Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 281: Growth hormone does not cause which of the following conditions?

A. Gigantism
B. Acromegaly
C. Diabetes mellitus
D. Hypothyroidism (Correct Answer)

Explanation: Growth hormone (GH) is a potent anabolic hormone with diverse metabolic effects. To answer this question, one must understand the physiological consequences of GH excess and its interaction with other endocrine axes. **Explanation of the Correct Answer:** **D. Hypothyroidism:** Growth hormone does not cause hypothyroidism; in fact, it has a complex relationship with the thyroid axis. While GH is necessary for the peripheral conversion of T4 to the more active T3, chronic GH excess (as seen in acromegaly) can sometimes lead to a goiter, but it does not characteristically cause a hypothyroid state. Conversely, thyroid hormones are required for normal GH secretion and action. **Analysis of Incorrect Options:** * **A. Gigantism:** This occurs due to GH hypersecretion **before** the fusion of epiphyseal plates in children, leading to excessive linear bone growth. * **B. Acromegaly:** This occurs due to GH hypersecretion **after** the fusion of epiphyseal plates in adults. It is characterized by the enlargement of hands, feet, and facial membrane bones. * **C. Diabetes Mellitus:** GH is a "diabetogenic" hormone. It decreases peripheral glucose uptake (anti-insulin effect) and increases hepatic gluconeogenesis. Chronic excess leads to "Pituitary Diabetes." **High-Yield Clinical Pearls for NEET-PG:** * **Metabolic Effects:** GH increases lipolysis (increasing FFA) and promotes protein synthesis (positive nitrogen balance). * **Mediator:** Most growth-promoting effects of GH are mediated by **IGF-1 (Somatomedin C)**, primarily produced in the liver. * **Screening vs. Gold Standard:** The best screening test for Acromegaly is **Serum IGF-1 levels**. The gold standard confirmatory test is the **Oral Glucose Tolerance Test (OGTT)**; failure of GH to suppress below 1 ng/mL after glucose load is diagnostic. * **Somatostatin:** Also known as GHIH (Growth Hormone Inhibiting Hormone), it inhibits GH release.

Question 282: Which hormone(s) are essential for the maintenance of spermatogenesis?

A. Testosterone (Correct Answer)
B. Follicle-stimulating hormone (FSH)
C. Luteinizing hormone (LH)
D. Prolactin

Explanation: **Explanation:** The maintenance of spermatogenesis is primarily dependent on **Testosterone**. While multiple hormones are involved in the initiation and regulation of the process, high intratesticular concentrations of testosterone (20–50 times higher than serum levels) are absolute requirements for the progression of germ cells through meiosis and their maturation into spermatozoa. * **Why Testosterone is Correct:** Testosterone is produced by Leydig cells under the influence of LH. It acts on **Sertoli cells** to stimulate the conversion of spermatids into mature spermatozoa (spermiogenesis). Without adequate local testosterone, the blood-testis barrier breaks down, and germ cells are prematurely released from the seminiferous epithelium. * **Why FSH is Incorrect:** FSH is essential for the **initiation** of spermatogenesis during puberty and for determining the total sperm count (by stimulating Sertoli cell proliferation). However, in adults, spermatogenesis can be maintained by testosterone alone, albeit at a reduced quantitative level. * **Why LH is Incorrect:** LH acts indirectly. Its primary role is to stimulate Leydig cells to produce testosterone. While LH is necessary for the *supply* of testosterone, it is the testosterone itself that directly maintains the spermatogenic process. * **Why Prolactin is Incorrect:** Prolactin in physiological doses increases the expression of LH receptors on Leydig cells, but it is not a primary driver of spermatogenesis. Pathological elevations (hyperprolactinemia) actually inhibit spermatogenesis by suppressing GnRH. **NEET-PG High-Yield Pearls:** * **Sertoli Cells:** Often called "Nurse Cells"; they contain the androgen receptors required for testosterone's action. * **Inhibin B:** Produced by Sertoli cells; provides negative feedback specifically to FSH. * **Blood-Testis Barrier:** Formed by tight junctions between Sertoli cells; protects developing sperm from the immune system.

Question 283: The feeding center is located in which of the following structures?

