Skin
Skin is the soft outer covering of vertebrates. 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 the largest 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. All mammals have some hair on their skin, even marine mammals which appear to be hairless. The skin is one of the most important parts of the body because it 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 and excessive water loss. 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 in 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 4 mm thick and the thickest skin in the body.
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Famous quotes containing the word skin:
“At first I said, “I will not bear
His cross upon my back;
He only seeks to place it there
Because my skin is black.””
—Countee Cullen (1903–1946)
“... the trouble is that most people in this country think that we can stay out of wars in other parts of the world. Even if we stay out of it and save our own skins, we cannot escape the conditions which will undoubtedly exist in other parts of the world and which will react against us.... We are all of us selfish ... and if we can save our own skins, the rest of the world can go. The best we can do is to realize nobody can save his own skin alone. We must all hang together.”
—Eleanor Roosevelt (1884–1962)
“If Americans could understand what a painful, searing experience it is when Negro children first begin to realize that the mere color of their skin is to be the source of a lifelong discrimination, it might do more to end our cruelty toward the Negro than all the preaching on justice and equality.”
—Agnes E. Meyer (1887–1970)