1, the human skin consists of what parts, how large the body skin, what are the characteristics of the skin appearance
The skin is a complex structure. The skin generally looks smooth on the outside and consists of many layers of tissue. The skin consists of epidermis, dermis and subcutaneous tissues from outside to inside. In addition to its own structure, the skin is rich in blood vessels, lymphatic vessels, nerves, muscles and various skin appendages (hair, hair follicles, sebaceous glands, sweat glands, nails). The skin covers our whole body and is the largest organ of the human body, with a total weight of about 16% of our body weight. The total area of the skin is about 1.5m2 in adults and 0.21m2 in newborns.
The appearance of the skin is mainly determined by the skin texture. The arrangement and traction of fiber bundles in the dermis make the skin form many furrows and ridges, and the dermal furrows divide the skin surface into long, parallel, slightly elevated dermal borders, and the furrows and ridges constitute the skin texture. The furrow divides the skin surface into many triangular, rhombic or polygonal mounds, and the depth of the furrow varies with location, age and gender.
Fine skin means that the skin has shallow and fine furrows, small and flat texture of the skin mound, and this skin can give a sense of beauty with fine texture. Sunlight or other factors can degenerate and break the dermal fibers, causing skin texture to deepen, such as photoaging-induced rhombic skin on the neck, mossy skin caused by long-term scratching, acne patients with large pores like orange peel-like appearance, and rough skin texture, which affects aesthetics. The purpose of cosmetology is to make the skin achieve fine texture and inconspicuous pores through sun protection, moisturizing and scientific treatment of skin diseases, giving a sense of beauty.
The skin on the inner surface of the fingertips has a special skin texture curve, which is a genetically determined, unchangeable structure. After a burn or abrasion, these textures reform. Almost no two people in the world have the same fingerprint, and as we see in detective novels, fingerprints can help police find suspects because it is our undeniable proof of identity.
2.How thick is our skin and does the thickness of the skin have an effect on skin beauty
The thickness of the skin varies according to age and location, and is about 0.5 to 4nm (the thickness referred to here does not include the subcutaneous tissue). The average thickness of the epidermis is about 0.1 nm, while the thickness of the dermis is 15 to 40 times that of the epidermis. The skin of the eyelids, vulva and breasts is the thinnest, only about 0.05nm, therefore, the most prone to wrinkles on our face is around the eyes. The skin of the extensor side of the limbs is thicker than the flexor side; the skin of the palmoplantar area is the thickest, about 3 to 4 nm.
The thickness of the epidermal stratum corneum, the hyaline layer and the granular layer of the skin and the scattering phenomenon on the skin surface can affect the skin tone. If the stratum corneum is thick, the skin will be yellowish; if the granular layer and the transparent layer are thick, the skin will appear white. In addition, the scattering phenomenon of light on the surface of the skin can also affect the color of the skin, in the thin skin, because the light transmission rate is larger, can refract the red color of the blood pigment in the blood vessels; in the thicker parts of the skin, the light transmission rate is poor, can only see the yellow carotene in the cuticle of the skin, so the skin is yellow, such as: the palms of our hands, the soles of the feet because the cuticle is very thick, the skin is yellow.
Therefore, skin beauty should maintain the appropriate skin thickness, the need for appropriate exfoliation of skin care, so that the skin color is rosy, smooth and delicate surface, but not excessive destruction of the stratum corneum to maintain the normal structure and function of the skin.
3.What is the outermost structure of the skin and what cells does it consist of?
The outermost layer of the skin is the epidermis. The epidermis is the structure most closely related to the beauty of our skin. The integrity, thickness, texture and hydration of the epidermis determine, to a certain extent, the beauty of the skin and the physiological function of the skin. The two most important cells of the epidermis are keratin-forming cells and dendritic cells.
Keratin-forming cells: they are the main cells of the epidermis, accounting for more than 80% of the epidermal cells. According to the differentiation stages and characteristics of keratin-forming cells, epidermis is divided into basal layer, spiny layer, granular layer, hyaline layer and stratum corneum in order from inside to outside under light microscope. The basal layer is connected to the dermis by means of a basement membrane band. Keratin-forming cells eventually form keratin, which migrates to the outermost layer of the epidermis.
Dendritic cells:There are four types, each with different functions and structures.
Melanocytes:are the only cells that synthesize melanin. Each melanocyte extends a slender dendritic projection that contacts a group of keratin-forming cells to form epidermal melanin units. Melanocytes absorb ultraviolet light and protect keratin-forming cells, Langerhans cells and deeper tissues from radiation damage.
