Endocrine Regulation of Metabolism — MCQs
Which of the following statements best describes the mechanism of action of insulin on target cells?
Metabolic changes seen in starvation include all of the following except?
All of the following are increased in Acute stress except
All are true about hormone functions except:
Which of the following enzyme activity decreases in fasting?
All of these cause hyperglycemia except:
Which of the following hormones are under inhibitory control of hypothalamus?
Hyperthyroid state is characterized by -
Which of the following inhibit gonadotropin-releasing hormone pulse secretion?
Insulin-like growth factor is secreted by:
Endocrine Regulation of Metabolism Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following statements best describes the mechanism of action of insulin on target cells?
- A. Insulin binds to a receptor on the outer surface of the plasma membrane, activating adenylate cyclase through the Gs protein.
- B. Insulin binds to a cytoplasmic receptor and is transferred as a hormone receptor complex to the nucleus to modulate gene expression.
- C. Insulin enters the cell and causes the release of calcium ions from intracellular stores.
- D. Insulin binds to a transmembrane receptor on the outer surface of the plasma membrane, activating the tyrosine kinase in the cytosolic domain of the receptor. (Correct Answer)
Explanation: ***Insulin binds to a transmembrane receptor on the outer surface of the plasma membrane, activating the tyrosine kinase in the cytosolic domain of the receptor.*** - **Insulin** is a **peptide hormone** and cannot freely pass through the lipid bilayer, thus it binds to a **transmembrane receptor** on the cell surface. - This binding leads to the activation of the receptor's intrinsic **tyrosine kinase activity** in the intracellular domain, initiating a signaling cascade. *Insulin binds to a cytoplasmic receptor and is transferred as a hormone receptor complex to the nucleus to modulate gene expression.* - This mechanism describes the action of **steroid hormones**, which are lipid-soluble and can cross the cell membrane, binding to **intracellular receptors**. - **Insulin** acts via a **cell surface receptor** and its downstream effects are mediated through signal transduction pathways, not direct nuclear translocation. *Insulin binds to a receptor on the outer surface of the plasma membrane, activating adenylate cyclase through the Gs protein.* - This mechanism is characteristic of **G-protein coupled receptors (GPCRs)**, which activate or inhibit enzymes like adenylate cyclase via G-proteins to produce second messengers like cyclic AMP. - The **insulin receptor** is a **receptor tyrosine kinase**, not a GPCR, and does not directly activate adenylate cyclase via Gs protein. *Insulin enters the cell and causes the release of calcium ions from intracellular stores.* - While some hormones and neurotransmitters can trigger the release of intracellular **calcium ions**, this is typically mediated by specific pathways (e.g., GPCRs linked to phospholipase C). - **Insulin** does not directly enter target cells to cause calcium release; its actions are primarily mediated through receptor tyrosine kinase signaling pathways.
Question 2: Metabolic changes seen in starvation include all of the following except?
- A. Ketogenesis
- B. Protein degradation
- C. Increased gluconeogenesis
- D. Increased glycolysis (Correct Answer)
Explanation: ***Increased glycolysis*** - In starvation, the body's primary goal is to conserve **glucose** for essential organs like the brain, as glucose supply is limited. Therefore, glycolysis, the breakdown of glucose, is *decreased*, not increased. - The body shifts to using alternative fuels such as **fatty acids** and **ketone bodies** to spare glucose. *Increased gluconeogenesis* - **Gluconeogenesis**, the synthesis of glucose from non-carbohydrate precursors like amino acids and glycerol, is *increased* during starvation to maintain blood glucose levels. - This process is crucial for providing glucose to tissues that primarily rely on it, such as the brain and red blood cells. *Ketogenesis* - **Ketogenesis**, the production of ketone bodies from fatty acids, is significantly *increased* during prolonged starvation. - **Ketone bodies** become a major energy source for the brain and other tissues when glucose is scarce, helping to spare muscle protein. *Protein degradation* - **Protein degradation** (proteolysis) is *increased* during starvation, especially in the initial phases, to provide amino acids for gluconeogenesis. - Muscle protein is a primary source of these amino acids, contributing to muscle wasting observed in prolonged starvation.
