Urinary Bladder

The urinary bladder is a hollow structure with prominent smooth muscle walls that is a temporary reservoir for urine. It is tetrahedral shaped and consists of a posterior surface (fundus or base), anterior surface, superior surface, apex and neck.

The relations of the urinary bladder to other structures are categorized as:

The right and left ureters transport urine into the bladder while the urethra transports urine out of the bladder. The position of the two ureters and one urethra can be marked on the internal aspect of the urinary bladder as the trigone area - a triangular area located within the fundus.

The walls of the bladder are composed of specialized smooth muscles known as the detrusor muscle. It’s fibres run in different directions to support its ability to stretch.

Blood Supply

The internal iliac artery supplies the urinary bladder.

Venous drainage:

The vesicle venous plexus along the inferolateral portion of the bladder drains the bladder.

Innervation

Sympathetic innervation to the urinary bladder is by the hypogastric nerve which causes relaxation of the detrusor muscle, promoting urine retention.

Parasympathetic innervation to the urinary bladder is the pelvic nerve (S2-S4) which causes contraction of the detrusor muscle, stimulating micturition.

Somatic innervation to the urinary bladder is by the pudendal nerve (S2-4) which innervates the external urethral sphincter, providing voluntary control over micturition.

Micturition reflex:

As the bladder fills with urine, stretch information associated with bladder fullness from stretch receptors in the bladder wall runs with the pelvic splanchnic nerves and serves as the afferent limb in the micturition reflex.

Pelvic splanchnic nerves are distributed to the detrusor muscle of the bladder, where they cause contraction of the detrusor muscle and relaxation of the internal urethral sphincter.

The external urethral sphincter is innervated by the pudendal nerve and is voluntarily relaxed.