Hepatic Disease And Treatment Flashcards
What is the percentage of oxygen consumed by the liver?
20-30%
Does the liver receive a lot of blood?
Yes it is highly vascularised
What are the 4 lobes of the liver called?
2 major lobes: (right and left)
2 minor lobes: (caudate and quadrate)
What is the functional unit of the liver called?
the liver lobule
What makes up the liver lobule?
- a central terminal hepatic venule
- interconnecting plates of hepatocytes
- peripherally arranged portal triad (terminal branches of hepatic artery, portal vein and bile duct)
Functions of the liver?
1) Xenobiotic detoxification and metabolism
2) Decomposition of erythrocytes and excretion of bilirubin
3) Bile Production
4) Cholesterol synthesis and Lipogenesis
5) Carbohydrate Metabolism
6) Protein synthesis
7) Hormone production
8) Storage
Proteins synthesised by the liver?
1) albumin
2) coagulation factors
Role of albumin?
an osmolar component of blood serum
Examples of coagulation factors?
1) fibrinogen
2) prothrombin
3) factors V, VII, IX, XI
4) proteins C and S
5) antithrombin
Hormones produced by the liver?
thrombopoieitin and angiotensin
Role of thrombopoietn?
regulates platelet production by bone marrow
Role of angiotensin?
raises blood pressure following renin activation
What is stored in the liver?
- glycogen
- vitamins A,D,E,K,B12
- Iron
- Copper
What is jaundice?
A symptom of underlying diseases or physiological dysfunction
What is the normal bilirubin level?
3-17 mmol/L
What causes pre-hepatic jaundice?
red blood cell haemolysis
What causes hepatocellular jaundice?
- infection
- chemical/drug
- genetic error
- autoimmune
- neonatal
What causes posthepatic jaundice?
- intrahepatic bile ducts
- extrahepatic bile ducts
Why is bilirubin insoluble in water?
The carboxylic group on the bilirubin forms hydrogen bonds with the NH group and the lactam oxygen on the bilirubin molecule making it insoluble in water.
How is the hydrogen bonds in bilirubin disrupted?
By enzyme-catalysed esterification of the carboxylic acid group with a glycosyl moiety - glucuronic acid.
Which of the two is toxic to cells conjugated or unconjugated bilirubin?
unconjugated bilirubin because it is insoluble in water so can’t be excreted via urine, so levels can increase leading to toxicity.
what is unconjugated bilirubin?
bilirubin that isn’t glucuronidated.
Where is unconjugated bilirubin found?
circulating in the plasma reversibly bound to albumin
Which of two, conjugated or unconjugated can be excreted into urine?
conjugated
Why is conjugated bilirubin able to be excreted into urine?
because it is soluble in water unlike the unconjugated form
why is there more albumin-bound bilirubin than unbound bilirubin in plasma?
coz albumin concentration exceeds that of bilirubin concentration so more is bound but also non-toxic (aka conjugated)
How does the uptake of bilirubin happen at hepatocytes?
- at the sinusoidal surface of hepatocytes, bilirubin dissociates from albumin
- it is taken up by facilitated diffusion requiring inorganic ions e.g. Cl-
- via a transporter that is a member of the organic anion transport protein family (OATP2)
What happens once bilirubin enters the hepatocytes?
-unconjugated bilirubin is glucuronidated by esterification of the carboxylic acid groups forming bilirubin di/monoglucuronide.
What catalyses the esterification of unconjugated bilirubin?
-this reaction is catalysed by uridine diphosphoglucuronate glucuronosyltransferase (UGT) isoform, UGT1A1
What happens once the unconjugated bilirubin becomes conjugated bilirubin?
it is secreted into the biliary canaliculi and bile in a unidirectional transport so that the conc in bile is higher than the conc in the hepatocyte. This process is energy dependent (active transport)
Conjugated bilirubin isn’t absorbed in the intestines, so what happens instead?
it is degraded by intestinal bacteria generating urobilinogen.
What colour is urobilinogen?
-colourless
What is the oxidation product of urobilinogen and what effect does it have on stool and urine colour?
- the oxidation product is urobilin
- it contributes to the colour of normal urine and stool
What is most urobilinogen oxidised to and how is it excreted?
- stercobilin
- excreted in faeces, although a small amount of it enters extrahepatic circulation and excreted in urine
Why do people get pale, clay-coloured stool during severe post-hepatic jaundice or complete obstruction of bile duct?
-coz the urobilinogen and urobilin are absent in urine and stool
What happens to urinary urobilinogen excretion if an individual has a liver disease and increased bilirubin production?
urinary urobilinogen excretion is increased.
What percentage of urobilinogen is oxidised to stercobilin and excreted in faeces?
80%
What percentage of urobilinogen enters te extrahepatic circulation and is excreted in urine?
20%
How is bilirubin formed in circulation?
- erythrocytes are broken down and haemoglobin is released
- 90% of haemoglobin is removed from the circulation by phagocytic activities of macrophages in the liver, spleen and lymph nodes
- 10% of haemoglobin remains in the circulation
- Globin is metabolised to amino acids which are recycled
- iron binds to transferrin and returns to liver stores
- haem is converted to bilirubin which binds to albumin and is insoluble.
4 types of jaundice?
- neonatal
- haemolytic
- hepatocellular
- obstructive
what is neonatal jaundice?
- bilirubin accumulates because bilirubin glucuronyl transferase levels are low at birth so bilirubin can’t undergo esterification as rapidly.
- so unconjugated bilirubin levels increase in blood
- bilirubin-albumin complex difuse into basal ganglia and cause toxic encephalopathy
How is neonatal jaundice treated?
-expose newborn skin to blue fluorescent light converting bilirubin to a more water-soluble isomer. These isomers can be excreted into bile without conjugation to glucuronic acid.
What is haemolytic jaundice?
-when excessive red blood cells undergo lysis so bilirubin is produced at a faster rate than it is conjugated.
What are the effects of haemolytic jaundice?
- blood unconjugated bilirubin levels increased
- urine urobilinogen increases and no bilirubin in urine. so urine is at normal colour
- stool has normal colour
What is hepatocellular jaundice?
- liver damage by hepatitis.
- so bilirubin isn’t conjugated efficiently
- and conjugated bilirubin isn’t efficiently secreted into bile