Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 681: What is the percentage of T4 and T3 released from the thyroid gland?

A. 50% T4; 50% T3
B. 90% T4; 10% T3 (Correct Answer)
C. 80% T4; 20% T3
D. 25% T4; 75% T3

Explanation: ***90% T4; 10% T3*** - The thyroid gland primarily secretes **thyroxine (T4)**, which accounts for approximately **90% of its total hormone output**. - **Triiodothyronine (T3)** is released in smaller amounts, making up approximately **10% of direct thyroid secretion**. - The majority of circulating T3 (about 80%) is derived from **peripheral deiodination of T4** in tissues like liver and kidneys, not from direct thyroid secretion. *80% T4; 20% T3* - This ratio **overestimates** the direct secretion of T3 from the thyroid gland. - While some older sources cite this ratio, the more widely accepted current value is **90:10**. - The higher circulating T3 levels seen in the body are due to **peripheral conversion**, not direct glandular secretion. *50% T4; 50% T3* - This ratio is incorrect as **T4 is the predominant hormone** released directly from the thyroid gland. - Equal secretion would not align with the thyroid's primary role as a **T4-producing gland** with T4 serving as a prohormone. *25% T4; 75% T3* - This ratio is completely incorrect and would reverse the actual secretory pattern. - **T4 is quantitatively the dominant hormone** secreted by the thyroid, with T3 playing a more active role after peripheral conversion.

Question 682: Which of the following hormones is released from the posterior pituitary?

A. Luteinizing hormone
B. Growth hormone
C. Antidiuretic hormone (Correct Answer)
D. ACTH

Explanation: ***Antidiuretic hormone*** - The **posterior pituitary** (neurohypophysis) stores and releases **antidiuretic hormone (ADH)** and oxytocin. - ADH, also known as **vasopressin**, is synthesized in the **hypothalamus** and transported to the posterior pituitary for release. *Luteinizing hormone* - **Luteinizing hormone (LH)** is released from the **anterior pituitary** in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus. - LH plays a crucial role in **reproduction**, triggering ovulation in females and testosterone production in males. *Growth hormone* - **Growth hormone (GH)** is synthesized and secreted by the **anterior pituitary gland**. - Its release is regulated by **growth hormone-releasing hormone (GHRH)** and **somatostatin** from the hypothalamus. *ACTH* - **Adrenocorticotropic hormone (ACTH)** is produced and secreted by the **anterior pituitary gland**. - ACTH stimulates the **adrenal cortex** to release cortisol, regulating stress responses and metabolism.

Question 683: 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 684: Regarding Ghrelin, which is false?

A. Secreted from oxyntic cells (Correct Answer)
B. Stimulates appetite
C. Secretion increased in anorexia
D. Increases fat deposition

Explanation: ***Secreted from oxyntic cells*** - Ghrelin is **NOT** secreted from oxyntic cells (parietal cells). - It is primarily secreted by **P/D1 cells (X/A-like cells)** in the **gastric fundus**. - Oxyntic cells produce **hydrochloric acid** and **intrinsic factor**, not ghrelin. - This is the **FALSE** statement. *Stimulates appetite* - Ghrelin is known as the "**hunger hormone**" and is the primary **orexigenic hormone**. - It acts on **NPY/AgRP neurons** in the arcuate nucleus of the hypothalamus. - Ghrelin levels **rise before meals** and **fall after eating**, directly stimulating appetite and food intake. *Secretion increased in anorexia* - In **anorexia nervosa** and states of **negative energy balance**, ghrelin levels are **elevated**. - This represents a **compensatory physiological response** to stimulate appetite and restore energy balance. - Paradoxically, despite high ghrelin, appetite remains suppressed in anorexia due to central resistance. *Increases fat deposition* - Ghrelin has **anabolic effects** and promotes **adipogenesis** (fat storage). - It reduces **fat oxidation** and increases **lipid accumulation** in adipocytes. - Beyond stimulating food intake, ghrelin has direct metabolic effects favoring a positive energy balance and fat deposition.

