Endocrinology Practice Questions

Q: What are important stimuli for prolactin secretion?

Estrogen. **Explanation:** **1. Why Estrogen is Correct:** Estrogen is a potent stimulator of prolactin secretion. It acts directly on the anterior pituitary to stimulate the hypertrophy and hyperplasia of **lactotrophs** (prolactin-secreting cells). Furthermore, estrogen decreases the sensitivity of lactotrophs to the inhibitory effects of dopamine and directly stimulates the expression of the prolactin gene. This is clinically evident during pregnancy, where rising estrogen levels lead to a significant increase in prolactin levels to prepare the breasts for lactation. **2. Why the Other Options are Incorrect:** * **Dopamine (Option C):** This is the primary **inhibitor** of prolactin. Unlike other anterior pituitary hormones, prolactin is under tonic inhibitory control by dopamine (Prolactin Inhibiting Hormone) secreted from the hypothalamus. * **Insulin (Option A):** While insulin is an anabolic hormone, it does not serve as a primary stimulus for prolactin release. * **Growth Hormone (Option B):** GH and Prolactin are structurally similar (both are somatomammotropins), but GH does not stimulate the secretion of prolactin. **3. High-Yield NEET-PG Clinical Pearls:** * **TRH (Thyrotropin-Releasing Hormone):** In primary hypothyroidism, elevated TRH levels can stimulate lactotrophs, leading to **hyperprolactinemia**. * **Suckling Reflex:** The most important physiological stimulus for prolactin release post-partum. It inhibits dopamine release, thereby "disinhibiting" prolactin secretion. * **Prolactinoma:** The most common secretory tubulointerstitial tumor of the pituitary. * **Drugs:** Dopamine antagonists (e.g., Metoclopramide, Haloperidol) are common causes of drug-induced hyperprolactinemia.

Q: What is the major adrenocortical hormone in the blood?

Cortisol. **Explanation:** The adrenal cortex secretes several steroid hormones, but **Cortisol** is the predominant glucocorticoid and the most abundant adrenocortical hormone in human plasma. **1. Why Cortisol is the correct answer:** In humans, cortisol accounts for approximately **95% of all glucocorticoid activity**. It is secreted at a much higher rate (8–25 mg/day) compared to other steroids. Its high plasma concentration (average 10–20 µg/dL in the morning) and its critical role in glucose metabolism, stress response, and immune modulation make it the "major" hormone of the adrenal cortex. **2. Why the other options are incorrect:** * **Corticosterone (B):** While it has glucocorticoid activity, it is significantly less potent than cortisol in humans. It serves as a major glucocorticoid in rodents, but in humans, it is primarily a precursor in the aldosterone pathway. * **Aldosterone (C):** This is the primary mineralocorticoid. Although it is physiologically vital for sodium and potassium balance, its plasma concentration is extremely low (measured in **nanograms/dL**) compared to cortisol (measured in **micrograms/dL**). * **Deoxycorticosterone (D):** This is a precursor to aldosterone with mild mineralocorticoid activity. It is secreted in trace amounts and does not reach the systemic levels of cortisol. **High-Yield Facts for NEET-PG:** * **Transport:** 90–95% of cortisol is bound to **CBG (Transcortin)**; only the free fraction is biologically active. * **Diurnal Variation:** Cortisol levels peak in the early morning (approx. 8 AM) and are lowest around midnight. * **Potency:** Cortisol has a 1:1 ratio of glucocorticoid to mineralocorticoid activity, whereas Aldosterone has negligible glucocorticoid effect.

Q: Milk ejection is facilitated by:

