Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 111: Insulin-like Growth Factor II plays an important role in which of the following?

A. Control of metabolism
B. Skeletal growth
C. Cartilage growth
D. Development of the fetus (Correct Answer)

Explanation: **Explanation:** **Insulin-like Growth Factor II (IGF-II)** is a polypeptide hormone structurally related to insulin. Its primary physiological role is as a **major regulator of fetal growth and development**. 1. **Why Option D is Correct:** During the prenatal period, IGF-II is highly expressed in fetal tissues. Unlike IGF-I, which is growth hormone (GH) dependent and dominates postnatal growth, **IGF-II acts independently of GH** during gestation. It promotes cell proliferation and tissue differentiation, making it the critical factor for fetal weight gain and organogenesis. 2. **Why Other Options are Incorrect:** * **Options B & C (Skeletal and Cartilage Growth):** These are primarily the functions of **IGF-I (Somatomedin C)**. Postnatally, Growth Hormone stimulates the liver to produce IGF-I, which then acts on the epiphyseal plates to promote linear bone growth and chondrocyte proliferation. * **Option A (Control of Metabolism):** While IGFs have insulin-like effects, the primary control of glucose and lipid metabolism is mediated by **Insulin** and counter-regulatory hormones (Glucagon, Cortisol, Epinephrine). **High-Yield Clinical Pearls for NEET-PG:** * **IGF-I vs. IGF-II:** Remember: **IGF-II = Fetal growth**; **IGF-I = Postnatal growth** (GH-dependent). * **Beckwith-Wiedemann Syndrome:** A classic clinical condition caused by the over-expression of the *IGF2* gene (genomic imprinting defect), leading to fetal overgrowth, macroglossia, and organomegaly. * **Receptor:** IGF-II binds primarily to the IGF-II receptor (which acts as a "sink" to clear IGF-II) but exerts its growth-promoting effects via the **IGF-I receptor**.

Question 112: Erythropoietin is mainly produced in:

A. Liver
B. Kidney (Correct Answer)
C. Intestine
D. Bone

Explanation: **Explanation:** **1. Why Kidney is Correct:** Erythropoietin (EPO) is a glycoprotein hormone essential for erythropoiesis. In adults, approximately **85–90%** of EPO is synthesized by the **peritubular interstitial fibroblasts** (specifically the extraglomerular mesangial cells) in the renal cortex and outer medulla. These cells act as "oxygen sensors"; when they detect renal hypoxia (via Hypoxia-Inducible Factor - HIF), they trigger the production of EPO, which then travels to the bone marrow to stimulate the production of red blood cells. **2. Why Other Options are Incorrect:** * **Liver:** While the liver is the **primary source of EPO in the fetus**, it only contributes about 10–15% of the total EPO in adults (produced by hepatocytes and Ito cells). * **Intestine:** The intestine does not produce EPO. It is primarily involved in the absorption of iron and B12, which are substrates for RBC production, but not the hormonal trigger. * **Bone:** The bone marrow is the **target organ** for EPO, not the site of production. EPO binds to receptors on erythroid progenitor cells (CFU-E) in the marrow to prevent apoptosis and promote differentiation. **3. NEET-PG High-Yield Pearls:** * **Stimulus:** The primary stimulus for EPO release is **hypoxia**, not the number of RBCs. * **Clinical Correlation:** In Chronic Kidney Disease (CKD), the loss of peritubular cells leads to **normocytic normochromic anemia** due to EPO deficiency. This is treated with recombinant human erythropoietin (Epoetin alfa). * **Polycythemia:** Ectopic EPO production is a classic paraneoplastic syndrome associated with **Renal Cell Carcinoma (RCC)** and **Hepatocellular Carcinoma (HCC)**.

Question 113: Prolactin is secreted by which part of the pituitary gland?

