Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 471: C-peptide is secreted by which type of pancreatic islet cell?

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

Explanation: **Explanation:** **Why Beta cells are correct:** C-peptide (Connecting peptide) is a byproduct of insulin synthesis within the **Beta cells** of the Islets of Langerhans. Insulin is initially synthesized as a precursor molecule called **Preproinsulin**, which is cleaved into **Proinsulin**. In the Golgi apparatus, proinsulin is packaged into secretory granules where it is cleaved by endopeptidases into equal amounts (equimolar concentrations) of **Insulin** and **C-peptide**. Both are then released into the portal circulation via exocytosis. **Why other options are incorrect:** * **Alpha cells:** These cells secrete **Glucagon**, which increases blood glucose levels by stimulating glycogenolysis and gluconeogenesis. * **Delta cells:** These cells secrete **Somatostatin**, which acts as a universal inhibitor, suppressing the release of both insulin and glucagon. * **F cells (PP cells):** These cells secrete **Pancreatic Polypeptide**, which helps regulate pancreatic exocrine secretions and gallbladder contraction. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Utility:** Since C-peptide is secreted in a **1:1 ratio** with endogenous insulin but has a longer half-life (~30 mins vs. ~5 mins for insulin), it serves as a reliable marker of endogenous Beta-cell function. * **Factitious Hypoglycemia:** In cases of exogenous insulin overdose, C-peptide levels will be **low** (because commercial insulin lacks C-peptide). In contrast, in an **Insulinoma**, both insulin and C-peptide levels will be **elevated**. * **Metabolism:** Unlike insulin, which is primarily cleared by the liver, C-peptide is mainly cleared by the **kidneys**.

Question 472: What is autocrine regulation of hormone secretion?

A. A hormone directly inhibits its own secretion.
B. A hormone inhibits its own secretion by affecting a regulatory hormone. (Correct Answer)
C. The nervous system inhibits the release of a hormone.
D. All of the above.

Explanation: ### Explanation In the context of endocrine feedback loops, **Autocrine Regulation** (specifically "Short-loop feedback") refers to a mechanism where a hormone secreted by a target gland or the anterior pituitary acts back on the hypothalamus or the pituitary itself to regulate its own production. **Why Option B is Correct:** The term "autocrine" in this specific MCQ context refers to the **Short-loop feedback mechanism**. For example, Growth Hormone (GH) secreted by the anterior pituitary can act directly on the hypothalamus to stimulate Somatostatin (GHIH), which then inhibits further GH secretion. Here, the hormone (GH) inhibits its own secretion by affecting a regulatory hormone (Somatostatin). **Analysis of Incorrect Options:** * **Option A:** This describes **Ultra-short-loop feedback**, where a hormone acts directly on the very cells that secreted it (e.g., a hypothalamic releasing hormone inhibiting its own release from the same hypothalamic neurons). While technically a form of self-regulation, it does not involve a "regulatory hormone" intermediary as specified in the standard definition of endocrine autocrine loops. * **Option C:** This describes **Neural Regulation** (e.g., the sympathetic nervous system stimulating adrenaline release from the adrenal medulla), not autocrine or feedback regulation. * **Option D:** Incorrect because the mechanisms are distinct and defined by the distance and pathway the hormone travels. **High-Yield NEET-PG Pearls:** 1. **Ultra-short-loop:** Hormone acts on the secreting cell itself (e.g., Somatostatin inhibiting its own release in the hypothalamus). 2. **Short-loop:** Pituitary hormone inhibits the Hypothalamic releasing hormone (e.g., ACTH inhibiting CRH). 3. **Long-loop:** Peripheral gland hormone inhibits the Pituitary or Hypothalamus (e.g., Cortisol inhibiting ACTH/CRH). This is the most common feedback mechanism in the body.

Question 473: Which of the following is NOT an effect of growth hormone?

