Functions include protection chemical barriers acid

• Functions include:
– Protection
• Chemical Barriers
– Acid mantle
– UV barrier
• Physical barriers
– Water barrier
– Tough and dry
• Biological barriers
– Langerhans’cells in epidermis
– Dermal macrophages
– Thermoregulation
• Cutaneous arteries and sweat glands
– Sensory functions
• Receptors for heat, cold, touch, pressure, vibration, & pain
– Vitamin D synthesis
– Blood reservoir (up to 5% of body’s blood volume)
– Absorption of lipids
– Excretion
• Some nitrogenous wastes, salts, alcohol, etc.
Know the cell layers of the epidermis in order and know the functions
• Composed of keratinized stratified squamous epithelium
– Outer portion of the skin is exposed to the external environment and functions in
protection
– Consists of four distinct cell types and four or five layers
– Cell types: Four or five distinct layers:
Keratinocytes Stratum basale
Melanocytes Stratum spinosum

Tactile (Merkel) cells Stratum granulosum
Dendritic (Langerhans) cells Stratum lucidum (only in
thick skin)
Stratum corneum
• Epidermis is made up of four or five distinct layers
– Thick skin contains five layers (strata) and is found in high-abrasion areas (hands,
feet)
– Thin skin contains only four strata
Stratum basale ( basal layer )
– Deepest epidermal layer firmly attached to the dermis
– Consists of a single row of stem cells
• Actively mitotic
• Produces two daughter cells
• One cell journeys from basal layer to surface
• Takes 25–45 days
• Dies as moves toward surface
• One cell remains in stratum basale as stem cell
– Since cells undergo rapid division, its alternate name is stratum germinativum
– Melanocytes compose 10 – 25% of this layer
Stratum spinosum ( prickly layer )
– Several cell layers thick
– Cells contain weblike system of intermediate prekeratin filaments attached to
desmosomes
• Allows them to resist tension and pulling
– Keratinocytes in this layer appear spikey, so they are called prickle cells
– Scattered among keratinocytes are abundant melanosomes and dendritic cells
Stratum granulosum ( granular layer )
– Thin - four to six cell layers
– Drastic changes in keratinocyte appearance occurs
• Cells flatten
• Nuclei and organelles disintegrate
• Accumulate two types of granules
• Keratohyaline granules (form keratin)
• Lamellated granules (waterproof)
– Granules cut off nutrients
• Cells above this layer die
• Too far from dermal capillaries
Stratum lucidum ( clear layer )
– Found only in thick skin
– Consists of thin, translucent band of two to three rows of clear, flat, dead
keratinocytes
– Lies superficial to the stratum granulosum

Stratum corneum ( horny layer )
– Outermost layer
– 20–30 rows of flat, anucleated, keratinized dead cells
– Accounts for ¾ of epidermal thickness
– Though dead, cells still function to:
• Protect deeper cells from the environment
• Prevent water loss
• Protect from abrasion and penetration
• Act as a barrier against biological, chemical, and physical assaults
– Outermost cells are exfoliated
Know the cell types and the functions of the cell types found in the epidermis
Keratinocytes