A. Anterior pituitary (Correct Answer)
B. Adrenal gland
C. Posterior pituitary
D. Ovary

Explanation: **Explanation:** The pituitary gland (hypophysis) is divided into two distinct functional parts: the **Anterior Pituitary (Adenohypophysis)** and the **Posterior Pituitary (Neurohypophysis)**. **Why the Correct Answer is Right:** Prolactin (PRL) is a polypeptide hormone synthesized and secreted by **Lactotrophs** (acidophilic cells) located in the **Anterior Pituitary**. Its primary function is to stimulate milk production (lactogenesis) in the mammary glands. Unlike other anterior pituitary hormones, prolactin is primarily under **tonic inhibitory control** by dopamine from the hypothalamus. **Analysis of Incorrect Options:** * **Adrenal Gland:** This gland secretes steroid hormones (cortisol, aldosterone, androgens) from the cortex and catecholamines (epinephrine, norepinephrine) from the medulla. * **Posterior Pituitary:** This part of the gland does not synthesize hormones; it only stores and releases **Oxytocin** and **Vasopressin (ADH)**, which are produced in the hypothalamus. * **Ovary:** The ovaries produce steroid hormones, specifically estrogens and progesterone, in response to gonadotropins (FSH and LH) from the anterior pituitary. **High-Yield NEET-PG Clinical Pearls:** * **Acidophils vs. Basophils:** Remember the mnemonic **"GPA"**—**G**rowth Hormone and **P**rolactin are secreted by **A**cidophils. (Basophils secrete B-FLAT: FSH, LH, ACTH, TSH). * **Dopamine Antagonism:** Drugs that block dopamine (e.g., antipsychotics like Metoclopramide or Risperidone) lead to **Hyperprolactinemia**, causing galactorrhea and amenorrhea. * **Prolactinoma:** This is the most common secretory tumor of the pituitary gland. * **TRH Effect:** Thyrotropin-releasing hormone (TRH) acts as a prolactin-releasing factor; thus, primary hypothyroidism can lead to increased prolactin levels.

Question 114: 5 percent dextrose solution is considered:

A. Hypotonic
B. Isotonic (Correct Answer)
C. Normotonic
D. Hypertonic

Explanation: **Explanation:** The tonicity of a solution is determined by its effective osmolality relative to plasma (normal range: 275–295 mOsm/L). **Why Isotonic is Correct:** A 5% Dextrose (D5W) solution contains 50 grams of glucose per liter. Its calculated osmolarity is approximately **252–278 mOsm/L**, which is nearly identical to the osmolarity of human plasma. Therefore, **in the IV bag (in vitro)**, D5W is considered an **isotonic** solution. **Analysis of Incorrect Options:** * **A. Hypotonic:** While D5W is isotonic in the bag, it behaves as a hypotonic solution **in vivo** (inside the body). Once infused, the dextrose is rapidly metabolized by insulin, leaving behind "free water." However, by standard classification based on initial concentration, it is categorized as isotonic. * **C. Normotonic:** This is not a standard physiological term used to describe IV fluids; "isotonic" is the correct terminology. * **D. Hypertonic:** A solution is hypertonic if its osmolarity is significantly higher than 300 mOsm/L (e.g., 10% Dextrose or 3% Normal Saline). D5W does not meet this threshold. **High-Yield Clinical Pearls for NEET-PG:** 1. **The "Physiological Paradox":** Remember that D5W is **Isotonic in the bottle but Hypotonic in the body.** 2. **Contraindication:** Because it becomes hypotonic in vivo, D5W should **never** be used for fluid resuscitation in patients with head injuries, as the free water can cross the blood-brain barrier and worsen **cerebral edema**. 3. **Caloric Value:** 1 liter of D5W provides 170 kcal (50g x 3.4 kcal/g). 4. **Drug of Choice:** It is the preferred fluid for treating **Hypernatremia** (to replace a pure water deficit).

Question 115: In which physiological state are serum prolactin levels highest?

