Skin layers: epidermis, dermis, and subcutis, showing a hair follicle, sweat gland & sebaceous gland. Epidermis is the outermost layer of the Skin. It forms the waterproof protective wrap over the body's surface and is made up of stratified squamous Epithelium with The dermis is a layer of Skin beneath the epidermis that consists of Connective tissue, and cushions the body from stress and strain The subcutaneous tissue or subcutis is the layer of Loose connective tissue directly underlying the Dermis. A hair follicle is part of the Skin that grows Hair by packing old cells together The skin contains two different groups of sweat glands: Apocrine sweat glands and Merocrine sweat glands. The sebaceous glands are Glands found in the Skin of Mammals Locations and morphology A branched type of Acinar gland, these

In zootomy and dermatology, skin is the largest organ of the integumentary system made up of multiple layers of epithelial tissues that guard underlying muscles and organs. Zootomy is a contraction of Zoological and Anatomy. It refers to the dissection of Animals as opposed to that of plants ( phytotomy) Dermatology (from Greek grc δέρμα derma, "skin" and grc -λογία -logia) is a branch of Medicine dealing with In Biology, an organ ( Latin: organum, "instrument tool" from Greek όργανον - organon "organ instrument The Integumentary System is an organ system that protects the body from damage comprising the Skin, Hair, scales, nails, sweat glands and their In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body Tissue is a cellular organizational level intermediate between cells and a complete organism Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the In Biology, an organ ( Latin: organum, "instrument tool" from Greek όργανον - organon "organ instrument ^[1] Skin pigmentation (see: human skin color or coloring) varies among populations, and skin type can range from dry skin to oily skin. Human skin color can range from almost black (due to very high concentrations of the dark brown pigment melanin to nearly colorless (appearing reddish white due to the Blood Xeroderma (literally " dry skin " is a condition involving the Integumentary system, which in most cases can safely be treated with emollients and/or moisturizers

The adjective cutaneous literally means "of the skin" (from Latin cutis, skin).

Because it interfaces with the environment, skin plays a very important role in protecting (the body) against pathogens. A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious Its other functions are insulation, temperature regulation, sensation, synthesis of vitamin D, and the protection of vitamin B folates. The term thermal insulation can refer to materials used to reduce the rate of Heat transfer, or the methods and processes used to reduce heat transfer Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Vitamin D is a group of fat-soluble Prohormones, the two major forms of which are vitamin D2 (or Ergocalciferol) and vitamin D3 (or The B vitamins are eight water-soluble Vitamins that play important roles in cell Metabolism.

Severely damaged skin will try to heal by forming scar tissue. Scars (also called cicatrices) are areas of fibrous tissue that replace normal Skin (or other tissue after injury This is often discolored and depigmented.

The use of natural or synthetic cosmetics to treat the appearance of the face and condition of the skin (such as pore control and black head cleansing) is common among many cultures. A blackhead (medically known as an open comedo, plural comedones) is a yellowish or blackish bump or plug on the skin Oily skin is caused by hormonal fluctuations. This leads to a DHT sensitivity. Dihydrotestosterone ( DHT) (Full name 5α-Dihydrotestosterone, abbreviating to 5α-DHT; INN: androstanolone; commonly called This abnormal sensitivity causes the skin to lose moisture and essential fatty acids (linoleic acid in particular). When thousands of skin cells die the skin compensates for this loss of moisture by producing higher levels of oil. ^[2] Oily skin can be cleaned quickly with a mild solution of detergent,^[1] when pure bath soaps fail (see below: Hygiene). Afterward, body lotions could be used to recondition cleansed skin,^[1] as would be used to treat dry skin.

Skin components

Also see below: Skin layers, at bottom.

