Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 71: A hormone with a distant site of action acts via which mechanism?

A. Autocrine
B. Paracrine
C. Endocrine (Correct Answer)
D. Any of the above

Explanation: ### Explanation **1. Why Endocrine is Correct:** The term **Endocrine** refers to the classic mechanism of hormone action where a gland secretes hormones directly into the **bloodstream**. These hormones travel through the systemic circulation to reach target cells located at a **distant site** from the point of secretion. This allows a single gland (like the pituitary) to regulate diverse organs throughout the body. **2. Why Other Options are Incorrect:** * **Autocrine (A):** In this mechanism, the chemical messenger acts on the **same cell** that secreted it. There is no distance involved (e.g., Interleukin-1 in monocytes). * **Paracrine (B):** This involves local signaling where the hormone diffuses through the interstitial fluid to act on **neighboring/adjacent cells**. It does not enter the systemic circulation for distant transport (e.g., Somatostatin acting on alpha and beta cells within the Islets of Langerhans). * **Any of the above (D):** This is incorrect because autocrine and paracrine mechanisms are specifically defined by their local, non-distant range of action. **3. High-Yield Clinical Pearls for NEET-PG:** * **Neuroendocrine:** A variation where neurons release hormones into the blood to act on distant targets (e.g., ADH/Vasopressin from the posterior pituitary). * **Juxtacrine:** A type of signaling requiring direct cell-to-cell contact (common in immune responses). * **Intracrine:** Hormones that act inside the cell without ever being secreted (e.g., certain steroid hormone precursors). * **Key Distinction:** The defining feature of the endocrine system compared to the exocrine system is the **absence of ducts** (ductless glands).

Question 72: All of the following statements concerning Atrial Natriuretic Peptide (ANP) are true except:

A. Its secretion is increased by an increase in blood volume
B. It increases glomerular filtration rate
C. It inhibits renin secretion
D. Its effects are mediated by decreased cyclic AMP (Correct Answer)

Explanation: **Explanation:** The correct answer is **D** because the effects of Atrial Natriuretic Peptide (ANP) are mediated by an **increase in cyclic GMP (cGMP)**, not a decrease in cAMP. ANP binds to its receptor (NPR-A), which has intrinsic **guanylyl cyclase** activity. This converts GTP to cGMP, which then activates Protein Kinase G (PKG) to produce physiological effects like vasodilation and natriuresis. **Analysis of Options:** * **Option A (Incorrect):** This is a true statement. The primary stimulus for ANP release is the **stretching of atrial myocytes** caused by increased blood volume or high atrial pressure. * **Option B (Incorrect):** This is a true statement. ANP increases GFR by **dilating afferent arterioles** and **constricting efferent arterioles**. It also increases the capillary surface area for filtration by relaxing glomerular mesangial cells. * **Option C (Incorrect):** This is a true statement. ANP acts as a natural antagonist to the Renin-Angiotensin-Aldosterone System (RAAS). It directly inhibits the release of **renin** from juxtaglomerular cells and **aldosterone** from the adrenal cortex. **High-Yield Clinical Pearls for NEET-PG:** * **Second Messenger:** ANP and Nitric Oxide (NO) both use **cGMP** as a second messenger. * **Brain Natriuretic Peptide (BNP):** Secreted by ventricles in response to pressure overload; used clinically as a marker for **Congestive Heart Failure (CHF)**. * **Nesiritide:** A recombinant form of BNP used in the treatment of acute decompensated heart failure. * **Net Effect:** ANP is "heart-protective" as it lowers blood pressure and reduces fluid volume (natriuresis and diuresis).

Question 73: In which part of the fallopian tube does fertilization take place?

