Endocrinology Practice Questions

Q: Normal thyroid weight varies with dietary iodine content?

Inversely. **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.

Q: Which of the following statements regarding calcitonin is FALSE?

Its actions are similar to parathyroid hormone.. **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.

Q: Melatonin is associated with all of the following except?

Vomiting. **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.

Q: Which of the following hormones does NOT modify growth?

Vasopressin. **Explanation:** Growth is a complex physiological process regulated by a specific set of hormones that influence protein synthesis, cell division, and skeletal maturation. **Why Vasopressin is the Correct Answer:** **Vasopressin (Antidiuretic Hormone/ADH)** is primarily involved in water homeostasis and vascular tone. It acts on the V2 receptors in the renal collecting ducts to increase water reabsorption and V1 receptors to cause vasoconstriction. It has **no physiological role** in stimulating or modifying systemic growth or skeletal development. **Analysis of Other Options:** * **Growth Hormone (GH) / Corticotrophin:** GH is the primary stimulator of postnatal growth via IGF-1. Corticotrophin (ACTH) influences growth indirectly; while essential in physiological amounts, chronic excess (Cushing’s) actually inhibits growth by antagonizing GH and causing protein catabolism. * **Insulin:** Insulin is a potent growth promoter, especially during **fetal development**. It stimulates amino acid uptake and protein synthesis. Children with insulin deficiency (Type 1 Diabetes) often exhibit stunted growth (Mauriac syndrome). * **Prolactin:** Prolactin belongs to the same structural family as Growth Hormone. While its primary role is lactation, it has weak GH-like effects and can influence the proliferation of specific tissues, including immune cells and mammary tissue. **High-Yield Clinical Pearls for NEET-PG:** * **Fetal Growth:** Primarily regulated by **Insulin** and **IGF-2**. Growth Hormone is *not* essential for intrauterine growth. * **Postnatal Growth:** Primarily regulated by **GH, IGF-1, and Thyroid hormones**. * **Pubertal Growth Spurt:** Driven by the synergistic action of **Androgens/Estrogens** and GH. * **Thyroid Hormone:** Essential for bone maturation and CNS development; deficiency leads to cretinism (stunted growth and mental retardation).

Q: Which of the following is NOT an adverse effect of excessive mineralocorticoid action?

Acidosis. Mineralocorticoids (primarily **Aldosterone**) act on the mineralocorticoid receptors in the principal cells and intercalated cells of the late distal tubule and collecting duct. **Why Acidosis is the Correct Answer:** Excessive mineralocorticoid action leads to **Alkalosis**, not acidosis. Aldosterone stimulates the secretion of Hydrogen ions ($H^+$) into the tubular lumen via $H^+$-ATPase pumps in the alpha-intercalated cells. Increased loss of $H^+$ in the urine results in **Metabolic Alkalosis**. Therefore, acidosis is the incorrect physiological effect. **Explanation of Incorrect Options:** * **A. Sodium and water retention:** Aldosterone increases the expression of ENaC (Epithelial Sodium Channels) in the principal cells, promoting $Na^+$ reabsorption. Water follows osmotically, leading to volume expansion. * **D. Rise in blood pressure:** Chronic sodium and water retention, coupled with increased peripheral vascular resistance, leads to secondary hypertension. * **C. Aggravation of CHF associated myocardial fibrosis:** Beyond electrolyte balance, aldosterone has "non-genomic" effects. It promotes fibroblast proliferation and collagen deposition in the heart. This is why Mineralocorticoid Receptor Antagonists (MRAs) like **Spironolactone** and **Eplerenone** are mortality-benefit drugs in Heart Failure. **High-Yield NEET-PG Pearls:** * **Conn’s Syndrome:** Primary hyperaldosteronism characterized by the triad of **Hypertension, Hypokalemia, and Metabolic Alkalosis.** * **Escape Phenomenon:** In primary hyperaldosteronism, edema is usually absent because the body "escapes" the sodium-retaining effects via ANP (Atrial Natriuretic Peptide) release. * **Drug of Choice:** Spironolactone is the drug of choice for hepatic cirrhosis with ascites and Conn’s syndrome.

Q: Removal of the parathyroid gland produces the following changes EXCEPT?

