Organisms that infect the urinary tract generally enter through the urethra and ascend toward the bladder. Although urinary tract infections (UTIs) do occur in males, they appear more commonly in females. Infection of the urinary bladder produces cystitis. The infecting organisms are usually colon bacteria carried in feces, particularly Escherichia coli. Cystitis is more common in females than in males because the female urethra is shorter than the male urethra and the opening is closer to the anus. Poor toilet habits and urinary stasis are contributing factors. In the hospital, UTIs may result from procedures involving the urinary system, especially catheterization, in which a tube is inserted into the bladder to withdraw urine (Fig. 13-5). Less frequently, UTIs originate in the blood and descend through the urinary system.
An infection that involves the kidney and renal pelvis is termed pyelonephritis. As in cystitis, signs of this condition include dysuria, painful or difficult urination, and the presence of bacteria and pus in the urine, bacteriuria and pyuria, respectively.
Although the name simply means inflammation of the kidney and glomeruli, glomerulonephritis is a specific disorder that occurs after an immunologic reaction. It is usually a response to infection in another system, commonly a streptococcal infection of the respiratory tract or a skin infection. It may also accompany autoimmune diseases such as lupus erythematosus. The symptoms are hypertension, edema, and oliguria, the passage of small amounts of urine. This urine is highly concentrated. Because of damage to kidney tissue, blood and proteins escape into the nephrons, causing hematuria, blood in the urine, and proteinuria, protein in the urine. Blood cells may also form into small molds of the kidney tubule, called casts, which can be found in the urine.
Most patients recover fully from glomerulonephritis, but in some cases, especially among the elderly, the disorder may lead to chronic renal failure (CRF) or end-stage renal disease (ESRD). In such cases, urea and other nitrogen-containing compounds accumulate in the blood, a condition termed uremia. These compounds affect the central nervous system, causing irritability, loss of appetite, stupor, and other symptoms. There is also electrolyte imbalance and acidosis.
Acute Renal Failure
Injury, shock, exposure to toxins, infections, and other renal disorders may cause damage to the nephrons, resulting in acute renal failure (ARF). There is rapid loss of kidney function with oliguria and accumulation of nitrogenous wastes in the blood. Failure of the kidneys to eliminate potassium leads to hyperkalemia, along with other electrolyte imbalances and acidosis. When destruction (necrosis) of kidney tubules is involved, the condition may be referred to as acute tubular necrosis (ATN).
Renal failure may lead to a need for kidney dialysis or, ultimately, renal transplantation. Dialysis refers to the movement of substances across a semipermeable membrane; it is a method used for removing harmful or unnecessary substances from the body when the kidneys are impaired or have been removed (Fig. 13-6). In hemodialysis, blood is cleansed by passage over a membrane surrounded by fluid (dialysate) that draws out unwanted substances. In peritoneal dialysis, fluid is introduced into the peritoneal cavity. The fluid is periodically withdrawn along with waste products and replaced (Fig. 13-7). The exchange may be done at intervals throughout the day in continuous ambulatory peritoneal dialysis (CAPD) or during the night in continuous cyclic peritoneal dialysis (CCPD).
Urinary lithiasis (condition of having stones) may be related to infection, irritation, diet, or hormone imbalances that lead to an increased level of calcium in the blood. Most urinary stones, or calculi, are formed of calcium salts, but they may be composed of other materials as well. Causes of stone formation include dehydration, infection, abnormal pH of urine, urinary stasis, and metabolic imbalances. The stones generally form in the kidney and may move to the bladder (Fig. 13-8). This results in great pain, termed renal colic, and obstruction that can promote infection and cause hydronephrosis (collection of urine in the renal pelvis). Because they are radiopaque, stones can usually be seen on simple radiographs of the abdomen. Stones may dissolve and pass out of the body on their own. If not, they may be removed surgically, in a lithotomy, or by
FIGURE 13-6. Schematic diagram of a hemodialysis system. A cellophane membrane separates the blood compartment and dialysis solution compartment. This membrane is porous enough to allow all of the constituents except the plasma proteins and blood cells to diffuse between the two compartments. (Reprinted with permission from Porth CM. Pathophysiology: Concepts in Altered Health States. 6th Ed. Philadelphia: Lippincott Williams & Wilkins, 2002.)
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.