Endocrinology — MCQs

A 70-year-old female patient with Alzheimer's disease, who has not eaten or drunk for 24 hours, is found mildly confused and dehydrated. Blood glucose levels are normal. Which one of the following hormones is responsible for maintaining normal blood glucose levels and acts on intracellular receptors?

Q337Easy

Melatonin is associated with all of the following except?

Q338Easy

Suprarenal medulla secretes which hormones?

Q339Easy

Which is the "showste" hormone?

Q340Medium

Removal of the parathyroid gland produces the following changes EXCEPT?

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 331: Steroid hormones exert their effects by binding to which of the following?

A. Cell surface receptors
B. G proteins
C. Transcription factors (Correct Answer)
D. Cyclic adenosine monophosphate (cAMP)

Explanation: **Explanation:** **Mechanism of Action (Steroid Hormones):** Steroid hormones (e.g., Cortisol, Aldosterone, Estrogen, Testosterone) are **lipophilic** (lipid-soluble) molecules derived from cholesterol. Due to their chemical nature, they easily diffuse across the lipid bilayer of the cell membrane. Once inside the cell, they bind to specific **intracellular receptors** located in the cytoplasm or nucleus. The resulting hormone-receptor complex then translocates into the nucleus (if not already there), where it binds to specific DNA sequences known as **Hormone Response Elements (HREs)**. In this capacity, the complex acts directly as a **transcription factor**, modulating the transcription of specific genes into mRNA, ultimately leading to new protein synthesis. **Analysis of Incorrect Options:** * **A & B (Cell surface receptors & G proteins):** These are typically utilized by **peptide/protein hormones** (e.g., Insulin, Glucagon, PTH) and catecholamines. These hormones are water-soluble and cannot cross the cell membrane, thus requiring membrane-bound receptors and G-protein coupling to relay signals. * **D (cAMP):** This is a **second messenger** used by many peptide hormones (via the Adenylyl Cyclase pathway). Steroid hormones do not generally require second messengers because they act directly on the genome. **NEET-PG High-Yield Pearls:** * **Exception to the Rule:** **Thyroid hormones (T3, T4)** are not steroids (they are amino acid derivatives), but they also act via nuclear receptors/transcription factors. * **Speed of Action:** Steroid hormone effects have a **slow onset** (hours to days) because they require gene transcription and protein synthesis, unlike peptide hormones which trigger rapid post-translational changes. * **Receptor Location:** Most steroid receptors are cytoplasmic (e.g., Glucocorticoids), but Estrogen and Progesterone receptors are primarily nuclear.

Question 332: A patient presents with a large, protruding jaw; large hands and feet; normal height; and an elevated blood glucose level. What is the most likely diagnosis?

A. Elevated blood levels of aldosterone and renin resulting from an atherosclerotic plaque in a renal artery.
B. Hyperprolactinemia due to a pituitary tumor.
C. Acromegaly due to a growth hormone-producing tumor that developed in adulthood. (Correct Answer)
D. Cushing syndrome due to an adrenal tumor.

Explanation: ### Explanation **Correct Option: C (Acromegaly)** The clinical presentation of a **protruding jaw (prognathism)**, **enlarged hands and feet (acral enlargement)**, and **hyperglycemia** is a classic description of **Acromegaly**. This condition results from the hypersecretion of Growth Hormone (GH) from a pituitary adenoma occurring **after the closure of epiphyseal plates** (adulthood). * **Why normal height?** Because the epiphyses have fused, linear bone growth is impossible; instead, bones increase in thickness and soft tissues hypertrophy. * **Why elevated glucose?** GH is a "diabetogenic" hormone; it increases hepatic gluconeogenesis and causes peripheral insulin resistance. **Incorrect Options:** * **Option A:** Renal artery stenosis leads to secondary hyperaldosteronism (Conn-like symptoms), causing hypertension and hypokalemia, not skeletal changes. * **Option B:** Hyperprolactinemia typically presents with galactorrhea, amenorrhea, and infertility, without the bony overgrowth seen here. * **Option C:** Cushing syndrome presents with "Moon facies," "Buffalo hump," and central obesity. While it causes hyperglycemia, it does not cause enlargement of the jaw or extremities. **NEET-PG High-Yield Pearls:** * **Screening Test:** Serum **IGF-1** levels (more stable than GH). * **Gold Standard Diagnostic Test:** **Glucose Suppression Test** (Failure to suppress GH below 1 ng/mL after 75g oral glucose). * **Most Common Cause of Death:** Cardiovascular disease (specifically Cardiomyopathy). * **Visual Field Defect:** Bitemporal hemianopia (due to optic chiasm compression by the pituitary macroadenoma). * **Gigantism vs. Acromegaly:** Gigantism occurs *before* epiphyseal fusion, leading to increased height.

