Skin is a soft outer network that includes vertebrates.
Other animal coverings, such as exoskeleton arthropods, have different developmental origins, structures and chemical compositions. The adjective cutaneous means "skin" (from Latin cutis , skin). In mammals, the skin is the organ of the covering system composed of several layers of ectodermal tissue, and maintains the underlying muscles, bones, ligaments and internal organs. The skins of different nature are in amphibians, reptiles, and birds. All mammals have hair on their skin, even marine mammals such as whales, dolphins, and dolphins that seem to be hairless. The skin interacts with the environment and is the first line of defense of external factors. For example, the skin plays a key role in protecting the body against pathogens and excessive water loss. Other functions are insulation, temperature regulation, sensation, and vitamin D folate production. The damaged skin can heal by forming scar tissue. It sometimes changes color and depigmentation. The thickness of the skin also varies from location to location in an organism. In humans for example, the skin that lies beneath the eyes and around the eyelid is the thinnest skin on the body with 0.5 mm thick, and is one of the first areas to show signs of aging such as "crow's feet" and wrinkles. The skin on palms and soles of feet is 4 mm thick and is the thickest skin on the body. The speed and quality of wound healing on the skin is promoted by estrogen acceptance.
Feather is a thick hair. Especially, the feathers add to the insulation provided by the skin but can also serve as secondary sexual characteristics or as camouflage. In some animals, the skin is very hard and thick, and can be processed to make the skin. Reptiles and fish have hard protective scales on their skin for protection, and birds have hard feathers, all made of tough? -keratin. Amphibian skin is not a strong barrier, especially regarding the travel of chemicals through the skin and is often subject to osmosis and diffusive strength. For example, a frog sitting in an anesthetic solution will be drugged quickly, as the chemical diffuses through the skin. Amphibious skin plays a key role in daily survival and their ability to exploit a variety of habitats and ecological conditions.
Structure
Video Skin
in humans and other mammals
The skin of a mammal consists of two main layers:
- epidermis , which provides waterproofing and serves as an obstacle to infection; and
- the dermis , which serves as the location for skin supplements; Epidermis
- Stratum corneum
- Stratum lucidum (only in palms and palms)
- Stratum granulosum
- Stratum spinosum
- Stratum germinativum (also called basal stratum)
- Protection: anatomical barriers from pathogens and damage between internal and external environments in the body's defenses. (See Skin Absorption.) Langerhans cells in the skin are part of the adaptive immune system.
- Sensation: contains various nerve endings that jump to hot and cold, touch, pressure, vibration, and tissue injury (see somatosensory system and haptic perception).
- Thermoregulation: eccrine glands (sweat) and dilated blood vessels (increased superficial perfusion) help heat loss, while narrowed vessels greatly reduce skin blood flow and heat preservation. The muscle piercing erector of a mammal adjusts the angle of the hair shaft to alter the level of insulation provided by hair or hair.
- Evaporation control: the skin provides a relatively dry and semi-impermeable barrier to reduce fluid loss.
- Storage and synthesis: serves as a storage center for lipids and water
- Skin absorption: Oxygen, nitrogen, and carbon dioxide can diffuse into the epidermis in small amounts; some animals use their skin as their sole respiratory organ (in humans, cells consisting of 0.25-0.40 mm outer shells "almost exclusively supplied by external oxygen", although "contribution to total respiration is negligible") Some medications are absorbed through the skin.
- Water resistance: The skin acts as an impermeable inhibitor so important nutrients are not swept out of the body. Nutrients and oils that help hydrate the skin are covered by the outermost layer of skin, the epidermis. This is partially assisted by the sebaceous glands that release sebum, oily fluids. Water itself will not cause oil removal of the skin, because the oil is in our dermis stream and will be affected by water without epidermis.
- Camouflage, whether bare skin or covered with feathers, scales, or feathers, skin structure provides color and protective patterns that help hide animals from predators or prey.
- Media related to human skin on Wikimedia Commons
- Definition of leather dictionary in Wiktionary
The epidermis is composed of the outermost layer of skin. It forms a protective barrier above the surface of the body, responsible for maintaining water in the body and preventing pathogens from entering, and is a stratified squamous epithelium, composed of basal proliferation and differentiated suprabacal keratinocytes.
Keratinocytes are the major cells, which constitute 95% of the epidermis, while Merkel cells, melanocytes and Langerhans cells are also present. The epidermis can be subdivided into the following strata layer (starting with the outermost layer):
Keratinocytes in the basal stratum proliferate through mitosis and child cells move up into the shape and composition of the strata that changes as they undergo several differentiation stages of the cell to eventually become nucleated. During the process, keratinocytes become highly organized, forming cellular connections (desmosomes) between each other and secreting keratin and lipid proteins that contribute to the formation of extracellular matrix and provide mechanical strength to the skin. Keratinocytes from the stratum corneum are finally released from the surface (desquamation).
