Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 81: Which of the following hormones act through nuclear receptors?

A. Estrogen, thyroxine, and glucagon
B. Estrogen, thyroxine, and TSH
C. Estrogen, TSH, and Gonadotropin releasing hormone (GnRH)
D. None of the above (Correct Answer)

Explanation: **Explanation:** The mechanism of hormone action is determined by the chemical nature of the hormone. Hormones that are lipid-soluble (lipophilic) can cross the cell membrane and bind to **nuclear or cytoplasmic receptors**, while water-soluble (hydrophilic) hormones bind to **cell surface (membrane) receptors**. **1. Why "None of the above" is correct:** For an option to be correct, *all* hormones listed in that group must act via nuclear receptors. In this question, every option contains at least one hormone that acts via a cell surface receptor (using second messengers like cAMP or IP3/DAG). **2. Analysis of Incorrect Options:** * **Option A:** Estrogen and Thyroxine (T4) act via nuclear receptors. However, **Glucagon** is a peptide hormone that acts via a G-protein coupled receptor (GPCR) and the cAMP second messenger system. * **Option B:** Estrogen and Thyroxine use nuclear receptors. **TSH (Thyroid Stimulating Hormone)**, despite acting on the thyroid gland, is a glycoprotein that binds to membrane-bound GPCRs. * **Option C:** Estrogen uses nuclear receptors. Both **TSH and GnRH** act via cell surface receptors (GnRH uses the Gq-IP3/DAG pathway). **High-Yield NEET-PG Clinical Pearls:** * **Nuclear Receptor Superfamily:** Includes Steroid hormones (Estrogen, Progesterone, Testosterone, Cortisol, Aldosterone), Thyroid hormones (T3, T4), Vitamin D, and Retinoic acid. * **Thyroid Exception:** Unlike most lipid-soluble hormones that bind in the cytoplasm, Thyroid hormone receptors are already bound to DNA in the nucleus even in the absence of the hormone. * **Speed of Action:** Hormones acting via nuclear receptors have a **slow onset** (hours to days) because they require gene transcription and protein synthesis, whereas membrane-receptor hormones (like Epinephrine or Insulin) act almost instantaneously.

Question 82: Which of the following statements about calcitonin is incorrect?

A. It inhibits osteoclast-mediated bone resorption.
B. It increases phosphate excretion in the kidneys.
C. It is useful in treating acute hypercalcemic crisis.
D. It plays a major role in the regulation of calcium levels in humans. (Correct Answer)

Explanation: ### Explanation **Why Option D is the correct (incorrect statement):** While calcitonin is a hypocalcemic hormone, it **does not play a major role** in the day-to-day regulation of serum calcium in healthy humans. This is evidenced by two clinical observations: 1. **Total Thyroidectomy:** Patients do not develop hypercalcemia despite the loss of calcitonin-producing Parafollicular (C) cells. 2. **Medullary Thyroid Carcinoma:** Patients with extremely high levels of calcitonin do not typically present with hypocalcemia. In humans, calcium homeostasis is primarily governed by **Parathyroid Hormone (PTH)** and **1,25-dihydroxyvitamin D3**. **Analysis of other options:** * **Option A (Correct statement):** Calcitonin’s primary mechanism is the direct inhibition of **osteoclasts** via specific receptors, which reduces bone resorption and lowers plasma calcium. * **Option B (Correct statement):** In the kidneys, calcitonin has a phosphaturic effect. It inhibits the reabsorption of phosphate (and to a lesser extent, calcium) in the renal tubules, increasing their excretion. * **Option C (Correct statement):** Due to its rapid onset in inhibiting bone resorption, salmon calcitonin is used clinically in the emergency management of **acute hypercalcemic crisis**, though its effect is short-lived due to tachyphylaxis (receptor downregulation). **High-Yield NEET-PG Pearls:** * **Source:** Secreted by **Parafollicular C-cells** of the thyroid (derived from the **ultimobranchial body** of the neural crest). * **Stimulus:** Hypercalcemia is the primary trigger; **Gastrin** also stimulates its release (preventing post-prandial hypercalcemia). * **Tumor Marker:** Calcitonin is the definitive tumor marker for **Medullary Thyroid Carcinoma (MTC)**. * **Therapeutic Use:** Used in Paget’s disease, osteoporosis, and hypercalcemia. Salmon calcitonin is preferred over human calcitonin due to its higher potency and longer half-life.

