Download Functions of the liver Assessment and interpretation of liver function

Hepatic Physiology
&
Assessment and interpretation of
liver function tests
Dr. M Sabra
• Liver is the largest internal organ & largest gland in the
human body.
• Liver is at the epicenter of intermediary metabolism ,
performs versatile & massive biochemical pathways and
destroys bacteria, inactivate antigens, detoxify harmful
chemicals.
• Dual blood supply: Portal vein = 75% of HBF (55% of 02) ,
Hepatic artery = 25% of HBF (45% of 02)
– Total hepatic blood flow = 25% of CO
• Surgery and anesthesia impact hepatic function primarily due
to their impact on hepatic blood flow and not primarily as a
result of the medications or anesthetic technique utilized
Physiological functions of liver
• Intermediary metabolism
Carbohydrate metabolism
Bile metabolsim
•
•
•
•
Coagulation
Heme metabolism
Bilirubin metabolism
Xenobiotics metabolism ( a foreign chemical
•
•
•
•
Storage
Endocrine functions
Immune & inflammatory response
Blood reservoir
Lipid metabolism
Protein metabolism
substance found within an
oraganism , not normally naturally produced by organism. Eg drugs antibiotics
Carbohydrate metabolism
• Liver is an important homeostatic regulator of blood
glucose. It can either produce glucose or store glucose
• In fed state- polymerize glucose to glycogen
• In unfed state- depolymerize glycogen to glucose
• Glucose → hepatocytes → glycogen
↑
→glucose
Lactate
Glycerol
aminoacids
Carbohydrate metabolism
• Glycogen metabolism
• Regulation – 2 rate limiting enzymes
1. Glycogen synthase- synthesis of glycogen from monomers
of UDP glucose.
2. Glycogen phosphorylase- clevage of glycogen to
glucose-1-phosphate.
Carbohydrate metabolism
Gluconeogenesis
• Liver glycogen stores depleted - hepatic gluconeogenesis
to replenish blood glucose.
• Substrates- lactate
- glycerol from hydrolysis of triglycerides
- gluconeogenic amino acid , alanine , glutamine
Hormonal regulation of carbohydrate metabolism
Glycogenolysis
+
+
Glycogenesis
Glucose 6-PO4
•Insulin
+
•Glucagon
•Epinephrine
 B. Glucose
 B. Glucose
• Blood glucose regulation within a narrow limit (70-100 mg/dl) 
not affected in liver disease due to large reserve of hepatic
function
 Effects of anaesthesia on carbohydrate metabolism
• Halothane
–  release of insulin
–  rate of glycogenolysis
– Inhibition of gluconeogenic response
• Isoflurane
– Impaired insulin secretion
Lipid Metabolism
•  Oxidation of fatty acids
• Fatty acids derived from plasma

• Enter into mitochondria

•  oxidation: fatty acids  AcetylCoA  citric acid cycle
• Regulators
- Glucagon - activates
- Insulin - inhibits
• Synthesis of lipoproteins
• One of the major functions of the liver
• Major classes
– VLDL
(Very low density lipoproteins )
– LDL
( low density lipoproteins )
– HDL
(High density lipoproteins)
• VLDL
• Acute or chronic liver disease – ability to produce VLDL is markedly
compromised
• Liver VLDLs are associated with an important class of proteins, the apo
B protein
• Apo B100 - important for hepatic secretion of VLDL.
• Decreased in ABETALIPOPROTEINEMIA
• LDLs and HDLs
• Liver produces them in a small amount
• Production of ketone bodies
• Most organs except the liver- use ketone bodies as fuel
• Ketone bodies –
acetoacetic acid, acetone,
 hydroxybutyrate
• Their formation by the liver is normal and physiologically important,
e.g.
– Fasting  rapid depletion of glycogen stores in the liver 
shortage of substrates for citric acid cycle
– AcetylCoA formed from  oxidation  ketone bodies
• Ketosis -  conc. of ketone bodies in blood
– Starvation
– DM
– After high fat diet
• Synthesis of cholesterol
• Important role in cholesterol homeostasis
• Liver cholesterol has both exogenous and endogenous source
 Uses of hepatic cholesterol
• Formation of bile acids- conjugated with other substances to form
cholic acid.
