Fasting State Metabolism Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Fasting State Metabolism. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Fasting State Metabolism Indian Medical PG Question 1: Major source of energy for brain in fasting/starvation?
- A. Glucose
- B. Glycogen
- C. Fatty acids
- D. Ketone bodies (Correct Answer)
Fasting State Metabolism Explanation: ***Ketone bodies***
- During **prolonged fasting or starvation**, the body depletes its **glycogen stores** and begins to break down fatty acids. The liver converts these fatty acids into **ketone bodies**, such as **acetoacetate and beta-hydroxybutyrate**.
- These **ketone bodies** can cross the **blood-brain barrier** and be used by the brain as an alternative energy source when glucose becomes scarce, preventing protein breakdown for gluconeogenesis.
*Glucose*
- While **glucose** is the primary and preferred energy source for the brain under normal physiological conditions, its availability significantly decreases during **prolonged fasting or starvation**.
- The brain requires a continuous supply of glucose, but in states of severe caloric restriction, the body must conserve glucose for other critical functions and adapt by using alternative fuels.
*Glycogen*
- **Glycogen** is a stored form of glucose found predominantly in the **liver and muscles**.
- The brain itself has minimal **glycogen stores**, which are rapidly depleted during fasting, and thus cannot be a major long-term energy source.
*Fatty acids*
- **Fatty acids** are a major energy source for many tissues in the body, especially during fasting, but they **cannot directly cross the blood-brain barrier** in significant amounts to fuel the brain.
- Instead, **fatty acids** are metabolized into **ketone bodies** in the liver, which then serve as the brain's alternative fuel.
Fasting State Metabolism Indian Medical PG Question 2: Liver produces ketones but cannot use it due to the deficiency of which of the following enzyme?
- A. Alkaline phosphatase
- B. Alanine transaminase
- C. Thiophorase (Correct Answer)
- D. Thiolase
Fasting State Metabolism Explanation: ***Thiophorase***
- The liver lacks **thiophorase (succinyl-CoA:3-ketoacid CoA transferase)**, which is crucial for converting **acetoacetate** to **acetoacetyl-CoA**.
- This enzyme deficiency prevents the liver from utilizing ketones as an energy source, even though it is a primary site for their production.
*Alkaline phosphatase*
- **Alkaline phosphatase** is a non-specific enzyme found in various tissues, including bone, liver, and intestine.
- Its primary role is to **hydrolyze phosphate esters**, and it is not directly involved in ketone metabolism.
*Alanine transaminase*
- **Alanine transaminase (ALT)** is a liver enzyme primarily involved in **amino acid metabolism**, specifically in the transfer of an amino group from alanine to α-ketoglutarate.
- It plays no direct role in the synthesis or utilization of ketone bodies.
*Thiolase*
- **Thiolase** is an enzyme involved in both the synthesis and breakdown of ketone bodies.
- It converts **two acetyl-CoA molecules into acetoacetyl-CoA** during ketogenesis and also cleaves acetoacetyl-CoA into two acetyl-CoA molecules during ketolysis in extrahepatic tissues.
Fasting State Metabolism Indian Medical PG Question 3: What is the main source of ketone bodies during fasting?
- A. Glucose
- B. Amino acids
- C. Glycogen
- D. Fatty acids (Correct Answer)
Fasting State Metabolism Explanation: ***Fatty acids***
- During **fasting**, the body shifts from carbohydrate to fat metabolism to produce energy.
- **Fatty acids** are broken down in the liver through **beta-oxidation** to form acetyl-CoA, which is then converted into ketone bodies.
*Glucose*
- **Glucose** is the primary energy source in the fed state, not during fasting.
- During fasting, **glucose levels** decrease, prompting the body to seek alternative fuel sources.
*Amino acids*
- While some **amino acids** can be converted into glucose (gluconeogenesis) or ketone bodies, they are a secondary source.
- **Protein breakdown** for energy is primarily a long-term adaptation to starvation, not the main initial source of ketone bodies.
