Dominic Stone
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, allowing urine to be released from the body. The detrusor muscle works in conjunction with the urethral sphincter muscles, which control the flow of urine. When the bladder is filling with urine, the detrusor muscle remains relaxed, and the sphincters contract to hold the urine. During urination, the detrusor muscle contracts, and the sphincters relax, allowing urine to be released. The detrusor muscle is controlled by the autonomic nervous system, with parasympathetic inputs stimulating contraction and sympathetic inputs inhibiting it.
| Characteristics | Values |
|---|---|
| Function | Contract during urination to push the urine out of the bladder and into the urethra |
| Relax to allow the storage of urine in the urinary bladder | |
| Composition | Smooth muscle |
| Interstitium | |
| Intrinsic nerves | |
| Microstructure | Three compartments |
| Layers of muscles | Longitudinal-circular-longitudinal from innermost to outermost |
| Control | Autonomic nervous system |
| Parasympathetic pelvic nerve | |
| Somatic pudendal nerve | |
| Sympathetic hypogastric nerve | |
| Pathology | Can lead to urinary retention, incontinence, or a combination of both |
| Can lead to deterioration of the upper urinary tracts | |
| Can cause issues in voiding the bladder, resulting in uncomfortable urinary retention |
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What You'll Learn
- The detrusor muscle is a smooth muscle that forms the bladder wall
- It contracts to release urine and relaxes to store urine
- Parasympathetic nerves stimulate contraction, while sympathetic nerves stimulate relaxation
- Abnormalities in the detrusor muscle can lead to urinary retention and incontinence
- The detrusor muscle has three microstructural components: smooth muscle, interstitium, and intrinsic nerves
The detrusor muscle is a smooth muscle that forms the bladder wall
The detrusor muscle, also known as the detrusor urinae muscle, is a smooth muscle that forms the bladder wall. It is responsible for the contraction of the bladder during urination, allowing urine to be released. At other times, the muscle remains relaxed, allowing the bladder to store urine. The detrusor muscle is composed of smooth muscle fibres oriented in multiple directions, providing the bladder with the ability to stretch as it fills with urine. This complex arrangement of fibres ensures the structural integrity of the bladder, even when it is stretched.
The detrusor muscle is innervated by both the sympathetic and parasympathetic nervous systems. During urination, parasympathetic nerves act on receptors to cause contraction of the detrusor muscle, while sympathetic branches keep the muscle relaxed to allow the bladder to fill at other times. The pelvic nerve, specifically, stimulates contraction of the detrusor muscle and micturition. In addition, sensory nerves in the bladder wall signal the need to urinate when the bladder is full.
In certain conditions, such as bladder outlet obstruction, the detrusor muscle can undergo hypertrophic changes, resulting in a characteristic appearance known as "trabeculation". This can be observed during cystoscopy and may also be visible on imaging as concentric and irregular bladder wall thickening. Benign prostatic hypertrophy in males and pelvic organ prolapse in females can lead to chronic bladder distension, affecting the detrusor muscle's ability to contract and empty the bladder effectively.
With ageing, the detrusor muscle may cause issues in voiding the bladder, leading to uncomfortable urinary retention. This can be a result of detrusor overactivity or a decrease in detrusor muscle function. Detrusor overactivity is often associated with urgency incontinence, which is the sudden urge to urinate that may result in leakage. It is commonly observed in older women, especially those with comorbid diseases. Treatment options for detrusor overactivity typically begin with conservative approaches, including lifestyle modifications, pelvic floor exercises, and bladder training. However, if these initial therapies prove ineffective, pharmacological and surgical interventions may be considered.
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It contracts to release urine and relaxes to store urine
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, receiving signals from both the sympathetic and parasympathetic nervous systems. The primary function of the detrusor muscle is to contract during urination to release urine and to relax to store urine in the bladder.
During urination, the detrusor muscle contracts to push urine out of the bladder and into the urethra. This contraction is stimulated by increased signals from the pelvic nerve (S2-S4), which is part of the parasympathetic nervous system. The combination of detrusor contraction and relaxation of the internal urethral sphincter allows for the release of urine.
At other times, when urine needs to be stored, the detrusor muscle remains relaxed, allowing the bladder to fill and expand. This relaxation is controlled by the sympathetic nervous system, specifically through sympathetic branches from the inferior hypogastric plexus. The bladder stretch reflex, a primitive spinal reflex, also plays a role in stimulating micturition in response to the stretch of the bladder wall.
In certain conditions, the normal functioning of the detrusor muscle can be disrupted. For example, in older adults over 60 years of age, the detrusor muscle may cause issues in completely emptying the bladder, resulting in uncomfortable urinary retention. Additionally, detrusor overactivity, which is common in older women, can lead to urgency incontinence, characterised by a sudden urge to urinate that may result in leakage.
