Anatomy - Hair, Skin and Nails

3 types of hair

1. Downy hair: Fine, unpigmented that appears on fetus in the last 3 months of development.

2. Vellus hair: Fine and pale hair

3. Terminal hair: longer, coarser hair

Structure of hair

• Shaft: hair above skin

• Root: beneath skin

• Medulla: core of loosely arranged cells and air spaces

• Cortex: most of the bulk of hair

• cuticle: Composed of multiple layers of scaly cells that overlap each other like roof shingles with their free edges

Follicle

Slender filament of keratinized cells that grow from an oblique tube in the skin

Arrector muscle

Bundle of smooth muscle cells extending from dermal collagen fibers to the connective tissue root sheath of the folic. It responds to cold, fear, or other stimuli. Makes hair stand (goose bumps)

Functions of hair

• Receptors can prevent infection by parasites, insects, fleas

• Retain heat (only on scalp)

• Advertise species, age, sex, “individual factor” (style, color)

• Guards entry into nose, ears, eyes

• facial expressions

Structure of nail:

• Nail: nail plate

• Root: under skin

• Free edge: top of nail

• Body: the whole nail

Types of sweat glands

1. Sweat glands

   • Apocrine: ducts empty onto hair follicle/root = sex pheromones

   • Eccrine: Ducts that secrete sweat onto skin surface, cools skin, forehead, hands and feet.

2. Sebaceous gland: associated with hair root. secretes sebum onto hair root, keeps hair and skin mosit

3. Ceruminous gland: ear —> ear wax, traps dust

4. Mammary glands: produces milk, develop during pregnancy