*Glycogen*
- **Glycogen stores** (mainly in the liver and muscles) are used during the initial hours of fasting.
- Once these stores are depleted, usually within 12-24 hours, the body relies on **fatty acid oxidation** for energy, leading to ketone body production.
Fasting State Metabolism Indian Medical PG Question 4: In a person fasting overnight with carnitine deficiency, which of the following chemicals increase in quantity in blood?
- A. Ketone body levels
- B. Fatty acid levels (Correct Answer)
- C. Glucose levels
- D. Amino acid levels
Fasting State Metabolism Explanation: ***Fatty acid levels***
- **Carnitine deficiency** impairs the transport of **long-chain fatty acids** into the mitochondria for beta-oxidation.
- This leads to an accumulation of **fatty acids** in the blood as they cannot be efficiently metabolized for energy during fasting.
- Therefore, **fatty acid levels increase** in the blood.
*Ketone body levels*
- **Ketone bodies** are produced from the **beta-oxidation of fatty acids** in the liver.
- With **carnitine deficiency**, fatty acid oxidation is impaired, thus **reducing** the production of ketone bodies, not increasing them.
*Glucose levels*
- During **fasting**, the body relies on **gluconeogenesis** and **glycogenolysis** to maintain glucose levels.
- With carnitine deficiency primarily affecting fat metabolism and preventing fatty acid utilization, the body cannot spare glucose effectively.
- This leads to **hypoglycemia** (decreased glucose), not increased glucose levels.
*Amino acid levels*
- **Amino acid metabolism** is largely independent of **carnitine**.
- While amino acids can be used for gluconeogenesis during fasting, carnitine deficiency does not directly cause an increase in circulating amino acid levels.
Fasting State Metabolism Indian Medical PG Question 5: Gluconeogenesis is inhibited by?
- A. Cholecystokinin
- B. 5-alpha reductase
- C. Insulin (Correct Answer)
- D. Glucagon
Fasting State Metabolism Explanation: ***Insulin***
- **Insulin** is a key hormone released in response to high blood glucose, promoting glucose uptake and storage, and **inhibiting hepatic glucose production** through gluconeogenesis and glycogenolysis.
- It achieves this by decreasing the transcription and activity of key gluconeogenic enzymes like **phosphoenolpyruvate carboxykinase (PEPCK)** and **glucose-6-phosphatase**.
*Cholecystokinin*
- **Cholecystokinin (CCK)** is a gastrointestinal hormone primarily involved in digestion, stimulating bile release and pancreatic enzyme secretion.
- It does not directly regulate gluconeogenesis; its main role is related to **fat and protein digestion**.
*5-alpha reductase*
- **5-alpha reductase** is an enzyme involved in steroid metabolism, converting testosterone to the more potent androgen, dihydrotestosterone (DHT).
- This enzyme has no direct role in the regulation of **gluconeogenesis**.
*Glucagon*
- **Glucagon** is a hormone that has the opposite effect of insulin, stimulating gluconeogenesis and glycogenolysis to increase blood glucose levels during fasting or hypoglycemia.
- Its primary action is to **promote** hepatic glucose output, not inhibit it.
Fasting State Metabolism Indian Medical PG Question 6: In a patient who has been in a state of starvation for 72 hours, which of the following is the primary mechanism for maintaining blood glucose levels?
- A. Increased gluconeogenesis (Correct Answer)
- B. Increased protein degradation
- C. Increased glycogenolysis
- D. Increased ketosis due to breakdown of fats
Fasting State Metabolism Explanation: ***Increased gluconeogenesis***
- After 72 hours of starvation, **hepatic glycogen stores** are completely depleted, making gluconeogenesis the primary and essential mechanism to maintain **blood glucose levels**.
- This process synthesizes glucose from non-carbohydrate precursors like **amino acids** (mainly alanine and glutamine), **lactate**, and **glycerol** to supply glucose for obligate glucose-dependent tissues like **red blood cells** and the **renal medulla**, and provides baseline glucose for the brain.
