5Waste Excretion and Storage
Once the kidneys have produced urine, it is transported to the urinary bladder through the ureters. When the volume of this area reaches around 150 to 400 ml, the walls start to stretch, which signals the spinal cord and brain. This eventually relaxes the involuntary urethral sphincter and makes you feel the need to urinate. Urination can be delayed unless the bladder reaches the maximum volume. However, more signals might result in more discomfort and urgency.
Urination starts with the relaxation of the muscles in your urethral sphincters. This allows urine to go through the urethra. Also, the smooth muscle in the urinary bladder’s walls contract to release urine. [8]