Question 333: Which of the following statements is correct regarding milk secretion?

A. The neuroendocrine pathway involving the posterior pituitary is implicated. (Correct Answer)
B. Secretion occurs due to the contraction of lactiferous sinuses stimulated by oxytocin.
C. Vasopressin hormone plays a role in milk secretion.
D. Milk secretion is affected by emotional state.

Explanation: ### Explanation **1. Why Option A is Correct:** Milk secretion (specifically **milk ejection** or the "let-down reflex") is a classic example of a **neuroendocrine reflex**. When an infant suckles, tactile receptors on the nipple send afferent impulses to the hypothalamus. This triggers the **posterior pituitary** to release **oxytocin** into the bloodstream. Oxytocin then travels to the breast, causing contraction of the myoepithelial cells surrounding the alveoli, forcing milk into the ducts. Because this process involves both neural signaling and hormonal secretion from the posterior pituitary, it is a neuroendocrine pathway. **2. Why the Other Options are Incorrect:** * **Option B:** Oxytocin does not act on the lactiferous sinuses; it stimulates the **myoepithelial cells** surrounding the **alveoli**. The sinuses are merely storage areas. * **Option C:** **Vasopressin (ADH)** is primarily involved in water reabsorption in the kidneys and vasoconstriction. While it is structurally similar to oxytocin and also stored in the posterior pituitary, it plays no physiological role in milk secretion. * **Option D:** While this statement is technically true in a physiological sense (stress can inhibit the reflex), in the context of standard medical examinations, **Option A** is the most definitive description of the mechanism. *Note: In some contexts, D is considered a secondary factor, but A defines the fundamental physiological pathway.* **3. High-Yield NEET-PG Pearls:** * **Prolactin vs. Oxytocin:** Prolactin (Anterior Pituitary) is for milk **production/synthesis**; Oxytocin (Posterior Pituitary) is for milk **ejection/let-down**. * **Inhibitory Factor:** Dopamine acts as the Prolactin Inhibiting Hormone (PIH). * **Galactopoiesis:** The maintenance of established milk secretion. * **Fergusson Reflex:** Oxytocin also causes uterine contractions during labor via a similar neuroendocrine mechanism.

Question 334: Normal thyroid weight varies with dietary iodine content?

A. Directly proportional
B. Inversely (Correct Answer)
C. Inverse cubically
D. Not fixed

Explanation: **Explanation:** The size and weight of the thyroid gland are primarily regulated by **Thyroid Stimulating Hormone (TSH)**. The relationship between dietary iodine and thyroid weight is **inversely proportional** due to the negative feedback loop of the Hypothalamic-Pituitary-Thyroid (HPT) axis. 1. **Why "Inversely" is correct:** When dietary iodine intake is low, the thyroid cannot produce sufficient T3 and T4. This lack of negative feedback causes the anterior pituitary to secrete more TSH. TSH acts as a growth factor, causing hypertrophy and hyperplasia of thyroid follicular cells to maximize iodine uptake. This results in an increase in thyroid weight (Goiter). Conversely, adequate iodine intake maintains normal TSH levels and normal gland weight. 2. **Why other options are wrong:** * **Directly proportional:** This would imply that more iodine leads to a larger gland, which is physiologically incorrect (except in rare cases of Jod-Basedow phenomenon, which is a pathological state, not a normal physiological variation). * **Inverse cubically:** There is no mathematical cubic relationship described in physiological literature for this mechanism. * **Not fixed:** While thyroid weight does vary, it follows a specific physiological pattern rather than being random or "not fixed." **High-Yield Clinical Pearls for NEET-PG:** * **Normal Thyroid Weight:** Approximately 15–25 grams in adults (varies by region). * **Wolff-Chaikoff Effect:** A transient reduction in thyroid hormone synthesis following ingestion of a large load of iodine. * **Goitrogens:** Substances (like cabbage, turnips, or cassava) that interfere with iodine uptake, leading to increased TSH and increased thyroid weight. * **Daily Iodine Requirement:** ~150 μg/day for adults; higher (220–290 μg/day) during pregnancy and lactation.

