Liver Function Test (AST & ALT), Liver Anatomy and Physiology, and Bilirubin (Bishop 7th ed. | P) Flashcards
What are the characteristics of liver?
1) It is a very large and complex organ responsible for performing vital tasks that impact all body systems
2) Large and complex organ
3) Weighing approx 1.2 - 1.5 kg (in healthy adult)
4) Located beneath and attached to the diaphragm
5) Protected by lower rib cage
6) Divided unequally in 2 lobes (right and left lobe)
7) An extremely vascular organ
8) It serves as a gatekeeper bet substances absorbed by GIT and those released into systemic circulation
What are the functions of the liver?
1) It is the major player in maintaining stable glucose concentrations due to its ability to store glucose as glycogen and degrade glycogen depending on the body’s needs
2) It plays an essential role in the development of hgb in infants
3) It is also responsible for synthesizing the (+) and (-) acute-phase reactants and coagulation proteins
4) It also serves to store a pool of AAs through protein degradation
What are the complex functions of liver?
1) Metabolism of carbohydrates, lipids, proteins, and bili
2) Detoxification of harmful substances
3) Storage for essential compounds
4) Excretion of substances
How is liver unique from other organs?
Liver is unique from other organs because it is a relatively resilient organ that can regenerate cells that have been destroyed by some short-term injury or disease or have been removed
What will happen if the liver is permanently damaged for a long period of time?
It may undergo irreversible changes that permanently interfere w/ its essential functions
What will happen if the liver becomes completely nonfunctional for any reason?
The individual will die within 24 hrs
Why will the individual (having a completely nonfunctional liver) will die?
Due to hypoglycemia
What is the purpose of ligamentous attachments?
They hold the liver in place
What is the difference bet right lobe and left lobe (in terms of size)?
Right lobe is approx 6 times larger than the left lobe
How many are the sources of blood supply of the liver?
2
What are the 2 sources of blood that supplies the liver?
1) Hepatic artery
2) Portal vein
What is hepatic artery and what are its purposes?
It is a branch of the aorta
1) It supplies oxygen-rich blood from the heart to the liver
2) It is responsible for providing approx 25% of total blood supply to the liver
What are the purposes of portal vein?
1) It supplies nutrient-rich blood (collected as food is digested) from the digestive tract
2) It is responsible for providing approx 75% of the total blood supply to the liver
The 2 blood supplies eventually merge into the what?
Hepatic sinusoid
What is the characteristic of hepatic sinusoid?
It is lined w/ hepatocytes
What is the purpose of hepatocytes?
They are capable of removing potentially toxic substances from the blood
What happens to the blood from the sinusoid?
The blood flows to the central canal (central vein) of each lobule
How do the blood leave the liver?
Through the central canal
What is the volume of blood that passes through the liver per min?
Approx 1,500 mL
The excretory system of the liver begins w/ what?
It begins at the bile canaliculi
What is bile canaliculi?
These are small spaces bet the hepatocytes
What is the action of bile canaliculi?
They form intrahepatic ducts
What is the purpose of intrahepatic ducts?
These is where the excretory products of the cell can drain
What are the actions of intrahepatic ducts?
They join to form the right and left hepatic ducts, w/c drain the secretions from the liver
What is the action of right and left hepatic ducts?
They merge to form the common hepatic duct
What is the action of common hepatic duct?
It eventually joins w/ the cystic duct of the gallbladder to form the common bile duct
The combined digestive secretions are then expelled into the what?
Into the duodenum
The liver is divided into microscopic units called what?
Lobules
What are lobules?
They are the functional units of the liver
What is the function of lobules?
They are responsible for all metabolic and excretory functions performed by the liver
What are the characteristics of lobules?
1) Each lobule is roughly six-sided structure
2) Has a centrally located vein
3) Has portal triads at each of the corners
What is the term used to denote the centrally located vein present in the lobules?
Central vein
What are the components of each portal triad?
