human skin is the outer layer of the body. In humans, it is the largest organ of the covering system. The skin has up to seven layers of ectodermal tissue and keeps the muscles, bones, ligaments and internal organs underlying it. Human skin is similar to most other mammalian skins, and human skin is very similar to pig skin. Although almost all human skin is covered with hair follicles, it can appear hairless. There are two common skin types, hairy and mumps (not hairy). The cutaneous adjective literally means "skin" (from Latin cutis , skin).
Because it interacts with the environment, the skin plays an important immune role in protecting the body against pathogens and excessive water loss. Other functions are isolation, temperature regulation, sensation, vitamin D synthesis, and vitamin B folate protection. The damaged skin will try to heal by forming scar tissue. It often changes color and depigmentation.
In humans, skin pigmentation varies among populations, and skin types can range from dry to oily. Such a variety of skins provides a rich and diverse habitat for bacteria numbering about 1000 species of 19 phyla, which are present in human skin.
Video Human skin
Structure
The skin has mesodermal cells, pigmentation, like melanin supplied by melanocytes, which absorb some potentially harmful ultraviolet (UV) radiation in the sun. It also contains DNA repair enzymes that help reverse UV damage, so people who lack the gene for this enzyme suffer from high levels of skin cancer. One form is predominantly produced by UV rays, malignant melanoma, highly invasive, causing it to spread rapidly, and often can be deadly. Human skin pigmentation varies among populations in striking ways. This has led to the classification of person (s) on the basis of skin color.
The skin is the largest organ in the human body. For average adult humans, the skin has a surface area of ​​between 1.5-2.0 square meters (16.1-21.5 square feet). The thickness of the skin varies greatly in all parts of the body, and between men and women and young and old. An example is the skin on the forearm which averages 1.3 mm in males and 1.26 mm in females. On average square inches (6.5Ã, cmÃ,²) the skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and more than 1,000 nerve endings. The average human skin cell is about 30 micrometers in diameter, but there are variants. Skin cells usually range from 25-40 micrometers (squared), depending on various factors.
The skin consists of three main layers: epidermis, dermis and hypodermis.
Epidermis
Epidermis , "epi" derived from Greek which means "over" or "upon", is the outermost layer of skin. It forms a waterproof protective layer and covers the surface of the body which also serves as an infection barrier and consists of a layered squamous epithelium with a basal lamina base.
The epidermis contains no blood vessels, and the cells in the deepest layers are maintained almost exclusively by oxygen scattered from the surrounding air and much lower levels by the blood capillaries that extend into the outer layers of the dermis. The main types of cells that make up the epidermis are Merkel cells, keratinocytes, with melanocytes and Langerhans cells also present. The epidermis can be subdivided into the following strata (beginning with the outermost layer): corneum, lucidum (only in the palms and buttocks of the feet), granulosum, spinosum, basale. Cells form through mitosis in the basal layer. The child cells (see cell division) rise to the shape and composition of the strata that changes as they die from isolation from their blood source. The cytoplasm is released and the protein keratin is inserted. They eventually reach the corneum and peel (desquamation). This process is called "keratinization". The skin keratinization layer is responsible for keeping the water in the body and keeping other harmful chemicals and pathogens out, making the skin a natural barrier to infection.
Components
The epidermis contains no blood vessels, and is nourished by diffusion from the dermis. The main types of cells that make up the epidermis are keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Epidermis helps the skin to regulate body temperature.
Layers
The epidermis is divided into several layers where cells are formed through mitosis in the innermost layer. They rise to the shape and composition of strata that change as they differentiate and become filled with keratin. They eventually reach the top layer called stratum corneum and are broken off, or ordered. This process is called keratinization and takes place in a few weeks. The outermost layer of the epidermis consists of 25 to 30 layers of dead cells.
Sublayer
The epidermis is divided into 5 sub layers or stratum:
- Stratum corneum
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum
- Stratum germinativum (also called "stratum basale").
Blood capillaries are found beneath the epidermis, and are associated with arterioles and venules. Arterial shunt vessels can cut tissue in the ears, nose and fingertips.