Oxytocin. **Explanation:** The correct answer is **Oxytocin**. **Mechanism of Milk Ejection:** Milk ejection (the "let-down reflex") is a neuroendocrine reflex. When an infant suckles, sensory receptors in the nipple send signals to the hypothalamus, specifically the **paraventricular and supraoptic nuclei**. This triggers the release of oxytocin from the **posterior pituitary** into the bloodstream. Oxytocin causes the contraction of **myoepithelial cells** surrounding the mammary alveoli, squeezing milk into the ductal system and out through the nipple. **Analysis of Incorrect Options:** * **A. Prolactin:** While essential for lactation, Prolactin is responsible for **milk production (synthesis)** within the alveolar cells, not its ejection. It is secreted by the anterior pituitary. * **C. Growth Hormone:** GH promotes general tissue growth and has a permissive role in mammary gland development, but it does not acutely trigger milk release. * **D. ACTH:** Secreted by the anterior pituitary, ACTH stimulates the adrenal cortex to release cortisol. It has no direct role in the milk ejection reflex. **High-Yield Clinical Pearls for NEET-PG:** * **The "Love Hormone":** Oxytocin also causes uterine contractions during labor (Ferguson reflex) and aids in uterine involution postpartum. * **Psychological Influence:** The milk ejection reflex can be conditioned; the sound of a baby crying can trigger oxytocin release, while stress or pain can inhibit it via catecholamines. * **Prolactin vs. Oxytocin:** Remember the mnemonic: **P**rolactin **P**roduces, **O**xytocin **O**ozes (ejects). * **Inhibition:** Prolactin secretion is tonically inhibited by **Dopamine** (Prolactin-inhibiting factor).

Q: Calcitriol causes all except?

Reduce plasma Ca2+ concentration. **Explanation:** The primary physiological role of **Calcitriol (1,25-dihydroxycholecalciferol)**, the active form of Vitamin D, is to **increase plasma calcium and phosphate levels**. Therefore, the statement that it reduces plasma calcium concentration is incorrect. **Why the correct answer is "Reduce plasma Ca2+ concentration":** Calcitriol acts as a hypercalcemic hormone. It maintains calcium homeostasis by increasing the influx of calcium into the extracellular fluid (ECF) from the gut, kidneys, and bone. Reducing plasma calcium is the function of **Calcitonin**, not Calcitriol. **Analysis of other options:** * **Option A (Increases renal reabsorption):** Calcitriol acts on the distal convoluted tubules of the kidney to increase the reabsorption of both Calcium and Phosphate, preventing their loss in urine. * **Option C (Promotes intestinal absorption):** This is the most important action of Calcitriol. It increases the synthesis of **Calbindin-D** (a calcium-binding protein) in intestinal epithelial cells, facilitating the active transport of Ca2+ from the diet. * **Option D (Reduces Ca2+ resorption by bone):** This is a nuanced point. While Calcitriol is necessary for bone mineralization (indirectly), its primary systemic effect at physiological levels is to work with PTH to mobilize calcium from bone (resorption) to maintain serum levels. However, in the context of this MCQ, the definitive "false" statement is the reduction of plasma calcium. **High-Yield NEET-PG Pearls:** * **Rate-limiting step:** The conversion of 25-OH Vitamin D to 1,25-(OH)₂ Vitamin D by the enzyme **1-alpha-hydroxylase** in the kidney. * **Stimulants for Calcitriol:** High PTH, low serum Calcium, and low serum Phosphate. * **Vitamin D Deficiency:** Leads to Rickets (children) and Osteomalacia (adults). * **Mnemonic:** Calci**tri**ol **tri**es to increase Calcium in **three** ways (Gut, Kidney, Bone).

Q: Glucocorticoids have all the following actions except:

Decrease in glucose uptake by the heart. **Explanation:** Glucocorticoids (primarily Cortisol) are "stress hormones" that function to increase the availability of metabolic fuels. The core physiological principle is to prioritize glucose delivery to vital organs (Brain and Heart) while limiting its use in peripheral tissues. **Why Option D is the Correct Answer:** Glucocorticoids induce peripheral insulin resistance to conserve glucose. However, this inhibitory effect on glucose uptake occurs in **skeletal muscle and adipose tissue** (via inhibition of GLUT-4 translocation). Crucially, glucocorticoids **do not decrease glucose uptake in the heart or the brain**. In fact, during stress, the heart's metabolic demands are maintained or increased, making Option D a false statement regarding glucocorticoid action. **Analysis of Incorrect Options:** * **Option A (Increase in blood glucose):** Correct action. Cortisol stimulates **gluconeogenesis** in the liver and decreases peripheral utilization, leading to hyperglycemia (Adrenal diabetes). * **Option B (Increase in protein catabolism):** Correct action. Glucocorticoids are catabolic in extra-hepatic tissues (muscle, lymphoid, and connective tissue) to provide amino acids for hepatic gluconeogenesis. * **Option C (Anti-insulin action):** Correct action. They antagonize insulin's effects in peripheral tissues by interfering with the insulin signaling pathway, leading to decreased glucose uptake in muscles. **High-Yield NEET-PG Pearls:** * **Permissive Action:** Small amounts of glucocorticoids are required for catecholamines to exert their calorigenic and lipolytic effects. * **Hematological effects:** They cause **"Lymphocytopenia"** and **"Eosinopenia"** but lead to **"Neutrophilia"** (due to decreased margination). * **Bone:** They inhibit osteoblast activity and decrease intestinal Calcium absorption, leading to osteoporosis in Cushing’s syndrome.

