Endocrinology Practice Questions

Q: All of the following developmental events are dependent on the production of maternal or fetal glucocorticoids, except?

Functional thyroid. Explanation: Glucocorticoids (cortisol) play a critical role in late fetal development, acting as a "maturation signal" for various organ systems to prepare the fetus for extrauterine life. **Why "Functional Thyroid" is the correct answer:** The development and functional maturation of the thyroid gland are primarily dependent on the **Hypothalamic-Pituitary-Thyroid (HPT) axis**, specifically the secretion of **Thyroid Stimulating Hormone (TSH)** from the fetal pituitary [2]. While cortisol influences many metabolic processes, it is not the primary inducer of thyroid functional maturation. **Analysis of Incorrect Options:** * **Production of Surfactant:** This is the most high-yield association. Glucocorticoids induce the maturation of **Type II pneumocytes** and stimulate the synthesis of surfactant-associated proteins and phospholipids [1]. This is the physiological basis for administering antenatal steroids (Betamethasone/Dexamethasone) in preterm labor. * **Induction of Thymic Involution:** High levels of fetal glucocorticoids (especially during stress or late gestation) lead to the depletion of cortical lymphocytes in the thymus, contributing to its structural changes [3]. * **Functional Hypothalamo-Pituitary Axis:** The maturation of the HPA axis itself is a feedback-regulated process where fetal cortisol plays a vital role in establishing the sensitivity and regulatory loops required for postnatal stress responses. **NEET-PG High-Yield Pearls:** 1. **Antenatal Steroids:** Given between 24–34 weeks of gestation to prevent Respiratory Distress Syndrome (RDS) [1]. 2. **Other Cortisol Effects:** It also promotes **glycogen deposition** in the fetal liver and the maturation of **intestinal enzymes** (e.g., lactase). 3. **Source:** Fetal cortisol production increases significantly near term due to the maturation of the fetal zone of the adrenal cortex.

Q: Which of the following substances is the most potent androgen?

Dihydrotestosterone. ### Explanation **Correct Answer: B. Dihydrotestosterone (DHT)** **Why it is correct:** In terms of biological activity, **Dihydrotestosterone (DHT)** is the most potent naturally occurring androgen. It is synthesized from testosterone by the enzyme **5α-reductase** in peripheral tissues (such as the prostate and skin). DHT has a significantly higher affinity (approximately 2–3 times) for the androgen receptor compared to testosterone and dissociates from the receptor much more slowly. This results in a more stable and potent hormone-receptor complex, amplifying the androgenic signal. **Why the other options are incorrect:** * **Testosterone (D):** While it is the primary circulating androgen secreted by the Leydig cells, it acts as a "pro-hormone" for DHT in many tissues. It is less potent than DHT but more potent than adrenal androgens. * **Androstenedione (C) and Dehydroepiandrosterone (A):** These are weak adrenal androgens. They have minimal intrinsic activity and primarily serve as precursors that must be converted into testosterone or estrogens in peripheral tissues to exert significant biological effects. **High-Yield Clinical Pearls for NEET-PG:** * **Potency Hierarchy:** DHT > Testosterone > Androstenedione > DHEA. * **5α-reductase Deficiency:** Leads to ambiguous genitalia in males at birth (pseudohermaphroditism) because DHT is essential for the development of external male genitalia. * **Pharmacology Link:** **Finasteride** is a 5α-reductase inhibitor used to treat Benign Prostatic Hyperplasia (BPH) and male pattern baldness by reducing DHT levels. * **Site of Action:** DHT is responsible for the growth of the prostate, male pattern baldness, and facial hair, whereas testosterone is responsible for internal genitalia (Wolffian duct development) and muscle mass.

Q: Thyroid peroxidase is required for all of the following steps in thyroid hormone synthesis except?

