Hair follicles and glands

• Hair Follicle Cycles
  • Anagen: Growth phase.
  • Telogen: Resting phase.
  • Telogen Effluvium: Stress-induced (e.g., pregnancy, surgery) diffuse hair loss; premature entry into telogen.
• Folliculitis
  • Infectious:
    • Staph aureus: Most common cause overall.
    • Pseudomonas aeruginosa: “Hot tub folliculitis” (exposure to contaminated water).
  • Non-Infectious:
    • Pseudofolliculitis barbae: “Razor bumps”; common in African American men; curly hair re-enters skin, causing inflammation.
• Gland Secretion Mechanisms (High-Yield)
  • Holocrine: Cell lysis releases contents (e.g., Sebaceous glands).
  • Apocrine: Budding of apical cytoplasm (e.g., Mammary glands).
  • Merocrine: Exocytosis; no cell loss (e.g., Eccrine/Sweat, Salivary).
• Sebaceous Glands
  • Product: Sebum.
  • Stimulus: Androgens (↑ in puberty).
  • Clinical: Acne vulgaris (obstructed follicles + C. acnes infection).
• Eccrine Glands (Sweat)
  • Function: Thermoregulation.
  • Innervation: Sympathetic Cholinergic (Unique: Sympathetic nervous system uses ACh).
  • Distribution: Body-wide; highest on palms/soles.
  • Clinical: Targets for botulinum toxin in severe hyperhidrosis (blocks ACh release).
• Apocrine Glands
  • Location: Axilla, areola, perineum.
  • Primary Function: Secretion of a thick, protein/lipid-rich fluid into hair follicles in response to emotional stress and sexual stimulation (unlike eccrine glands, which respond to heat).
  • Onset: Functional at puberty.
  • Odor: Due to bacterial breakdown of secretions.
  • Clinical: Hidradenitis suppurativa (chronic inflammation in these areas).

Tip

Sweat gland is only innervated by sympathetic nerve, while regarding nerve fibers, it is innervated by cholinergic nerve (M receptor; acting on the whole body, eccrine sweat glands) and adrenergic nerve (α1 receptor; acting on the palms and soles, ?)