Langerhans cells: They are cells closely related to skin immunity and play a key role in various immune responses. They can react immunely to bacteria and viruses that come in contact with the skin surface or enter the skin, and protect the organism from pathogenic microorganisms.
Michael cells: There are many granules in Michael cells, and these granules are mostly concentrated on the side near the nerve endings, presumably this is a kind of sensory cells, which can feel tactile or other mechanical stimuli.
Undetermined cells: often located in the lowermost layer of the epidermis, it can only be identified under electron microscopy. Its occurrence and function are unknown and may be related to Langerhans cells.
4.What is the structure of each layer of the epidermis and how does it relate to skin beauty
(1) Stratum corneum
Structure: A dense structure composed of interlocking layers of inanimate keratin-forming cells. (Cells are 30 microns wide and 0.8 microns thick). The thickness of the stratum corneum varies depending on the site, with about 5-20 layers of cells and a thickness of about 10-15 microns. In the palmoplantar region it can be 40-50 layers thick and several millimeters thick.
Composition: Filoprotein, tropoelastin and endoprotein (80% of the proteins in the stratum corneum) are cross-linked with each other and become insoluble dense structures.
Functions: The stratum corneum is one of the structures most closely related to skin beauty, and it has five major functions.
①Protection function: the main component of the stratum corneum, keratin, can effectively prevent the attack of external physical, chemical and biological harmful factors;
② Absorption function: The stratum corneum is the most important way for skin absorption, and can absorb topical drugs and cosmetics. The surface of the stratum corneum is sebaceous membrane, and the surface of the keratin-forming cell membrane is phospholipid, so lipid-soluble substances can easily pass through the stratum corneum, and topical drugs and cosmetic products of dermatology are mostly emulsions and creams;
③ Sun protection function: The keratin-forming cells in the stratum corneum can absorb a large amount of UVB and a small amount of UVC to protect the body from sun damage;
④Moisturizing function: the stratum corneum contains natural moisturizing factor (NMF), lipids and other substances, which keep the water content of the stratum corneum at about 20%;
⑤ Aesthetic function: the state and proper thickness of the stratum corneum directly reflects the beauty of the skin. If the stratum corneum is too thick, the skin color will be yellow, and it will look rough and dull; if the stratum corneum is too thin, such as excessive “exfoliation” and “peeling”, the skin barrier function will be incomplete, and the defense function of the skin will be weakened, and it will be easily attacked by external bad factors. Skin problems, such as skin flushing, capillary dilation, pigmentation, skin aging, and even skin diseases.
(2) Transparent layer
It is composed of two to three layers of flat, poorly defined, non-nucleated, eosinophilic, tightly linked cells between the stratum corneum and the stratum granulosum, with more hydrophobic protein-bound phospholipids in the cytoplasm and fused with tensegrity filaments, which acts as a barrier to prevent the passage of water and electrolytes.
(3) Granular layer
It is generally composed of two to four layers of spindle-shaped or flattened cells, and a large number of hyaline keratin granules are visible in the cells, containing post-filamentous polymeric proteins, which are formerly known as filamentous protein polymeric proteins. The filamentous polymeric proteins intertwine with keratin to provide tension to the granular layer and serve as its components. The granular layer has not only an anabolic but also a catabolic role and is a waterproof barrier to the skin.
(4) Spiny layer
Located above the basal layer, it consists of four to eight layers of polygonal cells. Keratin 1 and 10 were first found in this layer, and these proteins form a hard cellular frame that provides greater, mechanical tension to the cells. The lipids they release are wrapped around the skin surface and are part of the skin barrier (skin barrier), which prevents excessive water loss from the skin. After some cosmetic procedures, e.g., facial resurfacing and chemical peels, spiny cells near the basal layer can also undergo cell division and participate in repair.
(5) Basal layer
Located in the lowermost layer of the epidermis, it is also very closely related to skin aesthetics. Under normal conditions, cells in the basal layer continuously proliferate to produce new keratin-forming cells, also known as the anagen layer. Therefore, when trauma or surgery is performed, especially facial cosmetic grinding and laser treatment, care should be taken that the trauma does not break through the superficial dermis to avoid damaging the epidermal foot embedded in the superficial dermis and leaving a scar by the proliferation of dermal connective tissue to repair the trauma.
At the same time, cell renewal is a continuous process, which also suggests that basic skin care aesthetic is a gradual process and should be persistent.
In addition, the epidermal turnover cycle and cosmetology have a rather important relationship. Keratin-forming cells proliferation has a certain regularity, about 10% of the cells daily nuclear division activities, sequential and gradual upward movement, keratin-forming cells from the basal layer to the surface of the stratum corneum and shed a total of about 28 days, called the epidermal passage time or turnover time.