The epidermis does not contain blood vessels, and the cells in the innermost layer are nourished by the diffusion of blood capillaries that extend into the upper layers of the dermis.
Basal membrane
The epidermis and dermis are separated by thin sheets of fibers called basement membranes, and are made through the action of both tissues. The basement membrane controls the traffic of cells and molecules between the dermis and epidermis but also functions, through the binding of various cytokines and growth factors, as a reservoir for controlled release during physiological remodeling or repair processes.
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 provides tensile strength and elasticity to the skin through an extracellular matrix consisting of collagen fibrils, microfibrils, and elastic fibers, embedded in hyaluronan and proteoglycans. Proteoglycan skin varies and has a very specific location. For example, hyaluronan, versican and decorin are present throughout the dermis matrix and extracellular epidermis, whereas biglycan and perlecan are found only in the epidermis.
It harbors many mechanoreceptors (nerve endings) that provide a sense of touch and heat through nociceptors and thermoreceptors. It also 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 to the epidermis.
The dermis is closely connected to the epidermis via the basement membrane and 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. This is called for a finger-like projection called papillae that extends toward the epidermis. Papilla provides the dermis with a "wavy" surface that interdigitates with the epidermis, strengthening the relationship between two layers of skin.
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, sweat glands, sebaceous glands, receptors, nails, and blood vessels.
Subcutaneous network
Subcutaneous tissue (also hypodermis) is not part of the skin, and lies beneath the dermis. 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 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.
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.
Cross section details
StructureMaps Skin
in Fish, Amphibians, Birds and Reptiles
Fish
The fish epidermis and most amphibians are composed entirely of living cells, with only a small amount of keratin in the superficial cell layer. It is generally permeable, and in the case of many amphibians, can actually become the primary respiratory organ. The bony fish dermis usually contains relatively few connective tissue found in tetrapods. In contrast, in most species, most are replaced by solid protective bone scales. Apart from some very large dermal bones that form parts of the skull, these scales are lost in the tetrapod, although many reptiles have scales of different types, such as pangolins. Cartilage fish have as many denticles as teeth embedded in their skin, in place of the correct scale.
Sweat glands and sebaceous glands are equally unique to mammals, but other types of skin glands are found in other vertebrates. Fish usually have many skin cells that secrete individual mucus that helps in isolation and protection, but may also have poison glands, photophores, or cells that produce more dilute serous fluid. In amphibians, mucus cells gather to form glands such as sacs. Most living amphibians also have a granular gland in the skin, which secretes an annoying or toxic compound.
Although melanin is found in the skin of many species, in reptiles, amphibians, and fish, the epidermis is often relatively colorless. In contrast, skin tone is mostly due to chromatophore in the dermis, which, in addition to melanin, may contain guanine pigment or carotenoids. Many species, such as chameleons and flounders may be able to change their skin tone by adjusting the relative size of their chromatophores.
Amphibians
See also: amphibian
Overview
Amphibians have two types of glands, mucus and granular (serous). Both of these glands are part of the integument and are therefore considered skin. The mucosal and granular glands are both divided into three distinct parts that are all connected to the glandular structure as a whole. The three individual parts of the gland are the channel, the intercalary region, and the last of the alveolar gland (sac). Structurally, this channel originates through keratinocytes and passes to the surface of the epidermal or external skin layer thus enabling the external secretion of the body. The glandular alveolus is a sac-shaped structure found at the bottom or the base of the granular gland. The cells in these sacs specialize in secretions. Between the alveolar and ductal glands is a calculus system that can be summed up as a transition region that connects the channel to the large alveolar beneath the epidermal skin layer. In general, the granular gland is larger than the mucous gland, but the mucilage gland holds a much larger majority in total.
Granular Glands
The granular glands can be identified as venomous and often differ in the types of toxins as well as the concentration of secretions in various orders and species within the amphibians. They are in different groups in concentrations depending on the amphibian taxa. Toxins can be fatal to most vertebrates or have no effect on others. These glands are alveolar which means they have small sacs in which toxins are produced and held before being secreted in defensive behavior.
Structurally, the granular ducts of the gland initially retain the cylindrical shape. However, when the channel becomes mature and filled with toxic liquids, the drain base becomes swollen from internal pressure. This causes the epidermal layer to form a hole such as opening on the surface of the duct where the deep fluid will be secreted in an upward force.
The intercalary area of ​​the granular gland is more developed and matured compared to the mucous glands. This region is located as a cell ring that surrounds the basal portion of the duct which is said to have ectodermal muscle properties due to its influence over the ductal lumen (space in the tube) with dilation and the narrowing function during secretion. These cells are found radially around the ducts and provide different attachment sites for the muscle fibers around the body of the gland.
