Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 561: Human growth hormone has which of the following structural features?

A. One polypeptide chain and one intrachain disulfide bond
B. One polypeptide chain and two intrachain disulfide bonds (Correct Answer)
C. Two polypeptide chains joined by one disulfide bond
D. Two polypeptide chains joined by two disulfide bonds

Explanation: **Explanation:** Human Growth Hormone (hGH), also known as somatotropin, is a protein hormone synthesized and secreted by the somatotrophs of the anterior pituitary. **1. Why Option B is correct:** Structurally, hGH is a single-chain polypeptide consisting of **191 amino acids**. It contains **two internal (intrachain) disulfide bridges** that are crucial for maintaining its three-dimensional tertiary structure and biological activity. These bridges connect specific cysteine residues (Cys-53 to Cys-165 and Cys-182 to Cys-189), creating loops within the single chain. **2. Why the other options are incorrect:** * **Option A:** While hGH is a single chain, it has two disulfide bonds, not one. * **Options C & D:** These describe multimeric proteins. For example, **Insulin** consists of two polypeptide chains (A and B) joined by two interchain disulfide bonds (and one intrachain bond in the A chain). Growth hormone does not have a subunit structure; it is monomeric. **High-Yield Clinical Pearls for NEET-PG:** * **Gene Location:** The hGH gene is located on **Chromosome 17**. * **Homology:** hGH shares significant structural homology with **Prolactin** and **Human Placental Lactogen (hPL)**; all three belong to the "somatotropin family." * **Pulsatility:** Secretion is highly pulsatile, with the largest burst occurring during **Stage 3 or 4 (N3) Non-REM sleep**. * **Metabolic Effect:** It is a "diabetogenic" hormone because it causes insulin resistance and decreases glucose uptake in peripheral tissues. * **Mediator:** Most of its growth-promoting effects are mediated by **IGF-1 (Somatomedin C)**, produced primarily in the liver.

Question 562: What is the function of incretin?

A. Increased heart rate
B. Increased insulin secretion (Correct Answer)
C. Increased respiratory rate
D. Stimulate erythropoiesis

Explanation: **Explanation:** **Incretins** are gut-derived hormones, primarily **Glucagon-like peptide-1 (GLP-1)** and **Glucose-dependent insulinotropic polypeptide (GIP)**. They are secreted by the enteroendocrine cells (L-cells and K-cells) of the small intestine in response to nutrient ingestion. 1. **Why Option B is Correct:** The "Incretin Effect" describes the phenomenon where oral glucose triggers a significantly higher insulin response compared to an equivalent dose of intravenous glucose. Incretins bind to receptors on pancreatic beta cells, stimulating **glucose-dependent insulin secretion**. They also suppress glucagon release and slow gastric emptying, helping to maintain postprandial glycemic control. 2. **Why Incorrect Options are Wrong:** * **Option A & C:** Heart rate and respiratory rate are primarily regulated by the autonomic nervous system and chemoreceptors. Incretins do not have a primary physiological role in cardiorespiratory stimulation. * **Option D:** Erythropoiesis is stimulated by Erythropoietin (EPO), produced mainly by the peritubular interstitial cells of the kidneys in response to hypoxia. **High-Yield Clinical Pearls for NEET-PG:** * **DPP-4 Inhibitors (e.g., Sitagliptin):** These drugs prevent the breakdown of endogenous GLP-1, prolonging its half-life. * **GLP-1 Agonists (e.g., Liraglutide, Exenatide):** These are injectable analogs used in Type 2 Diabetes that also promote weight loss. * **Key Difference:** Unlike sulfonylureas, the insulinotropic action of incretins is **glucose-dependent**, meaning they carry a much lower risk of hypoglycemia. * **Site of Secretion:** GLP-1 (L-cells of ileum/colon); GIP (K-cells of duodenum/jejunum).

Question 563: What is the level of prolactin above which hyperprolactinemia is diagnosed?

