Micturation reflex by Dr Irum

2. MICTURITION Dr Irum Junaid

8. Urinary Bladder

9. 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.

10. 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 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’.

12. L 1 L 2 L 3 Sympathetic nerve supply Sympathetic chain Hypogastric ganglion Hypogastric 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

13. Bladder Innervation

14. Regulation of the Bladder Main 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.

15. What is micturition reflex? Spinal cord reflex activity. * facilitated or inhibited by higher centers * voluntary facilitation or inhibition

17. Bladder 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

21. Normal Control of Urination

26. 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 ………..

33. Adult Micturition Reflex Diagram

35. Cystometrogram

38. T 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)

40. 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 .