Lamina lucida

The basement membrane (BM) is a continuous layer of extracellular materials, forming a boundary between the basal layer of the epithelium and the connective tissues of the lamina propria and the submucosa. It can be subdivided into the lamina lucida,... 

Fig. 1. (A) Scanning electron micrograph of human skin. The epidermis has pulled away from part of the basement membrane. (B and C) Transmission electron micrograph through the epidermal-dermal junction of human skin. Keratinocytes (KF) are the cells in the human epidermis. LD, The lamina densa of the basement membrane LL, the lamina lucida. Typical anchoring fibrils (AF) formed from type VII collagen are shown at higher power in C. Courtesy of Dr. K. Holbrook, University of Washington.

The boundary between the epidermis and dermis is a basement membrane (see Figure 3.9) it can be described by four planes proceeding from the basal epidermal side to the dermal side (a) the border of the basal ker-atinocyte (b) the lamina lucida, an electron lucent layer that lies beneath the epidermis (c) the lamina densa, an electron dense layer also known as the basal lamina and (d) the reticular lamina or subepidermal zone consisting of connective tissue immediately below the epidermis. The mechanical continuity at the epidermal-dermal junction, as well as between keratinocytes, is key to normal transfer of internal and external mechanical forces between the epidermis and dermis. 

The basement membrane (BM) is a continuous layer of extracellular materials and forms a boundary between the basal layer of epithelium and the connective tissues of the lamina propria and the submucosa. The BM can be subdivided into the a) lamina lucida, b) lamina densa, and c) a sublayer of fibrous material. The functions of the BM include providing 1) adherence between epithelium and underlying connective tissues 2) mechanical support for epithelium and 3) a barrier to the passage of cells and some large molecules. 

FIGURE 1 Cellular and tissue alterations induced by HD that are proposed to result in blister formation. HD can have many direct effects, such as alkylation of proteins and membrane components (Memb), as well as activation of inflammatory cells. One of the main macromolecular targets is DNA, with subsequent activation of poly(ADP-ribose) polymerase (PARP). Activation of PARP can initiate a series of metabolic changes culminating in protease activation. Within the tissue, the penultimate event is the epidermal-dermal separation that occurs in the lamina lucida of the basement membrane zone. Accompanied by a major inflammatory response and changes in the tissue hydrodynamics (Hyd), fluid fills the cavity formed at this cleavage plane and presents as a blister. 

Hemidesmosomes (HDs) are membrane-associated adhesive junctions linked to the filamentous networks of the epithelial cell cytoskeleton and the lamina lucida ( light green/ dark blue region in Fig. 5.1). The cytoskeleton of all mammalian cells is composed of three kinds of filaments microfilaments, intermediate filaments and microtubules. Microfilaments... 

Leakage of cell contents and debris into lamina lucida of the basement membrane. 

Ultrastructurally, the basement membrane is composed of three distinct zones the lamina lucida (or rara), the lamina densa and the lamina fibroreticularis (see Figure 2). 

The lamina lucida is an electronlucent layer adjacent to the plasma membrane of the adherent basal epidermal cell and is composed largely of laminin. Bullous pemphigoid antigen (a disease-specific glycoprotein recognized by an antibody... 

The lamina densa is an electron-dense layer situated at the stromal side of the lamina lucida and is composed of type IV collagen and the KF-1 antigen, a non-collagenous antigen which appears to be restricted to the basement membranes of stratified squamous epitheliaandis completely absent in patients with the autosomal recessive condition of dystrophic epidermolysis bullosa (Katz, 1984 Burgeson, 1988). Recent evidence... 

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