1) A hepatic artery
2) A portal vein
3) A bile duct (surrounded by connective tissue)
What are the 2 major cell types of the liver?
1) Hepatocytes
2) Kupffer cells
What is the % distribution of hepatocytes in the liver?
Approx 80% of the volume of the liver
What is the characteristic of hepatocytes?
They are large cells that radiate outward from the central vein in plates to the periphery of the lobule
What are the purposes of hepatocytes?
1) They perform the major functions associated w/ the liver
2) They are responsible for the regenerative properties of the liver
What are Kupffer cells?
They are macrophages that line the sinusoids of the liver
What is the function of Kupffer cells?
They act as active phagocytes w/c are capable of engulfing bacteria, debris, toxins, and other substances flowing through the sinusoids
What are the 4 major functions performed by the liver?
1) Excretion / secretion
2) Metabolism
3) Detoxification
4) Storage
What does the liver excrete / secrete?
It excretes endogenous and exogenous substances into the bile or urine
Provide an ex of a substance that is excreted by the liver
Bilirubin
What are the characteristics of bili?
1) It is the major heme waste product
2) It is very sensitive to and is destroyed by light
What is the action that liver can only do?
It is the only organ that has the capability to excrete heme waste products
Bile is made up of what components?
1) Bile acids or salts
2) Bile pigments
3) Chole
4) Other substances extracted from the blood
What is the volume of bile that is produced by the body per day?
Approx 3 L of bile per day
What is the volume of bile that is excreted by the body per day?
1 L from the produced bile
What is the principal pigment in bile?
Bili
How is bili derived?
It is derived from the breakdown of RBCs
What happens approx 126 days after the emergence from the reticuloendothelial tissue?
RBCs are phagocytized and hgb is released
Hgb is degraded into what components?
1) Heme
2) Globin
3) Iron
What happens to iron (as a result of hgb degradation)?
It is bound by transferrin and is returned to iron w/c is stored in the liver or bone marrow for reuse
What happens to globin (as a result of hgb degradation)?
It is then degraded to its constituent AAs w/c are reused by the body
What happens to heme (as a result of hgb degradation)?
It is converted to bili w/c is then bound by albumin then transported to the liver
What is the time duration for the conversion of heme to bili?
2 - 3 hrs
What is unconjugated or indirect bili?
This is the type of bili derived from the conversion from heme (as a result of hgb breakdown) w/c is then bound by albumin and is then transported to the liver
What are the characteristics of unconjugated bili?
1) Insoluble in water
2) Cannot be removed from the body until it has been conjugated by the liver
3) Nonpolar
4) Found in plasma that is bound to albumin
5) Will only react w/ diazo rgnt in the presence of an accelerator
What happens to the unconjugated bili present in the liver?
It flows into the sinusoidal spaces and is released from albumin so that it can be picked up by a carrier protein
What is the carrier protein that picks up the unconjugated bili (after being released from albumin)?
Ligandin
What is the characteristic of ligandin?
It is located in the hepatocyte
What is the purpose of ligandin?
It is responsible for transporting unconjugated bili to the ER
Where do rapid conjugation of unconjugated bili happen?
In the ER
What is the other term for conjugation?
Esterification
What is the enzyme that conjugates unconjugated bili?
Uridyldiphosphate glucuronyl transferase (UDPGT)
What is the principle of action by UDPGT (in terms of conjugation of unconjugated bili)?
It transfers a glucuronic acid molecule to each of the 2 propionic acid side chains of bili to form bilirubin diglucuronide
Bilirubin diglucuronide is also known as what?
Conjugated bili
What are the characteristics of conjugated bili?
1) Water soluble
2) Able to be secreted from the hepatocyte into the bile canaliculi
3) Polar
4) Found in the plasma in its free state (not bound to any protein)
5) Will react w/ diazo rgnt directly w/out the need of an accelerator
What is the action that happen once the conjugated bili is in the hepatic duct?
It combines w/ secretions from the gallbladder through the cystic duct and is expelled through the common bile duct to the intestines
What is the purpose of intestinal bacteria (especially bacteria in the lower portion of intestinal tract)?
