LIVER –STRUCTURE AND FUNCTION
INTRODUCTION
- It is the largest organ in the body.
- It is involved in secretory and excretory function.
- It weighs about 1.3 to 1.5 kg, it is pinkish-brown in color, “boomerang shaped” organ.
- It is located in upper and right side of the abdominal cavity, right side of the stomach, just below diaphragm.
- Liver holds 13 % of body’s blood at any given moment.
The
liver is the largest parenchymal organ, lying just below the diaphragm.
The
right lobe (at the left in the photograph) is larger than the left lobe.
The
falciform ligament is the rough dividing line between the two lobes.
FUNCTIONAL
ANATOMY
- Important function of liver is to serve as a filter between blood coming from the gastrointestinal tract and blood in the rest of body.
- Blood from intestines and other viceral organs reach the liver via the portal vein.
- Blood percolates in sinusoid between plates of hepatic cells and eventually drains into hepatic veins, which enter the inferior vena cava.
- Bile is formed on the other side at each plate. The bile passes to intestine via the hepatic duct.
1. HEPACATI LOBES:-
Liver is
made up of many lobes called hepatic lobes. Each lobe consists of many lobules
called hepatic lobule.
2. HEPATIC LOBULE:-
It is the
structural and functional unit of liver. there are about 50,000-100,000 lobules
in the liver. The lobule is honey comb like structure. It is made up of liver
cells called hepatocytes.
3.
HEPATOCYTES
AND HEPATIC PLATES:-
Hepatocytes
are arranged in columns which form the hepatic plates. each plate is made up of
2 columns of cells.
4.
HEPATIC ARTERY:-
it arises directly from aorta and
supplies pure arterial blood to liver.it
then enters portal triad.
5. PORTAL VEIN:-
It
is formed by superior mesenteric vein and splenic vein.It brings deoxygenated
blood from stomach, intestine, spleen and pancreas.
6.
HEPATIC VEIN:-
The substances synthesized by hepatic
cells, waste products and CO2 are discharged into sinusoide.
FUNCTIONS OF LIVER
- Carbohydrate metabolism
* Glycolysis
* Glycogenolysis
–catabolism of glycogen
* Gluconeogenesis-metabolic
pathway that results in generation of glucose by non carbohydrate source.
- Lipid metabolism.
- Detoxification- removal of toxic property of harmful agent.
- Metabolism of vitamins A, D, K&B.
- Secretion of bile.
- Clotting factors, prothrombin- synthesis.
- Protein metabolism
* anabolism
* deamination –
removal of amine group from molecule
* Urea formation-
urea cycle.
* Excretory
function-excretion of cholesterol, bile pigments, heavy metals, toxins.
* Hemolytic
function- the senile RBCs after the life span of 120 days are destroyed in
kuffer’s cells.
* Inactivation of
hormones-liver categorizes hormones such as cortisol, insulin, glucogon,
estrogen, parathormone.
OTHER
FUNCTIONS
**
Breakdown of
insulin and other hormones.
**
Liver breaks down
hemoglobin, creating metabolites that are added to bile pigment.
**
In first
trimester fetus, the liver is the main site of red blood cell production.
**
Liver stores multitude
of substances, including glucose in the form of glycogen, vitamin B12, iron and
copper.
Detoxification
The
removal of toxic property of the harmful agent is known as detoxification.
**
Liver plays an
important role in detoxification of blood originating from the gut or elsewhere
in the body.
**
The reticuloendothelial
cells (Kuffer’s cells) of the liver play an important role in defense of body.
Detoxification occurs by 2 ways
1)
By total destruction of substances by means of metabolic degradation.
2)
By converting toxic substances into non toxic materials by means of conjugation
with glucoronic acid or sulphates.
Steps
involved in detoxification:
* The foreign bodies like bacteria or
antigens are swallowed and digested by reticuloendothelial cells of liver by
means of phagocytosis.
* In phase I large number of cytochrome P450
enzyme is expressed in hepatocytes, these convert xenobiotic and other toxins
to inactivate. it includes oxidation, hydroxylation and reactions mediated by
cytochrome P450s.
