Liver Function chem
List the most common enzymes used to assess liver disease
ALP (alkaline phosphatase) AST (aspartate aminotransferase) /SGOT (serum glutamate oxaloacetic transaminase), ALT (alanine aminotransferase) /SGPT (serum glutamate pyruvate transaminase, GGT (gamma glutamyltransferase), and 5'-NT (5'-nucleotidase)
What are the main physiologic functions of the liver
excretory and secretory functionssynthesis of major biologic compounds (proteins, carbohydrates and lipids) detoxification and drug metabolism
What is bilirubin, how is it formed and for what clinical reason is it measured in the laboratory
found in bile. As you may remember, bilirubin is derived mainly from the breakdown of RBCs. It is transported to the liver in the blood bound to proteins, chiefly albumin.
hepatic jaundice:
may result from impaired hepatocyte uptake of bilirubin, defective conjugation of bilirubin with albumin, or from abnormal secretion of bilirubin by the hepatocytes. With this form of jaundice, both conjugated and unconjugated bilirubin levels will be abnormal.
Kupffer cells:
phagocytic macrophages capable of ingesting bacteria or other foreign material from the blood that flows through the sinusoids
What is cirrhosis and what is the leading cause of this disorder in the United States
refers to the irreversible scarring of liver tissue. In the United States, the leading causes of cirrhosis are alcohol abuse and chronic hepatitis C virus infection.
posthepatic jaundice:
results from the impaired excretion of bilirubin caused by mechanical obstruction of the flow of bile into the intestines. This may be due to gallstones or a tumor. When bile ceases to flow into the intestines, there is a rise in blood level of conjugated bilirubin, and the stool loses its source of normal pigmentation and becomes clay colored.
prehepatic jaundice:
results when an excessive amount of bilirubin is sent to the liver for metabolism (breakdown), such as in excessive breakdown of RBCs (hemolytic anemia...). With this type of jaundice, abnormal unconjugated bilirubin levels will be seen in the blood.
lobules:
the structural unit of the liver is called the "lobule". These lobules are made up of liver cells called "hepatocytes". Each lobule contains a branch of the hepatic artery, a branch of the portal vein, and a bile duct
portal vein:
this vessel drains the gastrointestinal (GI) tract of absorbed materials (like absorbed nutrients from food that has been ingested)from the intestines to the liver
Why would it be important to know these three bilirubin levels?
Because knowing which level or levels is abnormal can help a physician to assess prehepatic, hepatic, or posthepatic liver dysfunction.
bile ducts:
Bile is collected in spaces in the liver . located within the lobules. As bile is formed, it collects into the smaller bile ducts, then passes into other larger bile ducts, until it collects in the "common" bile duct
Which forms of viral hepatitis are associated with parenteral transmission, and, therefore, an occupational hazard for clinical laboratory workers
Hepatitis B is also known as "serum hepatitis". There are three major routes of transmission: parenteral (e.g. needlestick injury), perinatal, and sexual. Hepatitis C is most often transmitted parenterally; however, it has also been transmitted by other sexual and oral-fecal routes, and through blood transfusions.
Unconjugated bilirubin does not become unattached from the albumin carry protein once in the liver. This means the molecule (bilirubin/albumin) cannot be excreted from the body because it is too big to be filtered out of the blood by the kidneys.
In the laboratory, there are tests available that measure TOTAL bilirubin and conjugated bilirubin levels. To obtain an unconjugated bilirubin level, you would simply subtract the results of the conjugated bilirubin level (taken from the analyzer) from the TOTAL bilirubin level (taken from the analyzer).TOTAL bilirubin - conjugated bilirubin = unconjugated bilirubin
Urobilinogen is also excreted by the kidneys in the urine.
Increased urobilinogen levels are found in hemolytic disease and in defective liver-cell function such as that seen in hepatitis. Absence of urobilinogen in the urine or feces is most often seen with complete biliary obstruction. Fecal urobilinogen is also decreased in biliary obstruction, as well as hepatocellular disease.
sinusoids
between the lobules are vascular spaces. The function is to receive blood from the hepatic artery and the portal vein. lined by endothelial cells and Kupffer cells.
Which drug/chemical is best known for being the most toxic to the liver
alcohol
What is unconjugated bilirubin, why is measurement important? How is unconjugated bilirubin measured in the laboratory
another form of bilirubin that is water insoluble. Most of the bilirubin found in the blood is in the unconjugated form. The unconjugated form of bilirubin is not excreted from the body, but continuously recirculates in the blood.
Briefly explain the liver's role in detoxification and drug metabolism
Another major function of the liver is that it serves to protect the body from potentially injurious substances absorbed from the intestinal tract and toxic by-products of metabolism. There are a variety of "detoxification" mechanisms that make this happen. Examples include: oxidation, reduction, hydrolysis, carboxylation, demethylation, etc. The type of injurious substance presented to the liver will determine which detoxification mechanism or mechanisms is necessary. These various mechanisms serve to convert many noxious or comparatively insoluble compounds into other forms that are either less toxic or water-soluble and therefore excretable by the kidneys.
