Integumentary System Accessory Structures and Repair

Hair Anatomy and Growth

Hair structure diagram

  • Hair Structure:

    • Medulla: Central core of hair.

    • Cortex: Intermediate layer surrounding medulla.

    • Cuticle: Outer protective surface layer.

    • Shaft & Root: Shaft is the visible upper section; root anchors hair in the dermal follicle.

  • Follicle Features:

    • Base surrounded by root hair plexus (sensory nerve network).

    • Attached to arrector pili muscle (involuntary smooth muscle responsible for erect hairs and "goose bumps").

    • Hair Matrix: Layer of dividing basal cells at the hair bulb surrounding the hair papilla (connective tissue with capillaries and nerves).

  • Growth Cycle Phases:

    • Anagen: Active growth period lasting 2–7 years.

    • Catagen: Transition stage lasting 2–3 weeks.

    • Telogen: Resting phase lasting 2–4 months before old hair sheds.

  • Hair Types:

    • Vellus: Soft, fine body hairs.

    • Terminal: Heavy, deeply pigmented hair on head, eyebrows, eyelashes, and adult body areas.

Nail Structure

Diagram of nail anatomy

  • Function: Dense, keratinized dead cells covering distal tips of digits to provide mechanical protection.

  • Anatomic Structures:

    • Nail Body: Main visible surface resting over nail bed, bounded by lateral nail folds and grooves.

    • Nail Root: Deep epidermal fold near phalanx bone where nail production occurs.

    • Eponychium: Cuticle formed by stratum corneum at proximal nail fold.

    • Lunula: Pale crescent area near root where underlying dermal blood vessels are obscured.

    • Hyponychium: Epidermal region beneath free distal edge of nail.

Exocrine Glands

  • Sebaceous Glands:

    • Holocrine glands secreting lipid-filled sebum to lubricate hair shafts, protect skin, and inhibit bacteria growth.

    • Sebaceous Follicles: Large standalone glands discharging directly onto skin surface (face, chest, back).

  • Sweat Glands:

    • Eccrine (Merocrine) Glands: Coiled tubular glands producing sensible perspiration (99%99\% water plus salts) directly to skin pores for thermoregulation and waste excretion.

    • Apocrine Glands: Secrete sticky, cloudy fluid into hair follicles in axillary and pubic regions; bacterial breakdown creates odor.

  • Other Modified Glands:

    • Mammary Glands: Produce milk.

    • Ceruminous Glands: Produce cerumen (earwax) to trap foreign particles near the eardrum.

Injury Repair Phases

  • Inflammation Phase: Immediate bleeding at injury site; mast cells trigger local inflammatory response.

  • Migration Phase: Scab forms within hours; stratum basale cells, macrophages, and fibroblasts migrate into area creating granulation tissue.

  • Proliferation Phase: Fibroblasts produce collagen meshwork beneath scab while phagocytic activity clears debris and fibrin clot dissolves.

  • Scarring Phase: Scab sheds after several weeks, leaving complete epidermis over noncellular collagenous scar tissue (excess formation leads to keloids).