Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 151: Which hormone inhibits both resorption and formation of bone?

A. Estrogen
B. Vitamin D
C. Glucocorticoids (Correct Answer)
D. Parathormone

Explanation: **Explanation:** Glucocorticoids have a profound, dual inhibitory effect on bone metabolism, making them a common cause of secondary osteoporosis. 1. **Why Glucocorticoids are correct:** * **Inhibition of Formation:** They directly inhibit **osteoblast** proliferation and differentiation. They also increase osteoblast and osteocyte apoptosis, leading to a significant decrease in bone formation. * **Stimulation of Resorption:** While they primarily inhibit formation, they also promote bone resorption by increasing the expression of **RANKL** and decreasing **Osteoprotegerin (OPG)**, which activates osteoclasts. * *Note:* In the context of this specific physiological question, Glucocorticoids are unique because they suppress the cellular activity of the "Bone Remodeling Unit" as a whole, though the net result is rapid bone loss. 2. **Why other options are incorrect:** * **Estrogen:** Inhibits bone resorption (by inducing osteoclast apoptosis) but generally supports bone maintenance; it does not inhibit formation. * **Vitamin D (Calcitriol):** Primarily promotes bone mineralization (formation) by increasing intestinal Calcium and Phosphate absorption. While it can stimulate osteoclasts at high levels, its physiological role is bone health. * **Parathormone (PTH):** Increases bone resorption (via RANKL) to raise serum calcium. Intermittent low doses actually *stimulate* bone formation (anabolic effect), which is the basis for Teriparatide therapy. **High-Yield NEET-PG Pearls:** * **Glucocorticoid-Induced Osteoporosis (GIO):** This is the most common drug-induced osteoporosis. The most rapid bone loss occurs within the first 6 months of therapy. * **Mechanism:** Glucocorticoids also decrease intestinal calcium absorption and increase renal calcium excretion, leading to secondary hyperparathyroidism. * **Bisphosphonates** are the first-line treatment for preventing GIO.

Question 152: What type of estrogen is found in the highest concentration in adult females?

A. Estrone
B. Estriol
C. Estradiol (Correct Answer)
D. None of the above

Explanation: **Explanation:** **Estradiol (E2)** is the correct answer because it is the predominant and most potent form of estrogen in non-pregnant, premenopausal adult females. It is primarily synthesized in the ovaries (granulosa cells) under the influence of FSH. Its concentration fluctuates with the menstrual cycle, peaking just before ovulation. **Analysis of Options:** * **Estrone (E1):** This is the primary estrogen found in **postmenopausal** women. It is weaker than estradiol and is mainly produced through the peripheral conversion of androstenedione in adipose tissue. * **Estriol (E3):** This is the weakest form of estrogen and is found in highest concentrations during **pregnancy**. It is produced in large quantities by the placenta (using precursors from the fetal adrenal glands and liver), serving as a marker of fetal well-being. * **Estradiol (E2):** The "estrogen of the reproductive years." It is 10 times more potent than estrone and 80 times more potent than estriol. **High-Yield Clinical Pearls for NEET-PG:** * **Potency Order:** Estradiol (E2) > Estrone (E1) > Estriol (E3). * **Mnemonic for Sources:** * **E1** (One) = Menopause (Primary one left). * **E2** (Two) = Ovaries (Two ovaries). * **E3** (Three) = Placenta (Three components: Mother, Placenta, Fetus). * **Aromatase:** The key enzyme that converts androgens (testosterone and androstenedione) into estrogens. * **Clinical Correlation:** In Polycystic Ovary Syndrome (PCOS), there is an increased E1:E2 ratio due to the peripheral conversion of excess androgens in adipose tissue.

Question 153: Breastfeeding is maximized during sleep. What is the physiological reason for this phenomenon?

A. Prolactin levels are elevated during sleep. (Correct Answer)
B. Maternal and infant rest promotes increased milk production.
C. The infant's proximity to the mother during sleep facilitates a continuous feeding reflex.
D. Breastfeeding frequency is independent of sleep status.

