Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 11: Which of the following inhibits prolactin secretion?

A. Dopamine antagonist
B. GABA
C. Neurophysin
D. Bromocriptine (Correct Answer)

Explanation: **Explanation:** The regulation of prolactin is unique among anterior pituitary hormones because it is under **predominant tonic inhibition** by the hypothalamus. The primary Prolactin Inhibiting Factor (PIF) is **Dopamine**, which acts on D2 receptors of the lactotrophs. **Why Bromocriptine is correct:** **Bromocriptine** is a potent **Dopamine (D2) receptor agonist**. By mimicking the action of endogenous dopamine, it directly inhibits the synthesis and secretion of prolactin from the anterior pituitary. It is the clinical gold standard for treating hyperprolactinemia and prolactinomas. **Analysis of Incorrect Options:** * **A. Dopamine antagonist:** These drugs (e.g., Metoclopramide, Haloperidol) block the inhibitory effect of dopamine, leading to **increased** prolactin levels (hyperprolactinemia) and potentially causing galactorrhea. * **B. GABA:** While GABA can have minor inhibitory effects on prolactin in some experimental models, it is not the primary physiological regulator. In the context of standard physiology and NEET-PG, Dopamine is the definitive inhibitor. * **C. Neurophysin:** These are carrier proteins for Oxytocin (Neurophysin I) and ADH (Neurophysin II). They are involved in the transport of posterior pituitary hormones and have no role in prolactin regulation. **High-Yield Clinical Pearls for NEET-PG:** * **TRH (Thyrotropin-Releasing Hormone):** Acts as a potent prolactin-releasing factor. This explains why patients with **primary hypothyroidism** (high TRH) often present with secondary hyperprolactinemia. * **Prolactin & GnRH:** High prolactin levels inhibit the pulsatile release of GnRH, leading to infertility and amenorrhea. * **Suckling Reflex:** Inhibits dopamine release, thereby disinhibiting prolactin to promote milk production.

Question 12: Which of the following is NOT a mechanism of action of insulin?

A. Tyrosine kinase-beta cell stimulation
B. Incoporation of GLUT-4 into cells
C. Inhibition of Na+K+ATPase (Correct Answer)
D. Hexokinase stimulation

Explanation: **Explanation:** The correct answer is **C (Inhibition of Na+K+ATPase)** because insulin actually **stimulates** the Na+K+ATPase pump, rather than inhibiting it. **Why Option C is correct:** Insulin increases the activity and number of Na+K+ATPase pumps on cell membranes (especially in skeletal muscle and adipose tissue). This leads to an increased influx of Potassium ($K^+$) into the cells and an efflux of Sodium ($Na^+$). This mechanism is clinically significant as it can lead to hypokalemia, which is why insulin is used in the emergency management of hyperkalemia. **Why the other options are incorrect:** * **Option A (Tyrosine kinase-beta cell stimulation):** The insulin receptor is a heterotetramer with intrinsic **Tyrosine Kinase** activity. When insulin binds to the alpha subunits, it causes autophosphorylation of the beta subunits, triggering the intracellular signaling cascade. * **Option B (Incorporation of GLUT-4):** Insulin promotes the translocation of **GLUT-4** (glucose transporter) from intracellular vesicles to the plasma membrane in skeletal muscle and adipose tissue, facilitating glucose uptake. * **Option D (Hexokinase stimulation):** Insulin enhances glucose utilization by inducing and activating key glycolytic enzymes, including **Hexokinase** (and Glucokinase in the liver), to trap glucose inside the cell as Glucose-6-Phosphate. **High-Yield NEET-PG Pearls:** * **GLUT-4** is the only insulin-dependent glucose transporter. * Insulin causes a **"Shift" of Potassium** into cells; always monitor $K^+$ levels when administering an insulin drip for DKA. * **Anabolic effects:** Insulin stimulates protein synthesis, glycogen synthesis (Glycogen Synthase), and lipogenesis, while inhibiting gluconeogenesis and ketogenesis.

Question 13: Which of the following is an amine hormone?

