stratum spinosum
Summary
The stratum spinosum is the "spiny" layer of the epidermis, lying between the stratum basale and the stratum granulosum. Its living keratinocytes are linked by many desmosomes, which give the layer mechanical strength. The usual test point is the layer order from deep to superficial.
Detail
Meaning: The stratum spinosum is the epidermal layer just above the stratum basale and below the stratum granulosum. Its keratinocytes are joined by many desmosomes that anchor keratin filaments, giving the layer mechanical strength. In prepared slides the cells shrink and pull apart except at the desmosomes, so they look spiny. The cells are still living and make more keratin as they are pushed upward. Langerhans cells, which are antigen-presenting immune cells, are also found here.
On the MCAT: Expect questions that order the layers from deep to superficial: basale, spinosum, granulosum, lucidum (present in thick skin such as palms and soles), corneum. A passage may describe defective desmosomes or keratin and ask which property fails, such as cell cohesion and resistance to mechanical stress. Others ask which layer holds dividing stem cells (basale) and which holds dead, flattened cells (corneum).
Common confusion: The spines are a preparation artifact, not real projections from the cell. Students also place cell division in this layer. The main dividing layer is the stratum basale, which supplies new cells that move upward. Spinosum cells are living, unlike the dead cells of the stratum corneum.
Sources
- Principles of Anatomy and Physiology
- Human Anatomy and Physiology
- Campbell Biology
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.