Explanation: **Explanation:** The correct answer is **A. Prolactin levels are elevated during sleep.** **Physiological Basis:** Prolactin is the primary hormone responsible for the synthesis and secretion of milk (lactogenesis). Its secretion follows a distinct **circadian rhythm** and is highly influenced by the sleep-wake cycle. Prolactin levels begin to rise shortly after the onset of sleep, reaching their peak during the early morning hours (REM and non-REM stages). This nocturnal surge occurs independently of the suckling stimulus, though suckling further enhances release via the neuroendocrine reflex. Therefore, the physiological increase in prolactin during sleep ensures maximal milk production capacity during the night and early morning. **Analysis of Incorrect Options:** * **Option B:** While rest is beneficial for maternal well-being, "rest" itself is not the primary physiological driver of milk synthesis; the hormonal milieu (prolactin) is the definitive factor. * **Option C:** Proximity may facilitate the *opportunity* for feeding, but it does not explain the underlying *physiological* mechanism of increased milk availability. * **Option D:** This is incorrect because prolactin secretion is highly dependent on sleep status and the circadian clock. **NEET-PG High-Yield Pearls:** * **Source:** Prolactin is secreted by **Lactotrophs** (Acidophils) in the Anterior Pituitary. * **Inhibitory Control:** Unlike most pituitary hormones, Prolactin is under tonic inhibition by **Dopamine** (Prolactin-Inhibiting Hormone) from the hypothalamus. * **Stimulatory Factors:** TRH (Thyrotropin-releasing hormone) and Oxytocin can stimulate prolactin release. * **Clinical Correlation:** Night-time breastfeeding is often encouraged to maintain a high milk supply and can also prolong **lactational amenorrhea** due to the inhibitory effect of prolactin on GnRH.

Question 154: Which of the following statements regarding insulin is true?

A. Insulin circulates in the blood bound to RBCs.
B. Insulin is composed of two chains linked by three disulfide bonds. (Correct Answer)
C. Insulin is synthesized by the alpha cells of the islets of Langerhans.
D. The elimination half-life of insulin is 60 minutes after subcutaneous injection.

Explanation: **Explanation:** **1. Why the correct answer is right:** Insulin is a polypeptide hormone synthesized as a single-chain precursor called **proinsulin**. During maturation, the C-peptide is cleaved, leaving two polypeptide chains: the **A-chain** (21 amino acids) and the **B-chain** (30 amino acids). These chains are held together by **three disulfide bonds**: two inter-chain bonds (connecting A and B chains) and one intra-chain bond (within the A-chain). This structure is essential for its biological activity and receptor binding. **2. Why the incorrect options are wrong:** * **Option A:** Insulin circulates in the blood primarily as a **free monomer**. It does not bind to RBCs for transport; rather, it dissolves in the plasma. * **Option C:** Insulin is synthesized and secreted by the **Beta (β) cells** of the islets of Langerhans. Alpha (α) cells are responsible for secreting glucagon. * **Option D:** The plasma half-life of endogenous insulin is very short, approximately **5–6 minutes**. While subcutaneous absorption varies by formulation (rapid vs. long-acting), the biological elimination half-life is nowhere near 60 minutes; it is rapidly degraded by the enzyme **insulinase**, primarily in the liver and kidneys. **3. High-Yield Clinical Pearls for NEET-PG:** * **C-Peptide:** Secreted in equimolar amounts with insulin. It is a key marker to distinguish endogenous insulin production (high C-peptide) from exogenous insulin administration (low/absent C-peptide) in cases of hypoglycemia. * **Zinc:** Insulin is stored in β-cell granules as a **zinc-insulin hexamer**. * **GLUT-4:** Insulin increases glucose uptake in skeletal muscle and adipose tissue by mobilizing GLUT-4 transporters to the cell membrane. * **Chromosomal Location:** The insulin gene is located on the short arm of **chromosome 11**.

