name | Skin |
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image2 | HumanSkinDiagram.jpg |
caption2 | A diagram of human skin. |
dorlandssuf | }} |
Skin is a soft outer covering of an animal, in particular a vertebrate. Other animal coverings such as the arthropod exoskeleton or the seashell have different developmental origin, structure and chemical composition. The adjective cutaneous means "of the skin" (from Latin ''cutis'', skin). In mammals, the skin is the largest organ of the integumentary system made up of multiple layers of ectodermal tissue, and guards the underlying muscles, bones, ligaments and internal organs. Skin of a different nature exists in amphibians, reptiles, and birds. All mammals have some hair on their skin, even marine mammals which appear to be hairless. Because it interfaces with the environment, skin plays a key role in protecting (the body) against pathogens and excessive water loss. Its other functions are insulation, temperature regulation, sensation, and the protection of vitamin D folates. Severely damaged skin will try to heal by forming scar tissue. This is often discoloured and depigmented.
Hair with sufficient density is called fur. The fur mainly serves to augment the insulation the skin provides, but can also serve as a secondary sexual characteristic or as camouflage. On some animals, the skin is very hard and thick, and can be processed to create leather. Reptiles and fish have hard protective scales on their skin for protection, and birds have hard feathers, all made of tough β-keratins. Amphibian skin is not a strong barrier to passage of chemicals and is often subject to osmosis. For example, a frog sitting in an anesthetic solution could quickly go to sleep.
#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. #Sensation: contains a variety of nerve endings that jump to heat and cold, touch, pressure, vibration, and tissue injury; see somatosensory system and haptic perception. #Heat regulation: increase perfusion and heatloss, while constricted vessels greatly reduce cutaneous blood flow and conserve heat. Erector pili muscles are significant in animals. #Control of evaporation: the skin provides a relatively dry and semi-impermeable barrier to fluid loss. #Storage and synthesis: acts as a storage center for lipids and water #Absorption: oxygen, nitrogen and carbon dioxide can diffuse into the epidermis in small amounts; some animals use their skin as their sole respiration organ (in humans, the cells comprising the outermost 0.25–0.40 mm of the skin are "almost exclusively supplied by external oxygen", although the "contribution to total respiration is negligible") #Water resistance: The skin acts as a water resistant barrier so essential nutrients aren't washed out of the body.
Mammalian skin is composed of two primary layers:
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 main type of cells which make up the epidermis are Merkel cells, keratinocytes, with melanocytes and Langerhans cells also present. 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. The daughter cells (see cell division) move up the strata changing shape and composition as they die due to isolation from their blood source. The cytoplasm is released and the protein keratin is inserted. They eventually reach the corneum and slough off (desquamation). 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. The epidermis helps the skin to regulate body temperature.
thumb |209px| [''also see: [[:File:HautFingerspitzeOCT.gif|image rotating (1.1 mb)'' ] Optical coherence tomogram of fingertip, depicting stratum corneum (~500 µm thick) with stratum disjunctum on top and stratum lucidum (connection to stratum spinosum) in the middle. At the bottom superficial parts of the dermis. Sweatducts are clearly visible.]]
Blood capillaries are found beneath the epidermis, and are linked to an arteriole and a venule. Arterial shunt vessels may bypass the network in ears, the nose and fingertips.
name | Dermis |
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graysubject | 234 |
graypage | 1065 |
image2 | Gray940.png |
style | "width:100px;"| Caption2 A diagrammatic sectional view of the skin (''click on image to magnify''). (Dermis labeled at center right.) |
meshname | Dermis |
meshnumber | A17.815.180 |
dorlands | seven/000097765 |
dorlandsid | Skin }} |
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''.
Microorganisms like ''Staphylococcus epidermidis'' colonize the skin surface. 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.
Sweat glands and sebaceous glands are both unique to mammals, but other types of skin gland are found in other vertebrates. Fish typically have a numerous individual mucus-secreting skin cells that aid in insulation and protection, but may also have poison glands, photophores, or cells that produce a more watery, serous fluid. In amphibians, the mucus cells are gathered together to form sac-like glands. Most living amphibians also possess ''granular glands'' in the skin, that secrete irritating or toxic compounds.
Although melanin is found in the skin of many species, in reptiles, amphibians, and fish, the epidermis is often relatively colourless. Instead, the colour of the skin is largely due to chromatophores in the dermis, which, in addition to melanin, may contain guanine or carotenoid pigments. Many species, such as chameleons and flounders may be able to change the colour of their skin by adjusting the relative size of their chromatophores.
Birds and reptiles have relatively few skin glands, although there may be a few structures for specific purposes, such as pheromone-secreting cells in some reptiles, or the uropygial gland of most birds.
The term hides or rawhide refers to the covering of a large adult animal such as a cow, buffalo, horse etc.
Skins and hides from different animals are used for clothing, bags and other consumer products, usually in the form of leather, but also furs.
Skin from sheep, goat and cattle was used to make parchment for manuscripts.
Skin can also be cooked to make pork rind or crackling.
Category:Soft tissue Category:Leathermaking Category:Skin Category:Organs Category:Animal anatomy
af:Vel am:ቆዳ ar:جلد an:Piel arc:ܓܠܕܐ ay:Janchi lip'ichi az:Dəri bn:ত্বক bjn:Kulimbit zh-min-nan:Phoê-hu be:Скура be-x-old:Скура bs:Koža br:Kroc'hen bg:Кожа ca:Pell cs:Kůže cy:Croen da:Hud de:Haut dv:ހަން et:Nahk el:Δέρμα es:Piel eo:Haŭto eu:Azal (anatomia) fa:پوست fr:Peau ga:Craiceann gd:Craiceann gl:Pel hak:Phì-fû xal:Арсн ko:피부 hi:त्वचा hr:Koža io:Pelo id:Kulit is:Húð it:Pelle he:עור jv:Kulit pam:Balat ka:კანი ht:Po lbe:Бурчу la:Cutis lv:Āda lb:Haut (Organ) lt:Oda ln:Lomposo hu:Bőr (anatómia) mk:Кожа ml:ചർമ്മം mr:जैविक त्वचा ms:Kulit nl:Huid ja:皮膚 no:Hud nn:Hud nrm:Pé (la) oc:Pèu pag:Baog pnb:کھل pl:Skóra pt:Pele ro:Piele (anatomie) qu:Qara ru:Кожа sah:Тирии scn:Peddi simple:Skin sk:Koža sl:Koža so:Maqaar sr:Кожни систем sh:Koža su:Kulit fi:Iho sv:Hud tl:Balat (anatomiya) ta:தோல் te:చర్మము th:ผิวหนัง tr:Deri uk:Шкіра ur:جلد ug:تېرە vi:Da fiu-vro:Nahk war:Panit yi:הויט bat-smg:Skūra zh:皮膚This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.
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