Question 3: All of the following are increased in Acute stress except
- A. Growth hormone
- B. Epinephrine
- C. Glucagon
- D. Insulin (Correct Answer)
Explanation: ***Insulin*** - During acute stress, **insulin secretion is actively suppressed** by catecholamines (epinephrine and norepinephrine) acting on **alpha-2 adrenergic receptors** on pancreatic beta cells. - This suppression is crucial for the stress response, as it allows **unopposed action of counter-regulatory hormones** to mobilize glucose and raise blood glucose levels. - The body prioritizes **immediate energy availability** (high blood glucose) over storage, making insulin the hormone that is **decreased, not increased**, during acute stress. *Growth hormone* - **Growth hormone** is a counter-regulatory hormone that **increases during acute stress** to mobilize energy stores, particularly by promoting lipolysis and gluconeogenesis. - Its actions contribute to the stress-induced elevation of **blood glucose levels**. *Epinephrine* - **Epinephrine** (adrenaline) is a primary catecholamine released during acute stress, leading to a rapid **fight or flight response**. - It significantly **increases heart rate**, blood pressure, and **glucose mobilization** through glycogenolysis and gluconeogenesis. *Glucagon* - **Glucagon** is a key hormone involved in **maintaining glucose homeostasis** and is significantly **increased during acute stress**. - It primarily acts on the liver to **stimulate glycogenolysis** and **gluconeogenesis**, thereby raising blood glucose levels to provide energy.
Question 4: All are true about hormone functions except:
- A. Cortisol regulates plasma volume (Correct Answer)
- B. Thyroid hormones regulate metabolism
- C. ADH regulates blood osmolality
- D. Insulin regulates blood glucose
Explanation: ***Cortisol regulates plasma volume*** - While cortisol plays a role in fluid balance by influencing **renal perfusion** and the action of other hormones like ADH, its primary role is not the direct regulation of plasma volume. - **Aldosterone** is the primary hormone directly responsible for regulating plasma volume through its effects on sodium and water reabsorption in the kidneys. *Thyroid hormones regulate metabolism* - **Thyroid hormones** (T3 and T4) are crucial for regulating the body's metabolic rate, influencing factors like energy production, protein synthesis, and cellular oxygen consumption. - They impact the metabolism of **carbohydrates, fats, and proteins**, affecting nearly every cell in the body. *ADH regulates blood osmolality* - **Antidiuretic hormone (ADH)**, also known as vasopressin, primarily regulates blood osmolality by controlling the reabsorption of water in the renal collecting ducts. - It increases the permeability of collecting ducts to water, thus concentrating urine and **reducing plasma osmolality** when it's high. *Insulin regulates blood glucose* - **Insulin** is a key hormone produced by the pancreas that regulates blood glucose levels by facilitating the uptake of glucose into cells for energy or storage. - It plays a crucial role in lowering blood glucose after meals by promoting **glucose utilization** and inhibiting glucose production by the liver.
Question 5: Which of the following enzyme activity decreases in fasting?