Skin has pigmentation, or melanin, provided by melanocytes, which absorb some of the potentially dangerous ultraviolet radiation (UV) in sunlight. For the drug referred to as "pigment" see Black tar heroin. Melanin is a class of compounds found in the Plant, Animal and Protista kingdoms, where it serves predominantly as a Pigment. Melanocytes are cells located in the bottom layer (the Stratum basale) of the skin's epidermis and in the middle layer of the eye (the Uvea) Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. It also contains DNA repair enzymes which help to reverse UV damage, and people who lack the genes for these enzymes suffer high rates of skin cancer. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Skin cancer is a Malignant growth on the Skin which can have many causes One form predominantly produced by UV light, malignant melanoma, is particularly invasive, causing it to spread quickly, and can often be deadly. Malignant (from the Latin roots mal- = "bad" and -genus = "born" is a medical term used to describe a severe and progressively worsening disease Melanoma is a Malignant Tumor of Melanocytes which are found predominantly in skin but also in the Bowel and the Eye (see Metastasis ( Greek: displacement μετά=next + στάσις=placement, plural metastases) sometimes abbreviated mets, Human skin pigmentation varies among populations in a striking manner. This has led to the classification of people(s) on the basis of skin color. Human skin color can range from almost black (due to very high concentrations of the dark brown pigment melanin to nearly colorless (appearing reddish white due to the Blood ^[3]

Mammalian skin often contains hairs, which in sufficient density is called fur. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Fur is a body hair of any non-human Mammal, also known as the Pelage. The hair mainly serves to augment the insulation the skin provides, but can also serve as a secondary sexual characteristic or as camouflage. Hair is a keratinised protein filament that grows through the epidermis from follicles deep within the Dermis. Secondary sex characteristics are traits that distinguish the two Sexes of a species but that are not directly part of the Reproductive system. Camouflage is a method of cryptic or concealing coloration that allows an otherwise visible Organism On some animals, the skin is very hard and thick, and can be processed to create leather. Leather is a material created through the Tanning of hides and Skins of Animals primarily Cattlehide The Tanning process Reptiles and fish have hard protective scales on their skin for protection, and birds have hard feathers, all made of tough β-keratins. Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Keratins are a family of fibrous structural proteins; tough and insoluble they form the hard but nonmineralized structures found in Reptiles Birds Amphibian skin is not a strong barrier to passage of chemicals and is often subject to osmosis. Prehistoric amphibian Amphibians (class Amphibia such as Frogs Toads Salamanders Newts Gymnophiona, Sirens and Osmosis is the Diffusion of a solvent (frequently water through a semi-permeable membrane, from a solution of low solute concentration (high water potential A frog sitting in an anesthetic solution could quickly go to sleep. This article is about the block cipher algorithm For the ultrafast laser pulse measurement technique see Frequency-resolved optical gating. Anesthesia, or anaesthesia (see spelling differences; from Greek grc αν- an-, "without" and grc αἲσθησις

The skin is often known as the largest organ of the human body. This applies to exterior surface, as it covers the body, appearing to have the largest surface area of all the organs. For the average adult human, the skin has a surface area of between 1. 5-2. 0 square meters (16. 1-21. 5 sq ft. ), most of it is between 2-3 mm (0. 10 inch) thick. The average square inch (6. 5 cm²) of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and more than a thousand nerve endings.

Functions

Skin performs the following functions:

