Endocrinology Practice Questions

Q: Which of the following is NOT a prolactin-releasing factor?

Dopamine. ### Explanation The regulation of prolactin (PRL) secretion is unique among anterior pituitary hormones because it is under **tonic inhibition** by the hypothalamus. **1. Why Dopamine is the Correct Answer:** Dopamine is the primary **Prolactin-Inhibiting Factor (PIF)**. It is secreted by the tuberoinfundibular dopaminergic (TIDA) neurons into the hypophyseal portal system. It acts on **D2 receptors** located on the lactotrophs of the anterior pituitary to decrease cAMP levels, thereby inhibiting the synthesis and release of prolactin. Therefore, it is not a releasing factor but a potent inhibitor. **2. Analysis of Other Options (Releasing Factors):** While there is no single "Prolactin Releasing Hormone," several substances stimulate its release: * **Vasoactive Intestinal Peptide (VIP):** A potent stimulator of prolactin release, often acting in a paracrine fashion within the pituitary. * **Vasopressin (ADH):** Known to stimulate lactotrophs, especially during stress responses. * **Acetylcholine:** Acts via muscarinic receptors to stimulate prolactin secretion (though its role is less dominant than TRH or VIP). * *Note:* **TRH (Thyrotropin-Releasing Hormone)** is also a major physiological prolactin-releasing factor. **3. NEET-PG High-Yield Pearls:** * **The "Disconnect" Effect:** Any injury to the pituitary stalk (trauma, tumors like Craniopharyngioma) leads to a decrease in all pituitary hormones **EXCEPT prolactin**, which rises because it is freed from dopamine's inhibitory control. * **Drug-Induced Hyperprolactinemia:** Antipsychotics (D2 antagonists) like Haloperidol or Risperidone commonly cause galactorrhea by blocking dopamine's inhibitory effect. * **Prolactin & Amenorrhea:** High prolactin levels inhibit **GnRH pulsatility**, leading to secondary amenorrhea and infertility.

Q: Plasma half-life of insulin is:

10 minutes. **Explanation:** The plasma half-life of insulin is a high-yield fact in endocrinology. Once secreted into the portal circulation, insulin is rapidly cleared from the plasma, primarily by the liver (about 50%) and the kidneys. **1. Why 10 minutes is correct:** In healthy individuals, the biological half-life of endogenous insulin is approximately **5 to 10 minutes**. This rapid turnover is physiological; it allows the body to make quick, minute-to-minute adjustments in blood glucose levels. If insulin persisted longer, post-prandial glucose regulation would be imprecise, leading to prolonged hypoglycemia after a meal. **2. Why the other options are incorrect:** * **1 minute (Option A):** This is too short. While insulin action begins quickly, the degradation process by the enzyme *insulinase* takes slightly longer than sixty seconds to reduce plasma concentration by half. * **1 hour (Option C) and 2 hours (Option D):** These durations are far too long for endogenous insulin. However, students often confuse this with the **pharmacokinetics of exogenous "Regular" insulin**, which has a peak action at 2–3 hours and a duration of 5–8 hours when injected subcutaneously. **Clinical Pearls for NEET-PG:** * **Degradation:** The primary enzyme responsible for insulin breakdown is **Insulin-degrading enzyme (IDE)** or insulinase, found mainly in the liver and kidneys. * **C-Peptide:** Unlike insulin, C-peptide has a longer half-life (approx. **30 minutes**). This makes it a better clinical marker for measuring endogenous insulin production (beta-cell function). * **Excretion:** The liver clears the majority of endogenous insulin, but the **kidneys** clear the majority of exogenous (injected) insulin. Therefore, insulin requirements often decrease in patients with chronic kidney disease (CKD).

Q: Tachycardia, nervousness, intolerance to heat, and exophthalmos are seen in which condition?

