Animal tissues. Connective.
Species: mouse (Mus musculus; mammal).
Technique: Masson's trichrome, 8 μm thick section, paraffin embedding.
In this image, a section of the trachea of a mouse is shown. From the top to the bottom (tracheal lumen), it can be observed hyaline cartilage, connective tissue and pseudostratified epithelium lining the free surface of the trachea. Hyaline cartilage has two parts: the innermost perichondrium and the wider mature cartilage. The extracellular matrix of the mature hyaline cartilage shows a bluish color and uniform appearance. Type II collagen is the most abundant organic molecule of the extracellular matrix, although other types of collagen and proteoglycans are present as well. The extracellular matrix is released by chondrocytes, which are found in cavities known as cartilage lacunae. The empty lacunae in this image is due to artifacts generated during the histological processing. Chondrocytes are usually associated in pairs or tetrads, forming the so-called isogenous groups, which are separated between from one another by the interterritorial matrix.
The perichondrium is a layer of dense connective tissue lining the inner surface of the mature cartilage. The external part of the perichondrium is known as fibrous perichondrium because collagen fibers are abundan. Fibroblasts and many blood vessels are also found. The deep part of the perichondrium is referred as chondrogenic perichondrium because new chondrocytes are differentiated from this layer and become integrated in the mature cartilage as they synthesize new extracellular matrix. This type of cartilage growth is known as appositional growth. When chondrocytes are able to divide, cartilage grows by interstitial growth.