Enzymes and bilirubin Flashcards
What is an enzyme?
A protein that catalyses a chemical reaction
How are enzyme amounts expressed, and why?
As activity rather than concentration because it is very difficult to measure their amount directly
Where are enzymes found?
Inside cells
- they have no function in blood
- they are tissue specific and have different localisations in cells e.g. cell membrane, mitochondria
What is the significance of increase enzyme activity?
- Cell damage
- Enzymes aren’t cleared from the blood at their normal rate
What is enzyme activity in serum measured to detect?
Damage to:
- Hepatocytes
- Exocrine pancreas cells
- Myocytes
What are some features that diagnostically useful enzymes should have?
- high sensitivity
- specific for one tissue
- be stable in the sample
- be cleared from the plasma at a rate appropriate to the diagnostic test
- show clear separation between normal and pathological values (small grey area)
Name 3 leakage enzymes that increase with cell damage
- Creatine kinase
- Aspartate aminotransferase
- Lactase dehydrogenase
What are 3 reasons that leakage enzyme leak from monocytes?
- Degeneration
- Necrosis
- Inflammation
What are the 2 functions of creatine kinase in muscle?
- makes ATP available for muscle contraction
- catalyses the production of high energy ATP via the transfer of a phosphate bond from creatine phosphate to ADP
What is the waste product of the spontaneous breakdown of creatine?
Creatinine
What is the major storage reservoir of energy during muscle rest?
Creatine phosphate
Which factors make creatine kinase sensitive and specific for muscle injury?
- levels rise and fall quickly
- Short half life
- Increases rapidly post injury
- Returns to normal levels quickly
Persistently high levels of creatine kinase indicates what?
Ongoing damage - muscle injury
Give some different examples of muscle injury types
- Degenerative e.g. hypoxia
- Metabolic e.g. hypothyroidism
- Nutritional
- Inflammatory
- Toxic
- Trauma
Which muscle enzymes are found in RBCs?
AST (aspartate aminotransferase)
LDH (Lactate dehydrogenase)
What can evaluation of AST and LDH help estimate?
When a muscle injury occurred, and if the injury is still occurring
An increase in only the serum CK activity suggests … ?
A very acute muscle injury
Increased serum activities of both AST and CK suggest … ?
Active or recent muscle injury
An increase in only the serum AST activity suggests … ?
That the muscle injury stopped more than 2 days earlier, and that the serum CK activity returned to normal as a result of its short half life
Levels of which enzymes are used to identify injury to pancreatic cells?
Amylase and lipase
What are the main features of amylase as an enzyme
- Catalyses the hydrolysis of complex starches
- Short half life
- Salivary and intestinal
- Most useful in dogs
- Can increase due to decreased GFR
What are the main features of lipase as an enzyme?
- Catalyses the hydrolysis of triglycerides
- Very short half life
- Mostly from pancreas
- Can increase due to decreased GRF
Name some enzymes that are indicative of hepatocellular damage
- ALT
- AST
- LDH
- SDH
- GLDH
Name some of the main functions of the liver
- Synthesis of cholesterol and bile acids
- Synthesis of plasma proteins
- Breakdown of RBCs
- Removal of bacteria
- Production of clotting factors
- Glycogen storage
What are the 2 cholestatic liver enzymes?
ALP (alkaline phosphatase)
GGT (gammaglutamil transferase)
What is cholestasis and which enzymes levels rise as a result of this?
- Bile duct obstruction causing decreased bile flow and excretion
- ALP
Which enzyme is preferred over ALP to detect cholestasis in cattle, horse, sheep, goats and birds?
GGT
Which bile components act as markers for cholestasis?
- bilirubin
- bile acids
- cholestatic enzymes
- ALP
- GGT
What is the cause of hyperbilirubinemia in horses?
Fasting/starving - causes a yellow serum colour
Most likely caused by unconjugated bilirubin
What are 3 causes of hyperbilirubinemia?
- Cholestasis
- Haemolytic anaemia
- Reduced hepatocellular function
Unconjugated bilirubin is carried by .. in the blood?
Albumin
What are 4 ways of testing liver function?
- Uptake and excretion of bilirubin and bile acids
- Conversion of ammonia to urea: increased ammonia
- Synthesis of metabolites: decreased albumin, cholesterol, urea
- Immunologic function: decreased clearance of toxins
What will be the effects of altered hepatic blood flow?
- Decreased uptake and excretion of bile acids
- Decreased conversion of ammonia to urea
- Decreased immunological function