A. 24 hours postpartum (Correct Answer)
B. 24 hours post-ovulation
C. During REM sleep
D. After one hour of running

Explanation: **Explanation:** **1. Why Option A is Correct:** Prolactin levels undergo a dramatic surge during pregnancy due to high estrogen levels stimulating the lactotrophs in the anterior pituitary. However, its milk-producing action is inhibited by high progesterone levels. Immediately after delivery, the sudden withdrawal of placental steroids (estrogen and progesterone) removes this inhibition. In the **24 hours postpartum**, prolactin levels reach their physiological peak (often >200 ng/mL) to initiate lactogenesis. While suckling maintains these levels later on, the immediate postpartum period represents the highest baseline physiological state. **2. Why the Other Options are Incorrect:** * **B. 24 hours post-ovulation:** While estrogen during the follicular phase can slightly increase prolactin, the levels are negligible compared to the massive surge seen in pregnancy and the postpartum period. * **C. During REM sleep:** Prolactin secretion is pulsatile and follows a diurnal rhythm, with levels rising 60–90 minutes after sleep onset. However, the peak occurs during **non-REM (NREM) sleep**, not REM sleep, and the magnitude is far lower than the postpartum state. * **D. After one hour of running:** Physical and emotional stress (including exercise) can cause a transient rise in prolactin via the inhibition of dopamine. However, this increase is acute and minor compared to the sustained high levels required for lactation. **High-Yield NEET-PG Pearls:** * **Inhibitory Control:** Prolactin is the only anterior pituitary hormone under **predominant inhibitory control** (by Dopamine from the hypothalamus). * **Prolactin & GnRH:** High prolactin levels inhibit GnRH secretion, leading to **lactational amenorrhea** (a natural contraceptive mechanism). * **TRH Effect:** Thyrotropin-releasing hormone (TRH) acts as a potent prolactin-releasing factor; hence, **primary hypothyroidism** is a common cause of hyperprolactinemia.

Question 116: Which of the following statements about melatonin secretion is false?

A. Melatonin is secreted by the pineal gland.
B. Melatonin secretion increases during the dark period of the day.
C. Melatonin secretion increases during daylight hours. (Correct Answer)
D. Diurnal variation in melatonin secretion is brought about by norepinephrine.

Explanation: ### Explanation **Core Concept:** Melatonin, often called the "hormone of darkness," is synthesized and secreted by the **pineal gland**. Its production follows a strict **circadian rhythm** regulated by the Suprachiasmatic Nucleus (SCN) of the hypothalamus. **Why Option C is the Correct Answer (False Statement):** Melatonin secretion is **inhibited by light** and stimulated by darkness. During daylight hours, light signals from the retina travel via the retinohypothalamic tract to the SCN, which ultimately suppresses pineal activity. Therefore, melatonin levels are at their lowest during the day and peak during the night (usually between 2 AM and 4 AM). **Analysis of Other Options:** * **Option A:** Correct. The pineal gland (epithalamus) is the primary site of melatonin synthesis from its precursor, **tryptophan** (via serotonin). * **Option B:** Correct. Darkness triggers the SCN to signal the pineal gland to increase melatonin production, promoting sleep. * **Option C:** Correct. The sympathetic nervous system regulates the pineal gland. Postganglionic sympathetic fibers from the superior cervical ganglion release **Norepinephrine**, which acts on **$\beta$-adrenergic receptors** to increase cAMP and activate the enzyme *N-acetyltransferase* (the rate-limiting enzyme), leading to melatonin release. **High-Yield NEET-PG Pearls:** * **Precursor:** Tryptophan $\rightarrow$ Serotonin $\rightarrow$ Melatonin. * **Rate-limiting enzyme:** Serotonin N-acetyltransferase (SNAT). * **Clinical Use:** Melatonin is used for **Jet Lag**, delayed sleep phase syndrome, and as a sleep aid in the elderly (where pineal calcification reduces natural secretion). * **The "Third Eye":** The pineal gland is often referred to as the "vestigial third eye" because of its role in photo-neuroendocrine transduction.

