Endocrinology Practice Questions

Q: Which of the following is NOT a prolactin-releasing factor?

Dopamine. ### Explanation The regulation of prolactin (PRL) secretion is unique among anterior pituitary hormones because it is under **tonic inhibition** by the hypothalamus. **1. Why Dopamine is the Correct Answer:** Dopamine is the primary **Prolactin-Inhibiting Factor (PIF)**. It is secreted by the tuberoinfundibular dopaminergic (TIDA) neurons into the hypophyseal portal system. It acts on **D2 receptors** located on the lactotrophs of the anterior pituitary to decrease cAMP levels, thereby inhibiting the synthesis and release of prolactin. Therefore, it is not a releasing factor but a potent inhibitor. **2. Analysis of Other Options (Releasing Factors):** While there is no single "Prolactin Releasing Hormone," several substances stimulate its release: * **Vasoactive Intestinal Peptide (VIP):** A potent stimulator of prolactin release, often acting in a paracrine fashion within the pituitary. * **Vasopressin (ADH):** Known to stimulate lactotrophs, especially during stress responses. * **Acetylcholine:** Acts via muscarinic receptors to stimulate prolactin secretion (though its role is less dominant than TRH or VIP). * *Note:* **TRH (Thyrotropin-Releasing Hormone)** is also a major physiological prolactin-releasing factor. **3. NEET-PG High-Yield Pearls:** * **The "Disconnect" Effect:** Any injury to the pituitary stalk (trauma, tumors like Craniopharyngioma) leads to a decrease in all pituitary hormones **EXCEPT prolactin**, which rises because it is freed from dopamine's inhibitory control. * **Drug-Induced Hyperprolactinemia:** Antipsychotics (D2 antagonists) like Haloperidol or Risperidone commonly cause galactorrhea by blocking dopamine's inhibitory effect. * **Prolactin & Amenorrhea:** High prolactin levels inhibit **GnRH pulsatility**, leading to secondary amenorrhea and infertility.

Q: Plasma half-life of insulin is:

10 minutes. **Explanation:** The plasma half-life of insulin is a high-yield fact in endocrinology. Once secreted into the portal circulation, insulin is rapidly cleared from the plasma, primarily by the liver (about 50%) and the kidneys. **1. Why 10 minutes is correct:** In healthy individuals, the biological half-life of endogenous insulin is approximately **5 to 10 minutes**. This rapid turnover is physiological; it allows the body to make quick, minute-to-minute adjustments in blood glucose levels. If insulin persisted longer, post-prandial glucose regulation would be imprecise, leading to prolonged hypoglycemia after a meal. **2. Why the other options are incorrect:** * **1 minute (Option A):** This is too short. While insulin action begins quickly, the degradation process by the enzyme *insulinase* takes slightly longer than sixty seconds to reduce plasma concentration by half. * **1 hour (Option C) and 2 hours (Option D):** These durations are far too long for endogenous insulin. However, students often confuse this with the **pharmacokinetics of exogenous "Regular" insulin**, which has a peak action at 2–3 hours and a duration of 5–8 hours when injected subcutaneously. **Clinical Pearls for NEET-PG:** * **Degradation:** The primary enzyme responsible for insulin breakdown is **Insulin-degrading enzyme (IDE)** or insulinase, found mainly in the liver and kidneys. * **C-Peptide:** Unlike insulin, C-peptide has a longer half-life (approx. **30 minutes**). This makes it a better clinical marker for measuring endogenous insulin production (beta-cell function). * **Excretion:** The liver clears the majority of endogenous insulin, but the **kidneys** clear the majority of exogenous (injected) insulin. Therefore, insulin requirements often decrease in patients with chronic kidney disease (CKD).

Q: Which of the following pituitary hormones does not have a corresponding releasing hormone from the hypothalamus?