• Synthesis of VLDLs
Bile metabolism & enterohepatic circulation
• Bile salts are end products of cholesterol synthesis
• Daily production – 600- 800 ml/d
• Functions- activate lipase
- promote micelle formation
- intestinal uptake of fat soluble vitamins, cholesterol
& lipids
- facilitate excretion of xenobiotics, lipophillic
substances, bilirubin, amphipathic steroid hormone
derivative
• Bile salts undergo enterohepatic circulation (20-30 times/day)
intrahepatic bile duct
↓
common hepatic duct
cystic duct
↓
gall bladder
CBD
↓
small intestine ( terminal ileum)
• Clinical implication
– Opioids can induce spasm of bile duct & spinter of oddi
– Reversed by – glucagon, opioid antagonists ( naloxone),
smooth muscle relaxant (NTG), antimuscarinic
drugs( atropine), volatile anaesthetics.
Protein and amino acid metabolism
• Deamination of amino acids
– Required before they can be used for energy or before they can be
converted into carbohydrates or fats
• Formation of urea for removal of ammonia from the body fluids
• Production of proteins and peptides.
Krebs- Hanseleit cycle
 Major pathway for removing NH3
& other nitrogenous wastes from body
 Captures nitrogen in form of urea.
 Failing liver- BUN remain low
- ammonia accumulates
in liver
↓
Hepatic encephalopathy
Proteins & peptides
Albumin
• Most abundant protein
• Normal plasma conc- 3 - 5 g%
• Daily production -12-15 g/d
• Plasma half life – 15-20 days
• Functions –
• maintains plasma oncotic pressure (80% by albumin)
• binds ions, bilirubin, hormones & drugs
• Hypoalbuminemia –  Colloid oncotic pressure  edema
ᾳ- feto protein
• Resembles albumin genetically & functionally
• Formation sites- yolksac, hepatocytes, enterocytes
• Fetal & neonatal life- major determinant of plasma oncotic
pressure
• 1 year of age- albumin largely replaces AFP
• ↑ ↑ AFP- HCC
Fibrinogen
• Synthesized exclusively by hepatocytes
• Plasma fibrinogen – 100-700 mg/dl
• Functions – polymerizes into long fibrin threads by the
action of thrombin  formation of clot
• Haptoglobins
– Forms stable complexes with free Hb  prevents loss of iron through
urinary excretion, protects kidney from damage
• Ceruloplasmin – binds with copper and helps in its transport
and storage
• Wilson’s disease
– Deficiency of ceruloplasmin  free Cu2+  in circulation 
deposited in brain and liver
Coagulation
• Synthesize most of the procoagulants excepta.
b.
c.
•
factor III ( tissue thromboplastin)
Factor IV ( calcium)
Factor VIII ( von Willebrand factor )
Produce protein regulators of coagulation & fibrinolytic
pathways
–
–
–
Protein C, protein S ( protein C – inactivate F VIIIa- Va complex)
protein Z ( degradation of Factor Xa )
plasminogen activator inhibitor (PAI) ( inhibits tissue plasminogen
activators to convert plasminogen to plasmin )
–
antithrombin III
Liver as a Storage Organ
• Vitamin A
• Important role in the uptake, storage and maintenance of vitamin A
levels by mobilizing its vitamin A store
• Vitamin K
• Vitamin K dependent factors II, VII, IX, X
• Absorption of Vit K depends on normal fat absorption: any malabsorption of lipid  vitamin K deficiency
• Storage in liver- limited  hypoprothrombinemia can develop within a
few weeks.
• Treatment –
• FFP
• Antidote- parenteral vit K
Vitamin K cofactor & ỳ- carboxylation
– Factor II, VII., IX, X , protein C & S- undergo Vit K dependent post
translational modifications
– Enables procoagulants to form complexes with calcium or other
divalent cations for participation in the clotting cascade.
Clinical implication
Warfarin inhibits vit K epoxide reductase
↓
traps Vit K in epoxide form
↓
Inhibits y- carboxylation
 T/T- Enteral / parenteral Vit K.
Storage & Homeostasis of Iron
• Major site of synthesis of proteins (Transferrin, Ferritin)
involved in iron transport & metabolism.
Heme metabolism
Clinical implication
• Porphyrias
• Acute Intermittent Porphyria – commonest
– Defects in the heme pathway- accumulation of porphyrinogens
– Trigger substances- barbiturates, sex hormones, glucocorticoides,
cigarette smoke, CYP inducers.
Bilirubin Metabolism
• Main source of bilirubin is heme metabolism
• Daily production- 300mg
• 80 % derived from senescent erythrocytes by macrophages
in RE system.
