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Integumentary
Anatomy
Laura E. Edsberg, Ph.D.
The Skin
• Epidermis
• Dermis
• Subcutaneous Fat
Largest Organ System
• 1/3 of cardiac output is directed to skin
• Surface area 18-20 Sq Ft
• 7% of body weight
• Thickness 1.5-4mm
Functions of The Skin
• Large & Complex
• Sensory Functions
• Barrier
– Harmful Chemicals
– Ultraviolet Radiation
– Infection
• Temperature Regulation & Sweating
• Required for Vitamin D Production
Epidermis
• Tough, leathery outer surface
• Composed mainly of Keratinocytes
• .06-.6mm, thickest portion palms and
soles
• Epidermis avascular, receives nutrients
by diffusion through semi-permeable
Basement Membrane (BM)
Epidermal Cellular Layers
• Five Layers
– Represent different stages of cellular
differentiation, gradual loss of nuclear
material & accumulation of keratin
proteins
– New cells form
– Older cells elongate, membranes thicken
as they are pushed up
Basal Layer
• Stratum Basale, deepest layer, attached to
dermis by thin, acellular (BM)
• Single row of keratinocytes
• Typically, mitotic activity of keratinocytes
is confined to this layer
• Epidermal turnover time Approx. 4 weeks
• Keratinocytes produce Keratin
(protective protein)
Stratum Spinosum
• Above Stratum Basale
• Several rows of more mature
keratinocytes
• Appear spiny due to keratin
filaments
Stratum Granulosum
• Above Stratum Spinosum
• Three to five flattened cell rows
• Increased concentration of Keratin
Stratum Lucidum
• Above Stratum Granulosum
• As keratinocytes migrate up away
from their dermal blood supply,
they slowly die
• Stratum Lucidum contains layers of
flattened dead keratinocytes
Stratum Corneum
•
•
•
•
•
“Horney” Layer
Consists of dead keratinocytes
20-30 cells thick
75% of thickness of the epidermis
Cells are continuously abraded & replaced
by cells below
• A cells journey from the basale layer up
through the corneum takes 14-21 days
• Friction or pressure will increase the
thickness of the stratum corneum (Callus)
Epidermal Cells
• Keratinocytes - Keratin (protective protein)
• Merkel Cells – Specialized
mechanoreceptors (light touch)
• Langerhan’s Cells – deeper layers of
epidermis assist in fighting infection (attack
& engulf foreign material)
• Melanocytes
Melanocytes
• Produce pigment Melanin
– Protects skin from UV
– Gives the skin its color
• More = Darker
• Less = Lighter
• Grey Hair - loss of melanocytes in hair bulb
– Faster turnover in scalp vs body
Epidermal Appendages
• Specialized epidermal structures, extend down into the
dermis - Hair, Glands, and Nails
• Hair Follicles (soft keratin)
– everywhere except palms and soles
– Helps regulate body temp by trapping air between
hair and skin surface
• Sebaceous Gland
– Each hair follicle contains a sebaceous gland
– Secretes Sebum – oily substance that lubricates skin
& hair
– May slow bacterial growth, reducing colonization
Epidermal Appendages
• Sudoriferous Glands
– Present everywhere except lips and ears
– Secrete sweat into ducts that lead to
skin’s surface
– Evaporation of sweat helps cool the body
• Nails – dorsal tips of digits
– Hard Keratin
– Protect terminal digit & assist with
function
Functions of the
Epidermis
• Provides a physical & chemical barrier
• Regulates fluid
• Provides light touch sensation
• Assists with thermoregulation
• Assists with excretion
• Assists with vitamin D production
• Contributes to appearance
Basement Membrane Zone
Dermo-Epidermal Junction
• Where epidermis and dermis join
• Contains many proteins and structures
• Site of inflammation in many diseases
• Congenital defects
• Important in skin neoplasia
Aging and the DermoEpidermal Junction
• Flattening with age
– Dermal papillae
– Epidermal rete pegs
• Flattening = Less Surface Area
– Less communication
– Less resistance to shearing
Dermis
• 2 to 4mm thick, fibrous part of skin
• Contains collagen and elastic fibers contained
in an amorphous ground substance, nerve fibers,
and nerve-end sensory organs
• Highly vascular
– Capillaries provide color (pale pink to rosy red)
