Blæremuskelen

Blæremuskelen, also known as the detrusor muscle, is a specialized smooth muscle found in the wall of the urinary bladder. Its primary function is to contract and expel urine from the bladder during urination. This muscle is involuntary, meaning its actions are not under conscious control. The detrusor muscle is composed of three layers of smooth muscle fibers: an inner longitudinal layer, a middle circular layer, and an outer longitudinal layer. This arrangement allows for powerful and efficient contraction of the bladder.

The bladder wall is lined internally by the urothelium, a transitional epithelium. The detrusor muscle is innervated by the autonomic nervous system. The parasympathetic nervous system stimulates contraction of the detrusor muscle, leading to urination, while the sympathetic nervous system generally inhibits contraction, promoting bladder filling and storage. During the filling phase, the detrusor muscle is relaxed, allowing the bladder to expand and hold urine. As the bladder fills, stretch receptors signal the brain, initiating the urge to urinate. When the decision to urinate is made, parasympathetic signals cause the detrusor muscle to contract, increasing pressure within the bladder and forcing urine through the urethra. Conditions affecting the detrusor muscle, such as overactive bladder or detrusor underactivity, can lead to urinary incontinence or difficulty emptying the bladder.