Question 83: Which of the following immunoglobulin is characteristic of LATS (Long-Acting Thyroid Stimulator)?

A. IgM
B. IgG (Correct Answer)
C. Glycoprotein
D. IgA

Explanation: **Explanation:** **1. Why IgG is the Correct Answer:** Long-Acting Thyroid Stimulator (LATS) is a historical term for **Thyroid Stimulating Immunoglobulins (TSI)**, which are the hallmark of **Graves' Disease**. These are autoantibodies directed against the TSH receptors on the thyroid follicular cells. Structurally, these antibodies belong to the **IgG class**. Unlike TSH, which has a short half-life, LATS (IgG) has a much longer duration of action, leading to persistent stimulation of the thyroid gland and subsequent hyperthyroidism. **2. Why Other Options are Incorrect:** * **IgM:** This is typically the first antibody produced in an acute immune response and exists as a pentamer. It is not associated with the chronic autoimmune stimulation seen in Graves' disease. * **Glycoprotein:** While TSH (the natural hormone) is a glycoprotein, LATS is an antibody (protein). This option confuses the hormone with the antibody that mimics it. * **IgA:** This immunoglobulin is primarily involved in mucosal immunity (secretory IgA) and is not the mediator of systemic autoimmune thyroiditis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** LATS/TSI acts as an **agonist** at the TSH receptor, stimulating the cAMP pathway. * **Placental Transfer:** Because LATS is an **IgG**, it can cross the placenta. This explains why infants born to mothers with Graves' disease may suffer from **Neonatal Thyrotoxicosis**. * **Diagnosis:** While LATS was the term used in early bioassays, modern clinical practice uses **TRAb (TSH Receptor Antibody)** assays. * **Type of Hypersensitivity:** Graves' disease is a classic example of **Type II Hypersensitivity** (Antibody-mediated cellular dysfunction).

Question 84: Prolactin secretion is inhibited by which of the following?

A. Dopamine excess (Correct Answer)
B. Metoclopramide
C. Hypothyroidism
D. Emotional stress

Explanation: **Explanation:** The regulation of prolactin (PRL) is unique among anterior pituitary hormones because it is under **tonic inhibitory control** by the hypothalamus. **1. Why Option A is Correct:** The primary Prolactin Inhibiting Factor (PIF) is **Dopamine**. Dopamine is secreted by the tuberoinfundibular neurons into the hypophyseal portal system. It binds to **D2 receptors** on the lactotrophs in the anterior pituitary, leading to the inhibition of prolactin synthesis and release. Therefore, an excess of dopamine directly suppresses prolactin levels. **2. Why the Other Options are Incorrect:** * **B. Metoclopramide:** This is a dopamine (D2) receptor antagonist. By blocking the inhibitory effect of dopamine, it causes a rise in prolactin levels (hyperprolactinemia). * **C. Hypothyroidism:** In primary hypothyroidism, low levels of thyroid hormones lead to a compensatory increase in **Thyrotropin-Releasing Hormone (TRH)**. TRH acts as a potent prolactin-releasing factor; thus, hypothyroidism is a common cause of hyperprolactinemia. * **D. Emotional Stress:** Prolactin is a stress-responsive hormone. Physical or emotional stress stimulates the release of prolactin via various neuroendocrine pathways. **High-Yield Clinical Pearls for NEET-PG:** * **Prolactinoma:** The most common secretory tumor of the pituitary. Treatment of choice is medical (Dopamine agonists like **Cabergoline** or Bromocriptine), not surgery. * **Stalk Effect:** Any lesion compressing the pituitary stalk prevents dopamine from reaching the pituitary, leading to elevated prolactin (the only pituitary hormone that increases when the stalk is cut). * **Hook Effect:** In cases of extremely high prolactin (giant prolactinomas), lab assays may show falsely low levels; serial dilution is required for accurate diagnosis.

Question 85: Which one of the following statements regarding Growth Hormone (GH) secretion is true?

