The Urinary System - Healthy Dog Experts

The urinary tract is made up of the kidneys, ureters, bladder urethra and in the male, the prostate. There are two kidneys - one on either side of the backbone just behind the last rib. Each kidney has a renal pelvis or funnel, that siphons the urine into a ureter.The ureters transport urine to the bladder. The bladder empties into the urethra. The opening of the urethra is found at the tip of the penis in the male and between the folds of the vulva in the female. In the male, the urethra also serves as the channel for semen. The prostate envelops the urethra just below the bladder. The top surface of the prostate can be felt by rectal examination. The chief functions of the kidneys are to regulate fluid, electrolyte and acid-base balance and to excrete the wastes of metabolism. This is accomplished by millions of nephrons, the basic working units of the kidneys. A nephron is composed of a globe of blood vessels (called the glomerulus) that filters waste from the blood plasma and passes it through a system of tubules that reabsorb water and electrolytes. This concentrates the waste liquid, which is now urine. Urine is normally yellow and clear. However, its appearance can be altered by the state of hydration and various drugs and diseases. The decision to void or urinate is under the conscious control of the brain. Teaching a dog when to void is the basis for successful housetraining. Once the dog decides to urinate, the actual mechanism of emptying the bladder is carried out by a complicated spinal cord reflex.

Signs of Urinary Tract Disease

Most urinary tract disorders cause some

disturbance in the normal pattern of voiding.

There are a number of signs to look for.

Dysuria (Painful Urination)

Signs of dysuria are obvious distress during urination with straining, dribbling, licking at the penis or vulva, crying out in pain, voiding frequently in small amounts, squatting but not passing urine after many tries, and/or passing mucus, blood clots or bloody urine. These signs indicate a disorder of the bladder, urethra or prostate. Pain and swelling in the lower abdomen suggest an overdistended bladder. A dog who does not pass urine after prolonged squatting or lifting of the leg is obstructed. This is usually caused by a stone, but could also be due to a tumor obstructing the urine flow.

Hematuria (Blood in the Urine)

Blood in the first portion of urine that clears with voiding indicates a problem in the urethra, penis, prostate, uterus or vagina. Blood that appears at the end of voiding suggests a disease of the bladder or prostate. A uniformly bloody urine is seen with diseases of the kidneys, ureters and bladder. Bleeding without pain suggests kidney disease. Vaginal bleeding may give a false impression of hematuria. Microscopic hematuria means finding red blood cells on microscopic examination of urine that appears normal to the naked eye.

Polyuria (excessive Urination)

Frequently passing large volumes of urine suggests kidney disease. The dog compensates by drinking large amounts of water. you may notice the increased thirst (polydipsia) first. Other common causes of polyuria include diabetes mellitur, Cushing's syndrome, a pituitary tumor, hyperparathyroidism and some types of poisoning. Polyuria should be distinguished from dysuria and urinary incontinence.

Diagnosing Urinary Tract Diseases

Because of overlapping symptoms and the fact that more than one organ may be involved, it is difficult to make an exact diagnosis based on the symptoms alone. Laboratory tests can be of considerable help. Routine tests are urinalysis, which tells your vet whether your dog has a urinary tract infection, and blood chemistries, which provide information about the function of the kidneys. Blood chemistries may include a BUN (blood urea nitrogen), which measure the efficiency of the kidney's filtering mechanisms. However, this value can be influenced by diet and other factors. Creatinine is another kidney function test. Your trained professional, doggy doctor, may ask you to bring in a urine specimen, which you can easily obtain by collecting a sample midstream in a plastic specimen container as the dog voids. These "free catch" samples may have some contamination from the dog's hair and penis or vulva. Steril urine specimens are obtained by aspirating urine from the bladder with a sterile needle and syringe, called cystocentesis or by passing a steril catheter into the bladder through the urethra. This will be done by your trained professional when it is important to culture the urine. A valuable urine test, called the UPC ratio, determines the urine protein:creatinine ratio-again showing the efficiency of the kidneys. The proportion of protein may also reflect inflammation or disease elsewhere in the body. X-ray films of the abdomen are particulary useful in diagnosing stones. Abdominal ultrasonography is an excellent, noninvasive test that provides images of the kidneys, ureters and bladder. An intravenous pyelogram (IVP) is an X-ray examination in which a dye is injected into a vein. The dye is excreted by the kidneys and outlines the renal pelvis and ureters. Other selective studies include CT scan and surgical exploration and biopsy of the kidneys or the bladder.

Diseases of the Bladder and Urethra

There are four basic problems, often interrelated, in the lower urinary tract. They are infection, obstruction, stones and urinary incontinence.

