Components • Skin, hair, nails, and glands • The body’s covering • Separates us from the outside world
Skin function • Protection: barrier against infection and injury • Temperature regulation • Removes waste products • Protects againstUV radiation from the sun
Epidermis • Outer layer of skin • Dead cells form the waterproof, flexible outside layer • Living cells move upward to replace them • Melanin: brown pigment that absorbs UV skin
Dermis • Has blood cells, nerve fibers • Oil glands keep skin flexible, waterproof • Helps regulate body temp: • Too cold, hairs stand up, blood vessels narrow. • Too hot: sweating cools, removes wastes • Blood vessels expand to cool blood
Glands of the dermis: sweat glands • Sweat glands: produce perspiration (water + salts). When the sweat evaporates, it takes heat away from the body. • Sweat also removes wastes from the blood. • We produce, on average, 500ml of sweat a day. • Doing strenuous work or with heat exposure, we can produce10 liters of sweat a day!
Sebaceous glands • Oil glands produce sebum: an oily secretion, onto the outer layer of skin. • Sebum keeps the epidermis flexible and waterproof. • Over-production of sebum leads to acne.
Skin cancer • Abnormal skin growth, caused by too much UV exposure • Prevention: sunscreen, hats, clothing. Basal, squamous, melanoma cancers
Hair • Keratin: makes hair (also horns, scales, quills and feathers). Is not living tissue. • Scalp hair: warmth, UV protection • Nose, eyelash, ear hairs: prevents dirt from entering • Follicles: living cells at the base push the hair outwards.
Nails • Cover and protect fingers and toes • Cells of the nail root fill with keratin to make the tough, platelike nail • Grow 3mm-12mm a month
Review questions • What are the main functions of skin? • What part of the hair is living? What part of the hair is dead cells? • Why is it important that skin be waterproof? • Why don’t you bleed if you get a light scratch? • What can we do to keep our skin healthy?