The microstructure of the detrusor muscle consists of smooth muscle, interstitium, and intrinsic nerves. The contractility of the detrusor is influenced by factors in all three compartments. Cholinergic axons and the release of acetylcholine are crucial for triggering the contraction of detrusor muscle cells and generating an action potential.
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Parasympathetic nerves stimulate contraction, while sympathetic nerves stimulate relaxation
The detrusor muscle, also known as the detrusor urinae muscle, is a smooth muscle that forms the wall of the bladder. It is innervated by the autonomic nervous system, receiving signals from both the sympathetic and parasympathetic nervous systems.
Parasympathetic nerves stimulate contraction of the detrusor muscle, which is essential for urination. During urination, the parasympathetic pelvic splanchnic nerves act on postganglionic M3 receptors, causing the detrusor muscle to contract. This contraction of the detrusor muscle, in combination with relaxation of the urethral sphincter, allows for the release of urine from the bladder.
The pelvic nerve, specifically the pelvic splanchnic nerves (S2-S4), plays a crucial role in stimulating contraction of the detrusor muscle. Increased signals from this nerve lead to detrusor muscle contraction and initiate the process of micturition. This contraction is a response to the stretch of the bladder wall, known as the bladder stretch reflex.
On the other hand, sympathetic nerves promote relaxation of the detrusor muscle, facilitating urine retention. The sympathetic branches from the inferior hypogastric plexus (T12-L2) keep the detrusor muscle relaxed, allowing the bladder to fill and store urine. This relaxation is vital for the bladder to accommodate and hold varying amounts of urine.
Disruptions in the functioning of the detrusor muscle can lead to urinary issues. For example, in the case of a spinal cord transection, the parasympathetic outflow to the bladder may be damaged, paralysing the detrusor muscle and resulting in overflow incontinence. Additionally, detrusor overactivity, often seen in older women, can lead to urgency incontinence, characterised by a sudden urge to urinate.
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Abnormalities in the detrusor muscle can lead to urinary retention and incontinence
The detrusor muscle is a smooth muscle that forms the wall of the bladder. It contracts during urination to push urine out of the bladder and into the urethra, and relaxes to allow the bladder to store urine. The muscle is innervated by the autonomic nervous system, which controls its contraction and relaxation.
Additionally, detrusor overactivity, which is common in older women, can lead to overflow incontinence. This occurs when the detrusor muscle contracts too frequently or strongly, causing an urgent need to urinate that may result in leakage. Urgency incontinence can be treated with conservative options such as lifestyle modifications, pelvic floor exercises, and bladder training. If these initial treatments are ineffective, pharmacologic and surgical therapies may be considered.
Detrusor muscle abnormalities can also be caused by spinal cord injuries or neurodegenerative diseases. In these cases, the spinal reflex that controls bladder function may be impaired, leading to overflow incontinence. Obstruction of the urine outflow, such as by prostate enlargement or a blood clot, can also affect detrusor muscle function and result in urinary retention.
In summary, abnormalities in the detrusor muscle can lead to urinary retention and incontinence due to its impaired ability to contract and relax properly. Treatment options vary depending on the underlying cause and may include pharmacological, surgical, or conservative approaches.
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The detrusor muscle has three microstructural components: smooth muscle, interstitium, and intrinsic nerves
The detrusor muscle, or 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 micturition or urination, allowing urine to be excreted from the bladder and into the urethra. At the inferior end of the bladder, the detrusor muscle connects with the internal urethral sphincter, and the combination of detrusor contraction and urethral sphincter relaxation leads to urination.
The contractility of the detrusor muscle is influenced by factors in all three microstructural compartments. Intact cholinergic axons and the release of acetylcholine are essential for triggering the contraction of detrusor muscle cells. To achieve a forceful contraction of the entire detrusor muscle, a mechanism is required to transmit neurally triggered contractions from innervated to non-innervated cells. This involves the shortening of the contracting muscle cell and mechanical coupling to transmit force to the next cell.
The detrusor muscle can be affected by various conditions, such as benign prostatic hypertrophy in males and pelvic organ prolapse in females, which can lead to poor bladder emptying and chronic bladder distension. Detrusor overactivity, often associated with urgency incontinence, is common in older women and can result in overflow incontinence. Abnormalities in the detrusor muscle, if left untreated, can lead to deterioration of the upper urinary tracts.
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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 allows the bladder to contract to excrete urine or relax to hold urine. The combination of detrusor contraction and urethral sphincter relaxation leads to urination.
The detrusor muscle is innervated by the autonomic nervous system. During urination, parasympathetic pelvic splanchnic nerves act on postganglionic M3 receptors to cause contraction of the detrusor muscle. At other times, the muscle is kept relaxed via sympathetic branches from the inferior hypogastric plexus to allow the bladder to fill.
