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The detrusor muscle, also known as the detrusor urinae muscle, is a smooth muscle that forms the muscular wall of the bladder. It is innervated by the autonomic nervous system and plays a crucial role in urination by contracting to release urine and relaxing to allow the bladder to store urine. The muscle fibres are arranged in a swirl pattern to facilitate mass contraction of the bladder. The detrusor muscle is also associated with urethral sphincter muscles, which control the flow of urine.
| Characteristics | Values |
|---|---|
| What is it? | The detrusor muscle, also detrusor urinae muscle, is a smooth muscle found in the wall of the bladder. |
| Function | The detrusor muscle contracts during urination to release urine and remains relaxed to allow the bladder to store urine. |
| Arrangement of fibres | The fibres of the detrusor muscle are arranged in a swirl/whorl pattern to act in unison to provide mass contraction of the bladder. |
| Layers | The detrusor muscle has three layers of muscles arranged longitudinal-circular-longitudinal from innermost to outermost. |
| Innervation | The detrusor muscle is innervated by the autonomic nervous system. |
| Contraction | The contraction of the detrusor muscle is caused by increased signals from the pelvic nerve (parasympathetic). |
| Pathology | Detrusor muscle pathology can lead to urinary retention, incontinence, or a combination of both. Abnormalities of the detrusor muscle can lead to deterioration of the upper urinary tracts. |
| Hypertrophy | The fibres of the detrusor muscle often become hypertrophic in conditions that obstruct urine outflow, such as benign prostatic hyperplasia. |
| Measurement | Detrusor strength is the best measure of detrusor muscle function, followed by contraction speed and duration. |
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What You'll Learn
- The detrusor muscle is the smooth muscle component of the urinary bladder
- The detrusor muscle contracts during urination and relaxes to store urine
- The muscle fibres of the detrusor are arranged in a swirl pattern to allow for mass contraction
- The detrusor muscle is innervated by the autonomic nervous system
- Abnormalities of the detrusor muscle can lead to urinary retention, incontinence, or deterioration of the upper urinary tracts
The detrusor muscle is the smooth muscle component of the urinary bladder
The detrusor muscle, also known as the detrusor urinae muscle, is a smooth muscle that forms the muscular wall of the urinary bladder. It is responsible for the contraction of the bladder wall during micturition (urination) and relaxation of the bladder wall to allow for the storage of urine. The detrusor muscle is composed of three layers of muscle fibres arranged in a longitudinal-circular-longitudinal pattern from the innermost to outermost layers. These muscle fibres are organised in a swirl or whorl pattern, allowing them to work together to facilitate bladder contraction.
The detrusor muscle is innervated by the autonomic nervous system, receiving signals from the pelvic nerve (S2-S4), which stimulates contraction and micturition. During urination, the detrusor muscle contracts while the internal urethral sphincter relaxes, allowing for the release of urine. At other times, the detrusor muscle remains relaxed, allowing the bladder to fill with urine. This relaxation is maintained by sympathetic branches from the inferior hypogastric plexus.
The function of the detrusor muscle is critical to bladder function, and abnormalities or pathologies can lead to urinary retention, incontinence, or deterioration of the upper urinary tracts. Increased electrical coupling in the detrusor smooth muscle cells has been associated with overactive bladder (OAB) symptoms. Additionally, hypertrophic changes in the detrusor muscle fibres can occur due to conditions such as bladder outlet obstruction, resulting in a characteristic appearance known as "trabeculation" visible during cystoscopy.
The strength, contraction speed, and duration of contraction of the detrusor muscle are important measures of its function. However, assessing detrusor muscle function is complex due to the interplay between contraction and urine flow. For example, while the pressure generated by the detrusor muscle to initiate urine flow can be measured, it underestimates the full bladder contractile function. Understanding the physiology and pathophysiology of the detrusor muscle is essential for managing various bladder conditions, such as lower urinary tract symptoms (LUTS) and bladder outlet obstruction.
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The detrusor muscle contracts during urination and relaxes to store urine
The detrusor muscle is a smooth muscle that forms the walls of the bladder. It is also known as the detrusor urinae muscle, muscularis propria of the urinary bladder, or simply muscularis propria. The detrusor muscle contracts during urination to release urine and relaxes to store urine in the bladder. This process is controlled by the autonomic nervous system, specifically the parasympathetic and sympathetic nervous systems, which work together to regulate bladder function during filling and micturition.
During urination, parasympathetic pelvic splanchnic nerves act on postganglionic M3 receptors, causing the detrusor muscle to contract. At the same time, the parasympathetic fibres inhibit the internal urethral sphincter, causing it to relax and allowing for bladder emptying. This coordinated contraction of the bladder and relaxation of the urethra is essential for urination.
When the bladder is filling with urine, the detrusor muscle remains relaxed, allowing the bladder to store urine. This relaxation is maintained by sympathetic branches from the inferior hypogastric plexus. As the bladder fills, the stretch receptors in the bladder wall become stimulated, triggering a sensation of bladder fullness.
The detrusor muscle is composed of smooth muscle fibres oriented in multiple directions, including longitudinal and circular arrangements. These fibres provide the bladder with the ability to stretch in response to the presence of urine. The detrusor muscle is continuous with the internal urethral sphincter, which is also composed of smooth muscle. This combination of detrusor contraction and urethral sphincter relaxation ensures effective urination.
Disturbances in the detrusor muscle's function can lead to urinary retention, incontinence, or a combination of both. Overactive bladder syndrome, for example, may be caused by involuntary contractions of the detrusor muscle during the storage phase. Additionally, functional changes in the detrusor muscle have been associated with lower urinary tract symptoms (LUTS) and bladder outlet obstruction. Understanding the mechanisms of contraction and relaxation of the detrusor muscle is crucial for developing therapeutic approaches to control micturition and treat bladder-related disorders.