Question 335: Which of the following statements regarding calcitonin is FALSE?

A. It has a short-term use in patients with hypercalcemia.
B. It inhibits osteoclastic activity.
C. High concentrations in the plasma are seen in medullary carcinoma of the thyroid.
D. Its actions are similar to parathyroid hormone. (Correct Answer)

Explanation: **Explanation** The correct answer is **D** because Calcitonin and Parathyroid Hormone (PTH) are **physiological antagonists**. While PTH acts to increase serum calcium levels (hypercalcemic hormone), Calcitonin acts to decrease them (hypocalcemic hormone). **Why Option D is False:** Calcitonin and PTH have opposing effects on bone and kidneys. PTH stimulates osteoclasts to resorb bone and increases renal calcium reabsorption. In contrast, Calcitonin inhibits bone resorption and promotes renal calcium excretion. **Analysis of Other Options:** * **Option A:** Calcitonin is used for the acute management of hypercalcemic crisis. However, its effect is short-lived due to **"tachyphylaxis"** (downregulation of receptors), making it unsuitable for long-term therapy. * **Option B:** The primary mechanism of Calcitonin is the direct inhibition of **osteoclasts**, which reduces the release of calcium and phosphate from the bone matrix into the plasma. * **Option C:** Calcitonin is secreted by the **Parafollicular cells (C-cells)** of the thyroid. Medullary Thyroid Carcinoma (MTC) originates from these cells; thus, serum Calcitonin serves as a specific tumor marker for diagnosis and monitoring recurrence. **High-Yield Clinical Pearls for NEET-PG:** * **Major Stimulus:** An increase in plasma calcium concentration is the primary stimulus for Calcitonin secretion. * **Salmon Calcitonin:** Used therapeutically (e.g., in Paget’s disease) because it is more potent and has a longer half-life than human calcitonin. * **Bone Sparing:** Unlike PTH, Calcitonin is "bone-sparing" and is sometimes used in the treatment of osteoporosis to reduce vertebral fractures.

Question 336: A 70-year-old female patient with Alzheimer's disease, who has not eaten or drunk for 24 hours, is found mildly confused and dehydrated. Blood glucose levels are normal. Which one of the following hormones is responsible for maintaining normal blood glucose levels and acts on intracellular receptors?

A. Epinephrine
B. Cortisol (Correct Answer)
C. Growth hormone
D. Glucagon

Explanation: **Explanation:** The patient is in a state of prolonged fasting (24 hours). To maintain blood glucose levels during fasting, the body initiates **gluconeogenesis** (the synthesis of glucose from non-carbohydrate sources like amino acids and glycerol). **1. Why Cortisol is correct:** Cortisol is a glucocorticoid produced by the adrenal cortex. It plays a vital role in the fasting state by stimulating gluconeogenesis in the liver and decreasing peripheral glucose utilization. Crucially, as a steroid hormone, cortisol is lipophilic and acts via **intracellular (cytoplasmic) receptors**. Once bound, the hormone-receptor complex translocates to the nucleus to modulate gene transcription. **2. Why other options are incorrect:** * **Epinephrine (A):** While it increases blood glucose via glycogenolysis, it is a catecholamine that acts on **cell surface G-protein coupled receptors (GPCRs)**, not intracellular receptors. * **Growth Hormone (C):** It has anti-insulin effects and promotes gluconeogenesis, but it acts via **cell surface receptors** (JAK/STAT pathway). * **Glucagon (D):** This is the primary hormone for acute hypoglycemia/fasting; however, it is a peptide hormone that acts via **cell surface GPCRs** (increasing cAMP). **Clinical Pearls for NEET-PG:** * **Receptor Location Rule:** Steroid hormones (Cortisol, Aldosterone, Estrogen, Progesterone, Testosterone) and Vitamin D act on **intracellular receptors**. Thyroid hormones (T3/T4) act on **intranuclear receptors**. * **Gluconeogenesis:** Cortisol is "permissive" for the actions of glucagon and catecholamines. * **Metabolic Effect:** In the fasting state, cortisol promotes muscle protein catabolism to provide amino acids (like alanine) for hepatic gluconeogenesis.