A. 50 ng/mL
B. 100 ng/mL
C. 150 ng/mL
D. 200 ng/mL (Correct Answer)

Explanation: **Explanation:** In clinical physiology and endocrinology, while the normal upper limit for serum prolactin is typically around **20–25 ng/mL**, the diagnostic threshold for a **prolactinoma** (specifically a macroprolactinoma) is significantly higher. **1. Why Option D (200 ng/mL) is Correct:** A serum prolactin level **>200 ng/mL** is considered diagnostic for a prolactin-secreting pituitary adenoma. At these levels, the elevation is almost always due to a primary secretory tumor rather than secondary causes. Levels between 100–200 ng/mL are suggestive, but >200 ng/mL provides high specificity for the diagnosis. **2. Why the other options are incorrect:** * **Option A (50 ng/mL):** This level represents mild hyperprolactinemia. It is commonly seen in physiological states (pregnancy, breastfeeding, stress) or due to "stalk effect" (compression of the pituitary stalk preventing dopamine from reaching the lactotrophs). * **Option B (100 ng/mL):** This is a "gray zone." While abnormal, it can be caused by various drugs (antipsychotics like risperidone, metoclopramide) or primary hypothyroidism. * **Option C (150 ng/mL):** Though highly suspicious of a microadenoma, it does not meet the classic diagnostic threshold of 200 ng/mL used to definitively identify a prolactinoma in standard medical examinations. **High-Yield Clinical Pearls for NEET-PG:** * **The Hook Effect:** In cases of massive macroprolactinomas, extremely high prolactin levels can saturate the assay, leading to a falsely low reading. Dilution of the sample is required for an accurate result. * **Drug of Choice:** **Cabergoline** (a dopamine agonist) is the first-line treatment for both micro and macroprolactinomas, preferred over Bromocriptine due to better efficacy and fewer side effects. * **Stalk Effect:** Any lesion compressing the pituitary stalk (e.g., Craniopharyngioma) causes mild hyperprolactinemia (usually <100 ng/mL) because it blocks the inhibitory action of **Dopamine** (the Prolactin Inhibiting Factor).

Question 564: Insulin secretion is inhibited by which of the following substances?

A. Secretin
B. Epinephrine (Correct Answer)
C. Growth hormone
D. Gastrin

Explanation: **Explanation:** Insulin secretion is primarily regulated by the autonomic nervous system and gastrointestinal hormones. **Why Epinephrine is correct:** Epinephrine (and Norepinephrine) acts as a potent inhibitor of insulin secretion. This occurs via the activation of **$\alpha_2$-adrenergic receptors** on the pancreatic beta cells. During "fight or flight" situations or exercise, the body needs to maintain high blood glucose levels for the brain and muscles. By inhibiting insulin, epinephrine prevents glucose storage and promotes hyperglycemia. While catecholamines can also bind to $\beta_2$ receptors (which stimulate insulin), the **$\alpha_2$ inhibitory effect is dominant.** **Why the other options are incorrect:** * **Secretin & Gastrin (Options A & D):** These are gastrointestinal hormones (Incretins). The "Incretin effect" explains why oral glucose causes a greater insulin spike than intravenous glucose. Both Secretin and Gastrin, along with GIP and GLP-1, **stimulate** insulin secretion in anticipation of rising blood glucose. * **Growth Hormone (Option C):** While GH is a counter-regulatory hormone that causes insulin resistance in peripheral tissues (diabetogenic effect), it actually **stimulates** the synthesis and secretion of insulin from the pancreas to compensate for the rising blood sugar. **High-Yield Clinical Pearls for NEET-PG:** * **Dominant Stimulus:** The most potent stimulator of insulin is **Glucose**. * **Receptor Logic:** * $\alpha_2$ stimulation = **Inhibition** of insulin. * $\beta_2$ stimulation / Parasympathetic (Vagus/ACh) = **Stimulation** of insulin. * **Somatostatin:** Produced by Delta cells, it is a potent universal inhibitor of both insulin and glucagon. * **Potassium Channels:** Insulin release is triggered by the **closure** of ATP-sensitive $K^+$ channels, leading to depolarization and $Ca^{2+}$ influx.