Q: What is the ratio of C-peptide to insulin in normal adults?

1:1. ### Explanation **Concept and Correct Answer:** The synthesis of insulin occurs in the pancreatic beta cells. It begins as **Preproinsulin**, which is cleaved into **Proinsulin**. Proinsulin is then packaged into secretory granules, where it undergoes proteolytic cleavage by endopeptidases. This process splits the proinsulin molecule into two distinct parts: one molecule of **Insulin** and one molecule of **C-peptide** (Connecting peptide). Because they are derived from the same precursor molecule and released together via exocytosis in a stoichiometric fashion, they are secreted into the portal circulation in a **1:1 molar ratio**. Therefore, **Option C** is the correct answer. **Analysis of Incorrect Options:** * **Option A (2:1) and B (1:2):** These ratios are incorrect because the cleavage of one proinsulin molecule cannot mathematically yield more of one component than the other. * **Option D (1:4):** This does not reflect the physiological production process. While peripheral blood levels may show higher C-peptide concentrations due to different half-lives, the initial secretion ratio remains 1:1. **High-Yield Clinical Pearls for NEET-PG:** * **Half-life:** Although secreted 1:1, C-peptide has a longer half-life (~30 mins) compared to insulin (~5 mins). Consequently, peripheral plasma levels of C-peptide are typically higher than insulin. * **Metabolism:** Insulin undergoes significant first-pass metabolism in the **liver**, whereas C-peptide is primarily excreted by the **kidneys**. * **Diagnostic Utility:** C-peptide is a reliable marker of **endogenous insulin production**. It is used to distinguish between Type 1 and Type 2 Diabetes and to differentiate Factitious Hypoglycemia (low C-peptide) from Insulinoma (high C-peptide).

Q: 25-dihydrocholecalciferol acts on which type of receptors?

Intranuclear receptors. **Explanation:** The correct answer is **C. Intranuclear receptors.** **Mechanism of Action:** 1,25-dihydroxycholecalciferol (Calcitriol), the active form of Vitamin D, is a steroid-like hormone derived from cholesterol. Due to its lipophilic nature, it easily crosses the lipid bilayer of the cell membrane. Once inside the cell, it enters the nucleus and binds to the **Vitamin D Receptor (VDR)**. The VDR then forms a heterodimer with the **Retinoid X Receptor (RXR)**. This complex binds to specific DNA sequences known as **Vitamin D Response Elements (VDREs)**, initiating gene transcription and the synthesis of proteins like Calbindin, which facilitates intestinal calcium absorption. **Analysis of Options:** * **A. Surface receptors:** These are typically for peptide hormones (e.g., Insulin, PTH) or catecholamines that cannot cross the cell membrane. Vitamin D is lipid-soluble and does not require surface signaling. * **B. Cytosolic receptors:** While some steroid hormones (like Glucocorticoids) initially bind in the cytosol before translocating to the nucleus, the Vitamin D receptor is primarily localized within the **nucleus** even in its unoccupied state. **High-Yield Clinical Pearls for NEET-PG:** * **Target Organs:** The primary sites of action for Vitamin D are the Intestine (increases Ca/PO4 absorption), Bone (mineralization/resorption), and Kidney (increases Ca/PO4 reabsorption). * **Steroid Superfamily:** Vitamin D, Thyroid hormones (T3/T4), Retinoic acid, and Steroid hormones all act via nuclear receptors. * **Rate-limiting step:** The conversion of 25-OH Vitamin D to 1,25-(OH)₂ Vitamin D occurs in the kidney via the enzyme **1-alpha-hydroxylase**, which is stimulated by PTH.

