Endocrinology Practice Questions

Q: Excess Aldosterone is associated with all of the following conditions except?

Hyperkalemia. **Explanation:** Aldosterone is a mineralocorticoid secreted by the *zona glomerulosa* of the adrenal cortex. Its primary site of action is the **Principal cells (P cells)** of the late distal tubule and collecting duct. **1. Why Hyperkalemia is the correct answer:** Aldosterone acts by increasing the activity of the Na+/K+ ATPase pump and opening epithelial sodium channels (ENaC). This leads to the reabsorption of Sodium ($Na^+$) and the **secretion of Potassium ($K^+$)** and Hydrogen ions ($H^+$) into the tubular lumen. Therefore, excess aldosterone (as seen in Conn’s Syndrome) leads to **Hypokalemia**, not Hyperkalemia. **2. Analysis of other options:** * **Sodium retention:** Aldosterone promotes $Na^+$ reabsorption. While this initially causes water retention, the "Aldosterone Escape" phenomenon eventually prevents overt edema, though total body sodium remains high. * **Hypertension:** Increased sodium reabsorption leads to increased plasma volume and peripheral resistance, resulting in secondary hypertension. * **Hypokalemia:** As explained, increased $K^+$ secretion into the urine leads to low serum potassium levels. **High-Yield Clinical Pearls for NEET-PG:** * **Conn’s Syndrome:** Primary hyperaldosteronism characterized by the triad of **Hypertension, Hypokalemia, and Metabolic Alkalosis.** * **Aldosterone Escape:** This refers to the spontaneous diuresis of sodium despite high aldosterone levels, mediated by **Atrial Natriuretic Peptide (ANP)**. This explains why patients with Conn’s syndrome have hypertension but **no edema**. * **Spironolactone/Eplerenone:** These are aldosterone antagonists used to treat hyperaldosteronism; they can cause hyperkalemia as a side effect.

Q: All of the following are true about Leptin EXCEPT:

It increases appetite. **Explanation:** Leptin is a peptide hormone primarily produced by **adipocytes** (white adipose tissue). It acts as a key regulator of long-term energy balance and body weight. **Why Option A is the correct answer (The Exception):** Leptin is an **anorexigenic** hormone, meaning it **decreases appetite** and increases energy expenditure. It achieves this by acting on the arcuate nucleus of the hypothalamus to inhibit NPY/AgRP neurons (which stimulate feeding) and stimulate POMC/CART neurons (which inhibit feeding). Therefore, the statement that it "increases appetite" is false. **Analysis of other options:** * **Option B (Increased in obesity):** Leptin levels are directly proportional to the total amount of body fat. In most cases of human obesity, leptin levels are high, but individuals develop **"leptin resistance,"** where the brain fails to respond to the satiety signal. * **Option C (Receptor in hypothalamus):** The leptin receptor (Ob-R) is a cytokine-family receptor (JAK-STAT pathway) located predominantly in the **arcuate nucleus of the hypothalamus**, which serves as the control center for hunger and satiety. * **Option D (Expressed in adipose tissue):** Leptin is the product of the *ob* (obese) gene and is synthesized and secreted by **adipose tissue** in proportion to fat stores. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Stimulates POMC (Anorexigenic) and inhibits NPY (Orexigenic). * **Congenital Leptin Deficiency:** A rare cause of severe, early-onset hyperphagia and morbid obesity. * **Ghrelin vs. Leptin:** Remember **G**hrelin makes you **G**row hungry (stomach), while **L**eptin makes you **L**ean (adipose). * **Sleep Deprivation:** Leads to decreased leptin and increased ghrelin, contributing to weight gain.

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: Gigantism is due to:

Increased secretion of growth hormone. ### Explanation **Correct Answer: C. Increased secretion of growth hormone** **Medical Concept:** Gigantism is a clinical condition caused by the **excessive secretion of Growth Hormone (GH)**, typically due to a somatotroph adenoma of the anterior pituitary. The defining feature of Gigantism is that this hypersecretion occurs **before the fusion of the epiphyseal plates** (pre-puberty). Because the long bones still have active growth plates, the excess GH (acting via IGF-1) stimulates dramatic linear bone growth, leading to tall stature and increased body proportions. **Analysis of Incorrect Options:** * **Options A & B (Cortisol):** Cortisol is a glucocorticoid from the adrenal cortex. Excess cortisol leads to **Cushing’s Syndrome** (characterized by weight gain and stunted growth in children), while a deficiency leads to **Addison’s Disease**. Neither causes gigantism. * **Option D (Decreased GH):** A deficiency of growth hormone during childhood leads to **Pituitary Dwarfism**, characterized by short stature and delayed skeletal maturation. **NEET-PG High-Yield Pearls:** * **Gigantism vs. Acromegaly:** Both are caused by GH excess. If it occurs *before* epiphyseal fusion, it is **Gigantism** (increased height). If it occurs *after* fusion, it is **Acromegaly** (thickening of bones, enlarged hands/feet, and soft tissue overgrowth, but no increase in height). * **Mediator:** GH does not act directly on bones for linear growth; it stimulates the liver to produce **IGF-1 (Somatomedin C)**, which is the actual mediator of bone growth. * **Screening Test:** The best initial screening test for GH excess is measuring **Serum IGF-1 levels** (due to its stable half-life). * **Confirmatory Test:** The gold standard is the **Oral Glucose Tolerance Test (OGTT)**; failure of GH to suppress below 1 ng/mL after glucose load confirms the diagnosis.

Q: Which steroid hormone is primarily involved in regulating water balance in the body?

Aldosterone. **Explanation:** **Aldosterone** is the correct answer because it is the primary mineralocorticoid secreted by the *zona glomerulosa* of the adrenal cortex. Its fundamental role is the maintenance of extracellular fluid volume and blood pressure. It acts on the **principal cells** of the distal convoluted tubule and collecting ducts to increase sodium reabsorption and potassium secretion. Since water follows sodium osmotically (obligatory water reabsorption), aldosterone effectively increases water retention, thereby regulating the body's water balance. **Analysis of Incorrect Options:** * **Estrogen:** While estrogens can cause some salt and water retention (often noticed during menstrual cycles), their primary role is the development of female secondary sexual characteristics and reproductive regulation. * **Testosterone:** This is an androgen responsible for male secondary sexual characteristics and spermatogenesis; it has negligible effects on acute water balance. * **Vitamin D (Calcitriol):** Though structurally a steroid hormone, its primary function is the regulation of **calcium and phosphate** homeostasis by increasing intestinal absorption, not water balance. **NEET-PG High-Yield Pearls:** * **Mechanism of Action:** Aldosterone binds to intracellular mineralocorticoid receptors (MR), leading to the up-regulation of **ENaC** (Epithelial Sodium Channels) and the **Na+/K+ ATPase** pump. * **Primary Stimulus:** The most potent stimulators of aldosterone secretion are **Hyperkalemia** (increased K+) and **Angiotensin II**. * **Conn’s Syndrome:** Primary hyperaldosteronism characterized by the triad of hypertension, hypokalemia, and metabolic alkalosis. * **Spironolactone:** A potassium-sparing diuretic that acts as a competitive antagonist to the aldosterone receptor.

Question 1

Excess Aldosterone is associated with all of the following conditions except?

Accepted Answer

Hyperkalemia

Answer

Hypokalemia

Answer

Sodium retention

Answer

Hypertension

Question 2

Which of the following is NOT a feature of glucocorticoid deficiency?

Accepted Answer

Hyperkalemia

Answer

Hyponatremia

Answer

Hypoglycemia

Answer

Fever

Question 3

All of the following are true about Leptin EXCEPT:

Accepted Answer

It increases appetite

Answer

It is increased in obesity

Answer

Its receptor is located in the hypothalamus

Answer

It is expressed in adipose tissue

Question 4

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 5

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 6

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 7

Gigantism is due to:

Accepted Answer

Increased secretion of growth hormone

Answer

Increased secretion of cortisol

Answer

Decreased secretion of cortisol

Answer

Decreased secretion of growth hormone

Question 8

Normal testicular development requires which of the following?

Accepted Answer

Y chromosome

Answer

XY chromosomes

Answer

XX chromosomes

Answer

X chromosome

Question 9

Decreased activity of type I 5’-monodeiodinase could lead to which physiologic effect?

Accepted Answer

Increased plasma reverse T3

Answer

Increased plasma triiodothyronine (T3)

Answer

Decreased plasma thyroxine T4

Answer

Increased TSH

Question 10

Which steroid hormone is primarily involved in regulating water balance in the body?

Accepted Answer

Aldosterone

Answer

Estrogen

Answer

Testosterone

Answer

Vitamin D

Endocrinology — MCQs

Endocrinology — MCQs

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