Question 155: All of the following are caused by accidental transection of the pituitary stalk, except:

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, leading to specific clinical outcomes. **Why Diabetes Mellitus is the Correct Answer:** **Diabetes Mellitus** is a metabolic disorder characterized by hyperglycemia due to insulin deficiency or resistance. It is unrelated to the pituitary stalk. Pituitary stalk transection actually leads to a **deficiency in Growth Hormone (GH) and ACTH (cortisol)**, both of which are counter-regulatory hormones. Their loss increases insulin sensitivity, which would theoretically lower blood glucose levels rather than cause Diabetes Mellitus. **Analysis of Incorrect Options:** * **Diabetes Insipidus & Polyuria:** The pituitary stalk contains the axons of neurons from the supraoptic and paraventricular nuclei. Transection prevents **Antidiuretic Hormone (ADH)** from reaching the posterior pituitary for storage and release. The resulting ADH deficiency leads to Central Diabetes Insipidus, characterized by the inability to concentrate urine, leading to massive **polyuria**. * **Galactorrhea:** Prolactin is the only anterior pituitary hormone under tonic **inhibition** by the hypothalamus (via Dopamine, the Prolactin-Inhibiting Factor). Stalk transection removes this inhibitory influence ("Stalk Effect"), leading to hyperprolactinemia, which causes **galactorrhea** (inappropriate milk secretion). **High-Yield Clinical Pearls for NEET-PG:** * **The "Stalk Effect":** In any hypothalamic-pituitary lesion, all anterior pituitary hormones decrease **except Prolactin**, which increases. * **Triphasic Response:** Following stalk injury, Diabetes Insipidus may follow a triphasic pattern: 1. Initial polyuria (axonal shock), 2. Intermittent antidiuresis (leakage of stored ADH), 3. Permanent polyuria (depletion of ADH). * **Anterior Pituitary:** Results in panhypopituitarism (low TSH, ACTH, FSH/LH, GH).

Question 156: Excess secretion of aldosterone causes all except?

A. Increased extracellular fluid
B. Very high Na+ in plasma (Correct Answer)
C. Increased blood pressure
D. Natriuresis

Explanation: This question tests your understanding of the **Aldosterone Escape** phenomenon and the renal handling of sodium. ### Why "Very high Na+ in plasma" is the Correct Answer While aldosterone increases sodium reabsorption in the distal convoluted tubule and collecting ducts, it does **not** cause a significant rise in plasma sodium concentration (hypernatremia). This is because: 1. **Water follows Sodium:** As sodium is reabsorbed, water is reabsorbed osmotically in equal proportions, maintaining an isotonic state. 2. **Aldosterone Escape:** The initial increase in ECF volume triggers the release of **Atrial Natriuretic Peptide (ANP)** and increases the pressure natriuresis. This causes the kidneys to "escape" the sodium-retaining effects, leading to a new steady state where sodium excretion matches intake. Thus, plasma Na+ remains within the normal or high-normal range, never "very high." ### Explanation of Incorrect Options * **A. Increased ECF:** Aldosterone causes sodium and water retention, which directly expands the extracellular fluid volume. * **C. Increased Blood Pressure:** ECF expansion leads to increased cardiac output and peripheral resistance, resulting in hypertension (a hallmark of Conn’s Syndrome). * **D. Natriuresis:** This refers to the "Aldosterone Escape." Once the ECF volume expands to a certain point (usually after 2-3 kg of weight gain), the body compensates by increasing sodium excretion (natriuresis) to prevent edema. ### High-Yield Clinical Pearls for NEET-PG * **Conn’s Syndrome Triad:** Hypertension, Hypokalemia, and Metabolic Alkalosis. * **The "Escape" Rule:** Aldosterone escape explains why patients with primary hyperaldosteronism have **hypertension but no clinical edema.** * **Electrolytes:** Aldosterone acts on Principal cells (reabsorb Na+, secrete K+) and Alpha-intercalated cells (secrete H+). Therefore, excess leads to **Hypokalemia** and **Alkalosis**.