Question 565: Which among the following is a true statement about Thymosin?

A. A pituitary hormone that regulates thymic development
B. A glycoprotein that confers passive immunity to non-sensitized hosts
C. An antiserum against thymocytes
D. A thymic hormone that induces maturation of pre-T cells (Correct Answer)

Explanation: **Explanation:** **1. Why Option D is Correct:** Thymosin is a primary polypeptide hormone secreted by the **epithelial reticular cells** of the thymus gland. Its fundamental physiological role is to stimulate the **differentiation, development, and maturation of T-lymphocytes**. It acts on "immature" or pre-T cells (prothymocytes) that have migrated from the bone marrow to the thymus, transforming them into immunocompetent, antigen-specific T-cells. This process is essential for maintaining **cell-mediated immunity**. **2. Why Other Options are Incorrect:** * **Option A:** Thymosin is an **endocrine secretion of the thymus**, not the pituitary. While the pituitary (Growth Hormone) can influence thymic size, it does not secrete Thymosin. * **Option B:** Thymosin is a peptide/protein, but it confers **active immunity** by training the host's own immune system. Passive immunity involves the transfer of pre-formed antibodies (e.g., IgA in colostrum). * **Option C:** An antiserum against thymocytes is known as **Anti-Thymocyte Globulin (ATG)**, which is a pharmacological preparation used for immunosuppression, not a physiological hormone. **3. High-Yield NEET-PG Pearls:** * **Thymic Involution:** The thymus is most active during childhood and undergoes **age-related atrophy** (replaced by fat) after puberty, leading to decreased thymosin levels in the elderly. * **Hassall’s Corpuscles:** These are characteristic histological features of the thymic medulla involved in T-cell education. * **DiGeorge Syndrome:** A congenital condition (22q11 deletion) where thymic hypoplasia leads to T-cell deficiency and recurrent infections. * **Other Thymic Hormones:** Besides Thymosin, the gland secretes **Thymopoietin** and **Thymulin**, which also aid in T-cell lymphopoiesis.

Question 566: Following trauma, which hormone is NOT released?

A. Thyroxine (Correct Answer)
B. Glucagon
C. ADH
D. GH

Explanation: **Explanation:** The metabolic response to trauma and surgery is characterized by a "neuroendocrine stress response" aimed at mobilizing energy substrates and maintaining hemodynamic stability. **Why Thyroxine (A) is the correct answer:** During acute trauma or critical illness, the body often enters a state known as **Euthyroid Sick Syndrome** (Non-Thyroidal Illness Syndrome). In this state, there is a decrease in the peripheral conversion of T4 to the active T3, and levels of **Thyroxine (T4) typically remain normal or decrease** in severe cases. Unlike stress hormones, thyroxine does not play an acute role in the immediate metabolic response to injury; therefore, it is not "released" or elevated as a result of trauma. **Why the other options are incorrect:** * **Glucagon (B):** Trauma triggers a catabolic state. Glucagon levels rise significantly to promote glycogenolysis and gluconeogenesis, leading to "stress hyperglycemia." * **ADH (C):** Also known as Vasopressin, ADH is released in response to pain, stress, and potential hypovolemia (blood loss) to conserve water and maintain blood pressure. * **GH (D):** Growth Hormone levels rise acutely after trauma. While GH is normally anabolic, in the context of stress, it contributes to insulin resistance and the mobilization of free fatty acids. **NEET-PG High-Yield Pearls:** * **Hormones that INCREASE in trauma:** Catecholamines (first to rise), Cortisol, Glucagon, GH, ADH, Prolactin, and Renin-Angiotensin-Aldosterone. * **Hormones that DECREASE in trauma:** Insulin (or relative resistance), Testosterone, and T3 (due to decreased peripheral conversion). * **Key Concept:** The primary goal of the stress response is to provide glucose to the brain and heart at the expense of peripheral tissues.

Question 567: Deficiency of cortisol causes which of the following conditions?