A. Interstitial
B. Ampulla (Correct Answer)
C. Isthmus
D. Fimbria

Explanation: **Explanation:** **1. Why Ampulla is Correct:** Fertilization typically occurs in the **ampulla** of the fallopian tube. The ampulla is the widest and longest part of the tube (approximately 5 cm long), characterized by a thin wall and a highly folded mucosal lining. Its anatomical structure provides an ideal environment for the meeting of the secondary oocyte and the capacitated spermatozoa. The ovum remains viable for fertilization for about 12–24 hours after ovulation, and this encounter most frequently happens in this specific segment. **2. Why Other Options are Incorrect:** * **Interstitial (Intramural):** This is the narrowest segment that traverses the muscular wall of the uterus. It is the site of the most dangerous type of ectopic pregnancy due to high vascularity. * **Isthmus:** This is the narrow, thick-walled segment medial to the ampulla. While sperm undergo final maturation here, it is not the primary site of fertilization. * **Fimbria:** These are finger-like projections at the distal end of the infundibulum. Their primary function is to "sweep" the ovulated oocyte from the peritoneal cavity into the fallopian tube. **3. High-Yield Clinical Pearls for NEET-PG:** * **Ectopic Pregnancy:** The **ampulla** is the most common site for ectopic pregnancies (approx. 70-80%). * **Ciliary Action:** The fallopian tube is lined with **simple columnar ciliated epithelium**. Ciliary beat frequency is highest during the periovulatory period to facilitate gamete transport. * **Capacitation:** This process (final sperm activation) occurs within the female reproductive tract, primarily in the isthmus, before the sperm reaches the ampulla. * **Zygote Transport:** After fertilization in the ampulla, the zygote takes approximately **3–4 days** to reach the uterine cavity.

Question 74: All of the following are features of Hyperthyroidism except?

A. Thin person
B. Decreased waist-to-hip ratio
C. Decreased excessive sleep
D. Increased muscular activity (Correct Answer)

Explanation: **Explanation:** In Hyperthyroidism, the excess of thyroid hormones ($T_3$ and $T_4$) leads to a generalized state of hypermetabolism. **Why "Increased muscular activity" is the correct (Except) option:** While hyperthyroidism increases the metabolic rate, it paradoxically leads to **muscle weakness and fatigability** (Thyrotoxic Myopathy), not increased activity. This occurs because excess thyroid hormone promotes the catabolism (breakdown) of muscle proteins and impairs mitochondrial efficiency. Patients often present with proximal muscle weakness, such as difficulty climbing stairs or rising from a chair. **Analysis of Incorrect Options:** * **Thin person:** Thyroid hormones increase the Basal Metabolic Rate (BMR) and stimulate lipolysis. Despite an increased appetite (polyphagia), the high caloric expenditure leads to significant weight loss, resulting in a thin habitus. * **Decreased waist-to-hip ratio:** Due to the mobilization of fat stores and overall weight loss, the waist circumference typically decreases, leading to a lower waist-to-hip ratio. * **Decreased excessive sleep:** Hyperthyroidism causes CNS overstimulation (due to increased $\beta$-adrenergic sensitivity). This manifests as anxiety, restlessness, and **insomnia**. Therefore, patients do not experience excessive sleep; rather, they struggle to sleep. **NEET-PG High-Yield Pearls:** * **Cardiovascular:** T3 increases the expression of $\beta_1$ receptors, leading to tachycardia, palpitations, and increased systolic BP (wide pulse pressure). * **Reflexes:** Characterized by **brisk deep tendon reflexes** (hyperreflexia) with a shortened relaxation phase. * **Tremors:** Fine, rapid tremors of the outstretched hands are a classic sign. * **Gastrointestinal:** Increased motility leads to frequent bowel movements or diarrhea (not constipation).

Question 75: Which of the following is NOT a feature of Grave's disease?

