In the evolving space of advanced wellness and performance optimization, targeted peptide protocols are becoming more refined and specialized. Explore advanced Peptides Costa Rica solutions created to enhance recovery, anti-aging, and overall wellness. Access high-quality, personalized treatments with expert guidance to enhance vitality, performance, and long-term health.. One emerging concept gaining attention is KLOW, representing a focused approach to internal balance, recovery, and sustained vitality.
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Longevity may refer to especially long-lived members of a population, whereas life expectancy is defined statistically as the average number of years remaining at a given age. For example, a population's life expectancy at birth is the same as the average age at death for all people born in the same year (in the case of cohorts).
Longevity studies may involve putative methods to extend life. Longevity has been a topic not only for the scientific community but also for writers of travel, science fiction, and utopian novels. The legendary fountain of youth appeared in the work of the Ancient Greek historian Herodotus.
There are difficulties in authenticating the longest human life span, owing to inaccurate or incomplete birth statistics. Fiction, legend, and folklore have proposed or claimed life spans in the past or future vastly longer than those verified by modern standards, and longevity narratives and unverified longevity claims frequently speak of their existence in the present.
A life annuity is a form of longevity insurance.
Various factors contribute to an individual's longevity. Significant factors in life expectancy include gender, genetics, access to health care, hygiene, diet and nutrition, exercise, lifestyle, and crime rates. Below is a list of life expectancies in different types of countries:[1]
Population longevities are increasing as life expectancies around the world grow:[2][3]
The Gerontology Research Group validates current longevity records by modern standards, and maintains a list of supercentenarians; many other unvalidated longevity claims exist. Record-holding individuals include:[4][5][6]
Evidence-based studies indicate that longevity is based on two major factors: genetics and lifestyle.[10]
Twin studies have estimated that approximately 20-30% of the variation in human lifespan can be related to genetics, with the rest due to individual behaviors and environmental factors which can be modified.[11] Although over 200 gene variants have been associated with longevity according to a US-Belgian-UK research database of human genetic variants[12] these explain only a small fraction of the heritability.[13]
Lymphoblastoid cell lines established from blood samples of centenarians have significantly higher activity of the DNA repair protein PARP (Poly ADP ribose polymerase) than cell lines from younger (20 to 70 year old) individuals.[14] The lymphocytic cells of centenarians have characteristics typical of cells from young people, both in their capability of priming the mechanism of repair after H2O2 sublethal oxidative DNA damage and in their PARP gene expression.[15] These findings suggest that elevated PARP gene expression contributes to the longevity of centenarians, consistent with the DNA damage theory of aging.[16]
In July 2020, scientists used public biological data on 1.75 m people with known lifespans overall and identified 10 genomic loci which appear to intrinsically influence healthspan, lifespan, and longevity – of which half have not been reported previously at genome-wide significance and most being associated with cardiovascular disease – and identified haem metabolism as a promising candidate for further research within the field. Their study suggests that high levels of iron in the blood likely reduce, and genes involved in metabolising iron likely increase healthy years of life in humans.[18][17]
Longevity is a highly plastic trait, and traits that influence its components respond to physical (static) environments and to wide-ranging life-style changes: physical exercise, dietary habits, living conditions, and pharmaceutical as well as nutritional interventions.[19][20][21] A 2012 study found that even modest amounts of leisure time physical exercise can extend life expectancy by as much as 4.5 years.[22]
As of 2021, there is no clinical evidence that any dietary practice contributes to human longevity.[23] Although health can be influenced by diet, including the type of foods consumed, the amount of calories ingested, and the duration and frequency of fasting periods,[24] there is no good clinical evidence that fasting promotes longevity in humans, as of 2021[update].[23][25][26]
Caloric restriction is a widely researched intervention to assess effects on aging, defined as a sustained reduction in dietary energy intake compared to the energy required for weight maintenance.[23][25] To ensure metabolic homeostasis, the diet during calorie restriction must provide sufficient energy, micronutrients, and fiber.[25] Some studies on rhesus monkeys showed that restricting calorie intake resulted in lifespan extension, while other animals studies did not detect a significant change.[23][27] According to preliminary research in humans, there is little evidence that calorie restriction affects lifespan.[23][25] There is a link between diet and obesity and consequent obesity-associated morbidity.