•
Heme
↓ ( heme oxygenase + o2 )
biliverdin IX + CO + free divalent iron
↓ ( biliverdin reductase)
bilirubin
Plasma
Fragile RBCs
BILIRUBIN METABOLISM
RE System
unconjugated bilirubin (protein – bound)
Liver
Urobilinogen
Kidneys
Liver
Conjugated bilirubin
Absorbed
Bacterial
action
Urobilinogen
Oxidation
Urobilin
Urobilinogen
Stercobilinogen
Oxidation
Stercobilin
Intestinal Contents
Urine
•
•
•
•
•
•
CO produced has many physiological roles
Vasodilation ( regulation of vascular tone)
Platelet aggregation
Vascular myocyte proliferation
Neurotransmitter release
Cytoprotective , antiapoptotic, antioxidant effects
• Biliverdin – confers protection from oxidative effects
• rapidly converts to bilirubin
Metabolism of Drugs (Xenobiotics)
Factor affecting drug metabolism:
microsomal enzyme system
liver blood flow
route of administration
competitive inhibition
 Phase-I reactions
• Alter the parent drug by inserting or unmasking a polar group
• Converts drugs to more polar compounds
• Reactions – oxidations, reduction, hydrolysis
• Cytochrome P450 – substrate binding site, located in the
endoplasmic reticulum
• Drugs– barbiturates, benzodiazepines, halogenated volatile
anaesthetics, pethidine etc.
• Phase-II reactions
• Creates conjugates of parent compound or its metabolite with
endogenous hydrophilic substrate
 Reactions
Glucoronidation
Sulphation
Methylation
Acetylation
Glucoronidation
• Most common type
• Hepatic microsomal enzyme, UDPglucuronyl transferase mediates
the transfer of glucoronic acid from UDP glucuronic acid to the
functional group on the xenobiotics
• Drug handled by phase-II – morphine, propofol, thiopentone (initially
oxidized subsequently conjugated)
 Phase-I reaction enzymes – more susceptible to destruction in
cirrhosis
 Phase-II reactions enzymes – more resistant, function even in
advanced liver disease
Phase-III reactions
• Involves ATP-binding cassette transport proteins (ABC)
• These proteins use the energy of ATP hydrolysis to drive molecular
transport
• Dysfunction of ABC proteins hinders flow of bile  predisposing to
drug accumulation and cholestatic liver injury
Microsomal enzyme induction
• Anticonvulsants, rifampicin, isoniazid, glucocorticoids,
chronic alcohol consumption
Consequences of enzyme induction
  duration of action of drugs that are inactivated by
metabolism
  intensity of action of drugs that are activated by
metabolism
Endocrine functions
• Liver can modify or amplify hormone action
• Metabolic conversion of Vitamin D to form 25(OH)D
• 25(OH)D  1,25(OH)2D in kidney
• Peripheral conversion of T4 to T3
 Pseudocholinesterase
• Hydrolysis of succinylcholine
• Plasma t½ - 14 days
• Severe liver disease   duration of action of succinylcholine
• Insulin-like growth factors or somatomedins – growth hormone like
action
• Important role in cartilage function by promoting uptake of sulphate
and synthesis of collagen
 Removes circulating hormones
• Insulin, glucagon, growth hormone, gastrointestinal hormones, e.g.
gastrin
• Blood reservoir
– Liver is an expandable organ
– 10 -15 % of total blood volume can be sequestered and quickly
released after sympathetic stimulation .
• Immune & inflammatory responses
– kuffer cells protect against foreign intrutions, degrade toxins,
process antigens, and phagocytose bacteria.
– Induce & intensify inflammation by recruiting neutrophils
– Release proinflammatory mediators
Liver Function Tests
• Uses
• To detect the presence of liver disease
• To distinguish among different type of liver disorders
• To guage the extent of known liver damage
• To follow the response to treatment
• Shortcomings of LFTs
Can be normal in pts with serious liver disease and abnormal
in pts with diseases that do not affect the liver
Only categorises into hepatocellular or cholestatic
• Classification of LFTs
Tests based on detoxification and excretory functions
• Serum bilirubin
• Breakdown product of porphyrin ring of heme containing proteins
• 2 fractions - conjugated (direct – 30%)
unconjugated (indirect – 70%)
• Normal total serum bilirubin 1 mg/dl
•  in unconjugated fraction is rarely due to liver disease
Fractionate bilirubin
>15% direct
<15% direct
Dubin Johnson syndr
Rotor’s syndr
Evaluation for
hemolysis
-ve
Crigler-Najjar syndr
Gilbert’s syndr
No further evaluation
required
+ve
Hemolysis
• Urine bilirubin
• Any bilirubin found in urine is conjugated, therefore bilrubinuria implies
presence of liver disease
• Blood ammonia
• Detection of encephalopathy, monitoring hepatic synthetic function
• Very poor predictor: presence/ degree of acute encephalopathy
• Serum enzymes
• No known function in serum
• ed level-  rate of entrance into serum from damaged liver cells
• Enzymes categories
• Enzymes that reflect damage to hepatocytes
• Enzymes that reflect cholestasis
• Enzymes that reflect damage to hepatocytes
– Aminotransferases
• Aspartate aminotransferase (AST or SGOT): Liver, cardiac muscle, skeletal
muscle, kidneys, brain, pancreas, etc.
