Morphology and Function of Skin Cells
In this chapter, the morphology of the cells that make the skin is discussed. To better interpret the cytological specimens collected from skin lesions, it is mandatory to know the morphology of the cells that compose the epidermis, the dermis and the sub
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Morphology and Function of Skin Cells
1.1
Introduction
In this chapter, the morphology of the cells that make the skin is discussed. To better interpret the cytological specimens collected from skin lesions, it is mandatory to know the morphology of the cells that compose the epidermis, the dermis and the subcutaneous tissue, in addition to the cells that normally reside in the dermis and finally, those produced from bone marrow that reach the skin via the bloodstream during inflammatory processes. Anatomically, the skin is made up of three main different anatomical parts: the epidermis, the dermis with the follicular and glandular adnexa, and the hypodermis, also known as the subcutis.
1.2
The Cells of the Epidermis
More than 90 % of the epidermis consists of nucleated cells that mature to become anucleate and completely keratinised cells. The remaining cells comprise melanocytes and Langerhans cells (dendritic antigen-presenting cells), which are only detectable in the case of proliferative/neoplastic processes, which occur in melanocytomas/melanomas and in cutaneous histiocytoma respectively. As epidermal cells are mainly composed of keratin, they are named keratinocytes, which make up the four strata of the epidermis: basale, spinosum, granulosum and corneum; because the latter is completely keratinised, its cells are called corneocytes (Fig. 1.1). Under normal conditions, it is possible to collect only a few corneocytes from healthy skin, as they are the only cells present on the surface of the epidermis as a result of the physiological keratinisation process.
© Springer International Publishing Switzerland 2017 F. Albanese, Canine and Feline Skin Cytology, DOI 10.1007/978-3-319-41241-2_1
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Morphology and Function of Skin Cells
Fig. 1.1 Histology of the epidermis: hyperplastic epidermis, in which the different epidermal layers are well defined: b stratum basale, s stratum spinosum, g stratum granulosum and c stratum corneum
1.2.1
Stratum Basale
The cells of the basal layer are the smaller among the keratinocytes and are also those less frequently observed on cutaneous specimens. They are cuboidal in shape in the tissue, but appear roundish when observed on cytological specimens; they measure 8–10 μm, have round nuclei, sometimes with a single evident nucleolus, and a high nucleus–cytoplasm ratio (N/C ratio). The cytoplasm is sparse and deep blue in colour. Sometimes, it can be difficult to differentiate between a basal keratinocyte and a nonactivated histiocytic cell. Two cytological characteristics of the basal keratinocytes that help the cytologist to recognise them are the presence of a thin clear halo that is interposed between the nucleus and cytoplasm and they are usually arranged in clusters (only rarely singularly; Fig. 1.2).
1.2.2
Stratum Spinosum
The cells of the spinosum layer are larger than basal ones, and are much more frequently observed as they are the most numerous nucleated cells of the epidermis. Spinous keratinocytes are large polygonal cells with angled borders and r
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