Biochemistry of Liver Metabolism

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Questions and Answers

During periods of fasting or starvation, what is the primary source of amino acids used by the liver for gluconeogenesis?

  • Liver protein breakdown
  • Muscle protein breakdown (correct)
  • Dietary protein
  • Fatty acid breakdown

Which of the following statements accurately describes the role of very low-density lipoproteins (VLDLs)?

  • VLDLs are produced by the liver to transport cholesterol from peripheral tissues to the liver.
  • VLDLs are produced by the liver to transport triglycerides from the liver to other tissues. (correct)
  • VLDLs are primarily involved in the synthesis of ketones from fatty acids.
  • VLDLs are responsible for scavenging cholesterol from the blood and peripheral tissues.

What is the primary function of high-density lipoproteins (HDLs)?

  • Providing a circulating reservoir of apoproteins for activating chylomicrons.
  • Scavenging cholesterol from the blood and peripheral tissues. (correct)
  • Transporting triglycerides from the liver to other tissues.
  • Synthesizing ketones from fatty acids.

Which of the following is NOT a ketone body produced by the liver?

<p>Pyruvate (A)</p> Signup and view all the answers

Why are ketone bodies important during periods of fasting or starvation?

<p>They are more soluble in water than fatty acids, allowing them to be transported to tissues. (A)</p> Signup and view all the answers

Which of the following is the primary site of glycogen storage in the body?

<p>Skeletal muscle (D)</p> Signup and view all the answers

What is the significance of the liver's ability to synthesize non-essential amino acids?

<p>It helps regulate blood glucose levels by providing a source of amino acids for gluconeogenesis. (D)</p> Signup and view all the answers

What is the main reason why fatty acids are not readily used as a fuel source by the brain?

<p>Fatty acids cannot cross the blood-brain barrier easily. (C)</p> Signup and view all the answers

What is the primary role of glucokinase in hepatocytes?

<p>To synthesize glycogen from glucose during the post-prandial state. (C)</p> Signup and view all the answers

Which plasma proteins are NOT primarily synthesized by hepatocytes?

<p>Gamma globulins (D)</p> Signup and view all the answers

What process directly links the liver's role in gluconeogenesis with its primary function in urea production?

<p>The removal of amine groups from amino acids. (C)</p> Signup and view all the answers

Which metabolic process is MOST closely linked to the liver's ability to maintain nutrient homeostasis during fasting?

<p>Glycogenolysis (D)</p> Signup and view all the answers

A deficiency in Vitamin K would most likely lead to which of the following?

<p>Prolonged bleeding due to impaired clotting factor production. (A)</p> Signup and view all the answers

How does albumin contribute to maintaining the osmolality of the plasma?

<p>Albumin's abundance contributes to the total osmotic pressure of the plasma, influencing fluid balance. (A)</p> Signup and view all the answers

Which scenario is most likely to lead to increased risk of edema formation?

<p>A decrease in plasma osmolality due to liver dysfunction. (D)</p> Signup and view all the answers

What is the primary function of triglycerides stored in the liver?

<p>To provide a readily available energy source for the body. (B)</p> Signup and view all the answers

Which of the following statements accurately describes the role of bile salts in fat digestion?

<p>Bile salts increase the surface area of fat globules, making them more accessible for digestion. (C)</p> Signup and view all the answers

Which of the following components is NOT directly involved in the process of bilirubin excretion?

<p>Insulin (A)</p> Signup and view all the answers

Which of the following is a key function of Phase I reactions in drug metabolism?

<p>Increase the drug's solubility in water. (A)</p> Signup and view all the answers

Which of the following pairs represents a drug that becomes MORE active after undergoing liver metabolism?

<p>Levodopa to Dopamine (B)</p> Signup and view all the answers

Which of the following best describes how bile salts facilitate fat digestion?

<p>By increasing the surface area of fat globules, making them more accessible for lipases. (D)</p> Signup and view all the answers

Which of the following is NOT a common compound involved in Phase II reactions of drug metabolism?

<p>Cytochrome P-450 (A)</p> Signup and view all the answers

Based on the information provided, which of the following statements is TRUE regarding the metabolism of steroid hormones in the liver?

<p>The liver converts steroid hormones to more hydrophilic forms for easier excretion. (B)</p> Signup and view all the answers

Which of the following best describes the relationship between bile salts and micelle formation?

<p>Bile salts facilitate micelle formation by interacting with the hydrophobic core of the micelle. (B)</p> Signup and view all the answers

What is the primary mechanism by which the liver prevents a vitamin A deficiency for an extended period?

