In contrast, where only strength is required, collagen fibers are more numerous and densely packed. Also, the cells are relatively sparse and limited to the fiber-forming cell, the fibroblast (Fig. 4.2b). This type of connective tissue is described as dense connective tissue.
Bone and cartilage are two other types of connective tissue characterized by the material associated with collagen (i.e., calcium [bones] and hyaluronan [cartilage]). Again, in both of these tissues, it is the extracellular material that characterizes the tissue, not the cells.
FIGURE 4.1  Simple epithelia. a. An H&E–stained section showing a pancreatic duct lined by a single layer of contiguous cuboidal epithelial cells. The free surface of the cells faces the lumen; the basal surface is in apposition to the connective tissue. 540. b. An H&E–stained section showing a single layer of tall columnar epithelial cells lining the gallbladder. Note that the cells are much taller than the lining cells of the pancreatic duct. The free surface of the epithelial cells is exposed to the lumen of the gallbladder, and the basal surface is in apposition to the adjacent connective tissue. 540.
FIGURE 4.2  Loose and dense connective tissue. a. Mallory-Azan–stained specimen of a section through the epiglottis, showing the lower part of its stratified epithelium (Ep), subjacent loose connective tissue (LCT ), and dense connective tissue (DCT ) below. Loose connective tissue typically contains many cells of several types. Their nuclei vary in size and shape. The elongated nuclei most likely belong to fibroblasts. Because dense connective tissue contains thick collagen bundles, it stains more intensely with the blue dye. Also, note the relatively fewer nuclei. 540. b. A Mallory-stained specimen of dense connective tissue, showing a region composed of numerous, densely packed collagen fibers. The few nuclei (N) that are present belong to fibroblasts. The combination of densely packed fibers and the paucity of cells characterizes dense connective tissue. Relatively few small blood vessels (BV ) are shown on this section. 540.
To function efficiently to effect movement, most muscle cells are aggregated into distinct bundles that are easily Muscle tissue is categorized on the basis of a functional distinguished from the surrounding tissue. Muscle cells property, the ability of its cells to contract. are typically elongated and oriented with their long axes Muscle cells are characterized by large amounts of the in the same direction (Fig. 4.3). The arrangement of contractile proteins actin and myosin in their cytoplasm nuclei is also consistent with the parallel orientation of and by their particular cellular arrangement in the tissue. muscle cells.
FIGURE 4.3  Muscle tissue. a. An H&E–stained specimen showing a portion of three longitudinally sectioned skeletal muscle fibers (cells). Two striking features of these large, long cells are their characteristic cross-striations and the many nuclei located along the periphery of the cell. 420. b. A Mallory-stained specimen showing cardiac muscle fibers that also exhibit striations. These fibers are composed of individual cells that are much smaller than those of skeletal muscle and are arranged end to end to form long fibers. Most of the fibers are seen in longitudinal array. The organized aggregation–that is, the parallel array of the fibers in the case of muscle tissue, allows for collective effort in performing their function. Intercalated disks (arrows) mark the junction of adjoining cells. 420.