They work on the conjugated bili to produce mesobilirubin, w/c is then reduced to mesobilirubinogen and then urobilinogen
Conjugated bili -> mesobilirubin -> mesobilirubinogen -> urobilinogen
What is the characteristic of urobilinogen?
It is a colorless product
What is the % distribution of excretion of urobilinogen?
1) Roughly 80% - excreted in the feces
2) Remaining 20%
- > majority: absorbed via extrahepatic circulation
- > very small quantity: enter systemic circulation and be excreted in the urine
Is urobilinogen excreted in the feces?
No, urobilin (stercobilin) w/c is the reduced form of urobilinogen is excreted in the feces
What is the purpose of urobilin (stercobilin)?
It gives the stool its brown color
Explain the mechanism of action that happen to the remaining 20% of urobilinogen
Majority: urobilinogen is absorbed by extrahepatic circulation to be recycled through the liver and re-excreted
Other very small quantity left: urobilinogen will enter the systemic circulation and will subsequently be filtered by the kidney and excreted in the urine
What is the amt of bili being produced per day by an individual having a normally functioning liver?
Approx 200 - 300 mg of bili
True or False
A healthy adult has very high lvls of total bili
False, because healthy adult has very low lvls of bili
What is the amt of total bili of healthy adults in the serum?
0.2 - 1.0 mg/dL
The majority of the total bili of healthy adults are in what form?
Unconjugated form
What is one of the most important functions of the liver?
Metabolism of carbohydrates
What are the things that the liver can do when carbohydrates are being ingested and absorbed?
1) Use the glucose for its own cellular energy requirements
2) Circulate the glucose for use at the peripheral tissues
3) Store glucose as glycogen within the liver itself or within other tissues
What is glycogen?
It is the principal storage form of glucose
What is the process done to store glucose as glycogen?
Glycogenesis
What is the process done when the glycogen is being degraded?
Glycogenolysis
Provide a situation whereas the principles of glycogenolysis and gluconeogenesis are present
If a person is stressed or in a fasting state when there is an increased requirement for glucose, the liver will break down the stored glycogen (glycogenolysis) and when the supply of O2 becomes depleted, the liver will create glucose from nonsugar carbon substrates (gluconeogenesis)
What are the examples of nonsugar carbon substrates where glucose can be derived from (via gluconeogenesis)?
1) Pyruvate
2) Lactate
3) AAs
Are lipids being metabolized by the liver? If yes, when and how? If not, why not?
Yes, lipids are being metabolized by the liver under normal circumstances when nutrition is adequate and the demand for glucose is being met
The liver is responsible for metabolizing lipids and lipoproteins
How is acetyl-CoA produced?
It is produced when the liver gathers free fatty acids from the diet including those fatty acids that are being produced by the liver itself whereas these fatty acids are broken down to produce acetyl-CoA
What are the purposes of acetyl-CoA?
It can enter several pathways to form:
1) TAG
2) Phospholipids
3) Chole
What is the greatest source of chole in the body?
The greatest source of chole in the body comes from what is produced by the liver, not from dietary sources
What is the percentage of chole being produced by the liver everyday?
Approx 70% (roughly 1.5 - 2.0 g)
What are the proteins that are being synthesized by the liver?
Almost all proteins except:
1) Igs
2) Adult hgb
What is one of the most important proteins synthesized by the liver?
Albumin
What are the most critical aspects of protein metabolism?
1) Transamination
2) Deamination of AAs
What is the enzyme present in transamination?
Transaminase
What is the result (or action) of transamination?
It results in the exchange of an amino grp on 1 acid w/ a ketone grp on another acid
What happens after transamination?
Deamination occurs, it degrades them to produce ammonium ions w/c are consumed in the synthesis of urea w/c is excreted by the kidneys
True or False
The liver must be extensively impaired before it loses its ability to perform these essential functions
True
What is the mechanism of action of liver in relationship w/ GIT?