<p>The liver efficiently stores and releases vitamin A as needed. (A)</p> Signup and view all the answers

Which of the following is NOT a direct function of the liver in relation to iron metabolism?

<p>Transporting iron to red blood cell precursors. (A)</p> Signup and view all the answers

How does the liver contribute to the regulation of blood glucose levels?

<p>By converting glycogen to glucose, providing a readily available source of energy. (A), By storing excess glucose as glycogen, decreasing blood glucose levels. (B)</p> Signup and view all the answers

What is the primary consequence of frequent drug administration on cytochrome P-450 activity?

<p>Decreased drug effectiveness due to faster inactivation. (C)</p> Signup and view all the answers

What is the primary reason why drugs administered orally may undergo "first-pass metabolism"?

<p>The drugs pass through the liver before entering systemic circulation. (D)</p> Signup and view all the answers

How do somatomedins, also known as Insulin-Like Growth Factors (IGFs), contribute to growth and development?

<p>By promoting the differentiation of chondrocytes into osteogenic cells. (A)</p> Signup and view all the answers

How does the liver contribute to the removal of intestinal bacteria from the circulatory system?

<p>By utilizing Kupffer cells to engulf and destroy bacteria that enter the blood. (D)</p> Signup and view all the answers

In the context of first-pass metabolism, why might certain medications be administered intravenously rather than orally?

<p>To bypass the liver and prevent significant drug inactivation before reaching circulation. (D)</p> Signup and view all the answers

Which of the following statements accurately describes the role of the liver in carbohydrate metabolism during periods of fasting?

<p>The liver breaks down glycogen to release glucose into the bloodstream. (C)</p> Signup and view all the answers

What is the primary function of VLDLs (very low-density lipoproteins) in the context of liver function?

<p>To transport triglycerides from the liver to peripheral tissues. (A)</p> Signup and view all the answers

How does the liver contribute to the maintenance of blood glucose levels during prolonged fasting?

<p>By synthesizing glucose from amino acids and glycerol through gluconeogenesis. (D)</p> Signup and view all the answers

Which two processes are primarily involved in the liver's role in maintaining blood glucose levels during periods of fasting?

<p>Gluconeogenesis and glycogenolysis. (B)</p> Signup and view all the answers

The liver plays a crucial role in the metabolism of dietary sugars. Which of the following dietary sugars is primarily utilized by the liver for energy or conversion into glucose?

<p>Galactose. (B), Fructose. (D)</p> Signup and view all the answers

What is the primary role of gluconeogenesis in the liver during periods of fasting?

<p>To produce glucose from sources other than carbohydrates, such as amino acids and glycerol. (D)</p> Signup and view all the answers

Which of the following is NOT a carbohydrate metabolic process directly involved in the liver's regulation of blood glucose levels?

<p>Lipogenesis. (B)</p> Signup and view all the answers

Which statement best explains the liver's central role in regulating blood nutrient levels?

<p>The liver transforms and releases nutrients into the bloodstream, maintaining a balance for different tissues. (A)</p> Signup and view all the answers

Flashcards

Liver Functions

Diverse roles of the liver essential for health.

Maintain Homeostasis

Regulation of blood nutrients and glucose supply.

Glycogen

Storage form of glucose in the liver.

Glycogenolysis

Breakdown of glycogen into glucose for energy.

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Gluconeogenesis

Creation of glucose from non-carbohydrate sources.

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Ketones

Water-soluble fats produced from fatty acids.

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Plasma Proteins

Proteins synthesized in the liver for blood functions.

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Detoxification

Process of removing harmful substances from blood.

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Glycogen Storage

Glycogen is stored in hepatocytes and skeletal muscle, with the highest concentration in liver cells.

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Hepatocytes

Liver cells responsible for glycogen storage, lipid regulation, and amino acid synthesis.

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VLDL

Very Low Density Lipoproteins, made by hepatocytes to transport triglycerides and fatty acids in the blood.

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HDL

High Density Lipoproteins, synthesized by hepatocytes, that scavenge cholesterol and provide apoproteins for lipoproteins.

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Amino Acids

Building blocks of proteins, with the liver synthesizing non-essential amino acids from skeletal muscle during catabolism.

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Non-essential Amino Acids

Amino acids that the body can synthesize, meaning they are not required in the diet unlike essential amino acids.

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Bile Salts

Compounds in bile that emulsify dietary fats for digestion.

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Micelles

Structures formed by bile salts that encapsulate dietary fats.

