Endocrinology Practice Questions

Q: Which of the following hormones act through nuclear receptors?

None of the above. **Explanation:** The mechanism of hormone action is determined by the chemical nature of the hormone. Hormones that are lipid-soluble (lipophilic) can cross the cell membrane and bind to **nuclear or cytoplasmic receptors**, while water-soluble (hydrophilic) hormones bind to **cell surface (membrane) receptors**. **1. Why "None of the above" is correct:** For an option to be correct, *all* hormones listed in that group must act via nuclear receptors. In this question, every option contains at least one hormone that acts via a cell surface receptor (using second messengers like cAMP or IP3/DAG). **2. Analysis of Incorrect Options:** * **Option A:** Estrogen and Thyroxine (T4) act via nuclear receptors. However, **Glucagon** is a peptide hormone that acts via a G-protein coupled receptor (GPCR) and the cAMP second messenger system. * **Option B:** Estrogen and Thyroxine use nuclear receptors. **TSH (Thyroid Stimulating Hormone)**, despite acting on the thyroid gland, is a glycoprotein that binds to membrane-bound GPCRs. * **Option C:** Estrogen uses nuclear receptors. Both **TSH and GnRH** act via cell surface receptors (GnRH uses the Gq-IP3/DAG pathway). **High-Yield NEET-PG Clinical Pearls:** * **Nuclear Receptor Superfamily:** Includes Steroid hormones (Estrogen, Progesterone, Testosterone, Cortisol, Aldosterone), Thyroid hormones (T3, T4), Vitamin D, and Retinoic acid. * **Thyroid Exception:** Unlike most lipid-soluble hormones that bind in the cytoplasm, Thyroid hormone receptors are already bound to DNA in the nucleus even in the absence of the hormone. * **Speed of Action:** Hormones acting via nuclear receptors have a **slow onset** (hours to days) because they require gene transcription and protein synthesis, whereas membrane-receptor hormones (like Epinephrine or Insulin) act almost instantaneously.

Q: Which of the following immunoglobulin is characteristic of LATS (Long-Acting Thyroid Stimulator)?

IgG. **Explanation:** **1. Why IgG is the Correct Answer:** Long-Acting Thyroid Stimulator (LATS) is a historical term for **Thyroid Stimulating Immunoglobulins (TSI)**, which are the hallmark of **Graves' Disease**. These are autoantibodies directed against the TSH receptors on the thyroid follicular cells. Structurally, these antibodies belong to the **IgG class**. Unlike TSH, which has a short half-life, LATS (IgG) has a much longer duration of action, leading to persistent stimulation of the thyroid gland and subsequent hyperthyroidism. **2. Why Other Options are Incorrect:** * **IgM:** This is typically the first antibody produced in an acute immune response and exists as a pentamer. It is not associated with the chronic autoimmune stimulation seen in Graves' disease. * **Glycoprotein:** While TSH (the natural hormone) is a glycoprotein, LATS is an antibody (protein). This option confuses the hormone with the antibody that mimics it. * **IgA:** This immunoglobulin is primarily involved in mucosal immunity (secretory IgA) and is not the mediator of systemic autoimmune thyroiditis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** LATS/TSI acts as an **agonist** at the TSH receptor, stimulating the cAMP pathway. * **Placental Transfer:** Because LATS is an **IgG**, it can cross the placenta. This explains why infants born to mothers with Graves' disease may suffer from **Neonatal Thyrotoxicosis**. * **Diagnosis:** While LATS was the term used in early bioassays, modern clinical practice uses **TRAb (TSH Receptor Antibody)** assays. * **Type of Hypersensitivity:** Graves' disease is a classic example of **Type II Hypersensitivity** (Antibody-mediated cellular dysfunction).

Q: Prolactin secretion is inhibited by which of the following?

Dopamine excess. **Explanation:** The regulation of prolactin (PRL) is unique among anterior pituitary hormones because it is under **tonic inhibitory control** by the hypothalamus. **1. Why Option A is Correct:** The primary Prolactin Inhibiting Factor (PIF) is **Dopamine**. Dopamine is secreted by the tuberoinfundibular neurons into the hypophyseal portal system. It binds to **D2 receptors** on the lactotrophs in the anterior pituitary, leading to the inhibition of prolactin synthesis and release. Therefore, an excess of dopamine directly suppresses prolactin levels. **2. Why the Other Options are Incorrect:** * **B. Metoclopramide:** This is a dopamine (D2) receptor antagonist. By blocking the inhibitory effect of dopamine, it causes a rise in prolactin levels (hyperprolactinemia). * **C. Hypothyroidism:** In primary hypothyroidism, low levels of thyroid hormones lead to a compensatory increase in **Thyrotropin-Releasing Hormone (TRH)**. TRH acts as a potent prolactin-releasing factor; thus, hypothyroidism is a common cause of hyperprolactinemia. * **D. Emotional Stress:** Prolactin is a stress-responsive hormone. Physical or emotional stress stimulates the release of prolactin via various neuroendocrine pathways. **High-Yield Clinical Pearls for NEET-PG:** * **Prolactinoma:** The most common secretory tumor of the pituitary. Treatment of choice is medical (Dopamine agonists like **Cabergoline** or Bromocriptine), not surgery. * **Stalk Effect:** Any lesion compressing the pituitary stalk prevents dopamine from reaching the pituitary, leading to elevated prolactin (the only pituitary hormone that increases when the stalk is cut). * **Hook Effect:** In cases of extremely high prolactin (giant prolactinomas), lab assays may show falsely low levels; serial dilution is required for accurate diagnosis.

