Download MICTURITION (Voiding\Urination)

MICTURITION
(Voiding\Urination)
…the discharge of urine from the bladder via the urethra…
Learning objective.
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At the end of lecture student should be bale to know,
Organs of micturations,
Neural control of micturation,
Clinical.
Organs of Micturition
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Ureters
Bladder
Urethra
Pelvic floor
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A pair from kidneys course obliquely for several cms through the bladder wall and
enters the bladder through the detruser muscles in the trigone of the bladder.
The normal tone of detruser muscles tends to compress the bladder thereby
preventing backflow of urine during micturation or bladder compression.
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URETERS
Clinical Implication:
Vesicoreteral Reflux,,, Backward flow of urine during micturation\bladder
contraction.
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BLADDER
The bladder has a dual role: Passive reservoir for temporary storage of urine; AND
to void the bladder content.
It can accommodate a range of volumes of urine - from 0 ml (immediately after the
bladder has been emptied), to a maximum of around 300-400ml.
BLADDER: Anatomy
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The bladder is a loose sack which sits in the pelvis.
In males, the base of the bladder lies between the rectum and pubic symphysis.
In females, the base is below the uterus and anterior to the vagina.
It is held in position by the peritoneum surrounding it (though only its top surface
lies within the peritoneum) and by strong umbilical ligaments.
The bladder is lined by three layers:mucosa, muscular, serosa.
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The bladder is anatomically divisible into a large, collapsible chamber or "body",
and a short, narrow "neck" that continues into the urethra.
The bladder mainly consist of:
Smooth muscle chamber
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detrusor muscle
• arranged in spiral, longitudinal & circular bundles
• contraction can increase pressure in the bladder to 40-60 mmHg
• ureters run obliquely through the detrusor muscle and then passes
another 1-2 cm beneath the mucosa before emptying into the bladder
Bladder trigone
– small triangular area in the posterior wall of bladder
– 2 ureters enter the bladder at the uppermost angles of the trigone
– inner lining of the bladder at trigone is smooth
• the rest is folded to form rugae
Internal & external sphincters
– internal sphincter – formed from detrussor muscle at bladder neck (posterior
urethra) with elastic tissue
• smooth muscle
• normal tone of internal sphincter prevents emptying of bladder
– external sphincter – formed from a layer of skeletal muscle
• skeletal muscle under voluntary control of the nervous system
URETHRA
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The urethra leaves the bladder at its most inferior point and extends from there to
the outside of the body.
In females, this exits near the anterior wall of the vagina and is 3-5cm long.
In men, the urethra extends to the tip of the penis, a total distance of up to 20cm
Because the urethra is short and exits so close to the anus, women are particularly
prone to urinary tract infections.
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Pelvic floor
Support pelvic visera
Allow passage of nerves, waste products, ie. Urine and faeces
Pelvic Support
Pelvic floor: MALE, FEMALE
NEURAL CONTROL OF THE BLADDER
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Two functional states of the urinary bladder must be distinguished:
The storage phase :
contraction of the striated sphincter (somatic innervation)
contraction of smooth muscle sphincter (sympathetic innervation)
inhibition of detrusor activity (sympathetic innervation)
The emptying phase (micturition, voiding)
relaxation of the striated sphincter (somatic innervation)
relaxation of the smooth muscle sphincter and opening of the bladder neck
(sympathetic innervation)
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detrusor contraction (parasympathetic innervation)
Transport of urine into the bladder
Urine flow out of collecting duct:
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No change in composition during its flow in renal calyces & ureter
Peristaltic contractions in ureter:
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initiated by pacemaker activity in renal calyces
calyces contain specialized smooth muscle cells that generate spontaneous
pacemaker potentials
• unstable resting potential
peristaltic waves sweep down the ureters
• frequency 1 every 10 seconds – 2/3 minutes
stimulated by parasympathetic nerves
inhibited by sympathethic nerves
forces urine into the bladder
• normal tone of detrusor muscle prevents backflow of urine into ureter
Micturition Reflex
…the micturition reflex is an autonomic (involuntary) spinal cord reflex or
self regenerative reaction that initiates urination…
Continue…
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It is a two phase cycle that serves as a protective mechanism for the kidneys. It
consists of the STORAGE (filling) PHASE and the EMPTYING PHASE.
