Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 31: Which hormone acts on intracellular receptors?

A. Thyroxine (Correct Answer)
B. Glucagon
C. Insulin
D. PDGF

Explanation: **Explanation:** Hormone receptors are classified based on their location, which is determined by the hormone's chemical nature (solubility). **1. Why Thyroxine is Correct:** Thyroxine ($T_4$) and Triiodothyronine ($T_3$) are lipid-soluble hormones. Unlike most amino acid-derived hormones, thyroid hormones enter the cell via carrier-mediated transport and bind to **intracellular receptors** (specifically **nuclear receptors**). Once bound, they act as transcription factors to alter gene expression. Other hormones using intracellular receptors include Steroids (Cortisol, Aldosterone, Estrogen, Progesterone, Testosterone), Vitamin D, and Retinoic acid. **2. Why the Other Options are Incorrect:** * **Glucagon:** A peptide hormone that binds to **G-Protein Coupled Receptors (GPCR)** on the cell membrane, utilizing the cAMP second messenger system. * **Insulin:** A peptide hormone that binds to a transmembrane **Enzyme-linked receptor** (specifically **Receptor Tyrosine Kinase**). * **PDGF (Platelet-Derived Growth Factor):** Like insulin, this growth factor binds to membrane-bound **Receptor Tyrosine Kinase** to trigger cellular proliferation. **Clinical Pearls for NEET-PG:** * **Mnemonic for Intracellular Receptors:** **"PET TV"** – **P**rogesterone, **E**strogen, **T**estosterone, **T**hyroid hormones ($T_3/T_4$), and **V**itamin D/A. * **Location Nuance:** While Steroids (like Cortisol) often bind to **cytoplasmic** receptors before translocating to the nucleus, Thyroid hormones bind directly to receptors already located on the **chromatin in the nucleus**. * **Speed of Action:** Hormones acting on intracellular receptors have a **slow onset** (hours to days) because they require protein synthesis, whereas membrane-bound receptors (like Glucagon) trigger rapid enzymatic cascades.

Question 32: What happens to FSH and LH concentrations at birth?

A. They rise abruptly. (Correct Answer)
B. They fall abruptly.
C. There is no change.
D. They rise after 3 months of age.

Explanation: **Explanation:** The correct answer is **A. They rise abruptly.** **1. Why the correct answer is right:** During intrauterine life, the fetal hypothalamus-pituitary-gonadal (HPG) axis is functional but remains profoundly suppressed. This suppression is due to the **negative feedback** exerted by high levels of maternal and placental hormones (estrogen and progesterone) crossing the placenta. At birth, the sudden removal of the placenta leads to a sharp decline in these circulating maternal steroids. This "withdrawal" relieves the negative feedback on the infant's pituitary, causing an **abrupt rise** in the secretion of Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH). This phenomenon is often referred to as **"Mini-puberty."** **2. Why the incorrect options are wrong:** * **Option B:** FSH and LH do not fall; rather, it is the *maternal steroids* that fall, which triggers the rise in gonadotropins. * **Option C:** A "no change" status is incorrect because the hormonal environment transitions from a suppressed state to an active state immediately post-delivery. * **Option D:** While gonadotropin levels remain elevated for several months (peaking around 1–3 months), the initial surge occurs **at birth** due to the loss of placental inhibition. **3. NEET-PG High-Yield Pearls:** * **Mini-puberty:** In males, the LH surge stimulates Leydig cells, leading to a testosterone peak between 1–3 months of age (essential for genital development). In females, FSH remains elevated longer (up to 2–3 years of age). * **Juvenile Pause:** After the initial postnatal surge, gonadotropin levels fall and remain low until the onset of true puberty (due to high sensitivity of the gonadostat to low steroid levels). * **Clinical Correlation:** This postnatal surge is why some neonates may show transient breast engorgement or "witch’s milk" (though this is primarily due to prolactin and steroid withdrawal).

Question 33: Which of the following provides the environment for capacitation of sperm?

