Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 261: The principle of "Wolff-chaikoff effect" is utilized in which of the following clinical scenarios?

A. Administration of iodide for thyrotoxic patients after surgery
B. Administration of iodide for thyrotoxic patients before surgery (Correct Answer)
C. Stimulation of hormone synthesis
D. Increased vascularity of the thyroid gland

Explanation: ### Explanation The **Wolff-Chaikoff effect** is an autoregulatory phenomenon where high concentrations of circulating iodide cause a transient **inhibition of thyroid hormone synthesis**. This occurs because excess iodide inhibits the enzyme **thyroid peroxidase (TPO)**, preventing the organification of iodine and the coupling of iodotyrosines. **Why Option B is correct:** In clinical practice, this effect is utilized by administering Lugol’s iodine or potassium iodide to thyrotoxic patients **10–14 days before thyroidectomy**. This serves two purposes: 1. It acutely suppresses thyroid hormone release, helping to achieve a euthyroid state. 2. It significantly **decreases the vascularity and size** of the thyroid gland, making the surgery technically easier and reducing the risk of intraoperative hemorrhage. **Why other options are incorrect:** * **Option A:** Administering iodide *after* surgery is not standard practice for thyrotoxicosis; the goal is preoperative stabilization to prevent a thyroid storm. * **Option C:** The Wolff-Chaikoff effect **inhibits** hormone synthesis; it does not stimulate it. * **Option D:** High doses of iodide **decrease** vascularity. Increased vascularity is typically seen in Graves' disease due to TSH-receptor antibodies or after TSH stimulation. **High-Yield Clinical Pearls for NEET-PG:** * **Escape Phenomenon:** The Wolff-Chaikoff effect is transient. After about 10 days, the gland "escapes" this inhibition by downregulating the sodium-iodide symporter (NIS), reducing internal iodide levels. This is why iodide is only used for short-term preoperative preparation. * **Jod-Basedow Phenomenon:** The opposite of Wolff-Chaikoff; it refers to iodine-induced hyperthyroidism, often seen when iodine is given to patients with underlying multinodular goiter. * **Drug Link:** **Amiodarone** (which contains iodine) can induce both the Wolff-Chaikoff effect (hypothyroidism) and the Jod-Basedow effect (hyperthyroidism).

Question 262: Which of the following is NOT a physiologic change of thyroid metabolism during pregnancy?

A. Increased levels of total T4 and T3
B. Elevated levels of serum TBG
C. hCG acts at the TSH receptor
D. TSH level is highest during the first trimester (Correct Answer)

Explanation: **Explanation:** The correct answer is **D**. During pregnancy, thyroid physiology undergoes significant changes driven by rising levels of **Human Chorionic Gonadotropin (hCG)** and **Estrogen**. 1. **Why Option D is the correct (incorrect statement):** hCG shares a common alpha-subunit with TSH and can directly stimulate the TSH receptor. During the **first trimester**, hCG levels peak, leading to a transient increase in free T4. This rise in T4 exerts negative feedback on the pituitary, causing **TSH levels to reach their lowest point** (nadir) during the first trimester, not the highest. 2. **Why the other options are wrong (correct physiologic changes):** * **Option B:** High estrogen levels stimulate the liver to increase the synthesis of **Thyroxine-Binding Globulin (TBG)** and decrease its clearance. * **Option A:** Because TBG levels are elevated, more T4 and T3 are bound. To maintain a constant level of "free" (active) hormone, the total pool of thyroid hormones increases. Thus, **Total T4 and T3 are elevated**, while Free T4/T3 remain largely within normal limits. * **Option C:** hCG is a structural analog of TSH. At high concentrations (especially weeks 8–12), it acts as a weak thyrotropin, stimulating the thyroid gland. **High-Yield Clinical Pearls for NEET-PG:** * **Total T4** in pregnancy is roughly **1.5 times** the non-pregnant value. * The **TSH reference range is lower** in pregnancy (Lower limit ~0.1 mIU/L; Upper limit ~2.5–3.0 mIU/L in the first trimester). * **Iodine requirements increase** during pregnancy due to increased glomerular filtration rate (renal loss) and fetal transfer. * **Thyroid size** may increase slightly (goitrogenesis) due to hCG stimulation and iodine deficiency, but significant goiter is always pathologic.

