Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 131: Which hormone increases with age?

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

Explanation: **Explanation:** The correct answer is **FSH (Follicle-Stimulating Hormone)**. **1. Why FSH increases with age:** As individuals age, there is a progressive decline in gonadal function (menopause in females and andropause in males). In females, the depletion of ovarian follicles leads to a significant decrease in **Estrogen and Inhibin**. Since Inhibin and Estrogen normally exert negative feedback on the anterior pituitary and hypothalamus, their absence leads to a compensatory, marked rise in **FSH** (and to a lesser extent, LH). FSH levels >40 mIU/mL are a diagnostic hallmark of menopause. **2. Why the other options are incorrect:** * **GH (Growth Hormone):** GH levels peak during puberty and decline steadily with age (somatopause), contributing to reduced muscle mass and increased adiposity in the elderly. * **Prolactin:** Prolactin levels generally remain stable or slightly decrease with age, particularly in postmenopausal women due to the lack of estrogenic stimulation of lactotrophs. * **Insulin:** While insulin *resistance* often increases with age (leading to Type 2 Diabetes), the actual basal insulin secretion and the pancreatic beta-cell response to glucose typically **decrease** or remain impaired due to islet cell atrophy. **3. High-Yield Clinical Pearls for NEET-PG:** * **Hormones that Decrease with Age:** GH, Melatonin, DHEA (Adrenopause), Testosterone, Estrogen, and Aldosterone. * **Hormones that Increase with Age:** FSH, LH, PTH (due to Vitamin D deficiency/renal decline), and Norepinephrine. * **Stable Hormones:** Thyroid hormones (T3/T4) generally remain stable, though the risk of hypothyroidism increases. * **Key Fact:** FSH is the most sensitive marker for the onset of menopause.

Question 132: Which one of the following is the best stimulus for the release of Arginine-vasopressin?

A. Hypertonicity (Correct Answer)
B. Hypokalemia
C. Intravascular volume depletion
D. Hypernatremia

Explanation: **Explanation:** Arginine-vasopressin (AVP), also known as Antidiuretic Hormone (ADH), is primarily regulated by two mechanisms: **plasma osmolality** and **hemodynamic status**. **1. Why Hypertonicity is the Correct Answer:** Hypertonicity (increased effective plasma osmolality) is the **most sensitive** stimulus for AVP release. Specialized osmoreceptors in the hypothalamus (OVLT and SFO) detect changes as small as a **1% increase** in osmolality. When osmolality rises above the threshold (approx. 280–285 mOsm/kg), AVP is rapidly released to promote water reabsorption in the renal collecting ducts. **2. Why the Other Options are Incorrect:** * **Intravascular volume depletion:** While a potent stimulus, it is **less sensitive** than hypertonicity. AVP release via baroreceptors requires a significant drop in blood volume or pressure (usually **>10–15%**). Therefore, it is not the "best" (most sensitive) stimulus under physiological conditions. * **Hypernatremia:** Sodium is the primary determinant of plasma tonicity, so hypernatremia usually causes hypertonicity. However, "Hypertonicity" is the more accurate physiological term because substances like urea (which cause hyperosmolality but not hypertonicity) do not trigger AVP release. * **Hypokalemia:** This is not a stimulus for AVP. In fact, chronic hypokalemia can cause Nephrogenic Diabetes Insipidus, making the kidneys resistant to AVP. **High-Yield NEET-PG Pearls:** * **Sensitivity vs. Potency:** Osmolality is the most *sensitive* stimulus (1% change), while volume depletion is a more *potent* stimulus (can cause massive AVP surges during hemorrhage). * **V1 vs. V2 Receptors:** V1 receptors cause vasoconstriction; V2 receptors (via Aquaporin-2) mediate water reabsorption in the kidney. * **SIADH:** Characterized by hyponatremia and inappropriately concentrated urine due to excessive AVP.

Question 133: Which of the following stimulates the release of growth hormone?