Decrease in plasma phosphate level. 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**.

Q: Which of the following hormones is NOT produced by the endocrine part of the pancreas?

Bombesin. **Explanation:** The pancreas is a dual-function organ consisting of an exocrine part (acini) and an endocrine part (Islets of Langerhans). The Islets of Langerhans contain several distinct cell types that secrete specific hormones directly into the bloodstream. **Why Bombesin is the correct answer:** Bombesin is a peptide originally isolated from the skin of amphibians. In humans, its equivalent is **Gastrin-Releasing Peptide (GRP)**. It is primarily found in the gastrointestinal tract and the brain, acting as a neurotransmitter and a stimulator of gastrin release. It is **not** a product of the pancreatic Islets of Langerhans. **Why the other options are incorrect:** * **Insulin (Option A):** Produced by the **Beta (β) cells**, which make up about 60-75% of the islet cells. It is the primary anabolic hormone responsible for lowering blood glucose. * **Somatostatin (Option B):** Produced by the **Delta (δ) cells** (approx. 5-10%). It acts locally (paracrine effect) to inhibit the secretion of both insulin and glucagon. * **Glucagon (Option C):** Produced by the **Alpha (α) cells** (approx. 20%). It is a catabolic hormone that increases blood glucose levels via glycogenolysis and gluconeogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **Cell Distribution:** Remember the mnemonic **"BAGS"** for islet cells: **B**eta (Insulin), **A**lpha (Glucagon), **G**amma/PP cells (Pancreatic Polypeptide), and **S**igma/Delta (Somatostatin). * **Epsilon (ε) cells:** A minor cell type in the pancreas that produces **Ghrelin** (the hunger hormone). * **Blood Flow Pattern:** Blood in the islets flows from the center (Beta cells) to the periphery (Alpha/Delta cells), allowing insulin to inhibit glucagon release directly.

Question 1

A 43-year-old female presents with galactorrhea. Investigations show increased prolactin levels. Which of the following conditions can cause increased prolactin secretion?

Accepted Answer

Dopamine

Answer

Sleep

Answer

Pregnancy

Answer

Stress

Question 2

Normal thyroid weight varies with dietary iodine content?

Accepted Answer

Inversely

Answer

Directly proportional

Answer

Inverse cubically

Answer

Not fixed

Question 3

Which of the following statements regarding calcitonin is FALSE?

Accepted Answer

Its actions are similar to parathyroid hormone.

Answer

It has a short-term use in patients with hypercalcemia.

Answer

It inhibits osteoclastic activity.

Answer

High concentrations in the plasma are seen in medullary carcinoma of the thyroid.

Question 4

Melatonin is associated with all of the following except?

Accepted Answer

Vomiting

Answer

Pituitary gland secretion

Answer

Sleep mechanism

Answer

Jetlag

Question 5

Which of the following hormones does NOT modify growth?

Accepted Answer

Vasopressin

Answer

Growth hormone / corticotrophin

Answer

Insulin

Answer

Prolactin

Question 6

Which of the following is NOT an adverse effect of excessive mineralocorticoid action?

Accepted Answer

Acidosis

Answer

Sodium and water retention

Answer

Aggravation of CHF associated myocardial fibrosis

Answer

Rise in blood pressure

Question 7

Removal of the parathyroid gland produces the following changes EXCEPT?

Accepted Answer

Decrease in plasma phosphate level

Answer

Decline in plasma calcium level

Answer

Neuromuscular hyperexcitability

Answer

Hypocalcemic tetany

Question 8

Which of the following hormones is NOT produced by the endocrine part of the pancreas?

Accepted Answer

Bombesin

Answer

Insulin

Answer

Somatostatin

Answer

Glucagon

Question 9

Continuous administration of testosterone leads to which of the following conditions?

Accepted Answer

Azoospermia

Answer

Increased sperm motility

Answer

Increased spermatogenesis

Answer

Increased gonadotrophins

Question 10

Which of the following is not controlled by the autonomic nervous system?

Accepted Answer

Aldosterone

Answer

Insulin

Answer

Growth Hormone (GH)

Answer

Somatostatin

Endocrinology — MCQs

Endocrinology — MCQs

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