Endocrinology Practice Questions

Q: A 16-year-old female patient presents to the OPD with hirsutism and masculinization. Which of the following hormones of the adrenal cortex is the likely culprit?

Dehydroepiandrosterone (DHEA). ### Explanation **Correct Option: A. Dehydroepiandrosterone (DHEA)** The clinical presentation of **hirsutism** (excessive male-pattern hair growth) and **masculinization** (virilization) in a female indicates an excess of androgens. The adrenal cortex produces weak androgens, primarily **Dehydroepiandrosterone (DHEA)** and its sulfate form (DHEA-S), in the **Zona Reticularis**. In conditions like Congenital Adrenal Hyperplasia (CAH) or androgen-secreting adrenal tumors, these androgens are overproduced. While weak, they are converted peripherally into potent testosterone, leading to clitomegaly, deepening of the voice, and hirsutism. **Why other options are incorrect:** * **B. Aldosterone:** Produced in the *Zona Glomerulosa*, it regulates sodium and potassium balance. Excess leads to hypertension and hypokalemia (Conn’s Syndrome), not virilization. * **C. Cortisol:** Produced in the *Zona Fasciculata*, it regulates glucose metabolism and stress response. Excess (Cushing’s Syndrome) causes weight gain and "moon face." While Cushing’s can coexist with androgen excess, cortisol itself is not androgenic. * **D. Epinephrine:** This is a catecholamine produced by the **adrenal medulla**, not the cortex. It regulates the "fight or flight" response. **High-Yield NEET-PG Pearls:** * **Layers of Adrenal Cortex (Outer to Inner):** **G**lomerulosa (Salt/Aldosterone), **F**asciculata (Sugar/Cortisol), **R**eticularis (Sex/Androgens) — Mnemonic: **"GFR"**. * **DHEA-S** is the most specific marker for adrenal androgen production because the ovaries do not produce it. * The most common cause of virilizing CAH is **21-hydroxylase deficiency**, which shunts precursors toward the androgen pathway.

Q: Hypocalcemia due to calcitonin is caused by which of the following mechanisms?

Decreased bone resorption. **Explanation:** Calcitonin is a peptide hormone secreted by the **parafollicular cells (C-cells)** of the thyroid gland. Its primary physiological role is to lower plasma calcium levels, acting as a functional antagonist to Parathyroid Hormone (PTH). **Why Option B is Correct:** The most potent and immediate effect of calcitonin is the **inhibition of osteoclastic bone resorption**. Calcitonin binds to specific receptors on osteoclasts, leading to a decrease in their absorptive activity and a reduction in their formation rate. By preventing the breakdown of the bone matrix, it stops the release of calcium and phosphate into the blood, thereby inducing hypocalcemia. **Why Other Options are Incorrect:** * **Options A & D:** While calcitonin does have a minor effect on the kidneys by increasing the excretion of calcium and phosphate (by decreasing reabsorption in the tubules), this effect is **clinically insignificant** and transient compared to its profound effect on bone. * **Option C:** Calcitonin has no significant direct effect on the intestinal absorption of calcium. Intestinal absorption is primarily regulated by Vitamin D3 (Calcitriol). **High-Yield Clinical Pearls for NEET-PG:** * **Stimulus:** Calcitonin secretion is stimulated by an increase in plasma calcium levels and the hormone **Gastrin**. * **Clinical Use:** Due to its ability to inhibit osteoclasts, synthetic calcitonin (Salmon calcitonin) is used therapeutically in **Paget’s disease**, severe hypercalcemia, and postmenopausal osteoporosis. * **Tumor Marker:** Serum calcitonin is a highly specific tumor marker for **Medullary Thyroid Carcinoma (MTC)**. * **Escape Phenomenon:** Prolonged exposure to calcitonin leads to a downregulation of receptors, causing the hormone to lose its effectiveness over time.

Q: Early epiphyseal closure is seen with _________?