Genes and proteins expressed in the epidermis
About 70% of all human protein coding genes are expressed in the skin. Nearly 500 genes have a high expression pattern in the skin. There are less than 100 genes specific to the skin and these are expressed in the epidermis. Analysis of suitable proteins indicates that it is mainly expressed in keratinocytes and has functions associated with squamous differentiation and cultivation.
Dermis
The dermis is a layer of skin beneath the epidermis which consists of connective tissue and body pads of stress and tension. The dermis is closely connected to the epidermis by the basement membrane. It also stores many nerve endings that give it a touch and heat. It contains hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels. The blood vessels in the dermis provide food and sewage from its own cells as well as from the base layer of the epidermis.
The dermis is structurally divided into two areas: the superficial area adjacent to the epidermis, called the papillary region , and the thicker area known as reticular region .
Papillary region
The papillary region consists of loose areolar connective tissue. Named for finger-like projection called papillae , which extends towards the epidermis. Papilla provides the dermis with a "wavy" surface that interdigitates with the epidermis, strengthening the relationship between two layers of skin.
In the palms, fingers, soles of the feet, and toes, the effect of papillae projecting onto the epidermis forms contours on the surface of the skin. This epidermal lump occurs in a genetically and epigenetically determined pattern of fingerprints and is therefore unique to the individual, making it possible to use fingerprints or footprints as an identification tool.
Reticular region
The reticular region lies deep within the papillary region and is usually thicker. It consists of an irregularly dense connective tissue, and receives its name from a dense concentration of collagen, elastic, and reticular fibers that weave throughout it. These protein fibers give their strength, elasticity, and elasticity properties to the dermis.
Also located within the reticular region are the hair roots, sebaceous glands, sweat glands, receptors, nails, and blood vessels.
The tattoo ink is held in the dermis. Stretch marks often from pregnancy and obesity, also located in the dermis.
Subcutaneous network
Subcutaneous tissue (also hypodermis and subcutis ) is not part of the skin, and lies beneath the dermis of the cutis. The goal is to attach the skin to the underlying bone and muscles and supply it with blood vessels and nerves. It consists of loose connective tissue, adipose tissue and elastin. The major cell types are fibroblasts, macrophages and adipocytes (subcutaneous tissue contains 50% body fat). Fats function as padding and insulation for the body.
Section
Maps Human skin
Development
Skin color
Human skin shows a high variation of skin tone from the darkest brown to the brightest white golden color. Human skin exhibits a higher color variation than other single mammal species and is the result of natural selection. Skin pigmentation in humans evolved to mainly regulate the amount of ultraviolet (UVR) radiation penetrating the skin, controlling the biochemical effects.
The actual skin color of different humans is influenced by many substances, although the most important substance that determines the color of human skin is the melanin pigment. Melanin is produced inside the skin in cells called melanocytes and that is the main determinant of dark-skinned human skin. The skin color of people with bright skin is determined primarily by the blue-white connective tissue under the dermis and by the hemoglobin circulating in the dermis vein. The underlying red color of the skin becomes more visible, especially in the face, when, as a consequence of physical exercise or nervous system stimulation (anger, fear), enlarged arterioles.
There are at least five different pigments that determine the color of the skin. These pigments are present at different levels and places.
- Melanin: The color is brown and is in the basal layer of the epidermis.
- Melanoid: It resembles melanin but diffusely present throughout the epidermis.
- Carotene: This pigment is yellow to orange. It is present in the stratum corneum and dermal fat cells and superficial fascia.
- Hemoglobin (also spelled hemoglobin ): Found in blood and not skin pigment but develops purple.
- Oxyhemoglobin: Also found in blood and not skin pigment. It develops red color.
There is a correlation between the geographical distribution of UV radiation (UVR) and the distribution of genuine leather pigmentation worldwide. Areas that highlight higher UVR numbers reflect dark-skinned populations, generally located closer to the equator. Areas far from the tropics and closer to the poles have lower UVR concentrations, which are reflected in lighter-skinned populations.
In the same population it has been observed that adult human females are much lighter in skin pigmentation than in men. Women need more calcium during pregnancy and lactation, and the synthesized vitamin D from sunlight helps in absorbing calcium. For this reason it is thought that women may have evolved to have lighter skin to help their bodies absorb more calcium.