A. Insulin
B. Glucocorticoid
C. Parathyroid hormone (PTH)
D. Thyroxine (Correct Answer)

Explanation: **Explanation:** Hormones are chemically classified into three main categories: **Amines, Peptides/Proteins, and Steroids.** **Thyroxine (T4)** is the correct answer because it is an **amine hormone**. Amine hormones are derivatives of the amino acid **Tyrosine**. This group includes thyroid hormones (T3, T4) and catecholamines (Epinephrine, Norepinephrine, and Dopamine). Although derived from tyrosine, thyroid hormones are unique because they are lipophilic and act on intracellular receptors, unlike catecholamines which are hydrophilic. **Analysis of Incorrect Options:** * **Insulin:** This is a **peptide hormone** consisting of 51 amino acids arranged in two chains (A and B) linked by disulfide bridges. * **Glucocorticoids (e.g., Cortisol):** These are **steroid hormones** derived from cholesterol. They are produced in the adrenal cortex and are lipid-soluble. * **Parathyroid Hormone (PTH):** This is a **polypeptide hormone** (84 amino acids) secreted by the chief cells of the parathyroid gland. **High-Yield NEET-PG Pearls:** 1. **Tyrosine Derivatives:** Remember the "T" rule—Tyrosine gives rise to **T**hyroid hormones and **T**ransmitters (Catecholamines). 2. **Tryptophan Derivative:** **Melatonin** and Serotonin are derived from the amino acid Tryptophan (frequently tested). 3. **Receptor Location:** Most amine and peptide hormones bind to cell surface receptors, but **Thyroid hormones** are the notable exception—they bind to **nuclear receptors**. 4. **Steroid Mnemonic:** All hormones from the Adrenal Cortex, Gonads, and Corpus Luteum are steroids (plus Vitamin D).

Question 14: Capacitation of sperms occurs in which of the following locations?

A. Seminiferous tubules
B. Epididymis
C. Vas deferens
D. Uterus (Correct Answer)

Explanation: **Explanation:** **Capacitation** is the final physiological maturation process that spermatozoa must undergo to gain the ability to fertilize an oocyte. While sperms are morphologically mature and motile upon leaving the male reproductive tract, they are functionally "decapacitated" by inhibitory factors in the seminal fluid. **Why Uterus is Correct:** Capacitation occurs within the **female reproductive tract** (primarily the uterus and fallopian tubes). The process involves the removal of cholesterol and glycoproteins from the sperm cell membrane, leading to increased calcium permeability. This triggers **hyperactivation** (whiplash-like tail movement) and prepares the sperm for the **acrosome reaction** upon contact with the zona pellucida. It typically takes 5–7 hours. **Why Incorrect Options are Wrong:** * **Seminiferous Tubules:** This is the site of **spermatogenesis** (production of immature sperms). Sperms here are non-motile and incapable of fertilization. * **Epididymis:** This is the site where sperms undergo **morphological maturation** and gain progressive motility. However, they remain inhibited by decapacitation factors. * **Vas Deferens:** This serves primarily as a storage and transport conduit for mature sperms prior to ejaculation. **High-Yield NEET-PG Pearls:** 1. **Site of Fertilization:** Usually the **Ampulla** of the fallopian tube. 2. **Acrosome Reaction:** Occurs only *after* capacitation, triggered by binding to **ZP3 receptors** on the zona pellucida. 3. **Key Ion:** **Calcium ($Ca^{2+}$)** influx is the critical trigger for both hyperactivation and the acrosome reaction. 4. **In Vitro Fertilization (IVF):** In lab settings, capacitation must be induced artificially using specific media to mimic the female tract environment.

Question 15: A patient has a goiter associated with high plasma levels of both TRH and TSH. Her heart rate is elevated. This patient most likely has which condition?

