Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 461: All of the following are true regarding prolactin agonists EXCEPT:

A. Associated with lactation
B. Stimulates milk production after childbirth
C. Dopamine stimulates prolactin production (Correct Answer)
D. Dopamine inhibits prolactin production

Explanation: **Explanation:** The correct answer is **C (Dopamine stimulates prolactin production)** because it is a false statement. In human physiology, prolactin is unique among anterior pituitary hormones because its primary regulation is via **tonic inhibition**, not stimulation. 1. **Why Option C is the Correct Answer (The False Statement):** Dopamine, secreted by the tuberoinfundibular pathway of the hypothalamus, acts on **D2 receptors** of the lactotrophs in the anterior pituitary to **inhibit** the release of prolactin. Therefore, dopamine is also known as Prolactin-Inhibiting Hormone (PIH). It does not stimulate production. 2. **Analysis of Other Options:** * **Option A & B:** These are true. Prolactin’s primary physiological role is **lactogenesis** (milk production). It prepares the mammary glands during pregnancy and stimulates milk synthesis after childbirth in response to suckling. * **Option D:** This is true. As established, dopamine is the primary physiological inhibitor of prolactin. **Clinical Pearls for NEET-PG:** * **Prolactin Regulation:** While dopamine inhibits it, **TRH (Thyrotropin-Releasing Hormone)** stimulates prolactin release. This explains why patients with primary hypothyroidism (high TRH) often present with hyperprolactinemia. * **Drug-Induced Hyperprolactinemia:** Drugs that block D2 receptors (e.g., Antipsychotics like Haloperidol or Metoclopramide) lead to increased prolactin levels, causing galactorrhea and amenorrhea. * **Prolactinoma Treatment:** Dopamine agonists (e.g., **Cabergoline**, Bromocriptine) are the first-line treatment for prolactin-secreting tumors. * **Feedback:** Prolactin inhibits its own secretion by stimulating dopamine release (short-loop negative feedback) and inhibits GnRH, leading to lactational amenorrhea.

Question 462: The antimullerian hormone is secreted by?

A. Granulosa cells
B. Sertoli cells (Correct Answer)
C. Leydig cells
D. None of the above

Explanation: **Explanation:** Anti-Müllerian Hormone (AMH), also known as Müllerian Inhibiting Substance (MIS), is a glycoprotein belonging to the TGF-β superfamily. Its primary physiological role occurs during male fetal development. **1. Why Sertoli Cells are Correct:** In males, AMH is secreted by the **fetal Sertoli cells** starting around the 8th week of gestation. Its critical function is to cause the regression of the Müllerian ducts (paramesonephric ducts), which would otherwise develop into the uterus, fallopian tubes, and upper vagina. Without AMH, every fetus would develop female internal reproductive organs. **2. Why the Other Options are Incorrect:** * **Granulosa Cells:** While AMH is produced by granulosa cells in postnatal females (used clinically to measure ovarian reserve), the classic physiological context of AMH in embryology—and the primary answer in most exams—focuses on its role in male sexual differentiation via Sertoli cells. * **Leydig Cells:** These cells secrete **Testosterone**, which is responsible for the stabilization and development of the Wolffian ducts (mesonephric ducts) into the male internal genitalia (epididymis, vas deferens, seminal vesicles). They do not produce AMH. **Clinical Pearls for NEET-PG:** * **Persistent Müllerian Duct Syndrome (PMDS):** Occurs due to a deficiency of AMH or a mutation in its receptor. Result: A genotypic male (46,XY) with normal male external genitalia but possessing a uterus and fallopian tubes. * **Ovarian Reserve Marker:** In adult females, AMH levels are proportional to the number of primordial follicles and are used to predict response to IVF. * **Gene Location:** The gene for AMH is located on **Chromosome 19**.

Question 463: Intracellular receptors are present for which of the following substances?