Estrogen. ### Explanation **Correct Option: C (Estrogen)** The primary hormone responsible for the fusion of the epiphyseal growth plates in both males and females is **Estrogen**. While Growth Hormone (GH) and Insulin-like Growth Factor-1 (IGF-1) drive linear bone growth, Estrogen acts on the estrogen receptors (ER-α) in the growth plate to trigger the maturation of chondrocytes and the eventual replacement of the cartilaginous plate with bone. In puberty, low levels of estrogen initially stimulate the "pubertal growth spurt," but as levels rise toward the end of puberty, they induce **epiphyseal senescence and closure**, effectively stopping linear growth. This is why conditions like precocious puberty (excess early estrogen) lead to short adult stature despite an initial growth spurt. **Why other options are incorrect:** * **LH and FSH (Options A & B):** These are gonadotropins secreted by the anterior pituitary. While they stimulate the gonads to produce sex steroids (estrogen/testosterone), they do not have a direct physiological effect on the epiphyseal plate closure themselves. * **Progesterone (Option D):** This hormone is primarily involved in the menstrual cycle and pregnancy maintenance; it has no significant role in bone maturation or epiphyseal fusion. **High-Yield Clinical Pearls for NEET-PG:** * **Aromatase Deficiency:** In individuals lacking the aromatase enzyme (which converts testosterone to estrogen), the epiphyses **fail to fuse**, leading to tall stature and continued growth into adulthood. * **Androgens:** Testosterone also contributes to bone growth, but its effect on plate closure is largely mediated by its peripheral conversion into estrogen. * **Thyroid Hormone:** Essential for bone age; deficiency (Hypothyroidism) causes significant **delayed bone age**. * **Glucocorticoids:** Excess levels (Cushing’s) inhibit bone growth and lead to stunted stature.

Q: Which of the following physiological states or substances promotes the secretion of Growth Hormone?

Glucagon. **Explanation:** Growth Hormone (GH) secretion is regulated by a complex interplay of hypothalamic factors (GHRH and Somatostatin) and metabolic signals. **Why Glucagon is Correct:** Glucagon is a potent stimulator of Growth Hormone secretion. While the exact mechanism is multifaceted, it is believed that glucagon stimulates the hypothalamus to release GHRH. Clinically, this is utilized in the **Glucagon Stimulation Test**, where glucagon is administered to provoke GH release to diagnose GH deficiency in children and adults. **Analysis of Incorrect Options:** * **Cortisol:** Chronic or high levels of glucocorticoids generally **inhibit** GH secretion by increasing somatostatin tone and decreasing GHRH sensitivity. * **REM Sleep:** GH secretion is characteristically associated with **Deep Sleep (Stage N3/Slow-wave sleep)**, typically occurring in the first 90 minutes of sleep. In contrast, GH secretion is inhibited during REM (Rapid Eye Movement) sleep. * **Glucose:** Hyperglycemia **inhibits** GH secretion. Conversely, hypoglycemia is one of the most potent physiological stimuli for GH release (used in the Insulin Tolerance Test). **High-Yield Clinical Pearls for NEET-PG:** * **Stimulators of GH:** Hypoglycemia, Fasting/Starvation, Exercise, Deep sleep, Amino acids (Arginine), and Ghrelin. * **Inhibitors of GH:** Hyperglycemia, Free fatty acids, Obesity, Somatostatin, and IGF-1 (via negative feedback). * **Gold Standard Test:** The **Insulin Tolerance Test (ITT)** is the gold standard for diagnosing GH deficiency, as it induces hypoglycemia to trigger GH release. * **Screening Test:** IGF-1 levels are used for screening acromegaly because GH is secreted in pulsatile bursts and has a short half-life.

Q: Which of the following is a lipophilic hormone that acts on nuclear receptors, while the others are hydrophilic hormones that act on cytosolic receptors?

Thyroxine. ### Explanation The classification of hormones based on their chemical nature and receptor location is a high-yield topic for NEET-PG. **Correct Answer: A. Thyroxine** Thyroxine ($T_4$) and Triiodothyronine ($T_3$) are amine-derived hormones, but unlike other amines, they are highly **lipophilic** (lipid-soluble). This property allows them to cross the cell membrane via transporters and bind to **nuclear receptors** (specifically TR$\alpha$ and TR$\beta$). Once bound, they act as transcription factors to modulate gene expression. **Analysis of Incorrect Options:** * **B. Epinephrine:** Although also an amine (derived from tyrosine), epinephrine is **hydrophilic**. It cannot cross the lipid bilayer and must bind to **G-protein coupled receptors (GPCRs)** on the cell surface. * **C. Growth Hormone (GH):** This is a large peptide hormone. Being hydrophilic, it binds to **extracellular receptors** (specifically JAK-STAT linked receptors) on the plasma membrane. * **D. ACTH:** This is a polypeptide hormone. Like GH, it is water-soluble and acts via **cell surface receptors** (specifically MC2R, which uses the cAMP second messenger system). **High-Yield Clinical Pearls for NEET-PG:** * **Exceptions to the Rule:** Most amine hormones (Catecholamines) are hydrophilic, but **Thyroid hormones** are the notable lipophilic exception. * **Receptor Locations:** * **Cytosolic Receptors:** Primarily Steroid hormones (e.g., Cortisol, Aldosterone, Vitamin D). * **Nuclear Receptors:** Thyroid hormones ($T_3/T_4$), Retinoic acid, and Estrogen (partially). * **Speed of Action:** Surface-acting hormones (Epinephrine) act within seconds via second messengers, while nuclear-acting hormones (Thyroxine) take hours to days to show effects due to the time required for protein synthesis.

