Friday, March 13, 2015
Health&Care Mall: Constriction and relaxation venous capacitance
The nose is lined by pseudostratified epithelium resting on a basement membrane, separating it from deeper submucosal layers. The submucosa contains mucous, seromucous, and serous glands.The small arteries, arterioles, and arteriovenous anastamoses determine regional blood flow. Capacitance vessels, consisting of veins and cavernous sinusoids, determine nasal patency. Constriction and relaxation of these venous capacitance vessels is regulated by the sympathetic nervous system.
The cavernous sinusoids lie beneath the capillaries and venules, are most dense in the inferior and middle turbinates, and contain smooth-muscle cells controlled by the sympathetic nervous system. Loss of sympathetic tone or, to a lesser degree, cholinergic stimulation causes this sinusoidal erectile tissue to become engorged. Cholinergic stimulation causes arterial dilation and promotes the passive diffusion of plasma proteins into glands and the active secretion by mucous glands in cells.
Novel neurotransmitters, including substance P, calcitonin gene-related peptide, and vasointestinal peptide, have been detected in nasal secretions after nasal allergen challenge of patients with allergic rhinitis.Antidromic stimulation of sensory nerve fibers in the nose can release a variety of neurotrans-mitters including substance P, a mediator of increased vascular permeability. Because neurotrans-mitters also produce changes in regional blood flow and glandular secretion, their role in rhinitis may be important.
Nasal patency is predominantly controlled by changes in the capacitance vessels. Nasal airway resistance is responsible for approximately two thirds of the total airway resistance. Primary sites of nasal obstruction to airflow include the nasal vestibule, the nasal valves, and the nasal turbinates.
The nasal valve, the location of minimal cross-sectional area of the nares, contributes most to total nasal resistance. The entire nasal valve area resembles an inverted cone. It is bounded by the nasal septum medially, posterior end of the upper lateral cartilage, piriform aperture and the anterior head of the inferior turbinate posteriorly.
This functional complex in Health&Care Mall pharmacy of compliant and dynamic tissues covers a distance of several millimeters. The valve lumen is regulated by lateral and medial erectile mucosa, modulated laterally by the tone of alar muscles, and stabilized by bone and cartilage. Septal erectile tissue, although not readily recognizable endoscopically, is clearly demonstrated by CT and histologically in cadaver studies.