Endocrinology — MCQs
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Which hormone inhibits both FSH and LH?
Which of the following is associated with a reduction of cAMP in the serum?
The provided diagram shows the adrenal gland. Identify the hormone produced from the area labeled 'A'.
Which of the following is both synthesized and stored in the hypothalamus?
Which finding would be present following selective destruction of Sertoli cells?
Vasopressin is secreted by which nucleus of the hypothalamus?
Obesity is ordinarily associated with low ghrelin levels. Which of the following conditions is an exception where obesity is associated with high ghrelin levels?
Cholecystokinin is mainly secreted by which part of the gastrointestinal tract?
Hypercalcemia is caused by all of the following except?
Lesion of which hypothalamic nuclei leads to loss of circadian rhythm?
Endocrinology Indian Medical PG Practice Questions and MCQs
Question 501: Which hormone inhibits both FSH and LH?
- A. Cortisol
- B. Aldosterone
- C. Estrogen (Correct Answer)
- D. Progesterone
Explanation: **Explanation:** The regulation of the hypothalamic-pituitary-ovarian (HPO) axis relies on a negative feedback mechanism. **Estrogen**, primarily secreted by the developing ovarian follicles, exerts a potent **negative feedback** effect on both the hypothalamus (decreasing GnRH pulse frequency) and the anterior pituitary. This results in the inhibition of both **Follicle-Stimulating Hormone (FSH)** and **Luteinizing Hormone (LH)** during most of the menstrual cycle (specifically the follicular phase). *Note: While estrogen can exert positive feedback leading to the LH surge, this only occurs when levels remain high for a sustained period (>200 pg/mL for ~48 hours) just before ovulation.* **Analysis of Incorrect Options:** * **Cortisol (A):** While chronic hypercortisolism (Cushing’s) can suppress the HPO axis, it is not the primary physiological regulator of FSH/LH. * **Aldosterone (B):** This mineralocorticoid regulates sodium and water balance via the Renin-Angiotensin-Aldosterone System (RAAS) and has no direct inhibitory effect on gonadotropins. * **Progesterone (D):** Progesterone primarily inhibits LH (by decreasing GnRH pulse frequency) during the luteal phase. However, its inhibitory effect on FSH is significantly weaker than that of estrogen and usually requires the synergistic presence of estrogen to be effective. **High-Yield Clinical Pearls for NEET-PG:** * **Inhibin B** specifically inhibits FSH (not LH) and is a marker of ovarian reserve. * **Negative Feedback:** Low/Moderate Estrogen → ↓ FSH & ↓ LH. * **Positive Feedback:** High Estrogen (Threshold effect) → ↑ LH (Surge) & ↑ FSH. * **Combined Oral Contraceptive Pills (OCPs)** work on this exact principle: providing exogenous estrogen and progestin to inhibit FSH/LH, thereby preventing ovulation.
Question 502: Which of the following is associated with a reduction of cAMP in the serum?
- A. Glucagon
- B. Somatostatin (Correct Answer)
- C. Thyroxine
- D. Prolactin
Explanation: **Explanation:** The correct answer is **Somatostatin**. The mechanism of action for various hormones is determined by their specific G-protein coupled receptor (GPCR) pathways. **1. Why Somatostatin is correct:** Somatostatin acts as a universal inhibitory hormone. It binds to **G$_i$ (inhibitory) protein-coupled receptors**. Activation of G$_i$ inhibits the enzyme **adenylyl cyclase**, which prevents the conversion of ATP to cyclic AMP (cAMP). Consequently, intracellular and serum levels of cAMP decrease. This inhibition is the primary reason somatostatin suppresses the release of growth hormone, insulin, glucagon, and gastrin. **2. Why the other options are incorrect:** * **Glucagon:** This hormone binds to **G$_s$ (stimulatory)** receptors, which activate adenylyl cyclase and **increase** cAMP levels to promote glycogenolysis and gluconeogenesis. * **Thyroxine (T4):** Thyroid hormones are lipid-soluble and act via **nuclear receptors** to alter gene transcription. They do not primarily utilize the cAMP second messenger system. * **Prolactin:** Prolactin acts via the **JAK-STAT pathway** (enzyme-linked receptor), not the cAMP pathway. **High-Yield Clinical Pearls for NEET-PG:** * **G$_s$ Pathway (Increases cAMP):** Remember the mnemonic **"FLAT ChAMP"** (FSH, LH, ACTH, TSH, CRH, hCG, ADH (V2), MSH, PTH) and Glucagon. * **G$_i$ Pathway (Decreases cAMP):** **MAD 2s** (M2, Alpha-2, D2) and **Somatostatin**. * **Somatostatin Analogues:** Octreotide is used clinically to treat acromegaly, carcinoid syndrome, and esophageal varices due to its potent inhibitory effects.
