cortex of keratinocytes and an inner medulla. The root sheath, which surrounds the hair bulb, is composed of an outer and inner layer. An erector pili muscle is assoc iated with the hair shaft and contracts with cold, fear and emotion to pull the hair erect, giv ing the skin goose bumps During the growing phase or anagen, the cells of the hair bulb actively devide and produce the growing hair. Then hair follicles go into the catagen, or transitional phase of activity, the matrix cells stop dividing. During catagen, the lower protion of the follicle disappears, leav ing behind a thin strand of epithelial cells surrounded by a thick basement membrane zone. During telogen, the ep ithelial strand subsequently shortens to the level of the arrector pili muscle 2) Sebaceous gland Sebaceous glands are derived from epidermal cells and are closely associated with hair follicles. Sebaceous glands are found in greatest abundance on the face and scalp, though they are distributed throughout all skin sites except the palms and soles. They are small in children, enlarging and becoming active at puberty, being sensitive to androgens. They produce an oily sebum by holocrine secretion in which the cells break down and release their lipid cytoplasm 3)Sweat glands Sweat glands are thought to be over 2.5 million on the skin surface and they are present over the majority of the body They are located within the dermis and are composed of coiled tubes, which secrete a watery substance They are classified into two different types: eccrine and apocrin a. Eccrine glands are found all over the skin especially on the palms, soles, axillae forehead. They are under psychological and thermal control. Sympathetic(choliner nerve fibres innervate eccrine glands. The watery fluid they secrete contains chloride, lactic acid, fatty acids, urea, glycoproteins and mucopolysaccharides b. apocrine glands are larger, the ducts of which empty out into the hair follicles. They are present in the axillae, anogenital region and areolae and are under thermal control They become active at puberty, producing a protein-rich secretion which when acted upon by skin bacteria gives out a characteristic odour. These glands are under the control f sympathetic( energi ic)nerve fibr 4)Nails Nails consist of a dense plate of hardened keratin between 0.3 and 0. 5mm thick The nail is made up of a nail bed, nail matrix and a nail plate. The nail matrix is composed of dividing keratinocytes, which mature and keratinise into the nail plate. Underneath the nail plate lies the nail bed. The nail plate appears pink due to adjacent dermal capillaries and the white lunula at the base of the plate. The thickened epidermis which underlies the free margin of the nail at the proximal end is called the hyponychium. Fingernails grow at 0. 1 mm per day; the toenails more slowly 2. Dermis The dermis derives from mesoderm, and is typically 3-5 mm thick and is the major component of human skin. It is composed of a network of connective tissue, predominantly collagen fibrils providing support and elastic tissue providing flexibility The dermis has numerous structures embedded within it: blood and lymphatic vessels nerve endings, pilosebaceous units and sweat glands(eccrine and apocrine). The extensive vasculature of the skin is essential for regulation of body temperature whilstcortex of keratinocytes and an inner medulla. The root sheath, which surrounds the hair bulb, is composed of an outer and inner layer. An erector pili muscle is associated with the hair shaft and contracts with cold, fear and emotion to pull the hair erect, giving the skin `goose bumps'. During the growing phase or anagen, the cells of the hair bulb actively devide and produce the growing hair. Then hair follicles go into the catagen, or transitional phase of activity, the matrix cells stop dividing. During catagen, the lower protion of the follicle disappears, leaving behind a thin strand of epithelial cells surrounded by a thick basement membrane zone. During telogen, the epithelial strand subsequently shortens to the level of the arrector pili muscle. 2) Sebaceous gland Sebaceous glands are derived from epidermal cells and are closely associated with hair follicles. Sebaceous glands are found in greatest abundance on the face and scalp, though they are distributed throughout all skin sites except the palms and soles. They are small in children, enlarging and becoming active at puberty, being sensitive to androgens. They produce an oily sebum by holocrine secretion in which the cells break down and release their lipid cytoplasm. 3) Sweat glands Sweat glands are thought to be over 2.5 million on the skin surface and they are present over the majority of the body. They are located within the dermis and are composed of coiled tubes, which secrete a watery substance. They are classified into two different types: eccrine and apocrine. a. Eccrine glands are found all over the skin especially on the palms, soles, axillae and forehead. They are under psychological and thermal control. Sympathetic (cholinergic) nerve fibres innervate eccrine glands. The watery fluid they secrete contains chloride, lactic acid, fatty acids, urea, glycoproteins and mucopolysaccharides. b. Apocrine glands are larger, the ducts of which empty out into the hair follicles. They are present in the axillae, anogenital region and areolae and are under thermal control. They become active at puberty, producing a protein-rich secretion which when acted upon by skin bacteria gives out a characteristic odour. These glands are under the control of sympathetic (adrenergic) nerve fibres. 4) Nails Nails consist of a dense plate of hardened keratin between 0.3 and 0.5mm thick. The nail is made up of a nail bed, nail matrix and a nail plate. The nail matrix is composed of dividing keratinocytes, which mature and keratinise into the nail plate. Underneath the nail plate lies the nail bed. The nail plate appears pink due to adjacent dermal capillaries and the white lunula at the base of the plate. The thickened epidermis which underlies the free margin of the nail at the proximal end is called the hyponychium. Fingernails grow at 0.1 mm per day; the toenails more slowly. 2. Dermis The dermis derives from mesoderm, and is typically 3–5 mm thick and is the major component of human skin. It is composed of a network of connective tissue, predominantly collagen fibrils providing support and elastic tissue providing flexibility. The dermis has numerous structures embedded within it: blood and lymphatic vessels, nerve endings, pilosebaceous units and sweat glands (eccrine and apocrine). The extensive vasculature of the skin is essential for regulation of body temperature whilst