Describe the skin as an organ. Include the various tissues that compose it, and briefly describe the role of each tissue.

The skin, as the largest organ in the human body, serves as the first line of defense and performs various vital functions. It is composed of two main layers: the epidermis and the dermis. The outermost layer, the epidermis, contains keratinocytes that produce keratin, melanocytes for melanin production, and Langerhans cells for immune responses. The dermis is divided into two sub-layers: the papillary dermis with loose connective tissue, blood vessels, nerve endings, and sensory receptors, and the reticular dermis with dense connective tissue, larger blood vessels, hair follicles, and glands. The hypodermis, though not officially part of the skin, is important for insulation, energy storage, and cushioning. Each tissue within the skin plays a specific role in maintaining the overall structure and function of the skin.