Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 371: D cells of the pancreas secrete which of the following hormones?

A. Glucagon
B. Insulin
C. Somatostatin (Correct Answer)
D. Pancreatic polypeptide

Explanation: ### Explanation The islets of Langerhans in the pancreas are composed of several distinct cell types, each responsible for secreting specific hormones that regulate glucose metabolism and gastrointestinal function. **Correct Answer: C. Somatostatin** **D cells (or Delta cells)** of the pancreas secrete **Somatostatin**. This hormone acts primarily as a potent inhibitory agent. In a paracrine fashion, it inhibits the secretion of both insulin (from Beta cells) and glucagon (from Alpha cells). It also slows gastric emptying and reduces digestive enzyme secretion, effectively modulating the rate at which nutrients enter the bloodstream. **Analysis of Incorrect Options:** * **A. Glucagon:** Secreted by **Alpha (α) cells**, which typically occupy the periphery of the islet. Glucagon increases blood glucose levels via glycogenolysis and gluconeogenesis. * **B. Insulin:** Secreted by **Beta (β) cells**, which are the most numerous (approx. 60-70%) and located centrally in the islet. Insulin is the primary anabolic hormone for glucose uptake. * **D. Pancreatic polypeptide:** Secreted by **F cells (or PP cells)**. This hormone inhibits pancreatic exocrine secretion and gallbladder contraction. **High-Yield Clinical Pearls for NEET-PG:** * **Cell Distribution:** Remember the mnemonic **"B-I-C"** (Beta-Insulin-Center) and **"A-G-P"** (Alpha-Glucagon-Periphery). * **Somatostatin Analogs:** Octreotide is a synthetic analog used clinically to treat acromegaly, carcinoid syndrome, and bleeding esophageal varices. * **Insulinoma vs. Glucagonoma:** Tumors of these specific cells lead to distinct syndromes (e.g., Whipple’s triad in insulinoma; Necrolytic Migratory Erythema in glucagonoma).

Question 372: Early epiphyseal closure is seen with which of the following?

A. LH
B. FSH
C. Estrogens (Correct Answer)
D. Progesterone

Explanation: **Explanation:** The correct answer is **Estrogens**. **1. Why Estrogens are correct:** While Growth Hormone (GH) and IGF-1 drive the linear growth of long bones, **Estrogens** are the primary hormones responsible for the **closure of the epiphyseal plates** in both males and females. During puberty, a surge in estrogen levels initially promotes a "growth spurt" by stimulating the GH-IGF-1 axis. However, estrogens simultaneously accelerate the maturation of chondrocytes in the growth plate. Eventually, estrogen induces the exhaustion of the proliferative zone and the replacement of cartilage with bone (ossification), leading to the fusion of the epiphysis and the cessation of linear growth. **2. Why the other options are incorrect:** * **LH (Luteinizing Hormone) & FSH (Follicle Stimulating Hormone):** These are gonadotropins secreted by the anterior pituitary. While they stimulate the gonads to produce sex steroids (like estrogen and testosterone), they do not have a direct effect on the epiphyseal plates. * **Progesterone:** This hormone is primarily involved in the secretory phase of the menstrual cycle and the maintenance of pregnancy. It has no significant role in bone maturation or epiphyseal closure. **3. Clinical Pearls for NEET-PG:** * **Precocious Puberty:** Early secretion of estrogens (or testosterone converted to estrogen) leads to an initial tall stature but results in **short adult stature** due to early epiphyseal closure. * **Aromatase Deficiency:** Individuals lacking the aromatase enzyme (which converts androgens to estrogens) fail to undergo epiphyseal closure and continue to grow well into adulthood (tall stature). * **Testosterone vs. Estrogen:** In males, testosterone also causes epiphyseal closure, but it does so largely after being **aromatized into estrogen** locally in the bone.

Question 373: Which of the following hormones is NOT secreted by the anterior pituitary?

