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The detrusor muscle, also known as the detrusor urinae muscle, is a smooth muscle that forms the wall of the bladder. It is responsible for the contraction of the bladder wall during urination and relaxation of the bladder wall to store urine. The detrusor muscle is innervated by the autonomic nervous system and is composed of three microstructural compartments: smooth muscle, interstitium, and intrinsic nerves. The contractility of the detrusor muscle is influenced by factors in all three compartments. Abnormalities in the detrusor muscle can lead to urinary retention, incontinence, or deterioration of the upper urinary tracts.
| Characteristics | Values |
|---|---|
| What is it? | The detrusor muscle, also known as the detrusor urinae muscle, is the smooth muscle component of the urinary bladder. |
| Location | The detrusor muscle is 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. |
| Structure | The detrusor muscle has three layers: longitudinal, circular, and longitudinal from innermost to outermost. |
| Innervation | The detrusor muscle is innervated by the autonomic nervous system, specifically the parasympathetic division. |
| Contraction | The contraction of the detrusor muscle is triggered by the release of acetylcholine from cholinergic axons and their terminals. |
| Age-related changes | In older adults over 60 years of age, the detrusor muscle may cause issues in voiding the bladder, leading to uncomfortable urinary retention. |
| Pathology | Detrusor muscle abnormalities can lead to urinary retention, incontinence, or deterioration of the upper urinary tracts if left untreated. |
| Imaging | Hypertrophic changes in the detrusor muscle due to conditions like bladder outlet obstruction can be seen during cystoscopy and may appear as "trabeculation" of the bladder wall thickening. |
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What You'll Learn
The detrusor muscle is a smooth muscle
The detrusor muscle, also known as the detrusor urinae muscle or muscularis propria of the urinary bladder, is a smooth muscle found in the wall of the bladder. It is composed of three layers of muscles arranged longitudinally, circularly, and longitudinally from the innermost to the outermost. The detrusor muscle is responsible for the contraction of the bladder wall during micturition or urination. It works in coordination with the urethral sphincter muscles, which envelop the urethra, to control the flow of urine. During urination, the detrusor muscle contracts to release urine, while the urethral sphincter muscles relax. At other times, the detrusor muscle remains relaxed, allowing the bladder to store urine.
The contractility of the detrusor muscle is influenced by factors in its three microstructural compartments: smooth muscle, interstitium, and intrinsic nerves. Intact cholinergic axons and their neuroeffector junctions are crucial for triggering detrusor muscle cell contraction through acetylcholine release. The detrusor muscle is innervated by the autonomic nervous system, specifically the parasympathetic division, which stimulates its contraction. On the other hand, the sympathetic division of the autonomic nervous system stimulates the contraction of the internal urethral sphincter, while somatic efferent neurons stimulate the contraction of the external urethral sphincter.
The bladder's ability to store and empty urine depends on the coordinated contraction and relaxation of the detrusor muscle and the urethral sphincters. During bladder filling, the parasympathetic input to the detrusor muscle is inhibited, allowing the muscle to relax and the bladder to expand. At the same time, the sympathetic and somatic efferent pathways are activated, causing the urethral sphincters to contract and prevent urine flow. When it is time to urinate, the parasympathetic efferents become active, leading to detrusor muscle contraction, while the sympathetic and somatic efferents are inhibited, resulting in urethral sphincter relaxation.
Abnormalities in the detrusor muscle can lead to urinary retention, incontinence, or a combination of both. In older adults over 60 years of age, the detrusor muscle may cause issues in completely emptying the bladder, resulting in uncomfortable urinary retention. New research has identified two types of detrusor muscle activity: phasic activity, involving localized stretches of small regions, and global contractions, where most of the bladder smooth muscle is involved. Understanding the physiology of the detrusor muscle is essential for developing effective treatments for urinary-related conditions.
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It contracts to excrete urine and relaxes to hold urine
The detrusor muscle, or detrusor urinae muscle, is a smooth muscle that forms the muscular wall of the bladder. It is innervated by the autonomic nervous system, which controls its contraction and relaxation. The detrusor muscle is responsible for two main functions: contracting to excrete urine and relaxing to hold urine.
During urination, the detrusor muscle contracts to release urine from the bladder. This contraction is triggered by parasympathetic inputs, specifically pelvic splanchnic nerves acting on postganglionic M3 receptors. The contraction of the detrusor muscle is coordinated with the relaxation of the urethral sphincter muscles, which envelop the urethra and control the flow of urine. This coordinated action allows for the excretion of urine.
At other times, when the bladder needs to store urine, the detrusor muscle remains relaxed. This relaxation is maintained by sympathetic inputs, allowing the bladder to fill with urine. The afferent information from the bladder provides a sense of bladder fullness and the urge to urinate. When the bladder is full, the parasympathetic efferents become active, triggering the contraction of the detrusor muscle for urination.
The microstructure of the detrusor muscle comprises three compartments: smooth muscle, interstitium, and intrinsic nerves. The contractility of the detrusor depends on factors in all three compartments. Intact cholinergic axons and the release of acetylcholine are essential for triggering the contraction of detrusor muscle cells. As the bladder fills, its walls stretch, and this is sensed by bladder afferent neurons located in the bladder wall.
In older adults over 60 years of age, the detrusor muscle may cause issues in completely emptying the bladder, resulting in uncomfortable urinary retention. Abnormalities in the detrusor muscle can lead to urinary retention, incontinence, or a combination of both. Understanding the physiology and contractile activity of the detrusor muscle is crucial for managing bladder function and treating related disorders effectively.