* In phase II ultimately metabolites are
secreted into bile for elimination via gastrointestinal tract.
LIVER
FUNCTION TESTS
Steps
involved
1. Detect the presence of liver diseases
2. Distinguish among the different types of
liver diseases
3. Gauge the extent of known liver damage
4. Follow response to treatment.
TESTS
BASED ON DETOXIFICATIONS AND EXCRETORY FUNCTIONS:
1.
SERUM BILIRUBIN – a breakdown product of porphyrin ring of heme containing
proteins (conjugated, unconjugated)
unconjugated/indirect
– insoluble in water; bound to albumin in the blood
conjugated/direct
– water soluble; excreted in kidneys.
Normal
serum bilirubin concentration: <17 micromol/L.Up to 30% of the total is
direct-reacting.
Elevation
of unconjugated fraction of bilirubin: rarely due to liver disease.
Hemolytic
disorder-genetic conditions:
Crigler-Najjar,Gilbert Syndrome
Elevation
of conjugated bilirubin: almost always implies liver or biliary tract disease.
2. URINE
BILIRUBIN:
presence of bilirubinuria à liver diseases à almost 100% accurate
3. BLOOD
AMMONIA: elevated in advanced liver
diseases with significant muscle wasting à Hyperammonimea.
There
is a poor correlation between either the presence or the degree of acute enceph
and elevation of blood ammonia
There
is a poor correlation of the blood serum ammonia and hepatic function.
4.
SERUM ENZYMES
2 categories of serum enzymes:
§ Enzymes whose elevation in serum reflects damage to
hepatocytes
§ Enzymes whose elevation in serum reflect cholestasis
§ Enzymes that do not fit precisely into either
patterns.
ENZYMES
THAT REFLECT DAMAGE TO HEPATOCYTES
AMINOTRANSFERASES:
Sensitive
indicator of liver cell injury and most helpful in recognizing acute
hepatocellular diseases such as hepatitis. These enzymes are normally present
in the serum in low concentrations. They are released in the blood in greater
amounts when there is damage to the liver cell membrane resulting in increased
permeability.
AST
(Aspartate aminotransferase): liver,
cardiac, skeletal, kidneys, brain, pancreas, lungs, leukocytes and erythrocytes.
ALT
(Alanine aminotransferase): found
primarily in the liver.
ENZYMES
THAT REFLECT CHOLESTASIS
* Alkaline
phosphatase and 5’ nuleotidase: found
near the bile canalicular membrane of hepatocytes
* Gamma Glutamyl
Transpeptidase: Endoplamic reticulum
and in bile duct epithelial cells à lacks specificity.
Alkaline
phosphatase:
Liver,
bone, placenta, less commonly small intestine
Elevation
of liver-derived alkaline phosphatase is not totally specific for cholestasis
and a less than 3 fold elevation can be seen in any type of liver disease.
TESTS
THAT MEASURE BIOSYNTHETIC FUNCTION OF THE LIVER
SERUM
ALBUMIN: synthesized exclusively by hepatocytes has a slow turn over not a good indicator of acute or mild hepatic dysfunction
SERUM
GLOBULINS: group of proteins made up
of gamma globulins (immunoglobulins) produced by B lymphocytes and alpha and
beta globulins produced primarily in hepatocytes
Increases
in the IgM levels are common in primary biliary cirrhosis
Increases
in the IgA levels occur in alcoholic liver diseases.
COAGULATION FACTORS:
With
the exception of Factor VIII, the blood clotting factors are made exclusively
in hepatocytes.Because of their rapid turnover, measurement of the clotting
factors is the single best acute measure of hepatic synthetic function and helpful
in both the diagnosis and assessing the prognosis of acute parenchymal liver
disease
v
Serum prothrombin
time: collectively measures factors II, V, VII, and X
Marked
prolongation of prothrombin time, >5s above control is a poor prognostic
sign in acute viral hepatitis and other acute and chronic liver diseases.
RELATED PICTURE:
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| MORPHOLOGICAL & ANATOMICAL FEATURES OF LIVER |
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