A. Increased plasma levels of thyroid hormones
B. Increased plasma levels of TSH (Correct Answer)
C. Exophthalmos
D. Increased heart rate

Explanation: **Explanation:** **Grave’s Disease** is an autoimmune disorder and the most common cause of primary hyperthyroidism. It is characterized by the production of **Thyroid Stimulating Immunoglobulins (TSI)**, which are antibodies that bind to and activate the TSH receptors on the thyroid gland. **Why Option B is the Correct Answer:** In Grave’s disease, the high levels of circulating T3 and T4 exert a potent **negative feedback** effect on the anterior pituitary. This results in the suppression of TSH secretion. Therefore, **plasma TSH levels are characteristically decreased (often undetectable)**, not increased. **Analysis of Incorrect Options:** * **Option A (Increased thyroid hormones):** TSI antibodies mimic the action of TSH, leading to autonomous overproduction of T3 and T4 by the thyroid gland. * **Option C (Exophthalmos):** This is a specific feature of Grave’s ophthalmopathy caused by the activation of TSH receptors on retro-orbital fibroblasts, leading to inflammation and accumulation of glycosaminoglycans. * **Option D (Increased heart rate):** Thyroid hormones upregulate $\beta$-adrenergic receptors in the heart, leading to tachycardia, palpitations, and increased cardiac output. **NEET-PG High-Yield Pearls:** 1. **Triad of Grave’s:** Hyperthyroidism with diffuse goiter, Exophthalmos (Proptosis), and Pretibial Myxedema (Dermopathy). 2. **Diagnosis:** Low TSH, High Free T4, and the presence of **TSH receptor antibodies (TRAb/TSI)**. 3. **Radioiodine Uptake (RAIU):** Shows **diffuse, increased uptake** (unlike toxic multinodular goiter which shows "hot" nodules). 4. **Wolff-Chaikoff Effect:** A transient reduction in thyroid hormone levels caused by the administration of a large amount of iodine.

Question 76: Osteoblasts express which of the following hormones?

A. Parathyroid hormone (PTH)
B. Vitamin D3
C. Glucocorticoid
D. All of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. All of the above**. Osteoblasts are not merely bone-forming cells; they serve as the primary regulatory hub for bone remodeling by expressing receptors for various systemic hormones. 1. **Parathyroid Hormone (PTH):** Paradoxically, osteoclasts (which resorb bone) do **not** have PTH receptors. PTH binds to receptors on **osteoblasts**, stimulating them to express **RANKL** (Receptor Activator of Nuclear Factor kappa-B Ligand). RANKL then binds to osteoclasts to initiate bone resorption. 2. **Vitamin D3 (Calcitriol):** Osteoblasts possess Vitamin D receptors (VDR). Calcitriol acts on osteoblasts to stimulate the production of **osteocalcin** and alkaline phosphatase, and it also synergizes with PTH to increase RANKL expression. 3. **Glucocorticoids:** Osteoblasts have glucocorticoid receptors. Chronic exposure to steroids inhibits osteoblast proliferation and increases their apoptosis, which is the primary mechanism behind **steroid-induced osteoporosis**. **Why "All of the above" is correct:** Osteoblasts act as the "sensor" for the endocrine system to regulate bone turnover. By expressing receptors for PTH, Vitamin D, and Glucocorticoids (as well as Estrogen and Thyroid hormone), the osteoblast coordinates the balance between bone formation and resorption. **High-Yield Clinical Pearls for NEET-PG:** * **RANKL/OPG Ratio:** Osteoblasts also secrete **Osteoprotegerin (OPG)**, a decoy receptor that binds RANKL and inhibits bone resorption. The ratio of RANKL to OPG determines the rate of bone loss. * **Teriparatide (Recombinant PTH):** When given intermittently, it stimulates osteoblasts more than osteoclasts, leading to an anabolic (bone-building) effect. * **Marker of Osteoblast Activity:** Serum **Alkaline Phosphatase (ALP)** and **Osteocalcin** are high-yield biochemical markers used to assess osteoblastic function.

Question 77: What is the sulfation factor?

