Hepatobiliary System
Bilirubin
Red blood cells contain haemoglobin. Old red blood cells are broken down in the spleen with haem as a breakdown product. This is converted (via a number of stages) to unconjugated bilirubin.
Unconjugated bilirubin is then conjugated (made water soluble) by the liver.Bilirubin is then predominantly excreted via the bile ducts into the gut to facilitate the removal of waste products. A small amount is excreted in urine.
Jaundice
The term โjaundiceโ refers to the yellowing of the skin and sclera. It is caused by an excess of bilirubin within the body. There are many different causes but it is nearly always pathological.
A patient may be jaundiced prior to, or at presentation to hospital. It may also occur during admission.
Types of Jaundice
Jaundice can be classified in the following three ways.
- Pre-hepatic: there is an increase in bilirubin due to an increased breakdown of red blood cells or failure to conjugate.
- Hepatic: refers to a problem with bilirubin metabolism within the liver.
- Post-hepatic: occurs when there is a disruption to bile excretion from the liver.
Causes of Jaundice
Pre-hepatic (unconjugated hyperbilirubinaemia)
- Haemolytic anaemia
- Gilbert’s syndrome
- Trauma
The commonest cause of an unconjuagated hyperbilirubinaemia is Gilbertโs syndrome which affects approximately 5% of the population.
Whilst Gilbertโs is due to an enzyme deficiency which affects bilirubin conjugation within the liver, it is probably easier to consider it pre-hepatic as it causes an unconjugated hyperbilirubinaemia.
Gilbert’s only ever results in a mild jaundice (30-50 ummol) and is not clinically significant.
Intra-hepatic
- Cirrhosis
- Hepatitis A
- Autoimmune hepatitis
This is usually the result of either an acute or chronic liver injury. Jaundice occurs due to multiple errors in bilirubin metabolism and excretion due to reduced liver function. This leads to a mixed picture of jaundice but conjugated hyperbilirubinaemia usually predominates.
Post-hepatic (obstructive)
- Gallstones
- Cholangiocarcinoma
- Pancreatic cancer
This occurs due to an impairment of excretion of bilirubin from the liver into the bowel. This is nearly always due to a structural blockage of the bile ducts.
Kehrโs Sign
Gallstone disease may refer pain to the right shoulder tip. This is known as Kehrโs Sign. There is an important anatomical explanation underlying this phenomenon. An inflamed or distended gallbladder may irritate the diaphragm which is supplied by the phrenic nerve (C3, C4, C5 keeps the diaphragm alive!). These very same nerve roots also provide sensation tothe right shoulder tip by way of the supraclavicular nerves (C3โC5). The body misinterprets the signals that it receives and interprets the painsignals as coming from the right shoulder tip.
Courvoisierโs Law
Courvoisierโs law states that, in the presence of obstructive jaundice, a palpable gallbladder is unlikely to be due to gallstones. The reason is that gallstones cause chronic inflammation, fibrosis and a shrunken gallbladder.
Note, however, that the law does not hold true in reverse (i.e. in the presence of obstructive jaundice, an impalpable gallbladder is always due to gallstones) as 50 per cent of dilated gallbladders cannot be palpated on clinical examination, due to patient obesity or because of overlap of the liver.
Factors to develop cholesterol gallstones?
- Bile stasis
- Supersaturation of bile with cholesterol (lithogenic bile)
- Nucleation factors.
Portosystemic Anastomoses
Portosystemic anastomoses are sites at which the portal venous circulation meets the systemic venous circulation.
There are five principal sites where this takes place:
- lower oesophagus
- upper anal canal
- periumbilical region of the anterior abdominal wall
- bare area of the liver
- retroperitoneum.
The veins from the lower third of the oesophagus drain downwards to the left gastric vein (portal system) and above this level oesophageal veins drain into the azygous and hemiazygous systems (systemic system).
Subsequently in portal hypertension dilatations of the veins within the lower end of the oesophagus may take place, resulting in oesophageal varices. These can cause life-threatening haemorrhage.