The Liver Flashcards
The Liver
Largest internal organ
Has multiple lobes
Can regenerate if damaged
The powerhouse of the body
What are the functions of the liver run by
Enzymatic reactions
What are the functions of the liver?
- Metabolism
- Production
- Secretion
- Detoxification
What does the liver metabolize?
Amino acids, carbohydrates, and lipids
What does the liver produce?
Cholesterol, plasma proteins, and clotting factors
What does the liver secrete?
Bile to aid in digestion
What does the liver detoxify?
drugs, chemicals, and toxins
Hepatobiliary Assays
Liver cells compartmentalize so that damage in one zone will not affect all liver functions
No single test is superior to any other
Tests are being developed to detect problems sooner
What percentage of cells are damaged before tests show abnormalities?
70%
What happens to test results in end-stage liver disease and why?
Can have a normal test
Because the remaining living cells are not producing enzymes
Gallbladder
the “biliary” part of hepatobiliary
Closely associated with the liver both anatomically and functionally
What is the primary function of the gallbladder?
Bile storage
What are the three types of tests?
Liver enzymes
Cholestasis Enzymes
Liver function
What are the hepatocyte function tests?
The test primarily run in veterinary settings
Bilirubin
Bile Acids
Cholesterol
What do bilirubin function tests determine?
Helps determine the cause during icterus
What is the best test for liver function?
Bile acids
What other liver function tests are there?
Cholesterol and albumin
Not as sensitive
Do not indicate a problem until 2/3 or 3/4 of tissue is damaged
What is bilirubin?
Orange bile pigment produced by the breakdown of the heme protein of hemoglobin
What happens if bilirubin is abnormally high?
Causes icterus
Yellow mucous membranes, sclera, and skin
What does Bilirubin Metabolism start with?
The breakdown of hemoglobin by macrophages in the spleen.
Where does iron go?
Back to the bone marrow to make new red blood cells
Where does Globulin go?
Back to the liver for reuse
Where does the heme go?
It is waste and becomes bilirubin
What happens to the unconjugated bilirubin during metabolism
It binds with albumin and is transported to the liver
What happens to the unconjugated bilirubin when it reaches the liver during metabolism?
The hepatic cells metabolize it and conjugate it (water-soluble)
It is a major component of bile
What happens to the conjugated bilirubin after a meal?
It exits the biliary tract with the bile and enters the GI system
What happens to the conjugated bilirubin when it enters the GI tract
The bacteria convert it into urobilinogen
What happens to the urobilinogens during metabolism?
It is reabsorbed and excreted in the kidney
Excreted through the feces as stercobilin
What are the causes of icterus?
The liver can not conjugate bilirubin because the hepatocytes are not functioning properly
Excessive RBC destruction that overwhelms the liver
Blockage of the biliary tract
What does bilirubin testing tell us?
The difference in the solubility between unconjugated and conjugated bilirubin
What does the presence of unconjugated bilirubin indicate?
A prehepatic or hepatic issue
Unconjugated bilirubin comprises approximately what of the total bilirubin in the serum?
Two thirds
What do increased levels of unconjugated bilirubin indicate?
The cells of the liver have not processed it
What causes an increase in unconjugated bilirubin
Excess hemolysis (prehepatic) Liver cells are not functioning properly (Hepatic)
What is conjugated bilirubin also known as?
Direct bilirubin
What does conjugated bilirubin indicate?
Posthepatic issue such as a bile duct obstruction
What does elevated conjugated bilirubin indicate
The cells of the liver did their job but there is a blockage somewhere preventing the bile from exiting
What are bile acids?
They are made from cholesterol in the liver
What is the job of the bile acids?
To help the body digest and absorb fats
What are normal serum bile acid levels?
Low but will be high right after eating
Bile Acid test
Paired serum samples
- Collect the first sample after 12 hours fast
- feed a small meal
- Collect the second sample 2 hours after eating
What does the bile acid test measure?
The difference in the bile acid concentration between the two samples
In what species do you only need one sample and why?
Horses because they do not have a gallbladder
What factors can create a false bile acid test
Inadequate fasting
Food aromas
Prolonged fasting or diarrhea
Why is food aromas a factor for false bile acid testing?
Because in dogs the bile acid system will kick in creating inappropriate results
What does an elevated bile acid indicate?
Liver disease.
What kind of liver disease does the elevated bile acid indicate?
Congenital portosystemic shunts Chronic hepatitis Hepatic cirrhosis Cholestasis Neoplasms
What is one problem with the bile acid test?
It is unspecific for the type of liver problem
It is only a screening test
What is Cholesterol
A lipoprotein produced mainly in the liver
Is high cholesterol due to diet common in animals?
No. More common in humans
In what conditions do veterinarians see high cholesterol?
Hypothyroidism (dogs) Cushing's Disease (dogs) Diabetes (dogs and cats) Hepatic Lipidosis (cats) Steroid use
Liver Enzyme Leakage tests
ALT
AST
ID
GLDH
What does liver leakage enzyme testing tell you?
The cells of the liver are damaged, dying, and the contents are “leaking” into the bloodstream
Dehydrogenase enzymes
Iditol dehydrogenase (ID) Glutamate dehydrogenase (GLDH) more commonly used in large animals
Alanine Transaminase or Aminotransferase
ALT
liver-specific in dogs and cats
What other organs does Alanine Transaminase come from?
Kidney
Heart
Pancreas
Muscle
In what species is ALT not liver-specific?
Horses
Ruminants
Pigs
Birds
How long, after liver damage does it take for ALT to increase?
12 hours
Considered an acute problem
After damage how long does ALT stay high?
A few weeks unless ongoing liver damage
What else can cause an increase in ALT?
Certain drugs
Is there a direct correlation between the severity of liver damage and ALT level?
NO
Aspartate transaminase or Aminotransferase
AST
NOT a liver-specific enzyme
What if there is an elevation in ALT and AST
Considered more severe liver damage
Where can AST be found?
Liver Heart KIdney Pancreas Muscle RBCs
What does a high AST indicate?
A more severe liver damage when compared to ALT
What could cause an elevated AST?
Liver disease
Muscle inflammation
Hemolysis of RBCs
How does muscle inflammation cause an elevated AST?
Strenuous exercise
IM injection
How does hemolysis of the RBCs cause an elevated AST?
By improper handling of the blood
What did ALT use to be called?
SGPT
serum glutamic pyruvate transferase
What did AST use to be called?
SGOT
Serum glutamic oxaloacetic transferase
Iditol Dehydrogenase or Sorbitol Dehydrogenase
Useful in evaluating liver disease in large animals because large animals do not have diagnostic levels of ALT
What is the primary source of iditol dehydrogenase?
Hepatocytes
Cholestasis Enzymes
AP or ALKP
Alkaline Phosphatase
Alkaline Phosphatase
leakage enzyme during cholestasis
Where is ALKP present?
Liver, bone, and other tissues
In what conditions can you also see an increase in levels of ALKP?
Young animals due to bone growth
Bone disease (neoplasia)
Corticosteroid use
Cushings disease
Other enzymes Associated with Cholestasis
Gamma-glutamyltransferase (GGT)
Gamma-glutamyltransferase (GGT)
Found in many tissues
What species have higher GGT levels?
Cattle Horses Sheep Goats Birds
