Endocrinology Practice Questions

Q: A lab technician notes that prolactin levels in a patient's blood sample are high. This could be due to all of the following except:

L-dopa. **Explanation:** The regulation of **Prolactin (PRL)** is unique among anterior pituitary hormones because it is under **tonic inhibition** by the hypothalamus. The primary Prolactin-Inhibiting Factor (PIF) is **Dopamine**. **Why L-dopa is the correct answer:** L-dopa is a precursor to dopamine. When administered, it increases dopamine levels in the brain. Since dopamine acts on the D2 receptors of the lactotrophs in the anterior pituitary to inhibit prolactin secretion, **L-dopa causes a decrease in prolactin levels**, not an increase. Therefore, it is the exception in this list. **Analysis of incorrect options:** * **Sleep:** Prolactin secretion is pulsatile and follows a diurnal rhythm. Levels rise significantly during sleep (especially non-REM sleep), peaking in the early morning hours. * **Pregnancy:** This is a physiological cause of hyperprolactinemia. High levels of estrogen during pregnancy stimulate the hypertrophy and hyperplasia of lactotrophs, leading to increased prolactin production to prepare the breasts for lactation. * **Stress:** Prolactin is considered a "stress hormone." Physical or emotional stress (including exercise, surgery, or hypoglycemia) triggers the release of prolactin via the suppression of dopamine and the release of Prolactin Releasing Factors (PRFs) like TRH. **NEET-PG High-Yield Pearls:** 1. **Dopamine Agonists** (e.g., Bromocriptine, Cabergoline) are the drugs of choice for Prolactinomas because they mimic dopamine's inhibitory effect. 2. **Antipsychotics** (D2 antagonists) are a common pharmacological cause of hyperprolactinemia/galactorrhea. 3. **TRH** (Thyrotropin-Releasing Hormone) stimulates prolactin; thus, **Primary Hypothyroidism** is a clinical cause of high prolactin levels.

Q: What effect does insulin have on cellular ion transport?

Potassium entry into cells. **Explanation:** Insulin plays a critical role in maintaining electrolyte balance by stimulating the **Na⁺-K⁺ ATPase pump** located in the cell membranes of skeletal muscle, adipose tissue, and the liver. 1. **Why Option D is correct:** Insulin increases the activity and translocation of the Na⁺-K⁺ ATPase pump. This pump actively transports **three Sodium (Na⁺) ions out** of the cell and **two Potassium (K⁺) ions into** the cell. By shifting potassium from the extracellular fluid (ECF) into the intracellular fluid (ICF), insulin effectively lowers serum potassium levels. 2. **Why other options are incorrect:** * **Option A:** While insulin can influence sodium transporters (like the Na-H exchanger), its primary and most clinically significant acute effect is on potassium sequestration. * **Option B:** Potassium exit (efflux) occurs during cell lysis or acidosis, which is the opposite of insulin’s action. * **Option C:** While the Na⁺-K⁺ pump does move sodium out, the question focuses on the most characteristic and clinically relevant ionic shift associated with insulin therapy, which is the inward movement of potassium. **Clinical Pearls for NEET-PG:** * **Management of Hyperkalemia:** Because insulin shifts K⁺ into cells, a combination of **Insulin + Dextrose** (to prevent hypoglycemia) is a standard emergency treatment for hyperkalemia. * **DKA Management:** In Diabetic Ketoacidosis, patients may have high serum K⁺ but low total body K⁺. Starting insulin therapy will cause a rapid drop in serum K⁺, necessitating careful monitoring and replacement to avoid life-threatening hypokalemia. * **Mechanism:** Insulin binds to its tyrosine kinase receptor, leading to the phosphorylation of IRS-1, which eventually activates the Na⁺-K⁺ ATPase pump.

Q: Which of the following inhibits aldosterone synthesis in the adrenal cortex?

