PERICHONDRIUM
Most pieces of hyaline and elastic cartilage are surrounded by a thin layer of dense irregular connective tissue called perichondrium. It does not exist on the surfaces of articular cartilages (that for this reason are very smooth) or around the fibrous cartilage.
Besides protecting the cartilage and producing new chondroblasts the perichondrium may repair damaged cartilage. The perichondrium contains blood vessels and as the cartilages are avascular and they supply nutrients and oxygen to the cartilage cells.
The perichondrium is formed by two layers: an outer fibrous layer and an inner chondrogenic layer. The fibrous layer contains fibroblasts and collagen fibers. It is usually embedded in the connective tissue of the structures or organs where the cartilage is placed.
The inner chondrogenic layer is attached to the cartilaginous tissue and is responsible for the appositional growth of cartilages. It contains chondroblasts, cells that behave as cartilage stem cells. After gradually differentiating into chondrocytes they are added to the already formed cartilage pieces.
Besides protecting the cartilage and producing new chondroblasts the perichondrium may repair damaged cartilage. The perichondrium contains blood vessels and as the cartilages are avascular and they supply nutrients and oxygen to the cartilage cells.
The perichondrium is formed by two layers: an outer fibrous layer and an inner chondrogenic layer. The fibrous layer contains fibroblasts and collagen fibers. It is usually embedded in the connective tissue of the structures or organs where the cartilage is placed.
The inner chondrogenic layer is attached to the cartilaginous tissue and is responsible for the appositional growth of cartilages. It contains chondroblasts, cells that behave as cartilage stem cells. After gradually differentiating into chondrocytes they are added to the already formed cartilage pieces.
The image shows a small region of the perichondrium of a hyaline cartilage.
Notice that its its outermost region (below, left) has features of a dense, connective tissue. The thicker inner region of the periosteum contains cells that are gradually differentiating into chondrocytes.
The arrow indicates the direction of the transition of chondrobllasts into chondrocytes. Notice the staining of the extracellular matrix, that changes from pink (collagen) to the bluish cartilage extracellular matrix.
