In the anatomy of mammals, the urinary bladder is the organ that collects urine excreted by the kidneys prior to disposal by urination. Urine enters the bladder via the ureters and exits via the urethra.

Anatomy

The urinary bladder is a hollow, muscular and distensible organ that sits on the pelvic floor (superior to the prostate in males). On its anterior border lies the pubic symphysis and, on its posterior border, the vagina (in females) and rectum (in males).

The ureters enter the bladder diagonally from its dorsolateral floor toward the midline. The smooth triangular area of the bladder between the entrance of the two ureters and the exit of the urethra is called the trigone. This part of the bladder expands least during filling.

A normal human bladder has a capacity of 400 to 500 ml. This is largely due to distention of the detrusor muscle in the wall and specialised urothelium lining the interior surface which is capable of significant stretching.

Emptying of the bladder is controlled by the micturition reflex via parasympathetic and sympathetic nerve fibres. Voluntary inhibition of this reflex is controlled by higher neural centres in the pons.

The study of the function of the bladder is called urodynamics.

Diseases of the bladder

• bladder sphincter dyssynergia, a condition where the sufferer cannot coordinate relaxation of the urethra sphincter with the contraction of the bladder muscles
• cystitis
• cystolithiasis
• cancer of the urinary bladder: bladder cancer
• hematuria, or presence of blood in the urine, is a reason to seek medical attention without delay, as it is a symptom of bladder cancer as well as bladder and kidney stones.
• interstitial cystitis
• ureterocele
• urinary bladder dysfunction
• urinary incontinence

Urinary system

Kidneys - Ureters - Urinary bladder - Urethral sphincters - Urethra

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