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The urinary bladder is a hollow, spherical organ that holds urine. The walls of the bladder are primarily made up of the detrusor muscle, which is composed of three layers of smooth muscle cells. The detrusor muscle contracts during urination to push urine out of the bladder and into the urethra, and relaxes to allow the bladder to store urine.
| Characteristics | Values |
|---|---|
| Main Purpose | Receives urine from the kidneys and stores it until it is convenient to void |
| Composition | Interwoven fibres of detrusor muscle, smooth muscle fibres, and three layers of smooth muscle cells |
| Function | Contracts during urination to release urine and relaxes to allow the storage of urine |
| Control | Autonomic control by the parasympathetic nervous system and the sympathetic nervous system |
| Location | Within the walls of the bladder |
| Structure | Longitudinal and circular smooth muscle fibres |
| Blood Supply | Superior vesical artery, vaginal artery, inferior vesicular artery, inferior gluteal artery, and obturator artery |
| Drainage | Vesical venous plexus, vesical veins, internal iliac veins, and external iliac lymph nodes |
| Related Structures | Urethral sphincter muscles, ureters, urethra, rectum, ductus deferens, seminal vesicles, vagina, cervix |
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What You'll Learn
- The detrusor muscle is composed of three layers of smooth muscle cells
- The inner and outer layers are oriented longitudinally, and the middle one is circular
- The detrusor muscle contracts during urination and relaxes to store urine
- Abnormalities of the detrusor muscle can lead to urinary retention, incontinence, or both
- The muscle is kept relaxed via sympathetic branches from the inferior hypogastric plexus
The detrusor muscle is composed of three layers of smooth muscle cells
The detrusor muscle, also known as the muscularis propria of the urinary bladder, is a smooth muscle found in the wall of the bladder. It is composed of three layers of smooth muscle cells, with the inner and outer layers oriented longitudinally and the middle one circularly. This orientation is important as it determines the shape of the bladder and its intraluminal pressure.
During the storage phase, the muscle cells relax and elongate to store urine, while during the voiding phase, they shorten in a synchronized manner over a short period to expel urine. The detrusor muscle contracts during urination to release urine and remains relaxed to allow the bladder to store urine. The primary function of the detrusor muscle is to contract during urination to push urine out of the bladder and into the urethra.
The detrusor muscle is under autonomic control, with the parasympathetic nervous system stimulating the muscarinic stretch receptors in the bladder through the pelvic nerve fibres. When the bladder fills with urine, the M3 receptors in the bladder become stretched and stimulated, leading to the contraction of the detrusor muscle for urination. Simultaneously, the parasympathetic fibres inhibit the internal urethral sphincter, causing relaxation and allowing the bladder to empty.
The detrusor muscle is composed of smooth muscle fibres that are longitudinal and circular. The layers of the detrusor muscle start longitudinally in the inner layer, become circular in the middle layer, and then shift back to longitudinal in the outer layer. This interwoven orientation of the detrusor muscle allows the bladder to stretch in response to the presence of urine.
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The inner and outer layers are oriented longitudinally, and the middle one is circular
The urinary bladder is a hollow, spherical-shaped organ that holds urine. The walls of the bladder are primarily formed by the detrusor muscle, which contracts to excrete urine and relaxes to hold urine. The detrusor muscle is composed of three layers of smooth muscle cells, with the inner and outer layers oriented longitudinally and the middle layer oriented circularly.
The detrusor muscle is under autonomic control and is composed of interwoven smooth muscle fibres that are collectively known as the detrusor muscle. This interwoven orientation allows the bladder to stretch in response to the presence of urine. The detrusor muscle contracts during urination to release urine, and relaxes to allow the bladder to store urine. The contraction of the detrusor muscle and the simultaneous relaxation of the urethral sphincter muscles lead to urination.
The detrusor muscle is located within the walls of the bladder and is composed of smooth muscle fibres that are longitudinal and circular. The layers of the detrusor muscle start longitudinally in the inner layer, become circular in the middle layer, and then longitudinal again in the outer layer. This orientation is important as it determines the bladder's shape and intraluminal pressure. During the storage phase, the muscle cells have to relax and elongate, whereas during the voiding phase, they shorten in a synchronised manner over a short period to expel urine.
The detrusor muscle is also known as the detrusor urinae muscle, muscularis propria of the urinary bladder, or simply muscularis propria. It is a smooth muscle found in the wall of the bladder. The fibres of the detrusor muscle pass in a longitudinal manner up the inferior surface of the bladder, over its apex, and then descend along its fundus. At the sides of the bladder, the fibres are arranged obliquely and intersect one another.
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The detrusor muscle contracts during urination and relaxes to store urine
The detrusor muscle is a smooth muscle that lines the wall of the bladder. It is composed of three layers of smooth muscle cells, with the inner and outer layers oriented longitudinally and the middle layer circularly. This orientation is important as it determines the shape of the bladder and its intraluminal pressure.
