Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 231: Thyroid-stimulating hormone (TSH) acts via which mechanism?

A. Cyclic adenosine monophosphate (cAMP) formation (Correct Answer)
B. Direct stimulation of cellular processes
C. Receptor stimulation
D. All of the above

Explanation: **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 232: What is a stimulus for insulin secretion?

A. Somatostatin
B. Growth hormone (Correct Answer)
C. Diuretics
D. a-agonist

Explanation: ### 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).

Question 233: Cutting of the pituitary stalk decreases all of the following hormones except?

A. ACTH
B. GH
C. Prolactin (Correct Answer)
D. FSH

Explanation: **Explanation:** The regulation of the anterior pituitary by the hypothalamus occurs via the **hypothalamic-hypophyseal portal system**. Most anterior pituitary hormones are under **stimulatory** control by hypothalamic releasing factors. However, **Prolactin** is the unique exception as it is under predominant **tonic inhibitory control** by **Dopamine** (also known as Prolactin-Inhibiting Hormone). 1. **Why Prolactin is correct:** When the pituitary stalk is severed, the delivery of dopamine from the hypothalamus to the anterior pituitary is interrupted. The removal of this tonic inhibition leads to "disinhibition," causing a paradoxical **increase** in Prolactin levels. 2. **Why other options are wrong:** * **ACTH, GH, and FSH** are all under stimulatory control (by CRH, GHRH, and GnRH, respectively). Cutting the stalk prevents these releasing hormones from reaching the pituitary, leading to a **decrease** in their secretion. * Posterior pituitary hormones (ADH and Oxytocin) also decrease because their transport via the nerve fibers in the stalk is halted. **Clinical Pearls for NEET-PG:** * **Stalk Effect:** Any lesion (like a craniopharyngioma) that compresses the pituitary stalk can cause hyperprolactinemia. * **Dopamine Agonists:** Drugs like Bromocriptine and Cabergoline mimic dopamine and are used to treat prolactinomas. * **TRH Exception:** While dopamine inhibits prolactin, **TRH (Thyrotropin-Releasing Hormone)** acts as a potent stimulator of prolactin release, which is why primary hypothyroidism can present with hyperprolactinemia.

Question 234: Which of the following best describes the function of the aromatase enzyme?

A. Converts estrogen to androgen
B. Converts androgen to estrogen (Correct Answer)
C. Helps in maintaining normal placental blood flow
D. Converts testosterone to dihydrotestosterone

Explanation: **Explanation:** The **aromatase enzyme** (also known as estrogen synthase) is a member of the Cytochrome P450 superfamily. Its primary function is the **aromatization of androgens into estrogens**. Specifically, it catalyzes the conversion of **androstenedione to estrone** and **testosterone to estradiol**. This process occurs in the granulosa cells of the ovaries (stimulated by FSH), the placenta, adipose tissue, and the brain. **Analysis of Options:** * **Option A is incorrect:** The pathway is unidirectional in the body; estrogens are derived from androgens, not vice versa. * **Option B is correct:** This is the fundamental biochemical role of aromatase, involving the removal of the C19 methyl group and the formation of an aromatic A-ring. * **Option C is incorrect:** While estrogens are vital for pregnancy, aromatase itself is not a direct regulator of placental hemodynamics. * **Option D is incorrect:** The conversion of testosterone to the more potent dihydrotestosterone (DHT) is catalyzed by the enzyme **5-alpha reductase**. **High-Yield Clinical Pearls for NEET-PG:** 1. **Aromatase Inhibitors (e.g., Letrozole, Anastrozole):** Used clinically to treat estrogen-receptor-positive breast cancer in postmenopausal women. 2. **Polycystic Ovary Syndrome (PCOS):** A relative deficiency or dysregulation in aromatase activity can lead to the accumulation of androgens, contributing to hirsutism and anovulation. 3. **Bone Health:** In males, aromatase is crucial because the conversion of testosterone to estrogen is necessary for the closure of epiphyseal plates and maintaining bone mineral density. 4. **Two-Cell, Two-Gonadotropin Theory:** LH stimulates Theca cells to produce androgens; FSH then stimulates Granulosa cells to use **aromatase** to convert those androgens into estrogens.

Question 235: Insulin release from pancreatic beta cells occurs via which mechanism?