A. An endemic goiter
B. A hypothalamic tumor secreting large amounts of TRH (Correct Answer)
C. A pituitary tumor secreting large amounts of TSH
D. Graves' disease

Explanation: ### Explanation **Concept Overview:** The diagnosis of thyroid disorders relies on understanding the **Hypothalamic-Pituitary-Thyroid (HPT) axis** and the principle of **negative feedback**. Normally, high levels of thyroid hormones (T3/T4) inhibit the release of TRH from the hypothalamus and TSH from the anterior pituitary. **Why Option B is Correct:** In this patient, both **TRH and TSH are elevated**. This indicates a "top-down" pathology. A **hypothalamic tumor** secreting TRH will overstimulate the pituitary to produce TSH. High TSH, in turn, overstimulates the thyroid gland, causing **goiter** (hyperplasia) and excessive T3/T4 production. The elevated heart rate (tachycardia) is a clinical manifestation of the resulting hyperthyroidism. **Why Other Options are Incorrect:** * **A. Endemic Goiter:** Caused by iodine deficiency. While TSH is high (due to lack of feedback inhibition), T3/T4 levels are low, and TRH is usually not the primary driver measured in this context. * **C. Pituitary Tumor (TSH-oma):** While this would cause high TSH and high T3/T4, the high circulating thyroid hormones would **suppress** the hypothalamus via negative feedback, leading to **low TRH** levels. * **D. Graves' Disease:** This is an autoimmune condition where TSH-receptor antibodies (TRAb) stimulate the thyroid. Because T3/T4 levels are very high, both **TRH and TSH would be suppressed (low)**. **NEET-PG High-Yield Pearls:** * **Secondary Hyperthyroidism:** High T3/T4 with high TSH (usually a pituitary adenoma). * **Tertiary Hyperthyroidism:** High T3/T4 with high TSH and high TRH (hypothalamic origin). * **Primary Hyperthyroidism:** High T3/T4 with low TSH (e.g., Graves', Toxic Multinodular Goiter). * **Wolff-Chaikoff Effect:** Reduction in thyroid hormone levels caused by ingestion of a large amount of iodine.

Question 16: Parasympathetic stimulation of nerves innervating the islets of the pancreas will:

A. Have no effect
B. Increase secretion of insulin from B cells (Correct Answer)
C. Decrease secretion of insulin from B cells
D. Increase secretion of glucagon from B cells

Explanation: ### Explanation **1. Why Option B is Correct:** The pancreas is innervated by the **Vagus nerve (Cranial Nerve X)**, which provides parasympathetic input. Parasympathetic stimulation is synonymous with the **"Rest and Digest"** state. When the vagus nerve is stimulated (often triggered by the anticipation of food or the presence of food in the gut—the cephalic phase of digestion), it releases **Acetylcholine (ACh)**. ACh binds to **Muscarinic (M3) receptors** on the pancreatic Beta (B) cells. This activates the phospholipase C pathway, increasing intracellular calcium and triggering the exocytosis of **insulin**. This mechanism ensures the body is prepared to store glucose even before blood sugar levels rise significantly. **2. Why Other Options are Incorrect:** * **Option A:** Incorrect because the autonomic nervous system plays a significant role in modulating islet hormone secretion. * **Option C:** This is the effect of **Sympathetic stimulation**. Activation of **Alpha-2 (α2) adrenergic receptors** on Beta cells inhibits insulin secretion to maintain blood glucose levels during "Fight or Flight" situations. * **Option D:** This is factually incorrect because **Glucagon is secreted by Alpha (A) cells**, not Beta (B) cells. While parasympathetic stimulation can also increase glucagon, the question specifically links the effect to B cells. **3. High-Yield Clinical Pearls for NEET-PG:** * **Dual Control:** Insulin secretion is stimulated by Parasympathetic (M3 receptors) and inhibited by Sympathetic (α2 receptors). * **The "Incretin Effect":** Oral glucose causes a much higher insulin spike than IV glucose due to GIP and GLP-1 (Incretins) and vagal stimulation. * **Beta-blockers:** Non-selective beta-blockers can mask hypoglycemia symptoms and further inhibit insulin release (via β2 receptors), though α2-mediated inhibition is the dominant sympathetic effect. * **Atropine:** As a muscarinic antagonist, atropine can block the vagally-mediated insulin response.

Question 17: Which of the following hormones stimulates increased testosterone production by ovaries in PCOD?

