MBBSKE BS PU DHA CCM FWHOUK MBAFACHE US MPHIL UOL Assist Prof Physiology KEMU Lahore MICTURITION Urination is the release of urine from the urinary bladder through the urethra to the urinary meatus outside of the body It is also known ID: 919942
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Slide1
Slide2Lecture Notes By
Dr. Syed Mohammad Zubair
MBBS(KE) BS (PU) DHA (CCM)
FWHO(UK) MBA;FACHE (US)
M.PHIL (UOL)
Assist. Prof Physiology
KEMU
, Lahore
Slide3Slide4MICTURITION
Urination
is the release of urine from the urinary bladder through the urethra to the urinary meatus outside of the body. It is also known
medically as
MICTURITION
voiding
uresis
emiction
.
COLLOQUIALLY
t
inkling
,
peeing
,
Weeing
pissing
.
Slide5In healthy humans (and many other animals) the process of urination is under voluntary control.
In
infants, some elderly individuals, and those with neurological injury, urination may occur as an involuntary reflex.
In
some animals, in addition to expelling waste material, urination can mark territory or express submissiveness.
Slide6Physiologically, urination involves coordination between the central, autonomic, and somatic nervous systems.
Brain centres
that regulate urination include the pontine micturition
centre, periaqueductal
gray, and the cerebral
cortex.
In male placental mammals, urine is ejected through the penis
.
In female placental mammals, urine is ejected through the vulva or pseudo-penis
Slide7MICTURITION
Slide8Slide9Physiological Anatomy of Urinary System
Kidneys
(cortex, medulla, nephron, pelvis )
Ureters
(mucosa, muscle, fibrous)
Urinary Bladder
(body, neck), (mucosa, muscle, fibrous) (detrusor, trigone)
Urethra
Internal and External
sphincters
Slide10Anatomy & Neurophysiology of the Lower Urinary Tract
Bladder
(detrusor)
Stores urine at low pressure
Compresses urine for voiding
Urethra
Conveys urine from bladder to outside world
Sphincter(s) internal & external
Controls urine flow & maintain continence between voidings
Slide11Transport of Urine from the Kidney through Ureters into Bladder
Kidneys
Calyces
Ureters
Bladder
Vesicoureteral Reflux
Pain and uerterorenal reflex
Slide12Urinary Bladder
Slide13Filling of the bladder
When urine collects in the renal pelvis, the pressure in the pelvis increases. This increase in the pressure initiates a peristaltic contraction beginning in the pelvis and spreading downward along the ureter to force urine toward the bladder.
Peristaltic waves occur
1-5 times/minute
The walls of ureters contain smooth muscle arranged in spiral, longitudinal and circular bundles.
Slide14In some people, the distance that the ureter courses through the bladder mucosa is less than normal, so that contraction of the bladder during micturition does not always lead to complete
occlusion
of the ureter. As a result some of the urine in the bladder is propelled backward into the ureter. This is called
‘Vesicoureteral reflux’.
Uerterorenal
reflex
The ureters are well supplied with pain nerve fibers. When a ureter is blocked
e.g..
by a ureteral stone, there will be intense reflex constriction which is associated with very severe pain. These pain impulses cause a sympathetic reflex back to the kidney to constrict the renal arterioles, thereby decreasing urinary output from that kidney. This effect is known as
‘Uerterorenal
reflex’.
Slide15INNERVATION OF BLADDER
PARASYMPATHETIC NERVES
(PELVIC NERVE)
(S
2-3
)
a) Sensory (stretch)
b) Motor (detrusor, Internal sphincter)
2. SKELETAL MOTOR FIBER
(PUDENDAL NERVES)
(S
2-3
)
a) Sensory (stretch)
b) Motor (external sphincter)
3. SYMPATHETIC NERVES
(HYOGASTRIC NERVES)
(L
2
) a) Sensory (fullness, pain) b) Motor (stimulate blood Vs) They prevent reflux of semen into the bladder during ejaculation. (MAIN)
Slide16L
1
L
2
L
3
Sympathetic nerve supply
Sympathetic
chain
Hypo gastric
ganglion
Hypo gastric
nerve
Urethra
External sphincter
Parasympathetic nerve supply
S
2
S
3
S
4
S
2
S
3
S
4
Pelvic nerve
Pudendal nerve
Somatic nerve supply
Slide17Bladder Innervation
Slide18Regulation of the Bladder
Main Influence: Parasympathetic
Pelvic nerve
Detrusor
muscle
Hypo gastric
nerve
Pudendal nerve
Internal sphincter
External sphincter
Para
Sym
Vol
1. Pressure builds up in the bladder
2. This causes the contraction of the
detrusor
muscle, via the pelvic nerve.
3. The internal sphincter relaxes due to decreased sympathetic stimulation.
4. The external sphincter relaxes due to voluntary decrease in stimulation.
Slide19What is micturition reflex?
Spinal cord reflex activity.
