Liver function + test Flashcards
1
Q
Describe the physiology of the liver:
A
- Liver receives blood from the portal vein (where blood is carried from the intestine to the liver as well as from the hepatic artery)
- The liver regenerates itself (unlike the kidney) - Hence in liver transplants only a part of the liver is transplanted, and it can regenerate into a new liver
2
Q
Describe the function of the liver:
A
- Liver is involved in cholesterol synthesis and triglyceride (fats)
- Important as it detoxifies the body as well as involved in drug metabolism
- Liver is also involved in glucose homeostasis; Gluconeogenesis (production of glucose from other sources), glycogenolysis (breakdown of glycogen) and glycogenesis (production of glycogen); It produces glucose by metabolising fat
- It also breaks down insulin and other hormones
- It also produces coagulation factors such as albumin
- Liver is also the storage organ for Vitamin K, D, A, E, iron and copper
- It breaks down haemoglobin (its metabolised in the bile)
- It breaks ammonia to urine (ammonia is toxic)
3
Q
Why does jaundice occur?
A
- Jaundice happens when there is accumulation of bilirubin – means that liver is not functioning well; the test is done in babies to check the liver is fully formed and functioning
- Bilirubin is a component of red blood cells
4
Q
What is the liver’s involvement with bile, and therefore what is the function of bile?
A
- Liver produces bile which is involved in fat breakdown in the stomach; Bile is stored in the gallbladder and is secreted when required
- Some of the bile is drained directly to the duodenum, and some is stored in the gallbladder .
5
Q
What does the liver function test measure?
A
- Used to aid in differential diagnosis of liver diseases and injury
o Bilirubin
o Aminotranferase (AST and ALT)
o Alkaline phosphatase (ALP)
o Gamma Glutamyl transferase (GGT)
o Albumin
o Prothrombin time
Increase in albumin and prothrombin time indicate chronic liver damage and hence are not always tested - only if there is potential for long term damage
Bilirubin, AST and ALT, and ALP are present in acute liver damage (e.g., infection)
People without a spleen have a higher risk of infection and therefore are given penicillin V for life (and sickle cell disease)
Spleen metabolises haemoglobin but if not present then the liver does this
6
Q
How does haemoglobin metabolism work?
A
- Spleen metabolises haemoglobin forming unconjugated bilirubin (albumin bound)
- When it enters the liver, it is metabolised into conjugated bilirubin (phase 2 metabolism)
- Then it is secreted into the bile duct
- Then it goes into the gut Where the bacteria converts it to stercobilinogen which is why stool is brown coloured
7
Q
Bilirubin test information:
A
- The normal bilirubin concentration is <17 micromol/l; High value is due to:
- Haemolysis (can be in immature newborns and haemolytic anemia)
- Failure of conjugating mechanism within the hepatocytes which can be due to infection or by toxins e.g. paracetamol overdose
- Obstruction in the biliary system (cholestasis - where bile flow is decreased)
- Gilbert syndrome (hyperbilirubinemia)
o Jaundice appears at bilirubin concentration >50micromol/L
o In pregnancy, if a women experiences itchiness, this can be a sign of bilirubin levels increasing which can be damaging for the foetus
- This symptom is treated by antihistamines, skin emollients or colestyramine (it causes the elimination of bile acids from the body)
8
Q
What are aminotransferases? (AST and ALT)
A
- AST (10-40 Units/L) and ALT (5-40 Units/L)
- ALT is mainly localised in the liver but is present in other tissue e.g. heart and kidney
- High enzyme levels indicate true liver damage, hepatitis or acute toxic injury (shows damage to liver where cells are leaked out)
- A small increase is seen in obstructive jaundice and cirrhosis (liver scarring)
- An AST:ALT ratio of more than 2:1 is characteristic in patients with alcoholic liver disease
o Alcoholics are depleted of vitamin B family especially (pyridoxine (B6)) which is required for the synthesis of these two enzymes
9
Q
What are alkaline phosphatase?
A
- Normal range 30-300 Units/L
- It is a membrane associated enzyme
- Main indicator of cholestasis (block in bile flow)
- Again, this is not specific to the liver but also to other areas e.g. bones
- It is also raised in pregnancy
10
Q
What is gamma glutamyl transpeptidase (GGT)?
A
- Male <50 Units/L vs. Female <32 Units/L
- GGT is a microsomal enzyme, found in tissue such as liver and renal tubules
- High GGT with no other LFT abnormalities is induced by alcohol or enzyme inducing drugs e.g. phenytoin, carbamazepine
- In cholestasis, rise in GGT is parallel with serum alkaline phosphotase (ALP)
- In acute hepatic damage changes in GGT IS PARALLEL TO aminotransferases
11
Q
What is albumin?
A
It is a factor for coagulation
- Normal range of 35-48g/L
- T1/2 of 3 weeks in the plasma hence a good marker of chronic liver damage
- Hypoalbuminaemia is often associated with ascites
- Sodium controls osmolarity (need to know how to calculate osmolarity)
- Albumin controls oncotic pressure (plasma protein levels)
- Ascites – term describing excessive fluid in the peritoneal cavity caused by:
o Sodium water retention (due to low oncotic pressure)
o Hypotension (RAAS system kicks in, therefore water and sodium retention)
- Therefore more water is retained in peritoneal cavity (positive feedback); we can add furosemide as a diuretic and a part of treatment is low salt diet
o Here, spironolactone can be used which antagonises aldosterone and hence prevents water retention activated by RAAS
o Portal hypertension which can cause oesophageal varices (obstructed blood flow)- blood leaking – first line is B BLOCKERS
12
Q
What is the prothrombin time?
A
Evaluates blood-clotting in the body
- PT indicator for hepatic synthesis function
- Does not become abnormal until more than 80% of liver synthetic capacity is lost
- Elevated PT can result from vit K deficiency, parental administration of Vit K will reverse abnormality
13
Q
Alfa-fetoprotein test:
A
o Synthesised by foetal liver
o Normal value for adults <20mg/l
o Can be increased in
- Neural tube defects
- Tumours of the testis and ovary
14
Q
What is hepatic encephalopathy?
A
- Reversible state of altered mental function associated with liver impairment
- Can go from drowsiness to coma
- Main neurotoxin is thought to be ammonia
- Management: The principal aim in the management of encephalopathy is to remove the precipitating factors and reduce the absorption of nitrogenous substances from the gut
15
Q
What is spider naevus?
A
Spider Naevus (a vascular lesion characterized by anomalous dilatation of end vasculature found just beneath the skin surface. The lesion contains a central, red spot and reddish extensions which radiate outward like a spider’s web.) - Accumulating of oestrogen causes this