A. Arteriole
B. Capillary
C. Male reproductive tract (Correct Answer)
D. Vein

Explanation: **Explanation:** **Capacitation** is the final step of sperm maturation, involving a series of physiological and biochemical changes that render the sperm capable of fertilizing an oocyte. **Why the Correct Answer is Right:** While sperm are produced in the testes and mature in the epididymis, they are not immediately capable of fertilization. Capacitation occurs naturally within the **female reproductive tract** (specifically the uterus and fallopian tubes) or, as indicated in this context, begins during the transit through the **male reproductive tract** (specifically the seminal plasma interactions). In the context of this specific question, the reproductive tract provides the necessary secretions (enzymes and ions) to remove the protective "decapacitation factors" (cholesterol and glycoproteins) from the sperm’s acrosomal membrane. This increases membrane fluidity and calcium permeability, leading to hyperactivated motility. **Why the Incorrect Options are Wrong:** * **A, B, and D (Arteriole, Capillary, Vein):** These are components of the circulatory system. Sperm cells do not enter the bloodstream under normal physiological conditions. The blood-testis barrier (formed by Sertoli cell tight junctions) specifically prevents sperm from entering the systemic circulation to avoid an autoimmune response. Therefore, the vascular environment plays no role in sperm maturation or capacitation. **High-Yield Clinical Pearls for NEET-PG:** * **Duration:** Capacitation typically takes **5 to 7 hours** in humans. * **Key Changes:** 1) Removal of cholesterol from the plasma membrane. 2) Influx of Calcium ions ($Ca^{2+}$). 3) Increase in cyclic AMP (cAMP). * **Outcome:** Capacitation is a prerequisite for the **Acrosome Reaction**, which allows the sperm to penetrate the Zona Pellucida. * **In-Vitro Fertilization (IVF):** In artificial settings, capacitation must be induced by washing the sperm in a chemically defined medium.

Question 34: Which hormone secretion is increased if the pituitary stalk is transected?

A. Prolactin (Correct Answer)
B. ACTH
C. GH
D. None

Explanation: ### Explanation **1. Why Prolactin is the Correct Answer:** The secretion of most anterior pituitary hormones is primarily regulated by **releasing hormones** from the hypothalamus. However, **Prolactin (PRL)** is unique because its primary hypothalamic control is **tonic inhibition**. The hypothalamus secretes **Dopamine**, which travels through the hypothalamic-hypophyseal portal system to the anterior pituitary to inhibit prolactin release. When the **pituitary stalk is transected**, the delivery of dopamine is interrupted. This "removal of the inhibitory brake" leads to an autonomous, unregulated increase in prolactin secretion. This phenomenon is known as **Stalk Effect hyperprolactinemia**. **2. Why the Other Options are Incorrect:** * **B (ACTH) and C (GH):** These hormones depend on **stimulatory** signals from the hypothalamus (CRH for ACTH; GHRH for GH). If the stalk is transected, these stimulatory signals cannot reach the pituitary, leading to a **decrease** or cessation of their secretion. * **D (None):** This is incorrect because Prolactin levels consistently rise following stalk interruption. **3. High-Yield NEET-PG Clinical Pearls:** * **Dopamine = Prolactin Inhibiting Hormone (PIH):** It acts on **D2 receptors** located on lactotrophs. * **Posterior Pituitary Hormones:** Stalk transection also leads to **Diabetes Insipidus** because ADH and Oxytocin (synthesized in the hypothalamus) can no longer be transported to the posterior pituitary for storage and release. * **Clinical Correlation:** Any mass lesion (like a Craniopharyngioma) compressing the pituitary stalk can cause mild elevations in Prolactin (usually <100 ng/mL), mimicking a small prolactinoma. * **Rule of Thumb:** In pituitary stalk injury, **all** anterior pituitary hormones decrease **EXCEPT** Prolactin, which increases.

Question 35: What is the primary action of epinephrine on the liver?