Epidermal turnover time is too fast or too slow for the beauty of the skin. This rule suggests that we should not artificially interfere with the “life cycle of the skin” when performing basic skin care. In addition, the melanin secreted by the melanocytes in the basal layer also takes 28 days to shed from the basal layer to the stratum corneum. Therefore, we should pay attention to the physiological metabolic characteristics of the skin when carrying out whitening and spot removal, and should not use strong exfoliating agents to break the law of melanin metabolism epidermis through time.
5.Do you know what is sebaceous film and what it is composed of?
The sebaceous film is a transparent film covering the surface of the skin, also known as the water-lipid film. It is mainly composed of sweat secreted by sweat glands as the water phase and sebum secreted by sebaceous glands as the oil phase emulsified to form the sebum film. Its main components are ceramide with moisturizing effect, squalene with sunscreen effect and linoleic acid and linolenic acid with anti-inflammatory effect and lipid components.
6.Why dermatologists compare skin barrier function to “brick wall doctrine”
The “brick wall structure” is an important structure of the epidermis. The “bricks” represent keratinocytes, which are differentiated by the proliferation of keratin-forming cells in the basal layer of the epidermis. The keratinocyte membrane is a lipid bilayer structure with the function of sealing membrane, which can prevent the loss of moisturizing factors and maintain a stable hydration state.
The “gray pulp” refers to the lipids in the interstitial space of keratinocytes, including ceramides, fatty acids, and cholesterol. These lipids originate from the dendrites of the granular layer cells and fill in between the keratin-forming cells, like “mortar” that holds the “bricks” together to form a stable structure of the skin, which can ensure the barrier function of the skin. Once the keratin-forming cells and intercellular material are destroyed, the brick wall structure of the skin is damaged and the skin loses its barrier function. Therefore, the barrier function of the skin is compared to the “brick wall doctrine”.
7.What is the role of sebaceous membrane and skin “brick wall structure” for our skin beauty?
The sebaceous membrane and the “brick wall structure” have four major functions.
(1) Barrier function: It constitutes the first barrier for physical, chemical and biological factors to enter the skin.
(2) Moisturizing function: The lipids in the sebaceous membrane can lock in water and prevent dermal nutrients, moisturizing factors and water from dissipating so that the water content of the stratum corneum is maintained at about 20%, which plays a role in moisturizing and hydrating the skin.
(3) Regulation of inflammatory response: Linoleic acid and linolenic acid in the sebaceous membrane can have a certain resistance to external stimuli.
(4) Sunscreen function: The “brick wall structure” itself is a barrier against sunlight, and the squalene in the sebaceous membrane has a sunscreen effect.
Once the sebaceous membrane and the “brick wall structure” are damaged, the skin loses its barrier role, and the skin ages, even causing many skin diseases to occur.
8.What is the relationship between cell membrane transmembrane proteins and skin beauty
Water channel proteins (AQPs): AQP3 is a complete transmembrane protein channel in keratinocytes with a molecular weight of 28 kDa. AQPs exist as tetramers in the cell membrane. Each monomer (i.e., one AQPs molecule) is an independent functional unit with a channel tube at its center.
One AQPs molecule can allow 3 billion water molecules to pass through it per second. Members of the AQPs family are mainly found in animals and plants. 13 types of AQPs have been identified in mammals, and AQP3 is the main one present in human skin.
AQP3 is a key factor in maintaining skin hydration by transporting not only water but also substances such as urea and glycerol in and out of the skin.AQP3 is closely related to cell migration and wound healing in the skin .AQP3 is an integral transmembrane protein channel in keratin-forming cells, and significant downregulation of AQP3 would subsequently cause a decrease in skin hydration and disrupt the skin’s The “brick wall structure” of the skin is disrupted, which ultimately leads to increased transepidermal water loss (TEWL), dryness and dehydration of the skin, and an increased likelihood of skin aging.
Ultraviolet (UV) rays, through a series of cellular signaling pathways, can also induce downregulation of AQP3 expression in keratin-forming cells, resulting in diminished cell migration and wound healing capacity. Therefore, in the daily skin care, you should do a good job of sun protection and moisturizing to slow down skin aging.
9, sebaceous membrane, skin “brick wall structure” and water channel protein under what circumstances will be damaged
(1) Long-term external use of hormones: long-term external use of hormones to remove spots or treat skin diseases, easy to make the epidermis thinning, skin immune function decline; certain skin diseases such as: hormone-dependent dermatitis, seborrheic dermatitis, solar dermatitis, acne, eczema, etc..
(2) Sun exposure: excessive exposure to the sun without sun protection measures.