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Bilirubin

Waste product derived from the breakdown of heme in red blood cells.

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Heme Catabolism

The process of breaking down hemoglobin to recycle iron and produce bilirubin.

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Phase I Reactions

Biotransformation reactions in the liver that make drugs more polar.

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Cytochrome P-450

A family of enzymes that play a key role in drug metabolism in Phase I.

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Phase II Reactions

Liver reactions that further increase drug polarity via conjugation.

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Conjugation

Chemical process in Phase II that attaches small compounds to drugs for detoxification.

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Urea

Primary nitrogenous waste product produced by the liver.

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Glucokinase

Enzyme that helps convert glucose to glycogen in the liver.

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Cholesterol Synthesis

The liver produces and accumulates cholesterol.

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Clotting Factors

Plasma proteins made by the liver that regulate bleeding.

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Albumin

Most abundant plasma protein, aids in fluid balance.

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Vitamin K

Essential vitamin for synthesis of clotting factors in the liver.

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Edema Formation

Swelling due to fluid buildup, linked to liver dysfunction.

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First-pass metabolism

The process where drugs are metabolized in the liver before reaching systemic circulation.

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Vitamin Storage in Liver

The liver temporarily stores vitamins A, D, and B12 to prevent deficiencies.

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Ferritin

A compound formed from iron and apoferritin, serving as a storage form of iron in the liver.

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Somatomedins

Polypeptide hormones that mediate the effects of Human Growth Hormone (HGH).

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Kupffer cells

Phagocytic cells in the liver that cleanse bacteria from the blood.

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Chondrocytes

Cells in cartilage that enhance growth influenced by somatomedins.

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Osteoblasts

Bone cells that are stimulated to grow and multiply due to somatomedins.

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Study Notes

Liver Functions

  • The liver plays a crucial role in maintaining overall health and life, fulfilling a broad range of functions.
  • Maintaining homeostasis of nutrients: The liver regulates blood nutrients, ensuring a consistent glucose supply for neurons and distributing fatty acids as ketones or triglycerides in very low-density lipoproteins (VLDLs).
  • Carbohydrates: The liver stores glucose as glycogen and releases it during needed times (glycogenolysis) and synthesizes glucose (gluconeogenesis) from other sources.
  • Glycogenolysis: Breaks down glycogen to provide glucose during times of fasting (low blood sugar) to maintain blood glucose levels and keep neurons functioning.
  • Gluconeogenesis: The liver converts, certain other substances like amino acids and glycerol, into glucose. This glucose is essential for neurons during periods of fasting.
  • Lipids: The liver synthesizes and releases various lipoproteins, including very low-density lipoproteins (VLDLs) for fatty acid distribution, high-density lipoproteins (HDLs) for cholesterol scavenging, and produces ketones (water-soluble fatty acid analogs) from fatty acids during times of fasting.
  • Amino Acids: The liver uses amino acids from skeletal muscle during periods of fasting for gluconeogenesis. The liver also synthesizes non-essential amino acids.
  • Storing Nutrients: The liver stores glycogen and lipids. Glycogen is crucial for sustaining blood glucose during fasting periods; lipids (triglycerides) are also stored, though diseases can lead to excessive accumulation.
  • Synthesizing and Releasing Plasma Proteins: The liver synthesizes many plasma proteins, critically including clotting factors and albumin. Albumin is vital for fluid balance in the body, and clotting factors are essential for blood clotting.
  • Synthesizing and Releasing Bile: The liver produces bile, containing bile salts/acids that are crucial for emulsifying dietary fats and increasing their surface area for efficient digestion. Bile also contains bilirubin and cholesterol
  • Processing and Excreting Bilirubin: Bilirubin, a waste product of heme breakdown, is processed and excreted in bile by the liver; this process involves conjugation with glucuronic acid.
  • Detoxification and Excretion: The liver neutralizes harmful substances, such as drugs, hormones, and toxins to prevent harm to the body and facilitates their excretion.
  • Storage of Vitamins: The liver stores vitamins A, D, and B12 for use by the body, preventing deficiencies for several months.
  • Iron Storage: The liver stores iron (bound to apoferritin), ensuring the body has a reserve of iron for essential processes like紅血球synthesizing.
  • Synthesizing and Releasing Somatomedins: The liver produces somatomedins/ Insulin-Like Growth Factors (IGFs) that work with Growth Hormone (GH) to influence various bodily functions.
  • Blood Cleansing: The liver filters blood and removes bacteria that can cause infection. Kupffer cells within the liver remove bacteria.

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