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OVERVIEW AND PHYSIOLOGY OF THE URINARY SYSTEM

The urinary system includes the kidneys, renal pelvis, ureters, urinary bladder, and urethra. 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. Urine passes down the ureters to the bladder by gravity and peristalsis filling the urinary bladder. At the ureterovesical junction the ureters are compressed by detrusor muscle tone as they pass obliquely through the bladder wall. This compression increases during detrusor contraction preventing urine from refluxing into the ureters. The detrusor actively relaxes as the bladder fills maintaining a low pressure within the bladder until it reaches capacity. Further filling stretches the bladder wall rapidly increasing intravesical pressure. The urethra exits the bladder through the urethral sphincter and the urogenital septum. This sphincter has involuntary smooth muscle under parasympathetic and sympathetic control, and voluntary striated muscle innervated via the lumbosacral plexus. Continence requires tonic urethral sphincter smooth muscle contraction and active inhibition of detrusor contraction. Voiding requires detrusor contraction and simultaneous relaxation of the urethral sphincter muscles.

URINARY SYSTEM ANATOMY

The kidneys lie posteriorly partially under the 11th and 12th ribs lateral to L1–4 (Chapter 9, Fig. 9-2, page 395). They lie retroperitoneally enclosed in a tight capsule and surrounded by Gerota fascia. The ureters descend in the retroperitoneum over the psoas muscle and into the pelvis running laterally and then anteriorly to enter the bladder inferiorly on either side of the midline. The bladder lies behind and below the symphysis pubis in the anterior pelvis. The urethra exits the bladder through the urogenital diaphragm formed by pelvic floor muscles, entering the male prostate and penis or the female perineum. The male’s proximal urethra is surrounded by the prostate gland and receives secretions from the prostate and seminal vesicles. The perineal portion of the female urethra is quite short. The urethral meatus is visible on inspection and the prostate is palpable during rectal exam. The other normal structures cannot be identified by physical exam.

EXAMINING THE URINARY SYSTEM

See also The Abdomen, Chapter 9; The Female Genitalia and Reproductive System, Chapter 11; and The Male Genitalia and Reproductive System, Chapter 12.

URINARY SYSTEM SYMPTOMS

Discolored Urine

See page 472.

Urethral Discharge

See page 474 and Urethritis page 479 and Chapter 12, page 523.

Ureteral Colic

See Abdominal Pain Chapter 9, pages 407 and 433 and ureteral colic Chapter 9, page 438. Vigorous contraction of ureteral smooth muscle against an obstruction is intensely painful. Obstructing stones in the renal pelvis, ureter, or bladder produce waves of severe acute pain, ureteral colic. The ...

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