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We examined the distribution of fibronectin and collagen types I and III in human fetuses under a confocal laser scanning microscope using immunohistochemical staining (at 16, 20, 24, 28, 32 weeks' gestation). The collagen types I and III form the collagenous matrix components in the connective tissue of the parotid and submandibular glands. These extracellular matrix components were detected at various stages around the terminal portion and in the capsule-like connective tissue of the parotid and submandibular glands. However, the extracellular matrix components in the connective tissue around the terminal portion had a stronger reaction than those in the capsule-like connective tissue found on the fringe of the terminal portion. The collagen type I of the parotid gland at 16 weeks' gestation had a weaker reaction than that of the submandibular gland. When results of the reaction at other stages and other extracellular matrix components of the two salivary glands were compared, collagen type I appeared as early as at 16 weeks' gestation in either gland. Since collagen type I serves as the core connective tissue, these observations suggest that the formation of connective tissue around the parotid gland occurs before or after 16 weeks' gestation lagging behind that of the submandibular gland., (Copyright 2003 S. Karger AG, Basel)

Parotid and submandibular glands from human fetuses (16, 20, 24, 28, 32 weeks of gestation) were examined under a scanning electron microscope. Changes were found in the arrangement of collagen fibers in the connective tissue surrounding the salivary gland. In particular, several layers around the salivary gland were formed by a collagen network structure. These structures, although in varied arrangements, were recognizable in each stage of fetal growth. They are thought to play the role of a "cushion" against pressure created by accumulation of granules because of the reflex activity of myoepithelial cells during secretion. These structural changes are related to the mechanical performance of granule formation in the salivary gland and secretion during the development of the fetus.

Scanning electron microscopy was used to examine the chordae tendineae in young (approximately 20 years old) and old (approximately 85 years old) cadavers. A network of collagen fibrils was observed in both the outer and intersurface layers of the chordae tendineae. In young subjects, a regularly arranged series of disconnected collagenous ring-like structures surrounded the longitudinal collagen bundles forming the inner core of the chordae tendineae. In old subjects, the ring-like structures of the chordae tendineae were few or absent. The ring-like structures may be related to reducing mechanical stress during the tightening, twisting, and slackening of the chordae tendineae., (Copyright 2002 Wiley-Liss, Inc.)