The gland alveolus is a sac divided into three specific regions/layers. The outer layer or fibrous tunica consists of a solid connective tissue that connects with the fibers of the intermediate layer of the sponge in which the elastic fibers as well as the nerves are located. The nerves send signals to the muscles as well as the epithelial lining. Finally, the epithelium or tunica propria enclose the gland.
Mucosal Gland
The mucilage is not venomous and offers different functions for amphibians than granular. The mucous gland covers the entire surface area of ​​the amphibian body and specializes in keeping the body lubricated. There are many other functions of the mucous gland such as pH control, thermoregulation, adhesive properties to the environment, anti-predator behavior, chemical communication, even anti-bacterial/viral properties for the protection of pathogens.
The mucus gland channel appears as a cylindrical vertical tube that pierces the epidermal layer to the skin surface. The cells lining the inner duct are oriented with its longitudinal axis forming a 90-degree angle surrounding the duct by helical means.
The intercale cells react synonymously with the granular glands but on a smaller scale. Among the amphibians, there are taxa that contain modified intercarious regions (depending on the function of the gland), but the majority share the same structure.
Mucous gland alveolors are much simpler and consist only of epithelial lining and connective tissue that form the top cover of the gland. This gland lacks proprietary tunica and appears to have delicate and delicate fibers that pass through the muscle glands and epithelial lining.
Birds and reptiles
The epidermis of birds and reptiles is closer to mammals, with layers of dead keratinized cells that are filled on the surface, to help reduce water loss. A similar pattern is also seen in some more terrestrial amphibians such as frogs. However, in all these animals there is no clear differentiation from the epidermis to different layers, as occurs in humans, with relatively gradual changes in cell types. The mammalian epidermis always has at least the strata of germinativum and stratum corneum, but other intermediate layers found in humans are not always distinguishable. Hair is characteristic of mammalian skin, while feathers (at least among living species) are as unique as birds.
Birds and reptiles have relatively few skin glands, although there may be some structures for specific purposes, such as cells that secrete pheromones in some reptiles, or the uropygial glands of most birds.
Development
Skin structure arises from the epidermis and includes features such as hair, feathers, claws and nails. During embryogenesis, the epidermis is divided into two layers: periderm (missing) and basal layer. The basal layer is the stem cell layer and through the asymmetric division, becoming the source of skin cells throughout life. It is maintained as a stem cell layer through autocrine signals, TGF-a, and via paracrine signal FGF7 aka keratinocyte growth factor (KGF) produced by the dermis beneath basal cells. In mice, the excessive expression of these factors causes excess granular cells and thick skin.
Hair and feathers are formed in a regular pattern and are believed to be the result of a diffusion-reaction system. This reaction-diffusion system combines activator, Sonic hedgehog, with inhibitor, BMP4 or BMP2, to form cell groups in a regular pattern. Epidermal cells expressing Sonic cells induce condensation of cells in the mesoderm. The mesodermal cell groups signal back to the epidermis to form the right structure for that position. BMP signals from the epidermis inhibit the formation of placodes near the ectoderm.
It is believed that the mesoderm defines the pattern. The epidermis instructs the mesodermal cell to condense and then the mesoderm instructs the epidermis of what structure is made through a series of mutual inductions. Transplant experiments involving new frogs and epidermis indicate that mesodermal signals are preserved between species but the epidermal response is a species-specific meaning that the mesoderm instructs the epidermis of its position and the epidermis uses this information to create a specific structure.
Function
The skin performs the following functions:
Mechanics
The skin is soft tissue and shows the key mechanical behavior of this tissue. The most prominent feature is the J-curve strain response, in which an area of ​​great strain and minimal stress exists, and corresponds to the micro alignment and reorientation of collagen fibrils. In some cases the intact skin is prestreched, such as wetsuits around the body of the diver, and in other cases the whole skin is under compression. Small circular holes that press against the skin may dilate or approach the ellipse, or shrink and remain circular, depending on pre-existing pressure.
Aging
Networked homeostasis generally decreases with age, partly because the stem/progenitor cells fail to renew themselves or differentiate. In mice skin, mitochondrial oxidative stress can increase cell aging and phenotype aging. Usually mitochondrial superoxide dismutase (SOD2) protects against oxidative stress. Using a mouse model of genetic SOD2 deficiency, it shows that failure to express this important antioxidant enzyme in epidermal cells causes cell aging, nuclear DNA damage, and irreversible capture of keratinocyte fraction proliferation.
Society and culture
The term "skin" can also refer to small animal hoods, such as sheep, goats (goatskin), pigs, snakes (snake skins), etc. Or a young man from a big animal.
The term hiding or raw skin refers to the cover of large adult animals such as cattle, buffalo, horses etc.
The skin and skin of different animals are used for clothing, bags and other consumer products, usually in the form of leather, but also as a feather.
The skin of sheep, goats and cattle is used to make parchments for manuscripts.
The skin can also be cooked to make pig skin or crackling.
See also
References
External links
Source of the article : Wikipedia
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