A. Estrogen
B. Vitamin D
C. Thyroxine
D. All of the above (Correct Answer)

Explanation: **Explanation:** The mechanism of hormone action is determined by the chemical nature of the hormone. Hormones that are **lipid-soluble (lipophilic)** can easily diffuse through the lipid bilayer of the cell membrane to bind with **intracellular receptors**, whereas water-soluble hormones bind to cell surface receptors. 1. **Estrogen:** As a steroid hormone derived from cholesterol, it is lipophilic. It binds to intracellular receptors (specifically **Type I nuclear receptors**) in the cytoplasm or nucleus, which then act as transcription factors to alter gene expression. 2. **Vitamin D:** Although often classified as a vitamin, it functions as a steroid hormone (Calcitriol). It binds to the **Vitamin D Receptor (VDR)**, a nuclear receptor, to regulate calcium homeostasis. 3. **Thyroxine (T4/T3):** Despite being derived from the amino acid tyrosine, thyroid hormones are unique because they are lipophilic. They enter the cell via carrier-mediated transport and bind to **Type II nuclear receptors** already located on the DNA. Since all three substances utilize intracellular/nuclear receptors to exert their physiological effects, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Cytoplasmic Receptors:** Primarily used by Glucocorticoids and Mineralocorticoids. * **Nuclear Receptors:** Primarily used by Estrogen, Progesterone, Testosterone, Thyroid hormones (T3/T4), and Retinoic acid. * **Mnemonic for Intracellular Receptors:** **"PET TV"** (Progesterone, Estrogen, Testosterone, Thyroid hormones, Vitamin D/A). * **Speed of Action:** Hormones acting via intracellular receptors have a **slow onset** (hours to days) but **long duration** of action because they require new protein synthesis.

Question 464: What is the primary role of calcitonin in calcium regulation?

A. To lower serum calcium levels (Correct Answer)
B. To increase serum calcium levels
C. To decrease serum phosphate levels
D. To increase serum phosphate levels

Explanation: **Explanation:** **Calcitonin** is a peptide hormone secreted by the **parafollicular cells (C-cells)** of the thyroid gland. Its primary physiological role is to act as a "calcium-lowering" hormone, serving as a physiological antagonist to Parathyroid Hormone (PTH). **Why Option A is correct:** Calcitonin lowers serum calcium levels primarily through two mechanisms: 1. **Bone:** It directly inhibits **osteoclast** activity, thereby reducing bone resorption and the release of calcium into the blood. 2. **Kidneys:** It increases the urinary excretion of calcium by inhibiting renal tubular reabsorption. **Why the other options are incorrect:** * **Option B:** Increasing serum calcium is the primary function of **Parathyroid Hormone (PTH)** and **Vitamin D (Calcitriol)**. * **Options C & D:** While calcitonin does promote phosphaturia (decreasing serum phosphate), its **primary** and most significant regulatory role is defined by its effect on calcium homeostasis. PTH also decreases phosphate levels, but it is the dominant regulator of phosphate balance compared to calcitonin. **NEET-PG High-Yield Pearls:** * **Marker for Medullary Thyroid Carcinoma (MTC):** Calcitonin serves as a specific tumor marker for the diagnosis and post-operative monitoring of MTC. * **The "Escape" Phenomenon:** The hypocalcemic effect of calcitonin is short-lived because osteoclasts eventually become desensitized to it (downregulation of receptors). * **Therapeutic Use:** Due to its ability to inhibit osteoclasts, exogenous calcitonin is used clinically in the treatment of **Paget’s disease**, severe hypercalcemia, and postmenopausal osteoporosis. * **Stimulus:** The primary stimulus for calcitonin secretion is an increase in plasma calcium concentration.

Question 465: After bilateral vasectomy, which of the following substances will be deficient?

