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Clin Path Quiz 12
Lecture 12: The Liver
| Question | Answer |
|---|---|
| liver cells | hepatocytes |
| function of the liver | largest digestive gland in the body, aids in digestion and absorption of nutrients; carbohydrate metabolism, fat metabolism, protein metabolism/production, formation of bile, hemoglobin metabolism, detoxification |
| blood flow to the liver comes from | hepatic portal vein and hepatic artery |
| function of the gallbladder | concentrate and store bile until it is needed (when fat is consumed) |
| bile exits the liver through | the hepatic ducts and empties into the common bile duct |
| carbohydrate metabolism | store carbohydrates as glycogen which can be broken down to glucose when the body needs an energy source |
| fat metabolism | fats can be broken down to produce glycerol and fatty acids; serves as an energy source and source of cholesterol production |
| protein metabolism and production | amino acids from protein metabolism can be reconfigured to make new proteins such as ALBUMIN |
| formation of bile | bile salts, fatty acids, and cholesterol combined, made by the liver and secreted into the duodenum to metabolize fat |
| hemoglobin metabolism | Hgb is released as RBCs are recycled (destroyed); bilirubin is produced from the breakdown of heme and excreted by the liver |
| detoxification | ability to change harmful substances (toxins) into inert substances that can be excreted |
| the liver is... | VERY IMPORTANT |
| liver tests detect: | hepatocellular injury, cholestasis, decreased liver function/hepatic function |
| hepatocellular injury | injury to the cells of the liver from various causes (hypoxia, toxins, inflammation, abscesses, cancer) |
| cholestasis | back up of bile into the liver due to bile duct obstruction |
| up to how much of the liver can be damaged before lab tests may detect damage? | 80% |
| leakage enzymes | Alanine aminotransferase (ALT), Aspartate aminotransferase (AST), Sorbitol dehydrogenase (SDH), Glutamate dehydrogenase (GDH) |
| enzymes that indicate cholestasis | Alkaline phosphatase (ALP/SAP), Gamma glutamyltransferase (GGT) |
| chemistry values that evaluate the liver | ALT, AST, SDH, GDH (leakage enzymes); ALP/SAP, GGT (indication of cholestasis), bile acids, bilirubin |
| leakage enzymes are indicators of... | liver (hepatocellular) injury; increase with enzymes occurs with mild/reversible changes to the liver cells as well as with severe, irreversible injury; magnitude of injury correlates with # of cells injured, NOT severity/type of injury |
| leakage enzymes to know | Alanine aminotransferase (ALT), Aspartate aminotransferase (AST) |
| Alanine aminotransferase (ALT) function | catalyzes transfer of amino groups from one amino acid to another; SENSITIVE AND SPECIFIC to liver injury in dogs and cats (hepatocytes are a major source of ALT) |
| interpretation of ALT elevation | indication of LIVER CELL INJURY; this includes hepatitis (inflammation), hepatic neoplasia, cholestasis, drugs or toxins causing liver damage |
| Aspartate aminotransferase (AST) | large amounts of AST are found in muscle and liver; increase seen with hepatocellular injury AND muscle injury, NOT liver specific (DOESN'T RULE IN liver disease) |
| what other values should you evaluate with AST? | other liver values and CK (creatine kinase) |
| Sorbitol dehydrogenase (SDH) | high amounts in hepatocytes of all species, unstable enzyme and difficult to measure, primarily used in large animals (but not widely available) |
| Glutamate dehydrogenase (GDH) | found in liver, kidney, and central nervous system; SENSITIVE and SPECIFIC for hepatocellular injury in all species, but not routinely offered; found in high amounts in cattle, sheep, goats, and birds |
| Lactate dehydrogenase (LDH) | found in many tissues, NOT SPECIFIC |
| causes of cholestasis | swelling of hepatocytes, liver neoplasia (infiltration), obstruction of the bile duct, gallbladder rupture |
| Alkaline phosphatase (ALP/SAP) | catalyze the reaction that releases glucose from a storage form; found in many different tissues in the body, but high amounts in hepatocytes |
| ALP/SAP | SENSITIVE but NOT SPECIFIC indicator of cholestasis in dogs (good rule OUT test) |
| interpretation of ALP elevation | cholestasis in ALL species, GLUCORTICOIDS in dogs, drug induction in dogs (not steroids; Phenobarbital), colostrum ingestion in puppies and kittens (should return to normal within 10 days) |
| interpretation of elevated ALP for CHOLESTASIS in DOGS | may see changes 2-3x upper end of the reference range; very SENSITIVE (rule OUT) |
| interpretation of elevated ALP for CHOLESTASIS in CATS | short half-life of ALP in the blood, meaning it is cleared quickly; ANY ALP elevation is considered significant |
| interpretation of elevated ALP for CHOLESTASIS in COWS | can be useful when combined with other liver tests, somewhere in the middle as far as sensitivity for cholestasis |
