The skin is the largest organ of the body, acting as the first line of defense to prevent harmful agents from outside from entering. In addition, the skin also plays an important role in the thermoregulation mechanism as well as in the synthesis of vitamin D for the body.
The structure of the skin consists of three layers: epidermis, dermis, and hypodermis.
The epidermis is a squamous epithelium with many layers, about 0.1mm thick, about 0.8-1.4mm in the palms and soles.
The main cell of the epidermis is the keratinocyte, which produces keratin (protein keratin). From the bottom to the epidermis, there are 4 layers (basal layer, spine layer, granular layer, stratum corneum), especially the palms and feet have 5 layers (add the light layer).
1.1 Bottom layer (stratum basale)
Is the deepest layer of the epidermis, consisting of a layer of cylindrical cells located just above the basement membrane. Scattered between the basal cells are pigment cells, Meckel cells. The basal layer produces new cells to replace old differentiated cells, creating renewal of the epidermis. In general, it takes 4 weeks for basal cells to gradually differentiate into the stratum corneum. In some diseases, such as psoriasis, powdery mildew, the process of differentiation from basal cells to keratinocytes is faster.
1.2 Lớp gai (stratum spinosum)
Is a layer of polyhedral cells, because the basal cells move up the wall. The squamous cells are located close to each other, connected by intercellular bridges, helping the skin not absorb water from the outside into the body, not being drained from the body to the outside, and resisting harmful agents of the skin. environment.
In the spiny layer, there are Langerhans cells with immune function. The squamous cells are also capable of mitotic reproduction contributing to epidermal renewal.
1.3 Grain layer (Stratum granulosum)
The granule layer consists of 4 rows of cells that are flatter than the spiny cells. The cytoplasm of this cell contains many keratohyalin granules made up of lipids and keratin filaments. There are also intercellular bridges between the seed layers, but they are shorter and larger than the spiny ones.
1.4 Light layer (stratum lucidum)
The light layer between the granular layer and the stratum corneum consists of 2-3 rows of very flattened cells parallel to the surface of the skin. Light layer cells have no nucleus, protoplasm, only fibers. The light layer is only found on the palms of the hands and feet. Other skin areas have no light layer.
1.5 The stratum corneum
The stratum corneum is the outermost layer of the epidermis, which are flattened cells without a nucleus filled with overlapping pieces of horn and fat, creating a protective membrane that protects the body from water infiltration, avoiding the effects of radiation. external environment as well as dehydration from inside the body.
In different skin areas, the horny layer is thick and thin, usually the horny layer on the palms and feet will be thicker than in other skin areas. Every day, the outer layer of stratum corneum separates and sheds continuously to form small chalk-like scales, which are mixed with sweat and sebum to form hate.
Cells in the epidermis are always renewed, gradually changing shape. The cells have a vertical axis at first, then gradually flatten out and have a horizontal axis. The higher the nucleus, the more damaged it becomes, eventually degenerating and the cell no longer has a nucleus. The higher the cell, the more infected the horny granules. The epidermis has no blood vessels, but is nourished by fluid located in the intercellular space. Nerve fibers branch only to the basal layer.
2. The dermis
The dermis is the layer immediately behind the epidermis, which is separated from the epidermis by the basement membrane, also known as the basal membrane. The fluid will penetrate from the dermis through the basement membrane to nourish the epidermis. The boundary between the epidermis and the dermis is not a straight line but a wavy line. The small wave protruding above is the dermis, the lower wavy part between the two dermis is the interspinous crest.
The mesoderm consists of two layers:
2.1 superficial dermis (papillary dermis)
This is a nurturing class. On the surface, there are raised spines, also called papillae or dermis, that go deep into the epidermis. The spines are made of connective tissue, with many capillaries. The dermal papillae vary in height and size depending on the skin area. The skin on the palms and soles is sometimes up to 0.2mm high, in the facial skin, the papillary layer is very thin.
2.2 Deep dermis (reticular dermis)
The deep dermis includes:
- Strands of support
+ Collagen fibers are unbranched straight fibers, composed of polypeptide chains, consisting of 20 different amino acids, mainly glycin and argenin. Acacia fiber is the main material that makes the skin firm against mechanical, physical and chemical influences from the outside. Acacia fibers are concentrated mainly in the deep dermis, a little in the dermis, hair follicles, sebaceous glands, sweat glands, and around blood vessels.
