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The cells in the outer or horny layer of the epidermis are constantly being shed and replaced by new cells from its bottom layers in the lower epidermis. The cells of the protective, horny layer are nonliving and require no supply of blood for nourishment. As long as the horny outer layer remains intact, microorganisms cannot enter.
The sweat glands are situated deep in the corium. They collect fluid containing water, salt, and waste products from the blood and carry it away in canals that end in pores on the skin surface, where it is deposited as sweat. Perspiration helps regulate body temperature as well, because cooling of the skin occurs when sweat evaporates. The sebaceous glands are also in the corium. They secrete the oil that keeps the skin surface lubricated.
Beneath the corium is a layer of subcutaneous tissue. This tissue helps insulate the body against heat and cold, and cushions it against shock.
The hair and nails are outgrowths of the skin. The roots of the hair lie in follicles, or pockets of epidermal cells situated in the corium. Hair grows from the roots, but the hair cells die while still in the follicles, and the closely packed remains that are pushed upward form the hair shaft that is seen on the surface of the skin.
The nails grow in much the same way as the hair. The nail bed, like the hair root, is situated in the corium. The pink color of the nails is due to their translucent quality which allows the blood capillaries of the corium to show through.
There are several types of skin tests, including the patch test, the scratch test, and the intradermal test.
The patch test is used most often in testing for skin allergies, especially contact dermatitis.
The scratch test is often used in testing for allergies. A complete screening for allergic sensitivity may require numerous skin tests. Only an extremely minute quantity of the substance can be used in each test since severe allergic reactions can occur.
The scratch test is also used in the diagnosis of tuberculosis. In Pirquet's reaction, for example, tuberculin is used, and the local inflammatory reaction that results is more marked in tuberculous persons than in normal ones.
In the intradermal test for tuberculosis, the Mantoux test, a purified protein derivative (PPD), prepared from tubercle bacilli, is injected. In a positive result, the area becomes reddened or inflamed within 72 hours. This indicates past or present infection with or exposure to the tubercle bacillus. An infection that has been present for at least 2 to 8 weeks will usually be revealed by the test.
The Schick test is used to determine susceptibility to diphtheria. A very small dose of diphtheria antitoxin is injected into the forearm. In a positive reaction the area becomes red and remains so for about a week. If no reaction occurs, the person is immune to the disease.
The trichophytin test is sometimes used in diagnosing suspected cases of superficial fungus infection of the skin, such as ringworm. In the presence of infection by the fungus Trichophyton, an injection of trichophytin, which is prepared from cultures of the fungus, will produce a reaction similar to the tuberculin reaction. Skin tests, of course, are always made in an area separate from the infected area.
In addition to their frequent use in testing for allergies, intradermal tests are employed in the diagnosis of parasitic infections, such as schistosomiasis, other fungus diseases besides trichophytosis, and mumps.
skin(skin) the outer protective covering of the body, consisting of the dermis (or corium) and the epidermis.
skinVox populi adjective Cutaneous noun Anatomy Cutis The outer integument of the body which consists of epidermis and dermis, the latter of which rests on subcutaneous tissue. See Aging skin, Artificial skin, Blue skin, Cigarette-paper skin, Composite cultured skin, Diamond skin, Elephant skin, Glossy skin, Harlequin skin, Hide-bound skin, Leopard skin, Lizard skin, Moleskin, Moroccan leather skin, Paper money skin, Red skin, Sandpaper skin, Second Skin®, Spray-on skin, Swiss cheese skin, Washerwoman skin.
Synonym(s): cutis [TA] .
Skin consists of two major divisions: the epidermis and the dermis. Depending on its location and local function, skin varies in terms of its thickness, strength, presence of hair, nails, or glands, pigmentation, vascularity, nerve supply, and keratinization. Skin may be classified as thin and hairy or thick and hairless (glabrous). Thin hairy skin covers most of the body. Glabrous skin covers the surface of the palms of the hands, soles of the feet, and flexor surfaces of the digits. See: illustration; hair for illus; burn; dermatitis; dermis; eczema; epidermis; rash
artificial skinHuman skin equivalent.
elastic skinEhlers-Danlos syndrome.
foreign bodies in the skin
For removal of a small foreign body, the area is cleaned first with mild soap and warm water. A clean needle can be sterilized by heating it to a dull or bright red in a flame; this can be done with a single match. Because both ends of the needle get hot, it is wise to hold the far end in a nonconductor such as a fold of paper or a cork. The needle is allowed to cool. A black deposit on its surface should be disregarded; it is sterile carbon and does not interfere with the procedure. The needle is introduced at right angles to the direction of the sliver, and the sliver is lifted out. Most people attempt to stick the needle in the direction of the foreign body and consequently thrust many times before they manage to lift the sliver out. When the sliver is removed, an antiseptic is applied and the wound covered with a sterile dressing. Tetanus antitoxin or a tetanus booster may be required, depending on the history of immunization.
photodamaged skinPhotoaged skin.
sun-damaged skinPhotoaged skin.
tissue-engineered skinHuman skin equivalent.
skinThe body's outer covering. The skin is a major organ, of area 5–6 m2. It is self-regenerating, self-lubricating and self-repairing and provides heat regulation. It is sensitive to touch, pressure, pain and temperature. It protects against solar radiation and bacterial infection and synthesizes vitamin D. The lower layer, the true skin (corium) is living, the outer layer (epidermis) has an external layer of dead, flattened horny cells.
skinan organ that forms the outer covering of an animal that is external to the main musculature, often bearing scales, hair or feathers. Skin is the most widespread organ of the body and consists of an EPIDERMIS derived from the embryonic ECTODERM, and a DERMIS originating from a MESODERMIS. The epidermis is often hardened and covered by a cuticle, but may be only one cell thick.
