Liver Flashcards
The _____ controls the flow of bile into the duodenum.
Sphincter of Oddi
The liver receives about __% of the cardiac output (or ____ L/min).
30%; 1.5 L/min
The portal vein provides _1__ of hepatic blood flow, and the hepatic artery supplies the remaining _2__. Each vessel contributes _3__% of the liver’s oxygen supply.
- 70% (PV) (Portal veins are partially desaturated flow from the intestines)
- 30% (HA)
- 50% of oxygen supply
T or F: Flow through the portal vein is autoregulated. So what?
(False) Flow through the portal vein is not autoregulated, making it susceptible to hypotension. When this happens, the hepatic arterial buffer response (through the washout of vasodilators such as adenosine) compensates by increasing flow through the hepatic artery. Liver disease and volatile anesthetics disrupt the hepatic arterial buffer response,
which predisposes the liver to ischemia.
Common bedside tests of liver function can be divided into those that assess what four things?
Synthetic function
Hepatocellular integrity
Hepatic clearance
Biliary duct obstruction
Synthetic function is commonly assessed by what two things? Which is a better indicator of acute injury and which is better for chronic injury?
Prothrombin time (acute)
Albumin (chronic impairment)
The PT is very sensitive for acute injury, because factors ___ and ___ have short half-lives that are less than 24 hours.
5 and 7
Albumin is a better measure of chronic liver impairment, because its half-life is ___.
A serum albumin concentration less than ___ suggests chronic liver dysfunction.
21- days
3 g/dl
Hepatocellular integrity is measured by? Give two examples.
Serum aminotransferases such as:
Alanine aminotransferase (ALT - found in the liver)
Aspartate aminotransferase (AST - found in liver, eart, skeletal muscle, kidney, brain, RBCs).
Aminotranseases catbolize amino acids fr entry into the citric acid cycle.
T or F: Enzymes spike in cases of extensive hepatocellular injury including acute viral hepatitis, ischemic hepatitis, and acute drug- or toxin-induced liver injury. These conditions are generally considered contraindications to elective surgery.
True
Keep in mind that serum aminotransferases can rise from other conditions that affect the liver such as systemic infection, heart failure, and cancer.
What test helps us assess hepatic clearance?
Serum bilirubin
What is the significance of measuring unconjugated vs conjugated bilirubin?
An increased conjugated bilirubin concentration suggests a hepatic or post-hepatic problem.
An elevated unconjugated bilirubin level suggests a pre-hepatic origin such as hemolysis or hematoma reabsorption.
What three tests do we use to assess biliary duct obstruction? Which is most sensitive? Least?
Alkaline phosphatase, gamma glutamyl transpeptidase, and 5’-nucleotidase.
Alkaline phosphatase is the least specific indicator of biliary duct obstruction, while 5’-nucleotidase is the most specific.
The Child-Turcotte-Pugh and MELD scoring systems predict what?
These systems require knowledge of the patient’s (1), (2), (3), (4), (5).
- The risk of surgery for patients with liver disease.
- International normalized ratio (INR)
Plasma bilirubin level
Plasma albumin level
Degree of encephalopathy
Volume of ascites
What lab tests evaluates the liver’s synthetic function?
INR
Serum albumin
Other serum proteins
Hepatic synthetic function is easily assessed by measurement of plasma albumin and fibrinogen and determination of the prothrombin time or the INR.
The branches of the vasculature and bile ducts demarcate the boundaries of the eight liver segments.
The hepatic acinus is the functional unit of the liver. It is elliptical in shape, centering along the vascular anastomoses connecting two portal triads and extending out toward the central hepatic venules.
Portal venule and hepatic arteriolar blood flows from the portal triads to the hepatic venules through the sinusoids (Figure 14-1).
Fibrosis leads to portal hypertension from compression of these blood vessels. Hepatocytes are described as being in zone 1, 2, or 3 based on their distance from the center of the acinus with its nutrient and oxygen supply. Those in zone 3 are at greatest risk of ischemic, viral, and toxic injury as they are more remote from their source of oxygen and nutrients. Zone 3 is the area of the hepatic acinus where bridging fibrosis first occurs following ischemic or metabolic injury.
Review Table with Physiologic and Biochemical Functions of the Liver
Look over the mechanism of acetaminophen toxicity.
Acetaminophen can be conjugated to a sulfate or a glucuronide prior to excretion. Alternatively, it can be oxidized to highly reactive compounds by P450 mixed-function oxidases. Binding to glutathione inactivates these toxic compounds. When glutathione is depleted, the reactive metabolites bind to hepatocellular macromolecules and cause cell necrosis. P450 enzyme activity is induced by chronic alcohol ingestion. Increased P450 enzyme activity can deplete glutathione and enhance the toxic binding to macromolecules. Acetylcysteine can augment glutathione and prevent hepatic necrosis if given early after the ingestion of a lethal dose of acetaminophen.
Fulminant hepatic necrosis and acute liver failure can occur 2–3 days following an acetaminophen overdose. The outcome of acetaminophen-induced hepatic necrosis can be predicted by measuring the plasma level of acetaminophen 4 hours after ingestion. Blood levels greater than 300 μg/mL predict that hepatic necrosis will occur. Blood levels less than 120 μg/mL usually do not result in hepatic necrosis.
The best laboratory tests of hepatic excretion are serum levels of –(1)–.
These lab values are also used in the determination of the Child-Pugh score.
- Indirect and direct bilirubin
Although most forms of liver disease will eventually produce an elevation of bilirubin, it is most common with biliary obstruction or secondary autoimmune biliary disease.
Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are hepatic –(1)–.
Elevated serum levels indicate –(2)– from a variety of causes, including viral infection, alcohol abuse, and obesity. The highest elevations (approximately 50 times normal values) of the transaminases occur with ischemic or toxic liver injury and acute viral hepatitis. Gamma-glutamyl transpeptidase (γ-GT) and lactate dehydrogenase are enzymes that can be elevated in both hepatocellular injury and bile duct obstruction.
- Mitochondrial enzymes
- Hepatocellular injury
The serum liver enzyme response to hepatocellular injury can be confusing because elevations occur in the early phase of injury. Decreasing enzyme levels may indicate either recovery or worsening to severe, irretrievable injury.