Question 503: The provided diagram shows the adrenal gland. Identify the hormone produced from the area labeled 'A'.
- A. Aldosterone (Correct Answer)
- B. Cortisol
- C. Epinephrine
- D. Androgen
Explanation: ***Aldosterone*** - Area 'A' represents the **zona glomerulosa**, the outermost layer of the adrenal cortex, which specifically produces **aldosterone**. - **Aldosterone** is a **mineralocorticoid** that regulates **sodium** and **potassium** balance and **blood pressure**. *Cortisol* - **Cortisol** is produced by the **zona fasciculata**, the middle layer of the adrenal cortex, not area 'A'. - This **glucocorticoid** primarily regulates **glucose metabolism** and **stress response**. *Epinephrine* - **Epinephrine** (adrenaline) is produced by the **adrenal medulla**, the innermost part of the adrenal gland. - This **catecholamine** is involved in the **fight-or-flight response** and **sympathetic nervous system** activation. *Androgen* - **Androgens** (like **DHEA**) are produced by the **zona reticularis**, the innermost cortical layer. - These **sex hormones** are precursors to **testosterone** and **estrogen**, not produced in area 'A'.
Question 504: Which of the following is both synthesized and stored in the hypothalamus?
- A. ADH
- B. Thyroid-stimulating hormone (TSH)
- C. LH
- D. Somatostatin (Correct Answer)
Explanation: **Explanation:** The correct answer is **Somatostatin**. To answer this question correctly, one must distinguish between hormones that are merely produced in the hypothalamus and those that are both produced and stored there. **1. Why Somatostatin is Correct:** Somatostatin (Growth Hormone Inhibiting Hormone) is a regulatory hormone **synthesized** in the periventricular nucleus of the hypothalamus. It is **stored** in the median eminence (the inferior-most portion of the hypothalamus) before being released into the hypophyseal portal system to inhibit the secretion of Growth Hormone and TSH from the anterior pituitary. **2. Why the other options are incorrect:** * **ADH (Antidiuretic Hormone):** While ADH is **synthesized** in the hypothalamus (supraoptic and paraventricular nuclei), it is **stored** and released from the **posterior pituitary** (neurohypophysis). * **TSH and LH:** These are trophic hormones **synthesized and stored** in the **anterior pituitary** (adenohypophysis) by thyrotropes and gonadotropes, respectively. Their release is controlled by hypothalamic "releasing hormones" (TRH and GnRH). **Clinical Pearls for NEET-PG:** * **The "Two-Site" Rule:** Remember that ADH and Oxytocin are hypothalamic hormones by origin but **pituitary hormones by storage**. * **Somatostatin Locations:** It is found in three main areas: the Hypothalamus (inhibits GH), Delta cells of the Pancreas (inhibits insulin/glucagon), and D cells of the GI tract (inhibits gastrin). * **Octreotide:** A high-yield synthetic analog of somatostatin used clinically to treat acromegaly, carcinoid syndrome, and esophageal varices.
Question 505: Which finding would be present following selective destruction of Sertoli cells?