Four well-studied biological pathways that are known to regulate aging, and whose modulation has been shown to influence longevity are Insulin/IGF-1, mechanistic target of rapamycin (mTOR), AMP-activating protein kinase (AMPK), and Sirtuin pathways.[28][29]
Emerging research suggests that vascular function and microcirculation play an important role in aging and longevity. Endothelial function, which regulates vascular tone, blood flow, and tissue perfusion, is increasingly recognized as an important determinant of cardiovascular and metabolic health.[30]
Hemodynamic forces such as shear stress influence endothelial signaling pathways, including nitric oxide production, which contributes to vascular homeostasis. Impairments in microcirculation and endothelial function have been associated with aging-related diseases and reduced healthspan.[31][32][33]
In preindustrial times, deaths at young and middle age were more common than they are today. This is not due to genetics, but because of environmental factors such as disease, accidents, and malnutrition, especially since the former were not generally treatable with pre-20th-century medicine. Deaths from childbirth were common for women, and many children did not live past infancy. In addition, most people who did attain old age were likely to die quickly from the above-mentioned untreatable health problems. Despite this, there are several examples of pre-20th-century individuals attaining lifespans of 85 years or greater, including John Adams, Cato the Elder, Thomas Hobbes, Christopher Polhem, and Michelangelo. This was also true for poorer people like peasants or laborers.[citation needed] Genealogists will almost certainly find ancestors living to their 70s, 80s and even 90s several hundred years ago.
For example, an 1871 census in the UK (the first of its kind, but personal data from other censuses dates back to 1841 and numerical data back to 1801) found the average male life expectancy as being 44, but if infant mortality is subtracted, males who lived to adulthood averaged 75 years. The present life expectancy in the UK is 77 years for males and 81 for females, while the United States averages 74 for males and 80 for females.
Studies have shown that black American males have the shortest lifespans of any group of people in the US, averaging only 69 years (Asian-American females average the longest).[35] This reflects overall poorer health and greater prevalence of heart disease, obesity, diabetes, and cancer among black American men.
Women normally outlive men. Theories for this include smaller bodies that place lesser strain on the heart (women have lower rates of cardiovascular disease) and a reduced tendency to engage in physically dangerous activities.[36] Conversely, women are more likely to participate in health-promoting activities.[37] The X chromosome also contains more genes related to the immune system, and women tend to mount a stronger immune response to pathogens than men.[38] However, the idea that men have weaker immune systems due to the supposed immuno-suppressive actions of testosterone is unfounded.[39]
There is debate as to whether the pursuit of longevity is a worthwhile health care goal. Bioethicist Ezekiel Emanuel, who is also one of the architects of ObamaCare, has argued that the pursuit of longevity via the compression of morbidity explanation is a "fantasy" and that longevity past age 75 should not be considered an end in itself.[40] This has been challenged by neurosurgeon Miguel Faria, who states that life can be worthwhile in healthy old age, that the compression of morbidity is a real phenomenon, and that longevity should be pursued in association with quality of life.[41] Faria has discussed how longevity in association with leading healthy lifestyles can lead to the postponement of senescence as well as happiness and wisdom in old age.[42]
Most biological organisms have a naturally limited longevity due to aging, unlike a rare few that are considered biologically immortal.
Given that different species of animals and plants have different potentials for longevity, the disrepair accumulation theory of aging tries to explain how the potential for longevity of an organism is sometimes positively correlated to its structural complexity. It suggests that while biological complexity increases individual lifespan, it is counteracted in nature since the survivability of the overall species may be hindered when it results in a prolonged development process, which is an evolutionarily vulnerable state.[43]
According to the antagonistic pleiotropy hypothesis, one of the reasons biological immortality is so rare is that certain categories of gene expression that are beneficial in youth become deleterious at an older age.