A. Lateral hypothalamus (Correct Answer)
B. Ventromedial nucleus
C. Supraoptic nucleus
D. Frontal lobe

Explanation: The regulation of food intake is primarily controlled by the hypothalamus through two opposing centers: the feeding center and the satiety center. **1. Why Lateral Hypothalamus (LH) is correct:** The **Lateral Hypothalamus** is known as the **Feeding Center**. Stimulation of this area leads to hyperphagia (increased eating). Conversely, bilateral lesions of the LH lead to aphagia (refusal to eat) and weight loss. It acts by sensing low glucose levels and secreting orexigenic peptides like **Melanin-Concentrating Hormone (MCH)** and **Orexins (A and B)**, which stimulate appetite. **2. Why other options are incorrect:** * **Ventromedial Nucleus (VMN):** This is the **Satiety Center**. Stimulation causes cessation of eating, while a lesion here leads to hyperphagia and "hypothalamic obesity." * **Supraoptic Nucleus:** This nucleus is primarily involved in water balance. It synthesizes **Antidiuretic Hormone (ADH/Vasopressin)**, which is then transported to the posterior pituitary for release. * **Frontal Lobe:** While the cortex is involved in the conscious desire for food and reward-seeking behavior, the primary physiological "center" for hunger is subcortical (hypothalamic). **Clinical Pearls for NEET-PG:** * **Glucostatic Hypothesis:** The VMN (Satiety center) has glucose receptors. Insulin is required for glucose to enter these cells; hence, in uncontrolled Diabetes Mellitus, the satiety center isn't "satisfied," leading to **polyphagia**. * **Arcuate Nucleus:** This is the "master regulator" that contains **NPY/AgRP** neurons (stimulate feeding) and **POMC/CART** neurons (inhibit feeding). * **Hormonal Control:** **Leptin** (from adipose tissue) and **Insulin** inhibit the feeding center, while **Ghrelin** (from the stomach) is the only peripheral hormone that stimulates the feeding center.

Question 284: A 35-year-old woman presents with heat intolerance and menstrual abnormalities. On examination, a diffusely enlarged thyroid gland is present. Which of the following features will not be present in her?

A. Increased heart rate
B. Increased stroke volume
C. Decreased peripheral vascular resistance
D. Decreased protein breakdown (Correct Answer)

Explanation: ### Explanation The clinical presentation of heat intolerance, menstrual abnormalities, and a diffusely enlarged thyroid gland in a 35-year-old woman is highly suggestive of **Hyperthyroidism** (most likely Graves' disease). #### Why "Decreased protein breakdown" is the correct answer: Thyroid hormones ($T_3$ and $T_4$) are primarily **catabolic** when present in excess. In hyperthyroidism, there is a significant **increase in protein breakdown** (proteolysis) to provide substrates for gluconeogenesis. This leads to negative nitrogen balance, muscle wasting (thyrotoxic myopathy), and proximal muscle weakness. Therefore, "decreased protein breakdown" is incorrect in the context of this disease. #### Why the other options are wrong: * **Increased heart rate (A):** Thyroid hormones increase the expression of $\beta_1$-adrenergic receptors in the heart and have direct chronotropic effects, leading to sinus tachycardia and palpitations. * **Increased stroke volume (B):** Hyperthyroidism increases cardiac contractility (inotropic effect) and decreases afterload, resulting in an increased stroke volume and widened pulse pressure. * **Decreased peripheral vascular resistance (C):** Thyroid hormones cause cutaneous vasodilation (to dissipate excess heat) and metabolic byproduct accumulation in tissues, leading to a decrease in systemic vascular resistance (SVR). #### High-Yield NEET-PG Pearls: * **Metabolic Effect:** Hyperthyroidism increases the Basal Metabolic Rate (BMR) by increasing $Na^+-K^+$ ATPase activity in almost all tissues. * **Lipid Metabolism:** It stimulates lipolysis and increases the expression of LDL receptors in the liver, typically resulting in **decreased** serum cholesterol levels. * **Carbohydrate Metabolism:** It is "diabetogenic" as it increases glucose absorption from the GI tract and enhances glycogenolysis. * **Cardiovascular:** Hyperthyroidism is a common cause of high-output heart failure and atrial fibrillation in the elderly.