- A. Hormone sensitive lipase
- B. Glycogen phosphorylase
- C. Acetyl CoA Carboxylase
- D. Phosphofructokinase I (Correct Answer)
Explanation: ***Phosphofructokinase I*** - **Phosphofructokinase I (PFK-1)** activity **decreases** during fasting due to **decreased insulin-to-glucagon ratio**, which reduces **fructose-2,6-bisphosphate (F-2,6-BP)** levels, a powerful allosteric activator of PFK-1. - This reduction in activity slows down **glycolysis**, conserving glucose for critical tissues like the brain and redirecting metabolism toward **gluconeogenesis**. - **PFK-1 is the rate-limiting enzyme of glycolysis**, making its regulation particularly significant in the fasted state. *Hormone sensitive lipase* - **Hormone sensitive lipase (HSL)** activity **increases** during fasting due to elevated **glucagon** and **epinephrine** levels, which stimulate its phosphorylation via **protein kinase A (PKA)**. - This increased activity promotes the breakdown of stored **triglycerides** in adipose tissue, releasing **fatty acids** for β-oxidation and energy production. *Glycogen phosphorylase* - **Glycogen phosphorylase** activity **increases** during fasting, primarily stimulated by **glucagon** and **epinephrine**, leading to the breakdown of **glycogen** stores. - This enzyme is crucial for **glycogenolysis**, providing glucose to maintain blood sugar levels when dietary intake is absent. *Acetyl CoA Carboxylase* - **Acetyl CoA Carboxylase (ACC)** activity also **decreases** during fasting, as it is inhibited by **phosphorylation** mediated by **AMP-activated protein kinase (AMPK)** and **protein kinase A (PKA)**. - This reduction in activity inhibits **fatty acid synthesis**, shifting metabolism towards fatty acid **oxidation** for energy production. - **Note:** While ACC activity does decrease during fasting, **PFK-1** is considered the primary answer as it represents the key regulatory point for **glucose metabolism** (glycolysis vs. gluconeogenesis), which is the central metabolic shift during fasting.
Question 6: All of these cause hyperglycemia except:
- A. Catecholamines
- B. Insulin (Correct Answer)
- C. Cortisol
- D. GH
Explanation: ***Insulin*** - Insulin's primary function is to **lower blood glucose levels** by facilitating glucose uptake into cells and promoting glycogen synthesis. - It counters the effects of hormones that elevate blood sugar, directly leading to a **decrease in hyperglycemia**. *Catecholamines* - **Catecholamines** (e.g., epinephrine, norepinephrine) increase blood glucose by promoting **glycogenolysis** and **gluconeogenesis**. - They also **inhibit insulin secretion**, further contributing to elevated blood sugar. *Cortisol* - **Cortisol** is a **glucocorticoid** that raises blood glucose by increasing **gluconeogenesis** and reducing peripheral **glucose utilization**. - It can also decrease insulin sensitivity, leading to **hyperglycemia**. *GH* - **Growth hormone (GH)** can induce **insulin resistance** in peripheral tissues, which leads to reduced glucose uptake. - It also promotes **gluconeogenesis**, both contributing to elevated blood glucose levels.
Question 7: Which of the following hormones are under inhibitory control of hypothalamus?
- A. Growth hormone only
- B. Prolactin only
- C. Both prolactin and growth hormone (Correct Answer)
- D. Neither prolactin nor growth hormone
Explanation: ***Both prolactin and growth hormone*** - The hypothalamus exerts **inhibitory control over prolactin release** primarily through **dopamine** (prolactin-inhibiting hormone/PIH). - Growth hormone (GH) secretion is inhibited by **somatostatin** (growth hormone-inhibiting hormone/GHIH), which is also secreted by the hypothalamus. - These are the **only two anterior pituitary hormones** predominantly under tonic inhibitory control from the hypothalamus. *Growth hormone only* - While **somatostatin** from the hypothalamus does inhibit growth hormone, this option is incomplete. - **Prolactin** is also under hypothalamic inhibitory control via dopamine, making this the wrong answer. *Prolactin only* - The hypothalamus does exert inhibitory control over prolactin via **dopamine**, making this statement partially correct. - However, **growth hormone** is also under inhibitory control by **somatostatin**, so this option is incomplete. *Neither prolactin nor growth hormone* - This is incorrect because both prolactin and growth hormone are under inhibitory hypothalamic control. - All other anterior pituitary hormones (TSH, ACTH, FSH, LH) are primarily under **stimulatory control** from the hypothalamus.
