Stratum spinosum

In the skin, the stratum spinosum is a multi-layered arrangement of cuboidal cells that sits beneath the stratum granulosum. Adjacent cells are joined by desmosomes, giving them a spiny appearance when the cells shrink during the staining process while the desmosomes hold firm. Their nuclei are often darkened (a condition called pyknosis), which is an early sign of cell death. Their fate is sealed because the nutrients and oxygen in interstitial fluid have become exhausted before the fluid is able to reach them by diffusion.

Cells of the stratum spinosum actively synthesize intermediate filaments called cytokeratins, which are composed of keratin. These intermediate filaments are anchored to the desmosomes, joining adjacent cells to provide structural support, helping the skin resist abrasion.