* facilitated or inhibited by higher centers
* voluntary facilitation or inhibition
Slide20Micturition Reflex
Micturition contractions begin
Role of sensory and motor
parasympathetic
nerves
Self regenerative once begins
Complete cycle
Rapid increase in pressure
Period of sustained pressure
Return to basal tone
Slide21Bladder Filling & Emptying Cycle
The cycle of
bladder filling
and emptying
1. Bladder fills
2. First desire to
urinate (bladder
half full)
Urination
3. Urination
voluntarily inhibited
until time and place
are right
Detrusor
muscle
contracts
Detrusor muscle relaxes
Urethral
sphincter
contracts
Urethral sphincter relaxes
Slide22Voiding Urine - Micturition
Micturition reflex
1) 300-400 ml urine in bladder, stretch receptors send signal to spinal cord (S2, S3)
2) parasympathetic reflex arc from spinal cord, stimulates contraction of detrusor muscle
3) relaxation of internal urethral sphincter
4) this reflex predominates in infants
Slide23Slide24Infants
Spinal reflex
Adults
Spinal reflex
Higher control
(pelvic muscles and external urethral sphincter)
Slide25Normal Control of Urination
Slide26Cystometrogram
100 200 300 400
Intravesical volume (mL)
Intravesical pressure
(cm of
Water)
80
60
40
20
0
0
Ia
Ib
Slide27Bladder filling –
Cystometrogram
Relation between bladder volume & pressure.
Empty bladder……P zero
30-50 ml urine……P 5-10 cm H
2
O
50 – 300 ml urine…. P 5-10 cm H
2
O
More than 400 ml…..rapid rise in P
Slide28LAW of LAPLACE
This is in accordance with law of Laplace. In the bladder tension increases as the urine is filled. At the same time, the radius also increases due to relaxation of the detrusor muscle. Because of this, the pressure rise is almost nil.
Slide29When bladder wall stretches during filling it will initiate a reflex contraction which has lower threshold. That does not trigger micturition reflex. When bladder is filled about 300 – 400 mL of urine, there will be sharp rise in the intravesical pressure as the micturition reflex is triggered.
At this point also voluntary control is possible. Beyond 600 – 700 mL of urine voluntary control starts failing.
Slide30Filling of the bladder – partially filled
Reflex contractions
Acute increase in pressure
Contractions relax spontaneously
Pressure falls back to baseline
Bladder continues to fill
Reflex contractions – more frequently and powerful
Filling of the bladder ………..
Slide31Facilitation or inhibition of micturition by brain
Pons
Facilitatory and inhibitory centers
Cortex
Mainly inhibitory centers
Voluntary Urination
Slide32Micturition center is located in the
Frontal lobe
Function of micturition center
Send tonically
inhibitory
signals to the detrusor muscle to prevent the bladder from emptying (contracting) until a socially acceptable time and place to urinate is available.
Slide33Next stop is the…..
Pons
The major relay center between the brain and the bladder
Pontine micturition center
The PMC
coordinates
the urethral sphincter relaxation and detrusor contraction to facilitate urination
Slide34Pontine Micturition Center
Bladder filling
detrusor muscle stretch receptors
signal to the pons
brain
Perception of this signal (bladder fullness) as a sudden desire to go to the bathroom
Normally, the brain sends an inhibitory signal to the pons to inhibit the bladder from contracting until a bathroom is found.
Brain
deactivating signal to PMC
Urge to urinate disappears
At appropriate time, brain sends excitatory signals to the pons, allowing voiding
Slide35Spinal cord
Function
Long communication pathway between the brainstem and the sacral spinal cord
Sensory information from bladder
Sacral cord
Pons
Brain
Pons
Spinal cord
Sacral cord Bladder
Spinal cord acts as an important intermediary between the pons and the sacral cord
Intact spinal cord is critical for normal micturition
Next Stop After the PMC….
Slide36Normal Micturition – Spinal Cord
Sacral spinal cord – what is the significance?
Sacral reflex center
Responsible for bladder contractions
Primitive voiding center
In infants, the brain is not mature enough to command the bladder
SRC controls urination in infants and young children
When urine fills the infant bladder, an excitatory signal
sacral cord
spinal reflex center
detrusor contraction
involuntary detrusor contractions with coordinated voiding
Slide37Adult Micturition Reflex Diagram
Slide38Slide39Cystometrogram
Slide40Abnormalities
Atonic bladder
Sensory nerve fibers from the bladder to the spinal cord are destroyed
Overflow incontinence
Crush injury, syphilis,
Slide41Automatic bladder
Above the sacral region with intact sacral cord segments
No longer controlled by the brain
Spinal shock
contd.
Slide42T
he urinary bladder looses its tone and becomes flaccid and unresponsive. So, the bladder is completely filled, and later urine overflows by dribbling. After the spinal shock has passed, the voiding reflex returns although there is no voluntary and higher centre control.
Whenever, the bladder is filled with some amount of urine, there is automatic evacuation of the bladder.
(Spastic neurogenic bladder)
Slide43Uninhibited Neurogenic Bladder
Partial damage in the spinal cord or the brain stem
interrupting most of the inhibitory signals
Slight quantity of urine elicits an uncontrollable micturition reflex
Slide44Nocturnal micturition (Bed wetting)
This is normal in infants and children below 3 years. It occurs due to incomplete myelination of motor nerve fibers of the bladder resulting loss of voluntary control of micturition .
Slide45Incontinence from impaired sphincter function
Of lesser degree
In response to sudden rise in intravesical pressure (coughing, sneezing)
After multiple child births in women
After prostatic surgery involving damage to sphincter
Slide46