The Liver: Your Pet's Bigest Gland
By Stephen M. Sheldon, DVM
So, how many of you out there actually knew the answer to that Trivial Pursuit question?
Indeed, the liver is your pet's biggest gland (and yours too but I don't want to get
personal!). The liver is located in the most forward part of the abdomen, resting against
the diaphragm, the muscular partition between the chest and abdominal cavities.
You can't live without your liver, as I'm sure many of your mothers have told you. It
performs over a hundred functions including some of the following: detoxifying poisons
and drugs, digestion and formation proteins, fats, and sugars, manufacturing bile, and
assist in blood clotting to name a few.
The liver is one of the few organ systems that can partially regenerate itself (can you
think of any others?). Combined with its tremendous size, this ability can make liver
diseases difficult to detect until the illness becomes severe. Some of the more common
symptoms are lack of appetite, weight loss, depression, lethargy, vomiting, diarrhea,
increased thirst, urination, and an enlarged abdomen. Perhaps the most familiar symptom
is jaundice, or icterus, which is yellowing of the skin, mucous membranes, and whites of
the eyes (sclera). This is due to an abnormal accumulation of the pigment bilirubin
(pronounced Billy Rubin). Jaundice is not, however, limited to just liver diseases; many
blood disorders also result in icterus.
The next logical question is "What causes liver disease?" Since the liver is responsible for
the detoxification of good and bad alike, bloodflow is very high through the liver. This
makes it very susceptible. Some common poisons are copper, arsenic and other heavy
metals, aflatoxins (fungal poisons), coal tars, petroleum products, and many insecticides.
However, poisons are not the only things to worry about. Infectious diseases by bacteria,
viruses, and fungi all affect the liver. Some examples of these agents are leptospirosis
(incidentally the Northeast United States is having a terrible time with a deadly new
strain of lepto), infectious canine hepatitis virus, and E. coli bacteria. Lepto and ICH are
the "L" and the "H" in your dog's annual vaccinations.
There are also what we call "infiltrative" diseases that attack the liver. These are diseases
like cancer and chronic hepatitis in which no infectious agents are identified. Many
cancers metastasize or spread to the liver because the liver is so centrally involved in
blood flow. Diseases and cancers of the bile duct, pancreas and gall bladder can all cause
liver disease as these organs live very near the liver. Rare metabolic disease can cause
accumulation of dangerous by-products in the liver; a glycogen storage disease would be
an example of this. Congestive heart disease also can cause abnormalities in the liver as
blood backs up in the liver, so to speak. Some puppies have congenital defects (birth
defects) like shunts and arteriovenous fistulas; fortunately, these are rare. Lastly, we have
cirrhosis, which is a scarred liver and is usually a fatal condition.
The diagnostic approach towards liver disease is aimed at determining if the liver is
primarily involved or if the liver has become diseased by relation to another organ system
(secondarily involved). A complete blood count may show anemia, increased white blood
cells, or decreased platelets--signs that may point towards the liver. Blood chemistries
may show an increase in the liver enzymes (ALT, AST, GGT, SAP), low blood sugar,
low albumin, or increased bilirubin. We also look for by-products of liver disease in the
urine sample. The last part of what I consider the basic liver work-up would be
radiographs of the abdomen; this will reveal any size abnormalities (small or large), some
cancers, and gall bladder stones.
Next, we move into the more specific liver function tests such as bile acid assays. These
can narrow down the list of possible causes. They are called liver function tests because
they tell us not just if the liver has suffered an insult but if the liver is actually functioning
and doing its job. BSP retention and Ammonia tolerance tests are also function tests but
are not routinely used as often.
If a cause is still not found, an ultrasound may be needed. This is a noninvasive way to
see the architecture, structure, and size of the liver. It's also a great way to get a biopsy or
piece of liver tissue to send to a pathologist for examination. This will yield a definite
answer to the problem. Most of the time we can get a handle on liver disease without a
biopsy; nevertheless, it is, without question, the definitive test for liver disease.
Unfortunately, it is invasive and is not risk free. It also almost always requires anesthesia.
Most of the treatment for liver disease is symptomatic. You know this to be true if you've
had any friends who've had hepatitis. Replace fluid losses and electrolytes with IV fluids
(or subcutaneous in animals that are not critical), cover the patient with broad-spectrum
antibiotics, control nausea, and start some nutritional support. Treatment for specific
diseases depends on the causative agent/disease and is beyond the scope of this article.
For example, fluids, antibiotics, and nutritional support won't do a patient with liver
cancer or a fungal infection much good!
Many conditions of the liver can be treated successfully and, conversely, many of them
are fatal. Monitoring the treatment involves repeated assessment of the abnormal
laboratory tests but also should include assessing subjective criteria like patient attitude,
appetite, playfulness etc. Oh, and by the way, if you are looking for other organ systems
that can regenerate themselves, try the skin, the bones, and the lining of the GI tract to
start with!