A. Somatostatin
B. Somatomedin (Correct Answer)
C. Gastric inhibitory peptide (GIP)
D. Vasoactive intestinal peptide (VIP)

Explanation: **Explanation:** The term **"Sulfation Factor"** is the historical name for **Somatomedins**, specifically **IGF-1 (Insulin-like Growth Factor 1)**. Growth Hormone (GH) does not act directly on bones to promote linear growth. Instead, it stimulates the liver to produce somatomedins. These peptides were originally called "sulfation factors" because they were found to be essential for the incorporation of sulfate into the chondroitin sulfate of the cartilage matrix, a critical step in bone growth and collagen synthesis. **Analysis of Options:** * **Somatomedin (Correct):** These are GH-dependent mediators. IGF-1 is the most important somatomedin in adults, mediating the growth-promoting effects of GH on skeletal and soft tissues. * **Somatostatin (Incorrect):** This is "Growth Hormone Inhibiting Hormone" (GHIH). It is produced by the hypothalamus and delta cells of the pancreas to inhibit the release of GH and various GI hormones. * **GIP (Incorrect):** Gastric Inhibitory Peptide (now called Glucose-dependent Insulinotropic Peptide) is an incretin that stimulates insulin secretion and inhibits gastric acid. * **VIP (Incorrect):** Vasoactive Intestinal Peptide is a neuropeptide that causes vasodilation, relaxes GI smooth muscle, and stimulates intestinal water secretion. **High-Yield NEET-PG Pearls:** * **Site of Synthesis:** Somatomedins are primarily synthesized in the **liver**. * **Half-life:** GH has a short half-life (~20 mins), whereas IGF-1 has a long half-life (~20 hours) because it is bound to binding proteins (IGFBP-3). * **Clinical Marker:** Due to its stability and lack of pulsatility, **Serum IGF-1 levels** are the best screening test for Acromegaly. * **Laron Dwarfism:** A condition caused by GH receptor mutations where GH levels are high, but Somatomedin (IGF-1) levels are very low.

Question 78: A 25-year-old male patient with seminiferous tubule dysgenesis was diagnosed as a case of Klinefelter syndrome. All of the following are true about Sertoli cells EXCEPT?

A. Sertoli cells are large, complex, glycogen-containing cells stretching from the basal lamina of the tubule to the lumen.
B. Tight junctions between adjacent Sertoli cells near the basal lamina form a blood-testis barrier.
C. Sertoli cells secrete androgen-binding protein (ABP), relaxin, and Müllerian-inhibiting substance (MIS). (Correct Answer)
D. Sertoli cells can produce estrogens.

Explanation: **Explanation** The correct answer is **C** because it contains a factual error regarding the secretion of **Relaxin**. In males, Relaxin is primarily secreted by the **prostate gland**, not the Sertoli cells. While Sertoli cells do secrete Androgen-Binding Protein (ABP), Müllerian-Inhibiting Substance (MIS/AMH), and Inhibin B, Relaxin is not one of their products. **Analysis of Options:** * **Option A (Incorrect):** This is a true anatomical description. Sertoli cells are "nurse cells" that span the entire thickness of the germinal epithelium, providing structural and nutritional support to developing spermatozoa. * **Option B (Incorrect):** This is true. The **Blood-Testis Barrier** is formed by tight junctions between adjacent Sertoli cells. This barrier creates an immunologically privileged site, preventing the immune system from attacking haploid sperm cells. * **Option D (Incorrect):** This is true. Sertoli cells contain the enzyme **aromatase**, which converts testosterone (provided by Leydig cells) into estrogens. **NEET-PG High-Yield Pearls:** * **Klinefelter Syndrome (47, XXY):** Characterized by seminiferous tubule dysgenesis, low testosterone, and elevated FSH/LH. Sertoli cell function is impaired, leading to low Inhibin B levels. * **Sertoli Cell Secretions:** Inhibin B (inhibits FSH), ABP (maintains high local testosterone), MIS (causes regression of Müllerian ducts in utero), and Estrogen. * **FSH Action:** FSH acts directly on Sertoli cells to stimulate spermatogenesis and the production of Inhibin B. * **Blood-Testis Barrier:** Divides the epithelium into a basal compartment (spermatogonia) and an adluminal compartment (meiotic cells).

