Overview
This lecture reviews the accessory structures of the integumentary system—hair, nails, and glands—including their anatomy, types, functions, and key characteristics.
Accessory Structures Overview
- Accessory structures include hair, nails, and glands, all derived from epithelial tissue.
- These structures support the skin’s protective and sensory roles.
Hair: Structure and Function
- Hair protects against mechanical trauma, UV light, and prevents entry of foreign particles into ears, eyes, and nose.
- Hair is absent on thick skin (palms, soles), lips, and certain genital areas.
- The hair follicle provides nutrients, with the hair matrix as the growth site.
- Sebaceous glands produce oil for hair, and arrector pili muscles raise hair ("goosebumps").
- Nerve endings wrap around hair follicles, enabling sensation.
- Hair grows in cycles: anagen (growth phase), telogen (resting phase), with the anagen phase determining maximum hair length (genetically controlled).
- Keratinization makes hair tough; more keratin means greater durability.
Types and Characteristics of Hair
- Lanugo: fine, non-pigmented fetal hair, disappears after birth.
- Vellus hair: thin, soft, usually non-pigmented, found all over the body.
- Terminal hair: thick, coarse, pigmented, found in scalp, eyebrows, beard, axillae, and genitalia.
- Hair color depends on pigment type and quantity; red hair contains extra iron-based pigment.
Nails: Structure and Function
- Nails are keratinized plates on fingers and toes, growing from the nail matrix.
- They protect digits and provide enhanced sensation.
- The eponychium and hyponychium are the proximal and distal folds under the nail, respectively.
Glands in the Integumentary System
- Eccrine (merocrine) sweat glands produce watery sweat for cooling, composed of water, electrolytes, and waste.
- Apocrine sweat glands (axilla, groin) secrete protein-rich sweat, becoming active after puberty, and can become odorous when bacteria metabolize secretions.
- Mammary glands are specialized apocrine glands producing milk.
- Ceruminous glands are modified apocrine glands that produce wax in the ear for protection.
- Sebaceous glands produce oily sebum via holocrine secretion to lubricate skin and hair, absent on palms and soles.
Key Terms & Definitions
- Integumentary system — the skin and its accessory structures.
- Keratinization — process making cells tough via keratin protein.
- Hair follicle — structure where hair grows; supplies nutrients.
- Sebaceous gland — oil-producing gland associated with hair.
- Arrector pili — smooth muscle that raises hair.
- Anagen phase — hair growth phase.
- Telogen phase — hair resting phase.
- Vellus hair — fine, soft body hair.
- Terminal hair — coarse, pigmented hair.
- Eccrine gland — sweat gland for thermoregulation.
- Apocrine gland — scent-producing gland active after puberty.
- Sebum — oily secretion from sebaceous glands.
- Holocrine secretion — entire cell disintegrates to release contents.
Action Items / Next Steps
- Review key differences between gland types and their secretions.
- Prepare for next lecture on thermoregulation and the skin’s role.
- Contact the instructor for questions via text, email, or office hours.