Ultrastructural and Cytochemical Studies on the Remodelling of the Tracheal Cartilage

Abstract

Summary. Ultrastructural and cytochemical studies on the remodelling of the rat tracheal cartilage have been carried out. The thickness of the tracheal cartilage was constant, during the observation periods (1 to 54 days after birth). The external perichondrium of the tracheal cartilage consisted of active fibroblasts and intercellular fibrils. The inner part of this perichondrium was a chondrogenic layer, where appositional growth was taking place. On the other hand, the internal perichondrium contained fibroblast-like cells, which were nearly twice as large as the external perichondrial fibroblasts in size and were arranged in three or four layers. The cells had well developed organella and large vacuoles which contained numerous fragments of fibrils and/or glycosaminoglycan. Many cytoplasmic processes protruded to the cartilage matrix, where the intercellular fibrils were particularly irregular in arrangement.Some vacuoles included collagen fibrils. Based on an intense acid phosphatase activity in these vacuoles and other findings, the fibrils were thought to be phagocytosed collagen of the cartilage matrix. An extensive alkaline phosphatase activity was demonstrated on the plasma membrane of fibroblasts and chondroblasts in the external perichondrium.The present investigation revealed distinct functional difference between the external and internal perichondrium of the tracheal cartilage. It is resorbed at the internal perichondrium, while it appositionally grows at the external perichondrium.The fibroblastlike cells of the internal perichondrium play an essential role in resorption of the matrix in cartilage remodelling.

Perivascular cells in cartilage canals of the developing mouse epiphysis

“…Prior to matrix calcification, enlarged fibroblastic cells appeared to be involved in matrix degradation. Their ability to degrade collagenous matrices is well established (Deporter and Ten Cate, 1973;Yajima, 1976).…”

“…At sites of uncalcified matrix degradation, cells with morphological characteristics of both macrophages and fibroblasts have been identified (Schenk et al, 1967;Kobayashi and Ziff, 1975;Yajima, 1976;Silvestrini et al, 1979;Sorrel1 andWeiss, 1980, 1982). On the other hand, both mononucleated and multinucleated cells have been identified at sites of calcified-cartilage matrix degradation.…”

The cellular organization of fibroblastic cells and macrophages at regions of uncalcified cartilage resorption in the embryonic chick femur as revealed by alkaline acid phosphatase histochemistry

“…In growing rats, uncalcified tracheal cartilage rings are resorbed on the inner aspect by fibroblastic cells, while other fibroblastic cells differentiate into chondroblasts on the outer aspects of the rings (Yajima, 1976). Fibroblasts have, under some con- Fig.…”

“…In addition to their ability to produce collagen and amorphous matrix, fibroblastic cells also have the capability to degrade collagen and other extracellular components of connective tissue through the secretion of degradative enzymes or possibly by phagocytosis (Deporter, 1978;Deporter and Ten Cate, 1973;Perez-Tamayo, 1970;Svoboda and Deporter, 1980;Vaes, 1980). In growing rats, uncalcified tracheal cartilage rings are resorbed on the inner aspect by fibroblastic cells, while other fibroblastic cells differentiate into chondroblasts on the outer aspects of the rings (Yajima, 1976). Fibroblasts have, under some con- Fig.…”