• Largest and heaviest organ of the body; accounts for about 15% of the total body weight
• Also called as cutaneous membrane
• Skin contains two layers, the epidermis and the dermis.
• The hypodermis is the layer underneath the skin.
• Skin is a protective covering that prevents harmful substances from entering the body.
• It helps regulate body temperature and water loss.
• It houses sensory receptors and contains immune system cells.
• It synthesizes chemicals and excretes some wastes.
• Hair develops from epidermal cells at the base of the hair follicle.
• Epidermal cells keep dividing continuously, grow, and die.
• The dead cells make up the shaft of the hair.
• The arrector pili muscle is a smooth muscle attached to the follicle.
• It causes hair to stand upright on the skin.
Hair is filament of keratinized cells
• shaft is visible above skin; root is below within follicle
FUNCTIONS OF HAIR
• Facial, pubic and auxiliary hair
• It is composed of stratified squamous epithelium (ET) and a simple basal layer of cuboidal cells.
• It lacks blood vessels, but the deepest layer, the stratum basale, is close to the dermis and receives nutrients.
• The thickness of the epidermis varies with region of the body.
CELLS OF EPIDERMIS
• Keratinocytes (90%)- waterproofs & protects skin, nails, hair, stratum corneum
• Melanocytes (8%)- produce melanin
• Merkel Cells- slow mechanoreceptors
• Langerhans’ Cells- immunological defense
• Thickness = 0.6mm to 3mm
• Composed mainly of collagen, but also contains elastic reticular fibers, blood vessels, sweat glands, sebaceous glands, hair follicles, nail roots, sensory nerve endings and muscular tissue (facial expressions are due to the skeletal muscle connection to the dermal collagen fibers to producesmile, frown, eyebrow movement)