Question 685: Thyroxine causes all the following except:

A. Increased basal metabolism
B. Decreased cell metabolism (Correct Answer)
C. Increased pulmonary ventilation
D. Increased oxygen consumption

Explanation: ***Decreased cell metabolism*** - **Thyroid hormones**, including thyroxine, are known to **increase the metabolic rate** of most body cells. - Therefore, a decrease in cell metabolism is contrary to the primary action of thyroxine. - This is the correct answer as thyroxine does NOT cause decreased cell metabolism. *Increased basal metabolism* - **Thyroxine** (T4) and triiodothyronine (T3) are crucial for regulating the body's **basal metabolic rate**. - They enhance **cellular oxygen consumption** and the production of ATP, leading to increased energy expenditure. *Increased pulmonary ventilation* - The elevated **metabolic rate** induced by thyroxine leads to an increased demand for oxygen and production of carbon dioxide. - This physiological response stimulates the respiratory centers, resulting in **increased pulmonary ventilation** to meet the body's gas exchange needs. *Increased oxygen consumption* - One of the principal actions of **thyroxine** is to stimulate **mitochondrial activity** and the electron transport chain in most tissues. - This directly leads to an increase in cellular oxygen utilization and overall **oxygen consumption** throughout the body.

Question 686: Which of the following hormones uses cell surface receptors?

A. Thyroxine
B. Glucagon (Correct Answer)
C. Cortisol
D. Testosterone

Explanation: ***Glucagon*** - **Glucagon** is a **peptide hormone** that cannot pass through the **hydrophobic cell membrane**. - It binds to specific **G protein-coupled receptors** on the surface of target cells (e.g., hepatocytes) to exert its effects. *Thyroxine* - **Thyroxine (T4)** is a **tyrosine-derived (amino acid-derived) hormone** that is lipid-soluble and can readily cross the cell membrane. - It acts on **intracellular receptors** in the nucleus to regulate gene expression. *Cortisol* - **Cortisol** is a **steroid hormone** that is lipid-soluble and can diffuse through the cell membrane. - It primarily binds to **intracellular receptors** in the cytoplasm or nucleus to modulate gene transcription. *Testosterone* - **Testosterone** is a **steroid hormone** that is lipid-soluble and can easily pass through the cell membrane. - Its receptors are located **intracellularly**, usually in the cytoplasm, forming a complex that moves to the nucleus to regulate gene expression.

Question 687: Which of the following hormones uses cGMP as a second messenger?

A. Insulin
B. Thyroxine
C. Growth hormone
D. Atrial natriuretic peptide (ANP) (Correct Answer)

Explanation: ***Atrial natriuretic peptide (ANP)*** - **ANP** binds to a receptor that has **guanylyl cyclase activity**, directly converting **GTP to cGMP**. - **cGMP** then acts as a second messenger, leading to vasodilation and increased sodium and water excretion. *Insulin* - **Insulin** primarily signals through a **tyrosine kinase receptor**, leading to phosphorylation cascades. - It does not directly use **cGMP** as a second messenger for its main effects. *Thyroxine* - **Thyroxine (T4)** and **triiodothyronine (T3)** are **thyroid hormones** (amino acid derivatives) that act directly on **intracellular nuclear receptors**. - They primarily regulate gene transcription and do not utilize **cGMP** as a second messenger. *Growth hormone* - **Growth hormone** binds to a **cytokine receptor** that activates the **JAK/STAT signaling pathway**. - Its downstream effects do not involve **cGMP** as a primary second messenger.