The subcutaneous fat of the dermis acts as insulation and reduces heat loss. Heat is also conserved by the skin in cold conditions by contraction of the superficial blood vessels which diverts blood to lower layers of the skin. In some structures, such as the ear, special shunt vessels occur which dilate in cold conditions and pass blood directly from arterioles to venules, thus bypassing the superficial capillaries to reduce heat loss.
skinhuman skin serves the functions of sensation, protection and insulation and has a major role in regulation of body temperature, by variations in heat loss or conservation (increasing loss by vasodilatation and sweating, decreasing it by vasoconstriction), under the control of the autonomic nervous system. Sensory nerve endings and receptors include those that mediate the sensations of touch, pain and pressure.
skin; cutis tissue investing the entire body, and in modified form lining the gut and respiratory systems; largest organ of the body; formed of four layered structures: epidermis, basement membranous zone, dermis, subcutaneous layer (Figure 1; Table 1 and Table 2)
|Epidermis||Stratified squamous epithelium formed from keratinocytes|
Basal layer: keratinocytes linked by desmosomal and hemidesmosomal and filamentous connections (cytoskeleton; prevents shear)
Spinous layer: keratinocytes shrink, retaining contact only at desmosomes and hemidesmosomes
Granular layer: keratinocytes secrete complex lipids which act as a semipermeable skin barrier
Corneal layer: cell and contents have become keratin to form squames moved towards the exterior
Melanocytes: lie between keratinocytes; secrete pigment and protect keratinocyte nuclei from ultraviolet radiation
Merkel cells: sensory cells
Langerhans cells: within spinous layer; antigen-presenting cells
|Basement membrane zone||Collagen, hemidesmosomes, laminin which aid adhesion of epidermis to dermis; dysfunctional in disease such as epidermolysis bullosa|
|Dermis||Mesodermal tissue containing blood vessels, nerve, muscle, skin appendages (sweat glands, sebaceous glands, hair follicles), immune cells (histamine-releasing mast cells) in a matrix of collagen, elastin and hyaluronic acid|
|Subcutaneous layer||Adipose tissue, blood vessels and nerves, acting as an insulating layer|
|Function||Skin constituent subserving that function|
|Physical barrier against friction and shearing forces||Keratinization of stratum corneum; undulating dermoepidermal junction; dermofibrillar and desmosomal links|
|Protective barrier to infection||Intact skin layer; desquamation; acid mantle; inflammatory response|
|Prevention of excessive water loss or absorption||Intact waterproof keratinized outer layer|
|Synthesis of vitamin D||Sunlight-induced formation of cholecalciferol (vitamin D3) from 7-dehydrocholesterol|
|Temperature regulation||Autonomic regulation of blood flow through skin capillaries and arterioles|
|Environmental awareness||Specialized skin nerve endings (Merkel's discs, Meissner's corpuscles, pacinian corpuscles, Ruffini endings, free nerve endings) subserve pain, touch, temperature, vibration, pressure, stereognosis|
|Antigen presentation||Langerhans cells|
|Immunological reactions||Keratinocytes release cytokines|
|Wound healing||Cellular elements of the dermis and epidermis|
|Protection from ultraviolet light||Melanosomes inject melanin granules into local keratinocytes to form a protective cap over the nucleus|
Synonym(s): cutis [TA] .
Patient discussion about skin
Q. What are the causes of viral blisters on the skin? For a few months now I've been having these hard viral blisters on my fingers. The only way to get rid of them is with freezed carbon. It does go away with that treatment- after a few weeks but then a new one appears. How can I prevent it from "attacking" again??
Q. anyone knows how to stop hard skin on the feet from becoming cracked??? during summer my feet got lots of hard skin and in the heel area the skin actually got cracked kinda deep. it hurts now and the cracks are starting to get infected I guess... do u guys know how to solve this?? I know there are some creams for that but I thought maybe now it's too late for that and I need something stronger?
Q. How can you know if a mole is a skin cancer or not? I'm only 15, but I’ve had this small thing on my right shoulder for a reeeeaaaally long time. It's the same color as my skin. It’s smaller than the head of a pencil eraser, perfectly round, and its smooth. I've never worried about it seriously, until about a week ago, when I read an article in a magazine about skin cancer. Even then I wouldn't have worried about it, because It didn't really match any of the symptoms, except one. It did bleed once about 2 1/2 years ago. And it said bleeding was a big sign I don't know, what do you think? And please try and say something other than," go have it checked out". Because I currently have no insurance. Thanks :]
look for one near your home.