A. Lipolysis
B. Increased protein synthesis
C. Glycolysis (Correct Answer)
D. Glycogenolysis

Explanation: **Explanation:** Growth Hormone (GH), secreted by the anterior pituitary, is primarily an **anabolic hormone for proteins** but a **catabolic hormone for fats and carbohydrates**. It aims to increase blood glucose levels and provide alternative energy sources (fatty acids) to spare glucose for the brain. **Why Glycolysis is the Correct Answer:** GH is **diabetogenic**. It decreases peripheral glucose uptake and utilization in tissues like muscle and adipose. **Glycolysis** (the breakdown of glucose for energy) is inhibited by GH to conserve glucose. Instead, GH promotes gluconeogenesis in the liver to raise blood sugar levels. **Analysis of Other Options:** * **Lipolysis (A):** GH is potent in mobilizing fatty acids from adipose tissue. It increases the breakdown of triglycerides into free fatty acids, which serve as the primary energy source under its influence. * **Increased Protein Synthesis (B):** GH promotes the transport of amino acids into cells and stimulates nuclear transcription and translation, leading to increased lean body mass and organ growth. * **Glycogenolysis (D):** To maintain high blood glucose levels, GH stimulates the breakdown of glycogen in the liver into glucose. **High-Yield Clinical Pearls for NEET-PG:** * **Somatomedins:** Most growth-promoting effects of GH are mediated by **IGF-1** (Insulin-like Growth Factor 1), primarily produced in the liver. * **Biphasic Effect:** While GH is acutely "insulin-like," its chronic metabolic effect is **anti-insulin**. * **Stimulators:** Deep sleep (Stage 3 & 4), hypoglycemia, fasting, and exercise are potent stimulators of GH secretion. * **Clinical Correlation:** Excess GH leads to **Gigantism** (pre-puberty) or **Acromegaly** (post-puberty), often presenting with secondary "Pituitary Diabetes."

Question 474: Which of the following conditions increases aldosterone secretion without affecting glucocorticoid secretion?

A. High potassium intake
B. Low sodium intake
C. Constriction of the inferior vena cava in the thorax
D. All of the above (Correct Answer)

Explanation: The regulation of the adrenal cortex is functionally divided: **Aldosterone** (mineralocorticoid) is primarily regulated by the Renin-Angiotensin-Aldosterone System (RAAS) and plasma potassium levels, whereas **Cortisol** (glucocorticoid) is strictly regulated by ACTH from the anterior pituitary. ### **Explanation of Options:** * **High Potassium Intake (Option A):** A direct increase in plasma $K^+$ concentration acts on the zona glomerulosa cells to stimulate aldosterone secretion. This is a protective mechanism to enhance renal $K^+$ excretion. It does not involve the ACTH pathway, so glucocorticoids remain unaffected. * **Low Sodium Intake (Option B):** Low $Na^+$ leads to a decrease in extracellular fluid (ECF) volume and decreased delivery of $NaCl$ to the macula densa. This triggers **Renin** release, leading to increased **Angiotensin II**, which specifically stimulates aldosterone production to conserve sodium. * **Constriction of Inferior Vena Cava (Option C):** This maneuver reduces venous return to the heart, decreasing cardiac output and effective arterial blood volume. This "perceived" hypovolemia activates the RAAS, increasing aldosterone to expand volume, without stimulating the hypothalamic-pituitary-adrenal (HPA) axis. ### **Why "All of the Above" is Correct:** All three stimuli activate the physiological pathways for mineralocorticoid release (RAAS or direct $K^+$ effect) without triggering the release of ACTH, thereby leaving glucocorticoid levels unchanged. ### **NEET-PG High-Yield Pearls:** * **Primary Regulator:** Angiotensin II and $K^+$ are the primary regulators of Aldosterone; ACTH has only a minor, permissive role. * **Zonation:** Remember **GFR** (Glomerulosa, Fasciculata, Reticularis) corresponds to **Salt, Sugar, Sex** (Mineralocorticoids, Glucocorticoids, Androgens). * **Conn’s Syndrome:** Primary hyperaldosteronism presents with hypertension and hypokalemia, but normal cortisol levels. * **Atrial Natriuretic Peptide (ANP):** The only major hormone that *inhibits* aldosterone secretion.

