Control of Micturition Flashcards
What is micturition?
Process by which urinary bladder is emptied when it becomes full
What is the function of the Interstitial cells of Cajal?
- sensory cells which interact with the smooth muscle cells to control and initiate contraction
- also found in the small and large intestines used to generate peristalsis
- interact with nerves to convey sensory information to the nerves and contractile information back to smooth muscle
What nerves innervate the bladder?
- Somatic nerves (enter and emerge from spinal cord between S2 and S4
- Pelvic nerves (enter and emerge at S2 and S4
- Sympathetic (enter and emerge at T11-L2
Describe the mucosal layer of the bladder?
- Lamina propria contains ICCs and nerves
- Muscularis mucosal move epithelium to limit exposure to urine
- Paracrine influences on underlying detrusor layer
Describe the Detrusor layer of the bladder wall?
- contains ICCs, smooth muscle and nerves
- stretch evoked spontaneous activity is inherent to the layer (basal tone)
- expulsion tone during micturition
What people may experience involuntary reflex urination?
- Elderly individuals
- neurological injury
- Infants
How do bladder muscle change during filing and emptying of the bladder?
- Bladder flaccid when empty
- Turgid when full
How do bladder muscle change during filing and emptying of the bladder?
- Bladder flaccid when empty
- When full muscles contract against pressure to make it turgid when full
Through what tube does urine enter the bladder?
ureters via the ureteric orifices
What structure stops urine leaving the bladder?
the two Sphincters, one smooth muscle (involuntary) and one skeletal muscle (voluntary)
What are the four layers of the bladder wall?
- Mucose
- Submucosa
- Detrusor muscle
- Serosa
What three muscle actions are needed to release urine from the bladder?
- Both sphincters must relax
- Detrusor muscle must contract
What is the function of the sensory nerves in the bladder?
- Relay information about bladder filling and pressure to the sphincters of the spinal cord
What nerves innervate the detrusor muscles?
- sympathetic efferent fibres from the lumbar spinal cord (inhibitory)
- parasympathetic efferent fibres from sacral spinal cord (excitatory)
What nerves innervate the internal and external sphincter muscles?
Internal - Sympathetic efferent fibres from lumbar spinal cord (noradrenaline release contracts smooth muscle)
External - Somatic efferent fibres of Puedendal nerves (constriction signal constant unless voiding the bladder), ACh neuromessenger used
What is the micturition reflex arc?
- parasympathetic afferent nerves synapse onto parasympathetic efferent nerves
- This would ordinarily result in detrusor muscle contraction and thus voiding but pressure on sphincter stimulates sympathetic reflex
- sympathetic reflex contacts internal sphincter and relaxes bladder
- parasympathetic afferent nerves also signal brain via Pons to consciously control micturition which overrides the parasympathetic reflex and allow bladder filling by closing external urethral sphincter
What is the action of the Pons in bladder control?
- receives signals from the parasympathetic sensory nerves
- Pons as a result stops its inhibition of the parasympathetic motor neurones allowing bladder to contract in response to wall stretch
- inhibit the sympathetic motor nerves so internal urethral sphincter can relax releasing urine
- also stops somatic motor signals and external urethral sphincter relaxes
What are the four types of incontinence?
1) stress incontinence (due to increased abdominal pressure under stress)
2) Urge incontinence (Due to involuntary contraction of bladder muscles)
3) Overflow incontinence due to blockage of urethra)
4) Neurogenic incontinence (due to impaired dysfunction of neurological system)
What are the causes of overflow incontinence?
- Chronic obstruction (prostate cancer, narrowing of urethra or benign prostatic hyperplasia)
- disturbance of innervation (lesions affecting sacral segments or damage during child birth)
What are the causes of disturbances in innervation leading to overflow incontinence?
- Lesions affecting sacral segments or peripheral autonomic fibres.
- Sensory nerve damage during child birth
- Degeneration of the peripheral nerves
- adverse effect of certain anticholinergic medications (force of detrusor contraction reduced)
- α-adrenergic agonists (internal urethral sphincter constriction)
- calcium channel blockers (block of contraction)
- Epidural anaesthesia and delivery also can cause the overflow incontinence
How is overflow incontinence treated?
Medications:
- bethanechol (improves contraction force)
- catheterisation (help to void)
- Surgery (removal of prostate)
What is Stress incontinence?
- Bladder leakage upon sneezing or coughing
- due to weakening of pelvic floor muscles with support external sphincter
What is the cause of stress incontinence in men and women?
Men: - post-surgical complication
Women: Pregnancy, child birth and menopause
What are the risk factors for stress incontinence?
- Smoking
- excess weight
- Caffeine consumption