In general, what will cause liver enzymes to become elevated in the blood
Any injury to the liver that results in cytolysis and necrosis causes increased liver enzyme levels in the blood.
Name two tests that can be performed to assess synthetic ability of the liver. Why would these tests be abnormal with impaired liver function
Most plasma proteins are produced in the liver, including albumin. So, it stands to reason, if a patient has a decreased level of albumin and total protein, this may indicate impaired liver function. The albumin level correlates well with the severity of functional impairment and is found more often in chronic rather than acute liver disease. Since the liver also synthesizes most of the clotting factors, a prolonged prothrombin time (a test for a deficiency of clotting factors of the extrinsic and common coagulation pathways), would indicate severe liver disease and a poor prognosis.
Briefly explain the formation and function of bile
One of the most important functions of the liver is the excretion of bile. Bile is formed in the liver from a variety of substances it absorbs from the blood. Bile is involved with the digestion and absorption of lipids from the intestines.
What are primary malignant tumors of the liver called What is the "cure"
Primary malignant tumors of the liver are called "hepatocellular carcinomas", "hepatocarcinomas" or "hepatomas".
Name two laboratory methods that are associated with assessment of bilirubin levels
The Malloy-Evelyn & Jendrassik-Grof methods
What is the method used in the laboratory to diagnose viral hepatitis
The diagnosis of hepatitis A, B, C, D, and/or E is made by the serologic detection of an antibody produced by the patient to the particles on the virus, or to the virus itself. These types of assays are usually run on an immunoassay analyzer.
Why could ammonia be increased in the bloodstream of patients with liver failure
The liver plays a major role in removing ammonia from the bloodstream and converting it to urea so that it can be removed by the kidneys. In liver failure, ammonia and other toxins increase in the bloodstream and may ultimately cause hepatic coma.
Briefly explain the liver's role in the synthesis of proteins, carbohydrates, and lipids
The liver plays a major role in the production of plasma proteins synthesizing albumin and the majority of the alpha and beta globulins. All the blood-clotting factors (except factor VIII) are synthesized in the liver. The liver plays a major role in the breakdown of ammonia to urea. (BUN...) The synthesis and metabolism of carbohydrates is also performed in the liver. Glucose is converted to glycogen, a portion of which is stored in the liver for future use. Gluconeogenesis from amino acids is also another important function of the liver. Fat is formed from carbohydrates in the liver when nutrition is adequate and the demand for glucose is being met by dietary sources. The liver also plays a key role in the metabolism of fat. The formation of ketone bodies, resulting from the breakdown of fat, is almost exclusively formed in the liver. Lipoproteins that are carrier proteins for triglycerides, cholesterol and chylomicrons are synthesized in the liver. The liver is the storage site for all the fat-soluble vitamins (Vitamins A, D, E, and K) and several water-soluble vitamins, such as B12. The liver plays a key role in the clearance of certain hormones in the body.The liver is involved in the transport, storage, and metabolism of iron, copper and other metals. Many enzymes are produced in the liver. Examples include: AST/SGOT, ALT/SGPT, ALP, GGT, and 5"NT. (Measurement of these enzymes can determine a liver dysfunction...)
How many lobes make up the liver
Two
What is jaundice
When the bilirubin concentration in the blood begins to rise, it begins to deposit in the sclera of the eyes and in the skin, causing a yellowish discolorization. This pigmentation of the sclera and skin is known as "jaundice". Jaundice can be caused by prehepatic, hepatic or posthepatic pathophysiologic mechanisms.
hepatic artery:
a branch of the aorta and the vessel that supplies most of the oxygen requirement to the liver
What is urobilinogen and why is it measured in the clinical laboratory
a colorless end product of bilirubin metabolism that can be converted by intestinal bacteria to the brown pigment urobilin. Urobilin gives stool its characteristic brown color.
What is Reye's syndrome
a disorder of unknown cause involving the liver and arising primarily in children. It is a form of hepatic destruction that usually occurs following recovery from a viral infection, such as chickenpox or influenza. It has been related to aspirin therapy.
What is conjugated bilirubin, why is measurement important
a form of bilirubin that is water-soluble. The water solubility property of conjugated bilirubin is important because it must have the capability of breaking down in the intestines so that it can be excreted as urobilin in the stool (urobilin gives stool its characteristic brown color), or as urobilinogen in the urine. If bilirubin were unable to be broken down and excreted from the body, excess bilirubin levels would be seen in the blood. Conjugated bilirubin is transported to the liver bound mostly to albumin. Once in the liver, it is separated from the albumin and taken up by the hepatocytes.