Question 79: Glucose transport in myocytes is stimulated by insulin. Which glucose transporter is involved?

A. GLUT-1
B. GLUT-2
C. GLUT-3
D. GLUT-4 (Correct Answer)

Explanation: **Explanation:** The correct answer is **GLUT-4**. This question tests the fundamental concept of insulin-dependent versus insulin-independent glucose uptake in human tissues. **Why GLUT-4 is correct:** GLUT-4 is the only **insulin-responsive** glucose transporter. It is primarily expressed in **skeletal muscle (myocytes)** and **adipose tissue**. In the resting state, GLUT-4 remains sequestered in intracellular vesicles. Upon insulin binding to its receptor, a signaling cascade (via PI3-kinase) triggers the translocation of these vesicles to the plasma membrane, facilitating glucose uptake. **Analysis of Incorrect Options:** * **GLUT-1:** Responsible for basal (insulin-independent) glucose uptake. It is found in almost all tissues but is most highly concentrated in **RBCs** and the **Blood-Brain Barrier**. * **GLUT-2:** A high-capacity, low-affinity transporter found in the **Liver, Pancreatic beta cells, and Kidney**. It acts as a "glucose sensor" in the pancreas and allows bidirectional transport in the liver. * **GLUT-3:** A high-affinity transporter found primarily in **Neurons** (Brain), ensuring glucose uptake even during low blood sugar levels. **High-Yield Clinical Pearls for NEET-PG:** * **Exercise & GLUT-4:** Muscle contraction during exercise can trigger GLUT-4 translocation to the membrane **independent of insulin**. This is why exercise helps lower blood glucose in diabetic patients. * **SGLT vs. GLUT:** Remember that SGLT-1 (Intestine) and SGLT-2 (Kidney) use **secondary active transport** (sodium-dependent), whereas all GLUT transporters use **facilitated diffusion**. * **GLUT-5:** Specifically transports **Fructose** and is located in the small intestine and spermatozoa.

Question 80: Which hormone initiates milk ejection?

A. Lactogen
B. Prolactin
C. LH
D. Oxytocin (Correct Answer)

Explanation: **Explanation:** The correct answer is **Oxytocin**. **1. Why Oxytocin is Correct:** Oxytocin is synthesized in the hypothalamus (paraventricular and supraoptic nuclei) and released from the posterior pituitary. It is responsible for the **Milk Ejection Reflex** (or "Let-down reflex"). When an infant suckles, sensory impulses travel to the brain, triggering oxytocin release. Oxytocin causes the contraction of **myoepithelial cells** surrounding the mammary alveoli, squeezing milk into the larger ducts and out through the nipple. **2. Why the Other Options are Incorrect:** * **Prolactin:** While essential for lactation, Prolactin is responsible for **milk production and secretion** (lactogenesis) within the alveolar cells, not the ejection of milk. * **Lactogen (Human Placental Lactogen):** This hormone is produced by the placenta during pregnancy. It prepares the breasts for lactation and alters maternal metabolism to ensure fetal glucose supply, but it does not trigger milk ejection. * **LH (Luteinizing Hormone):** This gonadotropin is involved in ovulation and the maintenance of the corpus luteum; it has no direct role in the milk ejection reflex. **3. NEET-PG High-Yield Pearls:** * **Ferguson Reflex:** Oxytocin also causes uterine contractions during labor via a positive feedback mechanism. * **Suckling Stimulus:** This is the most potent stimulus for both Oxytocin and Prolactin release. * **Inhibition:** Prolactin is inhibited by **Dopamine** (Prolactin-Inhibiting Factor), whereas Oxytocin release can be inhibited by emotional stress or fear. * **Mnemonic:** **P**rolactin **P**roduces milk; **O**xytocin **O**usts (ejects) milk.

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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