Longevity myths are traditions about long-lived people (generally supercentenarians), either as individuals or groups of people, and practices that have been believed to confer longevity, but for which scientific evidence does not support the ages claimed or the reasons for the claims.[44][45] A comparison and contrast of "longevity in antiquity" (such as the Sumerian King List, the genealogies of Genesis, and the Persian Shahnameh) with "longevity in historical times" (common-era cases through twentieth-century news reports) is elaborated in detail in Lucian Boia's 2004 book Forever Young: A Cultural History of Longevity from Antiquity to the Present and other sources.[46]
After the death of Juan Ponce de León, Gonzalo Fernández de Oviedo y Valdés wrote in Historia General y Natural de las Indias (1535) that Ponce de León was looking for the waters of Bimini to cure his aging.[47] Traditions that have been believed to confer greater human longevity also include alchemy,[48] such as that attributed to Nicolas Flamel. In the modern era, the Okinawa diet has some reputation of linkage to exceptionally high ages.[49]
Longevity claims may be subcategorized into four groups: "In late life, very old people often tend to advance their ages at the rate of about 17 years per decade .... Several celebrated super-centenarians (over 110 years) are believed to have been double lives (father and son, relations with the same names or successive bearers of a title) .... A number of instances have been commercially sponsored, while a fourth category of recent claims are those made for political ends ...."[50] The estimate of 17 years per decade was corroborated by the 1901 and 1911 British censuses.[50] Time magazine considered that, by the Soviet Union, longevity had been elevated to a state-supported "Methuselah cult".[51]
Robert Ripley regularly reported supercentenarian claims in Ripley's Believe It or Not!, usually citing his own reputation as a fact-checker to claim reliability.[52]
Longevity in other animals can shed light on the determinants of life expectancy in humans, especially when found in related mammals. However, important contributions to longevity research have been made by research in other species, ranging from yeast to flies to worms. In fact, some closely related species of vertebrates can have dramatically different life expectancies, demonstrating that relatively small genetic changes can have a dramatic impact on aging. For instance, Pacific Ocean rockfishes have widely varying lifespans. The species Sebastes minor lives a mere 11 years while its cousin Sebastes aleutianus can live for more than 2 centuries.[53] Similarly, a chameleon, Furcifer labordi, is the current record holder for shortest lifespan among tetrapods, with only 4–5 months to live.[54] By contrast, some of its relatives, such as Furcifer pardalis, have been found to live up to 6 years.[55]
There are studies about aging-related characteristics of and aging in long-lived animals like various turtles[56][57] and plants like Ginkgo biloba trees.[58] They have identified potentially causal protective traits and suggest many of the species have "slow or [times of][clarification needed] negligible[clarification needed] senescence" (or aging).[59][56][57] The jellyfish T. dohrnii is biologically immortal and has been studied by comparative genomics.[60][61]
Honey bees (Apis mellifera) are eusocial insects that display dramatic caste-specific differences in longevity. Queen bees live for an average of 1-2 years, compared to workers who live on average 15-38 days in summer and 150-200 days in winter.[62] Worker honey bees with high amounts of flight experience exhibit increased DNA damage in flight muscle, as measured by elevated 8-Oxo-2'-deoxyguanosine, compared to bees with less flight experience.[63] This increased DNA damage is likely due to an imbalance of pro- and anti-oxidants during flight-associated oxidative stress. Flight induced oxidative DNA damage appears to hasten senescence and reduce longevity in A. mellifera.[63]
Gene editing via CRISPR-Cas9 and other methods have significantly altered lifespans in animals.[71][72][73]
This article incorporates text from this source, which is available under the CC BY 4.0 license.Chuan xiong ... has long been a key herb in the longevity tradition of China, prized for its powers to boost the immune system, activate blood circulation, and relieve pain.
Taoist devotion to immortality is important to us for two reasons. The techniques may be of considerable value to our goal of a healthy old age, if we can understand and adapt them. Secondly, the Taoist longevity tradition has brought us many interesting remedies.