Every substance that is absorbed in the GIT must 1st pass through the liver
This mechanism is referred to as first pass
What is the importance of first pass?
This is an important function of the liver because it can allow important substances to reach the systemic circulation and can serve as a barrier to prevent toxic or harmful substances from reaching systemic circulation
What are the 2 mechanisms for detoxification of foreign mats (drugs and poisons) and metabolic products (bili and ammonia)?
It may either:
1) Bind the mat reversibly so as to inactivate the compound
2) Or it may chemically modify the compound so it can be excreted
What is the most important mechanism done by the liver?
The drug-metabolizing system
What is drug-metabolizing system?
It is a system that is responsible for the detoxification of many drugs
What are the diff methods of detoxification of many drugs?
1) Oxidation
2) Reduction
3) Hydrolysis
4) Hydroxylation
5) Carboxylation
6) Demethylation
Where do the diff methods of detoxifying many drugs occur and what is responsible for this action?
Many of the methods take place in the liver microsomes via the cytochrome P-450 isoenzymes
What did Ehrlich 1st describe (in connection w/ rxn of bili)?
The rxn of bili w/ a diazotized sulfanilic acid solution to form a colored product
Rxn of bili + diazotized sulfanilic acid solution = colored product
When did Ehrlich 1st described the rxn of bili?
1883
What sx did Ehrlich used for the rxn w/ bili w/c he 1st described?
Urine sxs
What is the classic diazo rxn?
Bili w/ a diazotized sulfanilic acid solution
In 1913, what did van den Bergh found out?
He found out that the diazo rxn may be applied to serum sxs but only in the presence of an accelerator
What is the other term for accelerator?
Solubilizer
In 1937, what did Malloy and Evelyn developed?
They developed the 1st clinically useful methodology for the quantitation of bili in serum sxs via the use of the classic diazo rxn w/ a 50% methanol solution as an accelerator
Bili (in serum) = classic diazo rxn + 50% methanol solution (accelerator)
In 1938, what did Jendrassik and Grof described?
They described a method using the diazo rxn w/ caffeine-benzoate-acetate as an accelerator
Diazo rxn + caffeine-benzoate-acetate (accelerator)
The methods being used today for measuring bili and its fractions are modifications of the method described by whom?
Malloy and Evelyn
What type/s of bili can be measured?
1) Total bili
2) Conjugated bili (direct bili)
What type/s of bili can’t be measured?
Unconjugated bili (indirect bili)
How can the bili that can’t be measured be determined?
Unconjugated bili (indirect bili) can be determined by subtracting conjugated bili from total bili
Total bili - conjugated bili = unconjugated bili
What is the other way of quantifying bili?
Bili can also be quantified via the use of bilirubinometry
At what population is bilirubinometry being used?
In the neonatal population
Is the principle of bilirubinometry applicable to adult population? Why or why not?
No, because the serum of adults has carotenoid compounds that causes strong (+) interference in the adult population
Explain the principle of action of bilirubinometry
The reflected light from the skin using 2 wavelengths that provide a numerical index based on spectral reflectance is being measured
What is the principle and its principle of action utilized by newer generation bilirubinometers?
They use microspectrophotometers w/c determine the optical densities of bili, hgb, and melanin located in the subcutaneous layers of the infant’s skin
What allows the measurement of optical density created by bili?
Mathematical isolation of hgb and melanin
What is the diazo rgnt?
Diazotized sulfanilic acid solution
True or False
Unconjugated bili will only react w/ the diazo rgnt in the presence of an accelerator
True, due to the characteristics of unconjugated bili w/c is for it being nonpolar and water-insoluble substance that is found in plasma bound to albumin
What is the characteristic w/c plays as a key of differentiating conjugated and unconjugated bili fractions?
Differentiated by solubility of the fractions
What are the older ways of reporting conjugated and unconjugated bili?
Direct and indirect
What is the 3rd fraction of bili?
Delta bili
What are the characteristics of delta bili?