Prolactin. **Explanation:** The secretion of anterior pituitary hormones is primarily regulated by **releasing hormones** produced in the hypothalamus. However, **Prolactin** is unique because its primary hypothalamic control is **tonic inhibition**, rather than stimulation. 1. **Why Prolactin is the correct answer:** Unlike other anterior pituitary hormones, there is no specific "Prolactin-Releasing Hormone" (PRH) that serves as its primary regulator. Instead, the hypothalamus exerts a constant inhibitory influence via **Dopamine** (acting on D2 receptors). When the connection between the hypothalamus and pituitary is severed (e.g., pituitary stalk transection), levels of all other hormones decrease, but **Prolactin levels rise** because the inhibitory "brake" of dopamine is removed. 2. **Why the other options are incorrect:** * **FSH (and LH):** Regulated by **Gonadotropin-Releasing Hormone (GnRH)**. * **TSH:** Regulated by **Thyrotropin-Releasing Hormone (TRH)**. * **ACTH:** Regulated by **Corticotropin-Releasing Hormone (CRH)**. **High-Yield Clinical Pearls for NEET-PG:** * **Dopamine = Prolactin-Inhibiting Hormone (PIH).** * **TRH Paradox:** While TRH is the releasing hormone for TSH, in pathological states (like primary hypothyroidism), high levels of TRH can also stimulate Prolactin release, leading to galactorrhea. * **Stalk Effect:** Any lesion compressing the pituitary stalk (e.g., Craniopharyngioma) causes **Hyperprolactinemia** due to the loss of dopamine delivery to the lactotrophs. * **Drug-Induced:** Antipsychotics (D2 receptor blockers) commonly cause hyperprolactinemia and gynecomastia/galactorrhea as a side effect.

Q: Most hormone levels decrease with aging. Which of the following hormones does NOT follow this trend?

Prolactin. ### Explanation The aging process is generally associated with a decline in the secretory capacity of various endocrine glands, a phenomenon often referred to as "somatopause," "andropause," or "adrenopause." However, **Prolactin** is a notable exception to this trend. #### Why Prolactin is the Correct Answer Unlike most pituitary and peripheral hormones, serum **Prolactin levels remain stable or may slightly increase** with age, particularly in men. In postmenopausal women, while there is an initial decline due to the loss of estrogen (which stimulates lactotrophs), the levels eventually stabilize and do not show the progressive, steep decline seen with other hormones. This is partly because the inhibitory dopaminergic control of prolactin may weaken with age. #### Why the Other Options are Incorrect * **A. Growth Hormone (GH):** GH secretion declines significantly with age (somatopause), leading to reduced muscle mass and increased visceral fat. * **C. Testosterone:** In men, bioavailable testosterone levels decrease by approximately 1% per year after the age of 30–40 (andropause). * **D. Aldosterone:** Aging is associated with a decrease in plasma renin activity and a subsequent decline in aldosterone levels, which can predispose the elderly to hyperkalemia. #### High-Yield NEET-PG Pearls * **Hormones that Decrease with Age:** GH, Testosterone, Estrogen, Aldosterone, DHEA (the most dramatic decline), and Melatonin. * **Hormones that Increase with Age:** **PTH** (due to Vitamin D deficiency/reduced calcium absorption), **FSH, and LH** (due to loss of negative feedback from gonads), and **Norepinephrine**. * **Thyroid Status:** TSH levels often slightly *increase* in the elderly, while T3 levels may decrease (Euthyroid Sick Syndrome is common in the elderly). * **Insulin:** While insulin levels may remain normal, **insulin resistance** increases with age.

Q: Zollinger-Ellison syndrome is due to a tumor of which of the following cell types?

G-cells. **Explanation:** **Zollinger-Ellison Syndrome (ZES)** is characterized by the development of a gastrin-secreting tumor, known as a **Gastrinoma**. 1. **Why G-cells are correct:** Gastrinomas originate from **G-cells**, which are neuroendocrine cells. While G-cells are normally found in the gastric antrum and duodenum, these tumors most commonly arise in the "Gastrinoma Triangle" (bounded by the confluence of the cystic and common bile ducts, the junction of the second and third portions of the duodenum, and the neck of the pancreas). The ectopic secretion of gastrin leads to hypergastrinemia, which causes massive hypersecretion of gastric acid, resulting in severe, recurrent peptic ulcers and secretory diarrhea. 2. **Why other options are incorrect:** * **Alpha cells:** These pancreatic islet cells secrete **glucagon**. A tumor of these cells is a Glucagonoma (presents with necrolytic migratory erythema and diabetes). * **Beta cells:** These secrete **insulin**. A tumor here is an Insulinoma (presents with Whipple’s triad of hypoglycemia). * **PP cells (F-cells):** These secrete **pancreatic polypeptide**. While they can form tumors (PPomas), they do not cause the acid-peptic symptoms seen in ZES. **Clinical Pearls for NEET-PG:** * **Diagnosis:** Best initial screening test is **Fasting Serum Gastrin** (>1000 pg/mL is diagnostic). The most sensitive provocative test is the **Secretin Stimulation Test** (Secretin normally inhibits gastrin but paradoxically increases it in ZES). * **Association:** Approximately 25% of ZES cases are associated with **Multiple Endocrine Neoplasia type 1 (MEN1)**. * **Location:** Most gastrinomas are found in the **duodenum** rather than the pancreas.

