Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 581: A decrease in basal metabolic rate (BMR) is seen in which of the following conditions?

A. Obesity (Correct Answer)
B. Hyperthyroidism
C. Starvation
D. Exercise

Explanation: **Explanation:** The Basal Metabolic Rate (BMR) represents the minimum energy expenditure required to maintain vital functions at rest. **Why Obesity is the correct answer:** In the context of standard medical examinations like NEET-PG, **Obesity** is associated with a **decrease in BMR per unit of body weight**. While a larger individual has a higher absolute BMR, their metabolic efficiency is often altered. Specifically, adipose tissue is metabolically less active compared to lean muscle mass. As the ratio of fat to lean mass increases, the overall BMR relative to body surface area or weight typically declines. **Analysis of Incorrect Options:** * **Hyperthyroidism:** Thyroid hormones ($T_3$ and $T_4$) are the primary regulators of BMR. In hyperthyroidism, there is an increase in $Na^+$-$K^+$ ATPase activity and oxygen consumption, leading to a significant **increase** in BMR. * **Starvation:** While prolonged starvation eventually lowers BMR as a compensatory mechanism to conserve energy, in the context of this specific MCQ comparison, **Obesity** is the classic clinical association for a pathologically low BMR relative to body composition. (Note: Some texts consider starvation a cause of decreased BMR; however, in standard physiological testing, obesity is the preferred answer regarding body state). * **Exercise:** Physical activity increases muscular demand and sympathetic outflow, leading to a sharp **increase** in metabolic rate. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Regulator:** The Thyroid gland is the most important endocrine regulator of BMR. * **Surface Area Rule:** BMR is directly proportional to the surface area of the body (Rubner’s Law). * **Factors Increasing BMR:** Fever (12% increase per 1°C), Pregnancy, Caffeine, and Male gender (due to higher testosterone/muscle mass). * **Factors Decreasing BMR:** Hypothyroidism, Aging, and Sleep (decreases by ~10-15%).

Question 582: Which substance is secreted by Sertoli cells?

A. Androgen binding protein (Correct Answer)
B. Testosterone
C. Luteinizing hormone
D. Follicle-stimulating hormone

Explanation: **Explanation:** The **Sertoli cells**, often referred to as the "nurse cells" of the testes, are located within the seminiferous tubules. Their primary function is to support and nourish developing germ cells during spermatogenesis. Under the influence of **Follicle-Stimulating Hormone (FSH)**, Sertoli cells synthesize and secrete **Androgen Binding Protein (ABP)**. **Why Option A is correct:** ABP is essential for male fertility because it binds to testosterone (secreted by Leydig cells) and prevents it from diffusing out of the seminiferous tubules. This maintains the **high local concentration of testosterone** required for the maturation of sperm, which is significantly higher than the concentration found in systemic circulation. **Why the other options are incorrect:** * **B. Testosterone:** This is secreted by the **Leydig cells** (interstitial cells) located outside the tubules, primarily under the influence of Luteinizing Hormone (LH). * **C. Luteinizing hormone (LH):** This is a gonadotropin secreted by the **gonadotrophs of the anterior pituitary gland**. * **D. Follicle-stimulating hormone (FSH):** Like LH, FSH is secreted by the **anterior pituitary**. It acts *on* the Sertoli cells but is not produced by them. **High-Yield NEET-PG Pearls:** * **Blood-Testis Barrier:** Formed by tight junctions between adjacent Sertoli cells; it protects developing sperm from the immune system. * **Inhibin B:** Also secreted by Sertoli cells, it provides negative feedback to the anterior pituitary to inhibit FSH secretion. * **Müllerian Inhibiting Substance (MIS):** Secreted by fetal Sertoli cells to cause regression of paramesonephric ducts in male embryos. * **Sertoli-cell-only syndrome:** A condition characterized by azoospermia despite normal testosterone levels, as germ cells are absent.

Question 583: Which hormone is synthesized as a peptide precursor?

