GENERAL LIVER FUNCTION AND ENZYMES Flashcards
What are the roles that the liver plays in lipid metabolism?
Cholesterol synthesis
Lipogenesis
Synthesis of lypoproteins to allow for serum transport of lipids (e.g chylomicrons)
What are the three metabolic processes involving carbohydrates that take place largely in the liver?
Gluconeogenesis
Glycogenolysis
Glycogenesis
What role does the liver have in protein metabolism?
Synthesis of non-essential amino acids (such as glutathione
Catabolism of proteins
Synthesis of enzymes
Name some important hormones synthesised in the liver. For each one give a brief description of its role in the body.
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
Name some of the things that are stored in the liver and state their main function in the body.
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
Name the coagulation factors produced by the liver.
I (fibrinogen) II (prothrombin) V VII VIII IX X XI, as well as protein C, protein S and antithrombin.
Which protein is made and released by the liver and makes up the major osmolar component of blood?
Albumin
What is the liver’s role in the bilirubin cycle?
Conjugation of unconjugated bilirubin bound to albumin.
Adding bilirubin to bile.
What is the liver’s role in the urea cycle?
Converts ammonia into urea
What is the name of the enzyme which conjugates bilirubin in the liver?
Glucuronyltransferase
In general terms, what increases the levels of liver enzymes found in the serum?
Increased synthesis Cell proliferation Tissue damage - Hepatitis, alcohol Cell death Defective clearance
In general terms, what decreases the levels of liver enzymes found in the serum?
Artefactual
Genetic defect affecting synthesis of enzyme
Deficiency in co-enzymes
Name the six enzymes that we should normally measure in a blood test regarding function of the hepato-pancreato-biliary system.
Alanine transaminase (ALT)
Aspartate transaminase (AST)
Alkaline phosphotase (ALP)
Gamma-GT (GGT)
Creatinine kinase (CK)
Amylase (AMY)
What are the three types of creatinine kinase?
MM
MB
BB
What percentage of MM and MB make up the creatinine kinase found in skeletal muscle?
99% MM
1% MB
What percentage of MM and MB make up the creatinine kinase found in cardiac muscle?
75% MM
25% MB
Which type of creatinine kinase is used as a cardiac marker?
MB
What are non-cardiac causes of raised CK?
Hypothyroidism
Post exercise
Statin-induced myositis
Dystrophies will show very high CK
Where are isoenzymes of amylase produced?
Salivary glands
Pancreas
Why might levels of amylase be raised?
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
How do we determine liver synthetic function?
Prothrombin time
Serum albumin
Other than liver impairment, what can cause hypoalbuminaemia?
Hypercatabolic states such as chronic inflammatory disease and sepsis.
Excessive renal clearing (nephrotic syndrome)
Intestinal loss of protein
Other than liver impairment, what can cause a prolonged prothrombin time?
Vitamin K deficiency as a result of biliary obstruction - Low concentration of intestinal bile salts results in poor absorption of vitamin K.
What are the most likely causes of an isolated rise in serum in bilirubin with otherwise normal liver biochemistry?
Prehepatic causes of jaundice:
An inherited defect in bilirubin metabolism (Gilbert’s disease)
Haemolysis
Ineffective erythropoeisis
What does a rise in aminotransferases tell you about the liver?
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.
Which of the transaminases in more specific to the liver?
ALT
Other than hepatocytes, where is AST found and what therefore might a rise in AST indicate?
Heart and skeletal muscle
Rise seen in MI and skeletal muscle damage
What part of the liver is alkaline phosphatase found?
Canalicular and sinusoidal membranes of the liver - biliary tree - therefore rise seen in cholestasis
Other than the biliary tree, where else is ALP made? What might a rise in ALP therefore signify?
Placenta - Pregnancy
Bone - Paget’s disease, Osteomalacia, growing children, bony metastases
What induces the production of gamma GT?
Alcohol
Liver inducing drugs such as phenytoin
Cholestasis - similar pathway of excretion to alkaline phosphate
What would a rise in ALP and bilirubin in excess of the aminotransferases likely indicate?
Cholestatic disorder such as primary biliary cirrhosis, primary sclerosing cholangitis or extrahepatic bile duct obstruction.
