Detailed handwritten medical student notes on ruled notebook paper, blue and black ink, titled "SKIN & ITS APPENDAGES" with underline. Notes organized with headings, subheadings, bullet points, arrows, small diagrams and labels. Content includes: HEADING: SKIN & ITS APPENDAGES (bold underlined) INTEGUMENTARY SYSTEM: - Skin = largest organ of body; surface area ~1.8 m²; 15-20% total body mass - Two main layers: EPIDERMIS (keratinized stratified squamous epithelium; from ectoderm) + DERMIS (dense irregular connective tissue; from mesoderm) - HYPODERMIS = subcutaneous fascia; variable adipose tissue EPIDERMAL APPENDAGES (boxed): Hair follicles + hair | Nails | Sweat glands (eccrine + apocrine) | Sebaceous glands | Mammary glands HAIR FOLLICLE: - Absent from: palms, soles, lips, urogenital orifices - Structure: Medulla (central; soft keratin; only in thick hairs) → Cortex (main bulk; hard keratin; melanin pigment) → Cuticle (outermost; overlapping scale-like cells) - Inner root sheath: Henle's layer + Huxley's layer + cuticle - External root sheath: continuous with epidermis; clear cytoplasm (glycogen-rich) - Follicular bulge = ES cell niche → stem cells for hair + sebaceous gland regeneration - Arrector pili muscle attached at follicular bulge (smooth muscle) - Glassy membrane = thick basal lamina separating follicle from dermis HAIR GROWTH CYCLES (small arrow diagram): ANAGEN (growing) → CATAGEN (transitional) → TELOGEN (resting) - Growth rate: ~0.4 mm/day (1.2 cm/month) - Gray hair = ↓ melanin in hair matrix - Baldness: terminal follicles → vellus follicles NAILS: - Hard keratin plates on dorsal fingertip/toe - Nail plate, nail bed, nail matrix (generates nail plate), lunula, eponychium (cuticle), hyponychium SEBACEOUS GLANDS: - Usually associated with hair follicle → Pilosebaceous unit (4 parts: hair follicle + hair shaft + arrector pili + sebaceous gland) - Absent from: palms + soles - Highest density: FACE - Not associated with hair: Meibomian glands (eyelids), Zeis glands (eyelids), areolae, lips - Secretion = SEBUM (holocene secretion); during 2nd trimester → vernix caseosa - Acne = blocked sebaceous duct + Propionibacterium acnes ECCRINE SWEAT GLANDS: - Simple coiled tubular gland; independent of hair follicle - Segments: Secretory (deep dermis/hypodermis) + Duct (opens to skin surface) - 3 cell types in secretory segment: Clear cells (water/electrolytes) + Dark cells (glycoproteins) + Myoepithelial cells (contractile) - Sweat: hypotonic; NaCl + urea + uric acid + ammonia - Function: thermoregulation (cholinergic) + emotional sweating (adrenergic; palms/soles/axillae first) - Cystic fibrosis → ↑↑ Na+ and Cl- in sweat (2-5× normal) ← diagnostic note - Urea frost = uremia sign (urea crystals on skin after evaporation) APOCRINE SWEAT GLANDS: - Found: axillae, areolae, pubic region, perianal region - Associated WITH hair follicles (open into follicular canal) - Secretion: viscous; carbohydrates + lipids + proteins + pheromones - Become functional at puberty Small diagram: cross-section of skin showing epidermis, dermis, hypodermis with labeled hair follicle, sebaceous gland, eccrine gland, arrector pili, blood vessels, nerve endings Handwritten style with mix of blue pen headings, black pen body text, some red underlines for important points, small neat diagrams in margins