Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 201: Which of the following hormones does NOT involve calcium as a second messenger in its action?

A. Gastrin
B. Oxytocin
C. ADH
D. Insulin (Correct Answer)

Explanation: **Explanation:** The mechanism of hormone action is determined by the type of receptor it binds to. Hormones that utilize **Calcium/Phospholipase C (PLC)** as a second messenger system typically bind to G-protein coupled receptors (GPCRs), specifically the **Gq subtype**. **1. Why Insulin is the correct answer:** Insulin does not use calcium or cAMP as a second messenger. Instead, it acts through an **Enzyme-linked receptor** (specifically, a **Receptor Tyrosine Kinase**). Upon insulin binding, the receptor undergoes autophosphorylation, which activates Insulin Receptor Substrates (IRS-1/2) and the PI3K/AKT pathway. This pathway is responsible for the translocation of GLUT-4 transporters to the cell membrane. **2. Why the other options are incorrect:** * **Gastrin:** Acts via Gq-coupled receptors on parietal cells and ECL cells to increase intracellular calcium, stimulating HCl secretion. * **Oxytocin:** Utilizes the Gq-PLC-IP3/DAG pathway to increase intracellular calcium, which is essential for smooth muscle contraction in the uterus (labor) and mammary glands (milk let-down). * **ADH (Vasopressin):** While ADH uses cAMP via **V2 receptors** in the kidney, it uses the **Calcium/IP3 pathway** via **V1 receptors** to cause systemic vasoconstriction. Since it *does* involve calcium in its V1 action, it is not the correct choice here. **High-Yield NEET-PG Pearls:** * **Tyrosine Kinase Pathway:** Remember the mnemonic **"PIG"** (Prolactin, Insulin, Growth Hormone) for hormones using kinase-related receptors (though Prolactin/GH use the JAK-STAT variant). * **Gq-coupled (Calcium) mnemonic:** **"GOAT HAG"** (GnRH, Oxytocin, ADH (V1), TRH, Histamine (H1), Angiotensin II, Gastrin). * **cAMP-mediated:** FSH, LH, ACTH, TSH, Glucagon, and ADH (V2).

Question 202: Which of the following is a non-osmotic stimulus for ADH secretion?

A. Uremia
B. Hyperglycemia
C. Hemorrhage (Correct Answer)
D. Excessive water ingestion

Explanation: ### Explanation **1. Why Hemorrhage is Correct:** Antidiuretic Hormone (ADH), or Vasopressin, is regulated by two primary mechanisms: **osmotic** and **non-osmotic**. * **Osmotic stimuli** involve changes in plasma osmolality detected by hypothalamic osmoreceptors. * **Non-osmotic stimuli** involve changes in blood volume or pressure. **Hemorrhage** leads to a decrease in effective circulating volume (hypovolemia) and a drop in blood pressure. This is sensed by **baroreceptors** (high-pressure receptors in the carotid sinus/aortic arch and low-pressure receptors in the left atrium). A decrease in stretch sends signals via the Vagus and Glossopharyngeal nerves to the hypothalamus to stimulate potent ADH release. Notably, the hypovolemic stimulus can override the osmotic stimulus; ADH will be secreted to maintain volume even if osmolality is low. **2. Analysis of Incorrect Options:** * **A. Uremia:** Urea is an "ineffective osmole" because it crosses cell membranes easily. It does not create an osmotic gradient across the blood-brain barrier to trigger osmoreceptors. * **B. Hyperglycemia:** While glucose is an osmole, it is generally less potent than sodium in triggering ADH unless levels are extremely high. Furthermore, hyperglycemia is an *osmotic* stimulus, not a non-osmotic one. * **D. Excessive water ingestion:** This causes a decrease in plasma osmolality, which **inhibits** ADH secretion rather than stimulating it. **3. High-Yield Clinical Pearls for NEET-PG:** * **Sensitivity vs. Potency:** The ADH system is highly **sensitive** to osmolality (1% change triggers a response) but more **potent** in response to volume changes (requires 5-10% loss but results in massive ADH surges). * **Other Non-osmotic Stimuli:** Nausea (the most potent non-osmotic stimulus), pain, stress, surgery, and drugs like morphine or nicotine. * **V2 vs. V1 Receptors:** At low (osmotic) concentrations, ADH acts on **V2 receptors** (aquaporins in collecting ducts). At high (non-osmotic/hemorrhagic) concentrations, it acts on **V1 receptors** to cause vasoconstriction.