A. Growth hormone
B. FSH
C. Oxytocin (Correct Answer)
D. Prolactin

Explanation: **Explanation:** The pituitary gland (hypophysis) is divided into the **Anterior Pituitary (Adenohypophysis)** and the **Posterior Pituitary (Neurohypophysis)**. The key distinction lies in their embryology and function: the anterior pituitary synthesizes its own hormones, whereas the posterior pituitary only stores and releases hormones produced in the hypothalamus. **Why Oxytocin is the Correct Answer:** Oxytocin is synthesized in the **paraventricular nuclei** (and to a lesser extent, the supraoptic nuclei) of the **hypothalamus**. It travels down the hypothalamo-hypophyseal tract to be stored in the posterior pituitary. Therefore, the posterior pituitary *releases* but does *not* secrete (synthesize) oxytocin. **Analysis of Incorrect Options:** * **Growth Hormone (GH):** Secreted by **Somatotrophs** in the anterior pituitary. It is the most abundant anterior pituitary hormone. * **FSH (Follicle-Stimulating Hormone):** A gonadotropin secreted by **Gonadotrophs** in the anterior pituitary. * **Prolactin:** Secreted by **Lactotrophs** (Mammotrophs) in the anterior pituitary. Unlike other hormones, its primary regulation is inhibitory (via Dopamine). **High-Yield NEET-PG Pearls:** 1. **Posterior Pituitary Hormones:** Only two—**Oxytocin** and **ADH (Vasopressin)**. Both are synthesized in the hypothalamus. 2. **Embryology:** The anterior pituitary develops from **Rathke’s pouch** (ectodermal outpocketing of the oropharynx), while the posterior pituitary develops from the **neuroectoderm** of the floor of the third ventricle. 3. **Cell Types:** Acidophils (GH, Prolactin) and Basophils (FSH, LH, ACTH, TSH). Remember the mnemonic: **"B-FLAT"** for Basophils.

Question 374: What is considered the normal sperm count?

A. 20-40 million/ml
B. 40-60 million/ml
C. 60-80 million/ml
D. 15 million/ml (Correct Answer)

Explanation: The correct answer is **D. 15 million/ml**. ### **Educational Explanation** **1. Why 15 million/ml is correct:** The definition of a "normal" sperm count has evolved based on the **World Health Organization (WHO) Laboratory Manual** for the examination and processing of human semen. According to the **WHO 5th Edition (2010)** and the latest **6th Edition (2021)**, the lower reference limit (5th centile) for sperm concentration is **15 million spermatozoa per ml**. Any value below this threshold is clinically defined as **Oligozoospermia**. **2. Why the other options are incorrect:** * **Options A, B, and C (20–80 million/ml):** Historically, 20 million/ml was considered the cutoff (WHO 4th Ed, 1999). While these ranges represent healthy concentrations, they are no longer the "minimum" threshold used for clinical diagnosis. In NEET-PG, when asked for the "normal count," the examiner is looking for the **minimum reference value** established by the most recent WHO guidelines. ### **High-Yield Clinical Pearls for NEET-PG** * **Total Sperm Number:** The minimum normal total count per ejaculate is **39 million**. * **Volume:** The lower reference limit for semen volume is **1.5 ml**. * **Motility:** At least **40%** total motility or **32%** progressive motility is considered normal. * **Morphology:** According to Kruger’s strict criteria, at least **4%** normal forms are required. * **Terminology:** * **Aspermia:** Absence of semen. * **Azoospermia:** Absence of sperm in the ejaculate. * **Asthenozoospermia:** Reduced sperm motility. * **Teratozoospermia:** Increased abnormal morphology.

Question 375: Posterior pituitary hormone secretion is mediated by which of the following mechanisms?

