Endocrinology Practice Questions

Q: Which one of the following makes epiphyseal cartilage matrix fail to calcify?

Hypovitaminosis D. **Explanation:** **Why Hypovitaminosis D is correct:** Vitamin D (Calcitriol) is essential for the mineralization of the bone matrix. Its primary role is to maintain adequate serum levels of Calcium and Phosphate by increasing intestinal absorption. In **Hypovitaminosis D**, there is a deficiency of these minerals in the extracellular fluid. Consequently, while the chondrocytes continue to proliferate and create the osteoid (organic matrix) at the epiphyseal plate, this matrix **fails to calcify**. This leads to the accumulation of unmineralized osteoid, resulting in the clinical condition known as **Rickets** in children and **Osteomalacia** in adults. **Why the other options are incorrect:** * **Thyroxine (A):** Thyroid hormones are essential for linear growth and skeletal maturation. Deficiency leads to delayed epiphyseal closure and stunting (Cretinism), but it does not specifically cause a failure of matrix calcification. * **Hypervitaminosis A (B):** Excessive Vitamin A accelerates the resorption of cartilage and bone, leading to premature closure of the epiphyses and thinning of the bone cortex, rather than a failure of calcification. * **Hydrocortisone (D):** Glucocorticoids generally inhibit bone formation by decreasing osteoblast activity and reducing intestinal calcium absorption, but they do not specifically target the calcification mechanism of the epiphyseal cartilage matrix in the same manner as Vitamin D deficiency. **High-Yield NEET-PG Pearls:** * **Rickets Hallmark:** Failure of osteoid mineralization + expansion of the epiphyseal plate (widening/cupping/fraying on X-ray). * **Vitamin D Pathway:** 7-dehydrocholesterol → Cholecalciferol (Skin) → 25-OH Vit D (Liver) → 1,25-(OH)₂ Vit D (Kidney via 1-alpha-hydroxylase). * **Alkaline Phosphatase (ALP):** Characteristically **elevated** in Vitamin D deficiency as osteoblasts attempt to compensate for the lack of mineralization.

Q: Hyperkalemia stimulates the secretion of which hormone?

Aldosterone. **Explanation:** **Aldosterone** is the primary mineralocorticoid secreted by the *zona glomerulosa* of the adrenal cortex. Its secretion is regulated by two main stimuli: the **Renin-Angiotensin-Aldosterone System (RAAS)** and **plasma potassium levels**. When plasma potassium levels rise (Hyperkalemia), it directly depolarizes the membranes of the zona glomerulosa cells. This opens voltage-gated calcium channels, leading to an influx of calcium, which triggers the synthesis and release of aldosterone. Once secreted, aldosterone acts on the **principal cells** of the late distal tubule and collecting duct to increase the activity of Na⁺/K⁺-ATPase pumps and ENaC channels. This results in sodium reabsorption and, crucially, **increased potassium secretion** into the urine, thereby restoring potassium homeostasis. **Why other options are incorrect:** * **Antidiuretic hormone (ADH):** Primarily regulated by plasma osmolarity and blood volume; its main role is water reabsorption via aquaporins. * **Secretin:** A gastrointestinal hormone stimulated by acidic chyme in the duodenum; it promotes bicarbonate secretion from the pancreas. * **Parathormone (PTH):** Regulated by low ionized serum calcium levels; it acts to increase calcium and decrease phosphate levels. **High-Yield NEET-PG Pearls:** * **Direct Stimulus:** Potassium is the most potent direct stimulus for aldosterone; even a 0.1 mEq/L rise can significantly increase secretion. * **Conn’s Syndrome:** Primary hyperaldosteronism typically presents with the triad of hypertension, hypokalemia, and metabolic alkalosis. * **Inverse Relationship:** While hyperkalemia stimulates aldosterone, aldosterone deficiency (as seen in Addison’s disease) leads to life-threatening hyperkalemia.

Q: Prolactin secretion is increased by all EXCEPT:

Dopamine. **Explanation:** The regulation of prolactin 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 portal hypophyseal vessels. It acts on **D2 receptors** located on lactotrophs to inhibit the synthesis and secretion of prolactin. Therefore, dopamine *decreases* prolactin levels, making it the correct "EXCEPT" choice. **2. Why the Other Options are Incorrect:** * **Sleep:** Prolactin secretion is pulsatile and follows a diurnal rhythm. Levels rise significantly during sleep (especially non-REM), peaking in the early morning hours. * **Pregnancy:** High levels of estrogen during pregnancy stimulate the hypertrophy and hyperplasia of lactotrophs, leading to a marked increase in prolactin secretion. * **Stress:** Prolactin is considered a "stress hormone." Physical or emotional stress (including exercise, surgery, or hypoglycemia) triggers a rapid release of prolactin via serotonergic and opioid pathways. **High-Yield Clinical Pearls for NEET-PG:** * **TRH Connection:** Thyrotropin-releasing hormone (TRH) acts as a potent prolactin-releasing factor. This explains why patients with **Primary Hypothyroidism** (high TRH) often present with hyperprolactinemia. * **Drug-Induced Hyperprolactinemia:** Any drug that blocks D2 receptors (e.g., Antipsychotics like Haloperidol, or Prokinetics like Metoclopramide) will cause elevated prolactin levels. * **Stalk Effect:** Any pituitary tumor or trauma that compresses the pituitary stalk prevents dopamine from reaching the lactotrophs, leading to increased prolactin (the only hormone that increases when the stalk is cut).

