Filament histology

The nervous system contains an unusually diverse set of intermediate filaments (Table 8-2) with distinctive cellular distributions and developmental expression [21, 22]. Despite their molecular heterogeneity, all intermediate filaments appear as solid, rope-like fibers 8-12 nm in diameter. Neuronal intermediate filaments (NFs) can be hundreds of micrometers long and have characteristic sidearm projections, while filaments in glia or other nonneuronal cells are shorter and lack sidearms (Fig. 8-2). The existence of NFs was established long before much was known about their biochemistry or properties. As stable cytoskeletal structures, NFs were noted in early electron micrographs, and many traditional histological procedures that visualize neurons are based on a specific interaction of metal stains with NFs. 

Histologically, the disease is characterized by a loss of adhesion between suprabasal keratinocytes (acantholysis) and abnormal keratinisation (dyskeratosis) of the epidermis. In HHD, acantholysis is the most prominent histological feature while in the clinically related Darier disease (OMIM 124200), dyskeratosis is much more apparent. Ultrastructural analysis of acantholytic cells reveals perinuclear aggregates of keratin filaments that have retracted from desmosomes (Harada et al., 1994 Hashimoto et al., 1995 Metze et al., 1996). 

Locker, R. H., and Leet, N. G. (1976). Histology of highly-stretched beef muscle. IV. Evidence for movement of gap filaments through the Z-line, using the N2-line and M-line as markers./ Ultrastruct. Res. 56, 31-38. 

Figure 8.9 Ultrastructure of the myofibril indicating the various bands observed microscopically. The I bands are largely the thin filaments, whereas the A bands are the thick filaments with partially overlapping thin filaments. The thick filaments are about 1600 nm in length, whereas the thin filaments are about 1000 nm in length. The Z line is a transverse tubule that serves to bind the thin filaments together. Thick filaments are bound together by a protein seen as a dark line (M line) in the middle of the H zone. (Reproduced by permission from Snell RS. Clinical and Functional Histology for Medical Students. Boston Little, Brown, 1984,...

In all the actin-based motility systems, and especially skeletal, cardiac and smooth muscle, contraction is initiated primarily by an increase in cytoplasmic [Ca +]. However, the major differences in histology and function of these muscle types are associated with great variety in how contraction is controlled. Smooth muscle especially differs from the model presented for skeletal muscle. Skeletal muscle is activated by Ca + released from SR in response to sarcolemmal action potentials. Ca + exerts its effect by binding to troponin on the thin filaments, which reverses the tropomyosin inhibition of cross-bridge formation. 

Intermediate filament protein (IFF) analysis has been an important cornerstone of immunohistochemical evaluation for nearly 20 years. In general terms it can still be stated with accuracy that immunostains for keratins, vimentin, desmin, neurofilament proteins, and glial fibrillary acidic protein (GFAP) are broadly capable of distinguishing between histologically similar classes of neoplasms with dissimilar lineages. ... 

Osborn M. Intermediate filaments as histologic markers an overview. J Invest Dermatol. 1983 81(Suppl l) 104s-109s. 

The histopathologic appearance of MRT is a densely cellular neoplasm composed of sheets or cords of cells with large vesicular round or oval nuclei, prominent central eosinophilic nucleoli, and abundant eccentric eosinophilic cytoplasm (Fig. 17.26). Histologic variability is typical, and some cases have smaller numbers of characteristic rhabdoid cells or display a primitive small blue cell pattern, a myxoid background, a lack of cellular cohesion, increased collagen deposition between bands of tumor cells, and scattered non-neoplastic osteoclastlike giant cells. Occasionally cases have focal epithelial areas. Mitoses are frequent. Electron microscopy reveals cytoplasmic whorls of intermediate filaments, which correspond to the eosinophilic globules of cytoplasm in the classic rhabdoid cells. 

To investigate their biocompatibifity with woimded tissue, SELP-7 and SELP-5 fibrous meshes were appfied to porcine dermal wounds. No adverse effects were observed and the wounds (2x2 cm partial and fiill dermal thickness) were completely epithelialized after 14 days. Histological evaluation revealed that some SELF filaments had been incorporated into the healing tissue. Similar results were observed with SELF sponges (2). 

Perisinusoidal Ito cells (fat-storing cells, hepatic h-pocytes, vitamin A-storing cells) are the primary matrix-producing cells in liver fibrosis. They are difficult to visualize in standard histological preparations but can be identified in sections of rat liver by immunohistochemical detection of the intermediate filament protein desmin this protein is not expressed by other sinusoidal cells (Yokoi etal. 1984, Burt etal. 1986). 

The histological structure of compact bone is more complex than that of cancellous bone, and it is therefore not surprising that compact bone appears only later in the ontogenic order. Compact bone is made of a system of tubes, disposed parallel to the long axis of bone. Each tube (Havers canal) is made of a series of tightly packed concentric lamellae. The lamellae contain lacunae with osteocytes and fine canaliculi containing the filamentous processes derived from the osteocyte. The center of the Havers canal forms a small cavity containing connective tissue and one or two small blood vessels [2]. 

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