The physiology and pharmacology of the urinary tract

The urinary bladder is a storage vessel for most of the time, when intravesical pressure remains low and the outflow resistance high. During voiding a switch occurs when intravesical pressure rises and the outflow relaxes. The control of this change of function is regulated by a complex interplay between sensations arising from the lower urinary tract (LUT), coordination of responses in the brain and sacral spinal cord and control over bladder and the outflow tract. LUT function can become disorganized and commonly shows as overactive bladder (OAB) with symptoms of urgency and frequency, with or without incontinence. Several pharmaceutical approaches to manage OAB are possible which rely predominantly on manipulating mechanisms that generate detrusor contraction, initiate sensations of bladder filling or reduce the magnitude of outflow obstruction. The introduction of successful agents requires knowledge of the mechanisms that generate contraction in LUT tissues both in the normal and overactive bladder. The upper urinary tract propels urine from the kidney to the bladder by peristalsis, a process modulated by agents such as prostaglandins, produced by the ureters. Urinary tract stones collect in the upper tract and cause considerable morbidity. They are commonly formed of Ca oxalate/phosphate or magnesium ammonium phosphate. Various endogenous and artificial agents promote or inhibit stone formation and along with various mechanical procedures are used to manipulate the formation of upper tract stones.