+ Elastic fibers or elastic fibers are thin, smooth fibers with wavy branches, derived from glue fibers.
+ Mesh fibers: structure like glue fibers, forming a thin network around blood vessels, sweat glands.
+ Reticulum fiber: is a special type of colloidal fiber, concentrated in the superficial dermis, skin appendages, and blood vessels.
- Basic substance: is a mucous membrane consisting of tryptophan, tyrosin, mucopolysaccharide, hyaluronic acid.
+ The fibrous cells are spindle-shaped or amoeba, have large oval nuclei, contain many mitochondrial granules, have the effect of scaring the skin.
+ Organization of rhombohedral or stellate cells, it can turn into phagocytosis, macrophage.
+ Mast cells participate in the metabolism of heparin, histamine, hyaluronic acid.
- Blood vessels, dermis only have small blood vessels concentrated in the dermis and around the glands.
The cerebrospinal nerve has a myelin sheath and has its own branch.
The unmyelinated sympathetic nerve runs in the vascular sheaths.
3. The dermis (hypodermis)
The dermis is located between the dermis and the fascia or periosteum, is a buffer organization differentiated into a fat organization, with many cells separated by walls, connected to the dermis in which blood vessels and nerves branch up. above. The thickness of the dermis depends on the condition of each person. This is the body’s largest store of fat, which regulates temperature.
4. Skin Substances
4.1 Sweat glands
An exocrine gland, consisting of 3 parts:
– The secretory sphere is circular in shape, located in the deep dermis, with two layers of cells: secretory cells and cortex cells.
– Duct through the dermis.
– The transepidermal duct, spiral-shaped, consists of a layer of cells infected with keratinized granules.
Depending on the body area, the number of sweat glands is different, in the palms and feet there are about 620 pieces/1 cm2, thighs about 120 pieces/cm2. The whole body has about 2.5 million glands. Sweat glands are responsible for regulating body temperature, contributing to a constant body temperature.
4.2 Sebaceous glands
An exocrine gland located next to the hair follicle, connected to the hair follicle by a secretory duct. It is a cystic gland with many lobes, each lobe consisting of many layers of cells. In the innermost are the cells that produce fat, fat is excreted through the ducts to the surface of the skin. There are two types of hair follicles:
– Long hair follicles: located on the scalp, beard, armpit hair, pubic hair. In these places the sebaceous glands of the hair follicles do not develop.
– Sebaceous hair follicles: This is a gland located all over the body except the palms and soles without sebaceous glands. The number of sebaceous glands varies according to different body regions. Sebaceous glands in the face are 5 times more developed than elsewhere.
4.3 Hair follicles
This is the deep recess of the epidermis that contains hairs and accesses the sebaceous glands. The structure of the hair follicle consists of: the basic substance of the hair, the hair, the inner shell, the outer layer, and the hair spine. The pigment cells present in the hair base give the hair its color.
There are two types of hair in humans
Smooth hair, also known as fluff: is the short hair that covers the body except the palms and legs.
Long hairs: are hairs that are long, stiff, and larger in diameter than smooth hair. Long hair is located on the scalp, around the mouth, armpit hair, pubic hair.
It is a thin plate about 0.3-0.5-0.75mm thick that fits in a groove of the dorsal surface of the tip.
The nail has four banks, the free margin is at the tip of the nail, the remaining three are covered by skin folds called the posterior and two lateral borders. The posterior margin and the fold in the base of the nail are called the supranail fold. The part of the nail at the posterior border has a beveled shape called the nail root. The remaining part is thick, meniscus called the nail body. The epidermis below the nail joins the epidermis in the posterior and lateral folds. The base of the nail has a semicircle shape called the nail sickle. The epidermis below the nail root is called the nail germ, which is the reproductive layer, with a rather thick layer of malpighi. The cells in the nail germ grow from the base of the nail to the nail bed and flatten to turn into a stratum corneum that covers the underside of the nail. The nail plate grows continuously from the base of the nail to the free edge. Nails grow about 0.1mm long every day. Toenails grow slower than fingernails. As you age, your nails grow slower. Time to completely replace 1 nail is about 3 months, toenail is about 6 months.