Micturition Flashcards
What are the basic processes of micturition?
→ Made in the kidneys
→ Urine stored in bladder
→ Urine released from bladder
Where does the urine pass from and to?
→ From collecting duct of renal tubules into renal pelvis
What aids the movement of the urine into the ureter?
→ Contraction of the smooth muscle of the pelvis
What pressure do the ureters squeeze urine to?
→ 10-20 mmHg
How do the ureters open into the bladder and why?
→obliquely
→ Prevents reflux of urine back into ureters by passive flap-wave
What type of peristalsis is the ureter under?
→ Myogenic in origin and not under CNS control
What do kidney stones form from?
→ Crystals that separate from urine within urinary tract
What does urine contain to prevent kidney stones?
→ citrate
What do kidney stones usually contain?
→ Calcium
Why are kidney stones more common in men?
→ Due to testosterone
What are kidney stones caused by?
→ Poor urine output → Obstruction → Altered urinary pH → Low concentration of inhibitors → Infection → Dietary intake of stone forming substances
Where can kidney stones form?
→ In the kidney
→ Ureter
→ Bladder
What are symptoms of kidney stones?
→ Dysuria
→ Haematuria
→ Pain
→ Reduced urine flow
→ Urinary tract obstruction - pressure reaches 50 mmHg
→ If stone is at tip of urethra- pain inhibits micturition
How much urine can the bladder hold without pressure?
→ 400ml without much pressure
→ Due to the spherical structure
What can the transitional epithelium do?
→ stretches without damage
→ has ridges that flatten out as the bladder fills
What allows separation of urine and blood in the bladder?
→ Impermeable to salts and water
→ No exchange between urine and capillaries of bladder wall
What is the muscle coat around the epithelium called and made from?
→ detrusor muscle
→ made from bundles of smooth muscle interlacing
What does the trigone region contain?
→ Opening of ureter
→ neck of urethra
What are the sphincters in the bladder?
→ Internal - extension of detrusor - NOT VOLUNTARY
→ External - 2 striated muscles
What is the external sphincter composed of?
→ 2 striated muscles
→ (compressor urethrae and bulbocavernosus surrounding urethra)
→ Responsible for continence - conscious, voluntary control
What is the internal sphincter formed from?
→ Loop of muscle that is an extension of the detrusor
→ When detrusor contracts the fibers forming the loop shorten and open the sphincter
What is the arrangement of the female bladder?
→ Short urethra - only carries urine
→ External sphincter poorly developed - prone to incontinence after childbirth
What is the arrangement of the male bladder?
→ Urethra carries urine and semen
→ urine elimination is aided by the contraction of bulbocavernosus muscle
What is the lining of the bladder?
→ transitional epithelium
What is the bladder muscle?
→ Detrusor
What is the bladder permeable and impermeable to?
→ Impermeable to salt and water
→ Permeable to lipophilic molecules
What do the neural circuits of the bladder act like?
→ an on and off switch to alternate between storage and elimination
What is the lower urinary tract innervated by?
→ 3 sets of peripheral nerves
→ Parasympathetic (pelvic)
→ Sympathetic ( hypogastric)
→ Somatic nervous system ( pudendal)
What are the two bladder innervations?
→ Sensory
→ Motor
What does sensory innervation do?
→ Gives a sensation of fullness
What does motor innervation do?
→ Causes contraction and relaxation of detrusor muscle and external sphincter to control micturition
Where does the parasympathetic motor innervation go from and to?
→ Sacral region of spinal cord S2- S4
→ Pre synaptic neurons synapse to post ganglionic neurons in the bladder wall
→ Synapse in the internal sphincters
Where does the sympathetic motor neurons go from and to?
→ lumbar region T-11 - L2
→ innervate onto post synaptic neurons in the hypogastric ganglia
→ Innervate directly to the internal sphincter
→ inhibiting the parasympathetic system
Where do the somatic neurons go from and to?
→ S2 - S4
→ innervate the external sphincter
What is the innervation of the detrusor muscle like?
→ Parasympathetic pre ganglion synapse onto post ganglion neurons in the bladder wall
→ release AcH
→ acts on nicotinic receptors
→ the post ganglionic neurons release AcH and ATP
What do ACh and ATP do to the detrusor?
→ cause it to contract
What receptor does ATP act on?
→ Purinergic
What inhibits detrusor contraction?
→ Atropine
What causes the detrusor to relax?
→ Noradrenaline
→ Inhibits transmission at parasympathetic ganglia indirectly
→ Directly via beta receptors
What relaxes the internal sphincter?
→ NO and ACh
→ Noradrenaline
What holds the external sphincter closed?
→ ACh (tonic and continual)
What effects do the parasympathetic neurons have?
→ Contract detrusor
- ACh (muscarinic) and ATP (purigenic)
→ Relax internal sphincter
- via NO (cGMP) & ACh
What effects do sympathetic neurons have?
Relax detrusor
- indirectly via NA on alpha receptors & directly via Beta receptors
→ Contract the internal sphincter
- NA (alpha receptors)
What effects do the somatic neurons have?