• Alanine aminotransferase (ALT or SGPT): 1° in liver
• Sensitive indicators of liver cell injury
• Normal levels <35-45 IU/L
•  in aminotransferases
• Mild - <250 IU/l
– Any pathologic process that causes hepatocellular injury, e.g. hepatic
steatosis, alcohol or drug induced liver disease, chronic viral hepatitis,
cirrhosis, hemachromatosis
• Moderate – 250-1000 IU/l
– Disorder that produces hepatocellular necrosis
– e.g. Acute viral hepatitis, drug induced hepatitis, exacerbation of
chronic hepatitis (alcoholic)
• Large - >1000 IU/l
– Viral or drug induced liver damage superimposed on ALD,
autoimmune hepatitis
• Extreme - >2000 IU/l
• Massive hepatic necrosis, usually from drugs (acetaminophan),
halothane hepatitis, toxins, ischemic hepatitis (shock liver), acute viral
hepatitis
• AST/ALT ratio – DERITIS QUOTIENT
– Normal - 1 or slightly > 1
• <1 – non-alcoholic steatosis or hepatitis without cirrhosis
• 2-4 – ALD
• >4 – Wilsonian hepatitis
AST/ ALT not ↑ in purely obstructive disorder except
Acute biliary obstruction caused by passage of
gallstones to CBD
• LDH
 Normal level -25-100 IU/L
 Massive but transient - Ischemic hepatitis
 Massive, sustained - Malignant infiltration of liver
• Other causes of  LDH
• Hemolysis
• Renal infarction
• Acute stroke
• Myocardial damage
• Skeletal muscle injury
• Glutathione S transferase
• Relatively sensitive and specific test for detecting drug-induced
hepatocellular injury
• Plasma t½ 90 min, rapidly released into the circulation following
hepatocellular injury
• Plasma GST ( isoenzyme B ) – reveal time course of hepatocellular
injury from onset to resolution
• GST – located in the centrilobular region (zone 3), where hepatocytes
are most susceptible to injuries from hypoxia and reactive drug
metabolism
• Bromosulphathein excretion test
• BSP dye- same mechanism as bilirubin
-binding
-conjugation
-excretion




BSP – i/v – 45 mins- levels in venous blood
Normally- <5%.
Slightly higher in old age
Sensitive test to detect mild impairement of liver
Enzymes reflecting cholestasis
• Alkaline phosphatase- present in cells of the bile duct
 Isoenzymes- bone , liver, intestine, placenta , kidney , leukocytes.
 Normal levels- 42-122 IU/L
- 3-13 KA units/dl
Non-pathological 
Age >60 yrs
Bld group – O & B
Growing children &
adolescents
Late in normal pregnancy
Pathological 
1° biliary cirrhosis
Choledocholithiasis
Hepatic malignancy
1° & 2°
Paget’s disease
  in serum ALP in an apparently healthy pt.
 Fractionate the ALP to identify source of isoenzyme
 ALP from different tissues differ in susceptibility inactivation by
heat
 Measure - 5' NT, GGT
• 5' NT
• Sensitive and specific for hepatobiliary disorders (HBD)
• Normal pregnancy, bone growth and bone diseases do not affect 5' NT
• In pts with HBD, changes in ALP are usually followed by similar
changes in 5' NT
• GGT
• Inducible microsomal enzyme. N levels – 5- 40 IU/L.
