1. Accessory StructuresAccessory Structures Chapter 6 Sections 3Chapter 6 Sections 3

2. Objectives Describe the accessory structures associated with the skin Explain the functions of each accessory structure of the skin Explain how the skin helps to regulate body temperature

3. Accessories of the Skin Accessory structures of the skin originate from the epidermis and include: Nails Hair follicles Skin glands As long as accessory structures remain intact, severely burned or injured dermis can regenerate

4. Nails Are the protective coverings on the ends of fingers and toes Consist of a nail plate, nail bed, & lunula The nail plate overlies the a surface of skin called the nail bed Specialized epithelial cells continuous with the epithelium of the skin produce the nail bed The lunula is the whitish, thickened, half moon-shaped region at the base of the nail plate It is the most active growing region of the nail The epithelial cell here divide and the newly formed cells become keratinized This creates tiny, keratinized scales that become part of the nail plate

5. Nail

6. General Characteristics of Hair Hair is present on all skin surfaces except for your palms, soles, lips, nipples, and parts of the external reproductive organs But not all places on your body have well developed hair, such as on your forehead 90% of the time your hair is in the growth phase A hair typically grows for 2-6 years and then rests for 2-3 months anchored in its folliclegrows A healthy person loses from 20-100 hairs a day Hair is composed of dead epidermal cells

7. Hair Follicles Each hair develops from a group of epidermal cells at the base of a tube-like depression called a hair follicle The follicle extends from the surface into the dermis and contains the hair root The hair root is the portion of your hair embedded in the skin The epidermal cells in the hair bulb at its base are nourished from dermal blood vessels in a projection of connective tissue called the hair papilla

8. Hair Follicle

9. Determining Hair Color Genes determine hair color by directing the type and amount of pigment that epidermal melanocytes produce Dark hair has more of the brownish-black pigment eumelanin Blonde and red hair have more of the reddish-yellow pigment pheomelanin White hair lacks melanin altogether A mixture of pigmented hairs and unpigmented hairs creates gray hair

10. Hair movement Each hair follicle is attached to a bundle of smooth muscle cells called the arrector pili muscle When this muscle contracts, a short hair in the follicle stands on end If a person is emotionally upset or very cold, the contraction of the arrector pili muscle creates goosebumps

11. Skin Glands Two types of skin glands: Sebaceous glands, which are epithelial cells associated with hair follicles Sweat glands, or sudoriferous glands, which are widespread in the skin

12. Sebaceous Glands Are holocrine glands Found scattered throughout the skin, but are not on the palms or the soles Their cells produce globules of a fatty material called sebum that accumulates, swelling and bursting cells Sebum is secreted into hair follicles through short ducts It helps to keep hair and skin soft, pliable, and waterproof Some sebaceous glans open directly to the skin rather than around hair follicles such as, at your lips, corners of your mouth, and parts of the external reproductive organs Excessive secretions of sebum leads to acne

13. Sweat Glands Each gland consists of a tiny tube that originates as a ball- shaped coil in the deeper dermis or superficial subcutaneous fat layer The coiled portion of the gland is closed at is deep end and is lines with sweat-secreting epithelial cells At the surface of the skin, the tube opens as a pore The most numerous sweat glands are called eccrine glands These glands respond the elevation of body temperature and are found abundantly in the forehead, neck and back They also produce sweat on your palms and soles when emotionally stressed

14. Composition of Sweat & Special glands It is mostly water It also contains: salts (urea) and wastes (uric acid) So, sweating is also an excretory functions Some secretions of certain sweat glands, apocrine glands, develop a scent as skin bacteria metabolize them Apocrine glands only become active at puberty Other sweat glands are specialized like ceruminous glands which produce ear wax and mammary glands which produce milk