A. Insulin (Correct Answer)
B. Parathyroid hormone (PTH)
C. Renin
D. Thyroid hormone

Explanation: **Explanation:** The synthesis of peptide hormones involves a multi-step process: translation of mRNA into a **preprohormone**, cleavage of the signal peptide to form a **prohormone**, and final proteolytic processing into the active hormone. **1. Why Insulin is the correct answer:** Insulin is the classic example of a peptide hormone synthesized as a precursor. It is first synthesized in the RER of pancreatic beta cells as **Preproinsulin**. After the removal of the signal sequence, it becomes **Proinsulin**. Proinsulin consists of the A-chain, B-chain, and a connecting **C-peptide**. In the Golgi apparatus, proinsulin is cleaved into active Insulin and C-peptide, which are then secreted in equimolar amounts. **2. Analysis of Incorrect Options:** * **Parathyroid Hormone (PTH):** While PTH is also a peptide hormone synthesized as Prepro-PTH and Pro-PTH, the question specifically tests the most classic and frequently examined model of precursor synthesis in medical exams. (Note: In some contexts, multiple options may be technically "peptide precursors," but Insulin is the gold-standard example for the "prepro-pro-hormone" pathway). * **Renin:** Renin is an **enzyme** (aspartyl protease) synthesized as prorenin. While it has a precursor, it is functionally categorized as a proteolytic enzyme rather than a primary metabolic hormone. * **Thyroid Hormone:** These are **amine-derived** hormones (derived from Tyrosine). They are synthesized on the thyroglobulin backbone but are not "peptide hormones" in the structural sense. **Clinical Pearls for NEET-PG:** * **C-peptide:** Since C-peptide is secreted 1:1 with insulin, it is used as a clinical marker to distinguish between Type 1 DM (low C-peptide) and Type 2 DM (normal/high C-peptide), and to diagnose insulinomas. * **Storage:** Peptide hormones are stored in secretory vesicles and released via exocytosis (calcium-dependent). * **Half-life:** Peptide hormones generally have a short half-life (minutes) compared to steroid or thyroid hormones.

Question 584: Amylin is secreted by which cell of the pancreas?

A. Alpha cells
B. Beta cells (Correct Answer)
C. Gamma cells
D. Delta cells

Explanation: **Explanation:** **Amylin (Islet Amyloid Polypeptide - IAPP)** is a 37-amino acid peptide hormone that is **co-secreted with insulin from the Beta (β) cells** of the pancreatic islets of Langerhans. It is stored in the same secretory granules as insulin and is released in response to the same stimuli (primarily glucose). Amylin functions as a synergistic partner to insulin by slowing gastric emptying, inhibiting glucagon secretion, and promoting satiety, thereby preventing postprandial glucose spikes. **Analysis of Options:** * **Option B (Correct):** Beta cells constitute about 60-75% of the islet cells and are the primary source of both Insulin and Amylin. * **Option A (Incorrect):** Alpha (α) cells secrete **Glucagon**, which increases blood glucose levels by stimulating glycogenolysis and gluconeogenesis. * **Option D (Incorrect):** Delta (δ) cells secrete **Somatostatin**, a universal inhibitor that suppresses the release of both insulin and glucagon. * **Option C (Incorrect):** Gamma (γ) cells, also known as PP cells, secrete **Pancreatic Polypeptide**, which regulates exocrine pancreatic secretions. **High-Yield Clinical Pearls for NEET-PG:** 1. **Pramlintide:** A synthetic analogue of amylin used as an adjunct treatment in both Type 1 and Type 2 Diabetes Mellitus. 2. **Amyloid Deposits:** In Type 2 Diabetes, amylin can aggregate to form amyloid deposits in the islets, which is a classic histopathological finding contributing to beta-cell dysfunction. 3. **Ratio:** Insulin and Amylin are secreted in a ratio of approximately 50:1 to 100:1.

Question 585: Which Cytochrome P450 enzyme is identified as 11-beta-hydroxylase?