A. A portal capillary system from the hypothalamus to the posterior pituitary
B. The fight-or-flight response
C. The hypothalamo-hypophyseal tract originating from magnocellular neurons in the supraoptic and paraventricular nuclei (Correct Answer)
D. The reticular activating system's input to the hypothalamus

Explanation: **Explanation:** The posterior pituitary (neurohypophysis) does not synthesize its own hormones. Instead, it serves as a storage and release site for **Antidiuretic Hormone (ADH/Vasopressin)** and **Oxytocin**. **Why Option C is Correct:** These hormones are synthesized in the cell bodies of **magnocellular neurons** located in the **Supraoptic Nucleus (SON)** and **Paraventricular Nucleus (PVN)** of the hypothalamus. They are transported down the axons via the **hypothalamo-hypophyseal tract** (bound to carrier proteins called neurophysins) and stored in axon terminals known as **Herring bodies** in the posterior pituitary. Secretion occurs via exocytosis into the systemic circulation upon electrical stimulation. **Why the other options are incorrect:** * **Option A:** The **hypophyseal portal system** connects the hypothalamus to the **anterior pituitary** (adenohypophysis). It carries releasing/inhibiting hormones (like TRH or CRH) to regulate glandular cells. * **Option B:** The fight-or-flight response primarily involves the sympathetic nervous system and the **adrenal medulla** (epinephrine/norepinephrine), not the direct secretion mechanism of the posterior pituitary. * **Option C:** While the **Reticular Activating System (RAS)** regulates consciousness and arousal, it is not the primary mediator for the specific axonal transport and release of posterior pituitary hormones. **High-Yield NEET-PG Pearls:** * **Primary sites:** SON is primarily associated with **ADH**; PVN is primarily associated with **Oxytocin**. * **Neurophysins:** Neurophysin I carries Oxytocin; Neurophysin II carries ADH. * **Embryology:** The posterior pituitary is derived from **neuroectoderm** (downward extension of the diencephalon), explaining its neural connection. * **Clinical Correlation:** Lesions to the hypothalamo-hypophyseal tract above the median eminence result in **Central Diabetes Insipidus**.

Question 376: Which hormone is secreted by alpha-cells in the pancreas in response to low blood glucose levels?

A. Insulin
B. Glucagon (Correct Answer)
C. Epinephrine
D. Somatostatin

Explanation: **Explanation:** The pancreas functions as both an exocrine and endocrine gland. The endocrine component consists of the **Islets of Langerhans**, which contain several distinct cell types. **1. Why Glucagon is Correct:** **Glucagon** is synthesized and secreted by the **alpha (α) cells**, which constitute about 20% of the islet cells. Its primary stimulus is **hypoglycemia** (low blood glucose). Glucagon acts as a counter-regulatory hormone to insulin; it increases blood glucose levels by stimulating **glycogenolysis** (breakdown of glycogen) and **gluconeogenesis** (synthesis of glucose from non-carbohydrate sources) in the liver. **2. Why Other Options are Incorrect:** * **Insulin:** Secreted by **beta (β) cells** (the most abundant type, ~65-70%). It is released in response to *high* blood glucose levels to facilitate glucose uptake into cells. * **Epinephrine:** While it also raises blood glucose, it is secreted by the **adrenal medulla**, not the pancreas. It acts during the "fight or flight" response. * **Somatostatin:** Secreted by **delta (δ) cells**. Its primary role is paracrine inhibition, suppressing the secretion of both insulin and glucagon. **3. NEET-PG High-Yield Pearls:** * **Major Stimulus:** The most potent stimulator for glucagon is a fall in blood glucose, but **increased amino acids** (especially arginine and alanine) also stimulate its release. * **Inhibitors:** Glucagon secretion is inhibited by hyperglycemia, insulin, and somatostatin. * **Glucagonoma:** A rare tumor of alpha cells characterized by the "4 Ds": Diabetes, Dermatitis (Necrolytic migratory erythema), Deep vein thrombosis, and Depression. * **Clinical Use:** Intramuscular glucagon is used as emergency treatment for severe hypoglycemia in diabetic patients.

Question 377: Disorganized lesions in which of the following locations would affect the release of ADH and oxytocin from the posterior pituitary?