1) It is a conjugated bili that is covalently bound to albumin
2) It is only seen when there is significant hepatic obstruction
3) When present, it will react in most lab methods as conjugated bili
Why is delta bili only seen when there is significant hepatic obstruction?
Because the molecule is attached to albumin, it is too large to be filtered by the glomerulus and excreted in the urine
What are the 3 fractions that makes up total bili?
1) Conjugated
2) Unconjugated
3) Delta bili
What are the sxs that can be used for total bili methods using diazo rgnt?
Either:
1) Serum
2) Plasma
What is the preferred sx for Malloy-Evelyn procedure and why?
Serum, because the addition of alcohol in the analysis can precipitate proteins and cause interference w/ the method
Is a fasting sx preferred when measuring the bili concentrations? Why or why not?
Yes, because the presence of lipemia will increase measured bili concentrations
Can hemolyzed sxs be used when measuring the concentrations of bili? Why or why not?
No, also, hemolyzed sxs should be avoided as they may decrease the rxn of bili w/ the diazo rgnt
What will happen if bili is left unprotected from light?
Bili values may reduce by 30% - 50% per hr
What are the stability if serum or plasma is separated from the cells and stored in the dark?
1) It is stable for 2 days at room temp
2) It is stable for 1 wk at 4 DC
3) It is stable indefinitely at -20 DC
Is there a preferred reference method or standardization of bili analysis?
None
What is the candidate reference method for total bili published by the American Association for Clinical Chemistry and the National Bureau of Standards?
A modified Jendrassik-Grof procedure
What is the principle of action being applied by the modified Jendrassik-Grof procedure?
It uses caffeine-benzoate as a solubilizer
True or False
The Jendrassik-Grof or Malloy-Evelyn procedure is the most frequently used method to measure bili
True, because they both have acceptable precision and are adapted to many automated instruments
Among the Jendrassik-Grof and Malloy-Evelyn procedure, what procedure is slightly more complex?
The Jendrassik-Grof procedure
What are the advantages of the Jendrassik-Grof method over Malloy-Evelyn procedure?
1) Not affected by pH changes
2) Insensitive to a 50-fold variation in protein concentration of the sx
3) Maintains optical sensitivity even at low bili concentrations
4) Has minimal turbidity and a relatively constant serum blank
5) Is not affected by hgb up to 750 mg/dL
What is the principle of Malloy-Evelyn procedure?
Bili pigments in the serum or plasma are reacted w/ a diazo rgnt
What is the principle of action of Malloy-Evelyn procedure?
The diazotized sulfanilic acid reacts at the central methylene carbon or bili to split the molecule forming 2 molecules of azobilirubin
The Malloy-Evelyn procedure is typically performed at what pH?
At pH 1.2
True or False
At pH 1.5, the azobili produced (in Malloy-Evelyn procedure) is red-purple in color w/ a maximal absorption of 500 nm
False, because at pH 1.2, the azobili produced is red-purple in color w/ a maximal absorption of 560 nm
What is the most commonly used accelerator and what is its purpose (in Malloy-Evelyn procedure)?
The most commonly used accelerator is methanol w/c is used to solubilize the unconjugated bili
What is the principle of the Jendrassik-Grof method for total and conjugated bili determination?
Bili pigments in serum or plasma are reacted w/ a diazo rgnt (sulfanilic acid in HCl and Na nitrite), resulting in the production of the purple azobili
Bili pigments (in serum / plasma) + diazo rgnt = purple azobili
True or False
The product w/c is azobili (in Jendrassik-Grof procedure) can be measured spectrophotometrically
True
How are the individual fractions of bili (in Jendrassik-Grof procedure) determined?
These are determined by taking 2 aliquots of sx and reacting 1 aliquot w/ the diazo rgnt only and the other aliquot w/ the diazo rgnt and an accelerator (caffeine-benzoate)
2 aliquots of sx
- > 1 aliquot + diazo rgnt
- > 1 aliquot + diazo rgnt + accelerator
What is the purpose of adding caffeine-benzoate (in Jendrassik-Grof procedure)?