The NEURORECEPTORS that control the micturition reflex are
PARASYMPATHETIC (cholinergic) and SYMPATHETIC (Alpha or Beta).
The PARASYMPATHETIC (cholinergic) receptors are throughout the “body” of the
bladder, trigone and bladder neck.
The SYMPATHETIC (beta) receptors are throughout the bladder, more densely
populating the “dome” and less dense in the trigone.
The SYMPATHETIC (alpha) receptors are densely located in the bladder neck
(proximal urethra) and more sparsely populate the trigone.
Distribution of Neuroreceptors in Bladder wall
(A: alpha receptors; B: beta receptors; C: cholinergic receptors)
During the STORAGE phase:
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Parasympathetic (cholinergic) receptors are inhibited,
prohibiting detrusor muscle contraction.
Sympathetic receptors are stimulated, resulting in:
Relaxation of beta controlled detrusor muscle and
increased stretch capacity of the bladder dome.
Contraction of the alpha controlled bladder neck.
During the EMPTYING phase:
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Sympatheic receptors are inhibited, resulting
in:
Cessation of the beta assisted stretch of
detrusor muscle.
Relaxation of the alpha controlled bladder neck.
Parasympathetic (cholinergic) receptors are
stimulated, strengthening the detrusor
contraction.
Regulation of micturition reflex by the brain
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Brain centers that control micturition reflex include:
1)centers in the brain stem, located mainly in pons; strong facilitative and inhibitory.
2)centers located in cerebral cortex; mainly inhibitory and occasionally excitatory.
MICTURITION: The Overall Process
When the volume of urine in the bladder reaches about 250ml, stretch receptors in
the bladder walls are stimulated and excite sensory parasympathetic fibres which
relay information to the sacral area of the spine.
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This information is integrated in the spine and relayed to two different sets of
neurones.
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Parasympathetic motor neurones are excited and act to contract the detrusor
muscles in the bladder so that bladder pressure increases and the internal
sphincter opens.
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At the same time, somatic motor neurones supplying the external sphincter via the
pudendal nerve are inhibited, allowing the external sphincter to open and urine to
flow out.
Completion of the emptying of the bladder is also facilitated by contraction of the
abdominal wall.
For normal micturition to occur we need:
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Intact nerve pathways to the urinary tract;
Normal muscle tone in the detrusors, sphincters and pelvic floor muscles;
Absence of any obstruction to urine flow in any part of the urinary tract;
Normal bladder capacity.
Clinical correlation
Urinary tract infection;
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Bladder and urethra irritation
Uninhibited contraction of detrusor muscles due to facilitation of micturition
reflex
Resulting in urinary frequency, leakage
Pelvic nerve injury
– Large, non contracting bladder – Acontractile bladder
– Urinary retention with overflow incontinence
– Loss of detrusor muscle contraction
Spinal cord injury;
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Continue…
Uninhibited contraction of detrusor muscles and non relaxation of
sphincter due to lack of inhibition of higher centre
„ Neurogenic bladder‟- high pressure bladder
Cerebral vascular accident (CVA) / Stroke;
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Loss of „fine‟ tuning from higher centers
Micturition reflex intact
Mixed presentation of incontinence and retention
Urinary incontinence;
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– Increase frequency of urination
– Urgency – desire to urinate with a volume of less than 50ml
– Dysuria
May result from
– Hyperactive micturition reflex
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due to irritation (urge incontinence)
– Effort/exertion/coughing/sneezing
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pelvic floor weakness (stress incontinence)
– Overdistension of bladder
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urethral obstruction (overflow incontinence)
MICTURATION: Age-related changes
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Frequency of involuntary bladder contraction increases
Total bladder capacity decreases
Bladder contractility decreases
– increased postvoid residuals
– increased sensation of urgency/fullness
Increase incidence of nocturia
Women
– menopausal estrogen decline
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urogenital atrophy
decrease in sensitivity of receptors in the internal
sphincter – less tone
Men
– Prostatic hypertrohpy
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increased urethral resistance
varying degrees of urethral obstruction
higher frequency of urination, however unable to urinate
much \ stream of urine not smooth
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