Hyperthyroidism. **Explanation:** The clinical presentation described—**tachycardia, nervousness, heat intolerance, and exophthalmos**—is the classic tetrad of **Hyperthyroidism**, specifically Graves' disease. 1. **Why Hyperthyroidism is correct:** Excess thyroid hormones ($T_3$ and $T_4$) increase the basal metabolic rate (BMR) and upregulate **$\beta$-adrenergic receptors**. This leads to increased sympathetic activity, causing tachycardia and nervousness. Heat intolerance occurs because increased metabolism generates excess internal heat. **Exophthalmos** (proptosis) is a hallmark of Graves' disease, caused by autoimmune-mediated inflammation and accumulation of glycosaminoglycans in the retro-orbital tissues. 2. **Why other options are incorrect:** * **Hypothyroidism:** Characterized by a "slowing down" of metabolism. Symptoms include bradycardia, lethargy, **cold intolerance**, and weight gain. * **Hyperparathyroidism:** Primarily affects calcium homeostasis. It presents with "stones, bones, abdominal groans, and psychic overtones" (renal stones, bone pain, constipation, and depression) due to hypercalcemia. * **Hypoparathyroidism:** Leads to hypocalcemia, characterized by neuromuscular irritability, tetany, and signs like Chvostek’s and Trousseau’s signs. **High-Yield NEET-PG Pearls:** * **Graves' Disease:** The most common cause of hyperthyroidism; characterized by the presence of **TSH-receptor antibodies (TRAb)**. * **Pretibial Myxedema:** Non-pitting edema over the shins, also specific to Graves' disease. * **Thyroid Storm:** A life-threatening exacerbation of hyperthyroidism presenting with high fever, extreme tachycardia, and altered mental status. * **Treatment:** Propranolol is used for immediate symptomatic relief of tachycardia and tremors by blocking $\beta$-receptors.

Q: Which of the following pituitary hormones does not have a corresponding releasing hormone from the hypothalamus?

Prolactin. **Explanation:** The secretion of anterior pituitary hormones is primarily regulated by **releasing hormones** produced in the hypothalamus. However, **Prolactin** is unique because its primary hypothalamic control is **tonic inhibition**, rather than stimulation. 1. **Why Prolactin is the correct answer:** Unlike other anterior pituitary hormones, there is no specific "Prolactin-Releasing Hormone" (PRH) that serves as its primary regulator. Instead, the hypothalamus exerts a constant inhibitory influence via **Dopamine** (acting on D2 receptors). When the connection between the hypothalamus and pituitary is severed (e.g., pituitary stalk transection), levels of all other hormones decrease, but **Prolactin levels rise** because the inhibitory "brake" of dopamine is removed. 2. **Why the other options are incorrect:** * **FSH (and LH):** Regulated by **Gonadotropin-Releasing Hormone (GnRH)**. * **TSH:** Regulated by **Thyrotropin-Releasing Hormone (TRH)**. * **ACTH:** Regulated by **Corticotropin-Releasing Hormone (CRH)**. **High-Yield Clinical Pearls for NEET-PG:** * **Dopamine = Prolactin-Inhibiting Hormone (PIH).** * **TRH Paradox:** While TRH is the releasing hormone for TSH, in pathological states (like primary hypothyroidism), high levels of TRH can also stimulate Prolactin release, leading to galactorrhea. * **Stalk Effect:** Any lesion compressing the pituitary stalk (e.g., Craniopharyngioma) causes **Hyperprolactinemia** due to the loss of dopamine delivery to the lactotrophs. * **Drug-Induced:** Antipsychotics (D2 receptor blockers) commonly cause hyperprolactinemia and gynecomastia/galactorrhea as a side effect.

Q: Most hormone levels decrease with aging. Which of the following hormones does NOT follow this trend?

Prolactin. ### Explanation The aging process is generally associated with a decline in the secretory capacity of various endocrine glands, a phenomenon often referred to as "somatopause," "andropause," or "adrenopause." However, **Prolactin** is a notable exception to this trend. #### Why Prolactin is the Correct Answer Unlike most pituitary and peripheral hormones, serum **Prolactin levels remain stable or may slightly increase** with age, particularly in men. In postmenopausal women, while there is an initial decline due to the loss of estrogen (which stimulates lactotrophs), the levels eventually stabilize and do not show the progressive, steep decline seen with other hormones. This is partly because the inhibitory dopaminergic control of prolactin may weaken with age. #### Why the Other Options are Incorrect * **A. Growth Hormone (GH):** GH secretion declines significantly with age (somatopause), leading to reduced muscle mass and increased visceral fat. * **C. Testosterone:** In men, bioavailable testosterone levels decrease by approximately 1% per year after the age of 30–40 (andropause). * **D. Aldosterone:** Aging is associated with a decrease in plasma renin activity and a subsequent decline in aldosterone levels, which can predispose the elderly to hyperkalemia. #### High-Yield NEET-PG Pearls * **Hormones that Decrease with Age:** GH, Testosterone, Estrogen, Aldosterone, DHEA (the most dramatic decline), and Melatonin. * **Hormones that Increase with Age:** **PTH** (due to Vitamin D deficiency/reduced calcium absorption), **FSH, and LH** (due to loss of negative feedback from gonads), and **Norepinephrine**. * **Thyroid Status:** TSH levels often slightly *increase* in the elderly, while T3 levels may decrease (Euthyroid Sick Syndrome is common in the elderly). * **Insulin:** While insulin levels may remain normal, **insulin resistance** increases with age.

