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:
“The Ethiopian cannot change his skin nor the leopard his spots.”
—Henry David Thoreau (1817–1862)
“The intellect,—that is miraculous! Who has it, has the talisman: his skin and bones, though they were of the color of night, are transparent, and the everlasting stars shine through, with attractive beams.”
—Ralph Waldo Emerson (1803–1882)
“The bottom line on bonding with multiples seems to be that if you see bonding as a static event—a moment in time at which you must have eye contact and skin contact simultaneously with two or more infants—you may indeed be in trouble.”
—Pamela Patrick Novotny (20th century)