Endocrinology Practice Questions

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.

Q: What is a stimulus for insulin secretion?

Growth hormone. ### Explanation **1. Why Growth Hormone (GH) is the Correct Answer:** Growth hormone is a potent **diabetogenic hormone**. It stimulates insulin secretion through two primary mechanisms: * **Direct Action:** GH directly stimulates the pancreatic beta cells to secrete insulin. * **Indirect Action (Insulin Resistance):** GH decreases glucose uptake in peripheral tissues (muscle and fat) and increases hepatic gluconeogenesis. This leads to an increase in blood glucose levels (post-receptor insulin resistance), which subsequently acts as a potent feedback stimulus for further insulin release. **2. Analysis of Incorrect Options:** * **A. Somatostatin:** This is a universal inhibitory hormone. In the pancreas, delta cells secrete somatostatin, which acts via paracrine signaling to **inhibit** the secretion of both insulin and glucagon. * **C. Diuretics:** Specifically, Thiazide diuretics are known to **inhibit** insulin secretion (often leading to hyperglycemia) by opening ATP-sensitive potassium channels or causing hypokalemia, which hyperpolarizes the beta-cell membrane. * **D. α-agonist:** Adrenergic control of insulin is dual-natured. However, **α2-adrenergic stimulation** is the dominant effect of catecholamines on the pancreas, resulting in the **inhibition** of insulin secretion. (Conversely, β2-agonists stimulate insulin release). **3. High-Yield Clinical Pearls for NEET-PG:** * **Most Potent Stimulus:** The most potent physiological stimulus for insulin secretion is **Glucose**. * **Incretin Effect:** Oral glucose causes a greater insulin response than intravenous glucose due to GIP and GLP-1 (Incretins). * **Amino Acids:** Arginine and Lysine are strong stimulators of insulin. * **Autonomic Control:** Parasympathetic (Vagal) stimulation **increases** insulin, while Sympathetic (α-effect) **decreases** it. * **Hormonal Stimuli:** Glucagon, Cortisol, and GH all increase insulin secretion (diabetogenic hormones).

Q: Low levels of dopamine produced by the hypothalamus is a pathologic condition associated with which of the blood hormone levels?

High prolactin (PRL). **Explanation:** The correct answer is **A. High prolactin (PRL)**. **1. Why it is correct:** In the hypothalamus-pituitary axis, dopamine acts as the primary **Prolactin-Inhibiting Hormone (PIH)**. Unlike most other anterior pituitary hormones which require a "releasing hormone" to be secreted, prolactin is under **tonic (constant) inhibition** by dopamine. Dopamine is secreted by the tuberoinfundibular neurons of the hypothalamus into the hypophyseal portal system, where it binds to D2 receptors on lactotrophs. Therefore, any pathological condition that lowers hypothalamic dopamine levels or obstructs its flow to the pituitary (e.g., pituitary stalk compression) results in "disinhibition," leading to **hyperprolactinemia**. **2. Why other options are incorrect:** * **B. High TSH:** TSH is primarily regulated by Thyrotropin-Releasing Hormone (TRH). While dopamine has a minor inhibitory effect on TSH, low dopamine is not the primary driver of pathological TSH elevation. * **C. High cortisol:** Cortisol is regulated by ACTH from the pituitary and CRH from the hypothalamus. Dopamine does not play a significant role in this axis. * **D. Low growth hormone (GH):** Dopamine actually stimulates GH secretion in healthy individuals. Therefore, low dopamine would more likely lead to decreased GH, but this is not the classic clinical association compared to the profound effect on prolactin. **Clinical Pearls for NEET-PG:** * **Stalk Effect:** Any lesion compressing the pituitary stalk (e.g., Craniopharyngioma) prevents dopamine from reaching the pituitary, causing elevated prolactin. * **Drug-Induced Hyperprolactinemia:** Antipsychotics (D2 antagonists) are a common cause of high prolactin, leading to galactorrhea and amenorrhea. * **TRH Connection:** In primary hypothyroidism, high TRH levels can also stimulate lactotrophs, causing hyperprolactinemia.

Q: c-AMP acts as a second messenger for all of the following hormones, EXCEPT:

GH. **Explanation:** The mechanism of hormone action is determined by the chemical nature of the hormone and its specific receptor. Hormones that utilize **c-AMP (Cyclic Adenosine Monophosphate)** as a second messenger typically bind to G-protein coupled receptors (GPCRs) that activate Adenylate Cyclase. **1. Why GH is the correct answer:** **Growth Hormone (GH)**, along with Prolactin and Insulin, does not use the c-AMP pathway. Instead, GH binds to a single-transmembrane receptor that activates the **JAK-STAT pathway** (Janus Kinase-Signal Transducer and Activator of Transcription). This involves tyrosine kinase activity rather than the activation of G-proteins and secondary messengers like c-AMP. **2. Why the other options are incorrect:** * **TSH (Thyroid Stimulating Hormone):** Acts via the Gs-protein coupled receptor to increase c-AMP, which stimulates thyroid hormone synthesis and release. * **LH (Luteinizing Hormone):** Like FSH and hCG, LH utilizes the c-AMP pathway to stimulate steroidogenesis in the gonads (Leydig cells in males and Theca cells in females). * **Glucagon:** Binds to GPCRs in the liver to increase c-AMP levels, which subsequently activates Protein Kinase A (PKA) to promote glycogenolysis and gluconeogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **JAK-STAT Pathway Mnemonic:** Remember **"PIG"** – **P**rolactin, **I**mmunomodulators (Cytokines/Interleukins), and **G**rowth Hormone. * **c-AMP Pathway:** Used by **FLAT ChAMP** (FSH, LH, ACTH, TSH, CRH, hCG, ADH (V2 receptor), MSH, PTH) and Glucagon. * **IP3/DAG Pathway:** Used by **GOAT** (GnRH, Oxytocin, ADH (V1 receptor), TRH). * **cGMP Pathway:** Used by ANP, BNP, and Nitric Oxide (NO).

Question 1

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 2

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 3

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 4

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 5

25-dihydrocholecalciferol acts on which type of receptors?

Accepted Answer

Intranuclear receptors

Answer

Surface receptors

Answer

Cytosolic receptors

Answer

None of the above

Question 6

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

Question 7

What is a stimulus for insulin secretion?

Accepted Answer

Growth hormone

Answer

Somatostatin

Answer

Diuretics

Answer

a-agonist

Question 8

A 48-year-old male patient, known diabetic on insulin with truncal obesity, presents for a routine checkup. The agent used in the treatment of this patient has all the following actions except?

Accepted Answer

Adipose tissue is less sensitive to it than many other tissues.

Answer

It inhibits the release of free fatty acids (FFA) from adipose tissue.

Answer

It enhances the uptake of glucose into adipose cells via the GLUT4 transporter.

Answer

In adipose tissue, it inhibits the activity of hormone-sensitive lipase.

Question 9

Low levels of dopamine produced by the hypothalamus is a pathologic condition associated with which of the blood hormone levels?

Accepted Answer

High prolactin (PRL)

Answer

High TSH

Answer

High cortisol

Answer

Low growth hormone (GH)

Question 10

c-AMP acts as a second messenger for all of the following hormones, EXCEPT:

Accepted Answer

GH

Answer

TSH

Answer

LH

Answer

Glucagon

Endocrinology — MCQs

Endocrinology — MCQs

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