Control of Micturition Mechanism & Control

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.

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.

Urinary System Two kidneys Two ureters Bladder Urethra

functional anatomy of urinary bladder Transitional epithelium

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

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

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 40-60 mm Hg.

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

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.

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

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

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

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

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

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

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.

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.

Neural innervation & Actions

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

Major Events of Micturition

Neural Control of Micturition

Micturition Reflex Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

Micturition; Voiding Urine Micturition reflex 1) 200-300 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

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

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.

Relationship between intravesical volume and pressure & cystometrogram

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.

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

Cystometrogram

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.

Effects of denervation on micturition reflex Abnormalities of micturition Effects of denervation on micturition reflex

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

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

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.

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.

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.

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 .