Microvascular anatomy of the nose.

The microvasculature of the nose consists of: 1) A dense subepithelial network of capillaries, with fenestrations between the endothelial cells. This network provides nutrients to the epithelium and glands, and allows passage of water into the lumen for evaporation and air-conditioning. 2) A system of capacitance vessels or sinuses, which when they distend, block the nasal lumen, and when they empty, open the nasal passages. Changes in their volume will affect the filtering and air-conditioning functions of the nose. 3) Arteriovenous anastomoses which allow rapid passage of blood through the mucosa. They are probably important in air-conditioning, and in the countercurrent mechanisms that tend to keep the brain cool in a hot dry climate. The anatomical interrelationships between these different systems is not well understood, nor is their differential control in terms of actions of mediators and nerves. In neurogenic inflammation sensory nerves are excited and release local mediators such as substance P via axon reflexes. These sensory neuropeptides will cause vasodilatation, vascular congestion and extravasation of liquid from the postcapillary venules, with resultant oedema and exudate. They may also cause secretion from the submucosal glands.