Iodide uptake. **Explanation:** **Thyroid Peroxidase (TPO)** is a multifunctional enzyme located on the apical membrane of follicular cells. It is essential for the synthesis of thyroid hormones, but it plays no role in the initial transport of iodide into the cell. 1. **Why "Iodide Uptake" is the correct answer:** Iodide uptake (trapping) is the first step in thyroid hormone synthesis. It is mediated by the **Sodium-Iodide Symporter (NIS)**, an active transport mechanism located on the basolateral membrane. This process is driven by the Na+/K+ ATPase pump and is regulated primarily by TSH, not TPO. 2. **Why the other options are incorrect:** TPO is a heme-containing enzyme that catalyzes three distinct reactions: * **Oxidation of Iodide (B):** TPO converts iodide ($I^-$) into reactive iodine ($I^0$) using hydrogen peroxide ($H_2O_2$). * **Iodination of Tyrosine (C):** Also known as **Organification**, where iodine is attached to tyrosine residues on thyroglobulin to form Monoiodotyrosine (MIT) and Diiodotyrosine (DIT). * **Synthesis of Iodothyronines (D):** Also known as **Coupling**, where TPO facilitates the joining of MIT and DIT to form $T_3$ and $T_4$. **High-Yield Clinical Pearls for NEET-PG:** * **Wolf-Chaikoff Effect:** An autoregulatory phenomenon where high levels of circulating iodide inhibit TPO, leading to a temporary decrease in thyroid hormone synthesis. * **Propylthiouracil (PTU) & Methimazole:** These antithyroid drugs work primarily by inhibiting the enzyme **Thyroid Peroxidase**. * **Pendred Syndrome:** Caused by a defect in the **Pendrin** transporter (iodide-chloride exchanger) on the apical membrane, leading to sensorineural hearing loss and goiter.

Q: What are the important metabolic effects of thyroxine?

All of the above.. Thyroid hormones (T3 and T4) are the primary determinants of the body’s metabolic pace. The correct answer is **Option D** because thyroxine exerts pleiotropic effects across multiple organ systems. **Explanation of Options:** * **A. Increases Basal Metabolic Rate (BMR):** Thyroxine increases oxygen consumption and heat production (thermogenesis) in almost all active tissues (except the brain, testes, and anterior pituitary). It achieves this by increasing the number and activity of mitochondria and upregulating Na+-K+ ATPase pumps. * **B. Shortened Stretch Reflexes:** Thyroid hormones are essential for normal neuromuscular function. In hyperthyroidism, the reaction time of stretch reflexes (e.g., the Achilles tendon reflex) is shortened (brisk), whereas in hypothyroidism, it is characteristically prolonged ("hung-up" reflex). * **C. Potentiates Catecholamines:** Thyroxine increases the expression and sensitivity of **beta-adrenergic receptors** in the heart and other tissues. This explains why hyperthyroid patients present with tachycardia, tremors, and anxiety, and why beta-blockers (Propranolol) are used for symptomatic relief. **High-Yield NEET-PG Pearls:** * **Lipid Metabolism:** Thyroxine decreases blood cholesterol levels by increasing the expression of **LDL receptors** in the liver (Hypothyroidism leads to hypercholesterolemia). * **Carbohydrate Metabolism:** It is diabetogenic; it increases glucose absorption from the GI tract and potentiates glycogenolysis. * **Growth:** It acts synergistically with Growth Hormone (GH) for skeletal maturation; deficiency in utero/infancy leads to **Cretinism** (mental retardation and stunted growth).

Q: Skeletal muscle primarily utilizes which glucose transporter for uptake?

GLUT-4 transporter. **Explanation:** The correct answer is **GLUT-4 transporter**. **1. Why GLUT-4 is correct:** GLUT-4 is the primary glucose transporter found in **skeletal muscle** and **adipose tissue**. It is unique because it is **insulin-dependent**. In the resting state, GLUT-4 molecules are stored in intracellular vesicles. Upon insulin stimulation (or during exercise), these vesicles translocation to the cell membrane, allowing glucose to enter the cell via facilitated diffusion. This mechanism is crucial for post-prandial glucose lowering. **2. Why other options are incorrect:** * **GLUT-1:** This is an insulin-independent transporter found in almost all tissues, but it is the primary transporter for the **Blood-Brain Barrier (BBB)** and **RBCs**. It maintains basal glucose uptake. * **GLUT-2:** A high-capacity, low-affinity transporter found in the **Liver, Pancreas (beta cells), and Kidney**. It acts as a "glucose sensor" in the pancreas and allows bidirectional transport in the liver. * **GLUT-3:** Found primarily in **Neurons** and the placenta. It has a very high affinity for glucose, ensuring the brain receives priority supply even during hypoglycemia. **3. High-Yield Clinical Pearls for NEET-PG:** * **Exercise & GLUT-4:** Muscle contraction during exercise can trigger GLUT-4 translocation *independent* of insulin. This is why exercise is a key management strategy for Type 2 Diabetes. * **GLUT-5:** This is a specialized transporter for **Fructose**, located primarily in the small intestine and spermatozoa. * **SGLT vs. GLUT:** Remember that SGLT (Sodium-Glucose Linked Transporters) perform **active transport** (secondary), whereas all GLUT transporters perform **facilitated diffusion** (passive).