Atrial natriuretic peptide (ANP). ### Explanation **Correct Answer: B. Atrial natriuretic peptide (ANP)** **Mechanism:** Aldosterone synthesis occurs in the **Zona Glomerulosa** of the adrenal cortex. Atrial Natriuretic Peptide (ANP) is the primary physiological inhibitor of aldosterone. It acts via two main pathways: 1. **Direct Inhibition:** ANP binds to its receptors (NPR-A) in the adrenal cortex, increasing cGMP, which inhibits the synthesis of aldosterone. 2. **Indirect Inhibition:** ANP inhibits the release of **Renin** from the juxtaglomerular cells, thereby decreasing the production of Angiotensin II, the primary stimulator of aldosterone. **Analysis of Incorrect Options:** * **A. ACTH:** While primarily controlling cortisol, ACTH has a **permissive effect** on aldosterone. It stimulates the initial step of steroidogenesis (cholesterol to pregnenolone). High levels of ACTH can acutely increase aldosterone secretion. * **C. Angiotensin I:** This is a relatively inactive precursor. It must be converted to Angiotensin II by ACE (Angiotensin-Converting Enzyme) to exert significant physiological effects. * **D. Angiotensin II:** This is the **most potent stimulator** of aldosterone synthesis. It acts via the $G_q$ protein-coupled receptor to increase intracellular calcium and activate Protein Kinase C, stimulating aldosterone synthase. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Stimulators of Aldosterone:** 1. Hyperkalemia (Direct effect), 2. Angiotensin II (via RAAS), 3. ACTH (Permissive). * **Primary Inhibitors:** 1. ANP/BNP, 2. Hypokalemia, 3. Dopamine. * **Rate-limiting step:** The conversion of corticosterone to aldosterone by the enzyme **Aldosterone Synthase**, which is unique to the Zona Glomerulosa. * **Conn’s Syndrome:** Primary hyperaldosteronism characterized by hypertension, hypokalemia, and metabolic alkalosis with low plasma renin levels.

Q: Which of the following statements regarding oxytocin is true?

All of the above. **Explanation:** Oxytocin is a peptide hormone synthesized in the **paraventricular nucleus** of the hypothalamus and released by the **posterior pituitary**. It plays a pivotal role in reproduction and fluid balance. * **Option A (Milk Ejection Reflex):** Oxytocin causes the contraction of **myoepithelial cells** surrounding the mammary alveoli. This forces milk into the ducts, a process known as "milk let-down" or milk ejection. (Note: Prolactin handles milk *production*, while Oxytocin handles *ejection*). * **Option B (Uterine Contraction):** During labor, stretching of the cervix triggers oxytocin release (Ferguson Reflex). It acts on the G-protein coupled receptors of the uterine myometrium to increase intracellular calcium, causing powerful contractions necessary for parturition. * **Option C (Water Retention):** Oxytocin is structurally very similar to **Vasopressin (ADH)**—both are nonapeptides differing by only two amino acids. At high pharmacological doses (e.g., during prolonged labor induction), oxytocin can cross-react with V2 receptors in the renal tubules, leading to water intoxication and hyponatremia. **Clinical Pearls for NEET-PG:** 1. **Ferguson Reflex:** A positive feedback loop where cervical stretch stimulates oxytocin release, further increasing contractions. 2. **Postpartum Hemorrhage (PPH):** Oxytocin is the first-line drug for PPH because it causes the uterus to contract, compressing bleeding vessels. 3. **Synthesis vs. Storage:** Remember, oxytocin is *synthesized* in the hypothalamus but *stored and released* from the posterior pituitary (Neurohypophysis).

Q: Receptors for thyroid hormone are located in which cellular compartment?

Nucleus. **Explanation:** Thyroid hormones ($T_3$ and $T_4$) are unique among amino acid-derived hormones because they act similarly to steroid hormones. Due to their lipophilic nature, they cross the cell membrane via carrier-mediated transport. **Why the Nucleus is Correct:** The thyroid hormone receptors (TR) are **nuclear receptors** that function as hormone-activated transcription factors. Specifically, $T_3$ binds to these receptors which are already bound to the **Thyroid Response Elements (TRE)** on the DNA. This binding typically triggers the dissociation of co-repressors and the recruitment of co-activators, leading to the transcription of specific mRNA and subsequent protein synthesis (e.g., $Na^+$-$K^+$ ATPase, beta-receptors). **Analysis of Incorrect Options:** * **Cell membrane:** Receptors for peptide hormones (e.g., Insulin, PTH) and catecholamines are located here. While some non-genomic thyroid actions occur at the membrane, the primary physiological receptors are nuclear. * **Cytoplasm:** Receptors for steroid hormones like **Glucocorticoids** are primarily located in the cytoplasm and then translocate to the nucleus. Thyroid receptors are already present in the nucleus. * **DNA strands:** While the receptors are *bound* to DNA, the receptor itself is a protein located within the **Nucleus**. "DNA strands" refers to the genetic material, not the receptor protein. **High-Yield NEET-PG Pearls:** * **Affinity:** $T_3$ has a much higher affinity (approx. 10 times) for the nuclear receptor than $T_4$; hence $T_3$ is the more active form. * **Retinoid X Receptor (RXR):** Thyroid receptors often form a **heterodimer** with RXR at the TRE to initiate transcription. * **Mitochondria:** Thyroid hormones also bind to receptors in the mitochondria to increase ATP production (the "calorigenic effect").