A. Cushing syndrome
B. Graves disease
C. Addison disease (Correct Answer)
D. Acromegaly

Explanation: **Explanation:** The correct answer is **Addison disease**. This condition, also known as primary adrenal insufficiency, occurs due to the destruction or dysfunction of the adrenal cortex, leading to a deficiency of **cortisol** and often aldosterone. In response to low cortisol, the pituitary gland increases ACTH production; since ACTH is derived from Pro-opiomelanocortin (POMC), it leads to increased alpha-MSH, causing the characteristic hyperpigmentation seen in these patients. **Analysis of Incorrect Options:** * **Cushing Syndrome:** This is the clinical state resulting from **excessive** levels of cortisol (hypercortisolism), the exact opposite of the question's premise. * **Graves Disease:** This is an autoimmune disorder characterized by hyperthyroidism due to thyroid-stimulating immunoglobulins (TSI) that mimic TSH. It is unrelated to cortisol levels. * **Acromegaly:** This condition is caused by the **excessive secretion of Growth Hormone (GH)**, usually from a pituitary adenoma, occurring after the closure of epiphyseal plates. **High-Yield NEET-PG Pearls:** * **Waterhouse-Friderichsen Syndrome:** Acute adrenal insufficiency caused by adrenal hemorrhage, typically secondary to *Neisseria meningitidis* septicemia. * **Cosyntropin Stimulation Test:** The gold standard diagnostic test for adrenal insufficiency (failure of cortisol to rise after ACTH administration). * **Electrolyte Triad in Addison’s:** Hyponatremia, Hyperkalemia, and Metabolic Acidosis (due to concomitant aldosterone deficiency). * **Secondary Adrenal Insufficiency:** Caused by pituitary dysfunction (low ACTH); unlike primary Addison’s, there is **no hyperpigmentation** and mineralocorticoid levels are usually normal.

Question 568: In a seriously ill patient, the addition of amino acids to the diet results in a positive nitrogen balance. What is the primary mechanism for this?

A. Increased growth hormone secretion
B. Enhanced rate of gluconeogenesis
C. Increased absorption of amino acids from the diet
D. Increased secretion of insulin (Correct Answer)

Explanation: ### Explanation The primary mechanism behind a positive nitrogen balance following amino acid administration is the **anabolic action of insulin**. **1. Why Option D is Correct:** Amino acids (especially arginine and leucine) are potent secretagogues for the pancreas. When amino acids enter the bloodstream, they trigger the **secretion of insulin**. Insulin is the body’s primary anabolic hormone; it promotes the uptake of amino acids into skeletal muscle and stimulates protein synthesis while simultaneously inhibiting protein degradation (proteolysis). By shifting the metabolic balance toward protein accretion, insulin ensures that nitrogen intake exceeds nitrogen excretion, resulting in a **positive nitrogen balance**. **2. Why Other Options are Incorrect:** * **Option A:** While Growth Hormone (GH) is anabolic, its secretion is primarily stimulated by hypoglycemia or GHRH. While certain amino acids can stimulate GH, insulin is the more immediate and dominant driver of protein synthesis in response to dietary intake. * **Option B:** Gluconeogenesis is a catabolic process where amino acids are broken down to produce glucose. This would lead to a *negative* nitrogen balance as the amino group is excreted as urea. * **Option C:** Increased absorption simply makes the amino acids available in the portal circulation; it does not dictate their metabolic fate. The "mechanism" for nitrogen retention lies in how the body *utilizes* those absorbed nutrients via hormonal signaling. **High-Yield Facts for NEET-PG:** * **Positive Nitrogen Balance:** Seen in growth, pregnancy, and recovery from illness. * **Negative Nitrogen Balance:** Seen in starvation, severe burns, fever, and untreated diabetes mellitus. * **Insulin vs. GH:** Insulin is required for the anabolic effects of GH. In the absence of insulin (e.g., Type 1 Diabetes), GH cannot promote growth (the "permissive" effect). * **Key Stimulants for Insulin:** Glucose is the strongest, followed by amino acids and GIP (Incretins).

Question 569: Secretion of estrogen is maximum at which point in the menstrual cycle?

