The integumentary system is the organ system that protects the body from damage, comprising the skin and its appendages. The integumentary system has a variety of functions, it may serve to waterproof, cushion, and protect the deeper tissue, excrete waste, and regulate temperature, and is the attachment site for sensory receptors to detect pain, sensation, pressure, ant temperature. In humans the integumentary system also provides vitamin D synthesis. The integumentary system is the largest organ system.
Epidermis:
This is the top layer of skin made up of epithelial cells. It does not contain blood vessels. Its main function is protection, absorption of nutrients, and homeostasis. In structure, it consists of a keratinized stratified squamous epithelium comprising four types of cells: keratinocytes, melanocytes, Merkel cells, and Langerhans' cells. The major cell of the epidermis is the keratinocyte, which produces keratin. Keratin is a fibrous protein that aids in protection. Millions of dead keratinocytes rub off daily. The majority of the skin on the body is keratinized, meaning waterproofed. The only skin on the body that is non-keratinized is the lining of skin on the inside of the mouth. Non-keratinized cells allow water to "sit" atop the structure.
Dermis:
The dermis is the middle layer of skin, composed of loose connective tissues such as collagen with elastin arranged in a diffusely bundled and woven pattern. These layers serve to give elasticity to the integument, allowing stretching and conferring flexibility, while also resisting distortions, wrinkling, and sagging. The dermal layer provides a site for the endings of blood vessels and nerves. Many chromatophores are also stored in this layer, as are the bases of integumental structures such as hair, feathers, and glands.
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