Question 475: 17-alpha-hydroxylase deficiency affects the release of which hormone?

A. Aldosterone
B. Growth hormone
C. Glucocorticoids (Correct Answer)
D. ACTH

Explanation: **Explanation:** The enzyme **17-alpha-hydroxylase** is a critical branch-point enzyme in the adrenal steroidogenesis pathway. It is required to convert Pregnenolone to 17-OH Pregnenolone and Progesterone to 17-OH Progesterone. These "17-hydroxylated" intermediates are the mandatory precursors for the synthesis of **Glucocorticoids (Cortisol)** and **Androgens**. 1. **Why Glucocorticoids is correct:** In 17-alpha-hydroxylase deficiency, the adrenal gland cannot produce 17-OH Progesterone. Since this is the direct precursor to Cortisol, glucocorticoid synthesis is severely impaired. 2. **Why Aldosterone is incorrect:** This enzyme is *not* required for the mineralocorticoid pathway. In its absence, steroid precursors are shunted toward the production of 11-deoxycorticosterone (DOC) and corticosterone. While aldosterone levels eventually drop due to feedback suppression of renin by high DOC levels, the primary *defect* is the inability to produce glucocorticoids and sex steroids. 3. **Why Growth Hormone is incorrect:** GH is secreted by the anterior pituitary and is not involved in the adrenal steroid biosynthetic pathway. 4. **Why ACTH is incorrect:** ACTH levels actually **increase** (rather than decrease) as a compensatory response to low cortisol levels (loss of negative feedback). **High-Yield Clinical Pearls for NEET-PG:** * **Presentation:** Patients present with **Hypertension** (due to excess DOC), **Hypokalemia**, and **Sexual Infantilism/Primary Amenorrhea** (due to lack of androgens/estrogens). * **Mnemonic:** In Congenital Adrenal Hyperplasia (CAH), if the enzyme starts with **1** (11 or 17), it causes **Hypertension**. If it ends with **1** (21 or 11), it causes **Virilization**. Therefore, 17-alpha-hydroxylase deficiency (starts with 1, ends with 7) causes Hypertension but *no* Virilization.

Question 476: Which of the following is considered a marker for epididymal function?

A. Fructose
B. Testosterone
C. Acid phosphatase
D. Carnitine (Correct Answer)

Explanation: **Explanation:** The correct answer is **Carnitine**. The composition of seminal fluid is derived from various accessory reproductive organs, and specific biochemical markers are used to assess the functional integrity of these glands. **1. Why Carnitine is correct:** L-Carnitine (and Glycerophosphocholine) is actively secreted by the **epididymis**. It plays a crucial role in the maturation of spermatozoa and the acquisition of motility. High concentrations of free carnitine in the semen are a direct indicator of normal epididymal function. A decrease in carnitine levels often suggests an epididymal obstruction or dysfunction. **2. Why other options are incorrect:** * **Fructose (Option A):** This is the primary marker for the **Seminal Vesicles**. It provides the main energy source for sperm motility. Absence of fructose indicates seminal vesicle agenesis or obstruction of the ejaculatory duct. * **Testosterone (Option B):** This is a steroid hormone produced by the **Leydig cells** of the testes. While essential for spermatogenesis, it is not a specific marker for the function of the exocrine ducts (like the epididymis) in semen analysis. * **Acid Phosphatase (Option C):** This is a classic marker for **Prostatic function**. Other prostatic markers include Citric acid, Zinc, and Prostate-Specific Antigen (PSA). **High-Yield Clinical Pearls for NEET-PG:** * **Epididymis:** Markers include Carnitine, Neutral α-glucosidase, and Glycerophosphocholine. * **Seminal Vesicles:** Marker is Fructose (contributes ~60% of total semen volume). * **Prostate:** Markers include Citric acid, Zinc, and Acid Phosphatase (contributes ~20-30% of volume; gives semen its milky appearance). * **Sperm Maturation:** While sperm are produced in the seminiferous tubules, they acquire **motility and fertilizing capacity** only during their passage through the epididymis.

