TABLE Multiadhesive Glycoproteins6.5 CAM, cell adhesion molecule; ECM, extracellular matrix; EGF, epithelial growth factor; kDa, kilodaltons. Molecular Name Weight (kDa) Molecular Composition Localization Function Fibronectin 250–280 Dimer molecule formed Present in the ECM of Responsible for cell adhesion from two similar peptides many tissues and mediate migration; possesses linked by a disulfide bond binding sites for integrins, type IV collagen, heparin, and fibrin Laminin 140–400 Cross-shaped molecule Present in basal laminae Anchors cell surfaces to the basal formed from three of all epithelial cells and lamina. It possesses binding polypeptides ( chain and external laminae of muscle sites for collagen type IV, heparan  two chains) cells, adipocytes, and sulfate, heparin, entactin, laminin, Schwann cells and integrin receptors on the cell surface Tenascin 1,680 Giant protein formed Embryonic mesenchyme, Modulates cell attachments to the from six chains connected perichondrium, perio-ECM; possesses binding sites for by disulfide bonds steum, musculotendi-fibronectin, heparin, EGF-like nous junctions, wounds, growth factors, integrins, and CAMs tumors Osteopontin 44 Single-chain glycosylated Bone Binds to osteoclasts; possesses polypeptide binding sites for calcium, hydroxyapatite, and integrin receptor on the osteoclast membrane Entactin/ 150 Single-chain rodlike Basal lamina–specific Links laminin and type IV collagen; Nidogen sulfated glycoprotein protein has binding sites for perlecan and fibronectin
FIGURE 6.19 • Fibroblasts in connective tissue. a. Photomicrograph of a connective tissue specimen in a routine H&E-stained, paraffin-embedded preparation shows nuclei of fibroblasts (F ). 600. b. During the repair process of a wound, the activated fibroblasts (F ) exhibit more basophilic cytoplasm, which is readily observed with the light microscope. 500.
Macrophages are phagocytotic cells derived from monocytes.
Connective tissue macrophages, also known as tissue histiocytes, are derived from blood cells called monocytes. Monocytes migrate from the bloodstream into the connective tissue, where they differentiate into macrophages.
In the light microscope and with conventional stains, tissue macrophages are difficult to identify unless they display obvious evidence of phagocytotic activity—for example, visible ingested material within their cytoplasm. Another feature that assists in identifying macrophages is an indented or kidney-shaped nucleus (Fig. 6.22a). Lysosomes are abundant in the cytoplasm and can be revealed by staining for acid phosphatase activity (both in the light microscope and with the TEM); a positive reaction is a further aid in identification of the macrophage. With the TEM, the surface of the macrophage exhibits numerous folds and fingerlike projections (Fig. 6.22b). The surface folds engulf the substances to be phagocytosed.
FIGURE 6.20 • Electron micrograph of fbroblasts. The processes of several fibroblasts are shown. The nucleus of one fibroblast is in the upper right of the micrograph. The cytoplasm contains conspicuous profiles of rER. The cisternae of the reticulum are distended, indicating active synthesis. The membranes of the Golgi apparatus (G) are seen in proximity to the rER. Surrounding the cells are collagen fibrils (CF), almost all of which have been cut in cross section and thus appear as small dots at this magnification.
11,000.