Cells and Extracellular Matrices in the Human Adult Vocal Fold Mucosa

Abstract

1. Adult vocal folds have a layered structure consisting of the epithelium; the superficial, intermediate, and deep layers of the lamina propria; and the vocalis muscle (Hirano, Otologia (Fukuoka) 21(Suppl. 1): 239–60, 1975). 2. The free edge of the membranous vocal fold is covered with stratified squamous epithelium. Microvilli (microridges) of the stratified squamous epithelium facilitate distribution and retention of minute amounts of mucus on the vocal fold surface, which is essential for normal vibration and phonation. 3. Langerhans cells with dendritic shape are situated in the suprabasal region of the stratified squamous epithelium in the larynx. 4. The viscoelastic properties of the lamina propria of the human vocal fold mucosa are very important for the vibratory behavior of the structure. They greatly depend on the extracellular matrices. Not only the three-dimensional structure of the extracellular matrices but also their qualitative and quantitative properties have an effect on the physical properties of the human vocal fold mucosa. 5. In the human vocal fold mucosa, the extracellular matrices are composed of two families of macromolecules: fibrillar proteins (collagen and elastin) which provide the fibrous scaffolding of the lamina propria of the mucosa and the interstitium between the fibrous scaffolding—the proteoglycans (glycosaminoglycans) and structural glycoproteins. 6. As fibrillar proteins, collagens, and reticular fibers are required for structural maintenance. They are responsible for tensile strength and resilience and serve as stabilizing scaffolds in the extracellular matrices. 7. The three-dimensional structure of reticular fibers (type III collagen) in the vocal fold mucosa appears to be one of the key components to maintain the structure and viscoelasticity of the vibrating tissue. The complex of reticular fibers and other extracellular matrices seems to be very important for the viscoelastic properties of the vocal fold mucosa. 8. The functions of the microfibril-associated macromolecules are likely to be specific to some aspect of the mechanical biology of the human vocal fold mucosa. 9. The hyaluronic acid glycosaminoglycan (hyaluronan) is a key molecule influencing tissue viscosity of the lamina propria of the human vocal fold mucosa.