Stratum Basale and Stratum Spinosum

This image shows the stratum basale and stratum spinosum. The cells of the stratum basale are cuboidal and undergo mitosis to give rise to all of the cells in the layers above. Estimate the position of the basement membrane. How do cells in this layer interact with the basement membrane? What is the dark staining material in the cytoplasm of the cells in the stratum basale? The keratinocytes in the stratum spinosum have a prickly appearance. The "prickles" are intercellular connections that do not retract during fixation of the tissue. What mediates the interactions between these cells? The cytoplasm of these cells are filled with keratin filaments called tonofilaments. What do the prominent nucleoli in these cells indicate about the metabolic activity of these cells?

Answer: Integrins along along the basal surface are organized into hemidesmosomes. The integrins interact with structural proteins in the basement membrane. The dark staining material is melanin. The connections between cells that give rise to the prickly appearance are desmosomes. The prominent nucleoli indicate that a large amount of protein synthesis is occurring. They are producing cytokeratin, the precursor to keratin.