Download The liver

The liver
Lec.8 Bioc. 416
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The liver is a metabolically active
organ responsible for many vital life
functions. The primary functions of
the liver are:
• Bile production and excretion
• Excretion of bilirubin, cholesterol,
hormones, and drugs
• Metabolism of fats, proteins, and
carbohydrates
• Enzyme activation
• Storage of glycogen, vitamins, and
minerals
• Synthesis of plasma proteins, such as
albumin, and clotting factors
• Blood detoxification and purification
The location of the liver
Places of the metabolic activity in the
liver
- The liver is composed
of hepatocyte
(parenchymal cell)
and non-parenchymal
cells, such as kuppfer
cell, sinusoidal
endothelial cell,
stellate cell
Bilirubin metabolism
• Bilirubin is derived mainly from haem
moiety of haemoglobin molecules.
• Mainly produce from the old RBC’s
• Iron in haem is reutilized and the
tetrapyrrole ring
degraded to
bilirubin
• Myoglobin
bilirubin
• Cytochromes
bilirubin
• Unconjugated bilirubin(not water soluble)
• It is transported in the bloodstream bound
to albumin).
• In the liver (hepatocyte) bilirubin is
transported to the smooth endoplasmic
reticulum.
• It extracted through the bile ducts to the gut.
• Then bilirubin is converted to urobilinogen.
• Urobilinogen is oxidized to stercobilin which
extract in the stool.
• Unconjugated bilirubin (95%) normally
present in the plasma.
• In health bilirubin is not detectable in
urine.
• Jaundice (yellow discoloration of tissues
due to bilirubin deposition) is a frequent
feature or liver disease.
• Clinically detecting more than 50µmol/L
in plasma bilirubin that means Jaundice
Biochemical assessment of liver
function
Bilirubin
• Unconjugated hyperbilirubinaemia:
- In the absence of liver disease it is due to
haemolysis or Gilbert’s syndrome.
- In haemolysis
increased production
of bilirubin.(exceed the capacity of liver to
remove and conjugate pigment)
• Conjugated hyperbilirubinaemia:
-Due to leakage of bilirubin from hepatocytes
or biliary system into the bloodstream.
- Water soluble Conjugated bilirubin is
excreted in the urine
deep orange
brown color.
- Complete biliary obstruction No bilirubin
reaches the gut No stercobilin and the
stool are pale in color.
Plasma enzymes
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The following enzymes are not specific
indicators of liver diseases.
Aspartate aminotransferase (AST)
Alanine aminotransferase (ALT)*
Alkaline phosphatase (ALP)
Gama -glutamyl trancferase (GGT)
• ↑ aminotransferase activities reflect cell
damage.
• In colestasis(lack of bile flow) plasma ALP
activity ↑
• ↑ in plasma activity of aminotransferase
and ALP associate liver diseases
Plasma proteins
• Albumin is synthesized in the liver.
• Its concentration in the plasma reflects the
functional capacity of the organ.
• Plasma albumin conc. ↓ in chronic liver
diseases.
• Its conc. is normal in early stages of acute
hepatitis due to its half life ~ (20 days)
• Prothrombin, or factor II, is one of several
clotting factors produced by the liver.
Adequate amounts of vitamin K are
needed to produce prothrombin.
• Prothrombin time (PT) is a blood test that
measures how long it takes blood to clot.
• The prothrombin time is a test of plasma
clotting activity.
• It reflects the activity of vit. k dependent
clotting factors.
• ↑ in prothrombin time i.e. acute liver disease.
• Prolonged prothrombin time may also vit k
deficiency.
Detecting of some liver diseases:
• Chronic liver disease lead to:
↑ immunoglobulins, ↑ in plasma total
protein
• In alcoholic liver disease ↑ plasma IgA.
• In autoimmune hepatits ↑ IgG
• In biliary cirrhosis ↑ IgM
• Viral infection detected by measuring viral
antigen and antibodies.
Non-biochemical investigation of
hepatobiliary disease
• Ultrasound examination (gallstones)
• Cholangiography (biliary system)
• Endoscopic retrograde Cholangiography for
hepatic tumours
• CT and MRI demonstrate space- eccupying
lesions.