Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 431: Testosterone is produced in Leydig cells in the fetus due to which of the following?

A. FSH
B. ssHCG (Correct Answer)
C. Cortisol
D. Estrogen

Explanation: **Explanation:** In the developing male fetus, the production of testosterone by fetal Leydig cells is essential for the differentiation of the Wolffian duct into internal male genitalia and the development of external genitalia. **Why ssHCG is correct:** During the first trimester (the critical period of sexual differentiation), the fetal pituitary gland is not yet functional enough to secrete significant amounts of Luteinizing Hormone (LH). Instead, **human Chorionic Gonadotropin (hCG)**, secreted by the syncytiotrophoblast of the placenta, acts as the primary stimulus. hCG is structurally similar to LH and binds to the same **LH/hCG receptors** on fetal Leydig cells, triggering testosterone synthesis. By the second trimester, the fetal pituitary takes over, and fetal LH becomes the primary driver. **Why the other options are incorrect:** * **FSH (Follicle-Stimulating Hormone):** In males, FSH primarily acts on Sertoli cells to support spermatogenesis and the production of Androgen Binding Protein (ABP). It does not stimulate Leydig cells to produce testosterone. * **Cortisol:** This is a glucocorticoid produced by the adrenal cortex. While it is vital for fetal lung maturity, it plays no role in stimulating fetal androgen production. * **Estrogen:** Estrogen is involved in female reproductive development. In a male fetus, high levels of estrogen would typically inhibit the male reproductive axis rather than stimulate it. **High-Yield Facts for NEET-PG:** * **Source of hCG:** Syncytiotrophoblast (hence the "ss" in the option, referring to syncytiotrophoblast hCG). * **Critical Period:** Fetal testosterone peaks between **8 to 12 weeks** of gestation. * **Müllerian Inhibiting Substance (MIS):** Produced by fetal **Sertoli cells**, it causes regression of Paramesonephric ducts. * **Dihydrotestosterone (DHT):** Responsible for the development of the penis, scrotum, and prostate; converted from testosterone by the enzyme **5-alpha-reductase**.

Question 432: Virilization of the female is present in all of the following conditions EXCEPT?

A. 17-α hydroxylase deficiency (Correct Answer)
B. 21-α hydroxylase deficiency
C. 11-α hydroxylase deficiency
D. 11-β hydroxysteroid deficiency

Explanation: This question tests your understanding of the steroid biosynthetic pathway in Congenital Adrenal Hyperplasia (CAH). The key to solving CAH questions is identifying which pathway is blocked and which "shunts" are created. ### **Why 17-α hydroxylase deficiency is the correct answer:** In **17-α hydroxylase deficiency**, the enzyme required to convert pregnenolone/progesterone into sex hormones (androgens) and cortisol is missing. * **The Result:** There is a total failure to produce androgens (testosterone/DHEA). * **Clinical Presentation:** Because no androgens are produced, a female (XX) will not undergo virilization; instead, she will fail to develop secondary sexual characteristics (primary amenorrhea). A male (XY) will present with ambiguous genitalia or a female phenotype. Additionally, there is an overproduction of mineralocorticoids, leading to **hypertension and hypokalemia**. ### **Why the other options are incorrect:** * **21-α hydroxylase deficiency (Option B):** This is the most common CAH. It blocks the mineralocorticoid and glucocorticoid pathways, shunting all precursors toward **androgen synthesis**. This causes salt-wasting and **marked virilization** in females. * **11-β hydroxylase deficiency (Option C):** This blocks the final step of cortisol and aldosterone synthesis. Precursors are shunted to androgens, causing **virilization**. Note: Hypertension occurs here due to the buildup of 11-deoxycorticosterone (DOC). * **11-β hydroxysteroid dehydrogenase deficiency (Option D):** While technically a disorder of cortisol-cortisone conversion (Apparent Mineralocorticoid Excess), in the context of adrenal enzyme defects, deficiencies that block the "downward" corticosteroid flow generally lead to androgen excess via ACTH-driven hyperplasia, unless the block is "above" the androgen pathway (like 17-α). ### **NEET-PG High-Yield Pearls:** * **The "1" Rule:** If the enzyme starts with **1** (11, 17), it causes **Hypertension**. * **The "Rule of Virilization":** If the enzyme ends with **1** (11, 21), it causes **Virilization** in females. * **17-α hydroxylase deficiency:** Think "High BP, Low Sex Hormones." * **21-α hydroxylase deficiency:** Think "Low BP, High Sex Hormones."

