MCAT Biology : Excretory and Digestive Systems
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Example Questions
Example Question #2 : Digestive System
What is the primary purpose of the liver?
Absorb macro- and micronutrients
Breakdown larger food particles
Release enzymes for food digestion
Filter and detoxify blood
Filter and detoxify blood
The purpose of the liver is to filter blood delivered from the systemic circulation by the hepatic artery, and from the intestines through the hepatic vein. The liver serves to use phase I, II, and III metabolism to oxidize, conjugate, and transport toxic chemicals to the urine or bile for excretion, respectively.
The purpose of the pancreas is to release enzymes for food digestion, while the purpose of the small intestine is to absorb micro- and macronutrients. Additionally, the purpose of the stomach is to breakdown larger food particles into smaller ones.
Example Question #1 : Pancreas And Liver
The liver primarily serves to help detoxify both endogenous and exogenous substances from the blood and intestines. Once blood from the intestines (delivered by the portal vein) or from the systemic circulation (delivered by the hepatic artery) enters the liver, it is filtered over liver cells called hepatocytes. Endogenous substances, such as bilirubin, and exogenous substances, such as drugs, are taken up by transporters on hepatocytes and undergo three phases of metabolism. The three phases allow the transported compound to be detoxified by a method of electron transfer (phase I), by addition of amino acid derivatives (phase II), and finally by exocytosis from the hepatocyte into the bile (phase III). The bile is then transported into the small intestine, and finally excreted from the body.
Amino acid derivatives are often taken from the Krebs cycle, added to sugar nucleotides, and transferred to molecules for detoxification. A common example of an enzyme responsible for this is UDP-glucuronosyl transferase.
How does phase I metabolism in the liver, conducted primarily by the cytochrome P450 system, serve to change an exogenous drug?
Oxidation
As we are told in the passage, phase I metabolism occurs by the transfer of electrons, commonly called an oxidation-reduction reaction. Phase I metabolism in the liver serves primarily to oxidize endogenous and exogenous molecules by passing electrons from a substrate to iron, and finally to oxygen. These oxidation reactions are carried out by the cytochrome P450 system and allow metabolites to become more soluble in urine for excretion. The other reactions listed are carried out by various transferases during phase II metabolism in the liver.
Example Question #4 : Pancreas And Liver
The liver primarily serves to help detoxify both endogenous and exogenous substances from the blood and intestines. Once blood from the intestines (delivered by the portal vein) or from the systemic circulation (delivered by the hepatic artery) enters the liver, it is filtered over liver cells called hepatocytes. Endogenous substances, such as bilirubin, and exogenous substances, such as drugs, are taken up by transporters on hepatocytes and undergo three phases of metabolism. The three phases allow the transported compound to be detoxified by a method of electron transfer (phase I), by addition of amino acid derivatives (phase II), and finally by exocytosis from the hepatocyte into the bile (phase III). The bile is then transported into the small intestine, and finally excreted from the body.
Amino acid derivatives are often taken from the Krebs cycle, added to sugar nucleotides, and transferred to molecules for detoxification. A common example of an enzyme responsible for this is UDP-glucuronosyl transferase.
How does phase II metabolism in the liver function to change highly reactive metabolites of phase I metabolism, or to change other endogenous molecules for excretion?
We are told in the passage that phase II metabolism occurs when a sugar nucleotide-amino acid derivative is affixed to a substance. Context clues are helpful for pinpointing the exact reaction taking place, as the passage provides us with an example of an enzyme that catalyzes the reaction, UDP-glucuronosyl transferase. We can infer from the answer choices that glucuronidation likely occurs using this enzyme. Furthermore, phase II metabolism in the liver is called conjugation, and uses various transferases (acetyltransferases, methytransferases, glucuronosyltransferases) to add function groups onto reactive metabolites from phase I metabolism and endogenous molecules, like bilirubin. Adding these functional groups serves to make the products more hydrophilic in order to be excreted in urine (if smaller) or bile (if larger).
Example Question #5 : Pancreas And Liver
The liver primarily serves to help detoxify both endogenous and exogenous substances from the blood and intestines. Once blood from the intestines (delivered by the portal vein) or from the systemic circulation (delivered by the hepatic artery) enters the liver, it is filtered over liver cells called hepatocytes. Endogenous substances, such as bilirubin, and exogenous substances, such as drugs, are taken up by transporters on hepatocytes and undergo three phases of metabolism. The three phases allow the transported compound to be detoxified by a method of electron transfer (phase I), by addition of amino acid derivatives (phase II), and finally by exocytosis from the hepatocyte into the bile (phase III). The bile is then transported into the small intestine, and finally excreted from the body.
Amino acid derivatives are often taken from the Krebs cycle, added to sugar nucleotides, and transferred to molecules for detoxification. A common example of an enzyme responsible for this is UDP-glucuronosyl transferase.
Phase III metabolism in the liver involves what action upon modified metabolites?
Oxidation
Methylation
Transport
Acetylation
Transport
The passage tells us that phase III metabolism typically occurs by exocytosis. Remember that exocytosis is the transport of a molecule from within the cell to outside the cell with the help of ATP and vesicle packaging. We know that phase III metabolism must involve transport of a molecule from one side of the plasma membrane to the other. Phase III of liver metabolism is the transport of proteins that have been oxidized (phase I) or conjugated (phase II) from the hepatocyte into the bile system. Remember, in contrast to smaller, hydrophilic molecules that result from phase I or II metabolism and can be excreted into the urine, larger molecules must be transported (phase III metabolism) into the bile for excretion.