Question 203: In a woman with a 28-day menstrual cycle, at what point does ovulation typically occur?

A. 14 days prior to the next menstruation (Correct Answer)
B. Just before the luteinizing hormone (LH) surge
C. Just after the maturation of the corpus luteum
D. As a result of the progesterone rise

Explanation: ### Explanation **1. Why Option A is Correct:** The menstrual cycle is divided into two phases: the **follicular phase** (variable in length) and the **luteal phase** (constant). The luteal phase, which follows ovulation, is governed by the lifespan of the corpus luteum and almost always lasts **14 days**. Therefore, regardless of the total cycle length (whether 28, 35, or 21 days), ovulation consistently occurs **14 days before the onset of the next menses**. In a standard 28-day cycle, this happens to be Day 14, but the physiological constant is the countdown to the next period. **2. Why the Other Options are Incorrect:** * **Option B:** Ovulation occurs **after** the LH surge, not before. The LH surge is the primary trigger for the release of the oocyte, occurring approximately 24–36 hours before ovulation. * **Option C:** The corpus luteum forms **after** ovulation from the remnants of the ruptured Graafian follicle. It reaches peak maturation (and progesterone production) about 7–8 days after ovulation. * **Option D:** Progesterone rise is a **consequence** of ovulation, not the cause. Progesterone is secreted by the corpus luteum; its rise confirms that ovulation has already taken place. **3. NEET-PG High-Yield Pearls:** * **LH Surge:** The most reliable predictor of impending ovulation. Ovulation occurs **10–12 hours after the LH peak** and 24–36 hours after the onset of the LH surge. * **Mittelschmerz:** Pelvic pain experienced by some women mid-cycle during ovulation. * **Fern Test & Spinnbarkeit:** Under estrogen influence (pre-ovulatory), cervical mucus becomes thin, stretchy, and shows a "ferning" pattern. Post-ovulation, progesterone makes the mucus thick and tacky. * **Basal Body Temperature (BBT):** Increases by 0.5–1.0°F after ovulation due to the thermogenic effect of progesterone.

Question 204: Which of the following hormones does not affect growth?

A. Oxytocin (Correct Answer)
B. Somatotropins
C. Thyroid hormone
D. Estrogen

Explanation: **Explanation:** The regulation of human growth is a complex process involving multiple endocrine axes. The correct answer is **Oxytocin**, as it is primarily involved in smooth muscle contraction rather than linear or cellular growth. **1. Why Oxytocin is the correct answer:** Oxytocin is a posterior pituitary hormone. Its primary physiological roles are the **milk-ejection reflex** (contraction of myoepithelial cells in the mammary glands) and **uterine contractions** during parturition. It does not possess receptors on epiphyseal plates or metabolic pathways that influence somatic growth or protein synthesis. **2. Why the other options are incorrect:** * **Somatotropins (Growth Hormone):** This is the primary regulator of growth. It acts directly on tissues and indirectly via **IGF-1 (Somatomedin C)** to promote bone elongation at the epiphyseal plates and protein anabolism. * **Thyroid Hormone (T3/T4):** These are essential for growth because they have a **permissive effect** on Growth Hormone. Thyroid hormones are critical for skeletal maturation and, most importantly, CNS development during the perinatal period. * **Estrogen:** Sex steroids are responsible for the **pubertal growth spurt**. While they eventually cause the closure of epiphyseal plates (ending linear growth), they are potent stimulators of bone formation and growth during adolescence. **High-Yield NEET-PG Pearls:** * **Laron Dwarfism:** Caused by GH receptor insensitivity (GH levels are high, but IGF-1 is low). * **Cretinism:** Untreated congenital hypothyroidism leading to stunted physical and mental growth. * **Precocious Puberty:** Early exposure to sex steroids (like Estrogen) leads to an initial growth spurt but results in **short stature** due to premature epiphyseal fusion.