Question 285: Hypothyroidism causes central nervous system features due to the presence of which receptor in the brain?

A. TR alpha 1
B. TR alpha 2
C. TR beta 1
D. TR beta 2 (Correct Answer)

Explanation: **Explanation:** Thyroid hormones act through nuclear receptors known as **Thyroid Hormone Receptors (TR)**, which are encoded by two genes: *THRA* (Alpha) and *THRB* (Beta). **Why TR-beta 2 is the correct answer:** The **TR-beta 2 (TRβ2)** isoform is highly specific in its distribution. It is primarily expressed in the **Hypothalamus** and the **Anterior Pituitary gland**. It plays a critical role in the negative feedback mechanism, regulating the secretion of Thyrotropin-Releasing Hormone (TRH) and Thyroid-Stimulating Hormone (TSH). In hypothyroidism, the lack of T3/T4 binding to TRβ2 leads to the neurological and neuroendocrine manifestations associated with the central nervous system's feedback loop. **Analysis of Incorrect Options:** * **TR-alpha 1 (TRα1):** This is the most abundant receptor in the **Heart** and **Skeletal Muscle**. It is responsible for the chronotropic and inotropic effects on the heart. * **TR-alpha 2 (TRα2):** Although widely expressed in the brain, it is considered an **orphan receptor**. It does not bind T3 and actually acts as an antagonist to the effects of other thyroid receptors. * **TR-beta 1 (TRβ1):** This is the predominant isoform found in the **Liver** and **Kidneys**. It is primarily responsible for the metabolic effects of thyroid hormones, such as cholesterol lowering. **High-Yield Clinical Pearls for NEET-PG:** * **Resistance to Thyroid Hormone (RTH) Syndrome:** Usually caused by mutations in the **TR-beta** gene. Patients present with high T3/T4 levels but inappropriately normal or high TSH. * **Most abundant TR in the Brain:** While TRβ2 is specific to the feedback centers, **TRα1** is the most widely distributed isoform in the brain overall, but TRβ2 is the classic answer for CNS-specific endocrine regulation. * **Metabolic Rate:** TR-beta is the primary mediator of the thermogenic and metabolic effects in the liver.

Question 286: Accidental transection of the pituitary stalk can cause which of the following?

A. Diabetes mellitus (Correct Answer)
B. Polyuria
C. Galactorrhea
D. Diabetes insipidus

Explanation: **Explanation:** Accidental transection of the pituitary stalk (infundibulum) disrupts the connection between the hypothalamus and the pituitary gland. This results in the loss of hypothalamic control over the pituitary hormones. **Why Option A (Diabetes Mellitus) is the "Correct" Answer (Context-Specific):** In the context of certain standardized medical exams, this question refers to the **loss of Growth Hormone (GH)** and **ACTH/Cortisol** axis. Since GH and Cortisol are "diabetogenic" (insulin-antagonistic) hormones, their sudden absence leads to increased insulin sensitivity and a drop in blood glucose. However, it is important to note that in standard clinical physiology, stalk transection typically causes **Diabetes Insipidus** and **Hyperprolactinemia**. If "Diabetes Mellitus" is marked as the key, it is likely a technical error in the question source or refers to a paradoxical historical observation; however, **Options B, C, and D are the actual physiological consequences.** **Analysis of Other Options:** * **B. Polyuria & D. Diabetes Insipidus:** These are the most common clinical findings. Transection stops the flow of **ADH (Vasopressin)** from the hypothalamus to the posterior pituitary. Lack of ADH leads to the inability to concentrate urine, resulting in Central Diabetes Insipidus and profound polyuria. * **C. Galactorrhea:** Proatctin is the only anterior pituitary hormone under tonic **inhibition** by the hypothalamus (via Dopamine). Stalk transection removes this "dopaminergic brake," leading to increased Prolactin levels (Hyperprolactinemia) and potential galactorrhea. **NEET-PG High-Yield Pearls:** 1. **Stalk Effect:** Disruption of the pituitary stalk causes a decrease in all anterior pituitary hormones **EXCEPT Prolactin**, which rises. 2. **Posterior Pituitary:** ADH and Oxytocin are synthesized in the **Supraoptic** and **Paraventricular** nuclei of the hypothalamus, not the pituitary itself. 3. **Triphasic Response:** Permanent Diabetes Insipidus often follows a triphasic pattern after stalk injury: (1) Initial DI, (2) SIADH-like phase due to leaking stored ADH, (3) Permanent DI.

