Endocrinology Practice Questions

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.

Q: Hypothyroidism causes central nervous system features due to the presence of which receptor in the brain?

TR beta 2. **Explanation:** Thyroid hormones act through nuclear receptors known as **Thyroid Hormone Receptors (TR)**, which are encoded by two genes: *THRA* (Alpha) and *THRB* (Beta). **Why TR-beta 2 is the correct answer:** The **TR-beta 2 (TRβ2)** isoform is highly specific in its distribution. It is primarily expressed in the **Hypothalamus** and the **Anterior Pituitary gland**. It plays a critical role in the negative feedback mechanism, regulating the secretion of Thyrotropin-Releasing Hormone (TRH) and Thyroid-Stimulating Hormone (TSH). In hypothyroidism, the lack of T3/T4 binding to TRβ2 leads to the neurological and neuroendocrine manifestations associated with the central nervous system's feedback loop. **Analysis of Incorrect Options:** * **TR-alpha 1 (TRα1):** This is the most abundant receptor in the **Heart** and **Skeletal Muscle**. It is responsible for the chronotropic and inotropic effects on the heart. * **TR-alpha 2 (TRα2):** Although widely expressed in the brain, it is considered an **orphan receptor**. It does not bind T3 and actually acts as an antagonist to the effects of other thyroid receptors. * **TR-beta 1 (TRβ1):** This is the predominant isoform found in the **Liver** and **Kidneys**. It is primarily responsible for the metabolic effects of thyroid hormones, such as cholesterol lowering. **High-Yield Clinical Pearls for NEET-PG:** * **Resistance to Thyroid Hormone (RTH) Syndrome:** Usually caused by mutations in the **TR-beta** gene. Patients present with high T3/T4 levels but inappropriately normal or high TSH. * **Most abundant TR in the Brain:** While TRβ2 is specific to the feedback centers, **TRα1** is the most widely distributed isoform in the brain overall, but TRβ2 is the classic answer for CNS-specific endocrine regulation. * **Metabolic Rate:** TR-beta is the primary mediator of the thermogenic and metabolic effects in the liver.

Q: Dwarfism is caused by all EXCEPT:

Castration before puberty. **Explanation:** The core concept in this question is the distinction between **short stature (dwarfism)** and **delayed epiphyseal closure**. **Why Castration before puberty is the correct answer:** Castration leads to a deficiency of sex steroids (testosterone/estrogen). These hormones are essential for the "pubertal growth spurt" and, more importantly, for the **closure of epiphyseal plates**. In their absence, the epiphyses remain open for a longer duration, allowing growth to continue under the influence of Growth Hormone (GH). This results in **Eunuchoidism**, characterized by tall stature and long limbs (the lower segment being longer than the upper segment), rather than dwarfism. **Analysis of incorrect options:** * **Thyroid deficiency (Hypothyroidism):** Thyroid hormones are permissive for GH action. Congenital hypothyroidism (Cretinism) leads to stunted physical and mental growth, resulting in disproportionate dwarfism. * **Growth hormone deficiency:** GH is the primary driver of postnatal linear growth. Deficiency (Pituitary dwarfism) leads to proportionate dwarfism with normal mental development. * **GH-receptor unresponsiveness:** Also known as **Laron Dwarfism**. Here, GH levels are actually high, but the receptors are defective, leading to a failure in IGF-1 production and subsequent short stature. **High-Yield Clinical Pearls for NEET-PG:** * **Laron Dwarfism:** High GH, Low IGF-1. * **African Pygmies:** Normal GH, Low IGF-1 (post-receptor defect). * **Most common cause of Dwarfism:** Achondroplasia (autosomal dominant, FGFR3 mutation). * **Bone Age vs. Chronological Age:** In endocrine dwarfism (GH/Thyroid deficiency), bone age is typically delayed compared to chronological age.

Q: Cyclic AMP (cAMP) acts as a second messenger of which hormone?

