Figure 19–44 elastic fibers. these scanning electron micrographs show (a) a low-power view of a segment of a dog’s aorta and (B) a high-power view of the dense network of longitudinally oriented elastic fibers in the outer layer of the same blood vessel. all the other components have been digested away with enzymes and formic acid. (From K.S. haas et al., Anat. Rec. 230:86–96, 1991. With permission from Wiley-Liss.) elastin and is essential for the integrity of elastic fibers. Mutations in the fibrillin gene result in Marfan’s syndrome, a relatively common human disorder. In the most severely affected individuals, the aorta is prone to rupture; other common effects include displacement of the lens and abnormalities of the skeleton and joints. Affected individuals are often unusually tall and lanky: Abraham Lincoln is suspected to have had the condition.
Fibronectin and Other Multidomain Glycoproteins help Organize the Matrix
In addition to proteoglycans, collagens, and elastic fibers, the extracellular matrix contains a large and varied assortment of glycoproteins that typically have multiple domains, each with specific binding sites for other matrix macromolecules and for receptors on the surface of cells (Figure 19–46). These proteins therefore contribute to both organizing the matrix and helping cells attach to it. Like the proteoglycans, they also guide cell movements in developing tissues, by serving
Figure 19–45 Stretching a network of elastin molecules. the molecules are joined together by covalent bonds (red) to generate a cross-linked network. In this model, each elastin molecule in the network can extend and contract in a manner resembling a random coil, so that the entire assembly can stretch and recoil like a rubber band.