1. Control of Micturition
Mechanism & Control

2. Learning Outcomes Describe functional anatomy of urinary bladder
Describe sympathetic and parasympathetic innervation of urinary bladder and sphincters
State the normal capacity of the urinary bladder
Explain the Micturition reflex
Explain the relationship between intravesical volume and pressure
Depict diagrammatically the cystometrogram
Explain the effects of denervation on the urinary bladder and Micturition reflex.

3. Micturition
Process of emptying of filled urinary bladder is called as Micturition.
involves two main steps:
First, progressive filling of the bladder until the tension in its walls rises above a threshold level;
Second step is a nervous reflex called the micturition reflex that empties the bladder or, if this fails, at least causes a conscious desire to urinate.
an autonomic spinal cord reflex but can be inhibited or facilitated by higher centers.

4. Urinary System
Two kidneys
Two ureters
Bladder
Urethra

5. functional anatomy of urinary bladder
Transitional
epithelium

6. Ureters ; Urine Transportation
from renal pelvis passes dorsal to bladder and enters it from below, about 25 cm long
enter the bladder through the detrusor muscle in the trigone region of the bladder, course obliquely through the bladder wall.
The normal tone of the detrusor muscle in the bladder wall tends to compress the ureter, thereby preventing back-flow of urine during micturition or bladder compression.
Entry of urine stretches and contracts in peristaltic wave increases the pressure within the ureter and allows urine to flow into the bladder

7. Features of the bladder
a normal capacity of 400–500 mL,
the ability to accommodate various volumes without a change in intra-luminal pressure,
ability to initiate and sustain a contraction until the bladder is empty,
voluntary control for initiation or inhibition of voiding

8. Urinary bladder; storage and emptying
Smooth muscle chamber consists of two parts
Body ~ major part, collect urine
Neck ~ funnel shaped lower part of bladder, connect the bladder to urethra, also called as posterior urethra.
Bladder muscles are detrusor muscle, act as syncytium~ each fiber fuse with other through low resistance gap junctions
Entire bladder contract as whole~ increase pressure from mm Hg.

10. Urethra
Is a tube that pass urine from the urinary bladder to the outside of the body
Its wall is lined with a mucous membrane
has a thick layer of longitudinal smooth muscle fibers

11. The Sphincteric Unit
In both males and females, there are 2 sphincteric elements:
an internal involuntary smooth-muscle sphincter at the bladder neck,
an external voluntary striated-muscle sphincter from the prostate to the membranous urethra in males and at the mid urethra in females.

12. Internal Urethral Sphincter
In both sexes: Composed of detrusor muscle interlaced with large amount of elastic fibers
Has natural tone
Keeps the bladder neck (posterior urethra) empty of urine.
Is under involuntary control , Prevent emptying of bladder
Innervated by postganglionic parasympathetic fibers

13. External Urethral Sphincter
In both sexes:
is a circular band of skeletal muscle
where urethra passes through urogenital diaphragm
Acts as a valve
Is under voluntary control, via perineal branch of pudendal nerve
Has resting muscle tone
Voluntarily relaxation permits micturition

14. Female Urethra 3 to 4 cm long Internal urethral sphincter
detrusor muscle thickened, smooth muscle, involuntary control
External urethral sphincter
skeletal muscle, voluntary control
between vaginal orifice and clitoris
External urethral orifice

15. Male Urethra 18 cm long Internal urethral sphincter
External urethral sphincter
3 regions
prostatic urethra
during orgasm receives semen
membranous urethra
passes through pelvic cavity
penile urethra

16. Innervation of the bladder
Sympathetic nerve supply
Parasympathetic nerve supply S2 S3 S4 L1 L2 L3
Pelvic nerve
Sympathetic
chain
Hypogastric
ganglion
nerve
Somatic nerve supply S2 S3 S4
Urethra
External sphincter
Pudendal nerve

17. Hypogastric nerve: Sympathetic
sympathetic nerves originate at L1–L3 through hypogastric nerve
noradrenergic postganglionic fibers innervate the smooth muscles of the bladder , internal sphincter, and proximal urethra.
Limited role in micturition but have role in fullness of bladder, pain

18. Pudendal Nerve: Somatic
Somatic afferent fibers
originates in S2–3 and travels to the external urethral sphincter
Control the voluntary skeletal muscle of the sphincter.
Responsible for conscious prevention of emptying of bladder inspite of regular involuntary signals to empty bladder.

