Anatomy of the Skin

1
Anatomy of the Skin

• Rich Callahan MSPA, PA-C
• ICM I
• Summer 2009

2
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 EDC.

3
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.

4
The first function of skin is physical protection
from the environment.

• Protection From
• UV radiation
• Physical trauma
• Liquids (there is a reason were waterproof)
• Dehydration
• Sudden temperature shifts
• Microbes
• First line of defense is the stratum corneum,
  which is primarily composed of laminated keratin.

5
Definition of Keratin (From Tabers 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.

6
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?

7
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

8
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.

9
The Horny Layer huh? That term has largely
been dropped in dermatology but is getting plenty
of utilization elsewhere
10
Dermis Divided into 2 layers from top to bottom

• Superficial layer is the papillary dermis, a thin
  layer primarily of collagen fibers.
• Arranged in dome-shaped 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.

11
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.

12
(No Transcript)