- Gluconeogenesis occurs primarily in the **liver** and to a lesser extent in the **kidney cortex** during prolonged fasting.
*Increased protein degradation*
- While **protein degradation** does occur to supply amino acids for gluconeogenesis, the body actively minimizes this to preserve muscle mass, especially after prolonged starvation.
- The initial phase of starvation (first 24-48 hours) sees more significant protein breakdown, but its rate decreases substantially after 72 hours as the body becomes increasingly **protein-sparing** and shifts to fatty acid oxidation and ketone body production.
*Increased glycogenolysis*
- **Hepatic glycogen stores** are typically depleted within **12-24 hours** of starvation.
- After 72 hours, there is essentially no glycogen remaining to break down, so **glycogenolysis** cannot contribute to maintaining blood glucose at this stage.
*Increased ketosis due to breakdown of fats*
- **Ketosis** does dramatically increase after 72 hours of starvation as the body shifts to using **fatty acids** for energy and producing **ketone bodies** (β-hydroxybutyrate and acetoacetate) for the brain and other tissues.
- However, while ketone bodies serve as an alternative fuel source for the brain (providing up to 60-70% of its energy needs), they **cannot replace glucose entirely** because certain tissues (red blood cells, renal medulla) are obligate glucose users and cannot utilize ketones.
- The question specifically asks about maintaining **blood glucose levels**, which requires gluconeogenesis, not ketone production.
Fasting State Metabolism Indian Medical PG Question 7: Not done by insulin:
- A. Glycolysis
- B. Lipogenesis
- C. Ketogenesis (Correct Answer)
- D. Glycogen synthesis
Fasting State Metabolism Explanation: ***Ketogenesis***
- **Ketogenesis** is primarily a catabolic process stimulated by low insulin levels or insulin resistance, particularly during prolonged fasting or uncontrolled diabetes.
- Insulin's main role is to promote anabolic processes and energy storage, thus it **inhibits ketogenesis** rather than performing it.
*Glycolysis*
- **Insulin** promotes **glycolysis** by increasing the expression and activity of key glycolytic enzymes, facilitating glucose breakdown for energy.
- It enhances the uptake of **glucose into cells**, where it can then be metabolized via glycolysis.
*Lipogenesis*
- **Insulin** is a potent stimulator of **lipogenesis**, promoting the synthesis of fatty acids and triglycerides from excess glucose.
- This process helps store excess energy in adipose tissue, converting carbohydrates into **fat**.
*Glycogen synthesis*
- **Insulin** directly stimulates **glycogen synthesis** (glycogenesis) in the liver and muscle cells.
- It promotes the uptake of **glucose** and activates enzymes like **glycogen synthase**, leading to storage of glucose as glycogen.
Fasting State Metabolism Indian Medical PG Question 8: Which hormone inhibits hormone-sensitive lipase?
- A. Insulin (Correct Answer)
- B. GH
- C. ACTH
- D. Thyroid hormone
Fasting State Metabolism Explanation: ***Insulin***
- **Insulin** is a key anabolic hormone that promotes energy storage and inhibits catabolic processes, including the breakdown of triglycerides.
- It directly inhibits **hormone-sensitive lipase (HSL)** activity, thus reducing the release of free fatty acids from adipose tissue.
*Thyroid hormone*
- **Thyroid hormones** (T3 and T4) generally promote catabolism and increase metabolic rate, including the mobilization of lipids.
- They tend to **stimulate rather than inhibit** hormone-sensitive lipase expression and activity.
*GH*
- **Growth hormone (GH)** has lipolytic effects, meaning it promotes the breakdown of fats to provide energy.
- GH typically **stimulates HSL activity** and increases the release of free fatty acids from adipocytes.
*ACTH*
- **Adrenocorticotropic hormone (ACTH)** primarily stimulates the adrenal cortex to produce cortisol.