19. Pelvic Nerve; Parasympathetic
Principal nerve supply to bladder is Pelvic nerve ;-sensory as well as motor nerve fibers.
originates in the second to fourth sacral segments.
Cholinergic postganglionic fibers supply both the bladder and sphincter.
Sensory detect degree of stretch
Motor signal cause emptying.

20. Neural innervation & Actions

21. Urinary bladder; normal capacity
Capacity of 400–500 ml without appreciable increase in intravesical pressure normally.
Has power of accommodation i.e. maintain almost constant intra-luminal pressure during filling phase , thus having higher compliance.
it is a feature of specialized “transitional epithelial mucosa” lining the bladder, responsible for distensibility of bladder

22. Major Events of Micturition

23. Neural Control of Micturition

24. Micturition Reflex
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25. Micturition; Voiding Urine
Micturition reflex
1) 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

26. Nerve endings sensitive to stretch
Stimulates contraction of detrusor muscle
Spinal cord
Simple reflex control of micturition seen in infants. The ability of voluntary control (inhibition) develops at the age of 2 – 3 years. 26

27. Voluntary Control of Micturition
5) Micturition center in pons receives stretch signals and integrates cortical input (voluntary control)
6) sends stimulatory signal to detrusor muscle and relaxes internal urethral sphincter
7) to delay urination, impulses sent through pudendal nerve to external urethral sphincter, to keep it contracted until you wish to urinate
8) Relaxation of external sphincter associated with contractions of the detrusor muscle ~ expel the urine.

28. Relationship between intravesical volume and pressure & cystometrogram

29. Relationship between intravesical volume and pressure
Represented by graph called cystometrogram.
studied by inserting a double lumen catheter.
the pressure is recorded by connecting one lumen of catheter to a suitable recording instrument and volume through the other lumen.
The pressure changes in the urinary bladder with rise in the volume of urine is recorded.
Explains the functional behavior of bladder and sphincter during storage of urine and micturition.
Indirectly measure the storage capacity and continence of bladder.

30. Cystometrogram
Relationship between intravesical pressure with changing volume of urine in the bladder.
Shows –three phases
an initial slight rise in pressure when the first increments in volume are produced;
a long, nearly flat segment as further increments are produced; and
a sudden, sharp rise in pressure as the micturition reflex is triggered

31. Cystometrogram

32. Cystometrogram- 3 components
Ia-Iniial rise: initial sharp rise due to increase in intravesicular pressure to about 10 cm of water.
Ib~ Long flat segment; slight or no change in intravesicular pressure inspite of additional 350 ml of urine (Law of Laplace)– pressure increases with simultaneous increase in radius.
II sudden sharp rise: due to addition of another 50to 100 ml of urine– triggers the micturition.

33. Effects of denervation on micturition reflex
Abnormalities of micturition
Effects of denervation on micturition reflex

34. Effect of denervation
all reflex contractions of the bladder are abolished.
bladder becomes distended, thin-walled, and hypotonic,
some contractions occur because of the intrinsic response of the smooth muscle to stretch

35. Effect of transection of spinal cord
Overflow incontinence;
the bladder is flaccid and unresponsive.
It becomes overfilled, and urine dribbles through the sphincters.
During recovery phase, the voiding reflex returns, without any voluntary control.
Some paraplegic patients train themselves to initiate voiding by pinching or stroking their thighs, provoking a mild mass reflex

36. Effect of transection of spinal cord
spastic neurogenic bladder.
the voiding reflex becomes hyperactive,
bladder capacity is reduced,
the wall becomes hypertrophied.
reflex hyperactivity is made worse by, and may be caused by, infection in the bladder wall.

37. Uninhibited neurogenic bladder
elicit the micturition reflex even with small quantity of urine collected in bladder
Results in increased frequency of micturition.
lesion in some parts of brain stem interrupts most of the inhibitory signals leading to continuous excitation of spinal micturition centers-- results in uncontrollable micturition.

38. Other Micturition Reflex Problems
Loss of tone of Sphincter muscles: leading to incontinence
Control of micturition can be lost due to:
a stroke
Alzheimer’s disease
CNS problems affecting cerebral cortex or hypothalamus
Compression of the urethra by enlarged prostate gland – causes restricted urine flow may result in urinary retention.

39. 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 .