The Fitzpatrick scale is a numerical numerical scheme for human skin color developed in 1975 as a way to classify the typical response of various skin types to ultraviolet (UV) light:
Aging
As the skin ages, it becomes thinner and more easily damaged. Intensifying this effect is the declining ability of the skin to heal itself as one gets older.
Among other things, skin aging is noted by the decrease in volume and elasticity. There are many internal and external causes for skin aging. For example, aged skin receives less blood flow and lower gland activity.
A validated comprehensive assessment scale has categorized clinical findings of aging skin as a weakness, rhytids (wrinkles), and various aspects of photoaging, including erythema (redness), and telangiectasia, dyspigmentation (brown alteration), solar elastosis (yellowing), keratosis (abnormal growth) and poor texture.
Cortisol causes collagen degradation, accelerating skin aging.
Anti aging supplements are used to treat skin aging.
Photoaging
Photoaging has two main problems: an increased risk for skin cancer and the appearance of damaged skin. In younger skin, sun damage will recover quickly because cells in the epidermis have a faster turnover rate, while in older populations the skin becomes thinner and the epidermal displacement rate for cell repair is lower which can result in the dermis layer become damaged.
Function
The skin performs the following functions:
- Protection : anatomical barriers from pathogens and damage between internal and external environments in the body's defenses; Langerhans cells in the skin are part of the adaptive immune system. Sweat contains lysozyme that breaks the bond inside the bacterial cell wall.
- Sensation : contains various nerve endings that react to heat and cold, touch, pressure, vibration, and tissue injury; see somatosensory and haptic systems.
- Heat regulation : the skin contains a much larger blood supply than it needs that allows precise control of energy loss by radiation, convection and conduction. Widening blood vessels increase perfusion and heatloss, while narrowed vessels greatly reduce skin blood flow and heat preservation.
- Evaporation control : the skin provides a relatively dry and semi-impermeable barrier to fluid loss. The loss of this function contributes to a very large fluid loss in burns.
- Aesthetics and communication : others see our skin and can judge our mood, physical state and attraction.
- Storage and synthesis : serves as a storage center for lipids and water, as well as a means of vitamin D synthesis with UV action on certain parts of the skin.
- Excression : sweat contains urea, but its concentration is 1/130th of urine, so sweat excretion is mostly a secondary function for temperature regulation.
- Absorption : cells consisting of 0.25-0.40 mm outer shells "almost exclusively supplied by external oxygen", although "contribution to total respiration is negligible". In addition, medicines can be administered through the skin, with ointment or by using adhesives, such as nicotine patches or ionophthalesis. Skin is an important place of transport in many other organisms.
- Water resistance : The skin acts as a watertight barrier so essential nutrients are not swept out of the body.
Skin Flora
Human skin is a rich environment for microbes. About 1000 species of bacteria from 19 bacterial phyla have been found. Most come from only four phyla: Actinobacteria (51.8%), Firmicutes (24.4%), Proteobacteria (16.5%), and Bacteroidetes (6.3%). Propionibacteria and Staphylococci species are the major species in the sebaceous area. There are three major ecological areas: moist, dry and sebaceous. In damp places on Corynebacteria bodies along with Staphylococci dominate. In dry areas, there is a mixture of species but is dominated by b-Proteobacteria and Flavobacteriales. Ecologically, the sebaceous area has a larger species richness than the wet and dry ones. Areas with the smallest resemblance between people in species are the distance between the fingers, the distance between the toes, the axilla, and the umbilical cord. Most closely resemble the nostrils, nares (inside the nostrils), and behind.
Reflecting on the diversity of human skin researchers on the human skin microbiome has observed: "Hairy, damp armpits lie at short distances from dry smooth arms, but these two niche possibilities are ecologically different as rainforests are for deserts."
NIH has launched the Human Microbiome Project to characterize human microbiota covering the skin and the role of this microbiome in health and disease.
Microorganisms such as Staphylococcus epidermidis colonize the skin surface. The density of the skin flora depends on the area of ​​the skin. Disinfected skin surfaces will be colonized from bacteria located in the deeper areas of hair follicles, intestines and urogenital openings.
Clinical interests
Skin diseases include skin infections and skin neoplasms (including skin cancer).
Dermatology is a branch of medicine that deals with skin conditions.