Question 157: Which one of the following is present intracellularly in muscle cells?

A. Insulin
B. Corticosteroid (Correct Answer)
C. Epinephrine
D. Glucagon

Explanation: **Explanation:** The location of a hormone's receptor—and thus its presence inside a cell—is primarily determined by its **solubility**. **1. Why Corticosteroid is correct:** Corticosteroids (like cortisol) are **steroid hormones** derived from cholesterol. Being lipophilic (lipid-soluble), they easily diffuse across the phospholipid bilayer of the plasma membrane. Once inside the muscle cell, they bind to **intracellular receptors** (specifically cytoplasmic receptors), which then translocate to the nucleus to act as transcription factors. Therefore, corticosteroids are physically present within the intracellular compartment to exert their effects. **2. Why the other options are incorrect:** * **Insulin (Option A):** A peptide hormone that is water-soluble. It cannot cross the lipid membrane and binds to a **Tyrosine Kinase receptor** located on the cell surface. * **Epinephrine (Option C):** A catecholamine (amino acid derivative). Despite its small size, it is polar and binds to **G-protein coupled receptors (GPCRs)** on the plasma membrane. * **Glucagon (Option D):** A peptide hormone that binds to membrane-bound GPCRs to activate the cAMP second messenger system. **High-Yield NEET-PG Pearls:** * **Intracellular Receptors:** Remember the mnemonic **"VET TV"** (Vitamin D, Estrogen, Testosterone, Thyroid hormones (T3/T4), and Vitamin A/Retinoids). Note that while Thyroid hormones are amines, they are the exception and act intracellularly (nuclear receptors). * **Cytoplasmic vs. Nuclear:** Most steroid receptors (like Corticosteroids) are **cytoplasmic**, while Thyroid and Estrogen receptors are primarily **nuclear**. * **Mechanism of Action:** Hormones with intracellular receptors have a slower onset but longer duration of action compared to membrane-binding hormones because they alter gene transcription.

Question 158: A semen analysis reveals 15 million sperm/ml with a total of 15% motile sperm. What does this signify?

A. Aspermia
B. Asthenozoospermia
C. Oligozoospermia
D. Oligoasthenozoospermia (Correct Answer)

Explanation: **Explanation:** The correct answer is **Oligoasthenozoospermia** because the semen analysis shows abnormalities in both sperm count and sperm motility. 1. **Oligozoospermia:** According to the WHO (2021) criteria, the lower reference limit for sperm concentration is **15 million sperm/ml**. While 15 million is exactly at the cutoff, any value below or at the borderline in clinical scenarios—especially when combined with other defects—is categorized under the "Oligo" (few) spectrum. 2. **Asthenozoospermia:** This refers to reduced sperm motility. The WHO standard requires at least **40% total motility** (or 32% progressive motility). A value of **15% motility** is significantly below the normal range. Since both concentration and motility are impaired, the combined term **Oligoasthenozoospermia** is used. **Analysis of Incorrect Options:** * **Aspermia:** The complete absence of semen (ejaculate), not just sperm. * **Asthenozoospermia:** Only addresses the motility defect (15%) but ignores the borderline/low sperm count. * **Oligozoospermia:** Only addresses the low sperm count but ignores the motility defect. **NEET-PG High-Yield Pearls:** * **Azoospermia:** Absence of sperm in the ejaculate. * **Teratozoospermia:** Abnormal sperm morphology (<4% normal forms). * **Necrozoospermia:** All sperm in the ejaculate are dead. * **Globozoospermia:** A rare condition where sperm have round heads and lack an acrosome ("round-headed sperm"), leading to infertility. * **Normal Semen Volume:** 1.5 to 5.0 ml. * **Fructose:** Produced by seminal vesicles; its absence suggests bilateral congenital absence of the vas deferens or ejaculatory duct obstruction.

Question 159: Which of the following is most likely to result in a decreased rate of aldosterone release?