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The muscle fibres of the detrusor are arranged in a swirl pattern to allow for mass contraction
The detrusor muscle, also known as the detrusor urinae muscle, is a smooth muscle found in the wall of the bladder. It is responsible for the contraction of the bladder during urination, allowing urine to be released. The muscle fibres of the detrusor are arranged in a swirl pattern, with the innermost and outermost layers running longitudinally and the middle layer running circularly. This arrangement allows for a mass contraction of the bladder during urination.
The detrusor muscle is innervated by the autonomic nervous system, specifically the parasympathetic pelvic splanchnic nerves, which act on postganglionic M3 receptors to cause muscle contraction. At other times, the muscle remains relaxed through sympathetic branches from the inferior hypogastric plexus, allowing the bladder to fill with urine. This process is crucial for the normal storage and release of urine.
The muscle fibres of the detrusor originate from the posterior surface of the body of the pubis in both males and females. These fibres travel longitudinally up the inferior surface of the bladder, over its apex, and then descend along its fundus. In males, the fibres attach to the prostate, while in females, they attach to the front of the vagina. At the sides of the bladder, the fibres intersect each other, creating a swirl pattern that enables the bladder to contract as a unit.
The arrangement of the detrusor muscle fibres in a swirl pattern is essential for the coordinated contraction of the bladder. During urination, the detrusor muscle contracts, while the urethral sphincter relaxes, allowing urine to be released. This coordinated action ensures the efficient excretion of urine from the body.
The swirl pattern of the detrusor muscle fibres also contributes to the bladder's ability to stretch and accommodate varying amounts of urine. The interlacing nature of the fibres allows for flexibility and expansion as the bladder fills. This unique arrangement showcases the intricate design of the detrusor muscle, which plays a vital role in maintaining urinary function and overall bodily homeostasis.
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The detrusor muscle is innervated by the autonomic nervous system
The detrusor muscle, also known as the detrusor urinae muscle, is a smooth muscle found in the wall of the bladder. It is responsible for the contraction of the bladder during urination and remains relaxed to allow the bladder to store urine. The detrusor muscle is innervated by the autonomic nervous system, which controls its function.
The autonomic nervous system plays a crucial role in maintaining the balance between bladder filling and emptying. During urination, the autonomic nervous system activates the parasympathetic branch, which stimulates the contraction of the detrusor muscle. Specifically, it acts on postganglionic M3 receptors, causing the detrusor muscle to contract and expel urine. This process is essential for effective urination.
At other times, when the bladder needs to fill and store urine, the autonomic nervous system activates the sympathetic branch. This branch promotes relaxation of the detrusor muscle, allowing the bladder to fill without triggering premature urination. The sympathetic nerves from the inferior hypogastric plexus play a key role in maintaining bladder relaxation. This coordinated interplay between the parasympathetic and sympathetic branches of the autonomic nervous system ensures proper bladder function and urinary control.
The detrusor muscle has a complex microstructure composed of smooth muscle fibres arranged in three layers: longitudinal, circular, and longitudinal from innermost to outermost. This unique arrangement allows the bladder to stretch and expand as it fills with urine. The muscle fibres arise from the posterior surface of the pubis and pass longitudinally along the bladder, intersecting at the sides. In males, these fibres attach to the prostate, while in females, they attach to the front of the vagina.
Understanding the physiology and innervation of the detrusor muscle is crucial for addressing bladder-related issues. For example, in older adults over 60 years of age, the detrusor muscle may cause difficulties in completely emptying the bladder, leading to uncomfortable urinary retention. Additionally, abnormalities in the detrusor muscle, if left untreated, can result in the deterioration of the upper urinary tracts. Therefore, studying the innervation of the detrusor muscle by the autonomic nervous system provides valuable insights into maintaining bladder health and treating urinary disorders.
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Abnormalities of the detrusor muscle can lead to urinary retention, incontinence, or deterioration of the upper urinary tracts
The detrusor muscle is a smooth muscle found in the wall of the bladder. It contracts during urination to release urine and remains relaxed to allow the bladder to store urine. The detrusor muscle is under control from the autonomic nervous system.
Abnormalities in the detrusor muscle can lead to urinary retention, incontinence, or a combination of both. Urinary retention is caused by issues in voiding the bladder, resulting in an uncomfortable retention of urine. Incontinence can be of two types: overflow incontinence and urgency incontinence. Overflow incontinence occurs when the bladder does not empty fully and is chronically over-distended. Urgency incontinence is common in older women with other comorbid diseases.
If left untreated, abnormalities in the detrusor muscle can lead to deterioration of the upper urinary tracts. Poor (decreased) bladder compliance is associated with upper urinary tract damage. Bladder compliance refers to the change in bladder pressure relative to the change in bladder volume. In children, the detrusor muscle has less contractility and more passive stiffness than in adults, which is likely due to a greater connective tissue-to-smooth muscle ratio. Pelvic surgery may also lead to bladder dysfunction and upper urinary tract damage.
Treatments for urinary retention and incontinence include conservative options such as lifestyle modifications, pelvic floor exercises, and bladder training. If these initial treatments do not improve symptoms, pharmacological and surgical therapies may be considered.
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Frequently asked questions
The detrusor muscle, also known as the detrusor urinae muscle, is the smooth muscle component of the urinary bladder. It is the main muscle of the bladder wall and allows the bladder to contract to excrete urine or relax to hold urine.
The detrusor muscle is found in the wall of the bladder. The muscle fibres are arranged in a swirl/whorl pattern to act in unison and provide mass contraction of the bladder.
The detrusor muscle contracts during urination to release urine and remains relaxed to allow the bladder to store urine. This process is controlled by the autonomic nervous system.