Q: Primary Adrenal Insufficiency causes all of the following, except?

Increased protein breakdown. **Explanation:** Primary Adrenal Insufficiency (Addison’s Disease) is characterized by the destruction of the adrenal cortex, leading to a deficiency of both **Mineralocorticoids (Aldosterone)** and **Glucocorticoids (Cortisol)**. **Why "Increased protein breakdown" is the correct answer:** Cortisol is a catabolic hormone. Its primary role in protein metabolism is to stimulate the breakdown of proteins in peripheral tissues (like muscle) to provide amino acids for gluconeogenesis. In adrenal insufficiency, there is a **deficiency of cortisol**, which leads to **decreased protein breakdown** and impaired gluconeogenesis. Therefore, increased protein breakdown does not occur. **Analysis of incorrect options:** * **Low Blood Pressure:** Aldosterone deficiency leads to "pressure natriuresis" (loss of sodium and water), resulting in hypovolemia. Additionally, cortisol is required to maintain the sensitivity of blood vessels to catecholamines. Lack of both leads to hypotension. * **Decrease in ECF:** The loss of sodium (and consequently water) due to lack of aldosterone directly reduces the extracellular fluid volume. * **Decreased sodium-potassium ratio:** Aldosterone normally causes Na+ reabsorption and K+ excretion. Its absence leads to **Hyponatremia** and **Hyperkalemia**, which mathematically decreases the Na+:K+ ratio (a classic diagnostic marker). **High-Yield Clinical Pearls for NEET-PG:** * **Hyperpigmentation:** Seen only in *Primary* Adrenal Insufficiency due to compensatory increase in ACTH (which shares a precursor with MSH, POMC). * **Electrolyte Triad:** Hyponatremia, Hyperkalemia, and Metabolic Acidosis. * **Gold Standard Test:** ACTH Stimulation Test (Cosyntropin test). * **Crisis Management:** Immediate IV Hydrocortisone and aggressive fluid resuscitation with Normal Saline.

Q: Laron dwarfism is caused by which of the following?

GH receptor defect. **Explanation:** **Laron Dwarfism (Laron Syndrome)** is an autosomal recessive condition characterized by a mutation in the **Growth Hormone Receptor (GHR)** gene. In this condition, the body produces normal or even elevated levels of Growth Hormone (GH), but the receptors are non-functional. Consequently, the liver cannot produce **Insulin-like Growth Factor-1 (IGF-1)** in response to GH. Since IGF-1 is the primary mediator of GH’s growth-promoting effects on bone and cartilage, its absence leads to severe short stature. **Analysis of Options:** * **Option B (Correct):** The primary pathology is a **GH receptor defect** (insensitivity to GH). Laboratory findings typically show **High GH** and **Low IGF-1**. * **Option A:** Deficiency of GH causes **Pituitary Dwarfism**. Unlike Laron syndrome, these patients respond to exogenous GH therapy. * **Option C:** Deficiency of thyroxin in childhood leads to **Cretinism**, characterized by stunted growth and significant mental retardation. * **Option D:** Thyroxin receptor defects lead to **Thyroid Hormone Resistance Syndrome (Refetoff Syndrome)**, which presents with features of hypothyroidism or goiter, but is not the cause of Laron dwarfism. **High-Yield Clinical Pearls for NEET-PG:** * **Hallmark Lab Profile:** ↑ GH, ↓ IGF-1, and ↓ GH-Binding Protein (GHBP). * **Clinical Feature:** Patients often have a characteristic "doll-like" face (prominent forehead, depressed nasal bridge) and a high-pitched voice. * **Metabolic Paradox:** Interestingly, individuals with Laron syndrome have a significantly **reduced risk of developing cancer and Type 2 Diabetes Mellitus**, despite their growth deficits. * **Treatment:** Since the defect is at the receptor level, exogenous GH is ineffective. Treatment requires **recombinant IGF-1 (Mecasermin)**.

