Endocrinology Practice Questions

Q: Decreased activity of type I 5'-monodeiodinase could lead to which of the following physiological effects?

Increased plasma reverse T3. The thyroid gland primarily secretes **Thyroxine (T4)**, which is a pro-hormone. To become biologically active, T4 must be converted into **Triiodothyronine (T3)**. This process is mediated by **deiodinase enzymes**: 1. **Type I and Type II 5'-deiodinase:** These remove iodine from the *outer* ring of T4 to produce active **T3**. 2. **Type III deiodinase:** This removes iodine from the *inner* ring of T4 to produce inactive **reverse T3 (rT3)**. **Why Option B is Correct:** Type I 5'-monodeiodinase is responsible for the peripheral conversion of T4 to T3 and also for the **clearance (degradation) of rT3**. When the activity of this enzyme decreases, two things happen: less T4 is converted to T3, and less rT3 is broken down. This leads to a characteristic rise in plasma **reverse T3** levels. **Analysis of Incorrect Options:** * **Option A:** T3 levels would **decrease**, not increase, because the conversion from T4 is impaired [1]. * **Option C:** T4 levels usually remain **normal or slightly elevated** because its peripheral utilization/conversion is blocked. * **Option D:** TSH typically remains **normal** in these scenarios (like Euthyroid Sick Syndrome) because Type II deiodinase in the pituitary remains active, maintaining local T3 levels and feedback inhibition [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Euthyroid Sick Syndrome:** Characterized by low T3, high rT3, and normal TSH. It is the most common clinical scenario involving decreased Type I deiodinase activity (seen in starvation, trauma, or severe illness). * **Drugs inhibiting Type I deiodinase:** Propylthiouracil (PTU), Propranolol, Glucocorticoids, and Amiodarone. * **Selenium:** This trace element is a crucial cofactor for deiodinase enzymes (selenoproteins). Deficiency can impair T4 to T3 conversion.

Q: Which of the following statements is incorrect regarding melatonin?

It is secreted by the pituitary gland.. **Explanation:** The correct answer is **C**, as melatonin is **not** secreted by the pituitary gland; it is synthesized and secreted by the **pineal gland** (epiphysis cerebri). **1. Why Option C is the correct (incorrect statement) answer:** Melatonin is a derivative of the amino acid **Tryptophan**. It is produced by the pinealocytes of the pineal gland. The secretion is regulated by the suprachiasmatic nucleus (SCN) of the hypothalamus, which acts as the body's master biological clock. The pituitary gland, conversely, secretes hormones like GH, TSH, ACTH, and LH/FSH, but not melatonin. **2. Analysis of other options:** * **Option A & B:** Melatonin is known as the "hormone of darkness." Its levels rise in the evening, promoting sleep onset and regulating the sleep-wake cycle. Clinically, exogenous melatonin is used to treat **circadian rhythm disorders**, such as insomnia and **jet lag syndrome**, to help reset the internal clock. * **Option D:** This is a factual statement. The pineal gland is the primary anatomical source of melatonin in the body. **High-Yield NEET-PG Pearls:** * **Precursor:** Tryptophan → Serotonin → Melatonin. * **Rate-limiting enzyme:** N-acetyltransferase (activity increases at night). * **Light Inhibition:** Light exposure to the retina inhibits melatonin secretion via the retinohypothalamic tract. * **Other Functions:** It is a potent antioxidant and plays a role in inhibiting reproductive function (antigonadotropic effect) in certain species by inhibiting GnRH release. * **Tumor Association:** Pineal tumors can lead to precocious puberty if they destroy the gland (removing the inhibitory effect of melatonin on gonadotropins).

Q: Which of the following findings shall be seen in a patient with hyperparathyroidism?