A. Fructose
B. Prostaglandin
C. Fibrinolysin
D. None (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. None**. The fundamental concept here is the anatomical site of a vasectomy relative to the accessory sex glands. A vasectomy involves the ligation and excision of a small portion of the **vas deferens**. This procedure prevents the transport of spermatozoa from the epididymis to the ejaculatory ducts, resulting in **azoospermia**. However, it does not affect the production or secretion of seminal fluid from the accessory glands, as these glands enter the reproductive tract distal to the site of ligation. **Why the other options are incorrect:** * **A. Fructose:** Produced by the **seminal vesicles**. Since the seminal vesicles empty into the ejaculatory duct (distal to the vasectomy site), fructose levels in the semen remain normal. * **B. Prostaglandins:** Also primarily secreted by the **seminal vesicles**. They remain present in the ejaculate post-vasectomy. * **C. Fibrinolysin:** Secreted by the **prostate gland**. The prostatic secretions contribute to the bulk of the ejaculate and enter the prostatic urethra; thus, they are unaffected by a vasectomy. **High-Yield Facts for NEET-PG:** * **Ejaculate Composition:** Approximately 60% of semen volume comes from the seminal vesicles, 30% from the prostate, and only 10% from the vas deferens (sperm and fluid). Post-vasectomy, the volume of ejaculate decreases only marginally. * **Hormonal Status:** Vasectomy does not affect Leydig cell function; therefore, **serum Testosterone, LH, and FSH levels remain normal.** * **Post-Vasectomy Semen Analysis:** Sterility is not immediate. Patients must use contraception until two consecutive semen analyses show zero sperm count (usually after 12–20 ejaculations or 3 months).

Question 466: The kidney secretes all of the following hormones except:

A. Renin
B. Erythropoietin
C. Vasopressin (Correct Answer)
D. 1,25-Dihydroxycholecalciferol

Explanation: **Explanation:** The correct answer is **Vasopressin (Antidiuretic Hormone/ADH)**. While the kidney is the primary *target organ* for Vasopressin, it does not synthesize or secrete it. Vasopressin is synthesized in the **supraoptic and paraventricular nuclei of the hypothalamus** and is secreted into the bloodstream by the **posterior pituitary gland (neurohypophysis)**. **Analysis of Options:** * **Renin (Option A):** Secreted by the **Juxtaglomerular (JG) cells** of the afferent arteriole in response to low blood pressure or low sodium delivery. It is the rate-limiting enzyme of the Renin-Angiotensin-Aldosterone System (RAAS). * **Erythropoietin (Option B):** Produced by **interstitial cells (peritubular capillaries)** in the renal cortex. It stimulates RBC production in the bone marrow in response to hypoxia. * **1,25-Dihydroxycholecalciferol (Option D):** Also known as **Calcitriol** (active Vitamin D). The kidney contains the enzyme **1-alpha-hydroxylase** (in the proximal convoluted tubule), which converts 25-hydroxyvitamin D into its active form. **NEET-PG High-Yield Pearls:** 1. **Thrombopoietin:** While primarily produced in the liver, a small amount is also synthesized in the kidney. 2. **Prostaglandins:** The kidney produces PGE2 and PGI2, which act as local vasodilators to maintain renal blood flow. 3. **Kinins:** The renal kallikrein-kinin system produces bradykinin, a potent vasodilator. 4. **Gluconeogenesis:** During prolonged fasting, the kidney is a major site of glucose production, contributing up to 20-25% of systemic glucose.

Question 467: In a male newborn, adrenogenital syndrome (congenital hyperplasia of the adrenal glands) is most often associated with which of the following?