Q: What are elevated urine levels of 5-hydroxyindoleacetic acid (5-HIAA) suggestive of?

Carcinoid tumors. **Explanation:** **1. Why Carcinoid Tumors is correct:** Carcinoid tumors are neuroendocrine tumors, most commonly found in the gastrointestinal tract (ileum) and lungs. These tumors secrete excessive amounts of **Serotonin (5-hydroxytryptamine)**. In the body, serotonin is metabolized by the enzyme monoamine oxidase (MAO) into **5-hydroxyindoleacetic acid (5-HIAA)**, which is then excreted in the urine. Therefore, a 24-hour urinary 5-HIAA test is the gold standard biochemical marker for diagnosing Carcinoid Syndrome. **2. Why other options are incorrect:** * **Colon Cancer:** Adenocarcinoma of the colon does not typically secrete serotonin; its primary tumor marker is Carcinoembryonic Antigen (CEA). * **Malignant Melanoma:** This is a malignancy of melanocytes. While melanocytes and neuroendocrine cells both share embryological origins (neural crest), melanoma is associated with urinary **VMA (Vanillylmandellic acid)** only in rare cases, but never 5-HIAA. The primary markers are S100 and HMB-45. **3. Clinical Pearls for NEET-PG:** * **The Pathway:** Tryptophan → 5-Hydroxytryptophan → Serotonin → 5-HIAA. * **Dietary Interference:** Patients must avoid serotonin-rich foods (bananas, walnuts, pineapples, avocados) for 48 hours before the test to prevent false positives. * **Pellagra Connection:** Because the tumor diverts up to 60% of the body's **Tryptophan** to make serotonin, patients may develop **Niacin (Vitamin B3) deficiency**, leading to Pellagra (Dermatitis, Diarrhea, Dementia). * **Rule of Thumb:** Carcinoid syndrome (flushing, diarrhea, wheezing) usually occurs only after the tumor has metastasized to the **liver**, bypassing the portal circulation's first-pass metabolism.

Question 1

Which of the following hormones act through nuclear receptors?

Accepted Answer

None of the above

Answer

Estrogen, thyroxine, and glucagon

Answer

Estrogen, thyroxine, and TSH

Answer

Estrogen, TSH, and Gonadotropin releasing hormone (GnRH)

Question 2

Which of the following statements about calcitonin is incorrect?

Accepted Answer

It plays a major role in the regulation of calcium levels in humans.

Answer

It inhibits osteoclast-mediated bone resorption.

Answer

It increases phosphate excretion in the kidneys.

Answer

It is useful in treating acute hypercalcemic crisis.

Question 3

Which of the following immunoglobulin is characteristic of LATS (Long-Acting Thyroid Stimulator)?

Accepted Answer

IgG

Answer

IgM

Answer

Glycoprotein

Answer

IgA

Question 4

Prolactin secretion is inhibited by which of the following?

Accepted Answer

Dopamine excess

Answer

Metoclopramide

Answer

Hypothyroidism

Answer

Emotional stress

Question 5

Which one of the following statements regarding Growth Hormone (GH) secretion is true?

Accepted Answer

GH secretion increases after exercise, stress, and hypoglycemia.

Answer

GH secretion is maximum during the evening.

Answer

GH is produced equally in all age groups.

Answer

GH decreases circulating IGF and somatostatin.

Question 6

Aldosterone secretion is controlled by all of the following except:

Accepted Answer

Increase in ECF volume

Answer

ACTH

Answer

Increase in potassium ion concentration in ECF

Answer

Decrease in the sodium ion concentration in ECF

Question 7

Primary Adrenal Insufficiency causes all of the following, except?

Accepted Answer

Increased protein breakdown

Answer

Low Blood Pressure

Answer

Decrease in Extracellular Fluid (ECF)

Answer

Decreased sodium-potassium ratio

Question 8

Laron dwarfism is caused by which of the following?

Accepted Answer

GH receptor defect

Answer

Deficiency of Growth Hormone (GH)

Answer

Deficiency of thyroxin

Answer

Thyroxin receptor defect

Question 9

What are elevated urine levels of 5-hydroxyindoleacetic acid (5-HIAA) suggestive of?

Accepted Answer

Carcinoid tumors

Answer

Colon cancer

Answer

Malignant melanoma

Answer

None of the above

Question 10

Corticosteroids increase all of the following components, EXCEPT:

Accepted Answer

Eosinophils

Answer

Platelets

Answer

RBCs

Answer

Monocytes

Endocrinology — MCQs

Endocrinology — MCQs

On this page

Practice by Chapter

Want unlimited practice?