1. Protection: an anatomical barrier from pathogens and damage between the internal and external environment in bodily defense; Langerhans cells in the skin are part of the adaptive immune system
2. Sensation: contains a variety of nerve endings that react to heat and cold, touch, pressure, vibration, and tissue injury; see somatosensory system and haptics. Not to be confused with the Beta cells making up the Islets of Langerhans. Immune system|Passive immunity|Innate immune system The adaptive immune system is composed of highly specialized systemic cells and processes that eliminate or prevent Pathogenic In Psychology, sensation is the first stage in the biochemical and neurologic events that begins with the impinging of a stimulus upon the receptor cells of a A thermoreceptor is a Sensory receptor, or more accurately the receptive portion of a sensory neuron that codes absolute and relative changes in temperature primarily Haptic communication is the means by which people and other animals communicate via touching
3. Heat regulation: the skin contains a blood supply far greater than its requirements which allows precise control of energy loss by radiation, convection and conduction. Dilated blood vessels increase perfusion and heat loss while constricted vessels greatly reduce cutaneous blood flow and conserve heat. Erector pili muscles are significant in animals. Arrectores pilorum (singular Arrector pili) are tiny Muscle fibers attached to each Hair follicle, which contract to make the
4. Control of evaporation: the skin provides a relatively dry and impermeable barrier to fluid loss. Loss of this function contributes to the massive fluid loss in burns. A burn is a type of Injury that may be caused by Heat, cold, Electricity, Chemicals, Light, Radiation, or
5. Aesthetics and communication: others see our skin and can assess our mood, physical state and attractiveness.
6. Storage and synthesis: acts as a storage center for lipids and water, as well as a means of synthesis of vitamin D by action of UV on certain parts of the skin. Vitamin D is a group of fat-soluble Prohormones, the two major forms of which are vitamin D2 (or Ergocalciferol) and vitamin D3 (or Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays
7. Excretion: sweat contains urea, however its concentration is 1/130th that of urine, hence excretion by sweating is at most a secondary function to temperature regulation. Urea is an Organic compound with the Chemical formula ( N[[hydrogen H]]22 C[[oxygen O]] Urine is a liquid waste product of the body secreted by the Kidneys by a process of filtration from Blood and Excreted through the Urethra. Excretion is the process of eliminating waste products of Metabolism and other non-useful materials
8. Absorption: Oxygen, nitrogen and carbon dioxide can diffuse into the epidermis in small amounts, some animals using their skin for their sole respiration organ. Breathing / Respiration organs are used by most or all animals to exchange the gases necessary for their life functions known as respiration. In addition, medicine can be administered through the skin, by ointments or by means of adhesive patch, such as the nicotine patch or iontophoresis. A transdermal patch or skin patch is a Medicated Adhesive patch that is placed on the Skin to deliver a specific Dose of medication A nicotine patch is a Transdermal patch that releases Nicotine into the body through the skin Iontophoresis is a non-invasive method of propelling high concentrations of a charged substance normally medication or bioactive agents transdermally by repulsive electromotive force The skin is an important site of transport in many other organisms.
9. Water resistance: The skin acts as a water resistant barrier so essential nutrients aren't washed out of the body

Hygiene

See also: Exfoliation (cosmetology)

Unclean skin favors the development of pathogenic organisms – the dead cells that continually slough off of the epidermis mix with the secretions of the sweat and sebaceous glands and the dust found on the skin to form a filthy layer on its surface. Exfoliation involves the removal of the oldest dead Skin cells on the skin's outermost surface and has been used for many years to help maintain the skin If not washed away, the slurry of sweat and sebaceous secretions mixed with dirt and dead skin is decomposed by bacterial flora, producing a foul smell. Functions of the skin are disturbed when it is excessively dirty; it becomes more easily damaged, the release of antibacterial compounds decreases, and dirty skin is more prone to develop infections. Cosmetics should be used carefully because these may cause allergic reactions. Each season requires suitable clothing in order to facilitate the evaporation of the sweat. Sunlight, water and air play an important role in keeping the skin healthy.

The skin supports its own ecosystems of microorganisms, including yeasts and bacteria, which cannot be removed by any amount of cleaning. An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually Yeasts are a growth form of eukaryotic Microorganisms classified in the kingdom Fungi, with about 1500 Species currently described The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Estimates place the number of individual bacteria on the surface of one square inch (6. 5 square cm) of human skin at 50 million though this figure varies greatly over the average 20 feet² (1. 9 m²) of human skin. Oily surfaces, such as the face, may contain over 500 million bacteria per square inch (6. 5 cm²). Despite these vast quantities, all of the bacteria found on the skin's surface would fit into a volume the size of a pea. ^[4] In general, the microorganisms keep one another in check and are part of a healthy skin. When the balance is disturbed, there may be an overgrowth and infection, such as when antibiotics kill microbes, resulting in an overgrowth of yeast. In modern usage an antibiotic is a Chemotherapeutic agent with activity against Microorganisms such as Bacteria, fungi or Protozoa A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually The skin is continuous with the inner epithelial lining of the body at the orifices, each of which supports its own complement of microbes. In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body

