Jaundice Flashcards
What is bilirubin?
Bilirubin is the end product of the breakdown of red blood cells.
RBCs circulate in the blood for roughly 120 days during which time they must distort to enter small vessels.
They are slowly worn out and lose their flexabilty.
The spleen filters these RBCs which are phagocytosed into bilirubin and amino acids.
It is the main constituent of bile which is important in lipid digestion.
How is bilirubin broken down in the body?
unconjugated bilirubin is hydrophobic and must be bound by the transport protein bilirubin to enter circulation. It travels from the spleen to the liver via the splenic vein which leads into the hepatic portal vein.
In the liver hepatocytes are able to then conjugate bilirubin into a soluble non-toxic form.
It is then able to enter the gallbladder as a constituent of bile and be excreted into the GI tract for expulsion from the body.
What is Jaundice.
Jaundice is not a pathology in itself but instead is a symptom of other conditions.
It is caused by a build up of bilirubin in the blood which leads to yellowing of the skin and sclera.
Bilirubin is believed to have a high affinity to elastin which is the reason for accumulation in the skin and eyes.
Long term jaundice can take on a greenish tinge as bilirubin turns green when oxygenated.
Describe the functional units of the liver.
Lobules are hexagonal shaped clusters of hepatocytes which form the functional units of the liver.
Within the centre of each lobule there is a central vein and the outer points of the hexagon are marked by portal triads consisting of a branch of the hepatic artery, a bile duct and a branch of the hepatic portal vein. The portal triads are contained within sinusoids lined with epithelia. Stellate cells in the epithelia play an important role in fibrosis. They work in a series of functional zones which allow for detoxification of the blood. They further from blood supply, they greater the risk of hypoxia.
What is the main blood supply and venous drainage of the liver?
The hepatic artery supplies 25% of the blood to the liver.
The remaining 75% is supplied by the hepatic portal vein.
The hepatic vein drains from the liver into the inferior vena cava.
What is Rotor syndrome
Rotor syndrome is a genetic condition which effects proteins involved with conjugated bilirubin re-uptake in the liver. As a result of a dysfunction in the clearance of bilirubin there is a build up of conjugated bilirubin in circulation causing jaundice.
In the liver in order to transport conjugated bilirubin there is an instance of re-uptake from plasma in the sinusoids. Due to the fact that there is a dysfunction of these receptors bilirubin accumulates and re-enters blood circulation.
What is haemolytic jaundice and give an example of a condition which can be classified this way.
Haemolytic jaundice refers to jaundice which is caused by excessive lysis of blood cells that overloads the liver. This results in mixed levels of conjugated and unconjugated bilirubin in the blood stream.
Unconjugated bilirubin can be converted in urobilinogen in the GI tract which can allow for reabsorption and excretion in the urine. Urine appears darker than normal.
Sickle cell anaemia- cells have a shorter life cycle than regular cells and therefor are broken down quicker.
What is obstructive jaundice and give an example of a condition?
Obstructive jaundice is caused by obstructions that prevent the transport of bilirubin. For example gallstones can get lodged in the bile duct preventing excretion. This can result in increased levels of conjugated bilirubin. This can be excreted via urinobilogen.
Hepatocellular jaundice
Caused by damage to hepatocytes. Alcoholic liver disease. Hepatocytes become damaged and can no longer function effectively. Results in large levels of un-conjugated bilirubin: pale stools and dark urine.
How are bilirubin levels measured?
Conjugated and total bilirubin levels can be detected in blood which can allow for levels of unconjugated bilirubin levels to be inferred.
