Week 8 - Micturition and Incontinence Flashcards
What is the anatomy of the bladder?
- A hollow, smooth-muscle organ
- Derivative of the hindgut
- Major functional divisions:
- – Body= temporary store of urine
- – Trigone = a triangle formed by the ureteric orifices and internal urethral orifice
- – Neck = connects bladder to the urethra
Describe the muscular components of the bladder
Detrusor muscle - Made from a meshwork of muscle fibres - In roughly 3 layers --- Inner longitudinal --- Middle circular --- Outer longitudinal - This arrangement gives the bladder strength, irrespective of which direction it is being stretched in - Supplied by the autonomic nervous system - Spinal nerve supply is bilateral Internal urethral sphincter - Continuation of the detrusor muscle and made of smooth muscle - Physiological sphincter --- No muscle thickening - Located at the bladder neck - Primary muscle of continence External urethral sphincter - Anatomical sphincter --- Localised circular muscle thickening to facilitate action - Derived from pelvic floor muscles - Skeletal muscle - Under somatic (i.e. voluntary) control - Contracts to constrict urethra and “hold in” urine
What is the innervation of detrusor muscle?
- Paraympathetic = pelvic nerve (S2-S4)
- – Acetylcholine is released
- – Acts on M3 receptor
- – Causes contraction
- Sympathetic = hypogastric nerve (T10-L2)
- – Noradrenaline is released
- – Acts on β3-receptor
- – Causes relaxation
What is the innervation of the internal urethral sphincter?
Sympathetic = hypogastric nerve (T10-L2)
- Noradrenaline is released
- Acts on α1-receptor
- Causes contraction
What is the innervation of the external urethral sphincter?
Somatic = pudendal nerve (S2-S4)
- Acetylcholine is released
- Acts on nicotinic receptor
- Causes contraction
What is micturition?
To want to pass urine
Describe the mechanism for storage of urine
- At around 400ml of filling, afferent nerves from the bladder wall start to signal the need to void the bladder
- Brain continence centres → spinal continence centres → sympathetic neurones
- – The increase in sympathetic stimulation to the bladder is via the hypogastric nerve
- – Causes the detrusor muscle to relax and the internal urethral sphincter to contract
- The cerebral cortex makes a conscious decision not to urinate
- – Increases somatic stimulation to the external urethral sphincter causing it to contract
- The relaxation of the detrusor muscle, coupled with the contraction of the internal and external urethral sphincters reduces intravesicular pressure and constricts the urethra
- – Preventing micturition
What is the continence phase?
Storage of urine in the bladder
- Controlled by continence neurones
- – Damage to this will lead to failure to store urine = urinary incontinence
- The ureters, urinary bladder, internal and external urethral sphincters work together to pass urine into the urinary bladder and store it over many hours
- The walls of the bladder have many folds (rugae)
- – These distend when filling with urine
- – Because of this, as the bladder fills intravesicular pressure hardly changes
- The urinary bladder has a capacity of around 550ml
Describe the voiding phase of urine
- Controlled by micturition neurones
— Damage to these will lead to failure to pass urine, resulting in urinary retention - The threshold for feelings suggestive of a full bladder is ~400ml
— When the bladder is full, an urge to urinate arises - The brain informs the spinal cord to void the bladder
— Brain micturition centres → spinal micturition centres → parasympathetic neurones
— Increase in parasympathetic stimulation is via the pelvic nerve
• Causes the detrusor muscle to contract and increase intravesicular pressure - The cerebral cortex then makes a conscious decision to urinate
— Reduces somatic stimulation to the external urethral sphincter, causing it to relax
What are the different types of incontinence?
- Stress
- – Involuntary leakage on effort or exertion, or on sneezing or coughing
- – Most common
- Urge
- – Involuntary leakage accompanied by or immediately proceeded by urgency
- Mixed
- – Involuntary leakage accompanied by or immediately proceeded by urgency and also with exertion, effort, sneezing or coughing
- Overflow
- – Retention of urine causing the bladder to swell
- – Can be low pressure and pain free
What are the risk factors for urinary incontinence?
- Pregnancy and childbirth
- Pelvic surgery
- Pelvic prolapse
- Co-morbidities
- Obesity
- Age
- Increased intra-abdominal pressure
- Cognitive impairment
- UTI
- Drugs
- Menopause
- Family predisposition
- Anatomical abnormalities
- Neurological
- Race
- Anything that can weaken the pelvic floor muscles!
- – The support of the urethra by the muscles and ligaments of the pelvic floor are important for the efficiency of the sphincter mechanisms of the urethra that enable continence
What should you consider when taking a history for urinary incontinence?
- Ask patient to record the amount of fluid they pass for 2-3 days can assess the frequency of micturition
- Incontinence can be judged by the number of pads that the patient has to use per day to cope with the urine leakage
- Should be possible to determine:
— Whether the leakage is continuous or intermittent
— What precipitating factors there are
• E.g. coughing, sneezing - Urgency and frequency of micturition can be made worse if there is an intravesicular inflammatory condition
— Typically a UTI, but other causes such as a stone in the bladder or even a tumour - Previous surgery of the pelvic floor
— Can lead to denervation of parts of the bladder - Childbirth can be an important factor in the development of stress urinary incontinence in women
— Due to sphincter damage
How can you investigate urinary incontinence?
- Mandatory:
— Urine dipstick
• UTI, haematuria, proteinuria, glycosuria - Basic non-invasive urodynamics
— Frequency-volume chart
— Bladder diary (~3 days)
— Post-micturition residual volume (patients with voiding dysfunction) - Optional
— Invasive urodynamics
— Pad tests
— Cystoscopy
How can you manage urinary incontinence using general lifestyle interventions?
- General lifestyle interventions:
— Modify fluid intake
— Weight loss
— Stop smoking
— Decrease caffeine intake
— Avoid constipation
— Timed voiding (fixed schedule) - Contained incontinence:
— For patients unsuitable for surgery who have failed conservative or medical treatment
• Indwelling catheter
• Urethral or suprapubic
• Sheath device
• Analagous to an adhesive condom attached to catheter tubing and bag
• Incontinence pads - Specific management of stress UI:
— Pelvic floor muscle training
• 8 contractions, 3x a day
• At least 3 months duration - Specific management of urge UI
— Bladder training
— Schedule of voiding
• Void every hour during the day
• Must not void in between (wait or leak)
• Intervals increased by 15-30 minutes a week until interval of 2-3 hours
— At least 6 weeks of training needed
What pharmacological interventions are there for urinary incontinence?
Duloxetine:
- Combined noradrenaline and serotonin uptake inhibitor
- Increased activity in the striated sphincter during filling phase
- Not recommended by NICE as first-line or routine second-line treatment
— May be offered as an alternative to surgery
Anticholinergics
- Act on muscarinic receptors
— M2, M3
- Side effects due to effects on M receptors at other sites:
— M1 – CNS, salivary glands
— M2 – heart smooth muscle
— M3 - smooth muscle (ocular and intestinal), salivary glands
— M4 – CNS
— M5 – CNS, eye
- E.g. oxybutynin
Botulinum toxin
- A potent biological neurotoxin that inhibits ACh release
- Prevents detrusor muscle contraction, as the pelvic nerve cannot release ACh to act on the M3 receptors