Question 337: Melatonin is associated with all of the following except?

A. Vomiting (Correct Answer)
B. Pituitary gland secretion
C. Sleep mechanism
D. Jetlag

Explanation: **Explanation:** Melatonin is a hormone synthesized by the **pineal gland** (derived from the amino acid Tryptophan) and is primarily responsible for regulating the body's **circadian rhythm**. **Why 'Vomiting' is the correct answer:** Melatonin has no physiological or clinical association with the induction or regulation of vomiting. Vomiting is controlled by the Area Postrema (Chemoreceptor Trigger Zone) in the medulla oblongata, which responds to dopamine, serotonin (5-HT3), and substance P, but not melatonin. **Analysis of other options:** * **Sleep mechanism:** Melatonin is known as the "hormone of darkness." Its secretion increases in the dark, signaling the body to prepare for sleep. It acts on MT1 and MT2 receptors in the Suprachiasmatic Nucleus (SCN) of the hypothalamus. * **Jetlag:** Exogenous melatonin is a standard treatment for jetlag. It helps "reset" the internal biological clock when traveling across time zones by shifting the circadian phase. * **Pituitary gland secretion:** Melatonin exerts an inhibitory effect on the hypothalamic-pituitary-gonadal axis. It inhibits the release of GnRH, thereby decreasing the secretion of LH and FSH from the anterior pituitary. This is why pineal tumors (which may decrease melatonin) can lead to precocious puberty. **High-Yield Clinical Pearls for NEET-PG:** * **Precursor:** Tryptophan → Serotonin → Melatonin. * **Rate-limiting enzyme:** N-acetyltransferase (activity peaks at night). * **Light inhibition:** Light hitting the retina inhibits the pineal gland via the retinohypothalamic tract. * **Clinical Use:** Used in delayed sleep phase syndrome and for blind individuals to regulate sleep-wake cycles.

Question 338: Suprarenal medulla secretes which hormones?

A. Glucocorticoids
B. Catecholamines (Correct Answer)
C. Androgens
D. Mineralocorticoids

Explanation: **Explanation:** The suprarenal (adrenal) gland is anatomically and functionally divided into two distinct parts: the outer **cortex** and the inner **medulla**. **1. Why Catecholamines is correct:** The **adrenal medulla** is embryologically derived from the neural crest cells (modified postganglionic sympathetic neurons). It contains **chromaffin cells** that synthesize and secrete **catecholamines**—specifically Epinephrine (80%) and Norepinephrine (20%)—directly into the bloodstream in response to sympathetic stimulation (the "fight-or-flight" response). **2. Why other options are incorrect:** Options A, C, and D are all steroid hormones secreted by the **Adrenal Cortex**, which is divided into three zones (Mnemonic: **GFR** – **G**lomerulosa, **F**asciculata, **R**eticularis): * **Mineralocorticoids (e.g., Aldosterone):** Secreted by the **Zona Glomerulosa** (Outer layer). * **Glucocorticoids (e.g., Cortisol):** Secreted by the **Zona Fasciculata** (Middle, widest layer). * **Androgens (e.g., DHEA):** Secreted by the **Zona Reticularis** (Inner layer). **High-Yield Clinical Pearls for NEET-PG:** * **Pheochromocytoma:** A tumor of the chromaffin cells of the adrenal medulla, leading to episodic hypertension, palpitations, and perspiration due to excess catecholamine release. * **Rate-limiting enzyme:** Tyrosine hydroxylase is the rate-limiting enzyme for catecholamine synthesis. * **PNMT Enzyme:** Phenylethanolamine N-methyltransferase (PNMT) converts Norepinephrine to Epinephrine; its activity is induced by **Cortisol** draining from the cortex to the medulla. * **VMA (Vanillylmandelic Acid):** The major urinary metabolite of catecholamines, used as a diagnostic marker for medullary tumors.

