In the adults, the growth rate slows with age. The healing mechanism of the different cells if damaged is different than that of the younger ones. If a cartilage is damage in the adults, the chondrocytes which are still surviving secrete more extracellular matrix in order to heal the damaged cartilage. The chondrocytes cells are present in the cartilage, and they function to maintain the cellular matrix of the cartilage.
I believe that on the Naive B-cell the antibodies exist as transmembrane proteins. A naive b-cell is a type of b-cell that has not been exposed to an antigen. When exposed it becomes either a memory B cell or a plasma cell that secrete antibodies specific to the antigen that was originally bound.