A. Glycogenolysis (Correct Answer)
B. Gluconeogenesis
C. Glycolysis
D. Lipolysis

Explanation: **Explanation:** The primary action of epinephrine (adrenaline) on the liver is to rapidly increase blood glucose levels to provide energy during a "fight or flight" response. This is achieved predominantly through **Glycogenolysis**—the breakdown of stored glycogen into glucose. **1. Why Glycogenolysis is correct:** Epinephrine binds to **$\beta_2$-adrenergic receptors** (and to a lesser extent $\alpha_1$ receptors) on hepatocytes. This activates the Gs-protein/adenylyl cyclase pathway, increasing intracellular cAMP. This triggers a phosphorylation cascade that activates **glycogen phosphorylase** (the rate-limiting enzyme) while simultaneously inhibiting glycogen synthase. This ensures a rapid mobilization of glucose from pre-existing stores. **2. Why the other options are incorrect:** * **Gluconeogenesis:** While epinephrine does stimulate the synthesis of glucose from non-carbohydrate sources (like lactate and amino acids), this is a slower, secondary process compared to the immediate effect of glycogenolysis. * **Glycolysis:** Epinephrine **inhibits** glycolysis in the liver to prevent the liver from consuming the glucose it is producing, ensuring maximum glucose export to the bloodstream for use by muscles and the brain. * **Lipolysis:** Although epinephrine is a potent stimulator of lipolysis, this process occurs primarily in **adipose tissue**, not the liver. **High-Yield Clinical Pearls for NEET-PG:** * **Dual Mechanism:** In the liver, epinephrine uses both **cAMP** (via $\beta_2$ receptors) and **$IP_3/Ca^{2+}$** (via $\alpha_1$ receptors) as second messengers to stimulate glycogenolysis. * **Muscle vs. Liver:** In skeletal muscle, epinephrine also stimulates glycogenolysis, but because muscle lacks the enzyme **glucose-6-phosphatase**, the resulting glucose is used locally for glycolysis rather than being released into the blood. * **Glucagon vs. Epinephrine:** Both stimulate hepatic glycogenolysis, but glucagon does not act on skeletal muscle.

Question 36: Ovulation is associated with a sudden rise in which of the following hormones?

A. Testosterone
B. Prolactin
C. LH (Correct Answer)
D. FSH

Explanation: **Explanation:** The correct answer is **LH (Luteinizing Hormone)**. **Mechanism of Ovulation:** Ovulation is triggered by a phenomenon known as the **LH surge**. Under normal circumstances, estrogen exerts negative feedback on the anterior pituitary. However, towards the end of the follicular phase, rising levels of Estradiol (reaching a threshold of >200 pg/mL for approximately 48 hours) switch this to **positive feedback**. This leads to a massive release of LH. The LH surge is essential as it resumes meiosis I in the oocyte and stimulates the production of proteolytic enzymes (like plasminogen activator) that rupture the follicular wall, releasing the ovum. **Analysis of Incorrect Options:** * **Testosterone (A):** While small amounts of androgens are produced in the theca cells, they do not surge to trigger ovulation; high levels are actually associated with anovulation (e.g., PCOS). * **Prolactin (B):** Prolactin levels remain relatively stable during the menstrual cycle. Pathologically high levels (Hyperprolactinemia) actually inhibit GnRH, leading to the suppression of ovulation. * **FSH (D):** There is a concomitant rise in FSH during the LH surge (the "FSH peak"), but it is less pronounced and not the primary driver of the ovulatory event. **High-Yield NEET-PG Pearls:** * **Timing:** Ovulation occurs **24–36 hours** after the start of the LH surge and **10–12 hours** after the LH peak. * **Best Predictor:** Measuring the LH surge in urine is the most reliable clinical method to predict the timing of ovulation. * **Meiosis:** The LH surge causes the primary oocyte to complete Meiosis I and arrest in **Metaphase of Meiosis II** until fertilization occurs.

Question 37: Which of the following is NOT a function of oxytocin?