| Gamma glutamyltranferase (GGT) | found in all tissues but increased amounts found in the tissue lining of the bile ducts; more SPECIFIC (rule IN) for cholestasis in all species |
| GGT in cats, ruminants, and horses | also a more SENSITIVE (rule OUT) indicator of cholestasis |
| interpretation of elevated GGT | cholestasis, colostrum ingestion (calves and puppies ONLY), drug induction (glucorticoids, phenobarbital; increase is much less than ALP) |
| canine patient wtih elevated ALP but normal GGT | consider cholestasis but also look for other potential causes like toxins, drug administration, stressors) |
| feline patient with elevated GGT but ALP is at the high end of the normal range | cholestasis is the most likely cause |
| equine patient has an elevated ALP and GGT | cholestasis is the most likely cause |
| hepatocellular carcinoma | aggressive liver cancer in dogs |
| increased liver enzymes on chemistry with a hepatocellular carcinoma | ALT, AST, ALP, GGT |
| bile acids | measure DECREASED liver function |
| bile acid metabolism | synthesized by liver cells from cholesterol and conjugate to increase water solubility, excreted into bile and mostly stored in the gallbladder, released from gallbladder into small intestine, intestinal reabsorption and entry into portal veins |
| how much of bile acids are cleared from portal blood at 'first pass' by hepatocytes? | 90% |
| bile acid testing detects... | conditions where the reabsorbed bile acids are escaping hepatocellular clearance OR where the liver in unable to excrete bile acids |
| indications for bile acid testing | performed when routine hepatic tests are NOT specifically altered or are inconclusive |
| interpretation of increased bile acids | test of choice to evaluate LIVER FUNCTION |
| an increase in bile acids is SENSITIVE AND SPECIFIC for what conditions in dogs and cats? | portosystemic vascular shunt, hepatocellular disease, cholestasis |
| portosystemic vascular shunt (PSS) | decreased clearance of bile acids from blood due to circulation bypassing the liver; abnormal connections between the portal system to the caudal vena cava |
| clinical signs of PSS | poor weight gain, stunted growth, poor recovery from certain anesthesia, neurologic abnormalities (head pressing, ataxia, seizures), vomiting, anorexia, and diarrhea |
| lab abnormalities seen with PSS | increased liver enzymes (ALT, AST, ALP, GGT), increased bile acids |
| hepatocellular disease | decreased hepatocellular intake |
| treatment for PSS | MEDICAL MANAGEMENT to stabilize pet and decrease anesthetic risk (low protein diet, antibiotic and lactulose administration to decrease bacterial population in the intestines, anti-seizure medication if necessary), SURGERY |
| breeds commonly affected by congential PSS | mini Schnauzers, Yorkshire Terriers, Irish Wolfhounds, Cairn Terriers, Maltese, Australian Cattle Dogs, Golden Retrievers, Old English Sheepdogs, Labrador Retrievers |
| bilirubin | indicator of DECREASED LIVER FUNCTION, less sensitive compared to bile acid test |
| bilirubin formation | formed when heme is broken down (normally occurs when RBCS are broken down), liver conjugates bilirubin to make it water soluble, conjugated bilirubin is excreted through the bile duct into the intestines |
| if the liver is diseased, bilirubin will... | build up in the BLOOD, which leads to the yellow color change that can be appreciated in MM, sclera, and plasma and is known as JAUNDICE/ICTERUS |
| unconjugated bilirubin | bilirubin formed when heme is broken down |
| conjugated bilirubin | when liver conjugates bilirubin to make it water soluble |
| total bilirubin | all forms are measured; test is available on routine chemistries |
| direct bilirubin | conjugated bilirubin |
| indirect bilirubin | unconjugated bilirubin (not directly measured); calculated by subtracting direct bilirubin from total |
| urinary bilirubin | bilirubin excreted in urine (small amount normal in dogs, NEVER normal in cats) |
| interpretation of INCREASED bilirubin (PRE-HEPATIC) | elevated bilirubin WITHOUT liver disease (mostly unconjugated; hemolysis, hemolytic anemia) |
| interpretation of INCREASED bilirubin (HEPATIC) | elevated bilirubin due to LIVER DISEASE (both unconjugated and conjugated); hepatic neoplasia, hepatitis, drugs/toxins affecting the liver |
| interpretation of INCREASED bilirubin (POST-HEPATIC) | elevated bilirubin due to disease distal to the liver (mostly conjugated); CHOLESTASIS |
| cholesterol | most common STEROID in the body, precursor of bile acids and steroid hormones; routinely measured on in-house chemistry in CAT and DOGS |
| hypercholesteremia (INCREASE) | more common in DOGS; altered lipid metabolism (hypothyroidism, diabetes mellitus, pancreatitis), decreased hepatic excretion, post-prandial (very small increase, not usually above the normal range) |
| hypocholesteremia (DECREASE) | decreased hepatic synthesis (hepatic disease including PSS), decreased intestinal absorption (intestinal loss) |
Created by:
mkroon26
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