Question 287: Dwarfism is caused by all EXCEPT:

A. Thyroid deficiency
B. Growth hormone deficiency
C. Castration before puberty (Correct Answer)
D. GH-receptor unresponsiveness

Explanation: **Explanation:** The core concept in this question is the distinction between **short stature (dwarfism)** and **delayed epiphyseal closure**. **Why Castration before puberty is the correct answer:** Castration leads to a deficiency of sex steroids (testosterone/estrogen). These hormones are essential for the "pubertal growth spurt" and, more importantly, for the **closure of epiphyseal plates**. In their absence, the epiphyses remain open for a longer duration, allowing growth to continue under the influence of Growth Hormone (GH). This results in **Eunuchoidism**, characterized by tall stature and long limbs (the lower segment being longer than the upper segment), rather than dwarfism. **Analysis of incorrect options:** * **Thyroid deficiency (Hypothyroidism):** Thyroid hormones are permissive for GH action. Congenital hypothyroidism (Cretinism) leads to stunted physical and mental growth, resulting in disproportionate dwarfism. * **Growth hormone deficiency:** GH is the primary driver of postnatal linear growth. Deficiency (Pituitary dwarfism) leads to proportionate dwarfism with normal mental development. * **GH-receptor unresponsiveness:** Also known as **Laron Dwarfism**. Here, GH levels are actually high, but the receptors are defective, leading to a failure in IGF-1 production and subsequent short stature. **High-Yield Clinical Pearls for NEET-PG:** * **Laron Dwarfism:** High GH, Low IGF-1. * **African Pygmies:** Normal GH, Low IGF-1 (post-receptor defect). * **Most common cause of Dwarfism:** Achondroplasia (autosomal dominant, FGFR3 mutation). * **Bone Age vs. Chronological Age:** In endocrine dwarfism (GH/Thyroid deficiency), bone age is typically delayed compared to chronological age.

Question 288: Cyclic AMP (cAMP) acts as a second messenger of which hormone?

A. Follicle-stimulating hormone (FSH) (Correct Answer)
B. Growth hormone
C. Thyroxine
D. Insulin

Explanation: ### Explanation **1. Why FSH is Correct:** Follicle-stimulating hormone (FSH) is a peptide hormone that binds to G-protein coupled receptors (GPCRs) on the cell membrane. Upon binding, it activates the enzyme **adenylyl cyclase**, which converts ATP into **cyclic AMP (cAMP)**. cAMP then acts as a second messenger to activate Protein Kinase A (PKA), leading to the physiological effects in the gonads (e.g., follicular development in females and spermatogenesis in males). Other hormones using the cAMP pathway include LH, ACTH, TSH, Glucagon, and PTH. **2. Why the Other Options are Incorrect:** * **Growth Hormone (GH):** GH utilizes the **JAK-STAT pathway** (Janus Kinase-Signal Transducer and Activator of Transcription). It binds to a receptor that lacks intrinsic kinase activity but recruits cytoplasmic kinases. * **Thyroxine (T4):** As a lipid-soluble thyroid hormone, it crosses the cell membrane and binds to **nuclear receptors**. It acts as a transcription factor to alter gene expression directly, requiring no second messenger. * **Insulin:** Insulin binds to a receptor with intrinsic **Tyrosine Kinase** activity. This triggers autophosphorylation and activates the MAP kinase and PI3K pathways. **3. High-Yield Clinical Pearls for NEET-PG:** * **cAMP Pathway Mnemonic:** "FLAT ChAMP" (FSH, LH, ACTH, TSH, CRH, hCG, ADH [V2 receptor], MSH, PTH). * **IP3/DAG Pathway Mnemonic:** "GOAT HAG" (GnRH, Oxytocin, ADH [V1 receptor], TRH, Histamine, Angiotensin II, Gastrin). * **cGMP Pathway:** Used by ANP, BNP, and Nitric Oxide (NO). * **Steroid/Thyroid Hormones:** Always remember they use intracellular/nuclear receptors because they are lipophilic.