Question 688: After a meal rich in carbohydrate, insulin secretion is stimulated by

A. CCK
B. GLP-1 (7-36) amide (Correct Answer)
C. VIP
D. Serotonin

Explanation: ***GLP-1 (7-36) amide*** - **Glucagon-like peptide-1 (GLP-1)** is an **incretin hormone** secreted from the small intestine in response to nutrient ingestion, especially carbohydrates. - GLP-1 (7-36) amide **stimulates insulin secretion** in a glucose-dependent manner and also **inhibits glucagon secretion**, thereby lowering blood glucose levels after a meal. *CCK* - **Cholecystokinin (CCK)** is a gastrointestinal hormone primarily stimulated by fat and protein in the duodenum. - Its main roles are to **stimulate pancreatic enzyme secretion** and **gallbladder contraction**, not directly insulin secretion. *VIP* - **Vasoactive intestinal peptide (VIP)** is a neuropeptide that relaxes smooth muscle in the gut, **stimulates intestinal fluid and electrolyte secretion**, and increases blood flow. - While it has some effects on metabolism, it is not a primary stimulator of post-meal insulin secretion. *Serotonin* - **Serotonin (5-hydroxytryptamine)** is a neurotransmitter found in the gut and brain, involved in mood, sleep, and gut motility. - It does not directly stimulate insulin secretion after a meal rich in carbohydrates.

Question 689: All the following hormones have receptors on the plasma membrane of target tissues except:

A. Epinephrine
B. Glucagon
C. Estradiol (Correct Answer)
D. Thyrotropin

Explanation: ***Estradiol*** - **Estradiol** is a **steroid hormone** derived from cholesterol, making it **lipid-soluble**. - Due to its lipid solubility, estradiol can readily pass through the **plasma membrane** and bind to **intracellular receptors** in the cytoplasm or nucleus. *Epinephrine* - **Epinephrine** is a **catecholamine hormone** and is **water-soluble**. - Water-soluble hormones cannot cross the lipid bilayer of the plasma membrane and thus bind to **receptors located on the cell surface**. *Glucagon* - **Glucagon** is a **peptide hormone** and is **water-soluble**. - Like other peptide hormones, it binds to **specific receptors embedded in the plasma membrane** to elicit its cellular effects via second messenger systems. *Thyrotropin* - **Thyrotropin**, also known as **Thyroid-Stimulating Hormone (TSH)**, is a **glycoprotein hormone** and is **water-soluble**. - TSH exerts its action by binding to **receptors on the plasma membrane** of thyroid follicular cells.

Question 690: Estradiol is a powerful inhibitor of FSH (follicle stimulating hormone). What is another factor that is a powerful inhibitor of FSH in the female?

A. LH
B. Inhibin (Correct Answer)
C. Testosterone
D. Progesterone

Explanation: ***Inhibin*** - **Inhibin** is a glycoprotein hormone primarily produced by the **granulosa cells** of the ovarian follicles. - It selectively inhibits the secretion of **FSH** from the anterior pituitary, providing negative feedback without significantly affecting LH. *LH* - **Luteinizing hormone (LH)** is primarily involved in stimulating ovulation and the production of progesterone, not directly inhibiting FSH. - While LH and FSH levels are intricately linked in the menstrual cycle, LH does not act as a primary inhibitor of FSH. *Testosterone* - **Testosterone** is an androgen primarily found at much lower levels in females compared to males and does not serve as a primary inhibitor of FSH in the female reproductive axis. - While androgens can influence follicular development, they are not a direct and potent inhibitor of FSH secretion. *Progesterone* - **Progesterone** is mainly involved in preparing the uterus for pregnancy and maintaining it, and it provides negative feedback on both LH and FSH, but its primary effect is often associated with LH suppression and the overall luteal phase regulation rather than specific, potent FSH inhibition like inhibin. - High levels of progesterone during the luteal phase do inhibit GnRH, which in turn reduces FSH and LH, but inhibin specifically targets FSH.

Practice by Chapter

Principles of Endocrine Regulation

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Hypothalamus and Pituitary Gland

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Thyroid Physiology

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Adrenal Cortex and Medulla

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Pancreatic Hormones and Glucose Metabolism

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Calcium and Phosphate Homeostasis

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Growth Hormone and Growth Factors

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Endocrine Regulation of Metabolism

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Hormone Receptors and Signaling

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Assessment of Endocrine Function

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