Question 433: What is the primary mechanism through which catecholamines stabilize blood glucose concentration in response to hypoglycemia?

A. Catecholamines stimulate glycogen phosphorylase to release glucose from muscle.
B. Catecholamines inhibit glycogenolysis in the liver.
C. Catecholamines stimulate the release of insulin from the pancreas.
D. Catecholamines stimulate gluconeogenesis in the liver. (Correct Answer)

Explanation: **Explanation:** The primary goal of catecholamines (Epinephrine and Norepinephrine) during hypoglycemia is to increase blood glucose levels rapidly. This is achieved through the activation of **$\beta_2$ and $\alpha_1$ receptors** in the liver. **Why Option D is correct:** Catecholamines are potent counter-regulatory hormones. They stimulate **gluconeogenesis** (the synthesis of glucose from non-carbohydrate precursors like lactate and amino acids) and **glycogenolysis** (breakdown of glycogen) in the liver. By increasing the expression of key enzymes like PEPCK (Phosphoenolpyruvate carboxykinase), they ensure a sustained release of glucose into the systemic circulation to protect the brain. **Why other options are incorrect:** * **Option A:** While catecholamines do stimulate glycogen phosphorylase in muscles, **muscle lacks the enzyme Glucose-6-Phosphatase**. Therefore, muscle glycogen is converted to lactate (via glycolysis) rather than free glucose, and cannot directly contribute to blood glucose levels. * **Option B:** Catecholamines **stimulate** liver glycogenolysis; inhibiting it would worsen hypoglycemia. * **Option C:** Catecholamines actually **inhibit insulin release** (via $\alpha_2$ receptors) and stimulate glucagon release (via $\beta_2$ receptors) to prevent further glucose uptake by peripheral tissues. **High-Yield NEET-PG Pearls:** * **Dual Action:** Catecholamines increase glucose **production** (liver) and decrease glucose **utilization** (peripheral tissues like muscle/adipose) to spare glucose for the CNS. * **Receptor Specificity:** Hepatic glucose production is mediated by both $\alpha_1$ and $\beta_2$ receptors, but the **inhibition of insulin** is primarily an **$\alpha_2$ effect**. * **Hierarchy:** In the defense against hypoglycemia, Glucagon is the first line of defense, followed closely by Epinephrine. Cortisol and Growth Hormone act much later.

Question 434: Which of the following most accurately describes the transmembrane signaling process involved in steroid hormone action?

A. Action on a membrane-spanning tyrosine kinase
B. Action of a G protein, which activates or inhibits adenylyl cyclase
C. Diffusion across the membrane and binding to an intracellular receptor (Correct Answer)
D. Opening of transmembrane ion channels

Explanation: **Explanation:** **1. Why Option C is Correct:** Steroid hormones (e.g., Cortisol, Aldosterone, Estrogen, Testosterone) are **lipophilic (hydrophobic)** molecules derived from cholesterol. Because of their lipid solubility, they can easily diffuse through the lipid bilayer of the plasma membrane. Once inside the cell, they bind to specific **intracellular receptors** located either in the cytoplasm or the nucleus. The hormone-receptor complex then acts as a ligand-activated transcription factor, binding to specific DNA sequences called **Hormone Response Elements (HREs)** to regulate gene expression and protein synthesis. **2. Why Other Options are Incorrect:** * **Option A:** This describes the mechanism for **Insulin** and various **Growth Factors** (e.g., IGF-1). These hormones bind to extracellular domains of receptors that have intrinsic enzymatic activity. * **Option B:** This is the **Second Messenger system** used by most peptide hormones (e.g., ACTH, Glucagon, PTH, TSH). These hormones are water-soluble and cannot cross the cell membrane, thus requiring G-protein coupled receptors (GPCRs). * **Option D:** This mechanism is typical for **neurotransmitters** (e.g., Acetylcholine at nicotinic receptors) or certain rapid-acting ligands, not steroid hormones. **3. High-Yield Clinical Pearls for NEET-PG:** * **Exceptions to the Rule:** While most lipid-soluble hormones use intracellular receptors, **Thyroid hormones (T3/T4)** are unique; they enter the cell via carrier-mediated transport but bind to receptors already located on the **chromatin in the nucleus**. * **Speed of Action:** Steroid hormone effects are generally **slow** (hours to days) because they require transcription and translation, unlike the rapid effects of ion channels or GPCRs. * **Mnemonic for Cytoplasmic Receptors:** Remember **"C-A-G-E"** (Cortisol, Aldosterone, Glucocorticoids, Estrogen/Progesterone—though Estrogen/Progesterone are increasingly recognized as primarily nuclear). Vitamin D and Thyroid receptors are strictly **Nuclear**.

