..... Click the link for more information. , hoofs hoof, horny epidermal casing at the end of the digits of an ungulate (hoofed) mammal . In the even-toed ungulates, such as swine, deer, and cattle, the hoof is cloven; in the odd-toed ungulates, such as the horse and the rhinoceros, it is solid.
..... Click the link for more information. , hair hair, slender threadlike outgrowth from the skin of mammals. In some animals hair grows in dense profusion and is called fur or wool . Although all mammals show some indication of hair formation, dense hair is more common among species located in colder climates and
..... Click the link for more information. (fur), feathers feathers, outgrowths of the skin, constituting the plumage of birds. Feathers grow only along certain definite tracts (pterylae), which vary in different groups of birds.
..... Click the link for more information. , and scales scale, in zoology, an outgrowth, either bony or horny, of the skin of an animal. The major component of the scales of fishes is bone, and they are formed directly in the skin membrane as the fish grows.
..... Click the link for more information. are evolutionary adaptations of the epidermis. Although the epidermis has no blood vessels, its deeper strata contain melanin, the pigment that gives color to the skin. The underlying dermis consists of connective tissue in which are embedded blood vessels, lymph channels, nerve endings, sweat glands, sebaceous glands sebaceous gland (səbā`shəs), gland in the skin of mammals that secretes an oily substance called sebum.
..... Click the link for more information. , fat cells, hair follicles, and muscles. The nerve endings, called receptors, perform an important sensory function. They respond to various stimuli, including contact, heat, and cold. Response to cold activates the erector muscles, causing hair or fur to stand erect; fright also causes this reaction. From the outer surface of the dermis extend numerous projections (papillae) that fit into pits on the inner surface of the epidermis so that the two layers are firmly locked together. In humans, whorls on the fingers show where the epidermis falls between rows of papillae, making the patterns used in fingerprinting. The skin provides a barrier against invasion by outside organisms and protects underlying tissues and organs from abrasion and other injury, and its pigments shield the body from the dangerous ultraviolet rays in sunlight. It also waterproofs the body, preventing excessive loss or gain of bodily moisture. Human skin performs several functions that help maintain normal body temperature: its numerous sweat glands excrete waste products along with salt-laden moisture, the evaporation of which may account, in certain circumstances, for as much as 90% of the cooling of the body; its fat cells act as insulation against cold; and when the body overheats, the skin's extensive small blood vessels carry warm blood near the surface where it is cooled. The skin is lubricated by its own oil glands, which keep both the outside layer of the epidermis and the hair from drying to brittleness. Human skin has remarkable self-healing properties, particularly when only the epidermis is damaged. Even when the injury damages the dermis, healing may still be complete if the wounded area occurs in a part of the body with a rich blood supply. Deeper wounds, penetrating to the underlying tissue, heal by scar formation. Scar tissue lacks the infection-resisting and metabolic functions of healthy skin; hence, sufficiently extensive skin loss by widespread burns or wounds may cause death.
skin
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skin
(1) A custom covering for a hardware device. For example, there are numerous coverings or replacement cases for cellphones and iPods in myriad colors and styles. Vinyl coverings for the outside of computer tower cases that depict sports, high-tech and other themes are also available.
(2) A custom look and feel of an application or graphical user interface (GUI). Media players and applications, typically in the multimedia genre, are often customizable. They either come with a selection of skins or accept skins from third parties. Windows enables developers to create an entirely different look for the window frames, scroll bars, buttons and elements on the Windows interface. See theme aware. See also skin effect.
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| Stardock's WindowBlinds comes with a host of custom skins for Windows that create a different look for the user interface. The skins as well as mouse actions on the Title bar can also be customized by the user. (Image courtesy of Stardock Corporation, Inc., www.stardock.com) |
skin
Skin
The entire outer surface of the body and the principal boundary between the external environment and the body's internal environment of cells and fluids. Skin serves as the primary barrier against the intrusion of foreign elements and organisms into the body, and also as a large and complex sense organ through which animals explore and learn about the external world. In addition, skin functions to maintain the homeostasis of the body's constituents, acting as a barrier to the loss of various ions and nutrients by diffusion. For terrestrial animals, it also serves as an effective barrier to water loss, without which most land animals would rapidly become desiccated and die.
The skin of humans and other mammals can be divided into two distinct regions, the epidermis and the dermis.
The epidermis is the outermost layer of the skin. It varies in thickness from 0.1 mm in most of the protected areas of the skin to approximately 1 mm in those regions exposed to considerable friction, such as the soles of the feet and palms of the hands. The epidermis consists of a great many horizontally oriented layers of cells. The outermost layer, the stratum corneum, consists of many layers of this packed cellular debris, forming an effective barrier to water loss from lower layers of the skin. The lowest levels of stratum germinativum constitute the portion of the skin that contains melanocytes, cells that produce the dark pigment melanin. Different levels of melanin secretion are responsible for the large range of pigmentation observed among humans.
The dermis plays a supportive and nutritive role for the epidermis. The epidermis has no blood supply of its own. However, nutrients and oxygen are apparently provided by diffusion from the blood supply of the underlying dermis. The average thickness of the dermis is 1–3 mm. It is in this layer that the sebaceous and sweat glands are located and in which the hair follicles originate. The products of all these sets of glands are derived from the rich blood supply of the dermis. Hair, sweat glands, and mammary glands (which are modified sweat glands) are skin inclusions unique to mammals. See Hair, Thermoregulation
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