- A. Increased plasma testosterone levels
- B. Increased plasma inhibin levels
- C. Increased plasma luteinizing hormone (LH) levels
- D. Increased plasma follicle-stimulating hormone (FSH) levels (Correct Answer)
Explanation: **Explanation:** The regulation of the male reproductive system involves the **Hypothalamic-Pituitary-Gonadal (HPG) axis**. Sertoli cells, located within the seminiferous tubules, play a crucial role in spermatogenesis and the feedback regulation of **Follicle-Stimulating Hormone (FSH)**. 1. **Why Option D is Correct:** Sertoli cells produce a glycoprotein hormone called **Inhibin B**. Inhibin B exerts specific negative feedback on the anterior pituitary to inhibit the secretion of FSH. When Sertoli cells are selectively destroyed, Inhibin B levels plummet. The loss of this negative feedback leads to a compensatory **increase in plasma FSH levels**. 2. **Why Other Options are Incorrect:** * **Option A & C:** Testosterone production and **Luteinizing Hormone (LH)** secretion are governed by **Leydig cells**. Since the destruction is selective to Sertoli cells, the Leydig cells remain functional. Therefore, testosterone levels remain normal, and consequently, LH levels (regulated by testosterone feedback) do not increase. * **Option B:** Inhibin is produced *by* Sertoli cells. Destruction of these cells leads to **decreased** plasma inhibin levels, not increased. **High-Yield Clinical Pearls for NEET-PG:** * **Sertoli Cells Only Syndrome (Del Castillo Syndrome):** A clinical condition where seminiferous tubules lack germ cells but contain Sertoli cells; however, if Sertoli function is impaired, FSH will be elevated despite normal LH/Testosterone. * **Blood-Testis Barrier:** Formed by tight junctions between Sertoli cells. * **Mnemonic:** **S**ertoli cells = **S**upport spermatogenesis, **S**ecrete Inhibin, and respond to F**S**H. **L**eydig cells = **L**iberate testosterone and respond to **L**H.
Question 506: Vasopressin is secreted by which nucleus of the hypothalamus?
- A. Suprachiasmatic nucleus
- B. Dorsomedial nucleus
- C. Paraventricular nucleus (Correct Answer)
- D. Premamillary nucleus
Explanation: **Explanation:** **Vasopressin (Antidiuretic Hormone - ADH)** and **Oxytocin** are synthesized in the cell bodies of magnocellular neurons located in the hypothalamus. Specifically, Vasopressin is primarily synthesized in the **Supraoptic nucleus (SON)** and the **Paraventricular nucleus (PVN)**. While the SON is often considered the primary site for ADH, the PVN contributes significantly to its production (and is the primary site for Oxytocin). From these nuclei, the hormones are transported via the hypothalamo-hypophyseal tract to the posterior pituitary (neurohypophysis) for storage and eventual release. **Analysis of Incorrect Options:** * **A. Suprachiasmatic nucleus:** This nucleus is the "master clock" of the body, responsible for regulating **circadian rhythms** in response to light-dark cycles. * **B. Dorsomedial nucleus:** This area is involved in emotional behavior, blood pressure regulation, and **gastrointestinal stimulation**. * **D. Premamillary nucleus:** This is part of the mammillary body complex, primarily involved in **olfactory reflexes** and memory processing. **High-Yield Clinical Pearls for NEET-PG:** * **The 5/6 Rule:** Roughly 5/6th of ADH is produced in the SON and 1/6th in the PVN; for Oxytocin, the ratio is reversed (5/6th in PVN, 1/6th in SON). * **V1 Receptors:** Located on vascular smooth muscle (cause vasoconstriction). * **V2 Receptors:** Located on the principal cells of the late distal tubule and collecting ducts (increase water reabsorption via Aquaporin-2). * **Diabetes Insipidus:** Central DI is caused by a lack of ADH secretion from the hypothalamus/posterior pituitary, whereas Nephrogenic DI is caused by renal resistance to ADH.
Question 507: Obesity is ordinarily associated with low ghrelin levels. Which of the following conditions is an exception where obesity is associated with high ghrelin levels?