A. Just before menopause
B. At puberty
C. At menstruation
D. Before ovulation (Correct Answer)

Explanation: **Explanation:** In a typical 28-day menstrual cycle, estrogen levels exhibit a **bimodal pattern**, characterized by two distinct peaks. 1. **The Primary (Maximum) Peak:** This occurs roughly **24–36 hours before ovulation** (late follicular phase). Under the influence of FSH, developing follicles secrete increasing amounts of estradiol. The dominant follicle eventually produces a massive surge of estrogen (reaching >200 pg/mL), which triggers the **LH surge** via positive feedback. This is the absolute highest point of estrogen secretion in the cycle. 2. **The Secondary Peak:** This occurs during the **mid-luteal phase**. After ovulation, the corpus luteum secretes both progesterone and estrogen, but this peak is lower than the pre-ovulatory one. **Analysis of Incorrect Options:** * **A. Just before menopause:** Estrogen levels fluctuate wildly but generally decline during perimenopause due to the depletion of ovarian follicles. * **B. At puberty:** While estrogen increases during puberty (leading to thelarche), it does not reach its physiological maximum until regular ovulatory cycles are established. * **C. At menstruation:** This is the point where estrogen and progesterone levels are at their **nadir** (lowest). The withdrawal of these hormones triggers the shedding of the endometrial lining. **High-Yield NEET-PG Pearls:** * **Estrogen Source:** Granulosa cells (via the "Two-Cell, Two-Gonadotropin" theory). * **Positive Feedback:** Estrogen is unique because it usually exerts negative feedback on the pituitary, but at high concentrations (>200 pg/mL for >48 hours), it switches to **positive feedback**, triggering the LH surge. * **Inhibin B** peaks in the follicular phase, while **Inhibin A** peaks in the luteal phase.

Question 570: Which of the following statements is NOT true about the pituitary gland?

A. It lies in the sella turcica.
B. Corticotrophs are acidophilic. (Correct Answer)
C. ADH is secreted by the posterior lobe.
D. The anterior lobe develops from Rathke's pouch.

Explanation: ### Explanation **1. Why Option B is the Correct Answer (The False Statement):** In the anterior pituitary (adenohypophysis), cells are classified based on their staining characteristics into **Acidophils**, **Basophils**, and **Chromophobes**. * **Acidophils** (stain red/pink) include **Somatotrophs** (GH) and **Lactotrophs** (Prolactin). * **Basophils** (stain blue/purple) include **Corticotrophs** (ACTH), **Thyrotrophs** (TSH), and **Gonadotrophs** (FSH/LH). Therefore, Corticotrophs are **Basophilic**, not acidophilic. A common mnemonic to remember this is **"B-FLAT"** (Basophils = FSH, LH, ACTH, TSH) and **"GPA"** (Growth hormone, Prolactin = Acidophils). **2. Analysis of Other Options:** * **Option A:** The pituitary gland sits in the **hypophyseal fossa** of the **sella turcica** (a saddle-shaped depression in the sphenoid bone). This is a fundamental anatomical fact. * **Option C:** The posterior pituitary (neurohypophysis) stores and releases **ADH (Vasopressin)** and **Oxytocin**. While these hormones are synthesized in the hypothalamus (supraoptic and paraventricular nuclei), they are "secreted" into the systemic circulation from the posterior lobe. * **Option D:** Embryologically, the anterior pituitary arises from **Rathke’s pouch** (an upward evagination of oral ectoderm), whereas the posterior pituitary develops from a downward extension of the neuroectoderm (diencephalon). **3. Clinical Pearls for NEET-PG:** * **Craniopharyngioma:** The most common suprasellar tumor in children, derived from remnants of **Rathke’s pouch**. It often shows calcification on imaging. * **Blood Supply:** The anterior pituitary is supplied by the **hypophyseal portal system**, making it highly susceptible to ischemic necrosis (e.g., **Sheehan Syndrome** post-partum). * **Surgical Access:** The preferred surgical route to the pituitary gland is the **Trans-sphenoidal approach**.

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Hypothalamus and Pituitary Gland

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