A. Endocytosis
B. Exocytosis (Correct Answer)
C. Active transport
D. Facilitated diffusion

Explanation: **Explanation:** **Mechanism of Insulin Release (The Correct Answer):** Insulin is a peptide hormone synthesized in the rough endoplasmic reticulum and stored in membrane-bound secretory granules within pancreatic beta cells. When blood glucose levels rise, glucose enters the beta cell via **GLUT-2** transporters and undergoes glycolysis, increasing the **ATP/ADP ratio**. This closure of ATP-sensitive K+ channels leads to membrane depolarization, opening **Voltage-Gated Calcium Channels**. The resulting influx of $Ca^{2+}$ triggers the fusion of insulin-containing vesicles with the plasma membrane, releasing insulin into the extracellular space. This process of bulk transport via vesicle fusion is known as **Exocytosis**. **Analysis of Incorrect Options:** * **A. Endocytosis:** This is the process of taking substances *into* the cell by engulfing them in a vesicle (e.g., cholesterol uptake via LDL receptors). Insulin is being secreted, not internalized. * **C. Active Transport:** This involves moving ions or small molecules against a concentration gradient using ATP-pumps (e.g., Na+/K+ ATPase). Insulin is too large for protein pumps. * **D. Facilitated Diffusion:** This is a passive process using carrier proteins to move molecules down a gradient (e.g., glucose entry into cells via GLUT transporters). **High-Yield NEET-PG Pearls:** * **Biphasic Release:** Insulin secretion is biphasic; the first phase is the release of pre-formed granules, while the second phase involves the synthesis of new insulin. * **C-Peptide:** It is secreted in equimolar amounts with insulin and serves as a clinical marker for endogenous insulin production. * **Drug Link:** **Sulfonylureas** act by binding to the SUR1 subunit of the ATP-sensitive K+ channel, mimicking the effect of ATP to trigger insulin exocytosis.

Question 236: Which hormone stimulates FSH secretion?

A. Luteinizing hormone-releasing hormone (LHRH) (Correct Answer)
B. Thyrotropin-releasing hormone (TRH)
C. Testosterone
D. Estradiol

Explanation: **Explanation:** The secretion of Follicle-Stimulating Hormone (FSH) is primarily regulated by the hypothalamus through the pulsatile release of **GnRH (Gonadotropin-Releasing Hormone)**, also known as **Luteinizing Hormone-Releasing Hormone (LHRH)**. 1. **Why LHRH is correct:** LHRH is a decapeptide synthesized in the preoptic area of the hypothalamus. It travels via the hypothalamo-hypophyseal portal system to the anterior pituitary, where it binds to G-protein coupled receptors on **gonadotrophs**. This stimulation triggers the synthesis and release of both LH and FSH. The frequency of LHRH pulses determines which hormone is preferentially secreted: lower frequency pulses favor FSH release, while higher frequency pulses favor LH release. 2. **Why other options are incorrect:** * **TRH:** Stimulates the release of Thyroid-Stimulating Hormone (TSH) and Prolactin; it has no physiological stimulatory effect on FSH. * **Testosterone & Estradiol:** These are gonadal steroids that typically exert **negative feedback** on the hypothalamus and anterior pituitary to *inhibit* the secretion of GnRH and FSH/LH (with the exception of the estrogen-induced LH surge during ovulation). **High-Yield Clinical Pearls for NEET-PG:** * **Inhibin:** Specifically inhibits FSH secretion from the anterior pituitary without affecting LH. Inhibin B is the primary marker for spermatogenesis in males. * **Kallmann Syndrome:** Characterized by delayed puberty and anosmia due to the failure of GnRH (LHRH) neurons to migrate to the hypothalamus, leading to low FSH/LH levels. * **Pulsatility:** Continuous (non-pulsatile) administration of LHRH analogs (e.g., Leuprolide) causes downregulation of receptors, leading to a paradoxical *decrease* in FSH and LH, a principle used in treating prostate cancer and endometriosis.

Question 237: Which hormone is dominant during the luteal phase of the menstrual cycle?