The caffeine-benzoate will solubilize the water-insoluble fraction of bili and will yield a total bili value (all fractions)
In Jendrassik-Grof procedure, the rxn w/out the use of an accelerator will yield what type of bili?
It will yield conjugated bili only
What are the purposes of ascorbic acid (in the rxns in the Jendrassik-Grof procedure)?
1) The aliquots w/ the diazo rgnt will be terminated by ascorbic acid
2) It will destroy the excess diazo rgnt
After the addition of ascorbic acid, what should be done (in Jendrassik-Grof procedure)?
The solution is then alkalinized using an alkaline tartrate solution
What are the purposes of alkaline tartrate solution?
1) It alkalinizes the solution
2) It shifts the absorbance spectrum of the azobili to a more intense blue color that is less subject to interfering substances in the sx
The final blue product is measured at what wavelength?
600 nm
When the final product is being measured, what is the relationship bet the intensity of color produced to the concentration of bili?
The intensity of color produced is directly proportional to bili concentration
What should be done to avoid occurrence of errors (in Jendrassik-Grof procedure)?
1) The instruments should be frequently standardized to maintain reliable bili results
2) Careful preparation of bili stds is critical (and should be done properly) because these stds can be deteriorated when exposed to light
3) Hemolysis and lipemia should be avoided because these will alter the concentration of bili
What will happen if bili is exposed to fluorescent, direct, or indirect sunlight?
Serious loss of bili will occur
What is the proper way of taking care (in terms of storage) of the sxs and bili stds?
They should be refrigerated in the dark until testing can be performed
What are the 2 most common aminotransferases measured in the clinical lab?
1) AST
2) ALT
AST is formerly referred to as what?
Serum glutamic oxaloacetic transaminase (SGOT)
ALT is formerly referred to as what?
Serum glutamic pyruvic transaminase (SGPT)
What is the function of aminotransferases?
They are responsible for catalyzing the conversion of aspartate and alanine to oxaloacetate and pyruvate
In the absence of acute necrosis or ischemia of other organs, AST and ALT are most useful in what?
These enzymes are most useful in the detection of hepatocellular (functional) damage to the liver
What is the difference bet AST and ALT based on where they are found?
ALT
-> found mainly in the liver (lesser amts in skeletal muscle and kidney)
AST
-> widely distributed in equal amts in the heart, skeletal muscle, and liver
What aminotransferase is a more “liver-specific” marker?
ALT, because it is found mainly in the liver
What happens to AST and ALT if liver diseases are present?
These aminotransferases rises rapidly in almost all diseases of the liver and may remain elevated for up to 2 - 6 wks
What are the conditions wherein the highest lvls of AST and ALT are found?
The highest lvls of these aminotransferases are found in acute conditions such as:
1) Viral hepatitis
2) Drug- and toxin-induced liver necrosis
3) Hepatic ischemia
True or False
The increase in AST activity is greater than that for ALT
False, because the increase in ALT activity is greater than that for AST
If less severe conditions are present, what happens to AST and ALT?
They moderately increases
What happens to AST and ALT if obstructive liver damage is present?
They are found to be normal or only mildly increased
Since AST and ALT are present in other tissues, elevations of these aminotransferases may be a result of what conditions?
Other organ dysfunction or failure such as:
1) Acute myocardial infarction
2) Renal infarction
3) Progressive muscular dystrophy
Conditions that result in secondary liver disease such as:
1) Infectious mononucleosis
2) Diabetic ketoacidosis
3) Hyperthyroidism
What should be done when following the course of a pt having acute or chronic hepatitis?
It is often helpful to conduct serial determinations of aminotransferases and caution should be used in interpreting abnormal lvls
Why should caution be considered when interpreting abnormal lvls of aminotransferases?
Because serum transferases may actually decrease in some pts w/ severe acute hepatitis, owing to the exhaustive release of hepatocellular enzymes
