Endocrinology Practice Questions

Q: Heat acclimatization is primarily due to which hormone?

Aldosterone. **Explanation:** Heat acclimatization is the process by which the body undergoes physiological adaptations to improve heat tolerance. The primary hormonal driver for this process is **Aldosterone**. **Why Aldosterone is Correct:** When an individual is repeatedly exposed to high temperatures, the body aims to minimize electrolyte loss while maximizing cooling through sweat. Aldosterone acts on the epithelial cells of the sweat glands to increase the **reabsorption of Sodium (Na+) and Chloride (Cl-)**. This results in: 1. **Conservation of salt:** Preventing hyponatremia during profuse sweating. 2. **Increased sweat volume:** By preserving total body salt, the body can maintain plasma volume, allowing for a higher sweat rate and better evaporative cooling. **Analysis of Incorrect Options:** * **Thyroxine (A):** This hormone increases the Basal Metabolic Rate (BMR) and heat production (thermogenesis). In hot environments, thyroid activity actually tends to decrease to prevent further heat load. * **Insulin (B):** Primarily regulates glucose metabolism and has no direct role in thermoregulation or electrolyte conservation during heat stress. * **Adrenaline (C):** While it can stimulate sweating (diaphoresis) during acute stress or "fight or flight" responses, it is not responsible for the long-term physiological adaptation seen in acclimatization. **Clinical Pearls for NEET-PG:** * **Acclimatization Timeline:** It typically takes **7 to 14 days** of exposure to a hot environment. * **Sweat Composition:** An acclimatized person produces sweat that is more **hypotonic** (lower salt concentration) compared to a non-acclimatized person. * **Plasma Volume:** Acclimatization leads to an expansion of plasma volume (by 10-12%), which helps maintain cardiac output during exercise in the heat.

Q: Decreased protein to lipid ratio is seen in which of the following membranes?

Myelin sheath membrane. The protein-to-lipid ratio of a biological membrane is directly proportional to its metabolic activity. Membranes involved in active transport, signal transduction, or energy production have high protein content, while membranes acting primarily as insulators have high lipid content. **1. Why Myelin Sheath is Correct:** The myelin sheath serves as an electrical insulator for axons to facilitate saltatory conduction. To minimize ion leakage and provide maximum insulation, it is composed of approximately **80% lipids** (mainly cholesterol and sphingomyelin) and only **20% proteins**. This results in the **lowest protein-to-lipid ratio (0.25:1)** in the human body. **2. Why Other Options are Incorrect:** * **Inner Mitochondrial Membrane (IMM):** This membrane has the **highest protein-to-lipid ratio (3:1)**. It is packed with electron transport chain complexes and ATP synthase, reflecting its intense metabolic role in oxidative phosphorylation. * **Outer Mitochondrial Membrane (OMM):** While less protein-dense than the IMM, it still contains numerous porins and enzymes, maintaining a ratio of approximately **1:1**. * **Sarcoplasmic Reticulum:** This membrane is highly specialized for calcium signaling and contains a high density of SERCA pumps (proteins), resulting in a high protein-to-lipid ratio (approx. **2:1**). **High-Yield Clinical Pearls for NEET-PG:** * **Highest Protein Content:** Inner Mitochondrial Membrane (approx. 75-80% protein). * **Highest Lipid Content:** Myelin Sheath (approx. 80% lipid). * **Plasma Membrane Average:** Typically a 1:1 ratio (50% protein, 50% lipid). * **Key Lipid in Myelin:** Galactocerebroside is the characteristic glycolipid of myelin. * **Clinical Correlation:** Demyelinating diseases like **Multiple Sclerosis** (CNS) and **Guillain-Barré Syndrome** (PNS) involve the destruction of these lipid-rich layers, leading to slowed nerve conduction.

Q: Which of the following is NOT an effect of the T3 hormone?