– Superficial Lymphatics
• Assist in returning H2O, proteins, and other substances
from tissue to blood stream
• Dermis should appear shiny or moist
due to high H20 content
Dermal Layers
• Two layers
– Papillary Dermis (thin superficial)
• Loosely woven fibers embedded in
gelatinous matrix (ground substance)
• Blisters occur here if friction between
epidermis & dermis
– Reticular Dermis
• Dense irregular arranged connective
tissue
• Provide increased structural support to
the skin
Aging and the Dermis
• Decreased thickness
• More Avascular
• Decrease in elastin content
Dermal Cell Types
• Fibroblasts – main cells found in dermis, produce
collagen & elastin fibers, ground substance
– Give dermis strength & flexibility
• Macrophages & Polymorphonuclear Leukocytes
(neutrophils)
– Help fight infection by engulfing harmful substances
& releasing destructive enzymes
Dermal Cell Types
• Mast Cells
– Specialized secretory cells
• Produce chemical mediators of inflammation
such as histamine
– Attract other cells and cause vasodilation
to fight infection or repair injury
• Dermis also contains sensory receptors for:
–
–
–
–
Touch
Vibration
Temperature
Pressure
Functions of the Dermis
• Support & nourish epidermis
• House epidermal appendages
• Assists with infection control
• Assists with thermoregulation
• Provides sensation
Subcutaneous Tissue
• Hypodermis
• Supports the skin
• Adipose Tissue
– Highly Vascular, loose connective tissue, stores fat for
energy, insulation, protection (cushion over structures
such as bony prominences)
– Healthy adipose is glisteny white to pale yellow (darker
if dehydrated)
• Fascia
– Highly fibrous connective tissue
– Separates and surrounds structures, facilitates
movement between adjacent structures (muscle, tendon,
bone)
• Deeper lymphatic vessels are located in subcutaneous tissue
Deeper Tissues
• Wounds can extend beyond subcutaneous tissue
• Muscle
– Regularly arranged fibers surrounded by fascia
– Rich vascular supply – red in color – bleeds easily
– Non-viable muscle will appear gray or black in color
• Tendons
– Regularly arranged fibers, may be enclosed in
fibrous sheath
Deeper Tissues
• Ligaments & Joint Capsules
–
–
–
–
–
consist of dense connective tissue
Ligaments – regularly arranged fibers
Joint Capsule – direction of fibers vary
When Healthy, glisteny (silky) white appearance
Non-viable, dry, leathery, dark, and may be disconnected
• Bone
– Shiny, smooth, milky white appearance, hard when probed
– Unhealthy – moth-eaten, irregular surface, dark discoloration
• Pressure ulcers, Diabetic lesions, or burns may involve
these deep tissues
Depth of Tissue
Involvement
• Extent of tissue involvement is
characterized as:
– Superficial
– Partial-thickness
– Full-thickness
Superficial Wounds
• Affect only the epidermis
– Ex. Abrasion – top layer of integument is
removed
• Dermis may
be exposed
Partial-thickness Wounds
• Involve epidermis & part of the
dermis
– Ex. Second degree burn (sunburn),
deep with
blistering
& peeling
Full-thickness Wounds
• Extends through epidermis & dermis to the
subcutaneous tissue layer
• May be further categorized as
– Subcutaneous
– Sub-dermal
** if tissues such as:
tendon,
muscle,
or bone are involved
Pressure Ulcer Stages
• National Pressure Ulcer Advisory Panel
(NPUAP) classification system
Stage I: Nonblanchable erythema of intact skin
Stage II: Partial-thickness skin loss involving
epidermis or dermis or both. The ulcer is
superficial and presents clinically as an
abrasion, blister, or shallow crater.
Pressure Ulcer Stages
Stage III: Full-thickness skin loss involving
damage or necrosis of subcutaneous tissue,
which may extend down to, but not through,
underlying fascia. The ulcer presents clinically
as a deep crater with or without undermining of
adjacent tissue.
Stage IV: Full-thickness skin loss with extensive
destruction, tissue necrosis or damage to muscle,
bone, or supporting structures (e.g., tendon,
joint capsule, etc.).
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