How do alpha-adrenergic blockers affect urinary elimination?

• A. They tighten the detrusor muscle
• B. They relax the internal urethral sphincter, improving urinary flow, especially in BPH
• C. They increase urine production
• D. They reduce kidney function

Answer: (B)

Alpha-adrenergic blockers work by relaxing smooth muscle in the urinary outflow tract, particularly the prostate and the internal urethral sphincter. By blocking alpha-1 receptors in this area, they lower the reservoir’s resistance to flow, allowing urine to pass more easily. This effect is especially beneficial in benign prostatic hyperplasia, where increased outlet tone and enlarged prostate hinder voiding. The detrusor muscle isn’t tightened by these drugs, and they don’t increase urine production or directly impact kidney function. They can cause dizziness or lightheadedness due to vasodilation, but their primary action relevant to urinary elimination is improving flow by relaxing the bladder neck and prostatic smooth muscle.