Micturition Flashcards
Define micturition?
. The normal process of the passive storage
and active voiding of urine
. Includes storage phase as well as the
voiding phase.
How is retrograde flow from the bladder into the ureters prevented?
. Retrograde flow prevented by the oblique angle of
entry through the bladder wall
The bladder is under what kind of control?
Involuntary. (smooth muscle)
The urethra is under what kind of control?
Urethra (voluntary an
Involuntary)
— Smooth muscle
— Skeletal muscle
What is the detrusor muscle?
A network of smooth muscle fibres within the bladder
wall. Supplied by both sympathetic and parasympathetic fibres.
What is the internal urethral sphincter?
. Thickening of the bladder musculature . Smooth muscle . Supplied by sympathetic supply
What is the external urethral sphincter?
. Striated muscle fibres
. Under voluntary control
of somatic nervous
system
What does the Parasympathetic supply
(cranio-sacral) to the bladder do?
Innervation — detrusor muscle
Neurotransmitter - ACh
Action — excitatory
Function — empty bladder
What does the Sympathetic supply to the
detrusor muscle allow?
. Neurotransmitter — Norepinephrine . Receptor - beta . Action — inhibitory on skeletal muscle fibres . Function — allows bladder filling
What is the detrusor reflex?
Increased vesicular pressure with filling achieves threshold resulting in contraction of the detrusor muscle involuntarily.
What does the positive feedback of the detrusor reflex achieve?
Once it has started positive feedback cause contractions to continue until the bladder is fully emptied.
This occurs at the SC level all a passive.
process.
The somatic motor supply outflows from S1-2 to form pudendal nerve it contains no synapses and Innervates the urethral skeletal muscle, specifically the External urethral sphincter. What function does this allow?
The retention of urine.
Sympathetic supply to the internaI sphincter outflows from L1-4. It synapses at the caudal mesenteric ganglion and innervates the internal sphincter. What function does this allow?
Retain urine, increase urethral
tone
What stimulates the micturition reflex in the voluntary state?
Intra abdominal pressure stimulates the micturition reflex in voluntary state.
A-adrenergic blocker do what?
Decrease sphincter tone by inhibiting the stimulatory outflow from L1-4 to the internal sphincter.
A-sympathomimetic does what?
Increase sphincter tone by increasing the stimulatory effect of outflow from L1-4.
Skeletal muscle relaxants do what?
Decrease sphincter tone by inhibiting somatic supply from S1-2.
Parasympathomimetic drugs do what?
Increase detrusor tone by stimulating parsympathetic fibres from S1-3.
The function of Sympathetic and somatic nerves are to?
Retain urine.
The function of parasympathetic nerves are to?
Void urine.
Define incontinence
Incontinence is the lack of voluntary control of excretory functions.
Can occur alongside normal micturition or separate to
micturition.
Define dysuria?
Difficult or painful passage of urine.
Define stranguria?
Straining or hesitancy associated with urination.
Define pollakuria?
Increased frequency of urination.
Define nocturia?
The urge need to urinate over night.
Define enuresis?
Unconscious leakage of urine during sleep.
What clinical signs do animals with upper motor neurone (high spinal cord or brain dysfunction) damage show with regards to the bladder?
*Retained reflexes with increased tone because reflex arcs are not damaged.
. Reflexes being there but hyper excitable and increased tone. Won’t have voluntary urination as UMN lesion. . Bladder tone will be increased and urethral sphincter tone increase so will have a large volume of urine with a difficult to express bladder.
. Absent voluntary micturition
. Increased urethral sphincter tone
. High volume urinary retention
. Development of automatic bladder
What clinical signs do animals with lower motor neurone (Sacral spinal segment damage or pelvic
plexus) damage show with regards to the bladder?
Low tone with areflexia due to sacral spinal or pelvic plexus damage.
. Will see permanent leakage as sphincters
all open with atonic bladder. Absence of
voluntary micturition and absent detrusal
reflex.
. Absent voluntary micturition . Atonic bladder . Atonic urethral sphincters . Absent detrusor reflex . Concurrent reduced perineal reflex and anal tone . Flaccid an easily expressed
What congenital malformation would you expect to be associated with a constant dribble?
Ectopic ureters.
If one goes in urethra and one in
bladder will see constant dribble and Ureter
normal micturition.
What are some acquired abnormalities of lower urinary
tract?
— neoplasia
— calculi
—Trauma (e.g ruptured ureters can cause
chemical peritonitis, scarring etc.)
Reflex dyssynergia is what?
Initiation of detrusor reflex with reflex contraction of the urethral sphincter. You get initiation of detrusor reflex and rather than normal micturition reflexyou
get a reflex contraction of urethral sphincter. So will see an animal that will strain and posture to urinate but there is not passage of urine. This can be dramatic and life threatening. Can get overfilling of bladder and
rupture. Can catheterise the bladder.
Sphincter mechanism incompetence?
A weak valve on the bladder that allows leakage of urine.
Normal micturition and contiunous leakage of urine or leakage of urine when dog gets excited.
More common in female dog because the effective length of sphincter in male urethra is longer.
More common in large/giant breeds
female
More common in speyed female (hormonal
influence involved in sphincter closer)
What are some treatment strategies for sphincter mechanism incompetence?
— a adrenergic agonists (E.g
phenylpropanolamine) Will tense up the
urethral sphincter
— Oestrogens
— Surgery — culposuspension (you pull the
bladder forward by putting sling of tissue
bladder neck with effectively stretches the urethra increasing tone within smooth muscle)
How is secondary detrusor muscle atony or decrease or absent tone in detrusor muscle so the bladder wont be able to void caused?
. Stretch injury
. Most common cause is failure to treat animal beforehand when it has a urethral blockage. Overexpansion of bladder and detrusor muscle looses the ability to contract.
. Detrusor muscle can repair overtime
Urge incontinence is caused when?
— Micturition reflex initiated at low volume.
— Bladder mucosa irritation. Commonest way to
get it is cystitis.