A. GH secretion increases after exercise, stress, and hypoglycemia. (Correct Answer)
B. GH secretion is maximum during the evening.
C. GH is produced equally in all age groups.
D. GH decreases circulating IGF and somatostatin.

Explanation: ### Explanation **Correct Answer: A. GH secretion increases after exercise, stress, and hypoglycemia.** Growth Hormone (GH) is a stress hormone regulated by the hypothalamus via Growth Hormone-Releasing Hormone (GHRH). Secretion is stimulated by physiological stressors such as **exercise, physical trauma, and emotional stress**. Additionally, **hypoglycemia** is a potent stimulator of GH (used clinically in the Insulin Tolerance Test), as GH acts as a counter-regulatory hormone that increases blood glucose levels by antagonizing insulin action. **Analysis of Incorrect Options:** * **Option B:** GH secretion is not maximum in the evening; it follows a **pulsatile, diurnal rhythm**. The largest burst occurs during **deep sleep (Stage 3 and 4 NREM)**, typically shortly after falling asleep. * **Option C:** GH production is not equal across age groups. It peaks during **adolescence** (pubertal growth spurt) and progressively declines with age (somatopause). * **Option D:** GH **increases** the synthesis of **IGF-1** (Insulin-like Growth Factor 1) in the liver, which mediates most of its growth-promoting effects. Furthermore, GH stimulates the release of **Somatostatin** from the hypothalamus as part of a negative feedback loop to inhibit further GH release. **High-Yield Facts for NEET-PG:** * **Inhibitors of GH:** Hyperglycemia, increased free fatty acids, obesity, and Somatostatin (GHIH). * **Stimulators of GH:** Arginine (amino acids), Ghrelin (from the stomach), and deep sleep. * **Clinical Correlation:** Laron Dwarfism is caused by GH receptor insensitivity (high GH, low IGF-1), whereas Pituitary Gigantism/Acromegaly is due to GH excess.

Question 86: Aldosterone secretion is controlled by all of the following except:

A. ACTH
B. Increase in ECF volume (Correct Answer)
C. Increase in potassium ion concentration in ECF
D. Decrease in the sodium ion concentration in ECF

Explanation: ### Explanation **Core Concept:** Aldosterone is the primary mineralocorticoid secreted by the **Zona Glomerulosa** of the adrenal cortex. Its primary function is to maintain blood pressure and electrolyte balance by promoting sodium reabsorption and potassium excretion. The regulation of aldosterone is a "negative feedback" loop triggered by factors indicating low blood pressure or electrolyte imbalance. **Why "Increase in ECF volume" is the correct answer:** Aldosterone secretion is stimulated by factors that signal a need to *increase* blood volume (like dehydration or hemorrhage). An **increase in ECF volume** actually **inhibits** aldosterone secretion. When ECF volume rises, stretch receptors in the atria release **Atrial Natriuretic Peptide (ANP)**, which directly inhibits aldosterone release to promote sodium and water excretion (natriuresis). **Analysis of Incorrect Options:** * **ACTH (Option A):** While not the primary regulator, ACTH is necessary for the "tonic" secretion of aldosterone. In acute stress, ACTH can cause a transient increase in aldosterone levels. * **Increase in Potassium (Option C):** This is the **most potent** direct stimulator of aldosterone. Even a slight rise in serum $K^+$ directly depolarizes the cells of the zona glomerulosa, triggering aldosterone release to facilitate $K^+$ excretion. * **Decrease in Sodium (Option D):** Hyponatremia (or decreased NaCl delivery to the macula densa) activates the **Renin-Angiotensin-Aldosterone System (RAAS)**. Angiotensin II then acts as a powerful secretagogue for aldosterone. **High-Yield Clinical Pearls for NEET-PG:** * **Potency Hierarchy:** $K^+$ concentration and Angiotensin II are the primary regulators; ACTH is permissive/secondary. * **Conn’s Syndrome:** Primary hyperaldosteronism characterized by hypertension, hypokalemia, and **low renin** levels. * **Aldosterone Escape:** In states of primary excess (like Conn’s), the body does not develop massive edema because the increased ECF volume eventually triggers ANP, leading to "escape" from further sodium retention.

Question 87: Primary Adrenal Insufficiency causes all of the following, except?