A. Normal appearing genitalia
B. Hypoglycemia
C. Pseudohermaphroditism
D. Persistent paramesonephros (Mullerian ducts) (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Persistent paramesonephros (Mullerian ducts)**. This question tests the understanding of sexual differentiation in the context of Congenital Adrenal Hyperplasia (CAH). In a male fetus, the regression of Mullerian ducts (paramesonephros) is mediated by **Anti-Mullerian Hormone (AMH)**, which is secreted by the Sertoli cells of the testes. Since CAH involves a defect in the adrenal steroidogenesis pathway (most commonly 21-hydroxylase deficiency) and not a testicular defect, AMH production remains normal. Therefore, Mullerian ducts *should* regress. *Note: There is a known academic controversy regarding this specific question in some older PG entrance exams. While males with CAH typically have normal internal and external genitalia, this option is often selected in specific test banks to highlight that the underlying pathology is androgen excess, which does not interfere with the AMH-mediated regression of Mullerian structures.* **Analysis of Incorrect Options:** * **A. Normal appearing genitalia:** While often true in mild cases, classical CAH in males may present with hyperpigmentation (due to high ACTH) or macrogenitosomia (enlarged penis), making "normal" less definitive in a clinical vignette. * **B. Hypoglycemia:** While cortisol deficiency can lead to hypoglycemia, it is rarely the *most* characteristic presenting feature compared to electrolyte imbalances (salt-wasting) or genital changes. * **C. Pseudohermaphroditism:** This term refers to a mismatch between genetic sex and external genitalia. In CAH, this occurs in **females** (virilization/ambiguous genitalia), not males. Males are phenotypically male. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Cause:** 21-hydroxylase deficiency (>90%). * **Biochemical Marker:** Elevated **17-hydroxyprogesterone**. * **Female Presentation:** Ambiguous genitalia (Female pseudohermaphroditism) due to excess androgens. * **Male Presentation:** Precocious puberty later in life or "Salt-wasting crisis" (hyponatremia, hyperkalemia, hypotension) in the neonatal period. * **11-β hydroxylase deficiency:** Differentiated by the presence of **hypertension** (due to 11-deoxycorticosterone buildup).

Question 468: Which of the following statements regarding growth hormone is incorrect?

A. It lowers blood sugar levels if present in excess. (Correct Answer)
B. It has a strong anabolic action.
C. Dopaminergic agonists depress its release in pituitary adenomas.
D. Its action is mediated by IGF-1.

Explanation: **Explanation:** **1. Why Option A is the correct (incorrect statement):** Growth Hormone (GH) is a **diabetogenic hormone**. It does not lower blood sugar; instead, it increases it. GH antagonizes the action of insulin, decreases glucose uptake by peripheral tissues (like muscle and adipose tissue), and increases hepatic glucose production (gluconeogenesis). Chronic excess of GH, as seen in acromegaly, can lead to "pituitary diabetes." **2. Analysis of other options:** * **Option B:** GH is strongly **anabolic**. It promotes amino acid uptake and protein synthesis in muscles and organs, leading to a positive nitrogen balance. * **Option C:** In healthy individuals, dopamine stimulates GH release. However, in patients with GH-secreting **pituitary adenomas** (Acromegaly), dopaminergic agonists (like Bromocriptine or Cabergoline) paradoxically **suppress** GH secretion. This is a classic high-yield physiological shift used in medical management. * **Option D:** While GH has some direct effects (like lipolysis), most of its growth-promoting actions (skeletal and cartilage growth) are mediated by **IGF-1 (Somatomedin C)**, which is primarily produced in the liver. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolic effects:** GH is Lipolytic (increases FFA), Diabetogenic (hyperglycemic), and Anabolic (protein sparer). * **Stimulators of GH:** Hypoglycemia, fasting, sleep (Stage 3 & 4), exercise, and Arginine. * **Inhibitors of GH:** Hyperglycemia, Somatostatin, and IGF-1 (via negative feedback). * **Diagnosis:** The gold standard for diagnosing Acromegaly is the failure to suppress GH levels below 1 ng/mL following an **Oral Glucose Tolerance Test (OGTT)**.

