Micturition Flashcards
(27 cards)
describe the anatomy of bladder?
Urinary bladder : Smooth muscular chamber consisting of :
Body –> where urine collect, made of smooth muscles, detrusor, the smooth muscle cells of it fuse to cause the whole bladder, contract together
Neck -> Funnel shaped extending into urogenital triangle and connecting with urethra
Trigone: triangular area above the bladder neck at the lowermost apex of trigone, bladder neck opens into posterior urethra at the uppermost angles the two ureters enter, the mucosa of the trigone is smooth in comparison to rest of bladder
Ureter: Enter the bladder, course obliquely through muscles and empty into the bladder(the oblique ensures the bladder fills and expand and then the increased presure compresses the ureteral openings, prevent backflow and reflux of urine back from ureter )
Internal sphincter: Formed of the bladder and neck and wall is composed of detrusor muscle with elastic tissue, tone in the sphincter keeps the bladder neck and posterior urethra empty of urine ( prevent backflow of semen as well )
External sphincter : Beyond posterior urethra, urethra passes through urogenital diaphragm containing a skeletal muscle layer, under voluntary control and can consciously prevent urination even if it the involuntary control attempts to empty bladder
Whats the benefit of transitional epithelium?
flexible and can expand allowing the bladder to stretch as it fills with urine without being a rigid structur
describe detrusor muscle?
composed of smooth muscle fibers
CONTRACT AS A UNIT in syncytium
innervation of the bladder?
parasympathetic —> PELVIC NERVE
Sympathetic nerve —> HYPOGASTRIC
Somatic —> PUDENDAL NERVE
describe parasympathetic innervation of urinary bladder?
BY PELVIC NERVES
Contain both sensory and motor nerve fibers
Sensory fibers in pelvic nerve carry impulses from STRETCH RECEPTORS present on the wall of the urinary bladder to spinal center of micrturition
Stimulates of the parasympathetic motor fiebrs causes CONTRACTION OF DETRUSOR MUSCLE LEADING TO EMPTYING OF BLADDER
LAEAD TO RELAXTION OF INTERNAL URETHRAL SPHINCTER AS WELL so urine can go out
Primary controller of bladder function
Long preganglionic fibers, short postganglionic
segments of micturition ?
S2-S3-S4
describe sympathetic nerve supplies?
Hypgastric nerves
Sympathetic nerves supply from sympathetic chain
Stimulates the mainly blood vessels
Supply the internal urethral sphincter BUT NO ROLE IN MICTURITION
they js prevent reflux of semen into the bladder during ejaculation
L1-L3
describe somatic nerves?
maintain tonic contractions of skeletal muscle fibers of the EXTERNAL SPHINCTER
so this sphincter is contracted always
During micturition this nerve IS INHIBITED causing relaxation of EXTENRAL SPHINCTER AND VOIDING OF URINE
SOMATIC NERVE SUPPLY – STORAGE OF URINE by maintaining contraction of external sphincter
describe innervation of the bladder?
Bladder conveys distension and pain through PELVIC, HYPOGASTRIC, PUDENDAL
Motor innervation of the bladder is SYMPATHETIC AND PARASYMPATHETICS
Sympathetic from first 2 lumbar; supply on blood vessels influence on bladder is UKNOWN
Parasympathetic are from 2-4 sacral segments , stimulate the bladder ( pelvic)
External sphincter is skeletal muscle SUPPLIED BY PUDENDAL NERVE originating from S3,S4
Ureter are supplied by both sympathetic and parasympathetic , peristalsis in ureter enhanced by parasympathetic and inhibited by sympathetic stimulation
describe hypogastric nerve ( Sympathetic?)
L1,L2
Sensory fibers :
Mediate the sensation of fullness and pain
Transmit impulses from pain receptors to the upper lumbar segment resulting from pain sensation from urethra and bladder
DETECT BLADDER FULLNESS
Inhibitory to the bladder wall
motor to internal urethral sphincter , seminal vesicles, ejaculatory duct and prostatic musculature mainly in BLOOD VESSELS
HAS LITTLE TO DO WITH BLADDER CONTRACTION JS PREVENT SEMEN FROM GOING BACK
Neurotransmitter —>Norepinphrine
B3 receptors- -> INHIBIT/RELAXX THE DETRUSOR MUSCLE ( prevent contractions and allow filling )
A1 receptors—> INTENRAL URETHRAL SPHINCTER —> STIMULATE CONC
Describe pelvic nerve? PARASYMP
S2-4
Input from stretch receptors
Transmit impulses from tension and pain receptors
Resulting in reflex micturition
MOTOR to bladder wall
Inhibitory to INTERNAL URETHRAL SPHINCTER
Contraction of bladder
SENSEROY FIBERS DETECT DEGREE OF STRETCH IN BLADDER WALL
it initiates micturition but urination wont occur unless EXTERNAL URETHRAL SPHINCTER RELAXES
NEUROTRANSMITTER –> ACH
M3 receptors —> Rlease NANC, NO–> relaxe muscles
describe pudendal nerve? SOMATIC NERVE
S3,S4
Transmit of impulses for the sensation of distension of URETHRA ( bladder distension = sympathetic ) and passage of urine through urethra
URETHRAL DESTENSION
MOTOR to external urethral sphincter
FIBERS INNERVAL AND CONTROL THE VOLUNTARY SKELETAL MUSCLES OF EXTERNAL SPHINCTER
Neurotransmitter —> ACH
Nicotine receptors –> INHIBIT THE EXTERNAL SPHINCTER
mechanism of micturition ?
