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Keywords Macula flava • Tissue stem cells • Stem cell niche • Vocal fold stellate
cells • Vocal fold
9.1 Introduction
Among mammals, only humans can speak and sing songs throughout their lifetime.
And only the human adult vocal fold has a vocal ligament, Reinke’s space, and a
layered structure (Kurita et al. 1986 ; Sato et al. 2000 ; Hirano 1975 ; Hirano and Sato
1993 ). Why do only human adults have such a characteristic vocal fold structure?
Why and how does the newborn vocal fold mucosa grow, develop and mature?
What are the factors for initiating and continuing the growth of the human vocal
fold mucosa? Why does the adult vocal fold maintain its characteristic layered
structure for many decades?
After birth, adult stem cells, including both germ-line stem cells and tissue stem
cells, reside in a specific microenvironment termed a “niche”, which varies in nature
and location depending on the tissue type (Li and Xie 2005 ). These adult stem cells
are an essential component of tissue homeostasis; they support ongoing tissue
regeneration replacing cells lost due to natural cell death (apoptosis) or injury (Li
and Xie 2005 ).
Adult tissue-specific stem cells (tissue stem cells) have the capacity to self-renew
and generate functionally differentiated cells that replenish lost cells throughout an
organism’s lifetime. Tissue-specific stem cells reside in a niche, whereby a complex
microenvironment maintains their multipotency.
Viscoelastic properties of the lamina propria of the human vocal fold mucosa deter-
mine its vibratory behavior and depend on extracellular matrices, such as collagen
fibers, reticular fibers, elastic fibers, proteoglycan, glycosaminoglycan and glycopro-
teins. The three-dimensional structures of these extracellular matrices are indispens-
able to the viscoelastic properties of the human vocal fold mucosa. Fine structures of
the human vocal fold mucosa influence vibrating behavior and voice quality.
Human adult maculae flavae are dense masses of cells and extracellular matrices
located at the anterior and posterior ends of the membranous portion of the bilateral
vocal folds. The histological structure of the maculae flavae in the human adult
vocal fold mucosa is unique and not suitable for vibration. Therefore, their roles in
the human vocal fold as a vibrating tissue are very interesting. However, their roles
in the human vocal fold have not been clarified until recently (Lanz and Wachsmuth
1955 ; Subotic et al. 1984 ; Vecerina-Volic et al. 1988 ; Campos Banales et al. 1995 ;
Fayoux et al. 2004 ).
The latest researches show that the human maculae flavae are involved in the
metabolism of extracellular matrices that are essential for the viscoelasticity of the
human vocal fold mucosa, and are considered to be an important structure in the
growth, development and ageing of the human vocal fold mucosa. In addition, there
is growing evidence to suggest that the cells in the maculae flavae are tissue stem
cells of the human vocal fold mucosa and maculae flavae are a candidate for a stem
cell niche.
K. Sato