A. Estrogen
B. Progesterone (Correct Answer)
C. Prolactin
D. Oxytocin

Explanation: **Explanation:** The menstrual cycle is divided into the follicular phase (pre-ovulatory) and the **luteal phase** (post-ovulatory). Following ovulation, the remnants of the Graafian follicle transform into the **corpus luteum** under the influence of Luteinizing Hormone (LH). The corpus luteum acts as a temporary endocrine gland, primarily secreting large quantities of **progesterone**. Progesterone is essential for preparing the endometrium for implantation by increasing its vascularity and secretory activity. **Analysis of Options:** * **Progesterone (Correct):** It is the hallmark hormone of the luteal phase. It induces the "secretory phase" in the uterus and exerts negative feedback on LH and FSH. * **Estrogen (Incorrect):** While estrogen is present during the luteal phase (secreted by the corpus luteum), it is the **dominant** hormone of the **follicular phase**, where it drives endometrial proliferation. * **Prolactin (Incorrect):** This hormone is primarily involved in milk production (lactogenesis) and is not a primary regulator of the normal menstrual cycle phases. * **Oxytocin (Incorrect):** Known for uterine contractions during labor and milk ejection, it plays no significant role in the hormonal dominance of the luteal phase. **NEET-PG High-Yield Pearls:** 1. **Length of Luteal Phase:** It is constant at **14 days**. Variations in cycle length are usually due to changes in the follicular phase. 2. **Basal Body Temperature (BBT):** Progesterone has a **thermogenic effect**, causing a rise in BBT (0.5–1.0°F) after ovulation. 3. **Luteal-Placental Shift:** If pregnancy occurs, the corpus luteum is maintained by hCG until the placenta takes over progesterone production at approximately 7–9 weeks.

Question 238: Low levels of dopamine produced by the hypothalamus is a pathologic condition associated with which of the blood hormone levels?

A. High prolactin (PRL) (Correct Answer)
B. High TSH
C. High cortisol
D. Low growth hormone (GH)

Explanation: **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.

Question 239: c-AMP acts as a second messenger for all of the following hormones, EXCEPT:

A. GH (Correct Answer)
B. TSH
C. LH
D. Glucagon

Explanation: **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 240: All of the following factors stimulate GH secretion, EXCEPT?

A. Hypoglycemia
B. Exercise
C. Hyperglycemia (Correct Answer)
D. Stress

Explanation: Growth Hormone (GH) secretion is regulated by the hypothalamus via **Growth Hormone-Releasing Hormone (GHRH)** and **Somatostatin** (GHIH). The primary physiological trigger for GH release is the body's need to mobilize energy substrates and promote growth. ### **Why Hyperglycemia is the Correct Answer** **Hyperglycemia** (high blood glucose) acts as a potent inhibitor of GH secretion. When blood glucose levels are high, the hypothalamus increases the release of Somatostatin, which suppresses the anterior pituitary from secreting GH. Since GH is a "diabetogenic" hormone that increases blood glucose, its inhibition during hyperglycemia is a classic negative feedback mechanism to maintain glucose homeostasis. ### **Explanation of Incorrect Options** * **Hypoglycemia:** Low blood sugar is one of the most powerful stimuli for GH secretion. GH acts as a counter-regulatory hormone that increases gluconeogenesis and decreases glucose uptake in tissues to restore normal levels. * **Exercise:** Physical exertion stimulates GH release through both neural pathways and the accumulation of metabolites (like lactate), helping in tissue repair and fat mobilization. * **Stress:** Both physical and emotional stress trigger the hypothalamus to release GHRH, leading to a surge in GH as part of the body’s adaptive metabolic response. ### **High-Yield Clinical Pearls for NEET-PG** * **Deep Sleep:** GH secretion peaks during **Stage 3 and 4 (NREM) sleep**. * **Amino Acids:** Arginine infusion is a clinical test used to stimulate GH secretion. * **Ghrelin:** Produced by the stomach, it is a potent stimulator of GH, linking nutritional status to growth. * **Somatomedins (IGF-1):** These mediate the growth-promoting effects of GH but provide negative feedback to inhibit further GH release.

Practice by Chapter

Principles of Endocrine Regulation

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Hypothalamus and Pituitary Gland

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Thyroid Physiology

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Adrenal Cortex and Medulla

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Pancreatic Hormones and Glucose Metabolism

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Calcium and Phosphate Homeostasis

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Growth Hormone and Growth Factors

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Endocrine Regulation of Metabolism

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Hormone Receptors and Signaling

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Assessment of Endocrine Function

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