Endocrinology Practice Questions

Q: Diurnal variation in eosinophil count is related to:

Cortisol. **Explanation:** The diurnal variation of eosinophil counts is inversely related to the circulating levels of **Cortisol**. **1. Why Cortisol is correct:** Cortisol follows a strict circadian rhythm, peaking in the early morning (approx. 8 AM) and reaching its nadir around midnight. Cortisol exerts an **eosinopenic effect** by promoting the sequestration of eosinophils into the lymphoid tissues and bone marrow, and increasing their apoptosis. Consequently, eosinophil counts are **lowest in the morning** (when cortisol is high) and **highest at night** (when cortisol is low). This inverse relationship is a classic physiological principle often tested in hematology and endocrinology. **2. Why other options are incorrect:** * **Thyroxine (B):** While thyroid hormones influence metabolic rate, they do not exhibit a significant diurnal rhythm that acutely fluctuates the white blood cell differential. * **Growth Hormone (C):** GH is secreted in pulsatile bursts, primarily during deep sleep (Stage N3). While it has a diurnal pattern, its primary effects are on growth and metabolism, not on the immediate sequestration of eosinophils. * **Testosterone (D):** Testosterone levels are generally higher in the morning, but they do not have a direct, acute regulatory effect on the circulating eosinophil count. **Clinical Pearls for NEET-PG:** * **Mnemonic (B-E-L-L):** Cortisol causes a decrease in **B**asophils, **E**osinophils, and **L**ymphocytes, but an increase in **L**eukocytes (specifically Neutrophils) and **L**iver glycogen. * **Diagnostic Significance:** The loss of diurnal variation in cortisol is an early sign of **Cushing’s Syndrome**. * **Eosinopenia** is also seen during acute stress (due to endogenous ACTH/cortisol surge) and after the administration of exogenous glucocorticoids.

Q: About Neuropeptide Y, all are true except?

Its level decreases during starvation. **Explanation:** **Neuropeptide Y (NPY)** is one of the most potent **orexigenic** (appetite-stimulating) peptides found in the brain, primarily synthesized in the arcuate nucleus of the hypothalamus. **1. Why Option C is the Correct Answer (The "Except" Statement):** In states of negative energy balance, such as **starvation or fasting**, the body attempts to restore energy stores by increasing hunger. Therefore, **NPY levels increase significantly during starvation** to stimulate food intake. The statement that it decreases is physiologically incorrect, making it the right choice for this "except" question. **2. Analysis of Other Options:** * **Option A:** NPY acts as an antagonist to the melanocortin system. It inhibits the release of Pro-opiomelanocortin (POMC) derivatives and competes with the melanocortin signaling pathway to promote feeding. * **Option B:** To conserve energy during periods of perceived food scarcity, NPY **decreases thermogenesis** (specifically by inhibiting brown adipose tissue activity) and lowers sympathetic nervous system activity. * **Option D:** Structurally, NPY is a member of the pancreatic polypeptide family and consists of **36 amino acid residues**. **Clinical Pearls for NEET-PG:** * **Orexigenic (Hunger) Signals:** NPY, Agouti-related peptide (AgRP), Ghrelin ("Hunger hormone"). * **Anorexigenic (Satiety) Signals:** Leptin, Insulin, POMC, CART (Cocaine-and-amphetamine-regulated transcript), and CCK. * **Leptin Connection:** Leptin normally **inhibits** NPY. In obesity, leptin resistance leads to a failure to suppress NPY, contributing to overeating. * **NPY Receptors:** Primarily acts via Y1 and Y5 receptors to stimulate feeding.

Q: Basal metabolic rate (BMR) is decreased in which of the following conditions?

Hypothyroidism. **Explanation:** **Basal Metabolic Rate (BMR)** is the minimum amount of energy required by the body to maintain vital functions (like breathing and circulation) at complete physical and mental rest in a post-absorptive state. **1. Why Hypothyroidism is Correct:** Thyroid hormones ($T_3$ and $T_4$) are the primary determinants of BMR. They increase oxygen consumption and heat production in almost all tissues by increasing the activity of the $Na^+-K^+$ ATPase pump. In **hypothyroidism**, there is a deficiency of these hormones, leading to a significant decrease in cellular metabolism and oxygen consumption, thereby **decreasing the BMR** (often by 30-40%). **2. Why Incorrect Options are Wrong:** * **Exposure to cold temperature:** Cold exposure **increases** BMR as the body generates heat through shivering and non-shivering thermogenesis (activation of brown adipose tissue) to maintain core temperature. * **Hyperthyroidism:** Excess thyroid hormones stimulate metabolic pathways, leading to a marked **increase** in BMR (up to 60-100% above normal). * **Exercise:** Physical activity involves muscular contraction, which significantly **increases** energy expenditure and metabolic rate. **High-Yield Clinical Pearls for NEET-PG:** * **Surface Area Rule:** BMR is directly proportional to the surface area of the body (Rubner’s Law). * **Gender & Age:** BMR is higher in males (due to testosterone and higher muscle mass) and decreases with advancing age. * **Specific Dynamic Action (SDA):** Protein has the highest SDA (30%), meaning it increases metabolic rate the most during digestion. * **Starvation:** BMR **decreases** during prolonged fasting or starvation as an adaptive mechanism to conserve energy.

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).

Question 1

All are true about the Hypothalamus-pituitary-Adrenal axis except?

Accepted Answer

Corticotropin-releasing hormone (CRH) stimulates the zona fasciculata leading to increased cortisol production.

Answer

CRH and vasopressin are released from neurosecretory nerve terminals at the median eminence.

Answer

Cortisol produced in the adrenal cortex will negatively feedback.

Answer

Epinephrine and norepinephrine will positively feedback to the pituitary.

Question 2

Diurnal variation in eosinophil count is related to:

Accepted Answer

Cortisol

Answer

Thyroxine

Answer

Growth hormone

Answer

Testosterone

Question 3

Which of the following sources of cholesterol is most important for sustaining adrenal steroidogenesis when it occurs at a high rate for a long time?

Accepted Answer

Cholesterol in LDL particles

Answer

De novo synthesis of cholesterol from acetate

Answer

Cholesterol in the plasma membrane

Answer

Cholesterol in lipid droplets within adrenal cortical cells

Question 4

Which of the following is NOT a function of insulin?

Accepted Answer

Increased protein synthesis in muscle

Answer

Increased glucose uptake in muscle

Answer

Increased lipolysis in adipose tissue

Answer

Decreased gluconeogenesis in the liver

Question 5

About Neuropeptide Y, all are true except?

Accepted Answer

Its level decreases during starvation

Answer

It is mediated through melanocorticotropin hormone

Answer

Decreases thermogenesis

Answer

Contains 36 aminoacid residues

Question 6

Basal metabolic rate (BMR) is decreased in which of the following conditions?

Accepted Answer

Hypothyroidism

Answer

Exposure to cold temperature

Answer

Hyperthyroidism

Answer

Exercise

Question 7

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 8

Which of the following substances is the most potent androgen?

Accepted Answer

Dihydrotestosterone

Answer

Dehydroepiandrosterone

Answer

Androstenedione

Answer

Testosterone

Question 9

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 10

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.

Endocrinology — MCQs

Endocrinology — MCQs

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