Society and culture
Hygiene and skin care
The skin supports the microbial ecosystem itself, including yeast and bacteria, which can not be removed by any amount of cleansing. Estimates put the number of individual bacteria on the surface of one inch square (6.5 cm) of human skin at 50 million, though this figure varies greatly above the average 20 square feet (1.9 m 2 ) skin human. Oily surfaces, such as faces, may contain more than 500 million bacteria per square inch (6.5 cm²). Although this amount is very much, all the bacteria found on the surface of the skin will match a volume of peas. In general, microorganisms maintain each other and are part of healthy skin. When balance is disrupted, there may be overgrowth and infection, such as when antibiotics kill microbes, resulting in overgrowth of yeast. The skin is continuous with epithelial lining in the body in the hole, each supporting its own microbial complement.
Cosmetics should be used with caution on the skin as this can cause allergic reactions. Each season needs a suitable outfit to facilitate the evaporation of sweat. Sunlight, water and air play an important role in keeping skin healthy.
Oily skin
Oily skin is caused by overactive sebaceous glands, which produce a substance called sebum, a healthy skin lubricant naturally. When the skin produces excessive sebum, the texture becomes thick and thick. Oily skin is characterized by shininess, stains and acne. Oily skin types are not always bad, because such skin is less susceptible to wrinkles, or other signs of aging, because the oil helps keep the required moisture locked into the epidermis (the outermost layer of skin).
The negative aspect of this type of oily skin is that oily skin is very susceptible to clogged pores, blackheads, and the buildup of dead skin cells on the skin surface. Oily skin can be pale and rough in texture and tend to have large pores, clearly visible everywhere, except around the eyes and neck.
Permeability
Human skin has low permeability; That is, most foreign substances can not penetrate and diffuse through the skin. The outermost layer of skin, stratum corneum, is an effective barrier to most of the inorganic nanoparticles. It protects the body from external particles like toxins by not letting them come into contact with the internal tissues. However, in some cases it is desirable to allow particles to enter the body through the skin. The potential medical applications of such particle transfer have encouraged the development of nanomedicine and biology to enhance skin permeability. One application of transcutaneous particle delivery can be to find and treat cancer. Nanomedical researchers seek to target the epidermis and other layers of active cell division where nanoparticles can interact directly with cells that have lost their growth control mechanisms (cancer cells). Such direct interactions can be used to diagnose specific tumor properties more accurately or to treat them by providing drugs with cellular specificity.
Nanoparticles
Nanoparticles with a diameter of 40Ã,nm and smaller have succeeded in penetrating the skin. Research confirms that nanoparticles larger than 40 n nm do not penetrate the skin through the stratum corneum. Most of the penetrating particles will diffuse through the skin cells, but some particles will flow into the hair follicles and reach the dermis layer.
Skin permeability relative to various forms of nanoparticles has also been studied. Studies have shown that spherical particles have a better ability to penetrate skin than ellipsoidal particles because the ball is symmetrical in all three spatial dimensions. One study compared two forms and recorded data showing spherical particles located deep within the epidermis and dermis whereas ellipsoidal particles were mainly found in layers of the stratum corneum and epidermis. Nanorods were used in experiments because of their unique fluorescent properties but have shown mediocre penetration.
Nanoparticles of different materials have shown the limitations of skin permeability. In many experiments, gold nanoparticles of 40 nm or less in diameter are used and have been shown to penetrate into the epidermis. Titanium oxide (TiO2), zinc oxide (ZnO), and silver nanoparticles are not effective in penetrating the skin through the stratum corneum. The quantum point of Cadmium selenide (CdSe) has been shown to penetrate very effectively when they have certain properties. Since CdSe is toxic to living organisms, the particles must be covered in a surface group. An experiment comparing permeability of coated quantum dots in polyethylene glycol (PEG), PEG-amine, and carboxylic acids concluded that PEG and PEG-amine surface groups permit the largest particle penetration. Carboxylic acid-coated particles do not penetrate through the stratum corneum.