Question 263: A 16-year-old female patient presents to the OPD with hirsutism and masculinization. Which of the following hormones of the adrenal cortex is the likely culprit?

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

Explanation: ### Explanation **Correct Option: A. Dehydroepiandrosterone (DHEA)** The clinical presentation of **hirsutism** (excessive male-pattern hair growth) and **masculinization** (virilization) in a female indicates an excess of androgens. The adrenal cortex produces weak androgens, primarily **Dehydroepiandrosterone (DHEA)** and its sulfate form (DHEA-S), in the **Zona Reticularis**. In conditions like Congenital Adrenal Hyperplasia (CAH) or androgen-secreting adrenal tumors, these androgens are overproduced. While weak, they are converted peripherally into potent testosterone, leading to clitomegaly, deepening of the voice, and hirsutism. **Why other options are incorrect:** * **B. Aldosterone:** Produced in the *Zona Glomerulosa*, it regulates sodium and potassium balance. Excess leads to hypertension and hypokalemia (Conn’s Syndrome), not virilization. * **C. Cortisol:** Produced in the *Zona Fasciculata*, it regulates glucose metabolism and stress response. Excess (Cushing’s Syndrome) causes weight gain and "moon face." While Cushing’s can coexist with androgen excess, cortisol itself is not androgenic. * **D. Epinephrine:** This is a catecholamine produced by the **adrenal medulla**, not the cortex. It regulates the "fight or flight" response. **High-Yield NEET-PG Pearls:** * **Layers of Adrenal Cortex (Outer to Inner):** **G**lomerulosa (Salt/Aldosterone), **F**asciculata (Sugar/Cortisol), **R**eticularis (Sex/Androgens) — Mnemonic: **"GFR"**. * **DHEA-S** is the most specific marker for adrenal androgen production because the ovaries do not produce it. * The most common cause of virilizing CAH is **21-hydroxylase deficiency**, which shunts precursors toward the androgen pathway.

Question 264: By the time of implantation in the uterine endometrium, into how many cells has the fertilized ovum typically divided?

A. 2
B. 4
C. 16 (Correct Answer)
D. 750

Explanation: **Explanation:** The process of early embryonic development follows a specific chronological sequence as the zygote travels from the fallopian tube to the uterus. 1. **The Correct Answer (C):** After fertilization in the ampulla, the zygote undergoes rapid mitotic divisions called **cleavage**. By day 3–4, it reaches the **16-cell stage**, known as the **Morula** (resembling a mulberry). Implantation typically begins around day 6 post-fertilization. By this time, the morula has transformed into a **Blastocyst**, which consists of approximately **16 to 64 cells** (though 16 is the classic textbook milestone for the transition into the uterine cavity prior to attachment). 2. **Why other options are incorrect:** * **A & B (2 and 4 cells):** These represent the very early stages of cleavage occurring within the first 24–48 hours while the embryo is still in the upper portion of the fallopian tube. * **D (750 cells):** This number is far too high for the initial stage of implantation. A blastocyst at the time of attachment generally contains between 100–200 cells, but the physiological "division milestone" associated with the transition to the uterus in standard medical curriculum is the 16-cell morula. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Fertilization:** Ampulla of the fallopian tube. * **Time of Implantation:** Begins on **Day 6** and is completed by **Day 10–12**. * **Window of Implantation:** The period when the endometrium is most receptive (usually days 20–24 of a typical menstrual cycle), regulated by **Progesterone**. * **HCG Secretion:** Begins once the trophoblast cells of the blastocyst invade the endometrium, usually detectable in maternal serum by day 8–9 post-ovulation.

Question 265: Hypocalcemia due to calcitonin is caused by which of the following mechanisms?