(3) Invasive treatment: such as laser treatment, chemical peeling, and medically-derived irritating drugs.
(4) Irregular cosmetic treatment: such as excessive “peeling” and “exfoliation”.
All these factors can damage the integrity of sebaceous membrane and skin “brick wall structure”, and reduce the expression of water channel protein, causing skin physiological dysfunction.
10.How to better maintain the barrier function of the skin
The integrity of sebum membrane and skin “brick wall structure” and the expression of AQP3 in skin cell membrane are closely related to the barrier function of skin. Maintaining the skin barrier function is the only way to keep the skin healthy and beautiful.
Therefore, while treating skin diseases, you should actively use medical skin care products containing ceramide, squalene, linoleic acid, linolenic acid and other ingredients that can repair the skin barrier function, such as Avène, etc.; prohibit long-term use of hormones on the face, avoid the use of irritating drugs and cleansers; pay attention to daily sun protection; and under the guidance of professional dermatologic physicians, take care of the skin in a scientific and standardized manner. Beauty.
11.What is the relationship between melanocytes and skin diseases?
Melanocytes are located between keratin-forming cells in the basal layer of the epidermis. Melanocytes work closely with a certain number (10~36) of their neighboring keratin-forming cells to deliver melanin granules to them, forming epidermal melanin units. The amount of melanin granules secreted by melanocytes can directly affect the color of the skin.
The melanin secreted by melanocytes can effectively protect the nucleus from UV damage and avoid skin damage, but the abnormal function of melanocytes will lead to some pigment metabolism disorders skin diseases, causing abnormal skin color deepening or fading, which directly affects people’s appearance and physical and mental health. The following diseases are common.
Diseases of pigment deepening.
Increased melanin production: In the process of melanin formation, the tyrosinase activity and the ability to transport melanin vesicles are enhanced, which causes melanin deposition on the skin. Common diseases include: freckles, acanthosis nigricans, seborrheic keratosis, chloasma, Addison’s disease, radiation dermatitis, and Rell’s melanosis.
Increased number of melanocytes: including pigmented nevus, café au lait, zygomatic brown nevus, nevus of Ota, nigra, etc.
Hypopigmented diseases
Decreased melanogenesis: Impaired transfer of melanin vesicles, such as lichen planus, the pathogen Malassezia can produce azelaic acid, which inhibits tyrosinase and interferes with melanin formation; diseases such as albinism and phenylketonuria, where tyrosine and tyrosinase are abnormal, affecting melanin formation and causing hypopigmentation.
Decrease in the number of melanocytes: such as vitiligo and pemphigus.
12, what is the structure of the skin underneath the epidermis
The structure underneath the epidermis is the dermis. The dermis is not only rich in blood vessels, lymphatic vessels, nerves, muscles, fibers, connective tissues and stroma, but also in hair follicles, sebaceous glands, sweat glands and other skin appendages.
The dermis is the foundation of the skin. Because there are no blood vessels in the epidermis, the dermis must provide the energy and nutrient supply for the cells in the basal layer. The dermis is an irregular dense connective tissue, composed of fibers, matrix and cellular components, with a predominantly fibrous component. Collagen and elastic fibers are interwoven with each other, and abundant thick collagen fibers are interwoven to form a dense lamellar structure, with a small amount of matrix and cellular components between the fibers.
The dermis is divided into papillary layer and reticular layer from top to bottom, and there is no clear boundary between the two layers. The papillae are papillary elevations convex to the bottom of the epidermis, which are connected to the epidermal protrusions in a staggered pattern and contain abundant capillaries and capillary lymphatic vessels, which are the main structures providing nutrition to the epidermal basal layer. There are also free nerve endings and vesicular nerve vesicles within the dermal papillae. The reticular layer is thicker and located below the papillary layer with larger blood vessels, lymphatic vessels, nerves, skin appendages and thicker fibers.
13.What is the elasticity of our skin maintained by, what are the fibers in the dermis and what are their main roles
Skin elasticity is determined by skin water content, dermal collagen fibers and elastic fibers, matrix and subcutaneous fat thickness. If the skin water content and subcutaneous fat thickness is moderate, and the dermal collagen fibers and elastic fibers are normal, the skin is elastic; conversely, skin aging occurs after the skin water content is reduced, subcutaneous fat atrophy, dermal collagen fibers and elastic fibers degeneration, resulting in skin relaxation and inelasticity.
(1) collagen fibers: is the main structural protein in human skin, collagen fibers in the dermal connective tissue is the most abundant, accounting for about 18%-30% of the dermal volume, 75% of the dermal dry weight. Most of the collagen fibers in the adult dermis are type I collagen, accounting for about 80% of the collagen composition of the skin, and a few are type III collagen. The collagen fibers near the dermal papillae, epidermal appendages and blood vessels are more slender and regularly arranged.