Q: Thyroid hormones in blood are transported by which of the following?

All of the above. **Explanation:** Thyroid hormones ($T_3$ and $T_4$) are highly lipophilic and virtually insoluble in water. Therefore, more than 99% of circulating thyroid hormones are bound to plasma proteins, while only the "free" fraction is biologically active. The transport involves three primary proteins: 1. **Thyroxine-binding Globulin (TBG):** This is the most important carrier. Although present in the lowest concentration, it has the highest affinity for thyroid hormones and carries approximately 70% of circulating $T_4$ and $T_3$. 2. **Transthyretin (Thyroxine-binding Prealbumin - TBPA):** It has a lower affinity than TBG but a higher affinity than albumin. It carries about 10–15% of $T_4$. 3. **Albumin:** It has the lowest affinity but the highest capacity (due to its high plasma concentration). It carries about 15% of $T_4$ and a significant portion of $T_3$. Since all three proteins listed (Albumin, Globulin, and Prealbumin) participate in the transport of thyroid hormones, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Affinity Order:** TBG > Prealbumin > Albumin. * **Capacity Order:** Albumin > Prealbumin > TBG. * **Half-life:** $T_4$ has a longer half-life (7 days) than $T_3$ (1 day) because it binds more tightly to plasma proteins. * **Clinical Correlation:** Conditions that increase TBG (Pregnancy, Estrogen therapy) increase *total* $T_4$ levels, but *free* $T_4$ remains normal (euthyroid state). Conversely, Liver failure or Nephrotic syndrome decreases TBG levels.

Q: Aldosterone secretion is stimulated by which of the following?

Hyperkalemia. **Explanation:** Aldosterone is a mineralocorticoid synthesized in the **Zona Glomerulosa** of the adrenal cortex. Its primary role is to maintain electrolyte balance by promoting sodium reabsorption and potassium excretion in the distal convoluted tubule and collecting ducts of the kidney. **Why Hyperkalemia is Correct:** Potassium concentration is the most potent direct stimulator of aldosterone secretion. An increase in serum $K^+$ levels causes direct depolarization of the adrenal cortical cells, opening voltage-gated calcium channels. The resulting calcium influx activates protein kinase C, leading to the synthesis and release of aldosterone to facilitate $K^+$ excretion. **Analysis of Incorrect Options:** * **Dopamine:** This acts as a tonic **inhibitor** of aldosterone secretion. Drugs that block dopamine (like Metoclopramide) can actually lead to a mild increase in aldosterone levels. * **Somatostatin:** This is a universal inhibitory hormone that suppresses various endocrine secretions, including growth hormone and insulin; it also has an **inhibitory** effect on aldosterone. * **Atrial Natriuretic Peptide (ANP):** Released in response to atrial stretch (volume overload), ANP **inhibits** aldosterone secretion to promote natriuresis (sodium loss) and lower blood pressure. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Stimulators:** The two most important stimulators of aldosterone are **Hyperkalemia** and **Angiotensin II** (via the Renin-Angiotensin-Aldosterone System). * **ACTH Role:** ACTH is necessary for aldosterone secretion (permissive action) but is not a primary regulator of its day-to-day levels. * **Conn’s Syndrome:** Primary hyperaldosteronism typically presents with the triad of Hypertension, Hypokalemia, and Metabolic Alkalosis.

Q: Down-regulation is:

Decrease in the number of receptors for a hormone. **Explanation:** **Down-regulation** is a physiological process where a cell decreases its sensitivity to a hormone or neurotransmitter. This is achieved by **decreasing the number of available receptors** on the cell surface. When a hormone is present in chronic excess, the target cell internalizes the receptors (via endocytosis) or degrades them to prevent overstimulation. This serves as a protective mechanism to maintain cellular homeostasis. **Analysis of Options:** * **Option D (Correct):** Down-regulation specifically refers to the reduction in receptor density or activity in response to high ligand concentrations. * **Option A:** Increased destruction of a hormone relates to metabolic clearance (e.g., hepatic or renal clearance), not receptor dynamics. * **Option B:** Feedback inhibition refers to the mechanism where the end-product of a pathway inhibits the *secretion* of the initial hormone (e.g., Cortisol inhibiting ACTH), rather than changing the receptor count. * **Option C:** A decreased concentration of hormone in the blood is a state of deficiency or hyposecretion, which usually triggers **up-regulation** (increasing receptors to capture every available hormone molecule). **Clinical Pearls for NEET-PG:** * **Type 2 Diabetes Mellitus:** A classic example of down-regulation where chronic hyperinsulinemia leads to a decrease in insulin receptors, contributing to insulin resistance. * **Tachyphylaxis:** Rapid down-regulation or desensitization of receptors (e.g., prolonged use of β-agonists in asthma) leads to a diminished drug response. * **Up-regulation:** Occurs in response to hormone deficiency or chronic use of antagonists (e.g., Beta-blockers), leading to "rebound tachycardia" if the drug is stopped abruptly due to an excess of receptors.