Increase permeability
Scientists previously believed that skin is an effective barrier to inorganic particles. Damage caused by mechanical stress is believed to be the only way to increase its permeability. Recently, more simple and more effective methods to improve skin permeability have been developed. For example, ultraviolet radiation (UVR) has been used to slightly damage the skin surface, causing time-dependent defects that allow easier nanoparticle penetration. High energy UVR causes cell restructuring, weakening the boundary between the stratum corneum and the epidermal layer. Skin damage is usually measured by transepidermal water loss (TEWL), although it may take 3-5 days for TEWL to reach its peak value. When TEWL reaches the highest value, maximum nanoparticle density can penetrate the skin. Studies confirm that UVR damaged skin significantly increases permeability. The effect of increased permeability after UVR exposure can lead to an increase in the number of particles that penetrate the skin. However, specific skin permeability after UVR exposure relative to particles of different sizes and ingredients has not been determined.
Other skin destruction methods used to increase nanoparticle penetration include stripping, abrasion, and chemical enhancement. Tape stripping is a process in which tape is applied to the skin and then lifted to lift the top layer of skin. Skin abrasion is done by shaving 5-10 micrometers above the surface of the skin. Chemical upgrading is a process in which chemicals such as polyvinylpyrrolidone (PVP), dimethyl sulfoxide (DMSO), and oleic acid are applied to the skin surface to increase permeability.
Electroporation is the application of short pulses of electric fields on the skin and has been shown to increase skin permeability. The pulses have high voltage and on the order of milliseconds when applied. The charged molecule penetrates the skin more often than the neutral molecule after the skin has been subjected to an electric field pulse. The results have shown molecules on the order of 100 micrometers to easily penetrate the electroporated skin.
Apps
The area of ​​great interest in nanomedicine is the transdermal patch because of the possibility of painless application of therapeutic agents with very few side effects. Transdermal patches have been limited to regulate small amounts of drugs, such as nicotine, due to skin permeability limitations. The development of techniques that improve skin permeability has led to more drugs that can be applied via transdermal patches and more options for patients.
Improving skin permeability allows nanoparticles to penetrate and target cancer cells. Nanoparticles along with multi-modal imaging techniques have been used as a way to diagnose non-invasive cancers. High permeability skins allow quantum dots with antibodies attached to the surface for active targeting to successfully penetrate and identify cancer tumors in mice. Targeting the tumor is beneficial because the particles can be excited using a fluorescence microscope and emit light and heat energy that will destroy cancer cells.
Sunblock and sunscreen
Sunblock and sunscreen are different skin care products that are different even though they offer full protection from the sun.
Sunblock - Sunblock is not translucent and stronger than sunscreen, because it is able to block most UVA/UVB rays and radiation from the sun, and does not need to be reapplied several times a day. Titanium dioxide and zinc oxide are two important ingredients in sunblock.
Sunscreen - Sunscreen is more transparent once applied to the skin and also has the ability to protect against UVA/UVB rays, although sunscreen ingredients have the ability to break down at a much faster rate after exposure to sunlight, and some radiation can penetrate to the skin. In order for more effective sunscreen, it needs to be re-applied consistently and use one with a higher sun protection factor.
Diet
Vitamin A, also known as retinoids, is beneficial for the skin by normalizing keratinization, decreasing sebum production that contributes to acne, and reversing and treating photodamage, striae, and cellulite.
Vitamin D and analogues are used to lower the regulation of the skin's immune system and epithelial proliferation while promoting differentiation.
Vitamin C is an antioxidant that regulates collagen synthesis, forms barrier lipids, regenerates vitamin E, and provides photoprotection.
Vitamin E is an antioxidant membrane that protects against oxidative damage and also provides protection against harmful UV rays.
Some scientific research confirms that changes in basic nutritional status affect skin conditions.
The Mayo Clinic lists the foods they claim to help the skin: fruits and vegetables, grains, green leafy vegetables, nuts, and seeds.
See also
- Acid Coat
- Anthropodermic Bibliopegy
- Artificial leather
- Callus, thick skin area
- List of skin conditions
- the development of skin structure
- Fingerprint, skin at the fingertips
- Hyperpigmentation, about color overload
- Intertriginat
- Meissner corpusclee
- Pacific corpuscle
- Polyphenol antioxidants
- Skin lesions
- Skin repair
References
External links
- MedlinePlus Skin Condition National Library of Medicine taken November 12, 2013.
Source of the article : Wikipedia
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