Porth's Essentials of Pathophysiology, 4e

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Disorders of Renal Function

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polydipsia, and enuresis (bed-wetting), which reflect impaired ability of the kidneys to concentrate urine. Other manifestations of the disorders include salt wast- ing, growth retardation, anemia, and progressive renal insufficiency. Simple and Acquired Renal Cysts Simple cysts are a common acquired disorder of the kid- ney. The cysts may be single or multiple, unilateral or bilateral, and they are commonly 1 to 5 cm in diameter, but may reach 10 cm or more. The cysts usually are confined to the cortex. In rare instances, massive cysts as large as 10 cm in diameter are encountered. 4,5 Most simple cysts do not produce signs or symptoms or com- promise renal function. When symptomatic, they may cause flank pain, hematuria, infection, and hypertension related to ischemia-produced stimulation of the renin- angiotensin system. They are most common in persons older than 50 years. Although the cysts are benign, the main concern is to differentiate them from renal cell carcinoma. Ultrasound and CT scanning are the recom- mended procedures for evaluating these masses. 4,5 An acquired form of renal cystic disease occurs in per- sons with chronic kidney disease who have undergone prolonged dialysis treatment. 4 Although the condition is largely asymptomatic, the cysts may bleed, causing hematuria. Tumors, usually adenomas but occasionally adenosarcomas, may develop in the walls of these cysts. ■■ Congenital abnormalities of the kidney include agenesis or failure of the kidneys to develop, which is incompatible with life if both kidneys are affected; hypogenesis or failure of the kidneys to develop to normal size, which usually causes no problems unless both kidneys are affected; and renal dysplasia, which is characterized by disorganized and maldifferentiated development of kidney tissue, usually accompanied by cyst formation. Other developmental kidney defects can result in kidneys that lie outside their normal position or are fused to form horseshoe-shaped kidneys. ■■ Cystic diseases of the kidney are hereditary and nonhereditary disorders in which there is dilation of tubular structures with cyst formation. ■■ There are two forms of polycystic kidney disease: autosomal dominant (ADPKD) and autosomal recessive (ARPKD). Autosomal dominant (adult) polycystic kidney disease results in the formation of numerous fluid-filled cysts in the tubular structures of both kidneys with the threat of progression to chronic kidney disease. ARPKD, SUMMARY CONCEPTS

which is rare compared with ADPKD and usually presents as severe renal dysfunction during infancy, is characterized by cystic transformation of the collecting ducts. ■■ Nephronophthisis and adult-onset medullary cystic kidney disease are characterized by the presence of similar progressive medullary cystic disease, but with different genetic causes and inheritance. Nephronophthisis is an autosomal recessive disorder, with onset in infancy, childhood, or adolescence; whereas adult- onset medullary cystic disease is an autosomal dominant disorder with onset in adolescence and renal failure in adulthood. ■■ Simple cysts are an acquired disorder of the kidney.They may be single or multiple, unilateral or bilateral, and are commonly 1 to 5 cm in diameter. Although the cysts are benign, the main concern is to differentiate them from malignancies.

Disorders of Glomerular Function

Glomerular disorders are one of the most common forms of kidney disease. The glomeruli may be the major site of disease (primary glomerular disease) or part of a disease affecting other organs (secondary glomerular disease). Hereditary glomerular diseases such as Alport syndrome, although relatively rare, are an important category of glomerular disease because of their associa- tion with progressive loss of renal function and trans- mission to future generations.

Etiology and Pathogenesis of Glomerular Injury

Many of the clinical manifestations of glomerular dis- orders result from dysfunction of specific components of the glomeruli, which consist of a network of capillar- ies, lined with a fenestrated endothelium invested in two layers of epithelium (Fig. 25-4A). The visceral epithe- lium is incorporated into and becomes an intricate part of the capillary wall, separated from the endothelium by a basement membrane. 4,5 The parietal epithelium, which lines Bowman space within which urine collects, is attached to the basement membrane by long, footlike processes ( podocyte s) that encircle the outer surface of the capillaries. The glomerular capillary membrane is selectively permeable, allowing water and small particles (e.g., electrolytes and dissolved particles, such as glu- cose and amino acids) to leave the blood and enter the Bowman space while preventing larger particles (e.g., plasma proteins and blood cells) from leaving the blood.