Urinary System

Pete Wedderburn
2nd January 2020 - 6 min read

The urinary system is one of the body’s essential organ systems: if it fails to work, an animal may fall ill and die within twenty four hours. More commonly, minor dysfunction of the urinary system can cause discomfort and distress, and this is the type of issue that’s more likely to affect pets in the care of kennel and cattery owners.

How The Urinary System Works

Most people already have a basic understanding of how the urinary system works but a short summary may be helpful. The two kidneys are the entrance gate to the system, extracting toxins, waste, and fluid from the blood as it flows through them. One type of fluid – blood – enters the kidneys, and two types of fluid – blood, and urine – leave them. The urine leaves each kidney via a fine tube called the ureter: this carries the urine straight to the bladder.

The bladder acts as a storage receptacle for the urine. It’s like a balloon made from a fine sheet of muscle rather than rubber. When empty, it may be as small as an old 10p coin, but when full, it can be as big as a grapefruit (in a cat) or even bigger than a football (in a large dog). The bladder stores the urine until the animal is ready to release it into the environment. The urine passes to the outside world via a short tube called the urethra: this ends in the vagina in females, and the penis in males. There are sphincters – living valves – at the exit of the bladder and in the urethra itself, and these allow the animal to turn the urine flow on and off. When these sphincters don’t close properly, urinary incontinence results.

Failure Of The Urinary System

Any part of the urinary system can fail, and the signs of illness depend on which area is affected.

golden retriever sitting on road

1. Kidneys

Kidney failure is the most fundamental problem that can develop. If the kidneys stop working, the blood cannot be filtered in the first place, so toxins accumulate in the blood rather than being extracted into the urine. These toxins cause animals to feel seriously unwell, with dullness, inappetence, nausea, and vomiting.  The feeling has been described as a nasty hangover that refuses to go away. If the issue is not resolved, the continued accumulation of toxins goes on to cause coma and death. 

Animals with kidney failure sometimes produce no urine at all, but more often, copious amounts of dilute urine are produced. This can mislead owners, who mistakenly link urine production with functioning kidneys. Often such animals also drink large amounts of water: again, owners sometimes believe that the fact that their pet is drinking is “good”: it just isn’t so simple. The amount of water drunk by an animal is significant, but it’s not possible to say that any particular quantity is “good” or “bad”. It’s useful to measure how much is drunk and to pass this information on to your vet.

Concentrate vs Weak Urine

Vets know exactly how much water a pet should drink in a 24 period: if more than 50ml water per kilogram body weight is consumed, this is too much. In such cases, vets know that some sort of further investigation should be carried out to find out the reason for the extra thirst. It’s useful for kennel owners to record how much an animal in their care is drinking so that the information can be passed on to their vet.

Vets can obtain important information about a pet’s urinary system by examining a urine sample. It can be helpful if kennel owners bring a fresh urine sample along to the clinic when an animal is suspected of having a urinary problem. Samples can be collected by placing a large clean dinner plate beneath a dog at the critical moment, then dispensing the fluid into a glass container that has been thoroughly cleaned then rinsed out with boiling water. For cats, it’s easiest to collect urine from a litter tray by using a special type of littering material that does not produce debris or dust that contaminates the sample: ask your vet to find out more about this.

There are many possible causes of kidney failure, from congenital problems (eg some cats have cystic kidneys) to toxins (pollen from lilies can cause kidney failure) to tumours, infections, and simply old age. The main message to kennel owners is that animals with kidney failure usually show clear signs of being unwell, and they should be taken to the vet for further investigation and treatment.

2. Ureters

The ureters are rarely involved in urinary tract disease. The most common problem happens when one ureter opens into the wrong part of the bladder, causing the animal to continually leak small amounts of urine. This is a congenital problem (meaning that animals are born with the defect) and it usually presents as young dogs or cats that dribble urine continuously. Surgical correction of the problem is the only answer.

3. Bladder

The bladder is perhaps the most common part of the urinary system to cause problems that develop during kennelling. The wall of the bladder may be prone to becoming inflamed, and the resulting condition is known as cystitis. The technical definition of inflammation sums up what happens to the bladder wall: there is redness, swelling, pain, heat, and loss of function. Affected animals are uncomfortable, wanting to pass a small amount of urine frequently. Sometimes there is blood in the urine, although this may not be visible (the vet may detect it with a dip stick test). 

There are many different causes of cystitis: it can be caused by a simple bacterial infection, by crystals or stones in the urine, or it may be linked with polyps or even tumours of the bladder wall. 

In cats, cystitis is common, although strictly it’s called Feline Lower Urinary Tract Disease (FLUTD), reflecting the fact that it’s not just the bladder that’s affected: the adjacent urethra is also red, swollen, and sore. In these cases, there is often no discernible cause: it’s something that develops for reasons that we don’t yet understand (so-called “ideopathic” disease). There is some link with that vague concept of “stress”, so cats may be more likely to develop signs when they are in a cattery than when they are at home.

In all cases of cystitis, it’s important to take the animal to the vet. The underlying cause of the problem needs to be identified so that the correct treatment can be given. This may include antibiotics, special diets, and other medications depending on the precise details of the case.

4. Urethra

The urethra, as mentioned, may be inflamed at the same time as the bladder, but there is one other condition of the urethra that is extremely serious: urinary obstruction. Small stones or plugs of cheesy material can develop in the urine, and while these may not cause a problem in the bladder, they can act like tiny corks in the urethra, preventing the flow of urine out of the bladder to the exterior. Affected animals strain to pass urine, but are unable to do so. 

Superficially, dogs and cats with urinary obstruction may resemble animals with cystitis, straining as they try to pass urine. The key difference is that they are unable to do so, and this can rapidly lead to a life threatening situation. The bladder fills up with urine, but it cannot be emptied: the pressure builds up, causing immense discomfort. The bladder may reach an immense size, two or three times its normal volume. The back-pressure means that urine can no longer be passed from the kidneys down to the bladder, and toxins can no longer be eliminated from the body. Affected animals can die within hours: in some cases, the bladder can even rupture, with the associated severe pain and distress. 

Total urinary obstruction is one of those extreme emergencies that are often not recognised until it is too late. The key message is that if you have an animal that is straining to pass urine, get it to the vet rapidly. And if you believe that the animal is straining without passing any urine, get it to the vet ultra-rapidly.