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Stratum spinosum
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<p>The stratum spinosum (or spinous layer/prickle cell layer) is a layer of the <a href="/facts/Epidermis_(skin)/JvRABubP">epidermis</a> found between the <a href="/facts/Stratum_granulosum/fVgEs1PX">stratum granulosum</a> and <a href="/facts/Stratum_germinativum/4UwmB3Qm">stratum basale</a>. This layer is composed of polyhedral <a href="/facts/Keratinocyte/drqhJjuS">keratinocytes</a>. These are joined with <a href="/facts/Desmosome/yoolx79n">desmosomes</a>. Their spiny (Latin, spinosum) appearance is due to shrinking of the <a href="/facts/Microfilament/TR7qU9Jv">microfilaments</a> between desmosomes that occurs when stained with <a href="/facts/H%2526E/TEa26lJ7">H&E</a>. <a href="/facts/Keratinization/tBh0bY47">Keratinization</a> begins in the stratum spinosum, although the actual keratinocytes begin in the <a href="/facts/Stratum_basale/4UwmB3Qm">stratum basale</a>. They have large pale-staining nuclei as they are active in synthesizing fibrillar proteins, known as <a href="/facts/Cytokeratin/HvVsDD3X">cytokeratin</a>, which build up within the cells aggregating together forming <a href="/facts/Tonofibrils/p56gq0jP">tonofibrils</a>. The tonofibrils go on to form the desmosomes, which allow for strong connections to form between adjacent keratinocytes. The stratum spinosum also contains <a href="/facts/Langerhans_cell/4UoNJ8K7">Langerhans cells</a>, which functions as a macrophage by engulfing bacteria, foreign particles, and damaged cells that occur in this layer. </p>