Q: Thyroid-stimulating hormone (TSH) acts via which mechanism?

Cyclic adenosine monophosphate (cAMP) formation. **Explanation:** **1. Why Option A is Correct:** Thyroid-stimulating hormone (TSH) is a glycoprotein hormone that acts via a **G protein-coupled receptor (GPCR)** located on the basal membrane of thyroid follicular cells. Upon binding to its receptor, TSH activates the enzyme **adenylyl cyclase**, which converts ATP into **cyclic adenosine monophosphate (cAMP)**. cAMP acts as a second messenger, activating Protein Kinase A (PKA), which subsequently triggers the synthesis and release of thyroid hormones (T3 and T4), iodine uptake, and thyroglobulin proteolysis. **2. Why Other Options are Incorrect:** * **Option B:** TSH does not directly stimulate cellular processes. As a large, water-soluble peptide hormone, it cannot cross the lipid bilayer of the cell membrane. It requires a second messenger system (cAMP) to relay the signal from the membrane to the interior of the cell. * **Option C:** While TSH does involve "receptor stimulation," this is a vague description of the initial step rather than the specific **mechanism of action** (signal transduction pathway) requested by the question. In medical exams, the most specific biochemical pathway (cAMP) is the preferred answer. * **Option D:** Since B and C are either incorrect or less specific, "All of the above" is invalid. **3. NEET-PG High-Yield Pearls:** * **FLAT ChAMP:** A useful mnemonic for hormones using the cAMP pathway: **F**SH, **L**H, **A**CTH, **T**SH, **C**RH, **h**CG, **A**DH (V2 receptor), **M**SH, **P**TH. * **Dual Signaling:** While cAMP is the primary pathway, at high concentrations, TSH can also activate the **Phospholipase C (IP3/DAG)** pathway. * **Trophic Effect:** TSH not only stimulates hormone production but also causes hypertrophy and hyperplasia of thyroid cells; hence, high TSH levels lead to goiter.

Question 1

Insulin sensitivity increases with the following treatments except:

Accepted Answer

Fasting

Answer

Metformin

Answer

Acarbose

Answer

Exercise

Question 2

What are important stimuli for prolactin secretion?

Accepted Answer

Estrogen

Answer

Insulin

Answer

Growth hormone

Answer

Dopamine

Question 3

What is the major adrenocortical hormone in the blood?

Accepted Answer

Cortisol

Answer

Corticosterone

Answer

Aldosterone

Answer

Deoxycorticosterone

Question 4

Milk ejection is facilitated by:

Accepted Answer

Oxytocin

Answer

Prolactin

Answer

Growth hormone

Answer

ACTH

Question 5

Calcitriol causes all except?

Accepted Answer

Reduce plasma Ca2+ concentration

Answer

Increases renal tubular reabsorption of Ca2+

Answer

Promotes intestinal absorption of Ca2+

Answer

Reduces Ca2+ resorption by bone

Question 6

Which of the following would you expect to find in a patient whose diet has been low in calcium for 8 weeks?

Accepted Answer

Increased parathormone secretion

Answer

Increased phosphate levels

Answer

Raised calcitonin levels

Answer

Activation of 24,25-dihydroxycholecalciferol

Question 7

Glucocorticoids have all the following actions except:

Accepted Answer

Decrease in glucose uptake by the heart

Answer

Increase in blood glucose level

Answer

Increase in protein catabolism

Answer

Anti-insulin action in peripheral tissues

Question 8

What is the ratio of C-peptide to insulin in normal adults?

Accepted Answer

1:1

Answer

2:1

Answer

1:2

Answer

1:4

Question 9

25-dihydrocholecalciferol acts on which type of receptors?

Accepted Answer

Intranuclear receptors

Answer

Surface receptors

Answer

Cytosolic receptors

Answer

None of the above

Question 10

Thyroid-stimulating hormone (TSH) acts via which mechanism?

Accepted Answer

Cyclic adenosine monophosphate (cAMP) formation

Answer

Direct stimulation of cellular processes

Answer

Receptor stimulation

Answer

All of the above

Endocrinology — MCQs

Endocrinology — MCQs

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