A. Estrogen
B. Luteinizing Hormone (Correct Answer)
C. Follicle-stimulating Hormone
D. Inhibin

Explanation: **Explanation:** In **Polycystic Ovarian Disease (PCOD/PCOS)**, the fundamental endocrine derangement is an **increased LH:FSH ratio** (typically >2:1 or 3:1). 1. **Why LH is correct:** The ovaries contain two primary functional cells: Theca cells and Granulosa cells. Under the influence of **Luteinizing Hormone (LH)**, the **Theca cells** convert cholesterol into androgens (primarily androstenedione and testosterone). In PCOD, abnormally high pulses of LH lead to hyperplasia of the theca cells, resulting in **hyperandrogenism** (excessive testosterone production). This excess testosterone is responsible for clinical features like hirsutism and acne. 2. **Why other options are incorrect:** * **FSH (Follicle-stimulating Hormone):** FSH acts on **Granulosa cells** to stimulate the enzyme *aromatase*, which converts androgens into estrogens. In PCOD, FSH levels are relatively low or insufficient, leading to a "bottleneck" where androgens accumulate because they aren't being converted to estrogen. * **Estrogen:** While estrogen levels (specifically estrone) are often chronically elevated in PCOD due to peripheral conversion of androgens in adipose tissue, estrogen itself does not stimulate the production of testosterone; it actually provides negative feedback to the pituitary. * **Inhibin:** Inhibin (specifically Inhibin B) is produced by granulosa cells and primarily functions to inhibit FSH secretion. It does not stimulate androgen production. **NEET-PG High-Yield Pearls:** * **The "Two-Cell, Two-Gonadotropin" Theory:** LH acts on Theca cells (Androgen synthesis); FSH acts on Granulosa cells (Aromatization to Estrogen). * **Insulin Resistance:** Hyperinsulinemia in PCOD further exacerbates the condition by stimulating theca cells to produce more androgens and decreasing **Sex Hormone Binding Globulin (SHBG)**, which increases "free" (active) testosterone. * **Gold Standard Diagnosis:** Rotterdam Criteria (requires 2 out of 3: Hyperandrogenism, Oligo/anovulation, and Polycystic ovaries on ultrasound).

Question 18: ACTH secretion is highest during which part of the day?

A. Noon
B. Evening
C. Morning (Correct Answer)
D. Night

Explanation: **Explanation:** The secretion of **ACTH (Adrenocorticotropic Hormone)** and its downstream product, **Cortisol**, follows a distinct **Diurnal (Circadian) Rhythm**. This rhythm is regulated by the suprachiasmatic nucleus (SCN) of the hypothalamus, which controls the release of Corticotropin-Releasing Hormone (CRH). **Why Morning is Correct:** ACTH levels begin to rise during the late stages of sleep and reach their **peak (nadir) between 6:00 AM and 9:00 AM**. This surge prepares the body for the physiological stresses of waking and the day's activities by increasing blood glucose levels and metabolic activity. **Why Other Options are Incorrect:** * **Noon:** Levels begin to decline steadily after the morning peak. * **Evening:** ACTH levels continue to drop throughout the afternoon and evening. * **Night:** ACTH and Cortisol reach their **lowest levels (trough)** shortly after the onset of sleep, typically around **midnight**. **High-Yield NEET-PG Pearls:** 1. **Pulsatile Secretion:** ACTH is secreted in pulses; however, the frequency and amplitude of these pulses are highest in the early morning. 2. **Clinical Correlation:** To diagnose **Cushing’s Syndrome**, we look for the loss of this diurnal rhythm (e.g., elevated late-night salivary cortisol). 3. **Stress Override:** While the circadian rhythm is the primary regulator, acute physical or emotional stress can override this cycle, causing a spike in ACTH at any time of day. 4. **Shift Workers:** The rhythm is not fixed to clock time but to the sleep-wake cycle; it takes about 1–2 weeks for the rhythm to shift after a change in sleep patterns.

Question 19: What is the Chvostek sign?