The Old Man of the Sea / Yaupa / a native of Futuna, one of the New Hebrides Islands / regularly worked his own farm at the age of 130 / He died in 1899 of measles — a children's disease ... Horoz Ali, the last Turkish gatekeeper of Nicosia, Cyprus, lived to the age of 120 ... Francisco Huppazoli (1587–1702) of Casale, Italy, lived 114 years without a day's illness and had 4 children by his 5th wife — whom he married at the age of 98
cite journal: CS1 maint: DOI inactive as of December 2025 (link)citation: CS1 maint: work parameter with ISBN (link)
Media related to Longevity at Wikimedia Commons
| Skin | |
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Elephant skin
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Human skin showing dermal ridges
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| Details | |
| Identifiers | |
| Latin | cutis |
| Greek | δέρμα (dérma) |
| MeSH | D012867 |
| 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]
The word skin originally only referred to dressed and tanned animal hide and the usual word for human skin was hide. Skin is a borrowing from Old Norse skinn "animal hide, fur", ultimately from the Proto-Indo-European root *sek-, meaning "to cut" (probably a reference to the fact that in those times animal hide was commonly cut off to be used as garment).[12]
| Dermis | |
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The distribution of the blood vessels in the skin of the sole of the foot. (Corium – TA alternate term for dermis – is labeled at upper right.)
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A diagrammatic sectional view of the skin (click on image to magnify). (Dermis labeled at center right.)
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| Identifiers | |
| MeSH | D012867 |
| Anatomical terminology | |
Mammalian skin is composed of two primary layers:
The epidermis is composed of the outermost layers of the skin. It forms a protective barrier over the body's surface, responsible for keeping water in the body and preventing pathogens from entering, and is a stratified squamous epithelium,[13] composed of proliferating basal and differentiated suprabasal keratinocytes.
Keratinocytes are the major cells, constituting 95% of the epidermis,[13] while Merkel cells, melanocytes and Langerhans cells are also present. The epidermis can be further subdivided into the following strata or layers (beginning with the outermost layer):[14]
Keratinocytes in the stratum basale proliferate through mitosis and the daughter cells move up the strata changing shape and composition as they undergo multiple stages of cell differentiation to eventually become anucleated. During that process, keratinocytes will become highly organized, forming cellular junctions (desmosomes) between each other and secreting keratin proteins and lipids which contribute to the formation of an extracellular matrix and provide mechanical strength to the skin.[15] Keratinocytes from the stratum corneum are eventually shed from the surface (desquamation).
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 epidermis and dermis are separated by a thin sheet of fibers called the basement membrane, which is made through the action of both tissues. The basement membrane controls the traffic of the cells and molecules between the dermis and epidermis but also serves, through the binding of a variety of cytokines and growth factors, as a reservoir for their controlled release during physiological remodeling or repair processes.[16]
The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis provides tensile strength and elasticity to the skin through an extracellular matrix composed of collagen fibrils, microfibrils, and elastic fibers, embedded in hyaluronan and proteoglycans.[15] Skin proteoglycans are varied and have very specific locations.[17] For example, hyaluronan, versican and decorin are present throughout the dermis and epidermis extracellular matrix, whereas biglycan and perlecan are only found in the epidermis.
It harbors many mechanoreceptors (nerve endings) that provide the sense of touch and heat through nociceptors and thermoreceptors. It also contains the hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels. The blood vessels in the dermis provide nourishment and waste removal from its own cells as well as for the epidermis.
Dermis and subcutaneous tissues are thought to contain germinative cells involved in formation of horns, osteoderm, and other extra-skeletal apparatus in mammals.[2]
The dermis is tightly connected to the epidermis through a basement membrane and 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.
The papillary region is composed of loose areolar connective tissue. This 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.
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. These protein fibers give the dermis its properties of strength, extensibility, and elasticity. Also located within the reticular region are the roots of the hair, sweat glands, sebaceous glands, receptors, nails, and blood vessels.