A. Hypoglycemia (Correct Answer)
B. Cortisol
C. Methylprednisolone
D. Glucose

Explanation: **Explanation:** Growth Hormone (GH) secretion is regulated by a complex interplay of metabolic, neural, and hormonal factors. The primary stimulus for GH release is a **decrease in energy substrates** within the blood. **Why Hypoglycemia is correct:** Hypoglycemia is one of the most potent physiological stimuli for GH secretion. When blood glucose levels fall, the hypothalamus is stimulated to release **Growth Hormone-Releasing Hormone (GHRH)** and inhibit Somatostatin. GH then acts as a "counter-regulatory" hormone; it antagonizes insulin action, decreases peripheral glucose uptake (diabetogenic effect), and stimulates gluconeogenesis and lipolysis to restore blood glucose levels. **Why the other options are incorrect:** * **Glucose (Hyperglycemia):** An increase in blood glucose levels inhibits GH secretion by stimulating the release of Somatostatin (GHIH) from the hypothalamus. * **Cortisol & Methylprednisolone (Glucocorticoids):** While acute stress can transiently raise GH, **chronic** exposure to high levels of glucocorticoids (like Cortisol or exogenous Methylprednisolone) actually inhibits GH secretion and interferes with its action at the epiphyseal plates, leading to growth retardation in children. **High-Yield Clinical Pearls for NEET-PG:** * **Stimulators of GH:** Hypoglycemia, Fasting/Starvation, Sleep (Stage 3 & 4 NREM), Exercise, Amino acids (Arginine), and Ghrelin. * **Inhibitors of GH:** Hyperglycemia, Free fatty acids, Obesity, Somatostatin, and IGF-1 (via negative feedback). * **Gold Standard Test:** The **Insulin Tolerance Test (ITT)**, which induces hypoglycemia, is the gold standard for diagnosing GH deficiency. * **Screening Test:** IGF-1 levels are used for screening as they remain stable throughout the day, unlike the pulsatile GH.

Question 134: Which of the following is NOT an action of GLP-1?

A. Increases insulin release
B. Decreases glucagon release
C. Increases gastric emptying (Correct Answer)
D. Reduces appetite

Explanation: **Explanation:** Glucagon-like peptide-1 (GLP-1) is an **incretin hormone** secreted by the L-cells of the distal ileum and colon in response to food intake. Its primary physiological role is to lower postprandial blood glucose levels and promote satiety. **Why Option C is the correct answer:** GLP-1 actually **slows gastric emptying** (decreases gastric motility). By delaying the passage of food from the stomach to the duodenum, it slows the absorption of nutrients into the bloodstream, preventing rapid spikes in postprandial glucose. Therefore, "increasing gastric emptying" is physiologically incorrect. **Analysis of Incorrect Options:** * **A. Increases insulin release:** GLP-1 stimulates glucose-dependent insulin secretion from pancreatic beta cells. This is known as the "incretin effect." * **B. Decreases glucagon release:** It suppresses glucagon secretion from pancreatic alpha cells, which reduces hepatic glucose production. * **D. Reduces appetite:** GLP-1 acts on the hypothalamus to increase satiety and reduce food intake, contributing to weight loss. **High-Yield Clinical Pearls for NEET-PG:** * **Incretin Effect:** Oral glucose causes a much higher insulin response than intravenous glucose due to the release of GLP-1 and GIP. * **Degradation:** Endogenous GLP-1 is rapidly degraded by the enzyme **Dipeptidyl Peptidase-4 (DPP-4)**. * **Pharmacology:** GLP-1 agonists (e.g., Liraglutide, Semaglutide) are used to treat Type 2 Diabetes and obesity. They are contraindicated in patients with a history of Medullary Thyroid Carcinoma or MEN 2 syndrome.

Question 135: The enzyme 5a-reductase is responsible for which of the following conversions?