Q: Calcium absorption from the gut is enhanced by which of the following?

1,25-dihydroxycholecalciferol. **Explanation:** The correct answer is **1,25-dihydroxycholecalciferol (Calcitriol)**. **1. Why 1,25-dihydroxycholecalciferol is correct:** Calcitriol is the active form of Vitamin D. Its primary function is to increase plasma calcium levels by enhancing intestinal absorption. It acts on the enterocytes of the duodenum and jejunum to increase the synthesis of **Calbindin-D9k** (a calcium-binding protein), **TRPV6** (calcium channels), and **Ca-ATPase**. These proteins facilitate the active transport of calcium from the gut lumen into the bloodstream. **2. Why the other options are incorrect:** * **Parathyroid Hormone (PTH):** While PTH is the master regulator of calcium, it does **not** have a direct effect on the gut. Instead, it acts on the kidneys to stimulate the enzyme **1-alpha-hydroxylase**, which converts 25-hydroxyvitamin D into active 1,25-dihydroxycholecalciferol. Thus, PTH increases gut absorption *indirectly* via Vitamin D. * **Calcitonin:** Secreted by the parafollicular (C-cells) of the thyroid, calcitonin is a "hypocalcemic" hormone. It inhibits osteoclast activity and increases renal calcium excretion. It has no significant role in enhancing gut absorption. **High-Yield Clinical Pearls for NEET-PG:** * **Rate-limiting step:** The conversion of 25(OH)D to 1,25(OH)₂D in the kidney is the rate-limiting step in Vitamin D activation. * **Vitamin D Receptors (VDR):** These are nuclear receptors; therefore, Vitamin D acts by altering gene transcription. * **Other factors increasing absorption:** Acidic pH (Gastric acid), Lactose, and Amino acids (Arginine, Lysine). * **Factors decreasing absorption:** Oxalates, Phytates, Phosphates, and Glucocorticoids.

Q: Which of the following is NOT a hydrophilic hormone acting on cytosolic receptors?

Thyroxine. To answer this question correctly, one must understand the relationship between a hormone's chemical nature (solubility) and its receptor location. ### **Explanation of the Correct Answer** **A. Thyroxine (T4):** This is the correct answer because it is **lipophilic** (lipid-soluble), not hydrophilic. Although derived from the amino acid tyrosine, thyroid hormones are unique because they cross the cell membrane via transporters and bind to **nuclear receptors** (not cytosolic) to alter gene transcription. ### **Analysis of Incorrect Options** * **B. Epinephrine:** This is a catecholamine and is **hydrophilic**. It cannot cross the lipid bilayer and must act on **cell surface receptors** (G-protein coupled receptors). * **C. Growth Hormone (GH):** This is a large peptide hormone and is **hydrophilic**. It acts on **cell surface receptors** (specifically JAK-STAT linked receptors). * **D. Atrial Natriuretic Peptide (ANP):** This is a peptide hormone and is **hydrophilic**. It acts on **cell surface receptors** associated with particulate guanylyl cyclase. **Note on the Question Stem:** The question asks for a hormone that is *NOT* hydrophilic acting on *cytosolic* receptors. While options B, C, and D are hydrophilic, they act on **membrane** receptors. Thyroxine is the "most" correct answer because it is fundamentally hydrophobic/lipophilic. ### **High-Yield NEET-PG Pearls** 1. **Lipophilic Hormones (Intracellular Receptors):** * **Cytosolic Receptors:** Steroids (Glucocorticoids, Mineralocorticoids, Progesterone, Testosterone). *Mnemonic: "C" for Cortisol and Cytosol.* * **Nuclear Receptors:** Thyroid hormones (T3/T4), Estrogen, Vitamin D, and Retinoic Acid. 2. **Hydrophilic Hormones (Cell Surface Receptors):** * **cAMP pathway:** ACTH, Glucagon, TSH, PTH. * **IP3/DAG pathway:** Oxytocin, GnRH, TRH. * **Tyrosine Kinase pathway:** Insulin, IGF-1. * **JAK-STAT pathway:** GH, Prolactin, Erythropoietin.