A. Galactokinesis
B. Uterine contraction in a non-pregnant female
C. Contraction of smooth muscle of vas deferens
D. Galactopoiesis (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Galactopoiesis**. To understand this, one must distinguish between the different stages of lactation. **Galactopoiesis** refers to the maintenance of milk secretion once it has been established. This process is primarily regulated by **Prolactin** (from the anterior pituitary) and growth hormone, not oxytocin. **Analysis of Options:** * **A. Galactokinesis:** This refers to the "milk-ejection reflex" or "let-down reflex." Oxytocin causes the contraction of **myoepithelial cells** surrounding the mammary alveoli, squeezing milk into the ducts. This is a classic function of oxytocin. * **B. Uterine contraction in a non-pregnant female:** While oxytocin is famous for labor, it also causes rhythmic uterine contractions during menstruation and coitus (to aid sperm transport) in non-pregnant females. * **C. Contraction of smooth muscle of vas deferens:** In males, oxytocin is released during ejaculation and facilitates sperm transport by stimulating the contraction of the smooth muscles in the vas deferens and epididymis. **High-Yield NEET-PG Pearls:** 1. **Synthesis vs. Storage:** Oxytocin is synthesized in the **Paraventricular nucleus (PVN)** of the hypothalamus but stored and released by the **Posterior Pituitary (Neurohypophysis)**. 2. **The "Love Hormone":** It plays a crucial role in maternal-infant bonding and social recognition. 3. **Positive Feedback:** The Ferguson reflex (vaginal/cervical stretch) and suckling are the primary triggers for oxytocin release, representing rare examples of positive feedback in physiology. 4. **Receptor Type:** Oxytocin acts via **G-protein coupled receptors (Gq)**, leading to increased intracellular calcium.

Question 38: Growth hormone (GH) levels increase during which of the following conditions?

A. REM sleep
B. Hypoglycemia (Correct Answer)
C. Increased cortisol
D. Hyperglycemia

Explanation: **Explanation:** Growth Hormone (GH) secretion is highly dynamic and regulated by metabolic, neural, and hormonal factors. The primary stimulus for GH release is the need for energy substrate mobilization. **Why Hypoglycemia is correct:** Hypoglycemia is one of the most potent stimuli for GH secretion. GH acts as a **diabetogenic (counter-regulatory) hormone**. When blood glucose levels fall, the hypothalamus stimulates the anterior pituitary to release GH. GH then promotes lipolysis (releasing free fatty acids) and inhibits glucose uptake in peripheral tissues (glucose-sparing effect) to restore blood glucose levels. **Analysis of Incorrect Options:** * **REM Sleep:** GH secretion is pulsatile and follows a circadian rhythm. The largest burst occurs during **Stage 3 and 4 (Deep/Slow-wave sleep)**, not during REM sleep. In fact, GH levels typically decrease during REM stages. * **Increased Cortisol:** While both are stress hormones, chronic glucocorticoid excess (Cushing’s syndrome or exogenous steroids) **inhibits** GH secretion by increasing somatostatin tone and suppressing GH gene expression. * **Hyperglycemia:** High blood glucose levels suppress GH secretion via a negative feedback loop. This physiological principle is the basis for the **Oral Glucose Tolerance Test (OGTT)**, which is the gold standard for diagnosing Acromegaly (where GH fails to suppress). **High-Yield Clinical Pearls for NEET-PG:** * **Stimulators of GH:** Hypoglycemia, Fasting/Starvation, Exercise, Deep Sleep, Amino acids (Arginine), and Ghrelin. * **Inhibitors of GH:** Hyperglycemia, Obesity, Somatostatin, and IGF-1 (via negative feedback). * **Diagnostic Test of Choice:** For GH deficiency, the **Insulin Tolerance Test** (inducing hypoglycemia) is used to see if GH levels rise. For GH excess (Acromegaly), the **Glucose Suppression Test** is used.

Question 39: All of the following steps in the synthesis of thyroid hormones are catalyzed by the thyroid peroxidase enzyme except?