Oily skin is caused by over-active glands, that produce a substance called sebum, a naturally healthy skin lubricant. The sebaceous glands are Glands found in the Skin of Mammals Locations and morphology A branched type of Acinar gland, these ^[1] When the skin produces excessive sebum, it becomes heavy and thick in texture. The sebaceous glands are Glands found in the Skin of Mammals Locations and morphology A branched type of Acinar gland, these Oily skin is typified by shininess, blemishes and pimples. A pimple is a result of a blockage of the Skin 's Pore. It can be a Pustule or Papule. ^[1] The oily-skin type is not necessarily bad, since such skin is less prone to wrinkling, or other signs of aging,^[1] because the oil helps to keep needed moisture locked into the epidermis (outermost layer of skin). Epidermis is the outermost layer of the Skin. It forms the waterproof protective wrap over the body's surface and is made up of stratified squamous Epithelium with

The negative aspect of the oily-skin type is that oily complexions are especially susceptible to clogged pores, blackheads, and buildup of dead skin cells on the surface of the skin. A blackhead (medically known as an open comedo, plural comedones) is a yellowish or blackish bump or plug on the skin ^[1] Oily skin can be sallow and rough in texture and tends to have large, clearly visible pores everywhere, except around the eyes and neck. ^[1]

The goal of treating oily skin is to remove excess surface sebum without complete removal of skin lipids. Lipids are broadly defined as any fat- Soluble ( lipophilic) naturally-occurring Molecule, such as fats oils waxes cholesterol sterols fat-soluble ^[1] Severe degreasing treatment can foster an actual worsening of sebum secretion, which defeats the aim of the cleansing. ^[1] A method of cleansing oily skin is to wash with a solution of a mild synthetic detergent^[1] (see: surfactant) containing no oils, waxes or other lipid agents that could aggravate the oily condition of the skin, sometimes combined with a toning lotion. A detergent (as a noun is a material intended to assist Cleaning. Surfactants are wetting agents that lower the Surface tension of a liquid allowing easier spreading and lower the Interfacial tension between two liquids Wax has traditionally referred to a substance that is secreted by Bees ( Beeswax) and used by them in constructing their Such a product removes the oily residue and debris from the skin surface. Some cleansing products have lower concentrations of hydroxy acids, which remove dead cells from the upper levels of the stratum corneum. α-hydroxy acids, or alpha hydroxy acids ( AHAs) are a class of chemical compounds that consist of a Carboxylic acid substituted with a hydroxy group The stratum corneum ("horny layer" is the outermost layer of the epidermis (the outermost layer of the Skin) ^[1] Those products should be used on a regular basis to work adequately. ^[1] A light moisturizer may be included in a product to counteract any drying effects of the cleanser. ^[1]

Aging

For more details on this topic, see senescence. Senescence refers to the biological processes of a living Organism approaching an advanced age (i

A typical rash

Skin infected with Scabies

As skin ages, it becomes thinner and more easily damaged. Scabies is a transmissible ectoparasite Skin Infection characterized by superficial Burrows intense pruritus (itching and Secondary Intensifying this effect is the decreasing ability of skin to heal itself as a person ages.

Skin aging is caused by the fall in elasticity. Aging skin also receives less blood flow and lower gland activity.

Disease

For more details on this topic, see list of skin diseases. In Medicine, a dermatosis is a generic term for disease of the skin.

In medicine, the branch concerned with the skin is called dermatology. Medicine is the art and science of healing It encompasses a range of Health care practices evolved to maintain and restore Human Health by the Dermatology (from Greek grc δέρμα derma, "skin" and grc -λογία -logia) is a branch of Medicine dealing with The skin is subject to constant attack and, so, can be afflicted by numerous ailments such as these:

Tumors:

• Benign tumors of the skin such as Squamous cell papilloma
• Skin cancer

Others:

