STRATUM GRANULOSUM

In microscopic views of skin, the 'stratum granulosum' layer of the epidermis lies between the stratum spinosum below and the stratum lucidum above in stratified squamous keratinized thick skin of palms and soles. Thin skin, which covers the rest of the body, lacks a definite stratum lucidum and stratum granulosum.
The 'stratum granulosum' layer typically contains 1 to 3 rows of squamous cells with many small basophilic granules in their cytoplasm. These prominent 'keratohyalin granules' are not membrane-bound. Keratin bundles pass through the granules, which contain a phosphorylated histidine-rich protein and other cystine-rich proteins. The cells in the stratum granulosum contain also large amounts of filaggrin, a protein thought to serve in bundling keratin. Membrane-coated lamellar granules (0.1 to 0.3 micrometers) are also present and contain lipids. The lamellar granules are exocytosed in this layer to generate a waterproof barrier. This waterproofing also prevents life-sustaining nutrient transport and thus leads to the characteristic cell death of the outer layers of keratinized epithelium.
This is the highest layer in the epidermis where living cells are found, the stratum lucidum above appears clear due to auto-digestion of cellular organelles.
This layer also includes 'lamellar granules' and 'tonofibrils'.
References:
1. L.P. Gartner and J.L. Hiatt, Color Textbook of Histology, 3rd ed., Elsevier, 2007, p 331-336.
2. Junqueria and Carneiro, Basic Histology Text & Atlas, 11th ed., McGraw-Hill, 2005, p 361.

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External links

★ - "Integument: thick skin"