Liver Function Flashcards
How are most water soluble drugs and substances excreted?
Usually unchanged
Excreted in urine or bile
How are lipid soluble compounds dealt with in the body?
Usually accumulate and affect cells unless they are converted to less active compounds or more soluble metabolites for excretion
What is a first stage reaction?
Reactions that involve chemical modification of reactive groups
Usually involving enzymatic systems
What are some processes a first stage reaction might achieve?
Inactivate or detoxify drugs
Activation of drugs
Conversion of nontoxic compounds to toxic ones
(ex acetaminophen, carcinogens)
What might induce a first stage reaction?
Drugs like ethanol and barbiturates
What might inhibit a first stage reaction?
Drugs
What is a second stage reaction?
Conjugation and conversion of substances to permit excretion in bile or urine
What is the most common second stage reaction?
Conjugation catalyzed by UDP-glucuronyltransferase to form glucuronide derivatives
What are the major constituents of bile?
Cholesterol
Bile salts
Bilirubin
How are hepatic cells involved with metabolism?
Exclusive metabolism of galactose and fructose, channels them to glucose pathways
Glycolysis
Glycogenesis
Glycogenolysis
Gluconeogenesis
How are hepatic cells involved with amino acids and proteins?
Synthesis of majority of serum proteins
Synthesis of many enzymes
Metabolism of amino acids
How do hepatic cells metabolize amino acids?
Gluconeogenesis (conversion to glucose)
Formation of urea from ammonia during deamination
Deamination
Transamination
How are hepatic cells involved with lipid metabolism?
Synthesis of: fatty acids from acetyl-CoA cholesterol bile acids from cholesterol formations of ketons
What are diseases associated with the liver?
Hepatitis
Cirrhosis
Cholestasis
What is hepatitis?
How is it caused?
Inflammation of the liver
Caused by infection, drugs, toxins, autoimmune
What is cirrhosis?
How is it caused?
Hepatocellular damage leading to scar tissue
Alcohol
What is cholestasis?
Blockage of normal bile flow
How is bilirubin formed?
Catabolism of heme from hemoglobin
Some from cytochromes, myoglobin, peroxidase
How does hemoglobin breakdown create bilirubin?
Hemoglobin -> globin + heme
Heme -> iron + protoporphyrin
Protoporphyrin -> biliverdin
Biliverdin -> unconjugated / indirect bilirubin
Where does hemoglobin catabolism take place?
In macrophages
What are features of indirect bilirubin?
Non-polar, non water soluble
Bound to albumin in plasma
How does bilirubin enter the liver?
In the sinusoids it attaches to receptors on the cell membranes and release from the albumin
Attaches to ligandin in the cell
What happens to bilirubin once it enters liver cells?
Indirect bilirubin is converted to conjugated / direct bilirubin
Attaches to glucuronic acid
Where does bilirubin go after being conjugated?
Secreted into the bile
Enters duodenum
What happens to bilirubin in the intestines?
Unconjugated
Bilirubin converted to urobilinogen
Small amount absorbed but most is excreted
What happens to reabsorbed urobilinogen?
Goes through liver and GI again
Small amount secreted by kidneys
What lab tests are done to assess liver function?
Serum and urine bilirubin ALP AST ALT GGT
sometimes protein, urine urobilinogen, serum ammonia
How should a sample for bilirubin analysis be handled?
Serum or plasma
Avoid hemolysis and lipemia
Should be tested quickly or protected from light
What can interfere with bilirubin analysis?
Hemolysis (decreases)
Extended light exposure (decreases)
What are 4 methods that cane be used to measure bilirubin?
Jendrassik-Grof Method
Vitros Method
Direct Spectrophotometry
Evelyn-Malloy Method
How does the Jendrassik-Grof Method work?
Diazo reaction with conjugated bili produces colored product
Measured spectrophotometrically
What are the steps of the Jendrassik-Grof Method?
Diazotized sulphanilic acid converts direct bili to azobilirubin
Ascorbic acid stops the reaction
Tartrate shifts absorbance from 585 to 600nm for reading
How can the Jendrassik-Grod Method measure total bilirubin?
Accelerator like caffeine-sodium benzoate quickly separates indirect bili from albumin
Then sulphanilic acid can convert all bili to azobilirubin
How can indirect bilirubin be calculated?
Total - direct
What is the reference range for direct bilirubin?
0-4 umol/L
What is the reference range for indirect bilirubin?
0-16 umol/L
What is the reference range for total bilirubin?
0-20 umol/L
What are the steps of the vitros bilirubin method?