Q: Which opioid is secreted from the anterior pituitary?

beta-endorphin. **Explanation:** The correct answer is **beta-endorphin**. The underlying medical concept revolves around the precursor molecule **Pro-opiomelanocortin (POMC)**. POMC is a large polypeptide synthesized in the corticotrophs of the anterior pituitary. Through the action of specific enzymes (prohormone convertases), POMC is cleaved into several biologically active peptides, including: 1. **ACTH** (Adrenocorticotropic Hormone) 2. **beta-lipotropin**, which is further cleaved into **beta-endorphin**. Beta-endorphin is an endogenous opioid peptide that binds primarily to mu-opioid receptors, playing a significant role in pain modulation and the "reward" system. **Analysis of Incorrect Options:** * **Growth Hormone (GH):** Secreted by somatotrophs in the anterior pituitary, but it is a peptide hormone, not an opioid. * **ACTH:** While ACTH is derived from the same precursor (POMC) as beta-endorphin, it is a trophic hormone that stimulates the adrenal cortex; it does not possess opioid activity. * **MSH (Melanocyte-Stimulating Hormone):** Also a derivative of POMC (specifically alpha-MSH is derived from the ACTH segment), but its primary function is skin pigmentation, not opioid signaling. **High-Yield Facts for NEET-PG:** * **POMC Derivatives:** Remember the "3 Ms" and "A" – MSH, Melancortin, beta-endorphin, and ACTH. * **Clinical Correlation:** In conditions like **Addison’s Disease**, high levels of ACTH (due to lack of feedback) are accompanied by high levels of MSH and beta-endorphin, leading to characteristic hyperpigmentation. * **Receptor Affinity:** Beta-endorphin has the highest affinity for **mu (μ) receptors** among the endogenous opioids.

Question 1

A 16-year-old female patient presents to the OPD with hirsutism and masculinization. Which of the following hormones of the adrenal cortex is the likely culprit?

Accepted Answer

Dehydroepiandrosterone (DHEA)

Answer

Aldosterone

Answer

Cortisol

Answer

Epinephrine

Question 2

Hypocalcemia due to calcitonin is caused by which of the following mechanisms?

Accepted Answer

Decreased bone resorption

Answer

Increased excretion in the kidney

Answer

Decreased intestinal absorption

Answer

Decreased renal reabsorption

Question 3

Early epiphyseal closure is seen with _________?

Accepted Answer

Estrogen

Answer

Luteinizing Hormone (LH)

Answer

Follicle-Stimulating Hormone (FSH)

Answer

Progesterone

Question 4

Regarding myxedema, which of the following statements is true EXCEPT:

Accepted Answer

Increased basal metabolic rate (BMR)

Answer

Swollen, edematous look of the face

Answer

Impotency, amenorrhea

Answer

Dullness, loss of memory

Question 5

Which of the following is NOT a physiological action of insulin?

Accepted Answer

Activation of lipoprotein lipase

Answer

Increased lipogenesis

Answer

Increased amino acid entry into the cell

Answer

Activation of key enzymes of glycolysis

Question 6

Which of the following physiological states or substances promotes the secretion of Growth Hormone?

Accepted Answer

Glucagon

Answer

Cortisol

Answer

REM sleep

Answer

Glucose

Question 7

Which of the following is a lipophilic hormone that acts on nuclear receptors, while the others are hydrophilic hormones that act on cytosolic receptors?

Accepted Answer

Thyroxine

Answer

Epinephrine

Answer

Growth Hormone (GH)

Answer

Adrenocorticotropic Hormone (ACTH)

Question 8

Calcium absorption from the gut is enhanced by which of the following?

Accepted Answer

1,25-dihydroxycholecalciferol

Answer

Parathyroid hormone

Answer

Calcitonin

Answer

All of the above

Question 9

Which of the following is NOT a hydrophilic hormone acting on cytosolic receptors?

Accepted Answer

Thyroxine

Answer

Epinephrine

Answer

Growth Hormone (GH)

Answer

Atrial Natriuretic Peptide (ANP)

Question 10

Which opioid is secreted from the anterior pituitary?

Accepted Answer

beta-endorphin

Answer

Growth Hormone (GH)

Answer

Adrenocorticotropic Hormone (ACTH)

Answer

Melanocyte-Stimulating Hormone (MSH)

Endocrinology — MCQs

Endocrinology — MCQs

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