Q: Which of the following hormones has a cytoplasmic receptor?

Cortisol. **Explanation:** The location of a hormone receptor is primarily determined by the hormone's chemical nature (solubility). **1. Why Cortisol is Correct:** Cortisol is a **steroid hormone** derived from cholesterol. Being lipophilic (lipid-soluble), it easily diffuses through the lipid bilayer of the plasma membrane. Once inside the cell, it binds to specific **cytoplasmic receptors** (Type 1 Nuclear Receptors). The hormone-receptor complex then translocates into the nucleus, where it binds to Hormone Response Elements (HRE) on DNA to regulate gene transcription. **2. Why the Other Options are Incorrect:** * **Epinephrine (Option A):** A catecholamine derived from tyrosine. It is water-soluble and cannot cross the cell membrane; it binds to **G-protein coupled receptors (GPCRs)** on the cell surface. * **Insulin (Option B):** A peptide hormone. It binds to a specific **Enzyme-linked receptor** (Receptor Tyrosine Kinase) located on the cell membrane. * **FSH (Option C):** A glycoprotein (peptide) hormone. Like other pituitary hormones, it is large and polar, requiring a **cell surface GPCR** to initiate its action via the cAMP second messenger system. **3. High-Yield NEET-PG Clinical Pearls:** * **Cytoplasmic Receptors:** Primarily used by Steroids (Glucocorticoids, Mineralocorticoids, Androgens, Progesterone). * **Nucleoplasmic (Nuclear) Receptors:** Primarily used by **Thyroid hormones (T3/T4)**, Retinoic acid, and Vitamin D. Note: Though T3/T4 are amino acid derivatives, they act like steroids. * **Mnemonic for Cell Surface Receptors:** All peptide hormones + Catecholamines. * **Exception:** Estrogen receptors are predominantly found in the **nucleus**, unlike most other steroids which start in the cytoplasm.

Q: Which of the following hormones is stored the longest within a cell?

T3. **Explanation:** The duration for which a hormone is stored within a cell depends on its chemical nature and the storage mechanism of the gland. **Why T3 is the Correct Answer:** Thyroid hormones (T3 and T4) are unique because they are stored **extracellularly** in the follicular lumen as part of the **thyroglobulin** molecule (colloid). This storage mechanism is exceptionally efficient, allowing the thyroid gland to store enough hormone to supply the body’s requirements for **2 to 3 months**. This is the longest storage duration of any hormone in the human body. **Why Other Options are Incorrect:** * **Insulin (Option A):** As a peptide hormone, insulin is stored in cytosolic secretory granules. However, the pancreas typically stores only about a **5-day supply**, and it is rapidly released in response to glucose. * **PTH (Option B):** Parathyroid hormone is also a peptide hormone stored in granules within chief cells. Its storage is minimal, usually lasting only a **few hours**, as it is synthesized and secreted almost immediately in response to low serum calcium. * **Testosterone (Option D):** Steroid hormones are **not stored** to any significant degree. They are highly lipophilic and would leak through the cell membrane. Instead, they are synthesized de novo from cholesterol precursors on demand. **High-Yield NEET-PG Pearls:** * **Thyroid Exception:** Most endocrine glands store small amounts of hormones; the thyroid is the only gland that stores large quantities in an inactive form (colloid). * **Clinical Correlation:** This long storage explains why patients starting anti-thyroid drugs (like Carbimazole) take several weeks to become euthyroid—the body must first deplete the pre-stored 2-3 month supply of colloid. * **Steroid Rule:** Remember: "Steroids are made on demand, not stored."