A. Twitching of circumoral muscles on tapping of the facial nerve (Correct Answer)
B. Involuntary blink on tapping of the facial nerve
C. Inability to open the eye on tapping of the facial nerve
D. Inability to close the eye on tapping of the facial nerve

Explanation: **Explanation:** The **Chvostek sign** is a clinical indicator of **latent tetany**, most commonly caused by **hypocalcemia**. **1. Why Option A is correct:** Hypocalcemia increases neuronal excitability by lowering the threshold for depolarization (it makes the resting membrane potential less negative and closer to the threshold). When the facial nerve is tapped anterior to the external auditory meatus (over the parotid gland), the mechanical stimulus triggers an abnormal neuromuscular discharge. This results in the twitching of the facial muscles, particularly the circumoral muscles (muscles around the mouth and nose) on the ipsilateral side. **2. Why the other options are incorrect:** * **Option B:** An involuntary blink on tapping the glabella is known as the **Myerson sign** (seen in Parkinson’s disease). While tapping the facial nerve may cause a blink as part of the Chvostek response, the classic definition specifically involves the twitching of the mouth or nose. * **Options C & D:** These options describe motor deficits (paralysis). Inability to close the eye is characteristic of **Bell’s Palsy** (lower motor neuron lesion of the facial nerve), not hypocalcemic tetany, which is characterized by hyper-excitability, not paralysis. **Clinical Pearls for NEET-PG:** * **Trousseau’s Sign:** Carpopedal spasm induced by inflating a BP cuff above systolic pressure for 3 minutes. It is **more sensitive and specific** than Chvostek’s sign for hypocalcemia. * **Erb’s Sign:** Hyperexcitability of muscles to subthreshold electrical stimulation. * **Causes of Hypocalcemia:** Hypoparathyroidism, Vitamin D deficiency, Acute Pancreatitis, and Alkalosis (which decreases ionized calcium).

Question 20: Where are the alpha-estrogen receptors located?

A. Membrane receptors in breast
B. Nuclear receptors in breast (Correct Answer)
C. Membrane receptors in ovaries
D. Nuclear receptors in ovaries

Explanation: **Explanation:** Estrogen receptors (ERs) are members of the **nuclear receptor superfamily** of intracellular transcription factors. Estrogen, being a lipid-soluble steroid hormone, diffuses across the cell membrane to bind with these receptors. Upon binding, the receptor-ligand complex translocates to the nucleus (if not already present), binds to Estrogen Response Elements (EREs) on DNA, and regulates gene transcription. **Why Option B is Correct:** There are two main subtypes of estrogen receptors: **ER-alpha (ERα)** and **ER-beta (ERβ)**. ERα is the predominant subtype found in the **breast** (specifically mammary epithelium) and the uterus. Its activation is responsible for the proliferative effects of estrogen in these tissues. **Analysis of Incorrect Options:** * **Options A & C:** While a small fraction of estrogen receptors (GPER) are membrane-bound for rapid non-genomic signaling, the classic alpha-estrogen receptors are fundamentally classified as **nuclear receptors**. * **Option D:** While ERα is present in the ovaries (theca cells), **ER-beta (ERβ)** is the predominant isoform found in the granulosa cells of the ovaries. **High-Yield NEET-PG Pearls:** * **Location Summary:** ERα is primarily in the breast, uterus, and liver; ERβ is primarily in the ovaries, prostate, and colon. * **Clinical Correlation:** ERα status is a critical biomarker in breast cancer; ER-positive tumors are candidates for endocrine therapies like **Tamoxifen** (a SERM). * **Mechanism:** Steroid receptors (Estrogen, Progesterone, Testosterone) are typically **Type I nuclear receptors**, whereas Thyroid and Vitamin D receptors are **Type II** (already bound to DNA).

Practice by Chapter

Principles of Endocrine Regulation

Practice Questions

Hypothalamus and Pituitary Gland

Practice Questions

Thyroid Physiology

Practice Questions

Adrenal Cortex and Medulla

Practice Questions

Pancreatic Hormones and Glucose Metabolism

Practice Questions

Calcium and Phosphate Homeostasis

Practice Questions

Growth Hormone and Growth Factors

Practice Questions

Endocrine Regulation of Metabolism

Practice Questions

Hormone Receptors and Signaling

Practice Questions

Assessment of Endocrine Function

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free