- A. Hypothyroidism
- B. Prader-Willi syndrome (Correct Answer)
- C. Hypoadrenalism
- D. Insulinoma
Explanation: ### Explanation **Core Concept: The Ghrelin Paradox** Ghrelin is an orexigenic (appetite-stimulating) hormone secreted primarily by the P-cells of the gastric fundus. In normal physiology, ghrelin levels follow an inverse relationship with Body Mass Index (BMI). In common obesity, ghrelin levels are **low** because the body attempts to suppress further food intake in response to positive energy balance. **Why Prader-Willi Syndrome (PWS) is the Exception:** Prader-Willi Syndrome is a genetic disorder (deletion of the paternal 15q11-q13 locus) characterized by hyperphagia and early-onset morbid obesity. Unlike common obesity, PWS is uniquely associated with **markedly elevated fasting ghrelin levels**. This hyperghrelinemia is believed to drive the insatiable hunger and lack of satiety characteristic of the syndrome, making it a classic "exception to the rule" in endocrinology. **Analysis of Incorrect Options:** * **A. Hypothyroidism:** Associated with weight gain due to a low metabolic rate, but ghrelin levels are typically normal or decreased, following the standard inverse relationship with BMI. * **C. Hypoadrenalism (Addison’s Disease):** Usually presents with weight loss and anorexia, not obesity. * **D. Insulinoma:** Causes hypoglycemia leading to increased appetite and weight gain. However, the hyperinsulinemia typically suppresses ghrelin levels. **High-Yield Clinical Pearls for NEET-PG:** * **Ghrelin vs. Leptin:** Ghrelin is the "Hunger Hormone" (levels rise before meals); Leptin is the "Satiety Hormone" (secreted by adipocytes). * **Sleep Deprivation:** Associated with increased ghrelin and decreased leptin, contributing to obesity. * **Post-Gastric Bypass:** Ghrelin levels significantly **decrease** after Roux-en-Y gastric bypass, which contributes to the surgery's success in weight loss. * **PWS Triad:** Hypotonia (infancy), Hyperphagia/Obesity, and Hypogonadism.
Question 508: Cholecystokinin is mainly secreted by which part of the gastrointestinal tract?
- A. Duodenum (Correct Answer)
- B. Pancreas
- C. Gallbladder
- D. Ileum
Explanation: **Explanation:** **Cholecystokinin (CCK)** is a peptide hormone primarily synthesized and secreted by the **I-cells** located in the mucosal epithelium of the **duodenum** and the proximal jejunum. Its secretion is stimulated by the presence of digestive products, particularly long-chain fatty acids and amino acids (tryptophan and phenylalanine), in the chyme entering the small intestine. **Analysis of Options:** * **A. Duodenum (Correct):** This is the primary site of CCK production. CCK acts to stimulate gallbladder contraction and pancreatic enzyme secretion while slowing gastric emptying to optimize digestion. * **B. Pancreas:** While the pancreas is a major *target* organ for CCK (stimulating acinar cells to release enzymes), it does not secrete CCK. * **C. Gallbladder:** The gallbladder is another target organ. CCK causes it to contract and relaxes the Sphincter of Oddi to release bile; it does not produce the hormone. * **D. Ileum:** While some CCK-producing cells exist in the distal small intestine, the concentration is significantly lower than in the duodenum. The ileum is more famously associated with **L-cells** which secrete GLP-1 and PYY. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Cells:** **"I"** eat **C**hicken **C**on **K**arne (**I**-cells secrete **CCK**). * **Functions:** CCK is the most potent stimulator of gallbladder contraction. It also acts as a satiety signal in the central nervous system via the vagus nerve. * **Diagnostic Use:** The **CCK-HIDA scan** is used clinically to assess gallbladder ejection fraction in suspected biliary dyskinesia. * **Contrast with Secretin:** While CCK stimulates enzyme-rich pancreatic juice, **Secretin** (from S-cells) stimulates bicarbonate-rich pancreatic juice.