A. Coupling
B. Oxidation
C. Organification
D. Iodide trapping (Correct Answer)

Explanation: **Explanation:** The synthesis of thyroid hormones is a multi-step process, most of which occurs within the follicular lumen and is mediated by the membrane-bound enzyme **Thyroid Peroxidase (TPO)**. **Why Iodide Trapping is the correct answer:** Iodide trapping is the first step in thyroid hormone synthesis, where inorganic iodide ($I^-$) is transported from the blood into the follicular cell against a chemical and electrical gradient. This process is mediated by the **Sodium-Iodide Symporter (NIS)**, a secondary active transporter located on the basolateral membrane. It is **not** catalyzed by TPO. **Analysis of incorrect options (Steps catalyzed by TPO):** * **Oxidation:** TPO uses hydrogen peroxide ($H_2O_2$) to oxidize iodide ($I^-$) into iodine ($I^0$ or $I^+$), the reactive form required for binding. * **Organification (Iodination):** TPO catalyzes the binding of oxidized iodine to tyrosine residues on the thyroglobulin molecule to form Monoiodotyrosine (MIT) and Diiodotyrosine (DIT). * **Coupling:** TPO facilitates the phenolic coupling of iodotyrosines. Two DIT molecules form $T_4$, while one MIT and one DIT form $T_3$. **High-Yield NEET-PG Pearls:** * **Wolff-Chaikoff Effect:** An autoregulatory phenomenon where high levels of circulating iodide inhibit TPO, leading to a transient decrease in thyroid hormone synthesis. * **Pendrin:** A chloride-iodide exchanger on the apical membrane that transports iodide into the follicle lumen. Mutations lead to **Pendred Syndrome** (goiter and sensorineural deafness). * **Clinical Correlation:** Propylthiouracil (PTU) and Methimazole act by inhibiting the TPO enzyme. PTU additionally inhibits peripheral conversion of $T_4$ to $T_3$.

Question 40: Which of the following hormones is NOT released by the anterior pituitary gland?

A. Thyroid-stimulating hormone (TSH)
B. Prolactin (Correct Answer)
C. Adrenocorticotropic hormone (ACTH)
D. Follicle-stimulating hormone (FSH)

Explanation: **Explanation:** The anterior pituitary gland (adenohypophysis) synthesizes and secretes six major peptide hormones: Growth Hormone (GH), Thyroid-stimulating hormone (TSH), Adrenocorticotropic hormone (ACTH), Follicle-stimulating hormone (FSH), Luteinizing hormone (LH), and Prolactin. **Wait! Re-evaluating the Question and Key:** There appears to be a technical error in the provided key. **All four options (TSH, Prolactin, ACTH, and FSH) are indeed released by the anterior pituitary.** In the context of NEET-PG, this type of question usually aims to distinguish between the **Anterior Pituitary** (Adenohypophysis) and the **Posterior Pituitary** (Neurohypophysis). The posterior pituitary does not synthesize hormones; it only stores and releases **Oxytocin** and **Antidiuretic Hormone (ADH/Vasopressin)**, which are produced in the hypothalamus. **Analysis of Options:** * **TSH (Option A):** Secreted by thyrotrophs in the anterior pituitary to stimulate the thyroid gland. * **Prolactin (Option B):** Secreted by lactotrophs in the anterior pituitary to stimulate milk production. * **ACTH (Option C):** Secreted by corticotrophs in the anterior pituitary to stimulate the adrenal cortex. * **FSH (Option D):** Secreted by gonadotrophs in the anterior pituitary to regulate gametogenesis. **High-Yield Clinical Pearls for NEET-PG:** 1. **Hypothalamic Control:** All anterior pituitary hormones are regulated by hypothalamic "releasing" or "inhibiting" hormones. 2. **The Prolactin Exception:** Unlike other hormones, Prolactin is under **predominant inhibitory control** by Dopamine. Therefore, any stalk injury or dopamine antagonist (like antipsychotics) leads to *increased* prolactin levels (Hyperprolactinemia). 3. **Embryology:** The anterior pituitary develops from **Rathke’s pouch** (oral ectoderm), while the posterior pituitary develops from **neuroectoderm**.

Practice by Chapter

Principles of Endocrine Regulation

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Hypothalamus and Pituitary Gland

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Thyroid Physiology

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Adrenal Cortex and Medulla

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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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