Q: Insulin-like Growth Factor II plays an important role in which of the following?

Development of the fetus. **Explanation:** **Insulin-like Growth Factor II (IGF-II)** is a polypeptide hormone structurally related to insulin. Its primary physiological role is as a **major regulator of fetal growth and development**. 1. **Why Option D is Correct:** During the prenatal period, IGF-II is highly expressed in fetal tissues. Unlike IGF-I, which is growth hormone (GH) dependent and dominates postnatal growth, **IGF-II acts independently of GH** during gestation. It promotes cell proliferation and tissue differentiation, making it the critical factor for fetal weight gain and organogenesis. 2. **Why Other Options are Incorrect:** * **Options B & C (Skeletal and Cartilage Growth):** These are primarily the functions of **IGF-I (Somatomedin C)**. Postnatally, Growth Hormone stimulates the liver to produce IGF-I, which then acts on the epiphyseal plates to promote linear bone growth and chondrocyte proliferation. * **Option A (Control of Metabolism):** While IGFs have insulin-like effects, the primary control of glucose and lipid metabolism is mediated by **Insulin** and counter-regulatory hormones (Glucagon, Cortisol, Epinephrine). **High-Yield Clinical Pearls for NEET-PG:** * **IGF-I vs. IGF-II:** Remember: **IGF-II = Fetal growth**; **IGF-I = Postnatal growth** (GH-dependent). * **Beckwith-Wiedemann Syndrome:** A classic clinical condition caused by the over-expression of the *IGF2* gene (genomic imprinting defect), leading to fetal overgrowth, macroglossia, and organomegaly. * **Receptor:** IGF-II binds primarily to the IGF-II receptor (which acts as a "sink" to clear IGF-II) but exerts its growth-promoting effects via the **IGF-I receptor**.

Q: In which physiological state are serum prolactin levels highest?

24 hours postpartum. **Explanation:** **1. Why Option A is Correct:** Prolactin levels undergo a dramatic surge during pregnancy due to high estrogen levels stimulating the lactotrophs in the anterior pituitary. However, its milk-producing action is inhibited by high progesterone levels. Immediately after delivery, the sudden withdrawal of placental steroids (estrogen and progesterone) removes this inhibition. In the **24 hours postpartum**, prolactin levels reach their physiological peak (often >200 ng/mL) to initiate lactogenesis. While suckling maintains these levels later on, the immediate postpartum period represents the highest baseline physiological state. **2. Why the Other Options are Incorrect:** * **B. 24 hours post-ovulation:** While estrogen during the follicular phase can slightly increase prolactin, the levels are negligible compared to the massive surge seen in pregnancy and the postpartum period. * **C. During REM sleep:** Prolactin secretion is pulsatile and follows a diurnal rhythm, with levels rising 60–90 minutes after sleep onset. However, the peak occurs during **non-REM (NREM) sleep**, not REM sleep, and the magnitude is far lower than the postpartum state. * **D. After one hour of running:** Physical and emotional stress (including exercise) can cause a transient rise in prolactin via the inhibition of dopamine. However, this increase is acute and minor compared to the sustained high levels required for lactation. **High-Yield NEET-PG Pearls:** * **Inhibitory Control:** Prolactin is the only anterior pituitary hormone under **predominant inhibitory control** (by Dopamine from the hypothalamus). * **Prolactin & GnRH:** High prolactin levels inhibit GnRH secretion, leading to **lactational amenorrhea** (a natural contraceptive mechanism). * **TRH Effect:** Thyrotropin-releasing hormone (TRH) acts as a potent prolactin-releasing factor; hence, **primary hypothyroidism** is a common cause of hyperprolactinemia.

