What are people made of? ..... In the final analysis, people are made up of cells. Skin is also made up of cells arranged and combined.
A complete cell consists of cell membrane, cytoplasm and nucleus.
1, cell membrane-through which it completes various physiological and metabolic functions inside and outside the body, absorbs nutrients and discharges wastes.
2. Cytoplasm-the main component is water, which stores the nutrients needed by cells.
3. Nucleus-contains life genetic genes (deoxyribonucleic acid) that determine the structure of newborn cells.
The tissue components of cells are 70%- water, 27%- protein, 2%- lipids, 1%- sugars and minerals.
Water and protein account for the majority, which constitute the basic substances of skin cells, allowing skin cells to maintain their own metabolism. In the nucleus of every cell, there is a miracle of life-DNA.
Second, the skin consists of epidermis, dermis and subcutaneous tissue, including accessory organs (sweat glands, sebaceous glands, nails and toenails) as well as blood vessels, lymphatic vessels, nerves and muscles.
Skin tissue chart
Epidermal layer is located in the outermost layer of skin, with an average thickness of about 0.1mm. It is like a "coat" of skin, which protects skin from sunlight, microorganisms, bacteria, cold and heat and pollution. It is the most closely related part of skin care products and undertakes the important function of cell self-renewal. Each layer of epidermis is formed by cells at different stages of keratinization.
There are no blood vessels in the epidermis, but there are many nerve endings.
Epidermis has the function of skin metabolism. Basal cells absorb nutrients directly from the dermis. Basal cells continue to divide and reproduce new cells, gradually move to the surface, form cells in all layers of epidermis, and finally become dead cells, which fall off in the form of dander.
Third, the "coat" of the skin-epidermis.
Skin "Coat"-Histogram of Epidermal Layer
1. stratum corneum:
The stratum corneum is composed of necrotic keratinocytes, and its main component is keratin. The cells are closely arranged and have little water content.
Generally speaking, a healthy stratum corneum contains 20% water. If the water content is lower than 20%, it will feel tight and itchy.
When the moisture in the stratum corneum drops to 10%, dryness, lack of water, peeling and other phenomena will occur, which will seriously cause fine lines and dry lines.
However, when the skin moisture content is too high, such as using moisturizing products that are not suitable for your skin and forcibly increasing the skin moisture content, skin problems such as small rashes and pustules will also occur. So just keep the best water content.
The moisture content of skin increases from the outside to the inside. The moisture content of the outermost stratum corneum is about 20%, the moisture content of granular stratum is 50% ~ 60%, the moisture content of prickly stratum is about 65%, the moisture content of basal stratum is about 70%, and the moisture content of dermis is about 80%.
Specifically, the stratum corneum has the following functions:
A. protect cells and organs inside the human body and prevent external injuries.
B. Preventing water loss
C. absorb a small amount of ultraviolet rays
D. Resistance to physical and chemical stimuli
E. keep 10-20% moisture.
2. Transparent layer: A transparent layer, such as a strip-shaped transparent band, is the prophase of the stratum corneum. It consists of 2-3 layers of flat seedless cells, which can prevent water and electrolyte from passing through the barrier, so it is also called barrier zone. The transparent layer only exists in the palm and sole (palm and sole).
3. Granular layer: it is a waterproof barrier, which makes it difficult for water to penetrate, and at the same time prevents epidermal water from oozing out to the stratum corneum. At the same time, the granular layer can prevent ultraviolet rays from penetrating into the skin, and can refract light to reduce ultraviolet rays from entering the body.
4. Spine layer: It consists of 4-8 layers of polygonal spinous cells, which gradually flatten from bottom to top, and the cells are connected with each other through desmosomes, forming a so-called intercellular bridge.
The spinous layer can absorb nutrients, supply basal cells, provide nutrients for cells and help basal cells divide. There are many nerve endings, which can sense all kinds of external stimuli. Newborn cells divide and proliferate in this layer.
5. Basal layer: It is the innermost layer of epidermis, consisting of rectangular or columnar basal cells and dendritic melanocytes, and the junction with dermis is wavy.
Cells in the basal layer have a strong ability to divide and grow (3% ~ 5% cells often divide), which is responsible for the growth of epidermis. New cells are constantly pushed up, and finally become dead cells and fall off in the form of dander.
It is generally considered that the time from basal cell division to shedding is 28 days, which is called metabolic cycle, in which the time from basal cell division to top layer of granular layer is 14 days, and the time from stratum corneum formation to final shedding is 14 days.
Melanocytes (also called dendritic cells) are mixed between basal cells. It accounts for 4% ~ 10% of the whole basal cells. Melanocytes produce melanin granules, and the number of melanin granules determines the depth of skin color. Melanin is an important line of defense to prevent ultraviolet rays from harming human body. The increase of melanin can enhance the skin's resistance to sunlight.
Fourth, the "preservative film" of epidermis-sebum film
The skin is not only guarded, but also covered with plastic wrap!
The plastic wrap of skin is what we call a natural protective film, which is invisible to the naked eye. We call it sebum membrane.
Sebum membrane is a slightly acidic membrane formed on the skin surface after emulsification of oil secreted by skin and sweat secreted by sweat glands, with a PH value of 4.5-6.5, which has the functions of protecting, moisturizing, softening skin and resisting bacteria.
Sebum membrane has important physiological functions on the skin and even the whole body, which are mainly manifested in the following aspects:
Barrier function: Sebum membrane can prevent excessive evaporation of skin moisture, prevent a large number of external moisture and some substances from penetrating, thus producing a normal skin moisture.
Moisturize skin: Sebum membrane is emulsified by sebum and water, and its lipid part can make skin flexible, smooth and shiny; The moisture in the sebum membrane can keep the skin moist and prevent chapping.
Anti-infection: Some free fatty acids in the sebum membrane can inhibit the growth of some pathogenic microorganisms, which has self purification to the skin.
Common reasons for destroying sebum membrane:
The sebum membrane is so thin that it is invisible to the naked eye. We often accidentally destroy it. The most common situation is excessive cleaning, such as using alkaline cleaning products, bathing too often, etc. , will destroy the sebum membrane.
Sebum membrane is damaged, what will happen to the skin?
The picture on the left shows the sebum membrane of healthy skin, which is distributed in the intercellular space between keratinocytes. Every floor is neat and looks healthy. The one on the right is more messy.
A healthy sebum membrane can protect the skin;
Unhealthy sebum membrane can't protect the skin;