Question 509: Hypercalcemia is caused by all of the following except?
- A. Hyperparathyroidism
- B. Secondary bone metastasis
- C. Thyrotoxicosis
- D. Tamoxifen (Correct Answer)
Explanation: **Explanation:** The correct answer is **Tamoxifen**. While Tamoxifen is a Selective Estrogen Receptor Modulator (SERM) used in breast cancer treatment, it is generally **not** a primary cause of hypercalcemia. In fact, in most clinical scenarios, Tamoxifen has a protective effect on bone mineral density in postmenopausal women. (Note: A rare "flare reaction" can cause transient hypercalcemia in patients with extensive bone metastases, but it is not a systemic cause of hypercalcemia like the other options). **Analysis of Options:** * **Hyperparathyroidism (Option A):** This is the most common cause of hypercalcemia. Increased Parathyroid Hormone (PTH) stimulates osteoclastic bone resorption and increases renal calcium reabsorption and intestinal absorption (via Vitamin D). * **Secondary Bone Metastasis (Option B):** Malignancy is the second most common cause of hypercalcemia. Metastatic lesions (especially from lung or breast cancer) cause local bone destruction through the release of cytokines and PTH-related peptide (PTHrP). * **Thyrotoxicosis (Option C):** Excess thyroid hormone (T3/T4) has a direct stimulatory effect on osteoclasts, leading to increased bone turnover and hypercalcemia in approximately 15-20% of thyrotoxic patients. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Hypercalcemia:** "Stones (Renal), Bones (Aches), Abdominal Groans (Constipation/Peptic ulcers), and Psychic Overtones (Depression/Confusion)." * **ECG Finding:** Hypercalcemia causes a **shortened QT interval**. * **Thiazide Diuretics:** These decrease urinary calcium excretion and can cause hypercalcemia, whereas **Loop Diuretics** (Furosemide) increase calcium excretion ("Loops Lose Calcium").
Question 510: Lesion of which hypothalamic nuclei leads to loss of circadian rhythm?
- A. Dorsomedial
- B. Ventromedial
- C. Supraoptic
- D. Suprachiasmatic (Correct Answer)
Explanation: ### Explanation The **Suprachiasmatic Nucleus (SCN)** is the correct answer as it serves as the body’s primary **master pacemaker** for circadian rhythms. #### 1. Why Suprachiasmatic Nucleus is Correct Located in the anterior hypothalamus, the SCN receives direct neural input from the retina via the **retinohypothalamic tract**. This allows the nucleus to synchronize internal biological processes (such as sleep-wake cycles, body temperature, and hormone secretion) with the external 24-hour light-dark cycle. Lesions of the SCN result in the complete loss of these rhythmic patterns, leading to disorganized physiological activity. #### 2. Analysis of Incorrect Options * **A. Dorsomedial Nucleus:** Primarily involved in emotional behavior, cardiovascular responses to stress, and gastrointestinal stimulation. * **B. Ventromedial Nucleus:** Known as the **Satiety Center**. Lesions here lead to hyperphagia (overeating) and obesity. * **C. Supraoptic Nucleus:** Responsible for the synthesis of **Antidiuretic Hormone (ADH/Vasopressin)**. Lesions here lead to Diabetes Insipidus. #### 3. NEET-PG High-Yield Pearls * **The "Master Clock" Pathway:** Light → Retina → Retinohypothalamic tract → SCN → Pineal Gland (via sympathetic fibers) → Melatonin inhibition. * **Melatonin:** Often called the "Dracula hormone" because its secretion from the pineal gland is inhibited by light and peaks during darkness. * **Mnemonic for Hypothalamic Centers:** * **V**entromedial = **V**ery Much (Satiety/Fullness). * **L**ateral = **L**ean (Hunger center; lesion leads to starvation). * **A**nterior = **A**C (Cooling/Parasympathetic). * **P**osterior = **P**oikilotherm/Heater (Heating/Sympathetic).
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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