Question 117: Angiotensin II causes all of the following, except:

A. Stimulation of thirst
B. Increased ADH secretion
C. Vasodilation (Correct Answer)
D. Aldosterone secretion

Explanation: **Explanation:** Angiotensin II (AT-II) is a potent effector peptide of the Renin-Angiotensin-Aldosterone System (RAAS), primarily functioning to increase blood pressure and maintain fluid volume. **Why Vasodilation is the Correct Answer:** Angiotensin II is one of the most powerful **vasoconstrictors** known. It acts directly on AT1 receptors located on vascular smooth muscle cells to cause systemic vasoconstriction, which increases Total Peripheral Resistance (TPR) and elevates blood pressure. Therefore, it causes vasoconstriction, not vasodilation. **Analysis of Other Options:** * **A. Stimulation of Thirst:** AT-II acts on the subfornical organ (SFO) in the brain to stimulate the thirst center in the hypothalamus, encouraging water intake to restore blood volume. * **B. Increased ADH secretion:** AT-II stimulates the posterior pituitary to release Antidiuretic Hormone (ADH/Vasopressin), which increases water reabsorption in the collecting ducts of the kidney. * **D. Aldosterone secretion:** AT-II acts on the Zona Glomerulosa of the adrenal cortex to stimulate the synthesis and release of aldosterone, leading to sodium and water retention. **High-Yield NEET-PG Pearls:** 1. **Receptor Specificity:** Most physiological effects (vasoconstriction, aldosterone release) are mediated via **AT1 receptors**. AT2 receptors generally mediate opposing effects (vasodilation) but are less dominant in adults. 2. **Renal Effects:** AT-II preferentially constricts the **efferent arteriole**, which helps maintain the Glomerular Filtration Rate (GFR) when renal perfusion pressure is low. 3. **Clinical Correlation:** ACE inhibitors (e.g., Enalapril) and ARBs (e.g., Losartan) are used in hypertension and heart failure to block these effects, leading to vasodilation and reduced fluid overload.

Question 118: Pubarche is primarily due to which hormone?

A. Growth Hormone (GH)
B. Prolactin
C. Estrogen
D. Testosterone (Correct Answer)

Explanation: **Explanation:** **Pubarche** refers to the first appearance of pubic hair during puberty. This physiological milestone is primarily driven by **androgens**. 1. **Why Testosterone is Correct:** Pubarche is a manifestation of **Adrenarche** (the activation of the adrenal cortex) and the subsequent maturation of the gonads. In both males and females, the development of pubic and axillary hair is stimulated by androgens. While adrenal androgens like DHEA and Androstenedione initiate the process, **Testosterone** (and its potent metabolite Dihydrotestosterone) is the definitive hormone responsible for the terminal hair growth in the pubic region. In males, it comes from the testes; in females, it is derived from adrenal precursors and peripheral conversion. 2. **Why Other Options are Incorrect:** * **Growth Hormone (GH):** Primarily responsible for the pubertal height spurt and somatic growth, not secondary sexual characteristics. * **Prolactin:** Primarily involved in lactation and reproductive inhibition; pathologically high levels actually inhibit puberty by suppressing GnRH. * **Estrogen:** Responsible for **Thelarche** (breast development) and the maturation of the female genital tract (vaginal mucosa and uterine growth), but it does not cause pubic hair growth. **High-Yield Clinical Pearls for NEET-PG:** * **Sequence in Girls:** Thelarche (usually first) → Pubarche → Peak Height Velocity → Menarche (usually last). * **Sequence in Boys:** Testicular enlargement (>4ml volume) → Pubarche → Growth Spurt. * **Adrenarche vs. Gonadarche:** Adrenarche (adrenal androgen increase) typically precedes Gonadarche (Hpg-axis activation) by about 2 years. * **Precocious Puberty:** If pubarche occurs before age 8 in girls or age 9 in boys, it warrants investigation for premature adrenarche or androgen-secreting tumors.

