Investigation of Disease Lectures 7-9 Flashcards
How much does the liver weigh in adults?
Approx 1500-1600 grams
Largest organ
What are some functions of the liver?
1) Gluconeogenesis/glycogen synthesis
2) Steroid catabolism, lipid metabolism, cholesterol and lipoprotein synthesis
3) Deamination
4) Bilirubin excretion
5) Bile salt production
6) Synthesis of coagulation factors
7) Vitamin (A, B12) and iron storage
Describe the blood flow between the liver and the heart
Hepatic artery into liver (25% of input)
Hepatic portal vein into liver (75% of input)
Hepatic vein from liver to inferior vena cava into heart
Briefly describe the structure of the liver
Liver lobules are functional units formed by hepatic plates
- middle of each is a central vein
- edge of each is portal triad (Bile duct, portal vein and hepatic artery)
- Bile canaliculus collects bile produced by hepatocytes and moves it to bile duct
Describe the process of bilirubin synthesis
- Erythrocytes destroyed in spleen
- Haemoglobin released
- Separated to haem and globin
- Haem to biliverdin by haem oxygenase
- Biliverdin to Bilirubin by biliverdin reductase
What colour is bilirubin and how is it carried in the blood?
Yellow
Carried in blood conjugated to albumin
Where, why and how is bilirubin conjugated?
Where? In the liver
Why? To render it more soluble
How? By the addition of glucuronic acid by uridine diphoshogluconate (UDP) glucuronosyl transferase
What happens to bilirubin after it is conjugated in the liver?
Secreted into first into the gall bladder, then into the bile duct for excretion into the intestine
What are the direct and indirect measurements of bilirubin and how are they performed?
Direct measures conjugated bilirubin
Indirect measures unconjugated bilirubin
Van den Bergh reaction measures conjugated bilirubin: React bilirubin with diazotised sulphanilic acid to give purple coloured azobilirubin that absorbs at 600nm
- Addition of caffeine breaks intramolecular hydrogen bonding in unconjugated bilirubin allowing it to react
What are the 4 fractions of bilirubin found in plasma?
1) Unconjugated (alpha)
2) Monoglucuronide conjugated (beta)
3) Diglucuronide conjugated (gamma)
4) Bilirubin covalently bound to albumin (delta)
What happens to bilirubin in the intestines?
Reduced by bacteria to Urobilinogen
- Most urobilinogen reabsorbed by portal vein to kidney and liver
> Urobilinogen in intestine converted first to stercobilinogen and then oxidised to stercobilin (brown)
How is urobilinogen detected in urine?
Reaction with Ehrlich’s reagent
- Degree of colour change (dark pink to red) is proportional to amount of urobilinogen
What is jaundice and whn does it occur?
Yellow pigmentation of skin, sclera (whites of eyes) and mucosa
- occurs when plasma bilirubin exceeds ~ 30-50 µmol/L (normal
What are the main causes of unconjugated hyperbilirubinemia and give examples
Increased bilirubin production > Hemolysis > Erythrocyte abnormality > Ineffective erythropoiesis (red blood cell production) Decreased hepatic bilirubin clearance > Fasting > Gilberts syndrome > Crigler-Naijar syndromes
What are the main causes of conjugated hyperbilirubinemia and give examples
Intrahepatic disorder >Hepatocellular disease of any cause > Cholestatic disease of any cause > Dubin-Johnson syndrome > Rotor syndrome Extrahepatic disorder > Biliary tarct pathology > Pancreatic pathology
What is Gilbert’s Syndrome?
- Autosomal dominant
- Decreased uptake of bilirubin and decreased conjugation
- Mild unconjucated hyperbilirubinaemia
What are Crigler-Naijer syndromes types 1 and 2?
Type 1:
- Autosomal recessive
- absense of UDPG transferase
- severe unconjugated hyperbilirubinaemia
- lethal
Type 2:
Autosomal recessive
Partial defect
What is Dubin-Johnsom syndrome?
- AR
- Decreased hepatic excretion of bilirubin
- mild conjugated hyperbilirubinaemia
What is Rotor syndrome?