• Rashes
• Blisters
• Acne
• Keratosis pilaris
• Fungal infections such as athlete's foot and ringworm
• Microbial infections. A Squamous cell papilloma is a generally benign Papilloma that arises from the stratified Squamous epithelium of the skin lip oral cavity tongue Skin cancer is a Malignant growth on the Skin which can have many causes A rash is a change of the Skin which affects its color appearance or Texture. A blister is a small pocket of fluid within the upper layers of the skin Acne vulgaris (commonly called acne) is a Skin disease caused by changes in the Pilosebaceous units (skin structures consisting of a Hair follicle Keratosis pilaris (KP also follicular keratosis is a very common genetic follicular condition that is manifested by the appearance of rough bumps on the skin A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Athlete's foot, also called Tinea Pedis, is a Parasitic fungal infection of the epidermis of the human foot Ringworm (also called serpigo) is an infection of the skin characterized by a reddish to brownish raised or bumpy patch of skin that may be lighter in the center A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually
• Calcinosis cutis
• Sunburn
• Keloid
• Scabies
• Vitiligo
• Albinism
• Eczema
• Psoriasis

There are several other skin diseases as well. Calcinosis cutis (or cutaneous calcification) is a type of Calcinosis wherein calcium deposits form in the skin A sunburn is a burn to living tissue such as Skin produced by overexposure to Ultraviolet (UV radiation commonly from the Sun 's rays A keloid is a type of Hypertrophic scar with mainly type I and some type III collagen which results in an overgrowth of tissue at the site of a healed skin injury Scabies is a transmissible ectoparasite Skin Infection characterized by superficial Burrows intense pruritus (itching and Secondary Vitiligo (ˈvɪtəˈlaɪgoʊ or leukoderma is a chronic skin disease that causes loss of pigment, resulting in irregular pale patches of Skin Albinism (from Latin albus, "white" see extended etymology) is a form of hypopigmentary Congenital disorder, Eczema (from Greek έκζεμα) is a form of Dermatitis, or Inflammation of the Epidermis. Psoriasis (səˈraɪəsɪs ( suh-RI-uh-sus) is a non-contagious disorder which affects the Skin and Joints It commonly causes red scaly

Variability in skin tone

Individuals with ancestors from different parts of the world can have highly visible differences in skin pigmentation. Individuals with Sub-Saharan African ancestry (black people) tend towards darker skin, while those of Northern European descent (white people) have paler skin. Sub-Saharan Africa is a geographical term used to describe the area of the African continent which lies south of the Sahara, or those African countries The term black people usually refers to a racial group of Humans with dark Skin color, but the term has also been used to categorise a number of diverse Northern Europe is a term for the northern part of Europe. The United Nations defines Northern Europe as (Finland White People is the second album by Handsome Boy Modeling School. Between these extremes are individuals of Asian, South-East Asian, Native American, Middle Eastern, Polynesian and Melanesian descent. Native Americans in the United States are the indigenous peoples from the regions of North America now encompassed by the continental United States The Middle East is a Subcontinent with no clear boundaries often used as a synonym to Near East, in opposition to Far East. Polynesia (from Greek: πολύς many, νῆσος island) is a Subregion of Oceania, comprising a large grouping of over Melanesia (from Greek: μέλας black, νῆσος island) means "islands of the black-skinned people"

The skin of black people has more variation in color from one part of the body to another than does the skin of other racial groups, particularly the palms of the hands and soles of the feet. The term black people usually refers to a racial group of Humans with dark Skin color, but the term has also been used to categorise a number of diverse Part of this is the result of the variations in the thickness of the skin or different parts of the body. The thicker the skin, the more layers of cell with melanin in them, and the darker the color. ^[5] In addition, these parts of the body do not have melanin-producing cells.

Darker skin hinders UV A rays from penetrating. Since vitamin B folats are degraded by UV A and vitamin D is synthesized different skin tones are more likely to produce different vitamin deficiencies.

Skin Types

Skin can be classified based on its reaction to ultraviolet radiation:^[6]

Animal skin products

The term skin refers to the covering of a small animal, such as a sheep, goat (goatskin), pig, snake (snakeskin) etc or the young of a large animal. Snakeskin can refer to a Material that is made from the hide of a Snake, which the snake usually sheds when it is stressed

The term hides or rawhide refers to the covering of a large adult animal such as a cow, buffalo, horse etc. Hides are Skins obtained from animals for human use Examples of animal hide sources are Deer and Cattle typically used for producing Leather, Rawhide is a hide or animal skin that has not been exposed to Tanning.