Follicle-stimulating hormone (FSH). ### Explanation **1. Why FSH is Correct:** Follicle-stimulating hormone (FSH) is a peptide hormone that binds to G-protein coupled receptors (GPCRs) on the cell membrane. Upon binding, it activates the enzyme **adenylyl cyclase**, which converts ATP into **cyclic AMP (cAMP)**. cAMP then acts as a second messenger to activate Protein Kinase A (PKA), leading to the physiological effects in the gonads (e.g., follicular development in females and spermatogenesis in males). Other hormones using the cAMP pathway include LH, ACTH, TSH, Glucagon, and PTH. **2. Why the Other Options are Incorrect:** * **Growth Hormone (GH):** GH utilizes the **JAK-STAT pathway** (Janus Kinase-Signal Transducer and Activator of Transcription). It binds to a receptor that lacks intrinsic kinase activity but recruits cytoplasmic kinases. * **Thyroxine (T4):** As a lipid-soluble thyroid hormone, it crosses the cell membrane and binds to **nuclear receptors**. It acts as a transcription factor to alter gene expression directly, requiring no second messenger. * **Insulin:** Insulin binds to a receptor with intrinsic **Tyrosine Kinase** activity. This triggers autophosphorylation and activates the MAP kinase and PI3K pathways. **3. High-Yield Clinical Pearls for NEET-PG:** * **cAMP Pathway Mnemonic:** "FLAT ChAMP" (FSH, LH, ACTH, TSH, CRH, hCG, ADH [V2 receptor], MSH, PTH). * **IP3/DAG Pathway Mnemonic:** "GOAT HAG" (GnRH, Oxytocin, ADH [V1 receptor], TRH, Histamine, Angiotensin II, Gastrin). * **cGMP Pathway:** Used by ANP, BNP, and Nitric Oxide (NO). * **Steroid/Thyroid Hormones:** Always remember they use intracellular/nuclear receptors because they are lipophilic.

Q: A patient has an elevated plasma thyroxine (T4) concentration, a low plasma TSH concentration, and her thyroid gland is smaller than normal. What is the most likely explanation for these findings?

The patient is taking thyroid extract. ### Explanation The clinical presentation described is a classic case of **Exogenous Thyrotoxicosis** (Factitious Thyrotoxicosis). **1. Why the Correct Answer is Right:** When a patient takes exogenous thyroid extract (T4), the plasma T4 levels rise. This high concentration of T4 exerts **negative feedback** on the anterior pituitary, significantly inhibiting the secretion of Thyroid Stimulating Hormone (TSH). Since TSH is the primary trophic hormone responsible for the growth and maintenance of the thyroid gland, its chronic suppression leads to **disuse atrophy**, resulting in a thyroid gland that is smaller than normal. **2. Analysis of Incorrect Options:** * **Option A (Pituitary Lesion):** While a pituitary lesion would cause low TSH, it would lead to **low** T4 levels (Secondary Hypothyroidism), not elevated T4. * **Option B (Graves' Disease):** In Graves' disease, Thyroid Stimulating Immunoglobulins (TSI) mimic TSH, leading to high T4 and low TSH. However, TSI also stimulates the growth of the gland, typically causing a **diffuse goiter** (enlarged gland), not a small gland. * **Option C (Propylthiouracil):** PTU inhibits thyroid hormone synthesis. This would lead to low T4 and a compensatory **increase in TSH**, which would likely cause an enlarged thyroid (goiter). **3. NEET-PG High-Yield Pearls:** * **Trophic Effect:** TSH is essential for thyroid cell hypertrophy and hyperplasia. Low TSH = Atrophy; High TSH = Goiter. * **Radioactive Iodine Uptake (RAIU):** In exogenous thyroid intake, RAIU is **decreased** (low) because the endogenous gland is suppressed. In Graves' disease, RAIU is **increased** (high). * **Thyroglobulin Levels:** Low serum thyroglobulin in a thyrotoxic patient is a key marker for exogenous hormone intake, as thyroglobulin is only released during endogenous hormone production.