Spreading layer contains caffeine-sodium benzoate to separate indirect bili from albumin
Screening layer traps other substances and lets bilirubin pass
Reaction layer is where bili binds to mordant
Reflectance measured at 400 for direct bili and 460 for indirect bili
How is bilirubin measured spectrophotometrically?
Bilirubinometer with capillary sample
Measures bili+hemoglobin at 454 nm
Hemoglobin only at 540
Hemoglobin - hemoglobin + bili = bili
Why is a bilirubinometer only used on babies?
After 3 months lipochromes can interfere
Absorb at 454 nm and cause positive interference
What are the reference ranges for bilirubin in babies?
birth < 34 24 hrs 34-103 48 hrs 103-120 3-5 days 68-103 1 week < 34
Why might premature babies have higher bilirubin levels?
Lack glucuronyltransferase
Cannot conjugate bili
Unconjugated bili builds up
What happens if bilirubin exceeds 225 umol/L?
Can cause kernicterus
What is kernicterus?
Bili entering the brain and nervous tissue and depositing causing neurological disorders
What is a critical level of bilirubin in babies?
> 300 umol/L
How is kernicterus treated?
Phototherapy or exchange transfusions
At what bilirubin level could kernicterus start to occur?
225 umol/L
What is jaundice?
Yellowing of skin and eyes due to bilirubin
When can jaundice occur?
Total bilirubin exceeds 35 umol/L
How does the Evelyn-Malloy method work?
Diazo reaction at acid pH
Direct bili measured at 1 minute
Methanol added to make indirect bili more soluble to read total bilirubin level
What causes pre-hepatic jaundice?
Increased RBC destruction
- hemolytic anemias
- ineffective erythropoiesis
- HDN/TR
- drugs
What blood results are expected with pre-hepatic jaundice?
Increased indirect bili
Decreased hemoglobin
Decreased LD
What effect does pre-hepatic jaundice have on excretions?
Presence of increased urobilinogen
Increased indirect bili = increased direct bili = increased urobilinogen
What might cause hepatic jaundice?
Necrosis from viruses, drugs, poison (alcohol)
Diseases impairing direct bili from entering bile
Cholestasis caused by cirrhosis or inflammation of bile ducts
Diseases causing failure of or decreased conjugation of bili
Impaired uptake of bilirubin into the liver
What is Gilbert’s disease?
Most common inherited cause of hepatic jaundice
Causes impaired uptake of bilirubin into hepatic cells
What blood results are expected with hepatic jaundice?
Increased indirect bili
Possible increased direct bili if conjugation can occur
What effect does hepatic jaundice have on excretions?
Decreased direct bili in bile
Decreased urobilinogen in excretion
If direct bili increased in blood, may be found in urine
What might cause post-hepatic jaundice?
Obstruction of bile duct preventing bile excretion
Bile duct cancer
Tumor compression of bile duct
Gallstones
Common bile duct inflammation
What are other names for post-hepatic jaundice?
Obstructive jaundice
Extrahepatic cholestasis
What blood results are expected in post-hepatic jaundice?
Increased direct bili (unable to enter bile)
Indirect usually normal but may build up if severe
How does post-hepatic jaundice affect excretions?
Direct bili present in urine
Decreased urobilinogen in stool and urine
Pale colored stool
Where does ALP come from?
Bone (osteoblasts)
Liver sinusoid cells, bile canaliculi
When would ALP be elevated?
Bone disease, pregnancy growth
Markedly elevated in cholestasis
Moderately in liver damage
Why is ALP so increased in cholestasis?
ALP is usually excreted into bile
When there is a blockage it spills over massively into the blood just like direct bilirubin
Serum ALP is increased but bilirubin is normal. Why might this be?
Bone disease
or
Possible lesion/carcinoma or obstruction of one of the radicles of the common bile duct
Where does GGT come from?
Widespread
Highest levels in cells lining bile canaliculi and ducts
What might cause elevated GGT?
Markedly elevated in cholestasis
Moderately in liver damage
Acute hepatitis, cirrhosis, tca abuse
Often first enzyme to rise
Increases with alcohol
How can GGT and ALP levels be used together for diagnosis?
GGT + ALP elevated = liver
ALP only elevated = bone
Where are ALT and AST found?
Highest in hepatocytes and heat and skeletal muscle
When might ALT and AST be elevated?
Markedly in hepatocellular damage
Moderately in cholestatis
How can the ratio of AST to ALT be used?
AST:ALT < 1.0 = acute (viral or toxic hepatitis)
AST:ALT = 1.0 obstructive jaundice
AST:ALT > 2.0 = chronic (hepatitis, alcoholism, cirrhosis)
Where is 5’-Nucleotidase found?
Bile canaliculi lining cells
When might 5’-Nucleotidase be increased?
Markedly in cholestasis
Moderately in liver damage