Skin Structure

Skin Structure
Layers of the Epidermis
Stratum Basale/Basal Layer
• All about that “Base”
• Deepest epidermal layer
• Attached to the Dermis beneath it along a
wavy texture
• Looks like corrugated cardboard
• Mostly single row of cells
• Continually renewing cell population
• Mitotic nuclei
Stratum Basale/Basal Layer
Also called Stratum
Stratum Spinosum
• “Prickly” layer
• Several cell layers thick
• Contain weblike system of intermediate
• Keratinocytes appear spiny in shape
• Langerhans’ cell are most abundant in this
Stratum Spinosum
Stratum Spinosum
Stratum Granulosum
Granular Layer
Thin – 3 to 5 cell layers thick
Keratinocyte appearance changes drastically
They flatten
Nuclei and organelles begin to disintegrate
Accumulate granules
• Keratohyaline: helps form keratin in the upper
• Lamellated: contain a waterproofing glycolipid
that is spewed into the extracellular space
• Slows water loss across the epidermis
Stratum Granulosum
• Plasma membrane thickens
• Cytosol proteins bind to inner membrane
• Lipids released by lamellated granules coat
the external surface
• Process of toughening up
• Above the stratum granulosum, the
epidermal cells are too far from the dermal
capillaries, so they die
Stratum Granulosum
Stratum Granulosum
Stratum Lucidum
• Appears as thin, translucent band
• A few rows of dead, flat keratinocytes with
indistinct boundaries
• Visible only in thick skin
Stratum Lucidum
Stratum Lucidum
Stratum Corneum
“Horny” layer
Outermost layer of epidermis
20-30 cell layers thick
Accounts for up to ¾ of the epidermal
• Durable “overcoat” for the body
• Protects deeper cells from the hostile
external environment
Stratum Corneum
Stratum Corneum
• Cornu = horn
• Dandruff, flakes the slough off dry skin
• Average person sheds 40lb of skin flakes in
a lifetime
• When you look at someone’s skin, you are
looking at dead cells. 
Skin Structure
• Strong, flexible connective tissue
• Fibroblasts, macrophages, mast cells and
white blood cells
• Heavily embedded with fibers
• Binds the body together like a stocking
• Your “hide”
Nerve fibers
Blood vessels
Lymphatic vessels
Hair follicles
Oil and sweat glands
2 layers
• Papillary & reticular
• Areolar connective tissue
• Heavily invested with blood vessels
• Dermal papillae
Dermal Papillae
Contain capillary loops
Free nerve endings (pain receptors)
Meisners corpuscles (touch receptors)
Dermal ridges
• Cause the epidermis to form epidermal ridges
• Friction
• Epidermal ridge patterns (fingerprints)
• Sweat pores open along their crests
Reticular Layer
• 80% of thickness
• Dense irregular connective tissue
• Cutaneous plexus
• Network of blood vessels that nourishes dermal
• Between reticular layer and hypodermis
Reticular Layer
• Extracellular Matrix
• Thick bundles of interlacing collagen fibers that
run in various planes
• Most run parallel to the skin surface
• Tension/cleavage lines
• Surgery and healing
Reticular Layer
• Collagen fibers
• Strength and resiliency prevents most jabs and
scrapes from penetrating the dermis
• Collagen binds water, keeping skin hydrated
Reticular Layer
• Flexure lines
• Dermal folds that occur at or near joints where
the dermis is tightly secured to deeper
• Ex. Palms of hands
Homeostatic Imbalance
• Extreme stretching of the skin can tear the
dermis. What is this called?
• Short-term but acute trauma can cause a
separation of the dermal and epidermal
layers by a fluid filled pocket. What is this
Skin Color
Skin Color
• 3 pigments contribute to skin color
• Melanin
• Carotene
• Hemoglobin
• Only melanin is made in the skin
• Polymer that ranges in color from yellow to
reddish-brown to black
• Its synthesis depends on an enzyme in
melanocytes , tyrosinase
• All humans have the same number of
• Differences in skin color reflect the kind
and amount of melanin made and retained
• Freckles and pigmented moles are local
accumulations of melanin
• Melanocytes are stimulated by exposure to
• Melanin buildup is designed to help protect
the DNA of viable skin cells from UV
radiation and dissipating the energy as heat
• Initial signal for speeding up melanin
synthesis appears to be a faster rate of repair
of photodamaged DNA
• This causes a physiological response.
• What is this response called?
• Yellow to orange pigment found in certain
plant products
• Tends to accumulate in the stratum corneum
and fatty tissue of the hypodermis
• Most obvious where the stratum corneum is
the thickest (skin of the heels)
• Pinkish hue of fair skin
• Reflecting the crimson color of oxygenated
hemoglobin in the red blood cells
circulating through the dermal capillaries
• Because Caucasion skin contains only small
amounts of melanin, the epidermis is nearly
transparent and allows hemoglobin’s color
to show through