A. Supraoptic and paraventricular nuclei (Correct Answer)
B. Ventromedial part of the hypothalamus
C. Lateral hypothalamus
D. Posterior hypothalamus

Explanation: **Explanation:** The posterior pituitary (neurohypophysis) does not synthesize hormones; instead, it stores and releases hormones produced in the hypothalamus. **1. Why Option A is Correct:** The hormones **Antidiuretic Hormone (ADH/Vasopressin)** and **Oxytocin** are synthesized in the cell bodies of magnocellular neurons located in the **Supraoptic (SON)** and **Paraventricular (PVN)** nuclei of the hypothalamus. * **SON** primarily synthesizes ADH. * **PVN** primarily synthesizes Oxytocin. These hormones are transported down the axons via the hypothalamo-hypophyseal tract (bound to carrier proteins called **neurophysins**) and are stored in terminal nerve endings (Herring bodies) in the posterior pituitary until release. Therefore, lesions in these nuclei directly disrupt the production and subsequent release of these hormones. **2. Why Other Options are Incorrect:** * **B. Ventromedial Nucleus:** Known as the **Satiety Center**. Lesions here lead to hyperphagia and obesity. * **C. Lateral Hypothalamus:** Known as the **Feeding Center**. Lesions here lead to aphagia and weight loss. * **D. Posterior Hypothalamus:** Primarily involved in **thermogenesis** (response to cold) and sympathetic regulation. Lesions result in poikilothermia (inability to regulate body temperature). **High-Yield Clinical Pearls for NEET-PG:** * **Diabetes Insipidus (DI):** Central DI occurs due to a deficiency of ADH, often resulting from trauma or lesions to the SON/PVN or the pituitary stalk. * **Neurophysins:** Neurophysin I is associated with Oxytocin, while Neurophysin II is associated with ADH. * **V2 Receptors:** ADH acts on V2 receptors in the collecting ducts of the kidney to insert Aquaporin-2 channels for water reabsorption.

Question 378: Erythropoietin production is inhibited by?

A. Estrogen (Correct Answer)
B. Progesterone
C. Thyroxine
D. Testosterone

Explanation: **Explanation:** The production of **Erythropoietin (EPO)**, the primary hormone regulating red blood cell production, is stimulated by hypoxia and various hormones. Among the options provided, **Estrogen** is the only hormone that exerts an inhibitory effect on erythropoiesis. **1. Why Estrogen is Correct:** Estrogen inhibits erythropoietin production and also blunts the bone marrow's response to EPO. This hormonal influence is a primary reason why females of reproductive age typically have lower hemoglobin levels and red cell counts compared to males. **2. Analysis of Incorrect Options:** * **Testosterone (D):** Androgens are potent stimulators of EPO production in the kidneys and directly stimulate erythroid stem cells in the bone marrow. This explains the higher hematocrit levels seen in males. * **Thyroxine (C):** Thyroid hormones increase oxygen consumption and metabolic rate, leading to relative tissue hypoxia, which triggers an increase in EPO production. * **Progesterone (B):** Unlike estrogen, progesterone does not have a significant inhibitory effect on erythropoiesis; in some physiological contexts, it may even mildly stimulate ventilation, indirectly affecting oxygenation. **Clinical Pearls for NEET-PG:** * **Site of Production:** In adults, 85-90% of EPO is produced by **peritubular interstitial cells** of the renal cortex; the remainder comes from the liver. * **Stimulus:** The fundamental stimulus for EPO is **hypoxia** (sensed by HIF-1α), not the number of RBCs. * **Other Stimulants:** Catecholamines (via β-receptors), Alkalosis, and Cobalt salts also increase EPO production. * **Clinical Correlation:** Chronic Renal Failure (CRF) leads to normocytic normochromic anemia due to EPO deficiency.

Question 379: Proteolytic enzyme Renin is primarily found in which organ?