Q: Relaxation of skeletal muscle occurs by?

Removal of sarcoplasmic calcium. ### Explanation **Correct Answer: D. Removal of sarcoplasmic calcium** The fundamental mechanism of skeletal muscle relaxation is the reduction of cytosolic calcium levels. In the resting state, the **Troponin-Tropomyosin complex** physically blocks the myosin-binding sites on actin. For relaxation to occur, calcium must be actively pumped back into the **Sarcoplasmic Reticulum (SR)** via the **SERCA (Sarcoplasmic/Endoplasmic Reticulum Calcium ATPase)** pump. As sarcoplasmic calcium concentrations drop, calcium dissociates from **Troponin C**, allowing the tropomyosin to return to its inhibitory position, thereby preventing cross-bridge cycling. **Analysis of Incorrect Options:** * **A & B:** While the removal of Acetylcholine (by Acetylcholinesterase) and the subsequent closure of nicotinic receptors stop the generation of new action potentials, they do not directly cause relaxation. Relaxation only occurs once the calcium already released into the sarcoplasm is sequestered. * **C:** Binding of calcium with Troponin C is the trigger for **contraction**, not relaxation. This binding causes a conformational change that moves tropomyosin away from the active sites on actin. **High-Yield NEET-PG Pearls:** * **SERCA Pump:** This is an ATP-dependent primary active transporter. Therefore, muscle relaxation is an **active process**. * **Calsequestrin:** A protein within the SR that binds to calcium, allowing the SR to store high concentrations of $Ca^{2+}$ without an osmotic penalty. * **Rigor Mortis:** Occurs because ATP is required for the SERCA pump to remove calcium and for the myosin head to detach from actin. Without ATP, the muscle remains locked in a contracted state. * **Malignant Hyperthermia:** Caused by a mutation in the **Ryanodine Receptor (RyR)**, leading to excessive calcium release and sustained contraction.

Question 1

A high parathyroid hormone (PTH) level affects which of the following processes to return plasma calcium levels toward normal?

Accepted Answer

Stimulate bone resorption, leading to the release of calcium into the plasma

Answer

Inhibit calcium secretion from the gastrointestinal tract

Answer

Reduce the expression of plasma calcium-binding proteins

Answer

Stimulate the release of calcium from muscle cells

Question 2

Which of the following is NOT a prolactin-releasing factor?

Accepted Answer

Dopamine

Answer

Vasopressin

Answer

Vasoactive intestinal peptide

Answer

Acetylcholine

Question 3

Plasma half-life of insulin is:

Accepted Answer

10 minutes

Answer

1 minute

Answer

1 hour

Answer

2 hours

Question 4

Which of the following hormones is mainly responsible for skeletal maturation?

Accepted Answer

Testosterone

Answer

Estrogen

Answer

Growth hormone

Answer

Insulin

Question 5

Which of the following is caused by congenital A-17 hydroxylase deficiency?

Accepted Answer

Hypertension

Answer

Hypercalcemia

Answer

Hyperkalemia

Answer

Hermaphroditism

Question 6

Tachycardia, nervousness, intolerance to heat, and exophthalmos are seen in which condition?

Accepted Answer

Hyperthyroidism

Answer

Hypothyroidism

Answer

Hyperparathyroidism

Answer

Hypoparathyroidism

Question 7

Which of the following pituitary hormones does not have a corresponding releasing hormone from the hypothalamus?

Accepted Answer

Prolactin

Answer

Follicle-stimulating hormone (FSH)

Answer

Thyroid-stimulating hormone (TSH)

Answer

Adrenocorticotropic hormone (ACTH)

Question 8

The probable source of relaxin is:

Accepted Answer

Bartholin's gland

Answer

Ovary

Answer

Adrenal cortex

Answer

Liver

Question 9

Most hormone levels decrease with aging. Which of the following hormones does NOT follow this trend?

Accepted Answer

Prolactin

Answer

Growth hormone

Answer

Testosterone

Answer

Aldosterone

Question 10

Relaxation of skeletal muscle occurs by?

Accepted Answer

Removal of sarcoplasmic calcium

Answer

Removal of Acetylcholine from the synaptic cleft

Answer

Closure of the nicotinic cholinergic receptor

Answer

Binding of calcium with troponin

Endocrinology — MCQs

Endocrinology — MCQs

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