Hypophosphatemia. **Explanation:** The primary function of **Parathyroid Hormone (PTH)** is to maintain calcium homeostasis by increasing serum calcium levels. In **Hyperparathyroidism**, the excess secretion of PTH acts on three main target organs: the bones, the kidneys, and the intestines (indirectly). **Why Hypophosphatemia is correct:** PTH has a potent **phosphaturic effect**. It acts on the proximal convoluted tubules (PCT) of the kidney to inhibit the sodium-phosphate cotransporter (NaPi-IIa). This leads to a decrease in the reabsorption of phosphate, causing increased urinary excretion of phosphate (**phosphaturia**) and a subsequent decrease in serum phosphate levels (**Hypophosphatemia**). **Analysis of Incorrect Options:** * **B. Hyperphosphatemia:** This is typically seen in *Hypoparathyroidism* or Chronic Kidney Disease (CKD). In hyperparathyroidism, the kidney is actively "wasting" phosphate. * **C & D. Magnesium levels:** While PTH can slightly increase magnesium reabsorption in the distal tubule, magnesium levels are not a primary diagnostic hallmark of hyperparathyroidism. In fact, chronic hyperparathyroidism can sometimes lead to mild *hypomagnesemia* due to associated hypercalciuria, but **Hypophosphatemia** is the classic, high-yield biochemical finding. **NEET-PG High-Yield Pearls:** 1. **Biochemical Triad:** Hypercalcemia + Hypophosphatemia + Hypercalciuria (the latter occurs because the filtered load of calcium exceeds the kidney's reabsorptive capacity). 2. **Bone Finding:** *Osteitis fibrosa cystica* (subperiosteal bone resorption, especially in phalanges). 3. **Renal Finding:** PTH stimulates **1-alpha-hydroxylase** in the kidneys, increasing the production of active Vitamin D [1,25(OH)₂D]. 4. **Mnemonic:** "Stones, bones, abdominal groans, and psychic overtones."

Q: Which of the following pituitary hormones does NOT decrease the stimulatory control of the pituitary?

Prolactin. ### Explanation The regulation of the pituitary gland primarily follows a **negative feedback mechanism**. In most endocrine axes, the pituitary hormone (or the peripheral hormone it stimulates) inhibits the hypothalamus to decrease further stimulation. **Why Prolactin is the Correct Answer:** Unlike most anterior pituitary hormones, **Prolactin** is unique because it is under **tonic inhibitory control** by the hypothalamus via **Dopamine** (Prolactin-Inhibiting Hormone). Prolactin does not decrease the "stimulatory control" because its primary regulator is an inhibitor. When Prolactin levels rise, they stimulate the hypothalamus to increase the secretion of Dopamine, which further *inhibits* the pituitary. It lacks a classic stimulatory releasing hormone (like TRH or GnRH) as its primary regulator. **Analysis of Incorrect Options:** * **FSH and LH (Options B & C):** These gonadotropins are regulated by **GnRH** (Gonadotropin-Releasing Hormone). Through the "short-loop" feedback mechanism, high levels of FSH and LH inhibit the hypothalamus, decreasing the stimulatory release of GnRH. * **Oxytocin (Option D):** While Oxytocin is known for **positive feedback** (e.g., Ferguson reflex during labor), in the context of the hypothalamic-pituitary axis, it does not function under a tonic inhibitory tone like Prolactin. **High-Yield Clinical Pearls for NEET-PG:** * **Dopamine is the primary Prolactin-Inhibiting Hormone (PIH).** Any drug that blocks Dopamine (e.g., Antipsychotics like Haloperidol or Metoclopramide) will cause **Hyperprolactinemia**. * **Stalk Effect:** Damage to the pituitary stalk interrupts the flow of Dopamine to the anterior pituitary, leading to a decrease in all pituitary hormones *except* Prolactin, which rises. * **TRH (Thyrotropin-Releasing Hormone)** can act as a minor prolactin-releasing factor; hence, patients with primary hypothyroidism (high TRH) often present with galactorrhea.

Q: Proopiomelanocortin is released from which gland?

Hypothalamus. **Explanation:** **Proopiomelanocortin (POMC)** is a large precursor polypeptide synthesized primarily in the **corticotrophs of the anterior pituitary** and the **arcuate nucleus of the Hypothalamus**. In the hypothalamus, POMC neurons play a critical role in energy homeostasis; they are processed into **α-MSH** (alpha-melanocyte-stimulating hormone), which acts on MC3/MC4 receptors to inhibit food intake (anorexigenic effect). **Analysis of Options:** * **A. Hypothalamus (Correct):** As mentioned, POMC is synthesized in the arcuate nucleus. It is also produced in the anterior pituitary (precursor to ACTH) and the intermediate lobe of the pituitary. * **B. Liver:** The liver is involved in the synthesis of proteins like albumin, clotting factors, and Angiotensinogen, but it does not produce POMC. * **C. Adrenal:** The adrenal cortex is the *target* for ACTH (a derivative of POMC), where it stimulates cortisol production. It does not synthesize the POMC precursor itself. * **D. Lung:** While small cell carcinoma of the lung can produce ACTH ectopically (paraneoplastic syndrome), the lung is not a physiological site of POMC release. **High-Yield Clinical Pearls for NEET-PG:** 1. **Post-translational Processing:** POMC is cleaved by **Prohormone Convertases (PC1 and PC2)**. PC1 leads to ACTH production (Pituitary), while PC2 leads to α-MSH production (Hypothalamus). 2. **Derivatives:** POMC is the parent molecule for **ACTH, β-endorphin, α-MSH, and γ-LPH**. 3. **Hyperpigmentation:** In Addison’s disease, high levels of POMC/ACTH lead to skin hyperpigmentation because ACTH shares a structural sequence with MSH and can bind to melanocortin-1 receptors. 4. **Appetite Regulation:** Leptin stimulates POMC neurons in the hypothalamus to decrease appetite. Mutations in the POMC gene can lead to early-onset severe obesity.