Q: Prolactin secretion is not stimulated by:

Levodopa. **Explanation:** The regulation of prolactin (PRL) is unique among anterior pituitary hormones because it is primarily under **tonic inhibition** by the hypothalamus. The major prolactin-inhibiting factor (PIF) is **Dopamine**, which acts on D2 receptors of the lactotrophs. **Why Levodopa is the Correct Answer:** Levodopa (L-Dopa) is a precursor to dopamine. When administered, it crosses the blood-brain barrier and increases dopamine levels in the brain. Since dopamine inhibits prolactin release, **Levodopa decreases prolactin secretion** rather than stimulating it. Therefore, it is the correct answer as it is an inhibitor. **Analysis of Incorrect Options:** * **Sleep:** Prolactin secretion follows a pulsatile and diurnal rhythm. Levels rise significantly during sleep (especially during non-REM sleep), peaking in the early morning hours. * **Estrogen:** Estrogen stimulates the hypertrophy and hyperplasia of lactotrophs and directly increases prolactin gene expression. This is why prolactin levels are higher in females after puberty. * **Pregnancy:** During pregnancy, high levels of estrogen and progesterone lead to a progressive increase in prolactin levels (up to 10-20 fold) to prepare the mammary glands for lactation. **High-Yield Clinical Pearls for NEET-PG:** * **TRH (Thyrotropin-Releasing Hormone):** While primarily for TSH, TRH is a potent stimulator of prolactin. This explains why patients with **Primary Hypothyroidism** often have hyperprolactinemia. * **Dopamine Antagonists:** Drugs like antipsychotics (Haloperidol) and prokinetics (Metoclopramide) block D2 receptors, leading to hyperprolactinemia and galactorrhea. * **Suckling Reflex:** This is the most potent physiological stimulus for prolactin release, mediated by a neuroendocrine reflex that inhibits dopamine release.

Q: What is true about glucagon?

Has no effect on muscle glycogenolysis. **Explanation:** Glucagon is a catabolic hormone secreted by the **alpha cells of the pancreas**, primarily acting to increase blood glucose levels during fasting or hypoglycemia. **Why Option B is correct:** Glucagon acts specifically on the liver because **skeletal muscle lacks glucagon receptors**. While muscle contains significant glycogen stores, these are reserved for local energy production during exercise. Muscle glycogenolysis is stimulated by epinephrine (via $\beta_2$ receptors) and calcium ions, but not by glucagon. In contrast, glucagon is the primary driver of **hepatic glycogenolysis**. **Analysis of Incorrect Options:** * **A. Hyperglycemia stimulates its release:** Incorrect. Glucagon is inhibited by hyperglycemia and stimulated by **hypoglycemia**. Its primary role is to prevent blood glucose from falling too low. * **C. Stimulates glycolysis:** Incorrect. Glucagon **inhibits glycolysis** (the breakdown of glucose for energy) in the liver to conserve glucose for release into the bloodstream. It does this by decreasing levels of Fructose-2,6-bisphosphate. * **D. Inhibits gluconeogenesis:** Incorrect. Glucagon **stimulates gluconeogenesis** (the synthesis of glucose from non-carbohydrate sources like amino acids) to maintain euglycemia during prolonged fasting. **High-Yield NEET-PG Pearls:** * **Mechanism of Action:** Glucagon acts via a **G-protein coupled receptor (Gs)**, increasing intracellular **cAMP** and activating Protein Kinase A. * **Amino Acids:** Arginine and Alanine *stimulate* glucagon release (this prevents hypoglycemia during a pure protein meal). * **Clinical Use:** Glucagon is the treatment of choice for **Beta-blocker overdose** because it increases cAMP in cardiac tissue independently of beta-receptors.

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.

Question 1

Which one of the following makes epiphyseal cartilage matrix fail to calcify?

Accepted Answer

Hypovitaminosis D

Answer

Thyroxine

Answer

Hypervitaminosis A

Answer

Hydrocortisone

Question 2

Hyperkalemia stimulates the secretion of which hormone?

Accepted Answer

Aldosterone

Answer

Antidiuretic hormone (ADH)

Answer

Secretin

Answer

Parathormone

Question 3

Prolactin secretion is increased by all EXCEPT:

Accepted Answer

Dopamine

Answer

Sleep

Answer

Pregnancy

Answer

Stress

Question 4

Prolactin secretion is not stimulated by:

Accepted Answer

Levodopa

Answer

Sleep

Answer

Estrogen

Answer

Pregnancy

Question 5

All of the following are true about osteoclasts except?

Accepted Answer

PTH acts directly on osteoclasts

Answer

Derived from monocytes

Answer

Associated with bone demineralisation

Answer

Can phagocytose foreign bodies

Question 6

What is true about glucagon?

Accepted Answer

Has no effect on muscle glycogenolysis

Answer

Hyperglycemia stimulates its release

Answer

Stimulates glycolysis

Answer

Inhibits gluconeogenesis

Question 7

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

Accepted Answer

Dopamine

Answer

Vasopressin

Answer

Vasoactive intestinal peptide

Answer

Acetylcholine

Question 8

Plasma half-life of insulin is:

Accepted Answer

10 minutes

Answer

1 minute

Answer

1 hour

Answer

2 hours

Question 9

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

Accepted Answer

Testosterone

Answer

Estrogen

Answer

Growth hormone

Answer

Insulin

Question 10

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)

Endocrinology — MCQs

Endocrinology — MCQs

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