Understand the process of micturition and how this is controlled in the body

Micturition

Once filtrate leaves the collecting duct, no further modifications can occur. Now called urine. Rhythmic contractions of ureter smooth muscle eject urine into the bladder

Bladder

composed of smooth muscle and stores urine until it is voided. Can hold ~500mL. Neck of bladder feeds into urethra. Opening of bladder and urethra closed by sphincters

Internal Sphincter

smooth muscle - passively contracted

external sphincter

skeletal muscle - stays contracted

when micturition in inconvenient

inputs from the CNS can inhibit the micturition reflex and cause contraction of the external urethral sphincter

Initiation and Control of the Micturition Reflex

When accumulation of urine reaches approximately 250–300 mL, mechanoreceptors in the bladder wall, which respond to the stretching of tissue, stimulate the micturition reflex. Control of the micturition reflex occurs when conscious control of the external sphincter takes place and urine is released from the bladder