Figure 3-9. Sagittal section through the male pelvis showing the urinary bladder in
relation to surrounding structures.
b. The function of the urinary bladder is to store the urine until a large enough
quantity is collected to excite the nerve impulses that will cause a relaxation of the
sphincter muscles surrounding the urethral opening and thus allow the contents of the
bladder to be emptied. In the infant, this action occurs involuntarily, but control of
urination comes with training. The urine escapes from the bladder by way of the
internal urethral orifice.
3-17. THE URETHRA
The urethra is a membranous canal by which urine is conveyed from the bladder
to the outside (figures 3-9 and 3-10).