Question 205: Aldosterone secretion is increased when there is a fall in:

A. Plasma K+
B. Plasma Na+ (Correct Answer)
C. pH of the plasma
D. Angiotensin II levels

Explanation: **Explanation:** Aldosterone, the primary mineralocorticoid secreted by the **Zona Glomerulosa** of the adrenal cortex, plays a crucial role in maintaining electrolyte balance and blood pressure. **Why Plasma Na+ is correct:** A fall in plasma sodium (**Hyponatremia**) acts as a direct stimulus for aldosterone secretion. More importantly, low sodium levels (often associated with low blood volume) trigger the **Renin-Angiotensin-Aldosterone System (RAAS)**. Decreased sodium delivery to the *macula densa* in the kidney stimulates renin release, leading to increased Angiotensin II, which is the most potent stimulator of aldosterone. Aldosterone then acts on the distal convoluted tubule and collecting ducts to promote **Na+ reabsorption** and water retention. **Analysis of Incorrect Options:** * **A. Plasma K+:** Aldosterone secretion is increased by a **rise** in plasma potassium (Hyperkalemia), not a fall. It functions to excrete excess K+ into the urine. * **C. pH of the plasma:** While aldosterone promotes H+ secretion (acid excretion), plasma pH is not a primary direct regulator of its secretion compared to electrolytes and the RAAS. * **D. Angiotensin II levels:** Aldosterone secretion increases when Angiotensin II levels **rise**, as it is the primary hormonal mediator of the RAAS. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Stimuli:** The two most important direct stimuli for aldosterone are **Hyperkalemia** and **Angiotensin II**. * **ACTH Role:** ACTH is necessary for aldosterone secretion (permissive action) but plays a minor role in its daily regulation compared to K+ and Angiotensin II. * **Conn’s Syndrome:** Primary hyperaldosteronism characterized by the triad of Hypertension, Hypokalemia, and Metabolic Alkalosis. * **Atrial Natriuretic Peptide (ANP):** The only major hormone that **inhibits** aldosterone secretion.

Question 206: All of the following hormones bind to cell surface receptors of the target tissues EXCEPT?

A. Thyroid stimulating hormone
B. Glucagon
C. Estrogen (Correct Answer)
D. Epinephrine

Explanation: ### Explanation The mechanism of hormone action is determined by the chemical nature of the hormone (solubility). Hormones are broadly classified into **Lipid-soluble** and **Water-soluble** groups. **1. Why Estrogen is the correct answer:** Estrogen is a **steroid hormone** derived from cholesterol. Being lipophilic (lipid-soluble), it easily diffuses through the lipid bilayer of the cell membrane. Therefore, it does not require a cell surface receptor; instead, it binds to **intracellular receptors** (specifically nuclear receptors). The hormone-receptor complex then acts as a transcription factor, binding to DNA to regulate gene expression. **2. Why the other options are incorrect:** * **Thyroid Stimulating Hormone (TSH):** This is a large glycoprotein hormone. Due to its size and water-soluble nature, it cannot cross the cell membrane and must bind to **G-protein coupled receptors (GPCR)** on the cell surface. * **Glucagon:** This is a peptide hormone. Like TSH, it is water-soluble and binds to cell surface **GPCRs**, primarily activating the Adenylyl Cyclase-cAMP pathway. * **Epinephrine:** This is a catecholamine (amino acid derivative). Although small, it is polar and cannot diffuse through the membrane, thus binding to **alpha or beta-adrenergic receptors** on the cell surface. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Intracellular Receptors:** *"PET CAT"* – **P**rogesterone, **E**strogen, **T**estosterone, **C**ortisol, **A**ldosterone, **T**hyroid hormones (T3/T4), and Vitamin D. * **Exception Note:** Although **Thyroid hormones (T3/T4)** are amino acid derivatives, they are lipophilic and use **intracellular (nuclear) receptors**, unlike Epinephrine. * **Fast vs. Slow:** Cell surface receptors (e.g., Epinephrine) usually trigger rapid enzymatic changes, while intracellular receptors (e.g., Estrogen) cause slower, genomic effects.

Question 207: Which hormone provides negative feedback in spermatogenesis?