It decreases pulse pressure. **Explanation:** The thyroid hormone (T3) has profound effects on the cardiovascular system, primarily acting to increase cardiac output and meet the body's metabolic demands. **Why Option D is the Correct Answer:** T3 **increases pulse pressure**, it does not decrease it. Pulse pressure is the difference between systolic blood pressure (SBP) and diastolic blood pressure (DBP). T3 increases SBP (due to increased stroke volume and contractility) and decreases DBP (due to vasodilation). This widening of the gap results in a **wide pulse pressure**, a classic clinical sign of hyperthyroidism. **Analysis of Incorrect Options:** * **A. Increases Heart Rate:** T3 has a direct chronotropic effect by upregulating $\beta_1$-adrenergic receptors in the heart and increasing the rate of depolarization in the SA node. * **B. Increases Stroke Volume:** T3 exerts a positive inotropic effect by increasing the expression of $\alpha$-myosin heavy chains and SERCA (sarcoplasmic reticulum calcium ATPase), enhancing myocardial contractility and stroke volume. * **C. Decreases Peripheral Resistance:** T3 causes direct vasodilation of peripheral arterioles by increasing local metabolic end-products and decreasing systemic vascular resistance (SVR). **NEET-PG High-Yield Pearls:** * **Hyperthyroidism:** Characterized by tachycardia, palpitations, and a "bounding pulse" (due to wide pulse pressure). * **Hypothyroidism:** Characterized by bradycardia and a "narrow pulse pressure." * **Molecular Mechanism:** T3 increases the transcription of the **SERCA2 pump**, which improves calcium sequestration during diastole, leading to faster relaxation (lusitropic effect) and stronger subsequent contraction.

Q: In tetany, hyperexcitability is due to which of the following mechanisms?

Low calcium levels cause increased sodium permeability.. **Mechanism of Hypocalcemic Tetany** The correct answer is **A: Low calcium levels cause increased sodium permeability.** **Explanation:** In the extracellular fluid (ECF), calcium ions ($Ca^{2+}$) play a critical role in stabilizing the resting membrane potential of excitable tissues (nerve and muscle). Calcium ions normally bind to the external surface of voltage-gated sodium channels, increasing the voltage threshold required to open them. When ECF calcium levels drop (**hypocalcemia**), there are fewer positive charges to "mask" the negative charges on the cell membrane. This reduces the threshold for excitation, making the sodium channels much easier to open. Consequently, sodium permeability increases even with slight stimuli, leading to spontaneous depolarization and repetitive firing of action potentials. This manifests clinically as involuntary muscle contractions (tetany). **Analysis of Incorrect Options:** * **B & C:** These options are incorrect because tetany is primarily a phenomenon of the **cell membrane threshold** and sodium influx, rather than a direct inhibition of potassium release or intracellular calcium sequestration. * **D:** While intracellular calcium is required for muscle contraction (excitation-contraction coupling), the *hyperexcitability* (the tendency to fire) is triggered by the **extracellular** calcium deficit affecting sodium channel gating. **High-Yield NEET-PG Pearls:** * **Trousseau’s Sign:** Carpopedal spasm induced by inflating a BP cuff above systolic pressure (more sensitive than Chvostek's). * **Chvostek’s Sign:** Twitching of facial muscles upon tapping the facial nerve. * **ECG Finding:** Hypocalcemia characteristically causes **prolonged QT interval**. * **Rule of Thumb:** "Hypocalcemia excites, Hypercalcemia excites (the heart) but depresses (the nerves)."

Q: Which hormone stimulates the synthesis of milk proteins?

Prolactin (PRL). **Explanation:** **Prolactin (PRL)** is the primary hormone responsible for the **synthesis of milk proteins** (such as casein and lactalbumin) and the initiation of lactation (lactogenesis). It is secreted by the lactotrophs of the anterior pituitary. During pregnancy, high levels of estrogen and progesterone stimulate breast development but inhibit the actual secretion of milk. Postpartum, the sudden drop in these steroid hormones allows Prolactin to stimulate the mammary alveolar cells to produce milk. **Analysis of Incorrect Options:** * **Luteinizing hormone (LH):** A gonadotropin that triggers ovulation in females and stimulates testosterone production by Leydig cells in males. It has no direct role in milk synthesis. * **Thyroid-stimulating hormone (TSH):** Regulates the production of thyroid hormones (T3 and T4) from the thyroid gland to control basal metabolic rate. * **Growth hormone (GH):** While structurally similar to Prolactin and possessing some lactogenic properties, its primary role is promoting linear growth and protein synthesis via IGF-1. **High-Yield NEET-PG Pearls:** * **Dopamine** (Prolactin-Inhibiting Hormone) is the primary physiological regulator that keeps Prolactin levels low in non-pregnant individuals. * **Oxytocin** is responsible for the **milk-ejection reflex** (let-down reflex) via contraction of myoepithelial cells, whereas Prolactin is for **milk production**. * **Suckling** is the strongest stimulus for both Prolactin and Oxytocin release. * **Hyperprolactinemia** often presents with galactorrhea and secondary amenorrhea (due to inhibition of GnRH).