A. Lungs
B. Kidney (Correct Answer)
C. Liver
D. Stomach

Explanation: **Explanation:** **1. Why Kidney is Correct:** Renin is a proteolytic enzyme (aspartyl protease) synthesized, stored, and secreted by the **Juxtaglomerular (JG) cells** of the afferent arterioles in the **Kidney**. It is the rate-limiting step of the Renin-Angiotensin-Aldosterone System (RAAS). Its primary function is to cleave Angiotensinogen (produced by the liver) into Angiotensin I. The release of renin is triggered by decreased renal perfusion pressure (baroreceptors), reduced sodium delivery to the macula densa, or sympathetic nervous system stimulation ($\beta_1$ receptors). **2. Why Other Options are Incorrect:** * **Lungs:** The lungs are the primary site for **Angiotensin-Converting Enzyme (ACE)**, which converts Angiotensin I to Angiotensin II. They do not produce renin. * **Liver:** The liver synthesizes **Angiotensinogen**, the substrate upon which renin acts. * **Stomach:** The stomach produces other proteolytic enzymes like **Pepsin**, but not renin. (Note: Do not confuse *Renin* with *Rennin/Chymosin*, an enzyme found in the stomachs of ruminants for milk curdling). **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Site of Action:** Renin acts exclusively on the circulating $\alpha_2$-globulin, Angiotensinogen. * **Stimulus for Release:** The most potent stimulus for renin release is a decrease in NaCl concentration at the **Macula Densa**. * **Inhibitors:** Direct Renin Inhibitors (e.g., **Aliskiren**) are used clinically to treat hypertension. * **Tumor Association:** Renin-secreting tumors (Robertson-Kihara syndrome) can lead to secondary hyperaldosteronism and severe hypertension. * **Goldblatt Kidney:** This experimental model demonstrates how renal artery stenosis leads to increased renin production and systemic hypertension.

Question 380: Diabetes insipidus is due to hyposecretion of which hormone?

A. Insulin
B. Arginine Vasopressin/ AVP (Correct Answer)
C. Angiotensin
D. Aldosterone

Explanation: **Explanation:** **Diabetes Insipidus (DI)** is a clinical syndrome characterized by the excretion of large volumes of dilute urine (polyuria) and excessive thirst (polydipsia). It occurs due to a deficiency in the action of **Arginine Vasopressin (AVP)**, also known as Antidiuretic Hormone (ADH). 1. **Why Arginine Vasopressin (AVP) is correct:** AVP is synthesized in the hypothalamus and stored in the posterior pituitary. Its primary role is to maintain water homeostasis by binding to V2 receptors in the renal collecting ducts, promoting the insertion of aquaporin-2 channels. This allows water reabsorption. **Hyposecretion** of AVP (Central DI) or resistance to its action (Nephrogenic DI) leads to an inability to concentrate urine, resulting in the hallmark symptoms of DI. 2. **Why other options are incorrect:** * **Insulin:** Hyposecretion of insulin leads to **Diabetes Mellitus**, characterized by hyperglycemia and osmotic diuresis due to glycosuria. * **Angiotensin:** Part of the RAAS pathway, Angiotensin II is a potent vasoconstrictor and stimulates aldosterone release; its deficiency does not cause DI. * **Aldosterone:** A mineralocorticoid responsible for sodium reabsorption and potassium excretion. Deficiency (as in Addison’s disease) leads to hyponatremia and hyperkalemia, not DI. **High-Yield Clinical Pearls for NEET-PG:** * **Water Deprivation Test:** The gold standard for diagnosing DI and differentiating it from primary polydipsia. * **Desmopressin (dDAVP):** A synthetic analog of AVP used to differentiate Central DI (responds to dDAVP) from Nephrogenic DI (no response). * **Urine Osmolality:** In DI, urine is characteristically dilute (typically <300 mOsm/kg).

Practice by Chapter

Principles of Endocrine Regulation

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Hypothalamus and Pituitary Gland

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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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