Micturition Prof. K. Sivapalan.

Ureters. Collecting ducts open into the renal pelvis which goes down as ureters. The walls contain smooth muscles. Regular peristaltic contractions, 1 – 5 times per minute, move urine from renal pelvis to the bladder. The ureters pass obliquely into bladder musculature so that the pressure in the bladder keeps it closed without reflux Micturition2

Bladder. Smooth muscle is arranged in spiral, circular and longitudinal bundles. Fibers at the origin of the urethra form the internal sphincter. Skeletal muscles of pelvic diaphragm form the external sphincter of the urethra. Smooth muscles are innervated by sacral and lumbar autonomics External sphincter is innervated by pudental nerve Micturition3

Bladder Volume and Pressure Initially, pressure increases [about 50 ml]. Second phase shows no appreciable increase of pressure [about 400 ml] – plasticity. Third phase- voiding occurs or pressure increases. Further increase causes pain Micturition4

Bladder Sensation Afferents in the pelvic parasympathetic nerves mediate sense of volume. This is transmitted to higher centers when the intensity goes above critical level. First urge to pass urine is sensed at about 150 ml. Second urge occurs with sense of fullness at ml. In further distention of bladder sympathetic afferents mediate pain Micturition5

Reflex Control of Micturition Bladder smooth muscle has some inherent contractile activity. With intact nerve supply, distention causes reflex contraction Center- sacral segments Efferent- sacral parasympathetics - contraction of detrusor muscles and relaxation of internal sphincter. The center can be facilitated or inhibited by higher centers Micturition6

Higher Control of Micturition Brain stem- pons facilitatory and mid brain inhibitory. Posterior hypothalamus- facilitatory. Superior frontal gyrus- involved with desire to pass urine. Voluntary facilitation of the reflex occurs probably through these pathways. Voluntary contraction of abdominal muscles also aids micturition. Sympathetic nerves relax detrusor muscles and contract internal sphincters Micturition7

Urge to urinate by filling or voluntary facilitation activates the sacral center. Parasympathetic outflow contracts detrusor muscles and relaxes internal sphincter. Voluntary relaxation of the external sphincter results in voiding. Female urethra empties by gravity and male urethra by contraction of bulbocavernosus muscle Micturition8

Effects of Deafferentation Loss of afferents as in tabes dorsalis Reflex contraction is abolished. Bladder is distended, thin walled, hypotonic and hypotonic. Occasional week inherent contraction causes expulsion of little urine Micturition9

Effects of Denervation As in tumor of cauda equina. The bladder is flaccid and distended for some time. It becomes active and frequent contractions expel dribbles of urine. The bladder becomes shrunken and hypertrophied. The efferents destroyed are preganglionic Micturition10

Effects of Spinal Cord Transection The bladder is flaccid and nonresponsive- overflow incontinence- during spinal shock. After 2 weeks voiding reflex returns without voluntary control. Mass reflex may help- pinching or stroking medial aspect of thighs. Emptying is not complete Micturition11