A. Low Blood Pressure
B. Decrease in Extracellular Fluid (ECF)
C. Decreased sodium-potassium ratio
D. Increased protein breakdown (Correct Answer)

Explanation: **Explanation:** Primary Adrenal Insufficiency (Addison’s Disease) is characterized by the destruction of the adrenal cortex, leading to a deficiency of both **Mineralocorticoids (Aldosterone)** and **Glucocorticoids (Cortisol)**. **Why "Increased protein breakdown" is the correct answer:** Cortisol is a catabolic hormone. Its primary role in protein metabolism is to stimulate the breakdown of proteins in peripheral tissues (like muscle) to provide amino acids for gluconeogenesis. In adrenal insufficiency, there is a **deficiency of cortisol**, which leads to **decreased protein breakdown** and impaired gluconeogenesis. Therefore, increased protein breakdown does not occur. **Analysis of incorrect options:** * **Low Blood Pressure:** Aldosterone deficiency leads to "pressure natriuresis" (loss of sodium and water), resulting in hypovolemia. Additionally, cortisol is required to maintain the sensitivity of blood vessels to catecholamines. Lack of both leads to hypotension. * **Decrease in ECF:** The loss of sodium (and consequently water) due to lack of aldosterone directly reduces the extracellular fluid volume. * **Decreased sodium-potassium ratio:** Aldosterone normally causes Na+ reabsorption and K+ excretion. Its absence leads to **Hyponatremia** and **Hyperkalemia**, which mathematically decreases the Na+:K+ ratio (a classic diagnostic marker). **High-Yield Clinical Pearls for NEET-PG:** * **Hyperpigmentation:** Seen only in *Primary* Adrenal Insufficiency due to compensatory increase in ACTH (which shares a precursor with MSH, POMC). * **Electrolyte Triad:** Hyponatremia, Hyperkalemia, and Metabolic Acidosis. * **Gold Standard Test:** ACTH Stimulation Test (Cosyntropin test). * **Crisis Management:** Immediate IV Hydrocortisone and aggressive fluid resuscitation with Normal Saline.

Question 88: Laron dwarfism is caused by which of the following?

A. Deficiency of Growth Hormone (GH)
B. GH receptor defect (Correct Answer)
C. Deficiency of thyroxin
D. Thyroxin receptor defect

Explanation: **Explanation:** **Laron Dwarfism (Laron Syndrome)** is an autosomal recessive condition characterized by a mutation in the **Growth Hormone Receptor (GHR)** gene. In this condition, the body produces normal or even elevated levels of Growth Hormone (GH), but the receptors are non-functional. Consequently, the liver cannot produce **Insulin-like Growth Factor-1 (IGF-1)** in response to GH. Since IGF-1 is the primary mediator of GH’s growth-promoting effects on bone and cartilage, its absence leads to severe short stature. **Analysis of Options:** * **Option B (Correct):** The primary pathology is a **GH receptor defect** (insensitivity to GH). Laboratory findings typically show **High GH** and **Low IGF-1**. * **Option A:** Deficiency of GH causes **Pituitary Dwarfism**. Unlike Laron syndrome, these patients respond to exogenous GH therapy. * **Option C:** Deficiency of thyroxin in childhood leads to **Cretinism**, characterized by stunted growth and significant mental retardation. * **Option D:** Thyroxin receptor defects lead to **Thyroid Hormone Resistance Syndrome (Refetoff Syndrome)**, which presents with features of hypothyroidism or goiter, but is not the cause of Laron dwarfism. **High-Yield Clinical Pearls for NEET-PG:** * **Hallmark Lab Profile:** ↑ GH, ↓ IGF-1, and ↓ GH-Binding Protein (GHBP). * **Clinical Feature:** Patients often have a characteristic "doll-like" face (prominent forehead, depressed nasal bridge) and a high-pitched voice. * **Metabolic Paradox:** Interestingly, individuals with Laron syndrome have a significantly **reduced risk of developing cancer and Type 2 Diabetes Mellitus**, despite their growth deficits. * **Treatment:** Since the defect is at the receptor level, exogenous GH is ineffective. Treatment requires **recombinant IGF-1 (Mecasermin)**.

Question 89: What are elevated urine levels of 5-hydroxyindoleacetic acid (5-HIAA) suggestive of?