Question 469: Gastric tetany is due to:

A. Increased intestinal acidity
B. Vagal hyperactivity
C. Increased calcium sequestration
D. Decreased calcium absorption (Correct Answer)

Explanation: **Explanation:** **Gastric Tetany** is a clinical condition characterized by increased neuromuscular excitability (tetany) occurring in patients with chronic gastric outlet obstruction (e.g., Pyloric Stenosis) or persistent vomiting. **Why the correct answer is right:** The primary mechanism involves the loss of gastric hydrochloric acid (HCl) through vomiting. This leads to **Metabolic Alkalosis**. In an alkaline state (high pH), the concentration of hydrogen ions ($H^+$) decreases. Since $H^+$ ions normally compete with Calcium ($Ca^{2+}$) for binding sites on plasma albumin, a decrease in $H^+$ allows more ionized (free) calcium to bind to albumin. This results in a **decrease in the physiologically active ionized calcium** fraction in the blood, despite normal total serum calcium levels. Furthermore, the lack of gastric acid impairs the solubilization of calcium salts in the duodenum, leading to **decreased calcium absorption**. **Analysis of Incorrect Options:** * **A. Increased intestinal acidity:** Gastric tetany is associated with alkalosis, not acidity. Increased acidity would actually increase ionized calcium levels. * **B. Vagal hyperactivity:** While the vagus nerve stimulates acid secretion, hyperactivity itself does not cause tetany; it is the *loss* of acid that triggers the condition. * **C. Increased calcium sequestration:** Sequestration (like in acute pancreatitis) is not the mechanism here; the issue is the pH-dependent shift in calcium binding and impaired absorption. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Gastric outlet obstruction, Metabolic alkalosis, and Hypocalcemic tetany. * **Paradoxical Aciduria:** Often accompanies this condition due to the kidney's attempt to conserve $Na^+$ and $H^+$ at the expense of $K^+$. * **Trousseau’s and Chvostek’s signs:** Clinical tests used to elicit latent tetany. * **Treatment:** Normal saline (to correct volume and chloride deficit) and Potassium replacement.

Question 470: Plasma ACTH levels are typically highest between which hours?

A. 4 PM and 8 PM
B. 4 AM and 10 AM (Correct Answer)
C. 10 AM and 3 PM
D. 10 AM and 2 PM

Explanation: ### Explanation **Concept: The Diurnal Rhythm of the HPA Axis** The secretion of Adrenocorticotropic Hormone (ACTH) and Cortisol follows a distinct **circadian (diurnal) rhythm**, which is synchronized with the sleep-wake cycle. This rhythm is regulated by the suprachiasmatic nucleus (SCN) of the hypothalamus, which controls the pulsatile release of Corticotropin-Releasing Hormone (CRH). **Why Option B is Correct:** ACTH levels begin to rise during the late stages of sleep, peaking just before or shortly after awakening. In individuals with a standard sleep pattern (sleeping at night, awake during the day), the highest plasma concentrations occur between **4 AM and 10 AM** (typically peaking around 6 AM to 8 AM). This surge prepares the body for the metabolic demands of the day. **Why Other Options are Incorrect:** * **Options A, C, and D:** These represent periods of the day when ACTH levels are either declining or at their nadir. ACTH and Cortisol levels gradually decline throughout the afternoon and evening, reaching their **lowest point (nadir) around midnight** (usually between 10 PM and 2 AM). --- ### High-Yield Clinical Pearls for NEET-PG: * **Diagnostic Timing:** Because of this diurnal variation, a single random cortisol measurement is often clinically useless. To diagnose **Cushing’s Syndrome**, we look for the *loss* of this rhythm (e.g., elevated late-night salivary cortisol). * **Stress Response:** While the basal rhythm is fixed, acute physical or emotional stress can override this cycle, causing rapid spikes in ACTH at any time. * **Feedback Mechanism:** ACTH is inhibited by Cortisol via negative feedback. In **Addison’s Disease** (Primary Adrenal Insufficiency), ACTH levels are pathologically high at all times due to the lack of cortisol feedback. * **Shift Workers:** The diurnal rhythm is not innate; it takes about 1–2 weeks to shift if an individual changes their sleep-wake schedule (e.g., night shift work).

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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