Question 339: Which is the "showste" hormone?

A. TRH (Correct Answer)
B. HCG
C. Insulin
D. Glucagon

Explanation: **Explanation:** The term **"shortest hormone"** refers to the chemical structure and the number of amino acids in a peptide hormone. **Correct Option: A (TRH)** Thyrotropin-Releasing Hormone (TRH) is a tripeptide, meaning it consists of only **three amino acids** (pyroglutamyl-histidyl-prolineamide). Secreted by the hypothalamus, it is the smallest known peptide hormone in the human body. Its primary function is to stimulate the release of TSH and Prolactin from the anterior pituitary. **Why other options are incorrect:** * **B. HCG:** Human Chorionic Gonadotropin is a large glycoprotein dimer consisting of 237 amino acids. It is significantly larger than TRH. * **C. Insulin:** Insulin is a peptide hormone consisting of **51 amino acids** arranged in two chains (A and B) linked by disulfide bonds. * **D. Glucagon:** Glucagon is a linear polypeptide consisting of **29 amino acids**. While smaller than insulin, it is nearly ten times the size of TRH. **High-Yield NEET-PG Pearls:** * **Smallest Peptide Hormone:** TRH (3 amino acids). * **Largest Peptide Hormone:** Growth Hormone (GH) or Placental Lactogen (~191 amino acids). * **TRH Stimulation Test:** Used clinically to differentiate between secondary (pituitary) and tertiary (hypothalamic) hypothyroidism. * **Hyperprolactinemia:** Elevated TRH (as seen in primary hypothyroidism) can lead to increased Prolactin levels, causing galactorrhea.

Question 340: Removal of the parathyroid gland produces the following changes EXCEPT?

A. Decline in plasma calcium level
B. Decrease in plasma phosphate level (Correct Answer)
C. Neuromuscular hyperexcitability
D. Hypocalcemic tetany

Explanation: The parathyroid glands secrete **Parathyroid Hormone (PTH)**, which is the primary regulator of calcium and phosphate homeostasis. To solve this question, one must understand the "Bone-Kidney-Gut" axis of PTH. ### **Why Option B is the Correct Answer** Removal of the parathyroid glands (hypoparathyroidism) leads to a **deficiency of PTH**. Under normal conditions, PTH acts on the proximal convoluted tubules of the kidney to **inhibit phosphate reabsorption** (phosphaturic effect). * **In the absence of PTH:** Phosphate reabsorption increases in the kidneys. * **Result:** Plasma phosphate levels **increase** (Hyperphosphatemia), not decrease. Therefore, Option B is the false statement. ### **Explanation of Incorrect Options** * **Option A (Decline in plasma calcium):** PTH normally increases calcium by mobilizing it from bone and increasing renal reabsorption. Its absence leads to profound **hypocalcemia**. * **Option C & D (Neuromuscular hyperexcitability and Tetany):** Low extracellular calcium lowers the threshold for action potentials in excitable tissues. This leads to increased permeability to sodium ions, causing spontaneous firing of motor neurons. This manifests clinically as **neuromuscular hyperexcitability**, which, if severe, results in **tetany** (carpopedal spasm). ### **NEET-PG High-Yield Pearls** * **The "P" Rule:** **P**TH dumps **P**hosphate in the **P**roximal tubule. * **Clinical Signs of Hypocalcemia:** 1. **Chvostek’s sign:** Tapping the facial nerve leads to facial twitching. 2. **Trousseau’s sign:** Inflating a BP cuff above systolic pressure induces carpal spasm (more sensitive than Chvostek). * **Most common cause of hypoparathyroidism:** Accidental removal or damage during thyroid surgery (Post-surgical). * **ECG Finding:** Hypocalcemia causes **prolonged QT interval**.

Practice by Chapter

Principles of Endocrine Regulation

Practice Questions

Hypothalamus and Pituitary Gland

Practice Questions

Thyroid Physiology

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Adrenal Cortex and Medulla

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Pancreatic Hormones and Glucose Metabolism

Practice Questions

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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