Q: Which adrenergic beta receptor has a role in lipolysis in fat cells?

Beta 3. **Explanation:** The correct answer is **Beta 3 (Option D)**. Adrenergic receptors are G-protein coupled receptors (GPCRs) that mediate the effects of catecholamines. The **Beta-3 ($\beta_3$) receptor** is primarily located in **adipose tissue** (both brown and white fat). When stimulated by norepinephrine, it activates the $G_s$ protein-adenylyl cyclase pathway, increasing intracellular cAMP. This activates Protein Kinase A, which phosphorylates **hormone-sensitive lipase (HSL)**, leading to the breakdown of triglycerides into free fatty acids and glycerol (**lipolysis**). In brown adipose tissue, $\beta_3$ stimulation also promotes thermogenesis via Uncoupling Protein 1 (UCP1/Thermogenin). **Analysis of Incorrect Options:** * **Alpha 1 ($\alpha_1$):** Linked to $G_q$ proteins; primarily causes smooth muscle contraction (vasoconstriction, pupillary dilation, and intestinal sphincter contraction). * **Alpha 2 ($\alpha_2$):** Linked to $G_i$ proteins; acts as a presynaptic autoreceptor to inhibit norepinephrine release. In fat cells, $\alpha_2$ stimulation actually **inhibits** lipolysis (antagonistic to $\beta_3$). * **Beta 1 ($\beta_1$):** Primarily located in the **heart** (increases heart rate and contractility) and the juxtaglomerular apparatus of the kidney (increases renin release). **High-Yield Clinical Pearls for NEET-PG:** * **Mirabegron:** A selective $\beta_3$ agonist used clinically for the treatment of **overactive bladder** (causes detrusor muscle relaxation). * **Lipolysis hierarchy:** While $\beta_3$ is the classic answer for fat cells, $\beta_1$ also contributes to lipolysis in humans, but $\beta_3$ is the specific "metabolic" receptor often tested. * **Mnemonic:** $\beta_1$ (1 Heart), $\beta_2$ (2 Lungs), $\beta_3$ (3 letters in FAT).

Q: All of the following hormones are increased during stress except?

Insulin. **Explanation:** The body’s response to stress (the "fight or flight" response) is designed to mobilize energy substrates—primarily glucose and free fatty acids—to meet increased metabolic demands. This is achieved through the activation of the **Sympathetic Nervous System (SNS)** and the **Hypothalamic-Pituitary-Adrenal (HPA) axis**. **Why Insulin is the correct answer:** Insulin is an **anabolic hormone** that promotes glucose storage (glycogenesis) and uptake into peripheral tissues. During stress, the body needs to maintain high blood glucose levels for the brain and muscles. Therefore, insulin secretion is **inhibited** by the sympathetic nervous system (via $\alpha_2$-adrenergic receptors on pancreatic beta cells). This state of "stress-induced hyperglycemia" ensures glucose availability. **Why the other options are incorrect:** * **Cortisol (Option A):** Known as the primary "stress hormone," it increases gluconeogenesis and protein catabolism to provide energy during prolonged stress. * **Adrenaline & Noradrenaline (Options C & D):** These catecholamines are released immediately during acute stress. They stimulate glycogenolysis in the liver and lipolysis in adipose tissue to rapidly elevate blood glucose and fatty acid levels. **NEET-PG High-Yield Pearls:** * **Glucagon and Growth Hormone** are also increased during stress; both are "counter-regulatory" hormones that oppose insulin action. * **Catecholamine effect on Insulin:** While $\beta_2$ stimulation can increase insulin, the **$\alpha_2$ inhibitory effect predominates** during stress, leading to a net decrease in insulin levels. * **ADH (Vasopressin):** Also increases during stress to maintain blood pressure and fluid volume.