Empty bladder
Filling of the bladder
EMPTYING OF THE BLADDER
IF reflex micturition repeatedly occurs but is volutnarily inhibited bladder pressure will continue to rise up , eventually the voluntary control of external urethral sphincter will be overriden, and micturition will occur involuntarily
describe the filling phase of micturition ?
the wall of ureter contain SMOOTH MUSCLES
Regular peristaltic contractions occuring one to five times per move the urine from renal pelvis to the bladder
Ureter pass OBLIQUELY through the bladder will and there NO SPHINCTER in them
The oblique passage keeps the ureter closed during peristalsis preventing reflux of the urine
describe mechanism of EMPTYING?
When theres no urine in the bladder, the intravesicular pressure is about to 0
by the time urine increase to around 30 to 50 ml the PRESSURE RISES 5 TO 10 CM of water
after that minimal changes in pressure occur when urine come CUZ THE BLADDER CAN DILATE
additional urine - 200-300 milimiters - CAN COLLECT with only a small additional rise in PRESSURE ; this constant lvl of pressure is caused by INTRINISC TONE OF BLADDER WALL ITSELF
Beyond 400 ml , COLLECTION OF MORE URINE IN THE BLADDER CAUSES THE PRESSURE RISE RAPIDLY
As the bladder fills, many superimosed micturition contractions begin to appear as a result of stretch reflex initiated by SENSORY STRETCH RECEPTOR in the bladder wall ESPECIALLY BY THE RECEPTOR IN THE POSTERIOR URETHRA WHEN THIS AREA BEGIN TO FILL WITH URINE AT HIGHER BLADDER PRESSURE
Perineal muscles and external urethral sphincter are relaxed –> the detrusor muscles contracts and urine passed through the urethra
150 ml–> urge to void
400 ml –> marked sense of fulness
What explains the flat segment?
Law of laplace
pressure in spherical viscus is equal to twice the wall tension divided by radius
in the bladder tensions increases as the organ fills but SO DOES THE RADIUS —> so the pressure increase is slightly UNTIL Khalas no more radius can increase
describe the micturition reflex?
Stretch reflex INITIATED by sensory stretch receptors in the bladder wall , especially receptors in posterior urethra when this area begins to fill with urine
Sensory signals from stretch receptors conducted to SACRAL segments of the cord through the PELVIC NERVE and then REFLEXIVELY back to the BLADDER through PARASYMPATHETIC FIBERS OF PELVIC NERVE
Partially filled bladder: The contraction usually relax after a fraction of a minute, detrusor muscle stops contracting and the pressure falls back to the baseline
as the bladder fills , the micturition reflexes become more FREQUENT and cause greater contraction of detrusor muscles
NOTE : when bladder pressure falls back to baseline, does not mean that the mictrution reflex has stopped, the reflex is still active but TEMPORARILY INHIBITED until threshold is reached again
characteristics of micturition reflex?
Self regenerative:
Initial contraction of the bladder - activation of stretch receptors , and increase in sensory impulses from bladder and posterior urethra, which causes further increase in reflex contraction of bladder
Cycle repeated again and again and again , until the bladder reached a strong degree of contraction
After a few seconds the self regenerative reflex begin to fatigue and the regenerative cycle stops, bladder relaxes
Once micturition reflex occurs BUT FAILS TO EMPTY THE BLADDER, the nervous elements of this reflex remain inhibited for a few minutes to one hour before another micturition reflex occurs
Bladder is more and more filled; micturition reflex becomes MORE POWERFUL and occurs MORE FREQUENTLY
When powerful enough, it causes another REFLEX which PASSES TO THE EXTERNAL SPHINCTER TO INHIBIT IT, if inhibition is strong enough it will override the voluntary and forcefully inhibit the external sphincter
role of the higher centers in micturition ?
Higher centers exert the final control of micturition
Higher centers keep micurition REFLEX PARTIALLY INHIBITED except when its desired
Higher centers can prevent micturition even if the reflex occurs by TONIC CONTRACTION OF EXTERNAL SPHINCTER until theres convenient time
When it is appropriate time higher centers facilitate SACRAL MICTRUITION CENTERS by initiating reflex and also inhibiting the external sphincter
Its role is both inhibitory, mainly and facilitative
describe control of micturition reflexes?
Complete autonomic spinal reflex to get urine outside the body and is facilitated or inhibited by HIGHER BRAIN CENTERS
describe un-conditioned AUTONOMIC -in infants?
urination occurs through the spinal reflexes called micturition reflex
Which are autonomic cuz NERVE TRACTS ARE NOT YET MYELINATED
the stimulus for these reflex is stretched receptors through raise in intravesical pressure
describe Conditioned ( voluntary ) in adults?
Voluntarily controlled by certain higher centers in the brain
Brainstem – MAINLY in pons ( STRONG facilitative and inhibitory centers )
Several centers in cerebral cortex – MAINLY INHIBITORY BUT CAN BECOME EXCITATORY
What happens when coniditon are favorable in higher centers?
1- stretching of sensory stretch receptors
2- Stimulation sacral segment
FAVORABLE CONDITIONS :
Cortical centers facilitate micrurition by discharging signals that lead to :
Stimulation of sacral mictrurition center
Inhibition of pudendal nerve- RELAXATION OF EXTERNAL URETHRAL SPHINCTER
Contraction of anterior abdominal muscle and diaphragm - in intra-abdominal pressure increases , intravesical pressure increases , the micturition reflex gets intesified
THEN URINATION
What happens when its not favorable condition ?
1- Stretch receptors
2- Stimulate sacral segments
UNFAVORABLE CONDITION :
higher center will inhibit micturition reflex
1-Inhibition of sacral micturition center
2- BLadder pressure comes down and sensation of fullness disappear
3- Stimulation of pudendal nerve – CONTRACTION OF EXTERNAL URETHRAL SPHINCTER
NO URINATION