Q: Negative Basal Metabolic Rate (BMR) is observed with which of the following?

Thyroid disturbance. **Explanation:** The **Basal Metabolic Rate (BMR)** is the minimum amount of energy required by the body to maintain vital functions (like breathing and circulation) at complete physical and mental rest. The **Thyroid gland** is the primary regulator of BMR. **1. Why Thyroid Disturbance is Correct:** Thyroid hormones (T3 and T4) directly regulate the metabolic activity of almost all tissues in the body by increasing oxygen consumption and mitochondrial activity. * **Hypothyroidism:** Leads to a **negative (decreased) BMR**, often falling 30% to 40% below normal. This results in symptoms like weight gain, cold intolerance, and bradycardia. * **Hyperthyroidism:** Leads to an increased BMR, often 50% to 100% above normal. **2. Why Other Options are Incorrect:** * **Pituitary Disturbance:** While the pituitary gland secretes TSH (which stimulates the thyroid), a pituitary disturbance only affects BMR *indirectly* via the thyroid axis. "Thyroid disturbance" is the more specific and direct physiological answer. * **Parathyroid Disturbance:** Parathyroid hormone (PTH) regulates calcium and phosphate homeostasis. It has no direct clinical impact on the body’s basal metabolic rate. **High-Yield Clinical Pearls for NEET-PG:** * **Surface Area Rule:** BMR is more closely related to surface area than to body weight. * **Specific Dynamic Action (SDA):** Proteins have the highest SDA (30%), meaning they increase metabolic rate significantly during digestion. * **Factors increasing BMR:** Fever (12% increase per 1°C), Pregnancy, Catecholamines (Epinephrine), and Male gender (due to testosterone). * **Gold Standard:** The most accurate way to measure BMR is via indirect calorimetry (measuring oxygen consumption).

Question 1

Which of the following is NOT a prolactin-releasing factor?

Accepted Answer

Dopamine

Answer

Vasopressin

Answer

Vasoactive intestinal peptide

Answer

Acetylcholine

Question 2

Plasma half-life of insulin is:

Accepted Answer

10 minutes

Answer

1 minute

Answer

1 hour

Answer

2 hours

Question 3

Which of the following hormones is mainly responsible for skeletal maturation?

Accepted Answer

Testosterone

Answer

Estrogen

Answer

Growth hormone

Answer

Insulin

Question 4

Which of the following pituitary hormones does not have a corresponding releasing hormone from the hypothalamus?

Accepted Answer

Prolactin

Answer

Follicle-stimulating hormone (FSH)

Answer

Thyroid-stimulating hormone (TSH)

Answer

Adrenocorticotropic hormone (ACTH)

Question 5

Most hormone levels decrease with aging. Which of the following hormones does NOT follow this trend?

Accepted Answer

Prolactin

Answer

Growth hormone

Answer

Testosterone

Answer

Aldosterone

Question 6

Zollinger-Ellison syndrome is due to a tumor of which of the following cell types?

Accepted Answer

G-cells

Answer

Alpha cells

Answer

Beta cells

Answer

PP cells

Question 7

Which of the following hormones has a cytoplasmic receptor?

Accepted Answer

Cortisol

Answer

Epinephrine

Answer

Insulin

Answer

FSH

Question 8

A 35-year-old man presents with a thyroid nodule. Laboratory studies reveal elevated serum calcitonin and normal serum calcium. Which of the following mechanisms best explains the normal calcium levels in this patient despite high serum calcitonin levels?

Accepted Answer

High levels of calcitonin downregulate its receptor

Answer

Concurrent parathyroid adenoma

Answer

Concurrent parathyroid hyperplasia

Answer

Increase in parathyroid hormone in response to hypocalcemia

Question 9

Which of the following hormones is stored the longest within a cell?

Accepted Answer

T3

Answer

Insulin

Answer

PTH

Answer

Testosterone

Question 10

Negative Basal Metabolic Rate (BMR) is observed with which of the following?

Accepted Answer

Thyroid disturbance

Answer

Pituitary disturbance

Answer

Parathyroid disturbance

Answer

All of the above

Endocrinology — MCQs

Endocrinology — MCQs

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