Skin

This article is about the skin of animals in general. For skin in humans, see Human skin.
For other uses, see Skin (disambiguation).
Skin
Elephant skin
Details
Identifiers
Latincutis
MeSHD012867
TA98A16.0.00.002
TA27041
Anatomical terminology

Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.

Other animal coverings, such as the arthropod exoskeleton, have different developmental origin, structure and chemical composition. The adjective cutaneous means "of the skin" (from Latin cutis 'skin'). In mammals, the skin is an 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.[1] Skin (including cutaneous and subcutaneous tissues) plays crucial roles in formation, structure, and function of extraskeletal apparatus such as horns of bovids (e.g., cattle) and rhinos, cervids' antlers, giraffids' ossicones, armadillos' osteoderm, and os penis/os clitoris.[2]

All mammals have some hair on their skin, even marine mammals like whales, dolphins, and porpoises that appear to be hairless. The skin interfaces with the environment and is the first line of defense from external factors. For example, the skin plays a key role in protecting the body against pathogens[3] and excessive water loss.[4] Its other functions are insulation, temperature regulation, sensation, and the production of vitamin D folates. Severely damaged skin may heal by forming scar tissue. This is sometimes discoloured and depigmented. The thickness of skin also varies from location to location on an organism. In humans, for example, the skin located under the eyes and around the eyelids is the thinnest skin on the body at 0.5 mm thick and is one of the first areas to show signs of aging such as "crows feet" and wrinkles. The skin on the palms and the soles of the feet is the thickest skin on the body at 4 mm thick. The speed and quality of wound healing in skin is promoted by estrogen.[5][6][7]

Fur is dense hair.[8] Primarily, fur augments 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 most fish have hard protective scales on their skin for protection, and birds have hard feathers, all made of tough beta-keratins. Amphibian skin is not a strong barrier, especially regarding the passage of chemicals via skin, and is often subject to osmosis and diffusive forces. For example, a frog sitting in an anesthetic solution would be sedated quickly as the chemical diffuses through its skin. Amphibian skin plays key roles in everyday survival and their ability to exploit a wide range of habitats and ecological conditions.[9]

On 11 January 2024, biologists reported the discovery of the oldest known skin, fossilized about 289 million years ago, and possibly the skin from an ancient reptile.[10][11]

  1. ^ Alibardi, Lorenzo (15 August 2003). "Adaptation to the land: The skin of reptiles in comparison to that of amphibians and endotherm amniotes". Journal of Experimental Zoology. 298B (1): 12–41. Bibcode:2003JEZB..298...12A. doi:10.1002/jez.b.24. PMID 12949767.
  2. ^ Nasoori, Alireza (August 2020). "Formation, structure, and function of extra-skeletal bones in mammals". Biological Reviews. 95 (4): 986–1019. doi:10.1111/brv.12597. PMID 32338826. S2CID 216556342.
  3. ^ Proksch E, Brandner JM, Jensen JM (2008). "The skin: an indispensable barrier". Exp Dermatol. 17 (12): 1063–1072. doi:10.1111/j.1600-0625.2008.00786.x. PMID 19043850. S2CID 31353914.
  4. ^ Madison, Kathi C. (August 2003). "Barrier Function of the Skin: 'La Raison d'Être' of the Epidermis". Journal of Investigative Dermatology. 121 (2): 231–241. doi:10.1046/j.1523-1747.2003.12359.x. PMID 12880413.
  5. ^ Thornton, M. J. (December 2002). "The biological actions of estrogens on skin: Estrogens and skin". Experimental Dermatology. 11 (6): 487–502. doi:10.1034/j.1600-0625.2002.110601.x. PMID 12473056.
  6. ^ Ashcroft, Gillian S.; Greenwell-Wild, Teresa; Horan, Michael A.; Wahl, Sharon M.; Ferguson, Mark W.J. (October 1999). "Topical Estrogen Accelerates Cutaneous Wound Healing in Aged Humans Associated with an Altered Inflammatory Response". The American Journal of Pathology. 155 (4): 1137–1146. doi:10.1016/S0002-9440(10)65217-0. PMC 1867002. PMID 10514397.
  7. ^ Oh, Desiree May; Phillips, Tania J. (2006). "Sex Hormones and Wound Healing". Wounds. 18 (1): 8–18.
  8. ^ "fur". Archived from the original on 3 March 2017. Retrieved 4 March 2017 – via The Free Dictionary.
  9. ^ Clarke, B. T. (August 1997). "The natural history of amphibian skin secretions, their normal functioning and potential medical applications". Biological Reviews of the Cambridge Philosophical Society. 72 (3): 365–379. doi:10.1111/j.1469-185X.1997.tb00018.x. PMID 9336100.
  10. ^ Golembiewski, Kate (11 January 2024). "Scaly Fossil Is the Oldest-Known Piece of Skin - The specimen came from a 289 million-year-old fossil deposit and might offer clues to how skin evolved". The New York Times. Archived from the original on 11 January 2024. Retrieved 12 January 2024.
  11. ^ Mooney, Ethan D.; Maho, Tea; Philp, R. Paul; Bevitt, Joseph J.; Reisz, Robert R. (January 2024). "Paleozoic cave system preserves oldest-known evidence of amniote skin". Current Biology. 34 (2): 417–426.e4. Bibcode:2024CBio...34E.417M. doi:10.1016/j.cub.2023.12.008.