Which of the following epidermal layer is dead layer?
Ans. is 'c' i.e., Stratum corneum Epidermal layers (from deep to superficial)Basal cell layer (Stratum basale or stratum germinatum)* Made up of single layer of columnar epithelial cells. It is the deepest layer of epidermis which is attached to basement membrane.* Continuously multiplying layer by mitosis and each basal cell produces keratinocytes which moves up, the so called epidermal proliferation unit (Basal cell plus keratinocytes produce by it).* Melanocytes are also found in basal layer and project their dendrites into superficial epidermis where they transfer melanosomes (melanin packed in membrane bound granules) to keratinocytes which in-turn contain the majority of cutaneous pigment. 36 Keratinocytes per melanocytes giving rise to epidermal melanin unit (melanocyte plus keratinocytes it supplies).Stratum spinosum (Prickle cell layer)* As the cell from basal layer are gradually displaced superficially by newly formed cell, columnar cells become flat and polygonal. These polygonal cells are connected to each other by desmosomal bridges that are seen as spines under ordinary microscope - Hence this layer is referred to as stratum spinosum.* These spines (produced by desmosomal bridges) give prickly appearance to this layer, therefore stratum spinosum is also referred as prickle cell layer. Cell in upper part of spinous layer contain organelles called lamellar granules.* Stratum basal and stratum spinosum, together these two are called stratum malpighii (malpighian layer).Stratum granulosum (granule cell layer)* With further maturation and upward movement, keratinocytes take diamond-shape. Characteristic feature of this layer is presence of keratohyaline granules within the cells. Keratohyaline granules contain a protein filaggrin which is responsible for aggregation of keratin filaments.* This layer also contains membrane coating granules or oadland bodies which contains lipids that are responsible for barriers function of this layer.Stratum corneum (Horny layer)* This is the most superficial layer of epidermis and skin. Cells are fully keratinized and end up as anucleate dead cells. Therefore, stratum corneum is dead layer.* Stratum corneum is last to develop - Therefore in premature newborn it is absent.Stratum lucidum* Between the stratum granulosum and corneum of palm and sole, there is an additional layer called stratum lucidum. Therefore, in palm and soles there are 5 layers (instead of four) in epidermis.* The cell degenerates as they move to stratum lucidum (from deeper layer). This layer contains reffactile droplets of eleidin.
Stratum basale
Stratum spinosum
Stratum corneum
Stratum granulosum
Anatomy of Skin