Q: Which of the following exerts the maximum effect on parathyroid hormone secretion?

Plasma calcium. **Explanation:** The primary regulator of **Parathyroid Hormone (PTH)** secretion is the ionized **plasma calcium** concentration. This is a classic example of a direct negative feedback loop. The parathyroid glands contain G-protein-coupled receptors called **Calcium-Sensing Receptors (CaSR)**. When plasma calcium levels fall (hypocalcemia), these receptors are less stimulated, leading to an immediate increase in PTH secretion to restore calcium homeostasis via bone resorption and renal reabsorption. **Why other options are incorrect:** * **Plasma Phosphate:** While hyperphosphatemia stimulates PTH secretion, it does so primarily **indirectly** by binding to ionized calcium (forming calcium phosphate salts) and by inhibiting the activation of Vitamin D. It is not as potent or direct a trigger as calcium itself. * **1,25-dihydroxycholecalciferol (Calcitriol):** This is the active form of Vitamin D. It exerts a negative feedback effect on the parathyroid gland to *decrease* PTH synthesis, but it acts on a longer timescale (genomic effect) compared to the rapid response triggered by plasma calcium. * **Calcitonin:** Produced by the parafollicular C-cells of the thyroid, calcitonin functions to lower plasma calcium. While it opposes the action of PTH on bone, it does not directly regulate the secretion of PTH from the parathyroid glands. **NEET-PG High-Yield Pearls:** * **Magnesium's Role:** Low magnesium stimulates PTH, but **severe hypomagnesemia** actually inhibits PTH secretion and action, leading to refractory hypocalcemia. * **PTH Action:** It increases calcium and decreases phosphate (phosphaturic effect) by acting on the proximal and distal tubules of the kidney. * **CaSR Mutation:** A mutation in the CaSR can lead to **Familial Hypocalciuric Hypercalcemia (FHH)**.

Question 1

A lab technician notes that prolactin levels in a patient's blood sample are high. This could be due to all of the following except:

Accepted Answer

L-dopa

Answer

Sleep

Answer

Pregnancy

Answer

Stress

Question 2

What effect does insulin have on cellular ion transport?

Accepted Answer

Potassium entry into cells

Answer

Sodium entry into cells

Answer

Potassium exit from cells

Answer

Sodium exit and potassium entry into cells

Question 3

Which of the following is NOT true about prolactin?

Accepted Answer

Hyperprolactinemia causes a reflex increase in central dopamine levels, which causes menorrhagia.

Answer

Primary hypothyroidism is associated with mild elevation in serum prolactin.

Answer

Normal prolactin level is less than 20 ng/mL in non-pregnant women.

Answer

Dopamine agonists decrease prolactin secretion.

Question 4

Which of the following inhibits aldosterone synthesis in the adrenal cortex?

Accepted Answer

Atrial natriuretic peptide (ANP)

Answer

Adrenocorticotropin (ACTH)

Answer

Angiotensin I

Answer

Angiotensin II

Question 5

Which of the following statements regarding oxytocin is true?

Accepted Answer

All of the above

Answer

Acts on myoepithelial cells of the breast

Answer

Causes contraction of the uterus during labor

Answer

May cause water retention

Question 6

Receptors for thyroid hormone are located in which cellular compartment?

Accepted Answer

Nucleus

Answer

Cell membrane

Answer

Cytoplasm

Answer

DNA strands

Question 7

Thyroid hormones in blood are transported by which of the following?

Accepted Answer

All of the above

Answer

Albumin

Answer

Globulin

Answer

Prealbumin

Question 8

Aldosterone secretion is stimulated by which of the following?

Accepted Answer

Hyperkalemia

Answer

Dopamine

Answer

Somatostatin

Answer

Atrial Natriuretic Peptide (ANP)

Question 9

Down-regulation is:

Accepted Answer

Decrease in the number of receptors for a hormone

Answer

Increased destruction of a hormone

Answer

Feedback inhibition of hormone secretion

Answer

Decreased concentration of a hormone in blood

Question 10

Which of the following exerts the maximum effect on parathyroid hormone secretion?

Accepted Answer

Plasma calcium

Answer

Calcitonin

Answer

Plasma phosphate

Answer

1,25-dihydroxycholecalciferol

Endocrinology — MCQs

Endocrinology — MCQs

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