Cystitis is a bacterial infection of the lining of the bladder. Urethral infections in both males and females often precede bouts of cystitis. Other predisposing causes include increasing age, diabetes mellitus and being on long-term corticosteroid therapy. In sexually intact males there may be a preexisting prostatitis. Dogs who go long periods of time without eliminating have a greater risk of developing bladder infections. Urinary stones can occur as a result of cystitis. The bacteria form a nidus (a central point) around which the stone develops. The principal sign of cystitis is frequent, painful urination. The urine may appear cloudy and have an abnormal odor. Females with cystitis may lick at the vulva and have a vaginal discharge. The diagnosis is confirmed by a urinalysis showing bacteria, white blood cells and often red blood cells in the urine.

Kidney stones are rare in dogs. Bladder stones are common. Stones that form in the bladder may pass into the urethra. All dogs can develop bladder stones. Breeds with an increased incidence include the Miniature Schnauzer, Dalmatian, Shih Tzu, Dachshund and Bulldog. Bladder and urethral stones may be large or small, single or multiple and may pass spontaneously or obstruct the lower urinary tract. Stones in the bladder eventually cause painful urination and blood in the urine. Most bladder stones are struvites (that is, they're composed of magnesium ammonium phosphate). They form in an alkaline urine and are usually preceded by a bladder infection. The bacteria and urinary sediment form a nidus around which the ammonium phosphate is deposited. Uric acid stones form in an acid urine and are frequently associated with inherited alterations in urate metabolism. Dalmatians and Bulldogs are genetically predisposed. Other stones are calcium oxalate and cystine stones. Cystine crystals have been found in Newfoundlands and many other breeds. Silica stones are rare; they occur most often in male German Shepherd Dogs. These stones are not usually associated with a pre-existing bladder infection. Stones that are large or numerous can sometimes be palpated through the abdomen. In most cases the diagnosis is made by X-ray. A contrast dye (not recommended) study may be needed for definitive diagnosis. Stones not visible on an abdominal X-ray can often be seen by ultrasonography or IVP. A urinalysis is routinely obtained. Stones that pass spontaneously and those that are removed surgically should be analyzed, if possible, since the composition of the stone influences the treatment of any remaining and future stones.

A stone is the most common cause of an obstructed bladder. Tumors and strictures are less common causes. Enlargement of the prostate gland is a rare cause of bladder obstruction in male dogs. A dog with an obstructed bladder is acutely uncomfortable or in dire distress. Males and females often assume a peculiar splayed-legged stance while attempting to void. A partial blockage can be suspected when the dog dribbles urine, voids frequently and has a weak, splattery stream. A partial obstruction, left untreated, may become a complete obstruction. With a complete obstruction no urine is passed. The lower abdomen becomes swollen and tender to pressure and feels as if there is a large ball in front of the pelvis. Note that the continuos straining associated with an obstructed bladder can be mistaken for constipation.

Incontinence is loss of voluntary control over the act of voiding. This medical condition must be differentiated from a house training problem and/or submissive urination, especially in young dogs. Incontinent dogs wet their bed or the floor where they are sleeping, urinate inappropriately in the house, sometimes dribble urine and may void more frequently than normal. There may be an ammonialike odor about the dogs bedding. The skin around the penis or vulva may be scalded. There are several types of urinary incontinence.

This common incontinence is seen most often in middle-aged and older spayed females and less commonly in young females and older neutered males. It is caused by a deficiency of estrogen in females and testosterone in males. Both these hormones are important in maintaining muscle tone of the urethral sphincter. Hormone-responsive incontinence is much like bed wetting. The dog urinates normally, but wets when relaxed or asleep.

This is another common problem, characterized by the release of urine caused by the contraction of the abdominal wall muscles along with relaxation of the muscles that support the urethra - the normal voiding process. The dog passes small amounts of urine when he is upset or in a stressful situation. It has also been called incontinence. This is most common in young puppies in their new homes and will simply outgrow it.

Spinal cord injuries, infections, tumors and inherited neuropathies can interfere with the nerves that control the bladder. A bladder with a compromised nerve supply lacks muscle tone and cannot contract. The bladder continues to fill until the pressure exceeds the resistance of the sphincter mechanism that closes the urethra. This results in intermittent, uncontrolled dribbling. Neurogenic incontinence can be confirmed with a cystometrogram. This is a test that measures how forceful the bladder contracts in reponse to the introduction of incremental volumes of fluid into it through a catheter. The results also suggest the site of the neurologic deficit (the spinal cord or the bladder).

This type of incontinence is due to a partially obstructed bladder, caused by urethral stones, tumors or stricture. The signs and symptoms are similar to those of neurogenic incontinence, but the nerve supply to the bladder is undamaged.

Dogs with failing kidneys are unable to concentrate their urine. They have a large urinary output and must drink more than usual to replace fluid losses. If they are not allowed to go outside to urinate as often as necessary, they may begin to urinate in the house. It is important to check kidney function in all incontinent dogs to be sure the incontinence is not due to kidney failure.