Q: Angiotensin II causes all of the following, except:

Vasodilation. **Explanation:** Angiotensin II (AT-II) is a potent effector peptide of the Renin-Angiotensin-Aldosterone System (RAAS), primarily functioning to increase blood pressure and maintain fluid volume. **Why Vasodilation is the Correct Answer:** Angiotensin II is one of the most powerful **vasoconstrictors** known. It acts directly on AT1 receptors located on vascular smooth muscle cells to cause systemic vasoconstriction, which increases Total Peripheral Resistance (TPR) and elevates blood pressure. Therefore, it causes vasoconstriction, not vasodilation. **Analysis of Other Options:** * **A. Stimulation of Thirst:** AT-II acts on the subfornical organ (SFO) in the brain to stimulate the thirst center in the hypothalamus, encouraging water intake to restore blood volume. * **B. Increased ADH secretion:** AT-II stimulates the posterior pituitary to release Antidiuretic Hormone (ADH/Vasopressin), which increases water reabsorption in the collecting ducts of the kidney. * **D. Aldosterone secretion:** AT-II acts on the Zona Glomerulosa of the adrenal cortex to stimulate the synthesis and release of aldosterone, leading to sodium and water retention. **High-Yield NEET-PG Pearls:** 1. **Receptor Specificity:** Most physiological effects (vasoconstriction, aldosterone release) are mediated via **AT1 receptors**. AT2 receptors generally mediate opposing effects (vasodilation) but are less dominant in adults. 2. **Renal Effects:** AT-II preferentially constricts the **efferent arteriole**, which helps maintain the Glomerular Filtration Rate (GFR) when renal perfusion pressure is low. 3. **Clinical Correlation:** ACE inhibitors (e.g., Enalapril) and ARBs (e.g., Losartan) are used in hypertension and heart failure to block these effects, leading to vasodilation and reduced fluid overload.

Q: Most of the testosterone secreted by the testes exists in the plasma in the form of?

Testosterone bound to sex-steroid-binding globulin. ### Explanation **Correct Answer: D. Testosterone bound to sex-steroid-binding globulin** **1. Why the Correct Answer is Right:** In the plasma, testosterone (a lipophilic steroid hormone) requires carrier proteins for transport. Approximately **98% of circulating testosterone is protein-bound**, while only about 2% exists in the "free" (biologically active) form. Of the bound fraction, the majority (**~60-70%**) is bound with high affinity to **Sex Hormone-Binding Globulin (SHBG)**, also known as sex-steroid-binding globulin. The remaining ~30-40% is loosely bound to **albumin**. **2. Why the Other Options are Wrong:** * **Options A & B (Dihydrotestosterone):** While Dihydrotestosterone (DHT) is a more potent androgen, it is primarily produced in peripheral tissues (like the prostate and skin) via the action of 5-alpha-reductase on testosterone. It is not the primary secretory product of the testes, nor is it the most abundant form of testosterone in the plasma. * **Option C (Free Testosterone):** Only a tiny fraction (**1-2%**) of testosterone exists in the free, unbound state. While this is the form that can readily diffuse into cells to exert biological effects, it does not represent the "most" common form in plasma. **3. NEET-PG High-Yield Pearls:** * **Bioavailable Testosterone:** This refers to the sum of **Free Testosterone + Albumin-bound Testosterone**. Because the binding to albumin is weak (low affinity), it dissociates easily for tissue use. * **SHBG Regulation:** SHBG levels are **increased** by estrogens and hyperthyroidism, and **decreased** by androgens, obesity, and insulin resistance. * **Site of Secretion:** Testosterone is secreted by the **Leydig cells** of the testes under the influence of **Luteinizing Hormone (LH)**.

Q: What is the primary action of insulin?

