Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 51: Secretion of prolactin is affected by which of the following?

A. GnRH analogue
B. Dopamine (Correct Answer)
C. Serotonin
D. FSH

Explanation: **Explanation:** The secretion of prolactin is unique among anterior pituitary hormones because it is under **predominant tonic inhibition** by the hypothalamus. **1. Why Dopamine is correct:** Dopamine, secreted by the tuberoinfundibular dopaminergic (TIDA) neurons of the hypothalamus, acts on **D2 receptors** located on the lactotrophs of the anterior pituitary. This interaction inhibits the synthesis and release of prolactin. Any disruption in this pathway (e.g., pituitary stalk compression or dopamine antagonists) leads to an increase in prolactin levels (hyperprolactinemia). **2. Why other options are incorrect:** * **GnRH Analogue:** Gonadotropin-Releasing Hormone primarily stimulates the release of LH and FSH. While prolactin can inhibit GnRH secretion (leading to lactational amenorrhea), GnRH does not directly regulate prolactin secretion. * **Serotonin:** While serotonin can stimulate prolactin release in certain physiological states, it is not the primary regulatory factor. The question asks for the most definitive factor affecting secretion, which is the inhibitory control by dopamine. * **FSH:** Follicle-Stimulating Hormone is a gonadotropin released in response to GnRH. It acts on the gonads and has no direct feedback or stimulatory effect on prolactin secretion. **High-Yield Clinical Pearls for NEET-PG:** * **Prolactin Inhibiting Factor (PIF):** Dopamine is the primary PIF. * **Prolactin Releasing Factors (PRF):** Thyrotropin-Releasing Hormone (TRH) and Vasoactive Intestinal Peptide (VIP) stimulate prolactin release. This explains why **primary hypothyroidism** (high TRH) can cause hyperprolactinemia. * **Hook Effect:** A laboratory phenomenon where extremely high prolactin levels (as in giant prolactinomas) give a falsely low reading; requires sample dilution for accurate measurement. * **Drug-induced Hyperprolactinemia:** Antipsychotics (D2 blockers) like Haloperidol or Metoclopramide are common causes of elevated prolactin.

Question 52: Prolactin production is controlled by:

A. Metoclopramide
B. Chlorpromazine
C. Dopamine (Correct Answer)
D. None of the above

Explanation: **Explanation:** **1. Why Dopamine is Correct:** In the endocrine system, Prolactin is unique because its primary regulation from the hypothalamus is **inhibitory**, rather than stimulatory. **Dopamine**, secreted by the tuberoinfundibular pathway, acts as the primary **Prolactin-Inhibiting Hormone (PIH)**. It binds to **D2 receptors** on the lactotrophs of the anterior pituitary to suppress the synthesis and secretion of prolactin. Therefore, prolactin levels are inversely proportional to dopamine activity. **2. Why Other Options are Incorrect:** * **Metoclopramide & Chlorpromazine:** These are **Dopamine (D2) antagonists**. While they certainly influence prolactin levels, they do so by *blocking* the natural inhibitory control, leading to **Hyperprolactinemia**. They are pharmacological agents that cause side effects (like galactorrhea), rather than being the physiological mechanism of "control" produced by the body. * **None of the above:** Incorrect, as Dopamine is the well-established physiological regulator. **3. NEET-PG High-Yield Pearls:** * **The "Disconnect" Effect:** Any injury to the pituitary stalk (trauma or tumors) leads to a decrease in all pituitary hormones **EXCEPT Prolactin**, which rises because it is freed from dopamine’s inhibitory control. * **Stimulators:** While dopamine inhibits, **TRH (Thyrotropin-Releasing Hormone)** and **Oxytocin** act as prolactin-releasing factors. This explains why patients with primary hypothyroidism (high TRH) often present with hyperprolactinemia. * **Clinical Correlation:** Dopamine agonists (e.g., **Cabergoline, Bromocriptine**) are the first-line treatment for Prolactinomas. * **Prolactin & GnRH:** High prolactin levels inhibit the pulsatile release of GnRH, leading to secondary amenorrhea and infertility.