- AR
- similar to D-J but no hepatic pigmentation
What is the typical profile of a liver function test (LFTs)
- Albumin
- Bilirubin (total and conjugated)
- Transaminases (alanine and aspartate)
- Alkaline phosphatase
- Gamma-glutamyl transferase
What are some other LFTs
- Prothrombin time (PT)
- Urinary bilirubin
- Urobilinogen
What are the 2 transamines that are measured in the LFT?
Alanine aminotransferase (ALT) Aspartate aminotransferase (AST)
High levels of ALT and/or AST indicate what about the liver?
Indicate liver disease due to heptocellular intergrity Causes include: Infective agents Autoimmune disorders Toxins
Is ALT or AST better for measuring liver function and explain why?
ALT more specific than AST
- ALT is cytoplasmic and so is more easily released into plasma than AST (cytoplasmic and mitochondrial)
What are the 2 biliary tract enzymes measured in LFTs?
Alkaline phosphatase (ALP) Gamma-glutamyl transferase (yGT)
What is the main cause of increased ALP and yGT in the plasma?
Cholestasis (obstruction of bile from the liver to small intestine)
Why are ALP and yGT raised in cholestasis?
Usually anchored to biliary canalicular and sinusoidal membranes
- In cholestasis these enzymes are rendered soluble
What other factors can cause an increase in plasma yGT?
Alcohol abuse: - >10 upper limit of normal Enzyme inducing drugs: - Phenytoin - Rifampicin Weight: - 50% higher yGT in patients with BMI >30
List some possible causes of Early Jaundice (
Haemolysis: - blood group incompatibility between mother and baby (commonest) - red cell membrane defects G6PD deficiency Pyruvate kinase deficiency Infection Genetic defects of bilirubin metabolism
What are some characteristics of physiological jaundice in babies (>48 hours)
- 30 to 70% affected
- Total bilirubin usually
What things can exacerbate physiological jaundice?
- Prematurity
- Dehydration
- Haemolysis
- injections
- Hypoglycemia
- Hypothyroidism
- Inadequate calorie intake
- Intestinal obstruction
Describe the causes and tests of prolonged jaundice (>14 days) caused by CONJUGATED bilirubin
- alpha1-antitrypsin deficiency (alphaAT concentration)
- Galactosaemia (red cell glalactose-1P-uridyltransferase)
- Cystic fibrosis (sweat test)
- Biliary atresia (pale stools)
- Dubin-Johnson and Rotor syndromes
Describe the causes and tests of prolonged jaundice (>14 days) caused by UNCONJUGATED bilirubin
- Breast milk jaundice (benign condition)
- G6PD deficiency
- Congenital hypothyroidism
- Crigler-Najjar syndrome
Describe the causes and LFT changes of acute & chronic hepatitis
Causes: - Hepatitis virus - Alcohol - Drugs/toxins - Cytomegalovirus - Autoimmune LFT changes: - Increased heptocellular enzymes (ALT, AST) - Mixed hyperbilirubinaemia - Urine bilirubin +ve - Increased PT time
Describe the causes and LFT changes of Cirrhosis
Causes: - Chronic alcohol abuse - Chronic hepatitis - Primary bilirary cirrhosis - Wilson's disease - Haemochromatosis LFT changes: - Reduced albumin, gamma/beta bridging - Normal or increased ALT, AST - Normal or mixed hyperbilirubinaemia - Increased PT time
Describe the causes and LFT changes of Cholestasis
Causes:
- Gallstones
- Malignancies (pancreas)
- Bile duct stricture (narrowing of ducts)
- Biliary atresia (congenital absense or closure of bile ducts)
LFT changes:
- Increased biliary tract enzymes (ALP, yGT)
- Conjugated hyperbilirubinaemia
- Urine bilirubin +ve
- Decreased urine urobilinogen
What is the prevalence of autoimmune hepatitis, how is it tested for and diagnosed and how is it treated?
- 1 in 10,000
- Positive for autoantibodies
- Conformation by liver biopsy
- Managed with prednisolone and azathioprine
What is primary biliary cirrhosis?
- Autoimmune disease
- common in middle-old aged women
- Positive for mitochondrial antibodies
What does IMD stand for?
Inherited metabolic disorder