Vascularization and cartilage mineralization of the thyroid cartilage of Munich minipigs and domestic pigs

Abstract

Thyroid cartilages of Munich minipigs and domestic pigs were investigated by polychrome sequential labeling, radiography, intravascular injections, histologic examination and scanning electron microscopy in order to gain further insight into the process of vascularization and cartilage mineralization. The relationship between vascularization and cartilage mineralization has only been studied in chondroepiphyses of long bones. Vessels branch off the perichondrial vascular network and enter parts of the thyroid cartilage with a large transverse diameter. Cartilage canals, which are perichondral invaginations, contain an arteriole, a venule, a capillary network and connective tissue. The capillaries form a glomerulus-like structure deep in the matrix of the cartilage. Neighbouring cartilage canals do not display any anastomoses. Cartilage mineralization occurs in large areas of the thyroid cartilage. It is only found in the interterritorial extracellular matrix. Mineralization of the cartilage is evident in areas supplied with cartilage canals as well as in non-supplied areas. Mineralized interterritorial matrix is composed of circular structures of different sizes fusing to form plaques. In scanning electron microscopy circular structures appear as globules. It is possible to visualize the dynamic process of cartilage mineralization with polychrome sequential labeling; it proceeds up to 4 μm per week. Distribution of cartilage canals reveals their nutritional role for the cartilage. According to investigations in chondroepiphyses, cartilage mineralization starts adjacent to the glomerular end of cartilage canals. In contrast, no correlation between cartilage vascularization and the beginning of cartilage mineralization of the thyroid cartilage of Munich minipigs and of domestic pigs has been found.