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Urinary Bladder:The urinary bladder is roughly pear-shaped situated in the pelvis behind the symphysis pubis. It is capable of storing 350 to 500 ml urine.  The wall of the bladder is made up four layers. 1) outer serous coat 2) muscular coat 3)sub-mucous coat 4) much folded mucous coat of transitional epithelium.  Bladder has three openings, two for ureters and one for urethra. The triangular area between these three openings is called as trigone.When fully distended by accumulation of urine, the sphincter guarding the opening of urethra relaxes that result in micturition (disposal of urine).medical billing training online teaches you all these in detail.