Aug 20, 2015
Physiological 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
Anatomy & 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
Transport of Urine from the Kidney through Ureters into Bladder
• Kidneys– Calyces
• Ureters• Bladder• Vesicoureteral Reflux• Pain and uerterorenal reflex
Filling 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.
In 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 occulusion of the ureter. As a result some of the urine in the bladder is propelled backward into the ureter. This is called ‘Vesicoureteral reflux’.
Ureterorenal reflexUreterorenal reflex
The ureters are well supplied with pain nerve fibers. When a ureter is blocked eg. 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 ‘Ureterorenal reflex’.
INNERVATION OF BLADDER
1. PARASYMPATHETIC NERVES (PELVIC NERVE) (S2-3) a) Sensory (stretch) b) Motor (detrusor, Internal sphincter)
2. SKELETAL MOTOR FIBER (PUDENDAL NERVES) (S2-3)
a) Sensory (stretch)b) Motor (external sphincter)
3. SYMPATHETIC NERVES (HYOGASTRIC NERVES) (L2)
a) Sensory (fullness, pain)b) Motor (stimulate blood Vs)
They prevent reflux of semen into the bladder during ejaculation.
(MAIN)
L1
L2
L3
Sympathetic nerve supply
Sympathetic
chain
Hypogastric
ganglion
Hypogastric
nerve Urethra
External sphincter
Parasympathetic nerve supply S2
S3
S4
S2
S3
S4
Pelvic nerve
Pudendal nerve
Somatic nerve supply
Regulation of the BladderMain Influence: Parasympathetic
Pelvic nerve Detrussor muscle
Hypogastric nerve
Pudendal nerve
Internal sphincter
External sphincter
Para
Sym
Vol
1. Pressure builds up in the bladder
2. This causes the contraction of the detrussor 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.
What is micturition reflex? Spinal cord reflex activity.
* facilitated or inhibited by higher centers
* voluntary facilitation or inhibition
Micturition 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
Bladder Filling & Emptying Cycle
The cycle ofbladder fillingand emptying
1. Bladder fills
2. First desire tourinate (bladder
half full)
Urination 3. Urinationvoluntarily inhibiteduntil time and place
are right
Detrusor muscle
contracts
Detrusor muscle relaxes
Urethralsphinctercontracts
Urethral sphincter relaxes
Voiding Urine - Micturition
• Micturition reflex1) 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 sphincter4) this reflex predominates in infants
• Infants– Spinal reflex
• Adults– Spinal reflex – Higher control
• (pelvic muscles and external urethral sphincter)
Cystometrogram
100 200 300 400
Intravesical volume (mL)
Intravesical pressure
(cm of
Water)
80
60
40
20
00
IaIb
Bladder filling –cystometrogram• Relation between bladder volume & pressure.• Empty bladder……P zero• 30-50 ml urine……P 5-10 cm H2O
• 50 – 300 ml urine…. P 5-10 cm H2O
• More than 400 ml…..rapid rise in P
LAW 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.
• When 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.
Filling 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 ………..
Facilitation or inhibition of micturition by brain
• Pons– Facilitatory and inhibitory centers
• Cortex– Mainly inhibitory centers
Voluntary Urination
• Micturition 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.
Next 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
Pontine 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
Spinal 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….
Normal 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
Abnormalities
• Atonic bladder Sensory nerve fibers from the bladder to the
spinal cord are destroyed Overflow incontinence Crush injury, syphilis,
Automatic bladder• Above the sacral region with intact sacral
cord segments• No longer controlled by the brain• Spinal shock
• contd.
TThe urinary bladder looses its tone and becomes flaccid he urinary bladder looses its tone and becomes flaccid and unresponsive. So, the bladder is completely filled, and and unresponsive. So, the bladder is completely filled, and later urine overflows by dribbling. After the spinal shock later urine overflows by dribbling. After the spinal shock has passed, the voiding reflex returns although there is no has passed, the voiding reflex returns although there is no voluntary and higher centre control. voluntary and higher centre control.
Whenever, the bladder is filled with some amount of urine, Whenever, the bladder is filled with some amount of urine, there is automatic evacuation of the bladder.there is automatic evacuation of the bladder.
(Spastic neurogenic bladder)(Spastic neurogenic bladder)
Uninhibited 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
Nocturnal 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 .
Incontinence 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