Porth's Essentials of Pathophysiology, 4e

631

Disorders of Renal Function

C h a p t e r 2 5

SUMMARY CONCEPTS

Obstructive Disorders Urinary obstruction can occur in persons of any age and can involve any level of the urinary tract, from the urethra to the renal pelvis 5,27 (Fig. 25-13). Obstruction may be sudden or insidious, partial or complete, and unilateral or bilateral. The conditions that cause urinary tract obstruction include congenital anomalies, urinary calculi (i.e., stones), pregnancy, benign prostatic hyper- plasia, scar tissue resulting from infection and inflam- mation, tumors, and neurologic disorders such as spinal cord injury. The causes of urinary tract obstructions are summarized in Table 25-1. Obstructive uropathy is usually classified according to site, degree, and duration of obstruction. Lower uri- nary tract obstructions are located below the ureteroves- ical junction and are bilateral in nature. Upper urinary tract obstructions are located above the ureterovesical junction and are usually unilateral. The condition caus- ing the obstruction can cause complete or partial occlu- sion of urine outflow. When the obstruction is of short duration (i.e., less than a few days), it is said to be acute and is usually caused by conditions such as renal calculi. ■■ Tubulointerstitial diseases affect the tubules and the surrounding interstitium of the kidneys. These disorders include acute and chronic pyelonephritis and the effects of drugs and toxins. Pyelonephritis, or infection of the kidney and kidney pelvis, can occur as an acute or a chronic condition. Acute pyelonephritis typically is caused by ascending bladder infections or infections that come from the bloodstream; it usually is successfully treated with appropriate antimicrobial drugs. Chronic pyelonephritis is a progressive disease that produces scarring and deformation of the renal calyces and pelvis. ■■ The susceptibility of the kidney to drug-induced damage reflects its significant exposure to medications and their metabolites. Some drugs, such as diuretics, high–molecular-weight radiocontrast media, the immunosuppressive drugs cyclosporine and tacrolimus, and the NSAIDs can cause acute prerenal failure by decreasing renal blood flow. Other drugs such as sulfonamides and vitamin C can form crystals that cause kidney damage by obstructing urinary flow in the tubules. Drugs can also directly damage tubulointerstitial structures, or provoke hypersensitivity reactions. Illicit drug use has also been implicated in a wide spectrum of kidney diseases.

Kidney stone

Pregnancy or tumor

Scar tissue

Uretero- vesical junction stricture

Neurogenic bladder

An obstruction that develops slowly and is longer last- ing is said to be chronic and is usually caused by con- ditions such as congenital ureterovesical abnormalities. Bilateral acute urinary tract obstruction causes acute renal failure. Because many causes of acute obstruction are reversible, prompt recognition is important. When left untreated, an obstructed kidney undergoes atro- phy, and in the case of bilateral obstruction, results in chronic kidney disease. Bladder outflow obstruction FIGURE 25-13. Locations and causes of urinary tract obstruction.

TABLE 25-1 Causes of UrinaryTract Obstruction Level of Obstruction Cause

Renal pelvis

Renal calculi Papillary necrosis

Ureter

Renal calculi Pregnancy Tumors that compress the ureter Ureteral stricture Congenital disorders of the uretero-vesical junction and ureteropelvic junction strictures Bladder cancer Neurogenic bladder Bladder stones Prostatic hyperplasia or cancer Urethral strictures Congenital urethral defects

Bladder and urethra