Question 435: What happens when the availability of oxygen to tissues decreases?

A. Vasodilation and increase in blood supply to the tissue takes place. (Correct Answer)
B. Vasoconstriction and decrease in blood supply to the tissue takes place.
C. Venoconstriction and increase in tissue perfusion pressure occurs.
D. Venodilation and decrease in tissue perfusion pressure occurs.

Explanation: ### Explanation **1. Why Option A is Correct (The Underlying Concept):** The regulation of local blood flow is primarily governed by the metabolic needs of the tissue. When oxygen availability decreases (**Hypoxia**), tissues shift toward anaerobic metabolism, leading to the accumulation of vasodilator metabolites (such as adenosine, $CO_2$, $H^+$, and $K^+$). According to the **Vasodilator Theory**, these metabolites act directly on the precapillary sphincters and arterioles, causing **vasodilation**. This reduces peripheral resistance, thereby increasing blood flow to the hypoxic area to restore oxygen delivery and "wash out" metabolic byproducts. This is a classic example of **Active Hyperemia**. **2. Why Other Options are Incorrect:** * **Option B:** Vasoconstriction would further decrease oxygen delivery, exacerbating tissue ischemia and leading to necrosis. This is the opposite of the physiological compensatory mechanism. * **Options C & D:** Perfusion pressure is primarily determined by the difference between arterial and venous pressure. While venous tone affects preload, the immediate local response to hypoxia is mediated at the **arteriolar level** (the resistance vessels) to regulate flow, not primarily through changes in venous diameter or systemic perfusion pressure. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **The Exception:** In the **Pulmonary circulation**, hypoxia causes **vasoconstriction** (Hypoxic Pulmonary Vasoconstriction) to shunt blood away from poorly ventilated alveoli to well-ventilated ones. In all other systemic tissues, hypoxia causes vasodilation. * **Adenosine:** This is considered the most important local vasodilator in the **coronary circulation** in response to hypoxia. * **Autoregulation:** The ability of an organ to maintain constant blood flow despite changes in arterial pressure is best seen in the **Brain, Kidneys, and Heart**.

Question 436: Basal metabolic rate (BMR) depends on which of the following factors?

A. Body weight
B. Body surface area
C. Amount of adipose tissue
D. Amount of lean body mass (Correct Answer)

Explanation: **Explanation:** The **Basal Metabolic Rate (BMR)** is the minimum amount of energy required to maintain vital functions (like breathing and circulation) at complete physical and mental rest. **Why Lean Body Mass (LBM) is the correct answer:** The primary determinant of BMR is the amount of **metabolically active tissue** in the body. Lean body mass—which includes skeletal muscle, organs (liver, brain, kidneys), and bone—is highly active and consumes significantly more oxygen and energy than fat. Skeletal muscle alone accounts for a large portion of the BMR; therefore, individuals with higher LBM (e.g., athletes or males) have a higher BMR. **Analysis of Incorrect Options:** * **Body Weight:** While BMR generally increases with weight, total weight is a poor predictor because it does not differentiate between fat and muscle. Two people of the same weight can have vastly different BMRs based on their body composition. * **Body Surface Area (BSA):** Historically, BMR was expressed per square meter of BSA (the "Surface Law"). While heat loss is proportional to surface area, BSA is a *proxy* measurement rather than the underlying physiological driver. LBM remains the most accurate biological determinant. * **Adipose Tissue:** Fat is metabolically sluggish. An increase in adipose tissue (obesity) actually leads to a **decrease** in BMR relative to total body weight. **High-Yield Clinical Pearls for NEET-PG:** * **Thyroid Status:** Thyroid hormones ($T_3$ and $T_4$) are the most important hormonal regulators of BMR. * **Specific Dynamic Action (SDA):** Protein has the highest SDA (30%), meaning it increases metabolic rate the most during digestion. * **Gender & Age:** BMR is higher in males (due to more LBM) and decreases with age (due to sarcopenia/loss of muscle). * **Starvation:** BMR decreases during prolonged fasting as a compensatory mechanism to conserve energy.

