Abstract
BACKGROUND: The urethral wall consists of layers of striated muscle, circular and longitudinal smooth muscles, collagen fibers, and a vascular plexus. However, the relative contributions of these components to urethral pressure in humans remain poorly understood. The circular and longitudinal smooth muscle components can develop a spontaneous contractile activity, generating a basal tone. They can further contract or relax in response to excitatory or inhibitory stimuli. Animal studies suggest that smooth muscle activity in the mid-urethra plays a crucial role in determining maximal urethral closing pressure. Notably, the highest sympathetic activity occurs in the middle segment of the female urethra during increasing smooth muscle tone. This finding is supported by human studies that did not detect any electromyographic activity from striated muscle in this region. OBJECTIVES: This study was conducted to review the contributions of the primary structural components and control mechanisms of urethral. CONCLUSION: In females, the external urethral striated sphincter is located at the distal urethra, which is not the segment associated with the highest closing pressure. Rather, the sphincter has been shown to modulate urethral pressure during exercise and physical stress. Basic science research does not support the notion that mid-urethral pressure is caused by the external striated sphincter tone in females. Instead, findings suggest that, at rest and during bladder filling, maximal urethral pressure is primarily determined by the activity of the urethral smooth muscles.