Quick Facts
The stratum granulosum, or granular layer of epidermis, is the layer of the epidermis between the stratum lucidum and stratum spinosum, which consists of cells containing keratohyalin granules. The stratum lucidum, or clear layer of epidermis, is the translucent layer of the epidermis, just beneath the stratum corneum, particularly noticeable in the thick skin of the palms and soles. The stratum corneum, or horny layer, is the outermost layer of the epidermis, consisting of cells that are dead and desquamating (Dorland, 2011).
Related parts of the anatomy
Structure/Morphology
The superficial layers of the epidermis are composed of the stratum corneum, stratum lucidum, and stratum granulosum. The stratum corneum is composed of about 20 layers of flattened, or squamous, highly keratinized cells. Cells in this layer lack desmosomes; thus, the cells easily dissociate and desquamate from the skin surface (Arda, Goksugur and Tuzun, 2014).
The stratum lucidum is only present in thick skin, i.e., the plantar and palmar skin. It appears as a translucent layer of about five rows of squamous cells.
The stratum granulosum has 1–5 cellular layers of flattened polygonal granulated cells. It is so called as it contains granules of filaggrin that cross links with keratin. Keratinocytes in the upper layer of the stratum granulosum also contain lamellar bodies, rich in glycolipids. The cells discharge this lipid-rich substance into the intercellular spaces, via exocytosis, thus forming the major epidermal permeability barrier of the skin (Arda, Goksugur and Tuzun, 2014).
Function
The epidermis is continuously renewing its epithelial layers. This ensures that the epidermis acts as the body's first line of defense, acting as a barrier against environmental hazards, such as physical, chemical, biochemical and immunological threats (Baroni et al., 2012).
References
Arda, O., Goksugur, N. and Tuzun, Y. (2014) 'Basic histological structure and functions of facial skin', Clin Dermatol, 32(1), pp. 3-13.
Baroni, A., Buommino, E., De Gregorio, V., Ruocco, E., Ruocco, V. and Wolf, R. (2012) 'Structure and function of the epidermis related to barrier properties', Clin Dermatol, 30(3), pp. 257-62.
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
