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Biology - Skin

Skin is the largest organ in the body. Our skin maintains our body temperature, senses our environment and guards us against microorganisms. The skin has three layers: epidermis, dermis and subcutaneous tissue. The outer surface is epidermis covered by dead cells called the stratum corneum. These cells are full of protein called keratin and form a barrier against invasion of microorganisms. The dermis is just below the epidermis. Here you find blood vessels, nerve endings, sebaceous glands, which secrete oils, and sweat glands. It is the sweat glands that release water and ions in warm weather. This keeps down temperature and also serves to maintain optimal levels of sodium and chloride in the body. Finally, there is the subcutaneous tissue which is mostly fat.