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It is innervated by the autonomic nervous system
The detrusor muscle, or detrusor urinae muscle, is a smooth muscle that forms the wall of the bladder. It is innervated by the autonomic nervous system, which controls the bladder. The autonomic nervous system has two divisions: the parasympathetic nervous system and the sympathetic nervous system. These two systems work together to control the contraction and relaxation of the detrusor muscle during urination and urine storage.
The parasympathetic nervous system stimulates the contraction of the detrusor muscle during urination. This contraction of the detrusor muscle, along with the relaxation of the urethral sphincter, allows urine to be released from the bladder. On the other hand, during urine storage, the parasympathetic input to the detrusor muscle is inhibited, and the sympathetic nervous system is activated. This activation causes the urethral sphincters to contract, preventing the release of urine.
The coordination between the parasympathetic and sympathetic nervous systems ensures the proper functioning of the detrusor muscle and the bladder. During urination, the parasympathetic system activates postganglionic M3 receptors, leading to the contraction of the detrusor muscle. Simultaneously, the sympathetic efferents are inhibited, allowing the internal urethral sphincter to relax. This coordination ensures a smooth release of urine.
In addition to the autonomic nervous system, the detrusor muscle is also influenced by the somatic efferent neurons. These neurons stimulate the contraction of the external urethral sphincter, which is composed of skeletal muscle. The complex interplay between the autonomic nervous system and the somatic efferent neurons ensures the controlled release of urine during urination and effective storage during filling.
The detrusor muscle plays a crucial role in maintaining bladder function. When at rest, the detrusor muscle remains relaxed, allowing the bladder to store urine. During urination, the muscle contracts, releasing urine. This coordination between the autonomic nervous system and the detrusor muscle ensures the efficient storage and release of urine, maintaining the overall health and functionality of the urinary system.
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Abnormalities can cause urinary retention and incontinence
The detrusor muscle is a smooth muscle that forms the walls of the bladder. It contracts during urination to release urine and remains relaxed to allow the bladder to store urine. The muscle is innervated by the autonomic nervous system, which controls the bladder. During urination, the parasympathetic nerves stimulate the contraction of the detrusor muscle, while the sympathetic nerves stimulate the contraction of the internal urethral sphincter.
Abnormalities of the detrusor muscle can lead to urinary retention and incontinence. Urinary retention occurs when there is difficulty in voiding the bladder, resulting in discomfort. This can be caused by issues with the detrusor muscle, such as in older adults over 60 years of age. In some cases, the detrusor muscle may not contract properly, leading to incomplete bladder emptying. This can be due to various factors, including neurological disorders, obstructions, or infections. For example, urinary tract infections (UTIs) can affect the upper urinary tract, including the kidneys, and impact the function of the detrusor muscle.
In contrast, incontinence refers to the involuntary leakage of urine. This can occur when the detrusor muscle contracts unexpectedly or too frequently, leading to urgent and frequent urination. This condition is known as overactive bladder (OAB) and can be caused by neurological disorders, obstructions, or infections as well. Additionally, in some patients with OAB, drugs such as antimuscarinics that target receptors on the detrusor muscle may not be effective. This may be due to the complex nature of the symptom, which may not solely affect the detrusor muscle but also involve other factors.
Furthermore, certain conditions can affect the appearance and function of the detrusor muscle. For instance, bladder outlet obstruction can cause hypertrophic changes in the detrusor muscle, resulting in a characteristic appearance known as "trabeculation" during cystoscopy. This condition can also be visualized through imaging as concentric and irregular bladder wall thickening. These abnormalities in the detrusor muscle can impact its ability to contract and relax properly, leading to urinary retention or incontinence.
It is important to address abnormalities of the detrusor muscle through proper diagnosis and treatment. Untreated detrusor muscle pathology can lead to deterioration of the upper urinary tracts, causing further complications. Therefore, seeking medical attention and following recommended treatments, such as pharmacological interventions or other therapies, is crucial for managing urinary retention and incontinence caused by detrusor muscle abnormalities.
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Research has identified two types of detrusor muscle activity
The detrusor muscle, or detrusor urinae muscle, is a smooth muscle found in the wall of the bladder. It is innervated by the autonomic nervous system and plays a crucial role in the storage and release of urine. During urination, the detrusor muscle contracts, allowing the bladder to expel urine. At other times, the muscle remains relaxed, enabling the bladder to store urine.
On the other hand, global contractions involve most of the bladder's smooth muscle. These contractions are brought about by high doses of muscarinics and high-frequency nerve stimulation. Immunohistochemistry has confirmed the presence of two distinct smooth muscle cell populations within the bladder. A thin layer of cells resides just beneath the bladder mucosa, while a larger layer comprises the bulk of the detrusor.
The thin, submucosal layer is believed to be responsible for autonomous pacemaker activity in the bladder, while the remaining detrusor layer is associated with traditional parasympathetic nerve-stimulated bladder contraction. This understanding of the two types of detrusor muscle activity contributes to our knowledge of how the detrusor muscle contracts in a coordinated manner.
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Frequently asked questions
The detrusor muscle, also known as the detrusor urinae muscle, is the smooth muscle that forms the wall of the bladder.
The detrusor muscle contracts to release urine from the bladder and relaxes to allow the bladder to store urine.
The detrusor muscle is controlled by the autonomic nervous system. Parasympathetic inputs stimulate contraction of the detrusor muscle, while sympathetic inputs stimulate relaxation of the muscle to allow the bladder to fill with urine.
Abnormalities in the detrusor muscle can lead to urinary retention, incontinence, or a combination of both. In older adults, the detrusor muscle may cause issues in emptying the bladder, resulting in uncomfortable urinary retention.
