GENERAL LIVER FUNCTION AND ENZYMES

Question 1

What are the roles that the liver plays in lipid metabolism?

Answer 1

Cholesterol synthesis
Lipogenesis
Synthesis of lypoproteins to allow for serum transport of lipids (e.g chylomicrons)

Question 2

What role does the liver have in protein metabolism?

Answer 2

Synthesis of non-essential amino acids (such as glutathione
Catabolism of proteins
Synthesis of enzymes

Question 3

Name some important hormones synthesised in the liver. For each one give a brief description of its role in the body.

Answer 3

Angiotensinogen - precursor for angiotensin

Insulin-like growth factor 1 (IGF-1) - stimulates growth. It itself is stimulated by growth hormone.

Thrombopoietin - stimulation of platelet precursors in bone marrow

Hepcidin - blocks release of iron from intracellular stores

Betatrophin - stimulates proliferation of insulin secreting Beta cells of pancreas

Question 4

Name some of the things that are stored in the liver and state their main function in the body.

Answer 4

Glycogen - energy store

Vitamin A - immune system, vision (combines with opsin to make rhodopsin)

Vitamin D - absorption of calcium, iron, magnesium, phosphate and zinc.

Vitamin B12 - nervous system, formation of red blood cells

Vitamin K - blood coagulation

Iron - haemoglobin

Copper - electron transport chain

Question 5

Name the coagulation factors produced by the liver.

Answer 5

I (fibrinogen) 
II (prothrombin)
V
VII
VIII
IX
X
XI, as well as protein C, protein S and antithrombin.

Question 6

Which protein is made and released by the liver and makes up the major osmolar component of blood?

Answer 6

Albumin

Question 7

What is the liver’s role in the bilirubin cycle?

Answer 7

Conjugation of unconjugated bilirubin bound to albumin.

Adding bilirubin to bile.

Question 8

What is the liver’s role in the urea cycle?

Answer 8

Converts ammonia into urea

Question 9

What is the name of the enzyme which conjugates bilirubin in the liver?

Answer 9

Glucuronyltransferase

Question 10

In general terms, what increases the levels of liver enzymes found in the serum?

Answer 10

Increased synthesis
Cell proliferation
Tissue damage - Hepatitis, alcohol
Cell death
Defective clearance

Question 11

What are the three metabolic processes involving carbohydrates that take place largely in the liver?

Answer 11

Gluconeogenesis
Glycogenolysis
Glycogenesis

Question 12

In general terms, what decreases the levels of liver enzymes found in the serum?

Answer 12

Artefactual
Genetic defect affecting synthesis of enzyme
Deficiency in co-enzymes

Question 13

Name the six enzymes that we should normally measure in a blood test regarding function of the hepato-pancreato-biliary system.

Answer 13

Alanine transaminase (ALT)

Aspartate transaminase (AST)

Alkaline phosphotase (ALP)

Gamma-GT (GGT)

Creatinine kinase (CK)

Amylase (AMY)

Question 14

What are the three types of creatinine kinase?

Answer 14

MM
MB
BB

Question 15

What percentage of MM and MB make up the creatinine kinase found in skeletal muscle?

Answer 15

99% MM

1% MB

Question 16

What percentage of MM and MB make up the creatinine kinase found in cardiac muscle?

Answer 16

75% MM

25% MB

Question 17

Which type of creatinine kinase is used as a cardiac marker?

Answer 17

MB

Question 18

What are non-cardiac causes of raised CK?

Answer 18

Hypothyroidism
Post exercise
Statin-induced myositis
Dystrophies will show very high CK

Question 19

Where are isoenzymes of amylase produced?

Answer 19

Salivary glands

Pancreas

Question 20

Why might levels of amylase be raised?

Answer 20

Infection - e.g. mumps

Neoplasm - e.g. pancreatic carcinoma

Vascular - e.g. mesenteric ischaemia

Inflammatory - e.g. acute pancreatitis, hepatitis, post-ERCP, peritonitis

Trauma - e.g. burns, posterior perforating duodenal ulcer, intestinal obstruction or perforation

Drugs - e.g. morphine and other opiates

Metabolic - e.g. renal failure, renal transplant, diabetic ketoacidosis, macroamylasaemia

Question 21

How do we determine liver synthetic function?

Answer 21

Prothrombin time

Serum albumin

Question 22

Other than liver impairment, what can cause hypoalbuminaemia?

Answer 22

Hypercatabolic states such as chronic inflammatory disease and sepsis.

Excessive renal clearing (nephrotic syndrome)

Intestinal loss of protein

Question 23

Other than liver impairment, what can cause a prolonged prothrombin time?

Answer 23

Vitamin K deficiency as a result of biliary obstruction - Low concentration of intestinal bile salts results in poor absorption of vitamin K.

Question 24

What are the most likely causes of an isolated rise in serum in bilirubin with otherwise normal liver biochemistry?

Answer 24

Prehepatic causes of jaundice:

An inherited defect in bilirubin metabolism (Gilbert’s disease)

Haemolysis

Ineffective erythropoeisis

Question 25

What does a rise in aminotransferases tell you about the liver?

Answer 25

Active liver damage - These enzymes are present in hepatocytes and leak into the blood with liver cell damage. Very high levels may occur with acute hepatitis.

Question 26

Which of the transaminases in more specific to the liver?

Answer 26

ALT

Question 27

Other than hepatocytes, where is AST found and what therefore might a rise in AST indicate?

Answer 27

Heart and skeletal muscle

Rise seen in MI and skeletal muscle damage

Question 28

What part of the liver is alkaline phosphatase found?

Answer 28

Canalicular and sinusoidal membranes of the liver - biliary tree - therefore rise seen in cholestasis

Question 29

Other than the biliary tree, where else is ALP made? What might a rise in ALP therefore signify?

Answer 29

Placenta - Pregnancy

Bone - Paget’s disease, Osteomalacia, growing children, bony metastases

Question 30

What induces the production of gamma GT?

Answer 30

Alcohol

Liver inducing drugs such as phenytoin

Cholestasis - similar pathway of excretion to alkaline phosphate

Question 31

What would a rise in ALP and bilirubin in excess of the aminotransferases likely indicate?

Answer 31

Cholestatic disorder such as primary biliary cirrhosis, primary sclerosing cholangitis or extrahepatic bile duct obstruction.