The subcutaneous tissue (also 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. It consists of loose connective tissue and elastin. The main cell types are fibroblasts, macrophages and adipocytes (the subcutaneous tissue contains 50% of body fat). Fat serves as padding and insulation for the body.
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.
The epidermis of fish and of most amphibians consists entirely of live cells, with only minimal quantities of keratin in the cells of the superficial layer.[18] It is generally permeable, and in the case of many amphibians, may actually be a major respiratory organ.[19] The dermis of bony fish typically contains relatively little of the connective tissue found in tetrapods.[18] Instead, in most species, it is largely replaced by solid, protective bony scales.[20] Apart from some particularly large dermal bones that form parts of the skull, these scales are lost in tetrapods, although many reptiles do have scales of a different kind, as do pangolins.[21] Cartilaginous fish have numerous tooth-like denticles embedded in their skin, in place of true scales.[22]
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 mucous 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.[23]
Although melanin is found in the skin of many species, in the reptiles, the amphibians, and fish, the epidermis is often relatively colorless. Instead, the color 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 color of their skin by adjusting the relative size of their chromatophores.[23]
Amphibians possess two types of glands, mucous and granular (serous). Both of these glands are part of the integument and thus considered cutaneous. Mucous and granular glands are both divided into three different sections which all connect to structure the gland as a whole. The three individual parts of the gland are the duct, the intercalary region, and lastly the alveolar gland (sac). Structurally, the duct is derived via keratinocytes and passes through to the surface of the epidermal or outer skin layer thus allowing external secretions of the body. The gland alveolus is a sac-shaped structure that is found on the bottom or base region of the granular gland. The cells in this sac specialize in secretion. Between the alveolar gland and the duct is the intercalary system which can be summed up as a transitional region connecting the duct to the grand alveolar beneath the epidermal skin layer. In general, granular glands are larger in size than the mucous glands, which are greater in number.[24]
Granular glands can be identified as venomous and often differ in the type of toxin as well as the concentrations of secretions across various orders and species within the amphibians. They are located in clusters differing in concentration depending on amphibian taxa. The toxins can be fatal to most vertebrates or have no effect against others. These glands are alveolar meaning they structurally have little sacs in which venom is produced and held before it is secreted upon defensive behaviors.[24]
Structurally, the ducts of the granular gland initially maintain a cylindrical shape. When the ducts mature and fill with fluid, the base of the ducts become swollen due to the pressure from the inside. This causes the epidermal layer to form a pit like opening on the surface of the duct in which the inner fluid will be secreted in an upwards fashion.[25]
The intercalary region of granular glands is more developed and mature in comparison with mucous glands. This region resides as a ring of cells surrounding the basal portion of the duct which are argued to have an ectodermal muscular nature due to their influence over the lumen (space inside the tube) of the duct with dilation and constriction functions during secretions. The cells are found radially around the duct and provide a distinct attachment site for muscle fibers around the gland's body.[25]
The gland alveolus is a sac that is divided into three specific regions/layers. The outer layer or tunica fibrosa is composed of densely packed connective-tissue which connects with fibers from the spongy intermediate layer where elastic fibers, as well as nerves, reside. The nerves send signals to the muscles as well as the epithelial layers. Lastly, the epithelium or tunica propria encloses the gland.[25]
Mucous glands are non-venomous and offer a different functionality for amphibians than granular. Mucous glands cover the entire surface area of the amphibian body and specialize in keeping the body lubricated. There are many other functions of the mucous glands such as controlling the pH, thermoregulation, adhesive properties to the environment, anti-predator behaviors (slimy to the grasp), chemical communication, even anti-bacterial/viral properties for protection against pathogens.[24]
The ducts of the mucous gland appear as cylindrical vertical tubes that break through the epidermal layer to the surface of the skin. The cells lining the inside of the ducts are oriented with their longitudinal axis forming 90-degree angles surrounding the duct in a helical fashion.[25]
Intercalary cells react identically to those of granular glands but on a smaller scale. Among the amphibians, there are taxa which contain a modified intercalary region (depending on the function of the glands), yet the majority share the same structure.[25]
The alveolar or mucous glands are much more simple and only consist of an epithelium layer as well as connective tissue which forms a cover over the gland. This gland lacks a tunica propria and appears to have delicate and intricate fibers which pass over the gland's muscle and epithelial layers.[25]
The epidermis of birds and reptiles is closer to that of mammals, with a layer of dead keratin-filled cells at the surface, to help reduce water loss.[26] A similar pattern is also seen in some of the more terrestrial amphibians such as toads. In these animals, there is no clear differentiation of the epidermis into distinct layers initially, as occurs in humans, with the change in cell type being relatively gradual.[27] The mammalian epidermis always possesses at least a stratum germinativum and stratum corneum, but the other intermediate layers found in humans are not always distinguishable.