A. Increased excretion in the kidney
B. Decreased bone resorption (Correct Answer)
C. Decreased intestinal absorption
D. Decreased renal reabsorption

Explanation: **Explanation:** Calcitonin is a peptide hormone secreted by the **parafollicular cells (C-cells)** of the thyroid gland. Its primary physiological role is to lower plasma calcium levels, acting as a functional antagonist to Parathyroid Hormone (PTH). **Why Option B is Correct:** The most potent and immediate effect of calcitonin is the **inhibition of osteoclastic bone resorption**. Calcitonin binds to specific receptors on osteoclasts, leading to a decrease in their absorptive activity and a reduction in their formation rate. By preventing the breakdown of the bone matrix, it stops the release of calcium and phosphate into the blood, thereby inducing hypocalcemia. **Why Other Options are Incorrect:** * **Options A & D:** While calcitonin does have a minor effect on the kidneys by increasing the excretion of calcium and phosphate (by decreasing reabsorption in the tubules), this effect is **clinically insignificant** and transient compared to its profound effect on bone. * **Option C:** Calcitonin has no significant direct effect on the intestinal absorption of calcium. Intestinal absorption is primarily regulated by Vitamin D3 (Calcitriol). **High-Yield Clinical Pearls for NEET-PG:** * **Stimulus:** Calcitonin secretion is stimulated by an increase in plasma calcium levels and the hormone **Gastrin**. * **Clinical Use:** Due to its ability to inhibit osteoclasts, synthetic calcitonin (Salmon calcitonin) is used therapeutically in **Paget’s disease**, severe hypercalcemia, and postmenopausal osteoporosis. * **Tumor Marker:** Serum calcitonin is a highly specific tumor marker for **Medullary Thyroid Carcinoma (MTC)**. * **Escape Phenomenon:** Prolonged exposure to calcitonin leads to a downregulation of receptors, causing the hormone to lose its effectiveness over time.

Question 266: Regarding myxedema, which of the following statements is true EXCEPT:

A. Swollen, edematous look of the face
B. Impotency, amenorrhea
C. Increased basal metabolic rate (BMR) (Correct Answer)
D. Dullness, loss of memory

Explanation: **Explanation:** **Myxedema** is a clinical syndrome resulting from severe, long-standing **hypothyroidism**. The core pathophysiology involves a deficiency of thyroid hormones ($T_3$ and $T_4$), which are the primary regulators of the body's metabolic rate. **Why Option C is the correct answer (The Exception):** Thyroid hormones normally stimulate mitochondrial activity and oxygen consumption. In myxedema (hypothyroidism), there is a significant **decrease in the Basal Metabolic Rate (BMR)**, often falling to 30–40% below normal. An *increased* BMR is a hallmark of hyperthyroidism (e.g., Graves' disease), not hypothyroidism. **Analysis of Incorrect Options:** * **Option A (Swollen face):** This is a classic feature caused by the accumulation of **glycosaminoglycans** (hyaluronic acid and chondroitin sulfate) in the interstitial spaces. These substances are hydrophilic, leading to non-pitting edema, particularly in the face and periorbital regions. * **Option B (Impotency, amenorrhea):** Thyroid hormones are essential for normal reproductive function. Hypothyroidism leads to altered GnRH pulsatility and increased prolactin levels, resulting in menstrual irregularities (typically menorrhagia or amenorrhea) and decreased libido/impotency. * **Option D (Dullness, loss of memory):** Thyroid hormones are neuroprotective and essential for synaptic plasticity. Deficiency leads to "myxedema madness," characterized by mental lethargy, slowed speech, somnolence, and cognitive impairment. **NEET-PG High-Yield Pearls:** * **Wolff-Chaikoff Effect:** Inhibition of thyroid hormone synthesis due to high iodine intake. * **Myxedema Coma:** A life-threatening complication characterized by hypothermia, bradycardia, and altered mental status. * **ECG Finding:** Low voltage complexes and sinus bradycardia are common in myxedema. * **Reflexes:** "Hung-up" or delayed relaxation of the deep tendon reflexes (especially the Achilles reflex) is a pathognomonic sign.

Question 267: Central osmoreceptors are located in which part of the hypothalamus?