Question 119: Which cells are responsible for bone resorption (bone removing)?

A. Osteoblasts
B. Osteoclasts (Correct Answer)
C. Stem cells
D. Cytotoxic T cells

Explanation: **Explanation:** The correct answer is **Osteoclasts**. Bone remodeling is a dynamic process involving a balance between bone formation and bone resorption. **1. Why Osteoclasts are correct:** Osteoclasts are large, multinucleated giant cells derived from the **monocyte-macrophage lineage** (hematopoietic stem cells). They are responsible for bone resorption. They function by adhering to the bone surface and creating a "sealed zone." Within this zone, they secrete hydrogen ions (via proton pumps) to dissolve hydroxyapatite crystals and lysosomal enzymes (like **Cathepsin K**) to digest the organic collagen matrix. **2. Analysis of Incorrect Options:** * **Osteoblasts:** These are bone-forming cells derived from mesenchymal stem cells. They synthesize the organic matrix (osteoid) and regulate mineralization. (Mnemonic: **B**lasts **B**uild bone). * **Stem cells:** While osteoblasts and osteoclasts originate from stem cells (mesenchymal and hematopoietic respectively), undifferentiated stem cells do not perform bone resorption themselves. * **Cytotoxic T cells:** These are immune cells involved in destroying virally infected or cancerous cells; they do not have a primary role in physiological bone resorption. **3. NEET-PG High-Yield Pearls:** * **Howship’s Lacunae:** The tiny depressions or pits on the bone surface where osteoclasts reside during resorption. * **RANKL Pathway:** Osteoblasts express RANKL, which binds to RANK receptors on osteoclast precursors to stimulate their differentiation and activation. * **Markers:** **TRAP** (Tartrate-Resistant Acid Phosphatase) is a key histological marker for osteoclasts. * **Hormonal Control:** Parathyroid Hormone (PTH) increases bone resorption indirectly by stimulating RANKL expression on osteoblasts, whereas **Calcitonin** directly inhibits osteoclast activity.

Question 120: Most of the testosterone secreted by the testes exists in the plasma in the form of?

A. Dihydrotestosterone bound to gonadal steroid-binding hormone
B. Free dihydrotestosterone
C. Free testosterone
D. Testosterone bound to sex-steroid-binding globulin (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Testosterone bound to sex-steroid-binding globulin** **1. Why the Correct Answer is Right:** In the plasma, testosterone (a lipophilic steroid hormone) requires carrier proteins for transport. Approximately **98% of circulating testosterone is protein-bound**, while only about 2% exists in the "free" (biologically active) form. Of the bound fraction, the majority (**~60-70%**) is bound with high affinity to **Sex Hormone-Binding Globulin (SHBG)**, also known as sex-steroid-binding globulin. The remaining ~30-40% is loosely bound to **albumin**. **2. Why the Other Options are Wrong:** * **Options A & B (Dihydrotestosterone):** While Dihydrotestosterone (DHT) is a more potent androgen, it is primarily produced in peripheral tissues (like the prostate and skin) via the action of 5-alpha-reductase on testosterone. It is not the primary secretory product of the testes, nor is it the most abundant form of testosterone in the plasma. * **Option C (Free Testosterone):** Only a tiny fraction (**1-2%**) of testosterone exists in the free, unbound state. While this is the form that can readily diffuse into cells to exert biological effects, it does not represent the "most" common form in plasma. **3. NEET-PG High-Yield Pearls:** * **Bioavailable Testosterone:** This refers to the sum of **Free Testosterone + Albumin-bound Testosterone**. Because the binding to albumin is weak (low affinity), it dissociates easily for tissue use. * **SHBG Regulation:** SHBG levels are **increased** by estrogens and hyperthyroidism, and **decreased** by androgens, obesity, and insulin resistance. * **Site of Secretion:** Testosterone is secreted by the **Leydig cells** of the testes under the influence of **Luteinizing Hormone (LH)**.

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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