Question 477: Which hormone is related to glucose fever?

A. Glucagon
B. Parathyroid hormone
C. Growth Hormone
D. Aldosterone (Correct Answer)

Explanation: **Explanation:** **Glucose fever** is a clinical phenomenon characterized by a rise in body temperature following the administration of hypertonic glucose solutions, particularly in patients with adrenal insufficiency or specific electrolyte imbalances. **Why Aldosterone is the correct answer:** The term is historically and physiologically linked to **Aldosterone** (the primary mineralocorticoid). Aldosterone plays a critical role in maintaining fluid and electrolyte balance. In states of aldosterone deficiency or during rapid shifts in osmolarity caused by hypertonic glucose, there is a significant movement of water from the intracellular compartment to the extracellular compartment. This sudden cellular dehydration, combined with the body's inability to regulate heat dissipation effectively due to altered sweat gland function (which is also influenced by aldosterone), leads to a febrile response known as "glucose fever." **Analysis of Incorrect Options:** * **Glucagon (A):** While glucagon increases blood glucose via glycogenolysis and gluconeogenesis, it does not directly cause the thermoregulatory failure associated with glucose fever. * **Parathyroid Hormone (B):** PTH regulates calcium and phosphate homeostasis. It has no direct involvement in glucose-induced osmotic shifts or temperature regulation. * **Growth Hormone (C):** GH is a counter-regulatory hormone that increases blood glucose, but its deficiency or excess is not the underlying mechanism for the acute febrile response to glucose. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Glucose fever is primarily due to **cellular dehydration** and the osmotic effect of glucose in the absence of adequate mineralocorticoid activity. * **Aldosterone Site of Action:** Acts on the **Principal cells (P cells)** of the late distal tubule and collecting duct to reabsorb $Na^+$ and secrete $K^+$. * **Conn’s Syndrome:** Primary hyperaldosteronism, characterized by hypertension, hypokalemia, and metabolic alkalosis.

Question 478: Which of the following suppresses the activity of osteoblasts?

A. Vitamin D3
B. T3 and T4
C. Corticosterone (Correct Answer)
D. Parathormone

Explanation: **Explanation:** The correct answer is **Corticosterone** (a glucocorticoid). Glucocorticoids are potent inhibitors of bone formation. They suppress osteoblast activity through several mechanisms: they decrease the proliferation and differentiation of osteoblast precursors, increase the apoptosis of mature osteoblasts and osteocytes, and shift the differentiation of mesenchymal stem cells away from the osteoblast lineage toward adipocytes. **Analysis of Options:** * **A. Vitamin D3 (Calcitriol):** It primarily promotes bone mineralization by increasing intestinal calcium and phosphate absorption. It also stimulates osteoblasts to secrete proteins like osteocalcin and RANKL (which indirectly activates osteoclasts), but its net physiological role is essential for healthy bone formation. * **B. T3 and T4 (Thyroid Hormones):** These are essential for normal bone growth and skeletal maturation. They stimulate osteoblast activity and protein synthesis. While hyperthyroidism can lead to increased bone turnover, thyroid hormones do not "suppress" osteoblasts. * **D. Parathormone (PTH):** PTH has a dual effect. While continuous high levels stimulate osteoclasts (via RANKL from osteoblasts), intermittent low doses of PTH are actually **anabolic** to bone and stimulate osteoblast activity (the basis for the drug Teriparatide). **Clinical Pearls for NEET-PG:** * **Glucocorticoid-Induced Osteoporosis (GIOP):** This is the most common cause of secondary osteoporosis. The hallmark is a decrease in bone formation rather than just an increase in resorption. * **Osteoblast Markers:** High-yield markers for osteoblast activity include **Alkaline Phosphatase (ALP)** and **Osteocalcin**. * **RANKL/OPG Ratio:** Osteoblasts regulate osteoclasts by secreting RANKL (stimulates osteoclasts) and Osteoprotegerin (OPG, inhibits osteoclasts). Glucocorticoids increase RANKL and decrease OPG, further damaging bone integrity.

