Micturition Flashcards
(24 cards)
What is micturition?
The process by which the urinary bladder empties when it becomes filled.
What transports urine from the kidneys to the bladder and how long is this?
The ureters.
25-35 cm long
Where does the ureter enter into the bladder wall?
It enters through the bladder wall through the detrusor muscle at the trigone.
What pushes the urine through the ureters? When enhances this action?
Smooth muscle contractions propel urine to the bladder.
Enhanced by parasympathetics and inhibited by sympathetic stimulation.
Where are the possible constrictions where kidney stones or other things can clog the ureters?
1) Ureteropelvic junction at ureter and bladder.
2) Behind testicular or ovarian a or v.
3) Pelvic brim (over external iliac a and v)
4) Where the ureter traverses the bladder wall
What is the vesicoureteral reflux?
What does it increase the risk of?
Urine goes back into ureter during micturition.
Pyelonephritis
What does the detrusor muscle do?
Smooth muscle of the bladder > contracts in micturition
What does the trigone do?
Mucosa on posterior wall of bladder above the bladder neck. Where ureters enter bladder and where the bladder neck opens into the posterior urethra.
What does the internal sphincter do?
Smooth muscle located in bladder neck > holds in urine when contracted (involuntary)
What does the external sphincter do?
Skeletal muscle located in urogenital diaphragm > holds in urine when contracted (voluntary)
What part of the spinal cord innervates the bladder?
S2-S4
What type of fibers detect bladder FULLNESS?
A(delta) fibers (myelinated) > wall tension (fullness)
What type of fibers detect bladder PAIN?
C fibers (unmyelinated) are “silent” and respond to noxious stimuli (chemical irritation and cooling)
What system is responsible for bladder emptying? Via what nerve? Via what neurotransmitter and receptor?
The parasympathetics.
Pelvic splanchnic nerve
ACh
Muscarinic (M3)
What systems work to stop micturition?
Sympathetics and somatic muscle innervation
What does the pontine micturition center (PMC) do?
Controls and coordinates activity of sacral micturition center
Activates external urethral relaxation and sacral parasympathetic outflow > micturition
What does the Periaqueductal gray (PAG) do?
Receives afferent bladder signals and passes on to higher brain centers > conscious sensation.
Primary excitatory input to the PMC
What can overturn the PAG?
The higher brain center (cortex)
Prevent incontinence
What happens if afferent or efferent fibers between bladder and cord are destroyed?
No detrusor contractions.
Urinary retention > overflow incontinence
If there is spinal cord damage above the sacrum what happens?
Destrusor does not work, urinary retention occurs.
Eventually micturition reflexes return, detrusor is overactive and sphincter dyssynergia presents.
Periodic incomplete urination.
What if there is damage above the pons? (from stroke, tumor, or brain trauma)
Interrupts all inhibitory signals from the brain > continuous stimulation of micturition center > overactive detrusor
Result: frequent, unpredictable urination (complete)
Describe urination in an infant.
There is involuntary start/stop.
Though detrusor and sphincter still work in coordination.
Describe urination in an adult.
Voluntary start/stop
Detrusor and sphincter work in coordination.
Describe urination in a paraplegic patient (spinal cord damage above sacrum).
Void occurs at lower bladder volumes.
Involuntary start/stop
Detrusor and sphincter are uncoordinated (dyssynergia)
