Given the intricate architecture of the canine digestive system, the interplay of its various components and the complex biochemical processes that it must undertake, it's no wonder that things go wrong with it from time to time. Indeed, digestive system disorders are among the most frequently observed of all canine health problems.
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Most of these disorders are associated directly or indirectly with the liver, pancreas or organs of the digestive tract, which play crucial roles in processing the food that your dog consumes. Often, however, serious health problems are centered in a dog's gallbladder, a small, tough-skinned, saclike structure, situated in the abdominal cavity, that plays a relatively dispensable role in digestion.
Consequently, notes James Flanders, DVM, an associate professor of surgery at Cornell University's College of Veterinary Medicine, if worse comes to worst and a disease of the gallbladder progresses to a life-threatening stage, this organ can be surgically removed without compromising the patient's health. This, of course, cannot be said for the organs that surround it, all of which are necessary for survival.
A Storage Device
The gallbladder, Dr. Flanders explains, is nestled deep within the abdomen in close proximity to the liver--to which it is attached--and to the pancreas. Compared to the liver, which among all organs is second in size only to the lungs, the gallbladder is small. 'In a large dog--a German shepherd, for example--the gallbladder might have about the diameter of a golf ball,' he says. 'In a small dog, of course, it would be even smaller than that.' This sac is not perfectly round, he adds, but is elongated and pear-shaped. And it is 'distensible'--able to expand in response to internal pressure.
The gallbladder serves as a storage reservoir for bile, an acrid, alkaline fluid containing water, electrolytes, various acids and a yellowish pigment called bilirubin. This fluid, secreted by the liver and discharged into the small intestine, enables the digestion and absorption of fats. A dog produces bile more or less constantly throughout the day; a healthy gallbladder regulates its release into the digestive tract as needed in response to the animal's intake of food.
Dr. Flanders explains: 'The liver is divided into several sections, called lobes, and the bile is produced in these lobes, each of which has a bile duct. All of these ducts come together in what we call the common bile duct, which leads to the duodenum--the first segment of the small intestine.
'The gallbladder is located off to the side of the common bile duct,' Dr. Flanders continues, 'to which it is connected by another duct. When excess bile is present in the common bile duct, it drains into the gallbladder and is stored there until the sac is stimulated to contract--usually by food entering the stomach. In response to this stimulation, the sac contracts and squirts the bile into the intestine to help with the digestion of fat.'
Two Categories
Cases of serious canine gallbladder malfunction or disease are not commonly handled at the neighborhood veterinary clinic, says Dr. Flanders: 'In a private practice, a veterinarian might have to deal with only one or two cases per year.' The condition is seen much more often, however, at veterinary referral institutions such as the Cornell University Hospital for Animals, where affected animals are sent for treatment, either medical or surgical. 'The medical people here,' he says, 'may treat three to five cases of gallbladder disease per month.' As for the veterinary surgeons, he says, 'A month might go by when we don't see even one case, but then we might have a month in which we'll need to perform two or three gallbladder surgeries.'
Canine gallbladder diseases fall into two categories--obstructive and nonobstructive. According to Dr. Flanders, the most common obstructive disorder occurs as the result of a swollen pancreas, which can be caused by inflammation (pancreatitis), by a pancreatic tumor or by scar tissue. 'Any of these conditions,' he notes, 'can compress the common bile duct. If that happens, bile is unable to get out of the biliary system, the dog will get a distended gallbladder, and the bile can actually back up into the bloodstream.'
Also, says Dr. Flanders, dogs--like people--can develop gallstones, which he characterizes as 'obstructive concretions' of bile that, over time, can block the bile duct and cause the gallbladder to expand and, if untreated, to burst. These stones are not like the hard, cholesterol-based gallstones that develop in humans, he notes, but are instead made up of a claylike sludge, formed from bilirubin, calcium and mucin, that blocks the biliary flow.
A third type of obstructive disorder is a biliary mucocele, a distension of the biliary duct and gallbladder caused by abnormally thick bile and mucus. A mucocele can also lead to nonobstructive gallbladder disease, a category typically caused by bacterial infection and severe inflammation. That is, if a mucocele progresses sufficiently, the abnormal bile can provide a nurturing environment for bacterial infection, inflammation and swelling that can eventually cause the gallbladder to burst.
Regarding the effects of severe injury, Dr. Flanders says: 'We occasionally see a dog whose gallbladder and common bile duct have been separated by trauma, but such cases are rare. The gallbladder is safely tucked away in the middle of the liver and behind the rib cage.'
Treatment Options
Antibiotic therapy to counter infection will usually be used to relieve a nonobstructive gallbladder disorder, says Dr. Flanders. And, he notes, 'There are other medications that can actually stimulate the secretion of bile, help liquify it, and move it into the intestinal tract. In these cases, medical management comes to the rescue.'
Surgery will be required, he points out, if mucocele is present or if there is an obstructive mass that does not respond to medical management. 'In some cases,' he points out, 'we'll simply remove the stones from the bile duct. Or we may reroute the bile duct so that it drains into an alternate part of the intestine. Or we may remove the gallbladder entirely.'
To what extent is the gallbladder expendable? Says Dr. Flanders: 'A dog will do absolutely fine without it. It's a nice storage device, but if it's removed, the rest of the biliary system will adapt and the necessary flow of bile from the liver into the intestine will carry on as needed.'
On the Lookout. ...
* Although the occurrence of canine gallbladder disease is by no means 'rampant,' says Dr. James Flanders of Cornell University, owners should nevertheless be aware of the associated clinical signs and their potential consequences--just in case!
* These indicators include: diminished appetite, lethargy, vomiting, pale-colored stools, weakness and poor coat condition. In many affected dogs, a telling sign will be the presence of icterus, commonly referred to as jaundice, a condition in which the animal's mucous membrances--eyes, gums and so forth--have a yellowish tint. This condition is attributable to increased blood levels of the yellow pigment bilirubin, a consequence of hepatic system malfunction in which this bile component is produced faster than an animal's body can metabolize it.
* Luckily, there is a wide array of medical and surgical treatments available, and a dog can lead a normal life in the event he needs to have his gallbladder removed.