A. Conversion of cholesterol to pregnenolone and enhancing steroidogenesis
B. Conversion of testosterone to dihydrotestosterone (Correct Answer)
C. Aromatization of testosterone to estradiol
D. Increasing the synthesis of Luteinizing Hormone (LH)

Explanation: **Explanation:** The enzyme **5α-reductase** is a critical enzyme in male reproductive physiology. It catalyzes the irreversible conversion of **Testosterone into Dihydrotestosterone (DHT)**. While testosterone is the primary circulating androgen, DHT is a significantly more potent agonist for the androgen receptor and is essential for the development of male external genitalia (penis, scrotum) and the prostate. **Analysis of Options:** * **Option B (Correct):** 5α-reductase reduces the double bond between the 4th and 5th carbon atoms of the testosterone molecule to form DHT. * **Option A (Incorrect):** The conversion of cholesterol to pregnenolone is mediated by the **Cholesterol side-chain cleavage enzyme (P450scc/Desmolase)**, which is the rate-limiting step in steroidogenesis. * **Option C (Incorrect):** The aromatization of testosterone to estradiol (estrogen) is performed by the enzyme **Aromatase (CYP19A1)**, primarily in adipose tissue and the ovaries. * **Option D (Incorrect):** LH synthesis is regulated by Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus; androgens actually exert negative feedback on LH secretion. **Clinical Pearls for NEET-PG:** 1. **5α-reductase Deficiency:** Leads to a form of 46,XY Disorder of Sex Development (DSD) where individuals have internal male structures (testes) but ambiguous or female-appearing external genitalia at birth. 2. **Pharmacology:** **Finasteride** and **Dutasteride** are 5α-reductase inhibitors used clinically to treat Benign Prostatic Hyperplasia (BPH) and male pattern baldness (androgenetic alopecia). 3. **Distribution:** Type 1 isoenzyme is found mainly in the skin/liver; Type 2 is predominant in the urogenital tract and liver.

Question 136: What is the main product of the fetal adrenal gland?

A. Cortisol
B. DHEA-S (Correct Answer)
C. Testosterone
D. Progesterone

Explanation: **Explanation:** The fetal adrenal gland is a unique, highly active organ characterized by a massive **"fetal zone"** (comprising about 80% of the gland), which lacks the enzyme **3β-hydroxysteroid dehydrogenase (3β-HSD)**. 1. **Why DHEA-S is correct:** Due to the deficiency of 3β-HSD, the fetal adrenal cannot convert pregnenolone to progesterone. Instead, it shunts precursors toward the androgen pathway. It produces large quantities (up to 200 mg/day) of **Dehydroepiandrosterone sulfate (DHEA-S)**. This DHEA-S serves as the essential precursor for the placenta to synthesize **Estriol (E3)**, which is a key marker of fetal well-being. 2. **Why other options are incorrect:** * **Cortisol:** While the definitive zone produces some cortisol (essential for lung maturation), it is not the *main* product. Most fetal cortisol is actually derived from maternal sources or converted from cortisone. * **Testosterone:** While DHEA-S is an androgen precursor, the adrenal gland itself does not primarily secrete testosterone; this occurs mainly in the fetal Leydig cells of the testes. * **Progesterone:** The fetal adrenal cannot produce progesterone due to the lack of 3β-HSD. Progesterone is primarily supplied to the fetus by the **placenta**. **High-Yield Clinical Pearls for NEET-PG:** * **Size:** At birth, the fetal adrenal is disproportionately large (similar in size to the kidney) but undergoes rapid involution of the fetal zone post-delivery. * **Estriol (E3) Marker:** A sudden drop in maternal serum estriol indicates **fetal distress**, as its synthesis requires a functional fetal adrenal (to produce DHEA-S) and a functional fetal liver (for 16-hydroxylation). * **ACTH Control:** The fetal zone is primarily regulated by fetal ACTH and hCG.

Question 137: Growth hormone is not produced during which of the following conditions?