Increased glucose uptake in muscle. **Explanation:** Insulin is the body’s primary anabolic hormone, secreted by the β-cells of the pancreatic islets. Its fundamental role is to lower blood glucose levels by promoting glucose utilization and storage while inhibiting glucose production. **Why Option B is correct:** Insulin facilitates glucose entry into specific tissues—primarily **skeletal muscle** and **adipose tissue**—by triggering the translocation of **GLUT-4** (an insulin-dependent glucose transporter) from intracellular vesicles to the cell membrane. Since skeletal muscle constitutes a large percentage of body mass, its increased glucose uptake is the primary mechanism for lowering postprandial blood glucose. **Why the other options are incorrect:** * **A & C (Gluconeogenesis and Glycogenolysis):** These are catabolic processes that *increase* blood glucose. Insulin **inhibits** these processes in the liver. Glucagon and epinephrine are the hormones that stimulate them. * **D (Glucose uptake in endothelium):** Glucose uptake in the vascular endothelium (as well as the brain, liver, and RBCs) is mediated by **GLUT-1** or **GLUT-2**, which are **insulin-independent**. These tissues do not require insulin to take up glucose. **High-Yield Clinical Pearls for NEET-PG:** * **GLUT-4** is the only insulin-dependent transporter. * **Exercise** can also trigger GLUT-4 translocation in muscles, which is why physical activity helps manage Diabetes Mellitus. * **Brain and RBCs** rely on GLUT-1/3 and do not require insulin for glucose uptake, protecting vital organs during hypoglycemia. * **SGLT-1/2** are involved in active transport (sodium-dependent) in the gut and kidneys, unlike the facilitated diffusion of GLUT transporters.

Question 1

All of the following developmental events are dependent on the production of maternal or fetal glucocorticoids, except?

Accepted Answer

Functional thyroid

Answer

Induction of thymic involution

Answer

Production of surfactant by type II alveolar cells

Answer

Functional hypothalamo pituitary axis

Question 2

Which of the following substances is the most potent androgen?

Accepted Answer

Dihydrotestosterone

Answer

Dehydroepiandrosterone

Answer

Androstenedione

Answer

Testosterone

Question 3

Thyroid peroxidase is required for all of the following steps in thyroid hormone synthesis except?

Accepted Answer

Iodide uptake

Answer

Oxidation of iodide

Answer

Iodination of tyrosine

Answer

Synthesis of iodothyronines

Question 4

What are the important metabolic effects of thyroxine?

Accepted Answer

All of the above.

Answer

Increases the basal metabolic rate.

Answer

Reaction time of stretch reflexes is shortened by hyperthyroidism.

Answer

Potentiates the effects of catecholamines.

Question 5

Skeletal muscle primarily utilizes which glucose transporter for uptake?

Accepted Answer

GLUT-4 transporter

Answer

GLUT-1 transporter

Answer

GLUT-2 transporter

Answer

GLUT-3 transporter

Question 6

Insulin-like Growth Factor II plays an important role in which of the following?

Accepted Answer

Development of the fetus

Answer

Control of metabolism

Answer

Skeletal growth

Answer

Cartilage growth

Question 7

In which physiological state are serum prolactin levels highest?

Accepted Answer

24 hours postpartum

Answer

24 hours post-ovulation

Answer

During REM sleep

Answer

After one hour of running

Question 8

Angiotensin II causes all of the following, except:

Accepted Answer

Vasodilation

Answer

Stimulation of thirst

Answer

Increased ADH secretion

Answer

Aldosterone secretion

Question 9

Most of the testosterone secreted by the testes exists in the plasma in the form of?

Accepted Answer

Testosterone bound to sex-steroid-binding globulin

Answer

Dihydrotestosterone bound to gonadal steroid-binding hormone

Answer

Free dihydrotestosterone

Answer

Free testosterone

Question 10

What is the primary action of insulin?

Accepted Answer

Increased glucose uptake in muscle

Answer

Gluconeogenesis

Answer

Glycogenolysis

Answer

Increased glucose uptake in endothelium

Endocrinology — MCQs

Endocrinology — MCQs

On this page

Practice by Chapter

Want unlimited practice?