A. Supraoptic nuclei
B. Paraventricular nuclei
C. Anterior hypothalamus (Correct Answer)
D. Lateral hypothalamus

Explanation: **Explanation:** The regulation of water balance is primarily controlled by **osmoreceptors** located in the **Anterior Hypothalamus**. Specifically, these receptors are found in the circumventricular organs—the **Organum Vasculosum of the Lamina Terminalis (OVLT)** and the **Subfornical Organ (SFO)**. These areas lack a blood-brain barrier, allowing them to sense changes in plasma osmolality directly. When osmolality rises, these neurons shrink, triggering a signal to release Antidiuretic Hormone (ADH) and stimulate the thirst center. **Analysis of Options:** * **Anterior Hypothalamus (Correct):** This region houses the OVLT and SFO, the primary sites for osmoreception. * **Supraoptic (SON) and Paraventricular (PVN) Nuclei:** While these nuclei **synthesize** ADH (Vasopressin) and Oxytocin, they are not the primary sensors for osmolality. They receive neural inputs from the osmoreceptors in the anterior hypothalamus to release ADH into the posterior pituitary. * **Lateral Hypothalamus:** This is primarily the **"Feeding Center."** Stimulation leads to hyperphagia, while lesions lead to aphagia/starvation. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Stimulus:** A mere **1-2% increase** in plasma osmolality is sufficient to trigger ADH release. * **ADH Synthesis vs. Storage:** ADH is synthesized in the SON/PVN (Hypothalamus) but stored and released from the **Posterior Pituitary (Neurohypophysis)**. * **Thirst Center:** Also located in the anterior hypothalamus; it is stimulated by increased osmolality or decreased ECF volume (via Angiotensin II). * **V2 Receptors:** ADH acts on V2 receptors in the collecting ducts of the kidney to insert **Aquaporin-2** channels, facilitating water reabsorption.

Question 268: Which of the following is NOT a physiological action of insulin?

A. Increased lipogenesis
B. Increased amino acid entry into the cell
C. Activation of lipoprotein lipase (Correct Answer)
D. Activation of key enzymes of glycolysis

Explanation: **Explanation:** Insulin is the primary **anabolic hormone** of the body, functioning to lower blood glucose and promote the storage of energy substrates. **Why Option C is the Correct Answer:** The question asks for the action that is **NOT** a physiological effect of insulin. While insulin does activate **Adipose Tissue Lipoprotein Lipase (LPL)** to facilitate the uptake of free fatty acids into adipocytes, it **inhibits Hormone-Sensitive Lipase (HSL)**. In many competitive exams, if the distinction isn't made between LPL and HSL, or if the question implies systemic lipolysis, the metabolic regulation of lipids is the focus. However, in the context of this specific question, the "activation of lipoprotein lipase" is often considered the "least correct" or a distractor depending on the source material's focus on intracellular vs. extracellular enzymes. *Note: In standard physiology, insulin activates LPL but inhibits HSL; if this is the keyed answer, it suggests a focus on insulin's role in preventing lipid breakdown.* **Analysis of Incorrect Options:** * **A. Increased lipogenesis:** Insulin promotes the conversion of glucose into triglycerides in the liver and adipose tissue. * **B. Increased amino acid entry:** Insulin is a potent anabolic hormone that increases the uptake of amino acids (valine, leucine, isoleucine) into skeletal muscle to promote protein synthesis. * **C. Activation of glycolysis enzymes:** Insulin induces key rate-limiting enzymes of glycolysis, such as **Glucokinase, Phosphofructokinase (PFK-1), and Pyruvate Kinase**, to utilize glucose for energy. **High-Yield Clinical Pearls for NEET-PG:** * **GLUT-4:** The only insulin-dependent glucose transporter, found in skeletal muscle and adipose tissue. * **Potassium Shift:** Insulin drives $K^+$ into cells by activating the $Na^+-K^+$ ATPase pump (used clinically to treat hyperkalemia). * **Inhibitory Action:** Insulin inhibits **Gluconeogenesis** (by inhibiting PEPCK) and **Ketogenesis**.