A. Carcinoid tumors (Correct Answer)
B. Colon cancer
C. Malignant melanoma
D. None of the above

Explanation: **Explanation:** **1. Why Carcinoid Tumors is correct:** Carcinoid tumors are neuroendocrine tumors, most commonly found in the gastrointestinal tract (ileum) and lungs. These tumors secrete excessive amounts of **Serotonin (5-hydroxytryptamine)**. In the body, serotonin is metabolized by the enzyme monoamine oxidase (MAO) into **5-hydroxyindoleacetic acid (5-HIAA)**, which is then excreted in the urine. Therefore, a 24-hour urinary 5-HIAA test is the gold standard biochemical marker for diagnosing Carcinoid Syndrome. **2. Why other options are incorrect:** * **Colon Cancer:** Adenocarcinoma of the colon does not typically secrete serotonin; its primary tumor marker is Carcinoembryonic Antigen (CEA). * **Malignant Melanoma:** This is a malignancy of melanocytes. While melanocytes and neuroendocrine cells both share embryological origins (neural crest), melanoma is associated with urinary **VMA (Vanillylmandellic acid)** only in rare cases, but never 5-HIAA. The primary markers are S100 and HMB-45. **3. Clinical Pearls for NEET-PG:** * **The Pathway:** Tryptophan → 5-Hydroxytryptophan → Serotonin → 5-HIAA. * **Dietary Interference:** Patients must avoid serotonin-rich foods (bananas, walnuts, pineapples, avocados) for 48 hours before the test to prevent false positives. * **Pellagra Connection:** Because the tumor diverts up to 60% of the body's **Tryptophan** to make serotonin, patients may develop **Niacin (Vitamin B3) deficiency**, leading to Pellagra (Dermatitis, Diarrhea, Dementia). * **Rule of Thumb:** Carcinoid syndrome (flushing, diarrhea, wheezing) usually occurs only after the tumor has metastasized to the **liver**, bypassing the portal circulation's first-pass metabolism.

Question 90: Corticosteroids increase all of the following components, EXCEPT:

A. Platelets
B. RBCs
C. Eosinophils (Correct Answer)
D. Monocytes

Explanation: ### Explanation Corticosteroids (Glucocorticoids) have a profound effect on the distribution and concentration of various blood cells. The key to answering this question lies in distinguishing between the cells that **increase** in the peripheral blood versus those that **decrease**. #### Why Eosinophils is the Correct Answer: Glucocorticoids cause a **decrease** in the peripheral count of **Eosinophils, Lymphocytes, Monocytes, and Basophils**. This occurs through two primary mechanisms: 1. **Redistribution:** Cells are sequestered away from the blood into other compartments (like the bone marrow, spleen, and lymph nodes). 2. **Increased Apoptosis:** Specifically in eosinophils and lymphocytes. Therefore, corticosteroids do **not** increase eosinophils; they cause eosinopenia. #### Why the Other Options are Incorrect: * **Platelets (A):** Corticosteroids typically cause a mild to moderate **increase** in the platelet count. * **RBCs (B):** Glucocorticoids stimulate erythropoiesis in the bone marrow and inhibit the phagocytosis of RBCs, leading to polycythemia (an **increase** in RBC count). * **Monocytes (D):** While chronic administration can eventually lead to monocytopenia, the most classic "increase" in the context of steroid-induced leukocytosis refers to **Neutrophils**. However, in the context of this specific question, Eosinophils are the most definitive "decrease" (Eosinopenia is a hallmark of steroid action). --- ### High-Yield NEET-PG Pearls: * **The "Steroid Rule":** Steroids **increase** "BPN" (**B**-cells/Platelets, **P**olycythemia/RBCs, **N**eutrophils) and **decrease** "ELMB" (**E**osinophils, **L**ymphocytes, **M**onocytes, **B**asophils). * **Neutrophilia Mechanism:** Steroids cause neutrophilia not by increasing production, but by **decreasing the margination** of neutrophils (demargination). They prevent neutrophils from sticking to the blood vessel walls, causing them to remain in the circulating pool. * **Clinical Correlation:** Because steroids cause lymphocytopenia and eosinopenia, they are used to treat leukemias and allergic conditions.

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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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