Question 289: A patient has an elevated plasma thyroxine (T4) concentration, a low plasma TSH concentration, and her thyroid gland is smaller than normal. What is the most likely explanation for these findings?

A. A lesion in the anterior pituitary that prevents TSH secretion
B. Graves' disease
C. The patient is taking propylthiouracil
D. The patient is taking thyroid extract (Correct Answer)

Explanation: ### Explanation The clinical presentation described is a classic case of **Exogenous Thyrotoxicosis** (Factitious Thyrotoxicosis). **1. Why the Correct Answer is Right:** When a patient takes exogenous thyroid extract (T4), the plasma T4 levels rise. This high concentration of T4 exerts **negative feedback** on the anterior pituitary, significantly inhibiting the secretion of Thyroid Stimulating Hormone (TSH). Since TSH is the primary trophic hormone responsible for the growth and maintenance of the thyroid gland, its chronic suppression leads to **disuse atrophy**, resulting in a thyroid gland that is smaller than normal. **2. Analysis of Incorrect Options:** * **Option A (Pituitary Lesion):** While a pituitary lesion would cause low TSH, it would lead to **low** T4 levels (Secondary Hypothyroidism), not elevated T4. * **Option B (Graves' Disease):** In Graves' disease, Thyroid Stimulating Immunoglobulins (TSI) mimic TSH, leading to high T4 and low TSH. However, TSI also stimulates the growth of the gland, typically causing a **diffuse goiter** (enlarged gland), not a small gland. * **Option C (Propylthiouracil):** PTU inhibits thyroid hormone synthesis. This would lead to low T4 and a compensatory **increase in TSH**, which would likely cause an enlarged thyroid (goiter). **3. NEET-PG High-Yield Pearls:** * **Trophic Effect:** TSH is essential for thyroid cell hypertrophy and hyperplasia. Low TSH = Atrophy; High TSH = Goiter. * **Radioactive Iodine Uptake (RAIU):** In exogenous thyroid intake, RAIU is **decreased** (low) because the endogenous gland is suppressed. In Graves' disease, RAIU is **increased** (high). * **Thyroglobulin Levels:** Low serum thyroglobulin in a thyrotoxic patient is a key marker for exogenous hormone intake, as thyroglobulin is only released during endogenous hormone production.

Question 290: Which of the following has the greatest effect on plasma osmolality?

A. Progesterone
B. Cortisol
C. Vasopressin (Correct Answer)
D. Aldosterone

Explanation: **Explanation:** **Correct Answer: C. Vasopressin (Antidiuretic Hormone - ADH)** Vasopressin is the primary regulator of **plasma osmolality**. It acts on the V2 receptors in the late distal tubule and collecting ducts of the kidney to insert aquaporin-2 channels. This allows for the selective reabsorption of **free water** without solutes. Because osmolality is defined as the concentration of solutes per kilogram of solvent, the addition or removal of free water is the most efficient way to dilute or concentrate the plasma, thereby directly controlling osmolality. **Why the other options are incorrect:** * **Aldosterone (D):** While aldosterone increases sodium reabsorption, it does so via an "isosmotic" process (water follows sodium). Therefore, it primarily affects **Extracellular Fluid (ECF) volume** rather than osmolality. * **Cortisol (B):** This is a glucocorticoid primarily involved in glucose metabolism and the stress response. While it has minor mineralocorticoid activity at high levels, its effect on osmolality is negligible compared to ADH. * **Progesterone (A):** This is a reproductive hormone. While it can compete with aldosterone at the mineralocorticoid receptor (leading to mild natriuresis), it plays no significant role in the acute regulation of plasma osmolality. **High-Yield Clinical Pearls for NEET-PG:** * **Osmoreceptors:** Located in the anterior hypothalamus (OVLT and SFO), they sense a change as small as **1%** in osmolality to trigger ADH release. * **Volume vs. Osmolality:** ADH regulates **Osmolality** (via water); Aldosterone regulates **Volume** (via sodium). * **SIADH:** Characterized by excessive ADH, leading to hyponatremia and low plasma osmolality. * **Diabetes Insipidus:** Characterized by ADH deficiency or resistance, leading to hypernatremia and high plasma osmolality.

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