Anatomy and Physiology of the Skin

The 2011 document details the skin's structure and function, highlighting its role as the body's largest organ involved in protection, sensation, and homeostasis. It describes the three main skin layers: the epidermis, dermis, and subcutaneous tissue, and their respective components and functions. The epidermis is a dynamic layer with keratinocytes and non-keratinocyte cells like melanocytes and Langerhans cells, responsible for skin pigmentation and immune responses. Hair follicles, associated with sebaceous glands and muscles, contribute to hair growth and color, which is regulated by genetic expression and hormones. Hair growth cycles include anagen, catagen, and telogen phases, with the anagen phase lasting 3-5 years on the scalp. Factors like age and hormones can affect these cycles, leading to conditions like alopecia. The dermis provides strength and elasticity through collagen, and the vasculature is essential for thermoregulation. Mast cells in the skin are involved in immune responses, and the subcutaneous tissue has endocrine functions. The document concludes that the skin's layers work together to protect against environmental damage, facilitate sensory perception, and maintain homeostasis, but are also susceptible to cancer due to high cell turnover.