Q: What is the naturally occurring glucocorticoid?

Cortisol. **Explanation:** The adrenal cortex consists of three layers, with the **Zona Fasciculata** being responsible for the secretion of glucocorticoids. In humans, **Cortisol** is the primary, most potent, and most abundant naturally occurring glucocorticoid. It plays a vital role in glucose homeostasis (gluconeogenesis), protein catabolism, and modulating the inflammatory response. **Analysis of Options:** * **Cortisol (Option B):** This is the principal endogenous glucocorticoid in humans. It is synthesized from cholesterol and regulated by the Hypothalamic-Pituitary-Adrenal (HPA) axis via ACTH. * **Hydrocortisone (Option A):** While chemically identical to cortisol, the term "Hydrocortisone" is typically used in a **pharmacological context** to refer to the pharmaceutical preparation of the hormone used for replacement therapy or topical application. * **Prednisolone (Option C):** This is a **synthetic** glucocorticoid. It is a derivative of cortisol designed to have higher anti-inflammatory potency and less mineralocorticoid activity. * **Corticosterone (Option D):** While it is a naturally occurring glucocorticoid, it is the primary glucocorticoid in **rodents** (rats/mice). In humans, it serves mainly as an intermediate in the aldosterone synthesis pathway and has very weak glucocorticoid activity. **High-Yield NEET-PG Pearls:** 1. **Diurnal Variation:** Cortisol levels are highest in the early morning (approx. 8 AM) and lowest at midnight. 2. **Transport:** 90% of cortisol is bound to **CBG (Corticosteroid-Binding Globulin)** or Transcortin; only the free fraction is biologically active. 3. **Metabolism:** Cortisol is metabolized in the liver and excreted in the urine as **17-hydroxycorticosteroids**. 4. **Potency Ratio:** Prednisolone is roughly 4 times more potent than Cortisol, while Dexamethasone (synthetic) is about 25–30 times more potent.

Q: The cortisol level returns to normal after hemorrhage in how many days?

3 days. **Explanation:** The correct answer is **3 days (Option D)**. **Underlying Medical Concept:** Hemorrhage acts as a potent physical stressor that triggers the **Hypothalamic-Pituitary-Adrenal (HPA) axis**. Following acute blood loss, there is an immediate and sharp increase in the secretion of **Corticotropin-Releasing Hormone (CRH)** and **Adrenocorticotropic Hormone (ACTH)**, leading to elevated plasma cortisol levels. Cortisol plays a vital role in the "fight or flight" response by maintaining vascular reactivity to catecholamines and mobilizing energy stores (gluconeogenesis) to cope with the stress of volume loss. In a typical physiological recovery following a non-fatal hemorrhage, the HPA axis stabilizes, and cortisol levels generally return to their baseline (pre-stress) values within **72 hours (3 days)**. **Analysis of Incorrect Options:** * **Option A (2 weeks) & Option B (10 days):** These timeframes are too long. While the body may take weeks to fully restore red blood cell mass (erythropoiesis), the hormonal/endocrine response to acute stress is much more rapid. * **Option C (7 days):** While some metabolic parameters take a week to normalize, the acute surge of cortisol specifically subsides much earlier as the immediate hemodynamic stress is managed. **NEET-PG High-Yield Pearls:** * **Cortisol & Catecholamines:** Cortisol has a "permissive effect" on catecholamines; it is essential for vasoconstriction. In its absence (Addisonian crisis), patients develop refractory hypotension. * **Diurnal Variation:** Remember that cortisol normally peaks at **8:00 AM** and is lowest at **midnight**. This rhythm is often lost during acute stress or in Cushing’s syndrome. * **Aldosterone vs. Cortisol:** While cortisol returns to normal in 3 days, aldosterone levels may remain elevated longer if the renin-angiotensin-aldosterone system (RAAS) is still compensating for residual volume deficit.