Example Question #65 : Excretory And Digestive Systems
The liver primarily serves to help detoxify both endogenous and exogenous substances from the blood and intestines. Once blood from the intestines (delivered by the portal vein) or from the systemic circulation (delivered by the hepatic artery) enters the liver, it is filtered over liver cells called hepatocytes. Endogenous substances, such as bilirubin, and exogenous substances, such as drugs, are taken up by transporters on hepatocytes and undergo three phases of metabolism. The three phases allow the transported compound to be detoxified by a method of electron transfer (phase I), by addition of amino acid derivatives (phase II), and finally by exocytosis from the hepatocyte into the bile (phase III). The bile is then transported into the small intestine, and finally excreted from the body.
Amino acid derivatives are often taken from the Krebs cycle, added to sugar nucleotides, and transferred to molecules for detoxification. A common example of an enzyme responsible for this is UDP-glucuronosyl transferase.
Metabolism of drugs and endogenous materials for excretion occurs in which cell type?
Smooth muscle cell
Hepatocyte
Endothelial cell
Enterocyte
Hepatocyte
The liver is the primary site of metabolism for all exogenous drugs and endogenous substances. Substances are delivered to the liver hepatocytes by the blood and undergo phase I, phase II, and/or phase III metabolism before being excreted into the bile or back into the blood to be passed to the kidney for excretion into the urine.
Remember that phase I metabolism is oxidation (turns lipophilic molecules into hydrophilic molecules), phase II metabolism is conjugation, and phase III metabolism is transport to the bile. All phases, however, take place in the liver by function of the hepatocytes.
Example Question #11 : Pancreas And Liver
The liver primarily serves to help detoxify both endogenous and exogenous substances from the blood and intestines. Once blood from the intestines (delivered by the portal vein) or from the systemic circulation (delivered by the hepatic artery) enters the liver, it is filtered over liver cells called hepatocytes. Endogenous substances, such as bilirubin, and exogenous substances, such as drugs, are taken up by transporters on hepatocytes and undergo three phases of metabolism. The three phases allow the transported compound to be detoxified by a method of electron transfer (phase I), by addition of amino acid derivatives (phase II), and finally by exocytosis from the hepatocyte into the bile (phase III). The bile is then transported into the small intestine, and finally excreted from the body.
Amino acid derivatives are often taken from the Krebs cycle, added to sugar nucleotides, and transferred to molecules for detoxification. A common example of an enzyme responsible for this is UDP-glucuronosyl transferase.
A decrease in the extraction of a drug by the liver may be observed under which of the following conditions?
Increase in hepatic blood flow
Decrease in binding of the drug to plasma proteins
Increasing the expression of phase I metabolic enzymes
Liver disease
Liver disease
The fraction of a drug that the liver can act on depends on how much of the drug is delivered to the liver. Often, this initial metabolism is called "first pass metabolism," and serves to determine the initial dose of each drug when it is taken orally. Decreasing blood flow, increasing binding of a drug to plasma proteins, liver disease (hepatocyte death), and genetic mutations that decrease the activity of the liver metabolism enzymes will all reduce the amount of drug available for the liver to act upon, leading to a decrease in drug extraction.
Example Question #512 : Biology
Which of the following is not a function of the liver?
Detoxify drugs in the blood
Gluconeogenesis
Synthesize albumin and clotting factors
Produce red blood cells
Produce red blood cells
The functions of the liver are many and varied. The liver is responsible for gluconeogenesis (making new glucose), beta-oxidation of fats, detoxification of drugs and toxins via the cytochrome P450 system, removal of dead red blood cells from circulation, and the creation of blood proteins, including albumin and clotting factors.
The bone marrow is responsible for generating new red blood cells.
Example Question #543 : Mcat Biological Sciences
Of the answers, which best describes bile?
An enzyme that breaks down fat.
The fluid secreted from the pancreas that breaks down complex sugars.
The fluid secreted from the liver that emulsifies fat.
The fluid secreted from the pancreas that emulsifies fat.
An enzyme that degrades carbohydrates.
The fluid secreted from the liver that emulsifies fat.
Bile is the substance released from the liver that digests fats through detergent-like mechanisms. This is not to be confused with the pancreas which secretes digestive enzymes, such as trypsin.
Example Question #13 : Pancreas And Liver
Bile is essential for healthy digestion and absorbtion of fats. Where is bile made in the body and where is it stored before use?
Bile is made in the liver and stored in the gallbladder.
Bile is made in the gallbladder and stored in the pancreas.
Bile is made in the pancreas and stored in the gallbladder.
Bile is made in the gallbladder and stored in the liver.
Bile is made in the liver and stored in the gallbladder.
Bile is made in the liver and stored in the gallbaldder. People can survive without a gallbladder, but having a gallbladder helps release a large amount of bile into the small intestine when it is needed most. This helps make digestion of fats much more effective.
Example Question #14 : Pancreas And Liver
Portal venous systems occur when blood exits from one capillary bed, and enters into another before first returning to the heart for re-oxygenation. Such arrangements are rare, and occur in only two main organs in mammals. Which of the following is an organ that uses a portal venous system?
Liver
Spleen
Kidney
Stomach
Liver
The liver utilizes the hepatic portal system, while the hypothalamus and anterior pituitary use the hypopheseal portal system. The kidneys, spleen, and stomach all use normal circulation, by which blood passes from arterioles to capillaries and immediately back to venules for transport back to the heart.
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