Gartner_BRS Cell Biology & Histology, 9e

Chapter 12 Skin

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B. Layers of the epidermis ( Fig. 12.1 and Table 12.1 )

Stratum corneum Stratum lucidum

Stratum granulosum

Epidermis

Stratum spinosum Langerhans cell Melanocyte Merkel cell Stratum basale Basement membrane Blood vessel

Dermis

FIGURE 12.1. Layers of epidermis. The stratum lucidum is present only in thick skin and is best observed in skin from the palms of the hands and the soles of the feet. Melanocytes lie between keratinocytes in the stratum basale. (Adapted with permission from Ham AH, Cormack DH. Histology . 8th ed. J.B. Lippincott; 1979:625.)

Table 12.1 Histologic Features of Skin

Divisions Layers Epidermis a Stratum corneum

Characteristics

The most superficial layer of the epidermis Many flattened dead “cells” called squames, packed with keratin filaments Surface cells are continuously sloughed. Indistinct homogeneous layer of dead keratinocytes; present only in thick skin Cells lack nuclei and organelles. Cytoplasm is packed with keratin filaments and eleidin. Flattened nucleated keratinocytes arranged in three to five Cells contain many coarse keratohyalin granules associated with tonofilaments. Membrane-coating (waterproofing) granules are occasionally present. Several layers of keratinocytes, called prickle cells because they appear spiny due to desmosomes between the cells (intercellular bridges) Keratinocytes in superficial region contain membrane-coating (waterproofing) granules. Keratinocytes are mitotically active, especially in deeper layers. Epidermal dendritic (Langerhans) cells are dispersed in this layer. Deepest layer of the epidermis, composed of a single layer of tall cuboidal keratinocytes Keratinocytes are mitotically active. Melanocytes and Merkel cells are dispersed in this layer. Superficial thin layer of connective tissue that interdigitates with epidermal ridges of the epidermis Forms dermal papillae where tactile (Meissner) corpuscles and capillary loops may be found Composed of loose connective tissue Extensive part of the dermis, deep to the papillary layer Composed of dense irregular connective tissue with thick bundles of

Stratum lucidum

Stratum granulosum

Stratum spinosum

Stratum basale (stratum germinativum)

Dermis b

Papillary layer

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Reticular layer

collagen (type I) fibers and elastic fibers Arteries, veins, and lymphatics are present.

Location of sweat glands and their ducts, lamellar (Pacinian) corpuscles, and nerves In thin skin, contains hair follicles, sebaceous glands, and arrector pili muscles

a Stratified squamous keratinized epithelium. b Connective tissue.