Question 437: Thyroid gland function is best monitored by which of the following?

A. Basal metabolic rate (BMR)
B. Thyroxine and tri-iodothyronine uptake
C. Level of thyroid stimulating hormone (Correct Answer)
D. Level of protein bound iodine

Explanation: **Explanation:** The **Serum TSH (Thyroid Stimulating Hormone)** level is considered the most sensitive and specific single test for monitoring thyroid function and screening for thyroid disorders. This is due to the **negative feedback loop** between the pituitary and the thyroid gland. Even minor changes in the levels of free T4 and T3 trigger a logarithmic change in TSH secretion. Therefore, TSH can detect subclinical thyroid dysfunction even when T3 and T4 levels are within the normal reference range. **Analysis of Incorrect Options:** * **Basal Metabolic Rate (BMR):** Historically used, but it is highly non-specific and influenced by numerous factors like anxiety, fever, and drugs. It is no longer used for primary monitoring. * **Thyroxine and Tri-iodothyronine uptake:** These tests measure the binding capacity of thyroid-binding globulin (TBG). While useful in specific contexts (like calculating the Free Thyroxine Index), they do not directly reflect the functional status of the thyroid as accurately as TSH. * **Protein Bound Iodine (PBI):** This is an obsolete test. It measures the total iodine in the blood, which includes both hormonal and non-hormonal iodine, making it unreliable due to interference from dietary iodine or contrast agents. **Clinical Pearls for NEET-PG:** * **Best Screening Test:** Serum TSH. * **Best test for monitoring Levothyroxine replacement:** Serum TSH (target range 0.5–2.5 mIU/L). * **Exception:** In **Secondary (Central) Hypothyroidism**, TSH is unreliable; monitoring must be done using **Free T4** levels. * **Subclinical Hypothyroidism:** Elevated TSH with normal Free T4.

Question 438: Which of the following directly inhibits insulin secretion?

A. Alpha2-adrenergic agonist (Correct Answer)
B. Beta2-adrenergic agonist
C. Cholecystokinin
D. Glucagon

Explanation: **Explanation:** The secretion of insulin by pancreatic beta cells is tightly regulated by the autonomic nervous system and various hormones. **1. Why Alpha2-adrenergic agonists are correct:** The sympathetic nervous system has a dual effect on insulin secretion, but the **inhibitory effect mediated by $\alpha_2$-adrenergic receptors** is dominant. When $\alpha_2$ receptors are stimulated (via norepinephrine or agonists), they couple with $G_i$ proteins, leading to a decrease in intracellular cAMP levels. This inhibits the exocytosis of insulin granules. This mechanism is physiologically vital during exercise or stress (the "fight or flight" response) to prevent hypoglycemia while ensuring adequate glucose is available for the brain and muscles. **2. Why the other options are incorrect:** * **B. Beta2-adrenergic agonist:** Stimulation of $\beta_2$ receptors (via $G_s$ proteins) actually **increases** insulin secretion. However, in a systemic sympathetic discharge, the $\alpha_2$ inhibitory effect overrides the $\beta_2$ stimulatory effect. * **C. Cholecystokinin (CCK):** This is a gastrointestinal hormone (incretin-like effect) that **stimulates** insulin secretion in response to food intake. * **D. Glucagon:** Glucagon has a direct paracrine effect on adjacent beta cells to **stimulate** insulin secretion, ensuring that the glucose released by the liver (via glycogenolysis) can be utilized by peripheral tissues. **High-Yield Clinical Pearls for NEET-PG:** * **Dominant Control:** While Parasympathetic (Vagus/M3) and $\beta_2$ stimulation increase insulin, **$\alpha_2$ stimulation is the most potent physiological inhibitor.** * **Somatostatin:** Produced by Delta ($\delta$) cells, it is a potent paracrine inhibitor of both insulin and glucagon. * **Incretin Effect:** Oral glucose causes a much higher insulin spike than IV glucose due to hormones like GLP-1 and GIP.