A. Deep sleep
B. Hypoglycemia
C. Low free fatty acid content in the body
D. Paradoxical sleep (Correct Answer)

Explanation: Growth hormone (GH) secretion is pulsatile and regulated by various physiological stimuli. Understanding the relationship between sleep architecture and metabolic states is crucial for NEET-PG. ### **Explanation of the Correct Answer** Growth hormone secretion is highly dependent on the stages of sleep. The primary surge of GH occurs during **Deep Sleep (Stage N3 of NREM sleep)**, specifically during the first few hours of the night. Conversely, during **Paradoxical Sleep (REM sleep)**, GH secretion is significantly inhibited. This is why GH levels are at their lowest during the REM phase, making Option D the correct answer. ### **Analysis of Incorrect Options** * **A. Deep Sleep:** This is the period of maximal GH secretion. The surge is linked to the onset of slow-wave sleep (SWS). * **B. Hypoglycemia:** Low blood glucose is a potent stimulator of GH. GH acts as a counter-regulatory hormone that increases blood glucose by antagonizing insulin and promoting gluconeogenesis. * **C. Low Free Fatty Acid (FFA):** GH promotes lipolysis. Therefore, a decrease in circulating FFAs acts as a stimulus for GH release, while high FFA levels inhibit it. ### **Clinical Pearls for NEET-PG** * **Stimulators of GH:** GHRH, Ghrelin (produced by the stomach), fasting/starvation, exercise, trauma, and amino acids (Arginine). * **Inhibitors of GH:** Somatostatin, Hyperglycemia, Obesity, and Somatomedins (IGF-1) via negative feedback. * **Gold Standard Test:** The Insulin Tolerance Test (ITT) is the gold standard for diagnosing GH deficiency because it induces hypoglycemia, which should normally trigger a GH surge. * **Screening Test:** IGF-1 levels are used for screening because GH levels fluctuate due to their pulsatile nature.

Question 138: Human chorionic gonadotropin (HCG) is produced by which of the following?

A. Kidney
B. Placenta (Correct Answer)
C. Pituitary
D. Liver

Explanation: **Explanation:** **Human Chorionic Gonadotropin (hCG)** is a glycoprotein hormone essential for the maintenance of early pregnancy. It is primarily produced by the **syncytiotrophoblast cells of the placenta**. 1. **Why the Placenta is Correct:** Shortly after implantation (around 8–10 days post-conception), the developing placenta begins secreting hCG. Its primary physiological role is to maintain the **corpus luteum** in the ovary, ensuring the continued secretion of progesterone until the placenta is mature enough to take over steroidogenesis (the luteal-placental shift). 2. **Why Other Options are Incorrect:** * **Kidney:** While hCG is excreted in the urine (forming the basis of pregnancy tests), it is not produced here. The kidney produces hormones like Erythropoietin and Renin. * **Pituitary:** The anterior pituitary produces LH, FSH, and TSH, which share a common alpha-subunit with hCG. However, hCG itself is placental in origin. * **Liver:** The liver is involved in the metabolism of hormones but does not synthesize gonadotropins. **High-Yield Clinical Pearls for NEET-PG:** * **Structure:** hCG consists of two subunits: **Alpha (α)** and **Beta (β)**. The α-subunit is identical to LH, FSH, and TSH; the **β-subunit is unique** and confers biological specificity. * **Doubling Time:** In a healthy intrauterine pregnancy, serum hCG levels roughly double every **48–72 hours**. * **Peak Levels:** hCG levels peak at approximately **8–10 weeks** of gestation and then decline to a lower plateau. * **Tumor Marker:** Pathologically high levels are seen in **Hydatidiform mole** and **Choriocarcinoma**. It can also be produced by certain germ cell tumors (e.g., dysgerminoma).