Q: Which of the following is NOT associated with progesterone?

Proliferative phase of the menstrual cycle. **Explanation:** The correct answer is **B. Proliferative phase of the menstrual cycle.** The menstrual cycle is divided into two main phases: the **proliferative (follicular) phase** and the **secretory (luteal) phase**. The proliferative phase is dominated by **Estrogen**, which is secreted by the developing ovarian follicles to stimulate endometrial growth. Progesterone levels remain baseline during this phase. **Analysis of Options:** * **A. Ovulation:** While LH triggers ovulation, the process is preceded by a small pre-ovulatory rise in progesterone. Furthermore, the presence of progesterone is the definitive marker that ovulation has occurred, as it is secreted by the resulting Corpus Luteum. * **C. Thermogenesis:** Progesterone has a direct effect on the hypothalamus, increasing the basal body temperature (BBT) by approximately 0.5°F (0.3°C) after ovulation. This is a classic clinical marker used to track the luteal phase. * **D. Secretory phase:** This phase is entirely dependent on Progesterone. It transforms the estrogen-primed endometrium into a secretory state, making it receptive for implantation by increasing vascularity and glycogen storage. **High-Yield NEET-PG Pearls:** * **Source:** Progesterone is primarily secreted by the **Corpus Luteum** (stimulated by LH) and later by the **Placenta** (after 8–10 weeks). * **Pregnancy:** It is the "hormone of pregnancy" because it maintains endometrial integrity and decreases uterine contractility (quiescence). * **Diagnostic Test:** A serum progesterone level >3 ng/mL on Day 21 of the cycle is the gold standard for confirming that ovulation has occurred.

Question 1

Heat acclimatization is primarily due to which hormone?

Accepted Answer

Aldosterone

Answer

Thyroxine

Answer

Insulin

Answer

Adrenaline

Question 2

Decreased protein to lipid ratio is seen in which of the following membranes?

Accepted Answer

Myelin sheath membrane

Answer

Inner mitochondrial membrane

Answer

Outer mitochondrial membrane

Answer

Sarcoplasmic reticulum

Question 3

Which of the following is NOT an effect of the T3 hormone?

Accepted Answer

It decreases pulse pressure

Answer

It increases the heart rate

Answer

It increases the stroke volume

Answer

It decreases the peripheral resistance

Question 4

In tetany, hyperexcitability is due to which of the following mechanisms?

Accepted Answer

Low calcium levels cause increased sodium permeability.

Answer

Prevent potassium release.

Answer

Prevent sodium and intracellular calcium release.

Answer

Increased intracellular calcium produces the generation of an action potential.

Question 5

Which of the following is an autocrine hormone?

Accepted Answer

Both Prostaglandins and Thromboxane A2

Answer

Prostaglandins

Answer

Thromboxane A2

Answer

None of the above

Question 6

Which hormone stimulates the synthesis of milk proteins?

Accepted Answer

Prolactin (PRL)

Answer

Luteinizing hormone (LH)

Answer

Thyroid-stimulating hormone (TSH)

Answer

Growth hormone (GH)

Question 7

A diet deficient in calcium will result in what physiological change?

Accepted Answer

Production of parathyroid hormone and bone resorption

Answer

Stimulation of the thyroid gland

Answer

Increased ability to cross-link fibrin

Answer

Production of Calcitonin and a low blood calcium level

Question 8

What is the naturally occurring glucocorticoid?

Accepted Answer

Cortisol

Answer

Hydrocortisone

Answer

Prednisolone

Answer

Corticosterone

Question 9

The cortisol level returns to normal after hemorrhage in how many days?

Accepted Answer

3 days

Answer

2 weeks

Answer

10 days

Answer

7 days

Question 10

Which of the following is NOT associated with progesterone?

Accepted Answer

Proliferative phase of the menstrual cycle

Answer

Ovulation

Answer

Thermogenesis

Answer

Secretory phase of the menstrual cycle

Endocrinology — MCQs

Endocrinology — MCQs

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