1. The Skin

2. The skin together with its accessory organs – sweat glands, sebaceous glands, hair and the nails forms the largest organ in the human body. This system covers 1.5-2m2 and represents 16% of body weight The skin and its accessory organs form the integumentary system. The functions of the skin are : protection against pathogens, regulation of the temperature, secreting fluids, housing nerve receptors, insulation and provides vitamin D synthesis.

4. Layers of the Skin The human skin is composed of three major layers of tissue: epidermis, dermis and subcutaneous layer. The epidermis is the top layer of skin made up of epithelial cells. The dermis is the middle layer of skin, composed of dense irregular connective tissue such as collagen with elastin. The subcutaneous layer is the innermost layer, containing fatty tissue

5. Epidermis The epidermis main functions are protection, absorption of nutrients and homeostasis. Also contains different types of cells: keratinocytes, melanocytes, Merkel cells and Langerhans cells. The major cell of the epidermis is the keratinocytes, which produces keratin. Keratin is a fibrous protein that aids in protection. The most common cells are squamous cells, scaly cells, basal cells and melanocytes. Melanocytes create melanin, the substance that gives skin its color. Accumulations of melanin are packaged in melanosomes. These granules form a pigment shield against UV radiation. It does not contain blood vessels

6. Dermis The dermis is the middle layer of the skin that offers elasticity. It is composed of connective tissues and collagen fibers. The dermis provides a site for the hair follicles, sweat glands, sebaceous glands, blood vessels, lymph vessels, sensory receptors, nerve fibers and muscle fibers.

8. Subcutaneous Layer The subcutaneous is the layer of tissue directly underneath the dermis. It is also called hypodermis. This layer of tissue is composed of fat cells and connective tissue. Its functions include insulation, the storage of energy and aiding in the anchoring of the skin. It is the thickest layer of the integumentary system

10. The Accessory Organs of the Skin The sebaceous glands secrete the oil sebum, which lubricates the hair and skin, helping prevent drying and cracking. The hair is make up of fibers composed of the protein keratin Nails are a flat plate of keratin called the nail body that covers the ends of fingers and toes. The sweat glands function is to cool the body. The accessory organs of the skin are located in the dermis .

11. References Marieb, Elaine; KatjaHoehn (2007). Human Anatomy & Physiology (7th ed.). Pearson Benjamin Cummings. p. 142. Martini & Nath: "Fundamentals of Anatomy & Physiology" 8th Edition, pp.158,Pearson Education, 2009 Fremgen & Frucht: “Medical Terminology” 4th Edition, Ch. 3 Pearson Edition 2009