A. CYMA-IB
B. CYPA-2B (Correct Answer)
C. CYPA-3B
D. CYPA-4B

Explanation: ### Explanation **Correct Option: B (CYP11B1)** In the steroidogenesis pathway within the adrenal cortex, **11β-hydroxylase** is the enzyme responsible for the final step in cortisol synthesis (converting 11-deoxycortisol to cortisol) and the penultimate step in aldosterone synthesis. In biochemical nomenclature, this enzyme is encoded by the gene **CYP11B1**. *Note on Nomenclature:* While the question uses the shorthand "CYPA-2B," in standard medical literature, 11β-hydroxylase is specifically designated as **CYP11B1**. **Analysis of Options:** * **CYP11B1 (Option B):** This is the correct designation for 11β-hydroxylase. It is primarily expressed in the *Zona Fasciculata* of the adrenal cortex. * **CYP11B2 (Option C/D context):** This refers to **Aldosterone Synthase**, which possesses 11β-hydroxylase, 18-hydroxylase, and 18-oxidase activities. It is found in the *Zona Glomerulosa*. * **CYP11A1 (Option A context):** This refers to the **Cholesterol Side Chain Cleavage enzyme (Desmolase)**, which converts Cholesterol to Pregnenolone—the rate-limiting step of steroidogenesis. **Clinical Pearls for NEET-PG:** 1. **11β-Hydroxylase Deficiency:** This is the second most common cause of Congenital Adrenal Hyperplasia (CAH). It leads to decreased cortisol but an accumulation of **11-deoxycorticosterone (DOC)**. Since DOC is a potent mineralocorticoid, patients present with **hypertension** and hypokalemia, alongside virilization. 2. **Metyrapone Test:** Metyrapone inhibits 11β-hydroxylase. It is used to test the HPA axis integrity by measuring the rise in 11-deoxycortisol and ACTH. 3. **Location:** Remember the mnemonic **"GFR"** for the adrenal layers (Glomerulosa, Fasciculata, Reticularis) and **"Salt, Sugar, Sex"** for their respective products.

Question 586: Sertoli cells play a key role in which of the following processes?

A. Spermiogenesis (Correct Answer)
B. Testosterone secretion
C. Secretion of seminal fluid
D. Production of germ cells

Explanation: **Explanation:** Sertoli cells, often referred to as "nurse cells," are essential for the maturation of male gametes. The correct answer is **Spermiogenesis**—the final stage of spermatogenesis where round spermatids transform into elongated, motile spermatozoa. Sertoli cells facilitate this by providing structural support, phagocytosing excess cytoplasm (residual bodies) from the developing spermatids, and secreting essential nutrients and regulatory proteins. **Analysis of Options:** * **A. Spermiogenesis (Correct):** Sertoli cells are directly involved in the remodeling of spermatids. They also form the **Blood-Testis Barrier**, protecting developing sperm from the immune system. * **B. Testosterone secretion:** This is the primary function of **Leydig cells** (interstitial cells), located in the connective tissue between seminiferous tubules, under the influence of LH. * **C. Secretion of seminal fluid:** The majority of seminal fluid is produced by the **seminal vesicles** (~60%) and the **prostate gland** (~30%), not the Sertoli cells. * **D. Production of germ cells:** Germ cells (spermatogonia) are derived from primordial germ cells. Sertoli cells do not produce them but rather provide the microenvironment required for their division and differentiation. **High-Yield Facts for NEET-PG:** * **Inhibin B:** Secreted by Sertoli cells to provide negative feedback on **FSH** secretion. * **Androgen Binding Protein (ABP):** Secreted by Sertoli cells to maintain high local concentrations of testosterone within the tubules. * **Anti-Müllerian Hormone (AMH):** Produced by fetal Sertoli cells to cause regression of Müllerian ducts. * **Blood-Testis Barrier:** Formed by **tight junctions** between adjacent Sertoli cells.