Q: Glucagon acts via which second messenger system?

cAMP. **Explanation:** Glucagon is a peptide hormone produced by the alpha cells of the pancreas. It exerts its primary metabolic effects by binding to specific **G Protein-Coupled Receptors (GPCRs)** on the surface of hepatocytes. 1. **Why cAMP is correct:** When glucagon binds to its receptor, it activates the **Gs (stimulatory) protein**, which in turn stimulates the enzyme **Adenylyl Cyclase**. This enzyme converts ATP into **cyclic AMP (cAMP)**. Increased levels of cAMP activate **Protein Kinase A (PKA)**, leading to the phosphorylation of key enzymes that promote glycogenolysis and gluconeogenesis while inhibiting glycogenesis. 2. **Why other options are incorrect:** * **cGMP:** This is the second messenger for Atrial Natriuretic Peptide (ANP) and Nitric Oxide (NO), primarily involved in vasodilation. * **Cytoplasmic Ca²⁺:** This is typically associated with the **Gq pathway** (via IP3/DAG), used by hormones like Oxytocin, Vasopressin (V1 receptors), and α1-adrenergic agonists. * **Intracellular K⁺:** While ion channels are involved in insulin secretion (ATP-sensitive K+ channels), they do not serve as the primary second messenger for glucagon signaling. **High-Yield Clinical Pearls for NEET-PG:** * **Glucagon in Beta-blocker Overdose:** Glucagon is the **antidote of choice** for beta-blocker poisoning. It bypasses blocked beta-receptors to increase cAMP directly in cardiac myocytes, exerting positive inotropic and chronotropic effects. * **Other cAMP users:** Remember the mnemonic "FLAT ChAMP" (FSH, LH, ACTH, TSH, CRH, hCG, ADH (V2), MSH, PTH, and Glucagon). * **Insulin vs. Glucagon:** While Glucagon uses cAMP, **Insulin** uses a **Receptor Tyrosine Kinase** pathway.

Question 1

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 2

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 3

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

Accepted Answer

Aldosterone

Answer

Estrogen

Answer

Testosterone

Answer

Vitamin D

Question 4

A 35-year-old woman presents with heat intolerance and menstrual abnormalities. On examination, a diffusely enlarged thyroid gland is present. Which of the following features will not be present in her?

Accepted Answer

Decreased protein breakdown

Answer

Increased heart rate

Answer

Increased stroke volume

Answer

Decreased peripheral vascular resistance

Question 5

Hypothyroidism causes central nervous system features due to the presence of which receptor in the brain?

Accepted Answer

TR beta 2

Answer

TR alpha 1

Answer

TR alpha 2

Answer

TR beta 1

Question 6

Accidental transection of the pituitary stalk can cause which of the following?

Accepted Answer

Diabetes mellitus

Answer

Polyuria

Answer

Galactorrhea

Answer

Diabetes insipidus

Question 7

Dwarfism is caused by all EXCEPT:

Accepted Answer

Castration before puberty

Answer

Thyroid deficiency

Answer

Growth hormone deficiency

Answer

GH-receptor unresponsiveness

Question 8

Cyclic AMP (cAMP) acts as a second messenger of which hormone?

Accepted Answer

Follicle-stimulating hormone (FSH)

Answer

Growth hormone

Answer

Thyroxine

Answer

Insulin

Question 9

A patient has an elevated plasma thyroxine (T4) concentration, a low plasma TSH concentration, and her thyroid gland is smaller than normal. What is the most likely explanation for these findings?

Accepted Answer

The patient is taking thyroid extract

Answer

A lesion in the anterior pituitary that prevents TSH secretion

Answer

Graves' disease

Answer

The patient is taking propylthiouracil

Question 10

Glucagon acts via which second messenger system?

Accepted Answer

cAMP

Answer

cGMP

Answer

Cytoplasmic Ca+

Answer

Intracellular K+

Endocrinology — MCQs

Endocrinology — MCQs

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