Another cause of incontinence is ectopic ureters. Females are 8 times more likely to suffer from this congenital problem than males. One or both ureters may enter the vagina instead of the bladder. There is then continous drainage of urine into the vagina. The incontinence of ectopic ureters is present from birth, but becomes more noticeable at 3 to 6 months of age when housetraining should be complete. Breeds with a predisposition include White West Highland Terriers, Fox Terriers and miniature and toy Poodles. Siberian Huskies and Labrador Retrievers may also have a familial predisposition. Incontinence in bitches shortly after spaying is usually caused by postoperative pelvic adhesions.

The prostate is an accessory sex gland in males that completely surrounds the urethra at the neck of the bladder. The prostate produces fluid that is added to the ejaculate when a male dog mates. This fluid provides nutrients and assists in the sperm's movement. The three conditions that cause prostatic enlargement are benign prostatic hyperplasia, prostatitis and cancer of the prostate. The diagnosis of prostate enlargement is made by digital rectal examination, during which the size, position and firmness of the prostate gland is assessed. Ultrasonography provides additional information and may be helpful in guiding a needle into the prostate to obtain a biopsy - a procedure indicated when cancer is suspected.

This is an increase in the size of the prostate gland. The disease is hormone-dependent and is influenced by testosterone. Benign prostatic hyperplasia begins in sexually intact males at about 5 years of age and progresses as the dog grows older. Thus, older dogs are more likely to have symptoms. As the prostate enlarges, it gradually expands backward and may eventually obstruct the rectum, causing constipation and straining while defecating. The feces may appear flat or ribbonlike. Defecation is difficult. Fecal impactions are common. Rarely the prostate pushes forward and presses on the urethra, causing straining during urination. Blood in the urine can be a sign of benign prostatic hyperplasia.

Prostatitis is a baterial infection of the prostate gland, usually preceded by a bout of cystitis. Signs of acute prostatitis are fever, depression, vomiting, diarrhea and painful urination. The dog may have an arched back or a tucked-up abdomen. Blood tinged or purulent secretions may drip from the prepuce. The prostate gland is enlarged, swollen and tender. The disease can become chronic, with periodic flare-ups. Chronic prostatitis is a significant cause of male infertility.

Congenital kidney problems are kidney problems that are present at birth. The actual signs of kidney failure may not immediately be apparent, but the process leading to the kidney problem is present - perhaps just a genetic defect or damaged tissue. Some congenital problems are hereditary, while others are a result of trauma in utero or at whelping, or the effects of chemicals or drugs the dam was exposed to while the pups were in utero. A congenital kidney problem may involve both kidneys or just one. Dogs can do very well with just one healthy kidney.

Dogs with this disease have multiple cysts on one or both kidneys. Depending on the degree of normal tissue versus cystic tissue, a dog may show minimal signs or be in renal failure. The disease is often diagnosed by ultrasound. Cairn Terriers seem to have familial predisposition to this problem, along with Beagles. Bull Terriers have an autosomal dominant version of polycystic kidney disease.

Renal dysplasia is a problem with the development of the tissues of the kidney itself. Depending on what tissues are malformed, kidney failure of various types and severity will result. Urine may not be concentrated or certain nutrients may not be retained. Dogs start to show increased urination and drinking at 6 to 24 months of age. If the problem is unilateral, the dog may appear normal throughout his life, as long as the remaining kidney stays healthy. A kidney biopsy is the only way to definitively diagnose this problem. Most dogs inherit this condition as an autosomal recessive gene, so both parents could be carriers and both sexes can be affected. In Samoyeds, it is an X-linked trait, which means many more males show clinical signs than females. Renal dysplasia has been identified in more than 20 breeds, including Alaskan Malamutes, Cocker Spaniels, Lhasa Apsos, Shih Tzus and Soft Coated Wheaten Terriers.

In dogs with this disease, the filtering mechanism of the kidneys is defective and the body loses protein. One of the first signs is increased urination and drinking. Excess protein in the urine may be picked up by a urinalysis. There appears to be an immune-mediated component to this illness. Breeds with a predisposition include soft Coated Wheaten Terriers, Bernese Mountain Dogs, Labrador Retrievers and Golden Retrievers.

In dogs with amyloidosis, the protein amyloid is deposited in the kidney, interfering with normal functions by locking the normal filter mechanisms, leading to dilute urine and/or protein loss in the urine. This disease can be seen in any breed, but is a particular problem for many Chinese Shar-Peis. In this breed, the problem tends to begin before 5 years of age with swollen joints and high fevers that come and go in a cyclic pattern.