Question 587: Which of the following hormones is NOT directly controlled by ACTH?

A. Glucocorticoids
B. Aldosterone
C. DHEA
D. Epinephrine (Correct Answer)

Explanation: **Explanation:** The correct answer is **Epinephrine**. The adrenal gland is divided into the **Adrenal Cortex** (outer) and the **Adrenal Medulla** (inner). ACTH (Adrenocorticotropic Hormone), secreted by the anterior pituitary, primarily regulates the zones of the adrenal cortex. **Why Epinephrine is the correct answer:** Epinephrine (Adrenaline) is a catecholamine synthesized in the **Adrenal Medulla**. Its release is controlled by the **sympathetic nervous system** (preganglionic sympathetic fibers releasing acetylcholine), not by the HPA axis. While cortisol is required for the induction of the enzyme *PNMT* (which converts norepinephrine to epinephrine), ACTH does not exert direct secretagogue control over the medulla. **Why the other options are incorrect:** * **Glucocorticoids (Cortisol):** Produced in the *Zona Fasciculata*. This is the primary target of ACTH; it stimulates both the synthesis and secretion of cortisol via a cAMP-dependent pathway. * **DHEA (Androgens):** Produced in the *Zona Reticularis*. ACTH is the main trophic hormone responsible for the secretion of adrenal androgens like DHEA and Androstenedione. * **Aldosterone:** Produced in the *Zona Glomerulosa*. While the **Renin-Angiotensin-Aldosterone System (RAAS)** and plasma Potassium levels are the primary regulators, ACTH has a permissive effect and can acutely stimulate aldosterone secretion. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Adrenal Layers:** **G**FR (**G**lomerulosa, **F**asciculata, **R**eticularis) corresponds to **S**alt, **S**ugar, **S**ex (Mineralocorticoids, Glucocorticoids, Androgens). * **Rate-limiting step:** ACTH stimulates the conversion of Cholesterol to Pregnenolone via the enzyme **Cholesterol Desmolase** (CYP11A1). * **Hyperpigmentation:** In primary adrenal insufficiency (Addison’s), high ACTH levels lead to skin pigmentation because ACTH is derived from **POMC**, which also produces Melanocyte-Stimulating Hormone (MSH).

Question 588: The feed-forward mechanism is employed in the regulation of which of the following?

A. Temperature (Correct Answer)
B. pH
C. Blood pressure
D. Blood volume

Explanation: ### Explanation **Correct Option: A (Temperature)** The **feed-forward mechanism** (also known as anticipatory control) is a regulatory process where the body initiates a response **before** a change in the internal environment actually occurs. It anticipates a disturbance based on sensory input from the external environment. In **temperature regulation**, peripheral thermoreceptors in the skin detect a drop in external temperature and signal the hypothalamus to initiate heat-conserving mechanisms (like shivering or vasoconstriction) *before* the core body temperature actually drops. This prevents a deviation from the set point rather than just reacting to it. **Why Incorrect Options are Wrong:** * **B, C, and D (pH, Blood Pressure, Blood Volume):** These parameters are primarily regulated by **negative feedback mechanisms**. In these systems, the body detects a deviation from the set point (e.g., a drop in BP detected by baroreceptors) and initiates a compensatory response to return the parameter to normal. These are reactive processes, not anticipatory. **High-Yield Clinical Pearls for NEET-PG:** * **Feed-forward Examples:** 1. **Cephalic phase of digestion:** Seeing or smelling food triggers insulin and gastric acid secretion before food reaches the stomach. 2. **Exercise:** Increased heart rate and ventilation occur at the onset of exercise (or even just before) due to cortical input, anticipating the metabolic demand. * **Negative Feedback:** The most common homeostatic mechanism (e.g., Thyroid hormone regulation, Glucose control). * **Positive Feedback:** Rare and leads to instability/climax (e.g., LH surge, Oxytocin in labor, Blood clotting cascade, Nerve action potential).

Question 589: ADH is released from which part of the pituitary gland?

