Both nasal glands and nasal vessels are supposed to be responsible for the humidification of inhaled air. After previous studies on the vasculature of the nasal septal mucosa in the rabbit, we examined vessels of the anterior concha in order to find a morphological equivalent to explain the role of endonasal vasculature in the secretory process of this tissue. The main findings of our study include the detection of fenestrated endothelial walls of both capillaries and venous sinuses located underneath and directly adjacent to the basal cell layers of the epithelium. The same phenomenon-fenestrated vessels underneath the epithelium with the fenestrated parts facing the epithelial cells-has been described in other parts of the body and has been called "polar differentiation." In accordance with the interpretations of other authors, we conclude that these features are responsible for the regulation of endonasal fluid exchange.
Animals Capillaries