Question 139: Somatostatin is secreted by:

A. Alpha cells
B. Beta cells
C. Gamma cells
D. Delta cells (Correct Answer)

Explanation: **Explanation:** The Islets of Langerhans in the pancreas are composed of several distinct endocrine cell types, each secreting specific hormones that regulate metabolism. **Delta cells (D cells)** are the specific endocrine cells responsible for the synthesis and secretion of **Somatostatin**. **Why Delta Cells are Correct:** Somatostatin acts primarily as a potent **inhibitory hormone**. In the pancreas, it functions via paracrine signaling to inhibit the secretion of both Insulin and Glucagon. This ensures a fine-tuned regulation of blood glucose levels by preventing over-secretion of pancreatic hormones. **Analysis of Incorrect Options:** * **Alpha cells (A cells):** These cells comprise about 20% of the islet and secrete **Glucagon**, which increases blood glucose levels via glycogenolysis and gluconeogenesis. * **Beta cells (B cells):** The most numerous (approx. 65-70%), these cells secrete **Insulin**, which lowers blood glucose, and **Amylin**. * **Gamma cells (F cells/PP cells):** These cells secrete **Pancreatic Polypeptide**, which regulates pancreatic exocrine secretions and gallbladder contraction. **High-Yield Clinical Pearls for NEET-PG:** * **Universal Inhibitor:** Somatostatin is often called the "hormonal brake" because it inhibits GH, TSH, Insulin, Glucagon, and various GI hormones (Gastrin, CCK). * **Dual Source:** Remember that Somatostatin is secreted by both the **Delta cells of the pancreas** and the **Hypothalamus** (where it inhibits Growth Hormone release). * **Clinical Use:** Octreotide is a synthetic long-acting analog of somatostatin used clinically to treat acromegaly, carcinoid syndrome, and bleeding esophageal varices.

Question 140: Which of the following inhibits prolactin secretion?

A. Haloperidol
B. GABA (Gamma-aminobutyric acid)
C. Neurophysin
D. Dopamine (Correct Answer)

Explanation: **Explanation:** The regulation of prolactin (PRL) is unique among anterior pituitary hormones because it is under **predominant tonic inhibition** by the hypothalamus. **1. Why Dopamine is Correct:** Dopamine is the primary **Prolactin-Inhibiting Hormone (PIH)**. It is secreted by the tuberoinfundibular dopaminergic (TIDA) neurons of the hypothalamus into the hypophyseal portal system. It binds to **D2 receptors** on the lactotrophs in the anterior pituitary, leading to the inhibition of adenylyl cyclase and a subsequent decrease in prolactin synthesis and secretion. **2. Analysis of Incorrect Options:** * **Haloperidol:** This is an antipsychotic medication that acts as a **D2 receptor antagonist**. By blocking the inhibitory effect of dopamine, it causes a rise in prolactin levels (**hyperprolactinemia**), often leading to side effects like galactorrhea and gynecomastia. * **GABA:** While GABA can exert some inhibitory influence on prolactin, it is not the primary physiological inhibitor. Its role is minor compared to the potent control exerted by dopamine. * **Neurophysin:** These are carrier proteins for oxytocin (Neurophysin I) and vasopressin (Neurophysin II). They are involved in the transport of hormones from the hypothalamus to the posterior pituitary and have no direct role in inhibiting prolactin. **High-Yield Clinical Pearls for NEET-PG:** * **The "Stalk Effect":** Any lesion that compresses the pituitary stalk (e.g., Craniopharyngioma) prevents dopamine from reaching the pituitary, resulting in **increased** prolactin levels. * **TRH Connection:** Thyrotropin-releasing hormone (TRH) acts as a prolactin-releasing factor. Therefore, in **primary hypothyroidism** (where TRH is elevated), patients may present with hyperprolactinemia. * **Drug of Choice:** For prolactinomas, the first-line treatment is medical management with dopamine agonists like **Cabergoline** (preferred due to longer half-life) or Bromocriptine.

Practice by Chapter

Principles of Endocrine Regulation

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Hypothalamus and Pituitary Gland

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Pancreatic Hormones and Glucose Metabolism

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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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