Liver and Gall Bladder
The liver is the largest gland of the body. It sits closest to the diaphragm in the abdomen. The portal vein feeds the liver with nutrient rich blood from the intestines. This blood from the intestines has recently digested food nutrients within it. Also contained in this blood may be substances that would be harmful to the body if allowed to circulate. The liver first removes these potentially harmful substances such as ammonia, certain amino acids as well as bacteria before allowing the blood to flow into the vena cava. A congenital defect allows this blood to flow directly into the vena cava (portal caval shunt). This condition is seen in young dogs and cats. They will have toxic reactions just after they eat. These reactions will cause them to seizure, pace, and press their head, circle, or collapse. A bile acid test is easy to perform on a blood sample of any suspected pet. Surgical correction is possible. The liver is the energy storehouse of the body. If the liver is removed surgically, the animals will die of low blood sugar before any accumulation of toxic substances. Inflammation of the liver is called hepatitis. Hepatitis just indicates inflammation – therefore a kick to the liver will cause hepatitis. In humans, this term is used to denote a contagious viral infection that can be fatal. In dogs and cats, there is not a common cause of viral hepatitis. The key word is common –we do vaccinate dogs for hepatitis but it is an uncommon disease. Liver inflammation is determined by three or four tests that are commonly done. Think of the liver cell as an egg. The yolk is the nucleus and the white is the cell body. When liver cells are damaged, they leak substances that indicate their damage into the blood. We call these substances liver enzymes. The enzymes that leak into the blood from the “yolk” indicate the liver cell is dead, the enzymes that leak from the “albumin” of the egg indicate the liver cell is damaged but not dead.
These enzymes are long lived in a dog and evidence of liver damage may be present long after the insult has come and gone. In the cat however their short-lived enzymes indicate disease at the time of the blood collection. Therefore, mild elevation of cat enzymes is considered very serious whereas a 10 to 50 fold elevation in dog’s enzyme levels is of the same magnitude. Jaundice is associated with liver disease in many cases. Jaundice and icterus are used interchangeably. Jaundice indicates that the animal has a yellow color to the mucous membranes. This color is from bilirubin pigment. Bilirubin is the name of a substance that is in high concentration in the bile of the gall bladder. Bilirubin excess causes jaundice or icterus. The excess of this pigment (yellow) can be fatal over a period of time. There are three causes of accumulation of this pigment in the tissues. One is the excessive production. The pigment is actually produced by the breakdown of red blood cells in the body. Anything that increases the destruction of these cells will cause excessive amounts of bilirubin. Think of a bruise on your arm – it starts out as a dark blue spot from blood leakage. As the blood breaks down the spot chagnges to a green then yellow color as the hemoglobin pigments are broken down in the tissues. It is these same colors causing the entire body to be yellow. During normal bilirubin production the liver will process the bilirubin and secrete it into the bile. The bile is collected and stored in the gall bladder. The bile is used as a detergent to help break down fats in the intestine. This detergent acts just like washing pots and pans with grease on them. Detergent makes fats water-soluble. In the intestine bile mixes with faty foods to make them water-soluble so they can go into the blood stream. The bile then lets the fats go and then the bile is recirculated through the liver. If the liver is sick, the bile will not be processed and will build up in the blood causing jaundice. Therefore, the second cause of jaundice is liver disease. The third cause is the obstruction of the bile duct. The gall bladder stores the bile then releases it through the common bile duct into the small intestine. This common bile duct passes through the pancreas on its way so inflammation of the pancreas (pancreatitis) can cause obstruction of the bile duct. Infection of the gall bladder or gall bladder stones can also cause poor bile flow and bilirubin builds up. Another cause of jaundice in newborn babies is related to poor liver function as well as bruising from a difficult delivery. These babies are put under “lights” these are ultraviolet lights which convert the bilirubin into a non-toxic metabolite. There are many breeds of dogs and cats with very specific forms of liver disease and routine blood screening is recommended for all our pets to diagnose this early.
- Describe the functions of the liver.
- Describe how bile is formed.
- Describe a protal caval shunt.
- What are the three causes of jaundice?