RT Book, Section A1 LeBlond, Richard F. A1 Brown, Donald D. A1 Suneja, Manish A1 Szot, Joseph F. SR Print(0) ID 1139369129 T1 The Urinary System T2 DeGowin’s Diagnostic Examination, 10e YR 2015 FD 2015 PB McGraw-Hill Education PP New York, NY SN 978-0-07-181447-8 LK accessmedicine.mhmedical.com/content.aspx?aid=1139369129 RD 2024/03/28 AB The kidneys, collecting systems of the renal pelvis, ureters, urinary bladder, and urethra constitute the urinary system. There are two sphincters, one involuntary and the other having both voluntary and involuntary components. The sphincter at the ureterovesical junction is formed by the oblique passage of the ureter through the bladder wall; detrusor muscle tone compresses the ureter preventing reflux of urine from the bladder. The other sphincter is at the bladder outlet as it passes through the urogenital septum. The urethral sphincter has an involuntary smooth muscle portion under parasympathetic and sympathetic control, and voluntary striated muscle innervated via the lumbosacral plexus. The kidney filters the blood at the glomerulus, reabsorbs and secretes solutes and fluid in the renal tubules, and concentrates the urine in the medullary collecting ducts. The urine passes down the ureters to the bladder by gravity and peristaltic contractions to fill the hollow urinary bladder. Active relaxation of detrusor muscle in the bladder wall maintains low pressure within the bladder until its capacity is reached. Further filling occurs by stretching the bladder wall at rapidly increasing pressures. Continence is maintained by tonic contraction of the smooth muscle sphincter and active inhibition of detrusor contraction. Voiding is a complex process involving simultaneous, coordinated relaxation of the urethral sphincters and contraction of the detrusor muscle.