Stratum spinosum

Stratum spinosum (also known as the spiny layer) is a layer of the epidermis found between the stratum granulosum and stratum basale. Its name comes from the fact that the cells appear spiny under a microscope. This is due to the numerous desmosomes and cell shrinkage in the spinous layer, which pull the cells into a spiny shape.

The stratum spinosum is composed of eight to ten layers of keratinocytes, formed as a result of cell division in the stratum basale. The keratinocytes in the stratum spinosum begin the synthesis of keratin, a protein that gives the skin, hair, and nails their hard, water-resistant properties.

The stratum spinosum is also the site of Langerhans cells, which function as macrophages by engulfing bacteria, foreign particles, and damaged cells that occur in this layer.

Structure

The stratum spinosum is composed of polyhedral keratinocytes. These cells contain thick bundles of intermediate filaments (tonofilaments) made from pre-keratin, which are attached to desmosomes on the cell surface. The desmosomes interlock with each other, strengthening the bond between the cells.

Function

The primary function of the stratum spinosum is to allow keratinocytes to mature. These cells are pushed up from the stratum basale and continue to change as they move closer to the surface of the skin. The stratum spinosum also provides both strength and flexibility to the skin.

Clinical significance

Changes in the stratum spinosum can lead to several skin conditions, including psoriasis and skin cancer. In psoriasis, the rate of cell division in the stratum basale is abnormally high, which leads to a thickened stratum spinosum. In skin cancer, changes in the cells of the stratum spinosum can lead to the formation of a squamous cell carcinoma.

See also

• Epidermis (skin)
• Stratum basale
• Stratum granulosum
• Keratin
• Langerhans cell

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