JOHN BAVOSI / SCIENCE PHOTO LIBRARY JOHN BAVOSI / SCIENCE PHOTO LIBRARY
Bladder. Artwork of a section through a man's healthy bladder (upper centre), also showing the muscles (red) that control urination. The bladder stores urine from the kidneys before discharging it through the urethra. This tube runs through the prostate gland (between muscles) and leaves the body through the penis (partially seen at lower right). The internal urethral sphincter muscle (sphincter vesicae) at the base of the bladder is thought to be controlled by an involuntary reflex arc, a nervous response that occurs without consc- ious control. Voluntary bladder control using the external urethral sphincter (sphincter urethrae, below the prostate) develops after infancy.
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