A. Androgen Binding Protein (ABP)
B. Inhibin (Correct Answer)
C. Progesterone
D. None of the above

Explanation: **Explanation:** The regulation of spermatogenesis occurs via the **Hypothalamic-Pituitary-Gonadal (HPG) axis**. In this system, the Anterior Pituitary secretes two primary gonadotropins: LH and FSH. 1. **Why Inhibin is correct:** FSH (Follicle Stimulating Hormone) acts on the **Sertoli cells** of the testes to stimulate spermatogenesis. In response to this stimulation, Sertoli cells secrete a glycoprotein hormone called **Inhibin (specifically Inhibin B)**. Inhibin travels through the blood to the anterior pituitary, where it exerts **negative feedback** specifically on the gonadotropes to inhibit further FSH secretion. This ensures that the rate of sperm production remains within physiological limits. 2. **Why other options are incorrect:** * **Androgen Binding Protein (ABP):** This is also secreted by Sertoli cells under the influence of FSH, but its function is to bind testosterone within the seminiferous tubules to maintain the high local concentrations required for sperm maturation. It is a transport protein, not a feedback hormone. * **Progesterone:** This is a female reproductive hormone (secreted by the corpus luteum). While it can inhibit GnRH at high doses, it plays no physiological role in the negative feedback loop of male spermatogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **Dual Feedback Loop:** Remember that **Testosterone** (from Leydig cells) provides negative feedback to both the **Hypothalamus (GnRH)** and **Pituitary (LH)**, whereas **Inhibin** provides selective negative feedback only to the **Pituitary (FSH)**. * **Sertoli Cell Markers:** Inhibin B is often used clinically as a serum marker for Sertoli cell function and the state of spermatogenesis. * **Mnemonic:** **S**ertoli cells secrete **S**perm and **I**nhibin (acts on FSH); **L**eydig cells secrete **L**ipids/Testosterone (acts on LH).

Question 208: Genetic expression of Na-K-ATPase is induced by which of the following?

A. Aldosterone (Correct Answer)
B. Cortisol
C. Thyroxine
D. ACTH

Explanation: **Explanation:** The correct answer is **Aldosterone**. Aldosterone is a mineralocorticoid that acts primarily on the **Principal cells (P cells)** of the late distal tubule and collecting ducts of the kidney. As a steroid hormone, it binds to intracellular mineralocorticoid receptors (MR). This hormone-receptor complex translocates to the nucleus, where it acts as a transcription factor to induce the **genetic expression** of specific proteins. Specifically, it increases the synthesis and activity of: 1. **Basolateral Na-K-ATPase pumps:** To pump sodium out of the cell into the blood. 2. **Apical ENaC (Epithelial Sodium Channels):** To facilitate sodium entry from the tubular lumen. 3. **Renal Outer Medullary Potassium (ROMK) channels:** To secrete potassium into the lumen. **Analysis of Incorrect Options:** * **Cortisol:** While cortisol can bind to mineralocorticoid receptors (due to structural similarity), it is normally inactivated in the kidney by the enzyme **11β-HSD2**. Its primary role is metabolic (gluconeogenesis) rather than direct induction of renal Na-K-ATPase for electrolyte balance. * **Thyroxine (T3/T4):** Thyroid hormones increase the *number* and *activity* of Na-K-ATPase pumps in almost all tissues to increase the Basal Metabolic Rate (BMR), but they are not the primary physiological regulators of renal sodium reabsorption in this context. * **ACTH:** ACTH stimulates the adrenal cortex to release cortisol. While it has a minor "permissive" effect on aldosterone secretion, it does not directly induce the genetic expression of renal Na-K-ATPase. **High-Yield Clinical Pearls for NEET-PG:** * **Liddle’s Syndrome:** A genetic mutation causing "gain of function" of ENaC channels, mimicking hyperaldosteronism (hypertension + hypokalemia) but with *low* aldosterone levels. * **Spironolactone/Eplerenone:** These are competitive aldosterone antagonists used as potassium-sparing diuretics. * **11β-HSD2 Deficiency:** Leads to "Apparent Mineralocorticoid Excess" (AME) because cortisol is not inactivated and starts overstimulating the Na-K-ATPase pumps.