Skins and hides from different animals are used for clothing, bags and other consumer products, usually in the form of leather, but also furs. Leather is a material created through the Tanning of hides and Skins of Animals primarily Cattlehide The Tanning process Fur is a body hair of any non-human Mammal, also known as the Pelage.

Skin can also be used to make products such as gelatin, glue and wool. Gelatin (also gelatine, from French gélatine) is a translucent colourless brittle nearly tasteless solid substance, extracted from the An animal glue is an Adhesive that is created by prolonged boiling of Animal Connective tissue. Wool is the fiber derived from the specialized skin cells called follicles of animals in the Caprinae family principally sheep, but the hair of certain species Mucus of skin from hagfish is still under research. Hagfish are marine Craniates of the class Myxini, also known as Hyperotreti.

Skin layers

Skin is composed of three primary layers: the epidermis, which provides waterproofing and serves as a barrier to infection; the dermis, which serves as a location for the appendages of skin; and the hypodermis (subcutaneous adipose layer). Epidermis is the outermost layer of the Skin. It forms the waterproof protective wrap over the body's surface and is made up of stratified squamous Epithelium with The dermis is a layer of Skin beneath the epidermis that consists of Connective tissue, and cushions the body from stress and strain An appendage in the broadest sense is an additional or subsidiary part existing on or added to something which can generally still function if the appendage has never existed or The hypodermis, also called the hypoderm, subcutaneous tissue, or superficial fascia is the lowermost layer of the Integumentary system in

Epidermis

Epidermis, "epi" coming from the Greek meaning "over" or "upon", is the outermost layer of the skin. It forms the waterproof, protective wrap over the body's surface and is made up of stratified squamous epithelium with an underlying basal lamina. In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body The basal lamina is a layer of extracellular matrix on which Epithelium sits and which is secreted by the epithelial cells

The epidermis contains no blood vessels, and cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the dermis. The blood vessels are part of the Circulatory system and function to transport Blood throughout the body The main type of cells which make up the epidermis are Merkel cells, keratinocytes, with melanocytes and Langerhans cells also present. Merkel cells are large oval cells found in the skin of vertebrates The keratinocyte is the major cell type of the epidermis, making up about 90% of epidermal cells Melanocytes are cells located in the bottom layer (the Stratum basale) of the skin's epidermis and in the middle layer of the eye (the Uvea) Not to be confused with the Beta cells making up the Islets of Langerhans. The epidermis can be further subdivided into the following strata (beginning with the outermost layer): corneum, lucidum (only in palms of hands and bottoms of feet), granulosum, spinosum, basale. Cells are formed through mitosis at the basale layer. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei The daughter cells, (see cell division) move up the strata changing shape and composition as they die due to isolation from their blood source. Cell division is a process by which a cell, called the parent cell divides into two or more cells called daughter cells. The cytoplasm is released and the protein keratin is inserted. Keratins are a family of fibrous structural proteins; tough and insoluble they form the hard but nonmineralized structures found in Reptiles Birds They eventually reach the corneum and slough off (desquamation). Desquamation is the shedding of the outer layers of the Skin. This process is called keratinization and takes place within about 27 days. This keratinized layer of skin is responsible for keeping water in the body and keeping other harmful chemicals and pathogens out, making skin a natural barrier to infection. A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious

[also see:  image rotating (1.1 mb) ]
Optical Coherence Tomography tomogram of fingertip, depicting stratum corneum (~500µm thick) with stratum disjunctum on top and stratum lucidum (connection to stratum spinosum) in the middle. The stratum corneum ("horny layer" is the outermost layer of the epidermis (the outermost layer of the Skin) For the layer of the Hippocampus, see Stratum lucidum of hippocampus. At the bottom superficial parts of the dermis. The dermis is a layer of Skin beneath the epidermis that consists of Connective tissue, and cushions the body from stress and strain Sweatducts are clearly visible.

