate in wound repair, contribute to the growth of hair and nails, absorb nutrition from lymph, provide nutrition for basal layer, and assist the division of basal layer cells.
⑤ basal layer
The basal layer, also known as mucus layer, is composed of dendritic cells in the basal cell nucleus, which is the innermost layer of epidermis and undulates with dermis.
Basal cells are a layer of columnar cells arranged in a grid, which have strong ability of division and reproduction. They can move upward continuously, grow and evolve into cells in the epidermis and finally become dead cells in the stratum corneum. The whole process of stratum corneum change takes 1-2 months.
Dendritic cells, including Langerhans cells, are derived from bones and distributed in the epidermis above the basal layer, with immune function; Meckel cells, located between basal cells, have sensory function; There is one melanocyte in every 10 basal cells. Melanocytes contain tyrosinase, which can produce melanin particles. The quantity and size of melanin determine the difference of skin color, and at the same time it can absorb and block ultraviolet rays and play a protective role. If melanin particles are poorly metabolized, it will lead to pigmentation and pigmentation.