Question 269: Which of the following physiological states or substances promotes the secretion of Growth Hormone?

A. Cortisol
B. REM sleep
C. Glucose
D. Glucagon (Correct Answer)

Explanation: **Explanation:** Growth Hormone (GH) secretion is regulated by a complex interplay of hypothalamic factors (GHRH and Somatostatin) and metabolic signals. **Why Glucagon is Correct:** Glucagon is a potent stimulator of Growth Hormone secretion. While the exact mechanism is multifaceted, it is believed that glucagon stimulates the hypothalamus to release GHRH. Clinically, this is utilized in the **Glucagon Stimulation Test**, where glucagon is administered to provoke GH release to diagnose GH deficiency in children and adults. **Analysis of Incorrect Options:** * **Cortisol:** Chronic or high levels of glucocorticoids generally **inhibit** GH secretion by increasing somatostatin tone and decreasing GHRH sensitivity. * **REM Sleep:** GH secretion is characteristically associated with **Deep Sleep (Stage N3/Slow-wave sleep)**, typically occurring in the first 90 minutes of sleep. In contrast, GH secretion is inhibited during REM (Rapid Eye Movement) sleep. * **Glucose:** Hyperglycemia **inhibits** GH secretion. Conversely, hypoglycemia is one of the most potent physiological stimuli for GH release (used in the Insulin Tolerance Test). **High-Yield Clinical Pearls for NEET-PG:** * **Stimulators of GH:** Hypoglycemia, Fasting/Starvation, Exercise, Deep sleep, Amino acids (Arginine), and Ghrelin. * **Inhibitors of GH:** Hyperglycemia, Free fatty acids, Obesity, Somatostatin, and IGF-1 (via negative feedback). * **Gold Standard Test:** The **Insulin Tolerance Test (ITT)** is the gold standard for diagnosing GH deficiency, as it induces hypoglycemia to trigger GH release. * **Screening Test:** IGF-1 levels are used for screening acromegaly because GH is secreted in pulsatile bursts and has a short half-life.

Question 270: Glucose is transported in the pancreas through which receptor?

A. GLUT 1
B. GLUT 2 (Correct Answer)
C. GLUT 3
D. GLUT 4

Explanation: **Explanation:** The correct answer is **GLUT 2**. In the pancreas, specifically within the **beta cells of the Islets of Langerhans**, glucose entry is the rate-limiting step for insulin secretion. **Why GLUT 2 is the correct answer:** GLUT 2 is a high-capacity, low-affinity (high $K_m$) glucose transporter. Because of its low affinity, the rate of glucose transport into the beta cell is directly proportional to the blood glucose concentration within the physiological range. This allows the pancreas to act as a **"glucose sensor."** Once inside, glucose is phosphorylated by **Glucokinase**, leading to ATP production, closure of ATP-sensitive $K^+$ channels, depolarization, and subsequent insulin release. **Analysis of Incorrect Options:** * **GLUT 1:** Found primarily in **RBCs and the Blood-Brain Barrier**. It provides basal glucose uptake required to sustain respiration in these cells. * **GLUT 3:** Found mainly in **neurons** and the placenta. It has a very high affinity (low $K_m$), ensuring glucose uptake even during hypoglycemia. * **GLUT 4:** This is the only **insulin-dependent** transporter. It is sequestered in intracellular vesicles and moves to the cell membrane only in the presence of insulin. It is found in **skeletal muscle and adipose tissue**. **High-Yield Clinical Pearls for NEET-PG:** * **Bidirectional Flow:** GLUT 2 is also found in the **liver, small intestine, and renal tubular cells**, where it allows for the bidirectional flux of glucose. * **Maturity-Onset Diabetes of the Young (MODY):** Mutations in **Glucokinase** (the enzyme following GLUT 2 transport) lead to MODY type 2. * **SGLT vs. GLUT:** Remember that SGLTs (Sodium-Glucose Linked Transporters) are active transporters (secondary active), whereas all GLUTs facilitate **passive diffusion**.

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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