Question 479: A hormone acts to stimulate its neighbouring cell to divide. To which category of signaling does this hormone's action best belong?

A. Paracrine signaling (Correct Answer)
B. Autocrine signaling
C. Endocrine signaling
D. None of the above

Explanation: **Explanation:** The correct answer is **Paracrine signaling**. This mode of communication involves a cell secreting a chemical messenger (hormone or cytokine) that diffuses through the interstitial fluid to act on **neighboring or adjacent cells** of a different type. Since the question specifies the hormone acts on its "neighboring cell," it perfectly fits the definition of paracrine action. **Analysis of Options:** * **Autocrine signaling:** In this mechanism, the hormone or chemical messenger acts on the **same cell** that secreted it (self-stimulation). This is common in cancer cell proliferation and immune responses (e.g., Interleukin-2 acting on the same T-cell). * **Endocrine signaling:** This involves hormones being secreted into the **bloodstream** to act on distant target organs. This is the classic mechanism for hormones like Insulin or Thyroxine. * **Juxtacrine signaling (Related Concept):** This requires direct physical contact between the membranes of two cells (e.g., Notch signaling). **High-Yield NEET-PG Pearls:** * **Paracrine Example:** Somatostatin secreted by Delta cells of the Islets of Langerhans inhibits the secretion of Insulin (Beta cells) and Glucagon (Alpha cells) in its immediate vicinity. * **Neuroendocrine:** A variation where a neuron releases a hormone into the blood (e.g., ADH from the posterior pituitary). * **Intracrine:** A hormone acts inside the cell without ever being secreted (e.g., Steroid hormones acting on nuclear receptors). * **Key Distinction:** The primary difference between these signaling types is the **distance** the messenger travels and the **medium** (interstitial fluid vs. blood) it uses.

Question 480: Which hormone stimulates the production of IGF?

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

Explanation: **Explanation:** **1. Why GH is the correct answer:** Growth Hormone (GH), secreted by the somatotrophs of the anterior pituitary, does not exert most of its growth-promoting effects directly. Instead, it acts primarily by stimulating the liver (and to a lesser extent, skeletal muscle and cartilage) to produce **Insulin-like Growth Factor-1 (IGF-1)**, also known as **Somatomedin C**. The GH-IGF-1 axis is the primary pathway for longitudinal bone growth and protein synthesis. While GH has direct metabolic effects (lipolysis and anti-insulin actions), its anabolic and growth-promoting functions are mediated by IGF-1. **2. Why other options are incorrect:** * **LH (Luteinizing Hormone):** Stimulates Leydig cells in testes to produce testosterone and triggers ovulation/progesterone production in ovaries. * **PRL (Prolactin):** Primarily responsible for milk production (lactogenesis) and inhibiting GnRH; it has no significant role in IGF production. * **TSH (Thyroid Stimulating Hormone):** Stimulates the thyroid gland to synthesize and release T3 and T4, which regulate the basal metabolic rate. **3. NEET-PG High-Yield Pearls:** * **Site of Production:** The **liver** is the principal source of circulating IGF-1. * **Feedback Loop:** IGF-1 exerts negative feedback on the anterior pituitary to inhibit GH secretion and stimulates the hypothalamus to release Somatostatin (GHIH). * **Clinical Correlation:** In **Laron Dwarfism**, there is a genetic GH receptor deficiency; GH levels are high, but IGF-1 levels are low, and patients do not respond to exogenous GH. * **Diagnosis:** Serum IGF-1 levels are more stable than GH levels (which are pulsatile) and are used as the primary screening tool for **Acromegaly**.

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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