The detrusor muscle is responsible for the contraction of the bladder during urination and relaxation during urine storage. When it is time to urinate, the parasympathetic nervous system stimulates the M3 muscarinic stretch receptors in the bladder through the pelvic nerve fibres, causing the detrusor muscle to contract and push urine out of the bladder. Simultaneously, the parasympathetic fibres inhibit the internal urethral sphincter, causing it to relax and allowing the bladder to empty.
During the storage phase, the detrusor muscle remains relaxed, allowing urine to fill the bladder. The bladder can expand like a balloon, stretching to accommodate increasing volumes of urine. The bladder is a hollow, spherical organ that can typically hold 500-700 mL of urine. When the bladder is full, nerves in the bladder signal to the brain that it is time to use the restroom.
The detrusor muscle can malfunction in two ways: by being overactive or underactive. An overactive detrusor muscle contracts when not needed, creating a strong urge to urinate. Conversely, an underactive detrusor muscle fails to contract when it should, leading to urinary retention and difficulty in emptying the bladder.
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Abnormalities of the detrusor muscle can lead to urinary retention, incontinence, or both
The bladder is a hollow, spherical-shaped organ that holds urine. The detrusor muscle, which makes up the walls of the bladder, contracts to excrete urine and relaxes to hold urine. The detrusor muscle is controlled by the autonomic system and is composed of smooth muscle.
Abnormalities in the detrusor muscle can lead to serious issues. Detrusor muscle pathology can result in urinary retention, incontinence, or both. If left untreated, these abnormalities can cause deterioration of the upper urinary tracts. Poor detrusor function can lead to overflow incontinence, where the bladder does not empty fully and becomes chronically over-distended. This can be caused by detrusor overactivity, where the bladder contracts out of a person's control, even when it is not full. Detrusor overactivity is often associated with urgency incontinence, which is the sudden urge to urinate that may lead to leakage. This condition is common in older women with other comorbid diseases.
There are several treatments available for detrusor abnormalities. Conservative options include lifestyle modifications, pelvic floor exercises, and bladder training. If these initial therapies do not improve symptoms, pharmacologic and surgical therapies are also available. Antimuscarinic drugs such as oxybutynin and tolterodine are commonly used to treat urgency incontinence. Beta-3-adrenergic drugs like mirabegron are another medication class that can be utilised. InterStim® therapy is a form of neuromodulation that has shown promising results for incomplete bladder emptying. Additionally, intermittent self-catheterisation techniques can be employed to teach patients to empty their bladders using a catheter.
It is important to note that an underactive bladder may have various causes, including neurogenic, myogenic, or idiopathic origins. Urodynamic studies, combined with cystoscopies, can help distinguish between poor detrusor function and blockages within the urinary tract. Imaging tests such as ultrasounds, CT scans, and MRIs can also be utilised to assess bladder function and identify potential structural issues.
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The muscle is kept relaxed via sympathetic branches from the inferior hypogastric plexus
The bladder is a hollow, muscular organ that holds urine. It is composed of detrusor muscle, which is made up of three layers of smooth muscle cells. The detrusor muscle contracts during urination to push urine out of the bladder and relaxes to allow the storage of urine.
The detrusor muscle is under autonomic control, with the parasympathetic nervous system stimulating the bladder to contract and the sympathetic nervous system stimulating the bladder to relax. The sympathetic nervous system is stimulated to relax the detrusor muscle when the bladder is emptied of urine.
The inferior hypogastric plexus is a collection of nerve fibres situated on each side of the rectum in males, or on sides of the rectum and vagina in females. It is formed by nerve fibres that originate from multiple sites, including the superior hypogastric plexus, which carries sympathetic fibres. The inferior hypogastric plexus supplies innervation to the urinary bladder, and it is involved in the regulation of smooth muscle sphincters.
Therefore, the detrusor muscle, which lines the bladder, is kept relaxed via sympathetic branches from the inferior hypogastric plexus. This relaxation allows the bladder to store urine.
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Frequently asked questions
The detrusor muscle, also known as the detrusor urinae muscle or muscularis propria, is the smooth muscle that lines the bladder.
The detrusor muscle is composed of three layers of smooth muscle cells. The inner and outer layers are longitudinal, while the middle layer is circular.
The detrusor muscle contracts during urination to push urine out of the bladder and into the urethra. It relaxes to allow the bladder to store urine.
Abnormalities in the detrusor muscle can lead to issues with urinary retention, incontinence, or both. Untreated detrusor muscle pathology can also cause deterioration of the upper urinary tracts.
The urethral sphincter muscles envelop the urethra and control the flow of urine when they contract or relax.
