Gastrointestinal Flashcards
What level enzymes demonstrate hepatocellular damage?
ALT (alaninine aminotransferase)
AST (aspartate aminotransferase)
GLDH (glutamate dehydrogenase)
What are the enzymes that demonstrate cholestasis?
gamma - GT
Alkaline Phosphatase
Bilirubin
What are the enzymes that monitor liver synthesis?
Albumin
Cholinesterase
Thrombocytopaenia
Coagulation factors
What is the role of alanine transferase within the hepatocyte?
Involved in gluconeogenesis + generation of urea
ALT is specific to hepatocytes only
What is the role of aspartate transaminase?
Amino acid metabolism
AST is not specific to hepatocytes, also found in: heart, muscle and erythrocytes
How may a AST/ ALT ratio be of use?
- Useful for determining severity of damage
- Ratio >1 is inidicative of severe damage
What does an isolated AST increase mean?
- Likely to be a non-hepatic cause.
- e.g. AST is elevated in pathology regarding muscle, heart and erythrocytes (e.g. MI)
What is the role of glutamate dehydrogenase within hepatocytes?
Amino acid metabolism
What are liver specific metabolic enzymes?
ALT and GLDH
What causes an elevated GLDH level?
- Severe hepatitis
- Toxins
- Hepatocellular carcinoma / liver mets
What differentials should be considered if AST/ALT ratio is between 0.7 - 1.0 ?
AST/ALT ratio at this level is indicative of an “inflammatory pathology”:
- Uncomplicated viral hepatits
- Minor fatty liver disease
- Extrahepatic cholestasis
What differentials should be considered if the AST/ALT ratio is >1 ?
AST/ALT ratio over this level indicates a “necrotic pathology”
- Alcoholic hepatisis ( ratios normally >2)
- Fulminant, necrotic hepatitis
- Liver cirrhosis
- Hepatocellular carcinoma / mets
What is the role of gamma glutamyl transpeptidase?
Membrane-bound enzyme of glutathione metabolism and amino acid transport
What does a elevated gamma GT suggest?
Gamma GT is the most sensitive marker for biliary disease
Differentials:
- Cholestasis
- Alcohol abuse - gamma GT is one of the most sensitive markers for albolic liver disease
Explain bilirubin metabolism:
- Haemoglobin is broken down into haem (80% by spleen, 20% by bone marrow)
- Haem metabolised by macrophages to form unconjugated bilirubin
- Unconjugated is bound to albumin and transported to the liver
- Bilirubin is conjugated in the liver and secreted into the bile (to reach the bile caniculli conjugated bilirubin enters the blood stream and then returns to the liver)
- Bile secreted into the intestines during digestion
- Intestinal bacteria convert some of the billirubin into urobillogen
- Most of the urobillogen remains in the intestine (80%) and is converted into stercobilogen and then stercobillin
- A small amount of the urobilogen (20%) is reabsorbed and secreted via the kidneys as urobilin (which gives urine is characteristic yellow)