→ Contract the external sphincter
- ACh
What is the main afferent pathway?
→ Via the pelvic nerve
→ Small myelinated A delta fibres → micturition reflex
What are A delta fibers linked with?
→ Stretch receptors - wall tension
→ Volume receptors - bladder filling
Where are Unmyelinated C fibres found?
→ near the epithelium
What are unmyelinated C fibres linked with?
→ Nociceptors - pain
What are hypogastric and pudendal pathways linked with?
→ Nociceptors
→ Flow receptors
What do A fibres sense?
→ Tension in detrusor
→ Detrusor contraction
→ bladder fullness - discomfort
What do C fibres sense?
→ Respond to damage
→ Inflammatory mediators
How does the bladder fill (flowchart)?
Initally bladder is empty - sphincters closed ↓ bladder pressure low ↓ arrival of urine ↓ detrusor relaxes progressively ↓ little increase in pressure ↓ sphincters still closed
When do we become conscious of bladder filling?
→ 100-150ml
When does discomfort begin?
→ 300-400
What kind of a reflex is micturition?
→ Autonomic
How is the micturition reflex modified?
→ By voluntary control
→ Inhibited by higher centres in the brain
What disrupts voluntary control of micturition?
→ Disease/injury/ageing
→ Bladder hyperactivity + urge incontinence
→ Stress incontinence
Flow chart of micturition
As receptors detect tension
↓
transmit information via afferents ( A delta system) to the spinal cord
↓
synapse to parasympathetic efferents to override storage
↓
detrusor contracts and internal sphincter relaxes
↓
bladder constricts
↓
urine forced out and activates flow receptors in the urethra
↓
activates flow receptors in urethra
↓
pudendal afferents are excited and switch off the tonic system
↓
Tonic contraction removed by inhibition of somatic input
What is the PMC?
→ Pontine micturition centre
functions as an on-off switch that is signalled by stretch receptors in the bladder wall and is, in turn, modulated by inhibitory and excitatory neurologic influences from the brain
How can higher centres modify micturition reflexes?
→ Contract external sphincter and levator muscle
What can the urine stream be stopped by?
→ Strangury ‘urethral pain’ due to urethritis
→ Pinching glans penis
→ at night if bladder fills to capacity PMC wakes you up
Flow chart of innervation to bladder
Cerebral cortex (frontal lobe) ↓ Brain stem ↓ Spinal tract ↓ Spinal efferents ↓ Ganglion ↓ Bladder
What sends signals from the bladder to the spinal efferents?
→ C unmyelinated afferent
What sends signals from the bladder to the spinal tract?
→ A delta myelinated afferent
Where is the bladder?
Floor of abdominal cavity
What helps to compress the urethra?
→ Reflex contraction of periurethral striated muscles
What is the result of contracting abdominal muscles?
→ Increased intra-abdominal pressure transmitted to the bladder and urethra
Why do you have to completely empty the bladder?
→ Restore sterility
→ Bacteria in retained urine seeds fresh urine
→ Retained urine - UTI
What can repeated infections do to kidney function?
→ destroy renal function
What is a UTI?
→ Urinary tract infection that can happen anywhere along the urinary tract
What is an infection in the bladder called?
→ Cystitis
What is an infection of the kidneys called?
→ Pyelonephritis
What is a urethra infection called?
→ Urethritis
What are risk factors for a UTI?
→ pregnancy → Enlarged prostate → Kidney stones → bowel incontinence → old age
What are the problems of an ageing bladder?
→ Prostate enlargement
Incontinence - weakening of sphincters
→ Overactive bladder
What is a consequence of slow urine stream?
→ Incomplete emptying
→ Infection
What are medications for incontinence?
→ anti muscarinics
→ detrusor relaxes
→ relax smooth muscle
What is bladder retraining?
→ Kegel exercises
Clench the muscles you would use to stop the flow of urine.
Hold the squeeze for 10 seconds, then relax.
Do three or four sets every day.
As these muscles grow stronger so will your bladder control.
What surgery can be carried out for the bladder?
→ Bladder neck suspension
→ collagen injections injections into muscles around urethra → relaxes OAB
→ botulinum toxin
What is SNS?
→ sacral nerve stimulation
→ electrical impulses to sacral nerve supplying lower urinary tract
What other treatments for incontinence?
→ stem cell therapy
→ tissue engineered bladder- Synthetic and natural scaffolds to form 3D structure using human tissue.
What is stress urinary incontinence?
when urine leaks out with sudden pressure on the bladder and urethra, causing the sphincter muscles to open briefly
→If there is damage to support around urethra, it becomes deformed in orientation and remains open
What is happening when bladder is empty?
→Sphincters closed
(tonic activity sympathetic & somatic nerves)
→Bladder pressure low
What happens with the arrival of urine?
→Detrusor relaxes progressively (sympathetic activity inhibiting parasympathetic transmission) →Little increase in pressure →Sphincters still closed →RECEPTIVE RELAXATION
What is the difference between the external sphincter muscle in men and women?
poorly developed and women are more prone to incontinence
