Skin Flashcards
Layers of epidermis
Mnemonic: Come Let’s Get Sunburnt Baby
- C: stratum corneum
- L: stratum lucidum
- G: stratum granulosum
- S: stratum spinosum
- B: stratum basale/germinativum
Stratum corneum
- most superficial layer of epidermis
- layer of dead keratinocytes (squames) packed with keratin
- cells are scraped/sloughed off; complete skin replacement takes 31 days
Stratum lucidum
- only found in thick skin
- faint staining layer
- flattened keratinocytes packed with keratin and eleidin proteins
Stratum granulosum
- flattened nucleated cell layer
- keratohylin granules (filaggrin) and bundles of keratin protein
- lamellar bodies release lipids extracellularly
- epidermal water barrier = extracellular lipids + intracellular proteins
Stratum spinosum
- eosinophilic cells with spiny appearance
- spines = desmosomes between cells, hold cells together
- superficial layer of cells begin forming membrane-coating granules (lamellar bodies) and keratin proteins
- contains Langerhans cells: dendritic cells (APC) that move to lymph nodes as part of immune response
Stratum basale or stratum germinativum
- deepest layer of epidermis
- cuboidal-shaped keratinocytes that make keratin protein
- attached to basal lamina by hemidesmosomes
- mitotically active cells; replenish cell layers above
- contains melanocytes: produce melanin (brown pigment); mobile cells
- contains Merkel cells: linked to sensory nerve terminals (mechanoreception); can’t be differentiated from melanocytes microscopically
Thick vs. thin skin
Thick skin:
- very thick stratum corneum
- visible stratum lucidum
- no hair, sebaceous glands, arrector pili muscles
- found on palmar and plantar surfaces
Thin skin:
- thin layer of stratum corneum
- no obvious layer of stratum lucidum
- contains hair follicles, sebaceous glands, arrector pili muscles
- found covering majority of body
Connections between dermis and epidermis
Rete ridges:
- extensions of epithelia into dermis (downward-pointing, into deeper skin)
Vascular/dermal papillae:
- extensions of dermis into epithelium (upward-pointing)
- often contain capillaries to nourish epidermis
Ridges and papillae are often longer in areas of higher mechanical stress (palms, fingers, soles).
Domains of dermis
Papillary dermis:
- superficial layer with papillae
- higher cell content
Reticular dermis:
- deeper layers of dermis
- higher protein fibers (collagen I and elastic fibers)
Types of glands
Eccrine sweat glands:
- sweat glands secrete fluids/proteins to make sweat for thermoregulation
- myoepithelial cells wrap around sweat glands; contract to push sweat into ducts
- sweat ducts channel sweat to surface of epidermis, reabsorbs some water and electrolytes
Apocrine glands:
- special sweat glands only found in axilla, areola, perianal, auditory canal; become active after puberty
- viscous protein secretions produce body odor
- larger lumen with irregular cells
Sebaceous glands:
- lipid filled glands that empty onto hair shaft
- produce sebum
- prevalent on face and scalp
Hair follicles
Hair follicles = epidermal invaginations into deep dermis
- cells become keratinized to form hair shaft
- Vellus hair = short fine hair
- Terminal hair = long coarse hair, pigmented
Arrector pili muscle:
- smooth muscle attached to hair and papillary dermis
- piloerection: contraction causing hair to stand up (sympathetic nervous system)
Sensory receptors
Meissner’s corpuscle:
- whorled shape (tulips, tornado)
- found in papillary dermis of thick skin
- sensitive to light touch
Pacinian corpuscle:
- onion shape
- found in subcutis of thin/thick skin
- sensitive to vibration and pressure
Free nerve endings:
- not visible
- sense touch, heat, cold, pain/nociception
Nails
- hard keratinized plates
- nail forms at nail root ==> grows over nail bed
- nail root is covered by eponychium (cuticle)
- lunula = white opaque region near nail root
- hyponychium holds nail in place (free edge)
Regional differences in skin: palmar, facial, axilla, scalp
Palmar: thick skin lacking hair follicles
Facial: thin skin, some sebaceous glands and hair present
Axilla: thin skin, increased hair, apocrine glands present
Scalp: thin skin, increased hair and sebaceous glands
