Diseases of the Urinary System

Chapter 12 Diseases of the Urinary System

Anatomically, the urinary system is composed of the kidneys, ureters, bladder, and urethra (Fig. 12-1). The main job of the urinary system is waste removal, although it is also instrumental in red blood cell production, the regulation of water and electrolyte balances, and control of blood pressure. The system is a blood plasma balancer. It processes blood plasma by adjusting the water and electrolyte content, removes waste materials not needed by the body, and returns those necessary substances to the systemic circulation. It also regulates the pH of the plasma. The final product is urine, which is stored for elimination.

The kidneys are located in the retroperitoneal space along the vertebral column from T13-L3. Internally, the kidney is divided structurally into the cortex (the outer region) and the medulla (the inner region) (Fig. 12-2). The “filtration units,” or glomeruli, are concentrated in the cortical region, whereas the “concentration/exchange tubules,” or nephron loops, are found in the medulla (Fig. 12-3). Blood enters the kidney and is filtered through the capillaries of the glomerulus. The nephron loop concentrates the filtrate and reabsorbs vital nutrients. The urine passes into the ureters and then on to the bladder for storage before elimination.

Clinical disease can result when any portion of this system fails to function properly. The most commonly seen clinical problems involving the urinary system include cystitis, cystic calculi, urinary obstruction, acute and chronic renal failure (CRF), and incontinence.


Feline Cystitis (Idiopathic [Interstitial] Cystitis)

Feline cystitis (idiopathic cystitis) is a nonmalignant inflammatory condition, previously known as feline urologic syndrome or feline lower urinary tract disease, that occurs frequently in cats. In a study at Ohio State University of 132 cats examined for symptoms of irritative voiding (dysuria, hematuria, and pollakiuria), 61% were found to have idiopathic cystitis. The cause for this disease is unknown, although a virus may be the causative agent. The disease appears to be self-limiting in most cats, with clinical signs subsiding within 1 week to 10 days. Any treatment appears to help because of the self-limiting nature of the cystitis.

Cats with undocumented bacteriuria should not be treated with antibiotics. Needless antibiotic treatment only results in an increased number of antibiotic-resistant organisms.

Change of diet may be the most beneficial treatment, especially if it results in dilute urine without an increase in urine pH. If possible, cats should be fed canned food or have water added to their dry food.

Cats should be given places to hide; toys and scratching poles allow cats to exercise normal play behavior and reduce stress, which has been shown to help in the treatment of this disorder.

Use of amitriptyline is advocated to reduce pain and decrease clinical symptoms. A dose just sufficient to calm the cat is given orally once daily at bedtime. Monitor liver enzymes while the cat is receiving this medication.

Canine Cystitis (Bacterial Cystitis)

Although bacterial urinary tract infection accounts for only 1% to 3% of all feline cystitis, it is the most common cause of cystitis in the dog. The urinary tract is normally sterile (free of bacteria) and resistant to infection. Natural defense mechanisms such as frequent voiding of urine, urethral and ureteral peristalsis, glycosaminoglycans in the surface mucosal layer, pH, and constituents of the urine assist in preventing the invasion of bacteria into lower urinary tract structures.

Urinary tract infections are most commonly the result of ascending migration of bacteria up the urethra. The blood-borne route does not seem of much importance in animal infections. The motility of some bacteria such as Escherichia coli and Proteus spp. may assist in this migration. Once in the bladder, the microorganisms must adhere and colonize the mucosal lining. Bacteria that may be nonpathogenic in the healthy animal may be virulent in hosts with altered immunity.


A detailed description of feline uroliths is beyond the scope of this text. Students are referred to veterinary medical texts for more information.

“Plugged” cats are a frequent occurrence in the small-animal hospital. The inability to pass urine may have serious and even fatal consequences. Two common causes of urethral obstruction in the cat are uroliths and urethral plugs. These terms should not be used synonymously because they are physically distinct from one another. Uroliths are polycrystalline concretions composed of minerals with a small amount of matrix. Urethral plugs consist of small amounts of minerals in a large amount of matrix. This section discusses each of these as they affect urinary tract disease in the cat.

Feline Uroliths

A number of different minerals can be found in feline uroliths (Fig. 12-5). These include the following:

Uroliths, also called bladder stones, may be located anywhere in the urinary tract. Some are radiopaque and are easily diagnosed by radiographs (e.g., calcium oxalate, urates, and struvites), whereas others are radiolucent and require double-contrast cystography to be seen.

In most cases, the cause of urolith formation cannot be determined, although studies show that diets high in magnesium produce struvite uroliths experimentally in cats. Obese, older cats (>2 years) appear to be predisposed to urolith formation. There appears to be no breed predisposition for struvite uroliths; however, Burmese, Himalayan, and Persian breeds have a greater prevalence of calcium oxalate uroliths. Cats that form uroliths typically have concentrated urine with altered pH (either too alkaline or too acidic). Cats with uroliths may be asymptomatic or may present with signs of lower urinary tract disease or urethral obstruction. Spontaneous reabsorption of uroliths has been documented.

Uroliths that remain in the bladder can damage the bladder lining, resulting in secondary bacterial infections and hematuria. Small uroliths that become lodged in the outflow tract present a special problem. As urine flow out of the bladder stops, the bladder distends with urine. This results in a backup of urine through the ureter and into the kidney, virtually halting renal filtration and urine production. The cat becomes azotemic within 24 hours, and clinical signs relating to this begin to be evident at this time. If the obstruction to urine flow is not relieved within 3 to 6 days, the cat will die.

This section focuses on struvite uroliths because they are the most commonly seen type. Please refer to medical texts for treatment of other types of uroliths.

Aug 31, 2016 | Posted by in GENERAL | Comments Off on Diseases of the Urinary System

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