Question 439: Which of the following is NOT produced by the ovary?

A. Gonadotropin (Correct Answer)
B. Testosterone
C. Estrogen
D. Inhibin B

Explanation: ### Explanation **1. Why Gonadotropin is the Correct Answer:** Gonadotropins, specifically **Follicle-Stimulating Hormone (FSH)** and **Luteinizing Hormone (LH)**, are peptide hormones synthesized and secreted by the **gonadotroph cells of the anterior pituitary gland**. Their primary role is to stimulate the ovaries (and testes) to produce sex steroids and gametes. Since they are the *stimulators* of the ovary rather than products *of* the ovary, they are the correct answer. **2. Why the Other Options are Incorrect:** * **Estrogen:** This is the primary female sex hormone produced by the **granulosa cells** of the ovarian follicles (via the aromatization of androgens). * **Testosterone:** While often considered a male hormone, the ovary (specifically the **theca cells**) produces androgens like androstenedione and testosterone. Most of this is converted to estrogen, but some is secreted into the systemic circulation. * **Inhibin B:** This is a glycoprotein hormone secreted by the **granulosa cells** of the developing follicles. It provides negative feedback to the anterior pituitary to specifically inhibit FSH secretion. **3. High-Yield Clinical Pearls for NEET-PG:** * **Two-Cell, Two-Gonadotropin Theory:** LH stimulates **Theca cells** to produce androgens (Cholesterol → Androstenedione); FSH stimulates **Granulosa cells** to convert those androgens into Estrogen (via Aromatase). * **Inhibin Markers:** **Inhibin B** is a marker of follicular reserve (produced by small antral follicles), while **Inhibin A** is produced by the corpus luteum. * **Human Chorionic Gonadotropin (hCG):** Although it is a gonadotropin, it is produced by the **syncytiotrophoblast** of the placenta, not the ovary.

Question 440: Which of the following hormones increases with age?

A. Growth Hormone (GH)
B. Prolactin
C. Insulin
D. Luteinizing Hormone (LH) (Correct Answer)

Explanation: **Explanation:** The correct answer is **Luteinizing Hormone (LH)**. This phenomenon is primarily driven by the age-related decline in gonadal function, known as the "somatopause" in men and menopause in women. **1. Why LH increases:** As individuals age, there is a progressive decrease in the production of sex steroids (Estrogen/Progesterone in females and Testosterone in males) due to primary gonadal failure. This loss of negative feedback on the hypothalamic-pituitary-gonadal (HPG) axis leads to a compensatory increase in the secretion of **Gonadotropins**, specifically **LH and FSH**. In post-menopausal women, FSH typically rises more significantly than LH, but both remain elevated compared to reproductive years. **2. Why other options are incorrect:** * **Growth Hormone (GH):** GH secretion declines significantly with age (approximately 14% per decade after age 30), contributing to reduced muscle mass and increased adiposity. * **Prolactin:** Levels generally remain stable or slightly decrease with age, particularly in post-menopausal women due to the lack of estrogenic stimulation on lactotrophs. * **Insulin:** While insulin *resistance* often increases with age, the actual basal secretion of insulin tends to decline due to progressive $\beta$-cell dysfunction and reduced pancreatic mass. **High-Yield Clinical Pearls for NEET-PG:** * **Hormones that Decrease with Age:** GH, Melatonin, DHEA (Dehydroepiandrosterone), Aldosterone, and Testosterone. * **Hormones that Increase with Age:** LH, FSH, PTH (Parathyroid Hormone), Norepinephrine, and Cortisol (slight increase in evening levels). * **Hormones that remain Unchanged:** Thyroid hormones (T3/T4) usually remain in the normal range, though TSH may show a slight upward shift in the elderly.

Practice by Chapter

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Hypothalamus and Pituitary Gland

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Thyroid Physiology

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Pancreatic Hormones and Glucose Metabolism

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Calcium and Phosphate Homeostasis

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Growth Hormone and Growth Factors

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Endocrine Regulation of Metabolism

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Hormone Receptors and Signaling

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Assessment of Endocrine Function

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