Components

The epidermis contains no blood vessels, and is nourished by diffusion from the dermis. The blood vessels are part of the Circulatory system and function to transport Blood throughout the body Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement The dermis is a layer of Skin beneath the epidermis that consists of Connective tissue, and cushions the body from stress and strain The main type of cells which make up the epidermis are keratinocytes, melanocytes, Langerhans cells and Merkels cells. The keratinocyte is the major cell type of the epidermis, making up about 90% of epidermal cells Melanocytes are cells located in the bottom layer (the Stratum basale) of the skin's epidermis and in the middle layer of the eye (the Uvea) Not to be confused with the Beta cells making up the Islets of Langerhans. Merkel cells are large oval cells found in the skin of vertebrates

Layers

Epidermis is divided into several layers where cells are formed through mitosis at the innermost layers. Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei They move up the strata changing shape and composition as they differentiate and become filled with keratin. Keratins are a family of fibrous structural proteins; tough and insoluble they form the hard but nonmineralized structures found in Reptiles Birds They eventually reach the top layer called stratum corneum and become sloughed off, or desquamated. This process is called keratinization and takes place within weeks. Keratins are a family of fibrous structural proteins; tough and insoluble they form the hard but nonmineralized structures found in Reptiles Birds The outermost layer of Epidermis consists of 25 to 30 layers of dead cells.

Sublayers

Epidermis is divided into the following 5 sublayers or strata:

• Stratum corneum
• Stratum lucidum
• Stratum granulosum
• Stratum spinosum
• Stratum germinativum (also called "stratum basale")

Mnemonics that are good for remembering the layers of the skin (using "stratum basale" instead of "stratum germinativum"):

• "Cher Likes Getting Skin Botoxed" (from superficial to deep)
• "Before Signing, Get Legal Counsel" (from deep to superficial)

Blood capillaries are found beneath the epidermis, and are linked to an arteriole and a venule. The stratum corneum ("horny layer" is the outermost layer of the epidermis (the outermost layer of the Skin) For the layer of the Hippocampus, see Stratum lucidum of hippocampus. In Microscopic views of Skin, the stratum granulosum layer of the epidermis lies between the Stratum spinosum, below and the Stratum lucidum In the Skin, the stratum spinosum is a multi-layered arrangement of cuboidal cells that sits beneath the Stratum granulosum. Stratum germinativum (also stratum basale or basal cell layer) is the layer of Keratinocytes that lies at the base of the epidermis immediately A mnemonic device (nəˈmɒnɪk is a Memory aid Commonly met mnemonics are often verbal something such as a very short poem or a special word used to help a person remember Arterial shunt vessels may bypass the network in ears, the nose and fingertips.

Dermis
The distribution of the bloodvessels in the skin of the sole of the foot. (Corium - TA alternate term for dermis - is labeled at upper right. )
A diagrammatic sectional view of the skin (click on image to magnify). (Dermis labeled at center right. )
Gray's	subject #234 1065
MeSH	Dermis
Dorlands/Elsevier	d_11/12289496

Dermis

The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. the Peripheral organs of the Special senses the organs of Taste ( Peripheral gustatory or Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books Elsevier, the world's largest Publisher of Medical and Scientific literature, forms part of the Reed Elsevier group Epidermis is the outermost layer of the Skin. It forms the waterproof protective wrap over the body's surface and is made up of stratified squamous Epithelium with Connective tissue is one of the four types of tissue in traditional classifications (the others being epithelial, Muscle, and Nervous tissue) The dermis is tightly connected to the epidermis by a basement membrane. The basement membrane is a structure that supports overlying Epithelial or Endothelial cells. It also harbors many Mechanoreceptor/nerve endings that provide the sense of touch and heat. It contains the hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels. A hair follicle is part of the Skin that grows Hair by packing old cells together The skin contains two different groups of sweat glands: Apocrine sweat glands and Merocrine sweat glands. The sebaceous glands are Glands found in the Skin of Mammals Locations and morphology A branched type of Acinar gland, these The lymphatic system in Vertebrates is a network of conduits that carry a clear fluid called Lymph. The blood vessels are part of the Circulatory system and function to transport Blood throughout the body The blood vessels in the dermis provide nourishment and waste removal to its own cells as well as the Stratum basale of the epidermis.