In the middle and lower dermis, collagen fibers are gathered into thick bundles of fibers almost parallel to the dermal surface and interwoven into a network that extends in all directions on a horizontal plane. And in the lower dermis, the collagen bundles are the thickest. Collagen fibers are an important component in maintaining the skin’s tension and tensile strength, and are the material basis for maintaining the skin’s fullness and plumpness. Collagen fibers are tough and have high tensile strength, but lack elasticity.
As the skin ages, the collagen fiber arrangement becomes disorganized and the skin’s toughness decreases. Type III collagen is a naive, slender collagen fiber, which is the main component of the reticular fibers. UV radiation can affect the formation of type I collagen and the relative increase of type III collagen, which eventually leads to a decrease in mature collagen bundles and the appearance of sagging and wrinkled skin.
(2) Elastic fibers: Elastic fibers are fine, and under electron microscopy, they are finer than collagen fibers, 1 to 3 nm in diameter, wavy in shape, interwoven into a network, and entwined between collagen fiber bundles. Elastin fibers are composed of elastin and microprogenitor fibers. Elastic fibers give the skin its elasticity. As the skin ages, the elasticity of the skin decreases as the elastic fibers break and curl.
Although elastin fibers account for only 1% to 2% of the dry weight of the skin, they play an important role in the elasticity and compliance of the skin. During the natural aging process of human skin, elastic fibers undergo degradation and fragmentation until they disappear. Sunlight-induced photoaging can cause elastic fibers to degenerate and accumulate in clumps, and their elasticity and compliance are then lost, resulting in skin laxity, wrinkles, and cracks after overstretching.
Sunlight exposure will cause the degeneration and reduction of elastic fibers and collagen fibers in the dermis of the skin, which will decrease the elasticity and toughness of the skin and accelerate the aging of the skin. Therefore, to slow down skin aging, sun protection is one of the necessary skin care procedures.
14.What are the matrixes in the dermis and what are their roles?
The matrix in the dermis is filled with various fibers and cells, responsible for providing nutrition and regulating nutrients, metabolism and water retention, and has great significance in skin physiology and bodybuilding. Aminoglycans in the matrix (hyaluronic acid, chondroitin sulfate, dermatan sulfate, keratin sulfate, heparin, etc.) play an important role in maintaining skin moisture. Synthetic or extracted substances with the same or similar composition as the matrix are added to cosmetics as active substances to moisturize the skin, anti-aging, whitening and spot removal.
Substrates in the dermis and their roles.
Chondroitin sulfate: moisturizes and promotes the maturation of collagen fibers.
Heparin: promote skin blood circulation, increase capillary permeability, supply cells with various nutrients from the body; activate blood, activate cell metabolism, promote cell regeneration ability, improve skin wrinkles and lighten pigmentation; restore skin luster, delicacy and elasticity, and inhibit the inflammatory effect of UV rays.
Hyaluronic acid: is a very good deep moisturizer, because of its good moisturizing properties make the dermis become the skin’s water reservoir. It can be used with NMF to constitute a total moisturizer for skin from superficial layer (stratum corneum) to deep layer (dermis); with lubricity and film-forming property, it can increase the sense of lubrication and wetness of skin; it can scavenge free radicals, nourish skin and participate in skin repair and nutrition.
Vitamin C, etc.: stimulates collagen production, lightens melanin in the dermis, softens capillaries, and improves capillary permeability.
As the skin ages, the matrix in the dermis, such as hyaluronic acid, gradually decreases in its content with age, and the water content of the skin gradually decreases, drying the skin and making it prone to wrinkles. Therefore, pay attention to the use of moisturizing skin care products in your daily skin care routine, which has an important role in delaying skin aging.
15.What is the structure of skin other than epidermis and dermis?
In addition to the epidermis and dermis, the skin is also composed of subcutaneous tissue and skin appendages. The structure of subcutaneous tissue is similar to the dermis, except that the fibrous tissue is loosely arranged and contains a large amount of adipose tissue, which is the body’s energy savings, and plays a key role in body temperature regulation due to its thermal insulation properties. Moreover, subcutaneous fat also has an important role in sculpting the human body. The right amount of subcutaneous tissue can show the beauty of female curves and plumpness, but the excessive deposition of subcutaneous fat caused by obesity will affect the beauty of the body.
Skin appendages include hair, sweat glands, sebaceous glands and nails. They are extensions of the epidermis, but some are deeply embedded in the dermis and even in the subcutaneous tissues.