It is well established that laryngeal secretions, produced in the glandular tissue, contribute to the local defence system of the larynx. In this study, the distribution of glandular tissues in the subglottic and supraglottic larynx was examined in 55 infants, using an image analysing system. The average area of the mucosa or glandular acini at the level of the false vocal fold was almost three times larger than that of the subglottis. At both levels, the area occupied by the glands increased according to the age at death and became more evident according to the total development score (TDS) which was estimated by adding the age at death and the gestational period. The results indicate that the glandular structure of the level of the sub- or supraglottic larynx develops constantly and equally after birth.

Development of the mucosal defence system and its relationship to the pathogenesis of laryngeal diseases was studied by examining the changes in the laryngeal structures at the level of subglottic larynx of 59 human infants who died within 1 year of birth. By making a transverse section at the level of the cricoid cartilage, the area and diameter of each subglottic structure were examined using an image analysis system. The results were analysed, not only by their age at death, but also based on the total development score. The areas of the whole structure, cricoid ring, subglottic mucosa and inner cavity (available area) increased in close correlation with the total development score. In contrast to the increased diameter of the inner cavity, the thickness of the mucosa was almost the same size. These results indicate the stability of the subglottic airway with advancing age in the human infant larynx.

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