Q: Insulin secretion is decreased by which of the following hormones?

Somatostatin. **Explanation:** The regulation of insulin secretion is a complex process involving nutrients, autonomic nerves, and gastrointestinal hormones. **Why Somatostatin is correct:** Somatostatin, secreted by the **Delta (δ) cells** of the pancreatic islets, acts as a potent universal inhibitor. It exerts a **paracrine effect** on neighboring Beta (β) cells to **decrease insulin secretion** and on Alpha (α) cells to decrease glucagon secretion. It acts via G-protein coupled receptors (SSTR-2 and SSTR-5) which decrease intracellular cAMP and inhibit calcium influx, thereby preventing exocytosis of insulin granules. **Why the other options are incorrect:** * **Glucagon:** While it has the opposite metabolic effect of insulin, glucagon actually **stimulates** insulin secretion. This ensures that as glucagon mobilizes glucose into the bloodstream, insulin is available to facilitate its utilization by peripheral tissues. * **Gastrin and Secretin:** These are gastrointestinal hormones (Incretins/Enterogastrones). The "Incretin effect" describes how oral glucose causes a higher insulin response than intravenous glucose. Gastrin, Secretin, CCK, and GIP all act to **increase** insulin secretion in anticipation of rising blood glucose levels following a meal. **High-Yield Clinical Pearls for NEET-PG:** * **Most potent stimulator** of insulin: Glucose. * **Most potent inhibitor** of insulin: Somatostatin (Physiological) and Epinephrine (via α2 receptors during stress). * **Incretin Effect:** Primarily mediated by **GLP-1** (Glucagon-like peptide-1) and **GIP** (Glucose-dependent insulinotropic peptide). * **Drug Link:** Octreotide is a synthetic somatostatin analogue used clinically to treat insulinomas and acromegaly due to its inhibitory properties.

Question 1

Decreased activity of type I 5'-monodeiodinase could lead to which of the following physiological effects?

Accepted Answer

Increased plasma reverse T3

Answer

Increased plasma triiodothyronine (T3)

Answer

Decreased plasma thyroxine T4

Answer

Increased TSH

Question 2

Which of the following statements is incorrect regarding melatonin?

Accepted Answer

It is secreted by the pituitary gland.

Answer

It induces sleep.

Answer

It is used in the treatment of jet lag syndrome.

Answer

It is a pineal hormone.

Question 3

Which of the following findings shall be seen in a patient with hyperparathyroidism?

Accepted Answer

Hypophosphatemia

Answer

Hyperphosphatemia

Answer

Hypermagnesemia

Answer

Hypomagnesemia

Question 4

What is the primary action of estrogen on bone?

Accepted Answer

Acts as an antiresorptive agent on trabecular bone

Answer

Stimulates bone matrix deposition

Answer

Has an anti-osteoblastic effect on compact bone

Answer

Acts as a resorptive agent on compact bone

Question 5

Estrogen receptors are typically located in which cellular compartment?

Accepted Answer

Nucleus

Answer

Microsomes

Answer

Membrane-bound organelles

Answer

Mitochondria

Question 6

Which of the following pituitary hormones does NOT decrease the stimulatory control of the pituitary?

Accepted Answer

Prolactin

Answer

Follicle-stimulating hormone (FSH)

Answer

Luteinizing hormone (LH)

Answer

Oxytocin

Question 7

Proopiomelanocortin is released from which gland?

Accepted Answer

Hypothalamus

Answer

Liver

Answer

Adrenal

Answer

Lung

Question 8

Which adrenergic beta receptor has a role in lipolysis in fat cells?

Accepted Answer

Beta 3

Answer

Alpha 1

Answer

Alpha 2

Answer

Beta 1

Question 9

All of the following hormones are increased during stress except?

Accepted Answer

Insulin

Answer

Cortisol

Answer

Adrenaline

Answer

Noradrenaline

Question 10

Insulin secretion is decreased by which of the following hormones?

Accepted Answer

Somatostatin

Answer

Glucagon

Answer

Gastrin

Answer

Secretin

Endocrinology — MCQs

Endocrinology — MCQs

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