Many events occur concurrently during the initiation of the secondary ossification center in the cartilaginous epiphyses of long bones. We have investigated the chronology of interactions between the vascular system and epiphyseal chondrocytes by culturing explanted heads of femurs and humeri from pre- and neonatal @entity95 on the chorioallantoic membrane (CAM) of growing @entity1573 embryos. We confirmed that, on the whole, the epiphyseal cartilage was resistant to vascular invasion, whereas the physeal growth plate was resorbed. However, new CAM-derived cartilage canals occasionally penetrated through the articular surface. This caused death of those chondrocytes in the immediate vicinity of the canal but no further reaction. If explants already contained a @entity2721 and were halved prior to culture, CAM-derived vessels were attracted to the spongiosa. From there they pushed into the uncalcified cartilage, indicating that calcification was not a prerequisite for vascular invasion. Where at least two vessels were in apposition, a new pseudo-ossification center was initiated: chondrocytes became @entity1184 and the matrix calcified. This suggests that cumulative release of diffusible factors from more than one vessel was the trigger for chondrocyte @entity1184 , which, in turn, led to the initiation of the @entity2721 . CAM cultures thus provide an experimental model for both the quiescent angiogenesis of cartilage canal formation and the reactionary angiogenesis associated with chondrocyte @entity1184 . By exploiting the different anatomy of CAM-derived vascularity, events that occur concurrently in vivo can be specially separated in CAM culture.

Initiation of the XXXX in long bones: chronology of interactions between the vascular system and the chondrocytes.

@entity1184 :: ('MESH:D006984', 'Disease') :: ['hypertrophic', 'hypertrophy'] @entity1573 :: ('9031', 'Species') :: ['chick'] @entity95 :: ('9986', 'Species') :: ['rabbits'] @entity2721 :: ('MESH:D018213', 'Disease') :: ['bony epiphysis']
@entity2721 :: (MESH:D018213,Disease) :: ['bony epiphysis']
