Anatomy of the Skin
Rich Callahan MSPA, PA-C
ICM I
Summer 2009
Before Pathophysiology Comes Anatomy
• One of the keys to your knowledge of skin
disease is understanding the anatomy of the
skin and the particular way a given skin
disease affects it.
• Anatomy of skin also important during
dermatologic procedures like skin biopsy,
excisions and ED&C.
Skin Anatomy – Basic Overview
• Skin essentially composed of 3 layers: epidermis,
dermis and subcutis (subcutaneous tissue.)
• Epidermis is outermost layer – primarily
functional and protective. Subdivided into five
layers which migrate upwards and whose purpose
is ultimately to form the end layer, or stratum
corneum – the outer layer of dead cells that
protects us from our environment. Process is
called keratinization.
The first function of skin is physical protection from
the environment.
Protection From:
• UV radiation
• Physical trauma
• Liquids (there is a reason we’re waterproof)
• Dehydration
• Sudden temperature shifts
• Microbes
First line of defense is the stratum corneum, which
is primarily composed of laminated keratin.
Definition of Keratin
(From Taber’s Medical Dictionary)
• “A family of durable protein polymers that are
found only in epithelial cells. They provide
structural strength to skin, hair and nails. The
fibrous protein is produced by keratinocytes.”
• Thoroughly understanding the process of
keratinization which takes place in the epidermis
will unlock answers for many skin diseases
because so many of them are disorders of it.
Keratin
• Comes from the Greek word “keras” for
horn.
• The outer layer of epidermis, the stratum
corneum, gets its name from the Latin word
for horn.
• My first question was: Where were the
people who make up these names seeing a
horn?
Perhaps it is because the phenomenon of cutaneous
horn is the most overt keratinizing process
• Multiple underlying pathologies can cause a
cutaneous horn:
• Verruca vulgaris (common wart)
• Actinic Keratosis (AK)
• Squamous Cell Carcinoma (SCC)
• Seborrheic Keratosis (SK)
• Psoriasis
• Sometimes no underlying pathology is found
Layers of the Epidermis: From Inside to
Outside
Basal (bottom) layer: A single layer of cells arranged like
columns – which divide and turn into the…
• Spinous layer (stratum spinosum)whose cells,
keratinocytes, begin to form keratin, an insoluble protein
critical in later stages.
• Granular layer (str. Granulosum) is where cells flatten out
and stretch into the
• Stratum lucidum and eventually die to form the
• Stratum corneum. Old school dermatologists called this
the “horny layer” (heh, heh.) Composed of laminated
keratin.
The “Horny Layer” huh? That term has largely been
dropped in dermatology but is getting plenty of
utilization elsewhere…
Dermis – Divided into 2 layers from top to
bottom
• Superficial layer is the
papillary dermis, a
thin layer primarily of
collagen fibers.
• Arranged in domeshaped inclusions
jutting into base of,
and feeding small
blood vessels into, the
epidermis above.
• Deep layer is
Reticular dermis –
composed of thickly
layered collagen
fibers.
• Contains numerous
small vessels,
cutaneous nerves and
apocrine glands.
Subcutis – The Deepest Layer of skin (AKA
superficial fascia or hypodermis)
• A layer of fat loosely marbled with
connective tissue and the deeper parts of
apocrine glands.
• Important route for small to medium-sized
blood vessels, sensory and autonomic
nerves, lymphatics.
• Deep to this is the deep fascia then skeletal
muscle.