Question 209: Which of the following is NOT a glycoprotein hormone?

A. Erythropoietin (EH)
B. Follicle-Stimulating Hormone (FSH)
C. Growth Hormone (GH)
D. Vasopressin (Correct Answer)

Explanation: **Explanation:** The classification of hormones based on their chemical structure is a high-yield topic for NEET-PG. Hormones are generally categorized into steroids, amines, peptides/proteins, and glycoproteins. **Why Vasopressin is the correct answer:** **Vasopressin (Antidiuretic Hormone/ADH)** is a **nonapeptide** (composed of 9 amino acids). It is synthesized in the hypothalamus (supraoptic and paraventricular nuclei) and stored in the posterior pituitary. Unlike glycoproteins, it is a simple short-chain peptide and does not contain carbohydrate side chains. **Analysis of Incorrect Options:** * **Erythropoietin (EPO):** This is a glycoprotein hormone primarily produced by the interstitial cells of the kidney. It contains about 40% carbohydrate content, which is essential for its stability and biological activity in vivo. * **Follicle-Stimulating Hormone (FSH):** FSH, along with LH, TSH, and hCG, belongs to the **glycoprotein family**. These hormones are unique because they consist of two subunits: an **alpha (α) subunit** (identical in all four) and a **beta (β) subunit** (which provides biological specificity). * **Growth Hormone (GH):** While GH is a large protein (191 amino acids), it is often categorized under "Protein/Peptide" hormones. However, in the context of this specific question, Vasopressin is the "most correct" answer because it is a small peptide, whereas EPO and FSH are classic glycoproteins. (Note: GH is a single-chain polypeptide, not a glycoprotein). **NEET-PG High-Yield Pearls:** 1. **The "Big Four" Glycoproteins:** Remember the mnemonic **"F-L-A-T"** (FSH, LH, ACTH is NOT one, it's TSH) or simply **FSH, LH, TSH, and hCG**. They all share the same alpha subunit. 2. **Vasopressin vs. Oxytocin:** Both are nonapeptides from the posterior pituitary, differing by only two amino acids. 3. **EPO Fact:** It is the glycoprotein hormone with the highest carbohydrate content by weight.

Question 210: Which organ participates in the formation of vitamin D?

A. Liver
B. Skin
C. Kidney
D. All of the above (Correct Answer)

Explanation: The synthesis of Vitamin D (Calcitriol) is a multi-organ process involving the skin, liver, and kidneys. It is a classic high-yield topic for NEET-PG, illustrating the endocrine coordination between different systems. ### **Mechanism of Synthesis** 1. **Skin:** The process begins when **7-dehydrocholesterol** in the skin is converted to **Cholecalciferol (Vitamin D3)** via exposure to ultraviolet B (UVB) radiation. 2. **Liver:** Cholecalciferol travels to the liver, where the enzyme **25-hydroxylase** converts it into **25-hydroxycholecalciferol [25(OH)D3]**, also known as Calcidiol. This is the major circulating form and the clinical marker for Vitamin D status. 3. **Kidney:** The final and rate-limiting step occurs in the proximal convoluted tubules. The enzyme **1-alpha-hydroxylase** (stimulated by PTH) converts Calcidiol into **1,25-dihydroxycholecalciferol [1,25(OH)2D3]**, the biologically active form known as **Calcitriol**. ### **Why "All of the above" is correct:** Since the absence of any of these three organs would halt the production of active Vitamin D, all three are essential participants in the pathway. ### **High-Yield Clinical Pearls for NEET-PG:** * **Rate-limiting step:** Occurs in the **Kidney** (1-alpha-hydroxylase). * **Storage form:** 25-hydroxycholecalciferol (measured in labs). * **Active form:** 1,25-dihydroxycholecalciferol (Calcitriol). * **Clinical Correlation:** Patients with **Chronic Kidney Disease (CKD)** develop secondary hyperparathyroidism and renal osteodystrophy because the kidneys cannot perform the final hydroxylation, leading to Calcitriol deficiency. * **Sarcoidosis:** Macrophages in granulomas can express 1-alpha-hydroxylase independently, leading to hypercalcemia.

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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