A. Anterior pituitary
B. Posterior pituitary (Correct Answer)
C. Hypothalamus
D. Intermediate pituitary

Explanation: ### Explanation **Correct Answer: B. Posterior Pituitary** **Mechanism and Concept:** Antidiuretic Hormone (ADH), also known as Vasopressin, is synthesized in the **magnocellular neurons** of the **Supraoptic (primarily)** and Paraventricular nuclei of the **Hypothalamus**. Once synthesized, it is transported down the axons of the hypothalamo-hypophyseal tract bound to carrier proteins called **Neurophysins**. It is stored in the axon terminals within the **Posterior Pituitary (Neurohypophysis)** in structures called **Herring bodies**. Upon physiological stimulus (increased plasma osmolarity or hypovolemia), ADH is **released** from the posterior pituitary into the systemic circulation. Therefore, while the hypothalamus is the site of production, the posterior pituitary is the site of release. **Analysis of Incorrect Options:** * **A. Anterior Pituitary (Adenohypophysis):** This gland synthesizes and secretes its own hormones (GH, TSH, ACTH, FSH, LH, and Prolactin) under the influence of hypothalamic releasing/inhibiting factors. It does not store or release ADH. * **C. Hypothalamus:** This is the site of **synthesis**, not release into the general circulation. NEET-PG questions often distinguish between "synthesis" (Hypothalamus) and "release/secretion" (Posterior Pituitary). * **D. Intermediate Pituitary:** In humans, this is a rudimentary zone (Pars intermedia) that secretes Melanocyte-Stimulating Hormone (MSH) during fetal life but has no role in ADH metabolism. **High-Yield Clinical Pearls for NEET-PG:** * **V1 Receptors:** Located on vascular smooth muscle (cause vasoconstriction via $IP_3/DAG$ pathway). * **V2 Receptors:** Located on the Principal cells of the Late Distal Tubule and Collecting Duct (increase water reabsorption via **Aquaporin-2** insertion using the $cAMP$ pathway). * **Diabetes Insipidus (DI):** Central DI is caused by a lack of ADH release; Nephrogenic DI is caused by renal resistance to ADH. * **Stimulus:** The most potent stimulus for ADH release is an increase in plasma osmolarity (detected by osmoreceptors in the OVLT).

Question 590: Which of the following hormones is secreted in response to TRH stimulation?

A. Prolactin
B. TSH
C. Prolactin and TSH (Correct Answer)
D. None of the above

Explanation: **Explanation:** The correct answer is **Prolactin and TSH (Option C)**. **Underlying Medical Concept:** Thyrotropin-Releasing Hormone (TRH) is a tripeptide synthesized in the paraventricular nucleus of the hypothalamus. While its primary physiological role is to stimulate the anterior pituitary to release **Thyroid Stimulating Hormone (TSH)**, it also acts as a potent **Prolactin-Releasing Factor (PRF)**. TRH binds to G-protein coupled receptors on both thyrotropes and lactotropes, leading to the secretion of both hormones. **Analysis of Options:** * **Option A (Prolactin):** While TRH does stimulate Prolactin, this option is incomplete because TSH is also secreted. * **Option B (TSH):** This is the primary target of TRH, but choosing this alone ignores the significant stimulatory effect TRH has on Prolactin. * **Option D (None):** Incorrect, as TRH has well-documented stimulatory effects on both hormones. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Primary Hypothyroidism Connection:** In patients with primary hypothyroidism (low T3/T4), there is a compensatory increase in TRH levels due to the loss of negative feedback. This elevated TRH can lead to **hyperprolactinemia**, which clinically manifests as galactorrhea, amenorrhea, or infertility. * **Dopamine's Role:** Remember that Dopamine is the primary *inhibitor* of both Prolactin (major) and TSH (minor). * **Diagnostic Use:** The TRH stimulation test was historically used to differentiate between secondary (pituitary) and tertiary (hypothalamic) hypothyroidism.

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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