- **Cortisol** can have lipolytic effects in certain contexts and does not directly inhibit HSL; instead, catecholamines act as direct stimulators of HSL.
Fasting State Metabolism Indian Medical PG Question 9: Which hormone is known to repress the biosynthesis of the enzyme pyruvate carboxylase?
- A. Cortisol
- B. Glucagon
- C. Insulin (Correct Answer)
- D. Growth hormone
Fasting State Metabolism Explanation: ***Insulin***
- **Insulin** is an anabolic hormone that promotes glucose utilization and opposes **gluconeogenesis**.
- While insulin does inhibit hepatic glucose production, it primarily acts by **repressing PEPCK (phosphoenolpyruvate carboxykinase)**, the rate-limiting enzyme of gluconeogenesis, rather than directly repressing pyruvate carboxylase biosynthesis.
- **Note:** Modern biochemistry emphasizes that insulin's main transcriptional target in gluconeogenesis is **PEPCK**, not pyruvate carboxylase. However, this was the expected answer for **NEET-2012**, reflecting the understanding at that time.
- Insulin also promotes dephosphorylation and inactivation of gluconeogenic enzymes and enhances glucose uptake and glycolysis.
*Glucagon*
- **Glucagon** is a catabolic hormone that **activates** enzymes involved in **gluconeogenesis** and glycogenolysis to raise blood glucose levels.
- It would **increase**, not repress, the biosynthesis and activity of gluconeogenic enzymes including **pyruvate carboxylase**.
*Cortisol*
- **Cortisol** is a glucocorticoid hormone that **stimulates gluconeogenesis** in the liver as part of the stress response.
- It typically **upregulates** the synthesis and activity of gluconeogenic enzymes like **pyruvate carboxylase** and **PEPCK**.
*Growth hormone*
- **Growth hormone** generally **increases insulin resistance** and can have a **diabetogenic effect**, promoting glucose production rather than repressing gluconeogenic enzymes.
- It does not directly repress gluconeogenic enzyme biosynthesis; its metabolic effects favor lipolysis and protein synthesis.
Fasting State Metabolism Indian Medical PG Question 10: Ketone body formation without glycosuria is seen in ?
- A. Diabetes mellitus
- B. Diabetes insipidus
- C. Starvation (Correct Answer)
- D. Obesity
Fasting State Metabolism Explanation: ***Starvation***
- During **starvation**, the body depletes its **glycogen stores** and begins to break down **fat for energy**. This process leads to the production of **ketone bodies** (acetoacetate, beta-hydroxybutyrate, and acetone) as an alternative fuel source for the brain and other tissues.
- Since there is no underlying problem with **insulin production** or action, blood glucose levels are typically low or normal, and therefore, **glycosuria** (glucose in the urine) is absent.
*Diabetes mellitus*
- In **uncontrolled diabetes mellitus**, especially Type 1, the body cannot effectively use **glucose** due to lack of insulin, leading to high blood glucose levels (**hyperglycemia**) and subsequently **glycosuria**.
- The body then compensates by breaking down **fats**, leading to the formation of **ketone bodies** (**diabetic ketoacidosis**), which results in both **ketonuria** and **glycosuria**.
*Diabetes insipidus*
- **Diabetes insipidus** is a condition characterized by the inability to conserve water due to insufficient **antidiuretic hormone (ADH)** production or action, leading to excessive urination and thirst.
- It does not involve abnormalities in **glucose metabolism** or **ketone body production** and therefore does not typically present with ketonuria or glycosuria.
*Obesity*
- While **obesity** can lead to **insulin resistance** and is a risk factor for Type 2 Diabetes, it does not directly cause **ketone body formation** in the absence of metabolic derangements such as those seen in uncontrolled diabetes or prolonged starvation.
- In most cases of obesity without diabetes, **glucose metabolism** is still adequate enough to prevent significant reliance on **fat breakdown** for energy, meaning there is usually no ketonuria or glycosuria.
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