Hair is a distinctive feature of mammalian skin, while feathers are (at least among living species) similarly unique to birds.[23]
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.[23]
Cutaneous structures arise from the epidermis and include a variety of features such as hair, feathers, claws and nails. During embryogenesis, the epidermis splits into two layers: the periderm (which is lost) and the basal layer. The basal layer is a stem cell layer and through asymmetrical divisions, becomes the source of skin cells throughout life. It is maintained as a stem cell layer through an autocrine signal, TGF alpha, and through paracrine signaling from FGF7 (keratinocyte growth factor) produced by the dermis below the basal cells. In mice, over-expression of these factors leads to an overproduction of granular cells and thick skin.[28][29]
Hair and feathers are formed in a regular pattern and it is believed to be the result of a reaction-diffusion system. This reaction-diffusion system combines an activator, Sonic hedgehog, with an inhibitor, BMP4 or BMP2, to form clusters of cells in a regular pattern. Sonic hedgehog-expressing epidermal cells induce the condensation of cells in the mesoderm. The clusters of mesodermal cells signal back to the epidermis to form the appropriate structure for that position. BMP signals from the epidermis inhibit the formation of placodes in nearby ectoderm.[30]
It is believed that the mesoderm defines the pattern. The epidermis instructs the mesodermal cells to condense and then the mesoderm instructs the epidermis of what structure to make through a series of reciprocal inductions. Transplantation experiments involving frog and newt epidermis indicated that the mesodermal signals are conserved between species but the epidermal response is species-specific meaning that the mesoderm instructs the epidermis of its position and the epidermis uses this information to make a specific structure.[31]
Skin performs the following functions:
Skin is a soft tissue and exhibits key mechanical behaviors of these tissues. The most pronounced feature is the J-curve stress strain response, in which a region of large strain and minimal stress exists and corresponds to the microstructural straightening and reorientation of collagen fibrils.[35] In some cases the intact skin is prestreched, like wetsuits around the diver's body, and in other cases the intact skin is under compression. Small circular holes punched on the skin may widen or close into ellipses, or shrink and remain circular, depending on preexisting stresses.[36]
Tissue homeostasis generally declines with age, in part because stem/progenitor cells fail to self-renew or differentiate. Skin aging is caused in part by TGF-β by blocking the conversion of dermal fibroblasts into fat cells which provide support. Common changes in the skin as a result of aging range from wrinkles, discoloration, and skin laxity, but can manifest in more severe forms such as skin malignancies.[37][38] Moreover, these factors may be worsened by sun exposure in a process known as photoaging.[38]
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The dictionary definition of skin at Wiktionary| International | |
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| National | |
Results can vary depending on the peptide and individual response, with some noticing improvements in energy and recovery within weeks, while more visible changes such as body composition or skin quality may take longer.
Peptides are short chains of amino acids that act as signaling molecules, helping the body regulate functions such as healing, metabolism, hormone balance, and cellular repair by enhancing natural biological communication systems.
Peptide therapy is commonly used to support injury recovery, reduce inflammation, improve body composition, balance hormones, enhance skin quality, and optimize physical and cognitive performance.
When sourced from reputable providers and used under professional supervision, peptide therapy is generally considered safe, with long-term outcomes depending on proper dosage, quality sourcing, and adherence to structured treatment protocols.