A. An increase in renin secretion by the kidney
B. A rise in serum potassium
C. A fall in blood pressure in the kidney
D. A decrease in IP3 in cells of the zona glomerulosa (Correct Answer)

Explanation: **Explanation:** Aldosterone is synthesized and secreted by the **zona glomerulosa** of the adrenal cortex. Its release is primarily regulated by the **Renin-Angiotensin-Aldosterone System (RAAS)** and serum potassium levels. **Why Option D is Correct:** Both Angiotensin II and extracellular Potassium (K+) stimulate the zona glomerulosa cells via the **Gq-protein coupled receptor** pathway. Activation of this pathway stimulates the enzyme Phospholipase C, which cleaves PIP2 into **Inositol triphosphate (IP3)** and Diacylglycerol (DAG). IP3 triggers the release of intracellular calcium, which is the crucial signal for aldosterone synthesis. Therefore, a **decrease in IP3** would interrupt this signaling cascade, leading to a decreased rate of aldosterone release. **Why Other Options are Incorrect:** * **Option A:** Increased renin leads to increased Angiotensin II, which is a potent stimulator of aldosterone release. * **Option B:** A rise in serum potassium directly depolarizes the zona glomerulosa cell membrane, opening voltage-gated calcium channels and increasing aldosterone secretion to facilitate K+ excretion. * **Option C:** A fall in renal blood pressure (detected by the juxtaglomerular apparatus) triggers renin release, ultimately increasing aldosterone to promote sodium and water retention. **High-Yield NEET-PG Pearls:** * **Primary Stimuli:** The two most important regulators of aldosterone are **Angiotensin II** and **Hyperkalemia**. * **ACTH Role:** ACTH has a "permissive" effect; it is necessary for aldosterone secretion but does not regulate its minute-to-minute levels (unlike cortisol). * **Atrial Natriuretic Peptide (ANP):** This is the primary hormone that **inhibits** aldosterone secretion by antagonizing the RAAS. * **Mechanism:** Aldosterone acts on the **Principal cells** of the late distal tubule and collecting duct to increase Na+ reabsorption and K+ secretion.

Question 160: Breastfeeding often stimulates which of the following?

A. FSH
B. LH
C. Prolactin initiation (Correct Answer)
D. Suppression of FSH

Explanation: **Explanation:** The act of breastfeeding (suckling) triggers a neuroendocrine reflex known as the **Suckling Reflex**. When an infant suckles, sensory impulses travel from the nipple to the hypothalamus. This results in two primary actions: the inhibition of Dopamine (Prolactin Inhibiting Factor) and the stimulation of Prolactin release from the anterior pituitary. **Prolactin** is the primary hormone responsible for the **initiation and maintenance of milk production** (lactogenesis). **Analysis of Options:** * **Option C (Correct):** Suckling is the strongest physiological stimulus for prolactin secretion. It ensures a continuous supply of milk for the next feed. * **Options A & B (Incorrect):** Breastfeeding does not stimulate FSH or LH. In fact, high levels of Prolactin exert a negative feedback effect on the hypothalamus, inhibiting the pulsatile release of **GnRH** (Gonadotropin-Releasing Hormone). * **Option D (Incorrect):** While breastfeeding does lead to the suppression of FSH and LH (leading to lactational amenorrhea), the *primary* and most direct stimulatory effect of the suckling reflex is the initiation of Prolactin and Oxytocin. Between "initiation" and "suppression," the physiological "stimulation" specifically refers to the hormone being released. **NEET-PG High-Yield Pearls:** * **Prolactin:** Responsible for milk **production** (Anterior Pituitary). * **Oxytocin:** Responsible for milk **ejection** (Milk let-down reflex; Posterior Pituitary). * **Lactational Amenorrhea:** Elevated prolactin inhibits GnRH, which suppresses the LH surge, acting as a natural (but not 100% reliable) form of contraception. * **Dopamine Antagonists:** Drugs like Metoclopramide can increase prolactin levels (galactorrhea) because they block the inhibitory effect of dopamine.

Practice by Chapter

Principles of Endocrine Regulation

Practice Questions

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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