Squamous cell layer overlying the basal cell layer is

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Squamous Cell LayerOverlying the basal cell layer is a layer of theepidermis that is 5-10 cells thick and known asthe squamous cell layer or stratum spinosum(Murphy, 1997).The squamous layer is composed of a variety ofcells that differ in shape, structure, andsubcellular properties depending on theirlocation.Suprabasal spinous cells, for example, arepolyhedral in shape and have a rounded nucleus,whereas cells of the upper spinous layers aregenerally larger in size, become flatter as theyare pushed toward the surface of the skin, andcontain lamellar granules (Chu, 2008).Lamellar granules are membrane-boundorganelles containing glycoproteins, glycolipids,phospholipids, free sterols, and a number of acidhydrolases, including lipases, proteases, acidphosphatases, and glycosidases.The abundance of hydrolytic enzymes indicatesthat the lamellar granules are a type of lysosome.Although the lamellar granules primarily areactive in cells at the interface between thegranular and cornified layers, they also function incells of the upper spinous layer to deliverprecursors of stratum corneum lipids into theintercellular space (Haake & Hollbrook, 1999).Intercellular spaces between spinous cells arebridged by abundant desmosomes that promotemechanical coupling between cells of theepidermis and provide resistance to physicalstresses.Organized concentrically around the nucleus,keratin filaments in the cytoplasm are bound todesmosomal plaques at one end and remain freeat the end closer to the nucleus (Murphy, 1997).The desmosomal plaques are composed of sixpolypeptides found on the cytoplasmic side of thecell membrane that are important in theregulation of the calcium required fordesmosomal assembly and maintenance.The spine-like appearance of the numerousdesmosomes along cell margins is where thestratum spinosum derives its name (Chu, 2008).Gap junctions are another type of connectionbetween epidermal cells. Essentially forming anintercellular pore, these junctions allow forphysiologic communication via chemical signalsthat is vital in the regulation of cell metabolism,growth, and differentiation (Caputo & Peluchetti, 1977).Granular LayerThe most superficial layer of the epidermiscontaining living cells, thegranular layerorstratum granulosum, is composed of flattenedcells holding abundant keratohyaline granules intheir cytoplasm. These cells are responsible forfurther synthesis and modification of proteinsinvolved in keratinization (Chu, 2008).The granular layer varies in thickness inproportion to that of the overlying horny cell layer.For example, under thin cornified layer areas, thegranular layer may be only 1-3 cell layers inthickness, whereas under the palms of the handsand soles of the feet the granular layer may be 10times this thickness.

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Term
Fall
Professor
professor_unknown
Tags
Anatomy, Human Anatomy, abdominopelvic cavity, Pelvic cavity

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