Question 8: Hyperthyroid state is characterized by -
- A. Decreased glycolysis
- B. Increased cholesterol
- C. Increased protein synthesis
- D. Lipolysis (Correct Answer)
Explanation: ***Lipolysis (Correct)*** - **Thyroid hormones** have potent **lipolytic effects**, stimulating the breakdown of **triglycerides** into free fatty acids and glycerol - This increased fat catabolism is a key metabolic feature of hyperthyroidism and contributes to the **weight loss** commonly observed despite increased appetite - Enhanced lipolysis also explains the increased free fatty acid levels seen in hyperthyroid patients *Decreased glycolysis (Incorrect)* - **Thyroid hormones** increase overall metabolic rate, including **carbohydrate metabolism** - **Glycolysis** (glucose breakdown) is typically **increased**, not decreased, in hyperthyroid states - This increased glucose utilization contributes to the hypermetabolic state *Increased cholesterol (Incorrect)* - **Thyroid hormones** accelerate both the synthesis and catabolism of cholesterol, with a net effect of **increased cholesterol degradation and excretion** - **Serum cholesterol levels** are typically **decreased** in hyperthyroidism (often used as a metabolic marker) - Conversely, hypothyroidism is associated with hypercholesterolemia *Increased protein synthesis (Incorrect)* - While physiological levels of thyroid hormones support anabolic processes, **excessive thyroid hormone levels** in hyperthyroidism create a net **catabolic state** - This results in increased **protein breakdown (proteolysis)** exceeding synthesis - Clinical manifestations include **muscle weakness, muscle wasting**, and negative nitrogen balance
Question 9: Which of the following inhibit gonadotropin-releasing hormone pulse secretion?
- A. Prolactin (Correct Answer)
- B. Oxytocin
- C. Thyroxine
- D. Insulin
Explanation: ***Prolactin*** - Elevated levels of **prolactin** inhibit the pulsatile secretion of **gonadotropin-releasing hormone (GnRH)** from the hypothalamus. - This inhibition leads to decreased production of **luteinizing hormone (LH)** and **follicle-stimulating hormone (FSH)** from the pituitary, ultimately affecting gonadal function. *Thyroxine* - **Thyroxine** (thyroid hormone) primarily regulates metabolism and growth, and while it interacts with the reproductive axis, its direct effect is not typically the **inhibition of GnRH pulse secretion**. - Extreme thyroid dysfunction can indirectly impact reproductive hormones, but it's not the primary mechanism of GnRH inhibition. *Oxytocin* - **Oxytocin** is largely involved in **uterine contractions** during labor and **milk ejection** during lactation, and has roles in social bonding. - It does not directly inhibit the pulsatile release of **GnRH**. *Insulin* - **Insulin** is a key hormone in **glucose metabolism** and energy regulation. - While insulin resistance and hyperinsulinemia can affect reproductive function (e.g., in polycystic ovary syndrome, PCOS), it does not **directly inhibit GnRH pulse secretion**.
Question 10: Insulin-like growth factor is secreted by:
- A. Liver (Correct Answer)
- B. Pituitary gland
- C. Pancreas
- D. Adrenal glands
Explanation: ***Liver*** - The **liver** is the primary site of **insulin-like growth factor 1 (IGF-1)** production in response to **growth hormone (GH)** stimulation. - IGF-1 mediates many of the growth-promoting effects of GH, affecting various tissues throughout the body. *Pituitary gland* - The **pituitary gland** secretes **growth hormone (GH)**, which then stimulates the liver to produce IGF-1, but it does not directly secrete IGF-1. - Its role is upstream in the GH-IGF-1 axis, initiating the signaling cascade. *Pancreas* - The **pancreas** is primarily known for secreting **insulin** and **glucagon**, which regulate blood glucose levels. - It does not produce significant amounts of IGF-1. *Adrenal glands* - The **adrenal glands** produce hormones like **cortisol**, **aldosterone**, and **androgens**. - They are not involved in the direct secretion of IGF-1.
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