Enzymes and bilirubin

Question 1

What is an enzyme?

Answer 1

A protein that catalyses a chemical reaction

Question 2

How are enzyme amounts expressed, and why?

Answer 2

As activity rather than concentration because it is very difficult to measure their amount directly

Question 3

Where are enzymes found?

Answer 3

Inside cells

• they have no function in blood
• they are tissue specific and have different localisations in cells e.g. cell membrane, mitochondria

Question 4

What is the significance of increase enzyme activity?

Answer 4

• Cell damage

- Enzymes aren’t cleared from the blood at their normal rate

Question 5

What is enzyme activity in serum measured to detect?

Answer 5

Damage to:

• Hepatocytes
• Exocrine pancreas cells
• Myocytes

Question 6

What are some features that diagnostically useful enzymes should have?

Answer 6

• 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)

Question 7

Name 3 leakage enzymes that increase with cell damage

Answer 7

• Creatine kinase
• Aspartate aminotransferase
• Lactase dehydrogenase

Question 8

What are 3 reasons that leakage enzyme leak from monocytes?

Answer 8

• Degeneration
• Necrosis
• Inflammation

Question 9

What are the 2 functions of creatine kinase in muscle?

Answer 9

• 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

Question 10

What is the waste product of the spontaneous breakdown of creatine?

Answer 10

Creatinine

Question 11

What is the major storage reservoir of energy during muscle rest?

Answer 11

Creatine phosphate

Question 12

Which factors make creatine kinase sensitive and specific for muscle injury?

Answer 12

• levels rise and fall quickly
• Short half life
• Increases rapidly post injury
• Returns to normal levels quickly

Question 13

Persistently high levels of creatine kinase indicates what?

Answer 13

Ongoing damage - muscle injury

Question 14

Give some different examples of muscle injury types

Answer 14

• Degenerative e.g. hypoxia
• Metabolic e.g. hypothyroidism
• Nutritional
• Inflammatory
• Toxic
• Trauma

Question 15

Which muscle enzymes are found in RBCs?

Answer 15

AST (aspartate aminotransferase)

LDH (Lactate dehydrogenase)

Question 16

What can evaluation of AST and LDH help estimate?

Answer 16

When a muscle injury occurred, and if the injury is still occurring

Question 17

An increase in only the serum CK activity suggests … ?

Answer 17

A very acute muscle injury

Question 18

Increased serum activities of both AST and CK suggest … ?

Answer 18

Active or recent muscle injury

Question 19

An increase in only the serum AST activity suggests … ?

Answer 19

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

Question 20

Levels of which enzymes are used to identify injury to pancreatic cells?

Answer 20

Amylase and lipase

Question 21

What are the main features of amylase as an enzyme

Answer 21

• Catalyses the hydrolysis of complex starches
• Short half life
• Salivary and intestinal
• Most useful in dogs
• Can increase due to decreased GFR

Question 22

What are the main features of lipase as an enzyme?

Answer 22

• Catalyses the hydrolysis of triglycerides
• Very short half life
• Mostly from pancreas
• Can increase due to decreased GRF

Question 23

Name some enzymes that are indicative of hepatocellular damage

Answer 23

• ALT
• AST
• LDH
• SDH
• GLDH

Question 24

Name some of the main functions of the liver

Answer 24

• Synthesis of cholesterol and bile acids
• Synthesis of plasma proteins
• Breakdown of RBCs
• Removal of bacteria
• Production of clotting factors
• Glycogen storage

Question 25

What are the 2 cholestatic liver enzymes?

Answer 25

ALP (alkaline phosphatase)

GGT (gammaglutamil transferase)

Question 26

What is cholestasis and which enzymes levels rise as a result of this?

Answer 26

• Bile duct obstruction causing decreased bile flow and excretion
• ALP

Question 27

Which enzyme is preferred over ALP to detect cholestasis in cattle, horse, sheep, goats and birds?

Answer 27

GGT

Question 28

Which bile components act as markers for cholestasis?

Answer 28

• bilirubin
• bile acids
• cholestatic enzymes
• ALP
• GGT

Question 29

What is the cause of hyperbilirubinemia in horses?

Answer 29

Fasting/starving - causes a yellow serum colour

Most likely caused by unconjugated bilirubin

Question 30

What are 3 causes of hyperbilirubinemia?

Answer 30

• Cholestasis
• Haemolytic anaemia
• Reduced hepatocellular function

Question 31

Unconjugated bilirubin is carried by .. in the blood?

Answer 31

Albumin

Question 32

What are 4 ways of testing liver function?

Answer 32

• 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

Question 33

What will be the effects of altered hepatic blood flow?

Answer 33

• Decreased uptake and excretion of bile acids
• Decreased conversion of ammonia to urea
• Decreased immunological function