Fanconi Syndrome is an impairment in the function of the kidney that causes certain compounds which should be absorbed into the bloodstream by the kidneys to be excreted in the urine instead. Compounds that may be lost in the urine include glucose, amino acids, uric acid and phosphate. Loss of these compounds can cause problems such as failure to grow and bone abnormalities. When too much bicarbonate is excreted in urine, excess acid can build up in the blood.The disease can be seen in any breed of dog, but Basenjis have a breed predisposition. Many dogs first show signs at 4 to 8 years of age. With the dramatic nutrient loss, these dogs will rapidly lose condition and die unless they are treated.

Pyelonephritis is a bacterial infection of the kidney, including the renal pelvis and ureter. Most cases are caused by an ascending bladder infection. There may be a predisposing blockage or congenital malformation of the urinary tract. Occasionally, the infection is blood-borne.

Acute pyelonephritis begins with fever, loss of appetite, vomiting and pain in the lower back. A stiff-legged gait and a hunched up posture are characteristic. Some dogs exhibit signs of painful urination. On microscopic examination, the urine contains white blood cell casts, which are plugs of cells expelled from kidney tubules. An IVP or renal ultrasound may show an enlarged kidney or a dilated renal pelvis.

Chronic pyelonephritis is an insidious disease that may or may not be preceded by an acute pyelonephritis. Signs are loss of appetite, weight loss and excessive urination and thirst. This disease smolders for months or years, eventually culminating in kidney failure. Early treatment of acute pyelonephritis may prevent this.

Nephritis and nephrosis are diseases of the kidneys that produce scarring and kidney failure. The diagnosis of nephritis or nephrosis is established by kidney biopsy.

Nephritis is an inflammatory process associated with certain infectious diseases, including canine hepatitis, canine ehrlichiosis, Lyme disease, Rocky Mountain spotted fever and others. Dogs with systemic lupus erythematosus and chronic pancreatitis can develop nephritis. A familial predisposition for a condition called glomerulonephritis occurs in Doberman pinschers, Samoyeds and Bull Terriers. In Bull Terriers this is an autosomal dominant problem.

Nephrosis is the result of degenerative changes caused by toxins and poisons that target the kidneys or by ischemia (inadequate blood flow to the kidneys). The most important nephrotoxins are aspirin, ibuprofen and butazolidin. Certain antibiotics are nephrotoxic, particularly when given for prolonged periods or in high doses. They include polymyxin B, gentamicin, amphotericin B and kanamycin.

The nephrotic syndrome may develop in dogs with nephritis or nephrosis. Large amounts of protein are excreted into the urine from the damaged kidneys. In consequence, serum protein levels are low. This results in loss of fluid from the blood, which pools in the legs (edema), the abdominal cavity (ascites) and the chest cavity (pleural effusion). The swollen limbs and pot-bellied appearance of the nephrotic syndrome suggest right-sided congestive heart failure, but laboratory studies will distinguish between this condition and kidney problems.

Kidney failure is defined as the inability of the kidneys to remove waste products from the blood. The buildup of toxins produces the signs and symptoms of uremic poisoning. Kidney failure can appear suddenly (acute kidney failure) or come on gradually over months. Most cases are of the gradual onset type and are caused by nephritis and nephrosis.

4Congestive heart failure with low blood pressure and reduced blood flow to the kidneys

Dogs with kidney failure do not show signs of uremia until 75 percent of functioning kidney tissue is destroyed. Thus, a considerable amount of damage occurs before the signs are noticed.

One of the first things you may notice is that your dog drinks and urinates more than usual and indicates her need to go outside to eliminate several times a day.If not allowed to do so, the dog may begin to have housetraining accidents in the house. These signs are due to the failure of the kidneys to concentrate the urine. This results in a large urine output over which the dog has no control, with subsequent dehydration and thirst. As kidney function declines, the dog retains ammonia, nitrogen, acids and other chemical wastes in her blood and tissues. This is called uremia. The degree of uremia is determined by measuring serum blood urea nitrogen (BUN), creatinine and electrolytes. Signs of uremia are apathy and depression, loss of appetite and weight, a dry haircoat, a brownish discoloration to the surface of the tongue and an ammonialike odor to the breath. Dogs at this stage may urinate less than normal. Ulcers may arise in the mouth. With the nephrotic syndrome the dog develops ascites and adema. Vomiting, diarrhea and gastrointestinal bleeding may occur. At the end stages of kidney failure, the dog falls into a coma. A condition called rubber jaw may be seen with chronic kidney failure. It is characterized by loosening of the teeth and ulcerations of the mouth and gums. This can also occur with a diet low in calcium or an imbalance of calcium and phosphorus. Your veterinarian may wish to make an exact diagnosis by performing exploratory surgery and biopsy of the kidney, or doing an ultrasound-guided biopsy. This helps guide treatment and determine whether the disease is treatable.