Stratum Corneum Anatomy - The Key to Healthy, Attractive Skin

Stratum Corneum Anatomy - The Key to Healthy, Attractive Skin

The stratum corneum is the outermost of the 5 layers of the epidermis and is largely responsible for the vital barrier function of the skin. Before the mid-1970's the stratum corneum was thought to be biologically inert, like a thin plastic sheet protecting the more active lower layers of the skin. In the past 30 years, and especially the past 5 years, scientists have discovered that the biological and chemical activity of the stratum corneum is very intricate and complex.

Understanding the structure and function of the stratum corneum is vital because it is the key to healthy skin and its associated attractive appearance. These illustrations will take you through the important components of the stratum corneum.

Stratum Corneum Anatomy - The Corneocyte

The structure of the stratum corneum has been described as a "brick and mortar" type structure. In this analogy, the corneocytes are the bricks. A corneocyte is a protein complex that is made of tiny threads of keratin in an organized matrix. The keratin can hold large amounts of water between the fibers/threads. The stratum corneum is contains about 12-16 layers of corneocytes and each corneocyte has a mean thickness of 1 micrometer, depending on the following factors:

Stratum Corneum Anatomy - Lamellar Bodies

Lamellar bodies are formed in the keratinocytes of the stratum spinosum and stratum granulosum. When the keratinocyte matures to the stratum corneum, enzymes degrade the outer envelope of the lamellar bodies releasing types of lipids called free fatty acids and ceramides.

Stratum Corneum Anatomy - Intercellular Lipids

Free fatty acids and ceramides that are released from the lamellar bodies fuse together in the stratum corneum to form a continuous layer of lipids. Because there are two types of lipids, this layer is referred to as a lamellar lipid bilayer. This lipid bilayer plays a major role in maintaining the barrier properties of the skin and is analagous to the "mortar" in the brick and mortar model.

Stratum Corneum Anatomy - Cornified Envelope

Each corneocyte is surrounded by a protein shell called a cell envelope. The cell envelope is composed primarily of two proteins, loricirn and involucrin. These proteins contain extensive links between each other making the cell envelope the most insoluble structure of the corneocyte. The two sub-types of cell envelopes are described as "rigid" and "fragile" based on the interaction of lamellar bilayer with the cell envelope.

Stratum Corneum Anatomy - Cornified Envelope Lipids

Attached to the cell envelope is a layer of ceramide lipids that repel water. Because the lamellar lipid bilayer also repels water, water molecules are held between the cell envelope lipids and the lipid bilayer. This helps maintain the water balance in the stratum corneum by trapping water molecules instead of letting them absorb into the lower layers of the epidermis.

Stratum Corneum Anatomy - Corneodesmosomes

The "rivets" that hold the corneocytes together are specialized protein structures called corneodesmosomes. These structures are also a part of the "mortar" in the "brick and mortar" analogy. Corneodesmosomes are the major structure that must be degraded for the skin to shed in a process called desquamation.

Stratum Corneum Anatomy - Natural Moisturizing Factor (NMF)

Natural moisturizing factor (NMF) is a collection of water-soluble compounds that are only found in the stratum corneum. These compounds compose approximately 20-30% of the dry weight of the corneocyte. NMF components absorb water from the atmosphere and combine it with their own water content allowing the outermost layers of the stratum corneum to stay hydrated despite exposure to the elements. Because NMF components are water soluble, they are easily leached from the cells with water contact - which is why repeated contact with water actually makes the skin drier. The lipid layer surrounding the corneocyte helps seal the corneocyte to prevent loss of NMF.

Stratum Corneum Anatomy - Desquamation Process

The desquamation, or exfoliation, process of the stratum corneum is actually very complex and only parts of this process are fully understood. We do know that several enzymes degrade the corneodesmosomes in a specific pattern, but we don't know the exact nature of these enzymes or how they become activated to start the exfoliation process. We do know that water and pH play a significant role in the activity of these enzymes.


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