Structure

The dermis is structurally divided into two areas: a superficial area adjacent to the epidermis, called the papillary region, and a deep thicker area known as the reticular region.

Papillary region

The papillary region is composed of loose areolar connective tissue. Areolar tissue (a type of "loose connective tissue" exhibits loosely organized fibers abundant blood vessels and a lot of seemingly empty space It is named for its fingerlike projections called papillae, that extend toward the epidermis. The papillae provide the dermis with a "bumpy" surface that interdigitates with the epidermis, strengthening the connection between the two layers of skin.

In the palms, fingers, soles, and toes, the influence of the papillae projecting into the epidermis forms contours in the skin's surface. These are called friction ridges, because they help the hand or foot to grasp by increasing friction. Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e Friction ridges occur in patterns (see: fingerprint) that are genetically and epigenetically determined and are therefore unique to the individual, making it possible to use fingerprints or footprints as a means of identification. A fingerprint is an impression of the friction ridges of all or any part of the finger In Biology, the term epigenetics refers to changes in Gene expression caused by mechanisms other than changes in the underlying DNA sequence

Reticular region

The reticular region lies deep in the papillary region and is usually much thicker. It is composed of dense irregular connective tissue, and receives its name from the dense concentration of collagenous, elastic, and reticular fibers that weave throughout it. Collagen is the main Protein of Connective tissue in Animals and the most abundant protein in Mammals making up about 50% of the whole-body protein A material is said to be elastic if it deforms under stress (e Cross-links are bonds that link one Polymer chain to another They can be Covalent bonds or Ionic bonds "Polymer chains" can refer These protein fibers give the dermis its properties of strength, extensibility, and elasticity. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl

Also located within the reticular region are the roots of the hair, sebaceous glands, sweat glands, receptors, nails, and blood vessels. The root of the hair ends in an enlargement the hair bulb, which is whiter in color and softer in texture than the shaft and is lodged in a follicular involution of the The sebaceous glands are Glands found in the Skin of Mammals Locations and morphology A branched type of Acinar gland, these The skin contains two different groups of sweat glands: Apocrine sweat glands and Merocrine sweat glands. A cutaneous receptor is a type of Sensory receptor found in the dermis or epidermis A nail is a horn -like structure at the end of an animal's Finger or Toe. The blood vessels are part of the Circulatory system and function to transport Blood throughout the body

Tattoo ink is held in the dermis. Stretch marks from pregnancy are also located in the dermis.

The hypodermis is not part of the skin, and lies below the dermis. Its purpose is to attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves. Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the It consists of loose connective tissue and elastin. The main cell types are fibroblasts, macrophages and adipocytes (the hypodermis contains 50% of body fat). A fibroblast is a type of cell that synthesizes and maintains the Extracellular matrix of many Animal tissues Macrophages ( Greek: "big eaters" from makros "large" + phagein "eat" ( Mø) are cells within the tissues that Adipocytes are the cells that primarily compose Adipose tissue, specialized in storing energy as Fat. Fat serves as padding and insulation for the body.

Microorganisms like Staphylococcus epidermidis colonize the skin surface. Staphylococcus (in Greek σταφυλη staphyle means bunch of grapes and κοκκος coccos means granule is a genus of Gram-positive The density of skin flora depends on region of the skin. The disinfected skin surface gets recolonized from bacteria residing in the deeper areas of the hair follicle, gut and urogenital openings.

See also

• Acid mantle
• Anthropodermic bibliopegy
• Callus - thick area of skin
• Cosmetics and cosmetic surgery
• Cutaneous structure development
• Diseases - list of skin diseases
• Dermatology - branch of medicine
• Fingerprint - skin on fingertips
• Hair - including hair follicles in skin
• Skin color
• Hyperpigmentation - about excess skin color
• Meissner's corpuscle
• Nails - fingernails or toenails
• Pacinian corpuscle
• Polyphenol antioxidant
• Sweat - description of perspiration
• Superficial fascia

References

External links

• Skin care - The British Association of Cosmetic Doctors