• Less specific than 5' NT as a marker for HBD
• Unlike 5' NT, GGT may be released from many sites beside the
hepatobiliary tree
 Bone – important source of ALP, has little GGT thus GGT useful for
differentiating hepatic & osseous sources of ALP
 Tests for bio-synthetic function of the liver
• Estimation of plasma proteins
• Tests for reversal of A:G ratio
• Tests for coagulability of blood
Plasma protein
Total
Normal levels
6.4 – 8.3 g%
S. Albumin
3 – 5 g%
Serum globulin
2 – 3 g%
Serum fibrinogen
0.3 g%
Serum prothrombin
40 mg%
A:G ratio
1.7 : 1
• Serum albumin
• S. albumin <3 g/dl  suspect chronic liver disease
• Hypoalbuminemia – not specific for liver disease
– Protein malnutrition of any cause
– Protein losing enteropathies
– Nephrotic syndrome
– Chronic infections
– Burns
• Reversal of A : G ratio  chronic liver dysfunction.
• Serum globulin
•  in gamma globulin  chronic liver disease
• Ig M - ↑↑ Primary billiary cirrhosis.
• Ig A – Alcoholic liver disease.
• Ig G - ↑↑ Auto immune hepatitis.
• Thymol turbidity test
• Test for reversal of A:G ratio
• Marked  turbidity – liver insufficiency
• Coagulation factors
 Factor I, II, V, VI, VII
 Short t1/2 – single best measure of acute hepatic synthetic function
 Tests –PT- N 11-16 sec
- PTTK – N 30- 40 sec
• Prognostic value PT > 5 sec above control – indicative of poor prognostic sign in acute
viral hepatitis.
  in hepatitis, cirrhosis, disorders leading to vit K deficiency such as
obstructive jaundice or fat malabsorption
Immunological tests
• Antibodies to specific etiologic agents–
–
–
•
HBV- HBsAg , HBcAg, HBeAg
Antibody to Entamoeba histolytica
Antibody to CMV, HCV, EBV
Non specific antibodies
–
–
–
Antimitochondrial antibody- PBC
Antismooth muscle antibody- Auto immune hepatitis
pANCA- Primary sclerosing cholangitis
• Serum tumor markers
•  feto-protein - ↑ in HCC.
• Hepatobiliary imaging
• USG, CT scan - 1st line investigation
• ERCP, PTC- visualization of biliary tract
• Doppler USG& MRI- hepatic vasculature & heamodynamics
• CT & MRI- hepatic masses & tumours
• Others
• FNAC
• Biopsy – percutaneous needle liver biopsy
a) VIM –SILVERMAN ( cutting ) needle
b) MENGHINI’S ( aspiration ) needle
• Indications
–
–
–
–
–
–
Unexplained hepatomegaly
Cholestasis of unknown cause
Persistent abnormal LFTs
Infiltrative disorders- sarcoidosis, tuberculosis
Pyrexia of unknown origin
Primary/ metastatic liver diseases
Blood tests & D/D of hepatic dysfunction
Bilirubin overload
(hemolysis)
Parenchymal
dysfunction
cholestasis
Aminotransferases
Normal
↑ ( may be N or ↓ in
advanced stages
N ( may be ↑in
advanced stages)
ALP
Normal
Normal
Increased
serum bilirubin
↑ unconjugated
↑ conjugated
↑ conjugated
Serum proteins
Normal
Decreased
N (may be ↓ in
advanced stages)
Prothrombin time
Normal
↓ (may be N in early
stages)
N (may be prolonged in
advanced stages)
Blood urea nitrogen
Normal
N (may be ↓ in
advanced stages)
Normal
Sulfobromophthalein /
indocyanine green
Normal
Retention
Normal or retention
Summary
• Functions of liver
I. synthetic
Plasma protein (albumin)
Hypoproteinimea → oedema
Coagulants
Haemorrhagic disorders
Enzymes
Hepatocellular disorders
Urea / removal of NH3
↓ bld urea, ↑bld NH3
II. Metabolic
Carbohydrate
↓ glycogen – more damage
↓ bld. Glucose – muscle weakness, personality changes,
tremors, slurred speech, convulsion, coma , death → pre
hepatic coma
Protein metabolism
↑ blood ammonia – aminoaciduria
lipid metabolism
Acc. Of FA in liver → fatty liver →pre hepatic hepatitis→
fibrosis→ cirrhosis→ ↑ portal pressure→ portal
hypertension
III. Bile secretion
Bile salts & acids
steatorrhea
Conjugation of bilirubin
Hepatocellular jaundice
IV. Miscellaneous
Vit A, K
Deficiency- ↓vit A , K
Antibacterial action
Prevent infections
Destruction of RBCs
Anemia , ↑ bilirubin
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