Question 53: Which of the following statements about the action of somatomedins is true?

A. They inhibit protein synthesis
B. They antagonize the effect of insulin
C. They promote growth of bone and cartilage (Correct Answer)
D. They mediate the local effects of Somatostatin

Explanation: **Explanation:** **Somatomedins**, primarily **Insulin-like Growth Factor-1 (IGF-1)**, are peptides produced mainly by the liver in response to Growth Hormone (GH) stimulation. While GH exerts direct metabolic effects, its growth-promoting actions are mediated indirectly through somatomedins. **1. Why Option C is Correct:** Somatomedins are the primary mediators of GH-induced skeletal growth. They act on the epiphyseal plates of long bones to stimulate **chondrocyte proliferation**, increase collagen synthesis, and promote the deposition of chondroitin sulfate. This results in increased bone length and cartilage formation, making them essential for linear growth. **2. Why the Other Options are Incorrect:** * **Option A:** Somatomedins are **anabolic**. They stimulate amino acid uptake and increase protein synthesis in muscles and other tissues, rather than inhibiting it. * **Option B:** Somatomedins have **insulin-like activity** (hence the name IGF). Unlike GH, which is "diabetogenic" and antagonizes insulin, somatomedins can lower blood glucose and promote glucose uptake into peripheral tissues. * **Option C:** Somatomedins mediate the effects of **Growth Hormone**, not Somatostatin. Somatostatin is actually a potent inhibitor of GH secretion from the anterior pituitary. **High-Yield Facts for NEET-PG:** * **Site of Production:** Primarily the **Liver** (stimulated by GH). * **Laron Dwarfism:** A condition caused by GH receptor mutations; GH levels are high, but **IGF-1 levels are low**, resulting in growth failure. * **Feedback:** IGF-1 exerts negative feedback on the hypothalamus (stimulating somatostatin) and the anterior pituitary to inhibit further GH release. * **African Pygmies:** They possess normal GH levels but have a congenital deficiency in IGF-1, leading to short stature.

Question 54: Which hormone(s) utilize the cyclic adenosine monophosphate (cAMP) as a second messenger system?

A. Calcitonin (Correct Answer)
B. Angiotensin Converting Enzyme
C. Prolactin
D. All of the above

Explanation: **Explanation:** The mechanism of hormone action is a high-yield topic for NEET-PG. Hormones that are water-soluble (peptides and catecholamines) cannot cross the lipid bilayer and must bind to cell surface receptors, triggering **second messenger systems**. **1. Why Calcitonin is Correct:** Calcitonin, secreted by the parafollicular (C-cells) of the thyroid, binds to G-protein coupled receptors (GPCRs). This activates the enzyme **Adenylate Cyclase**, which converts ATP into **cyclic AMP (cAMP)**. Other major hormones using this pathway include ACTH, Glucagon, TSH, PTH, and ADH (via V2 receptors). **2. Why Incorrect Options are Wrong:** * **Angiotensin-Converting Enzyme (ACE):** This is an **enzyme**, not a hormone. It converts Angiotensin I to Angiotensin II. While Angiotensin II is a hormone, it primarily utilizes the **IP3/DAG (Phospholipase C)** pathway, not cAMP. * **Prolactin:** Prolactin (along with Growth Hormone and Insulin) utilizes the **JAK-STAT pathway** (Enzyme-linked receptor). It does not use cAMP as a second messenger. **3. Clinical Pearls & High-Yield Facts:** * **cAMP Pathway Mnemonic (FLAT ChAMP):** **F**SH, **L**H, **A**CTH, **T**SH, **C**alcitonin, **h**CG, **A**DH (V2), **M**SH, **P**TH. * **IP3/DAG Mnemonic (GOAT):** **G**nRH, **O**xytocin, **A**ngiotensin II, **T**RH. * **ANP/NO:** Utilize **cyclic GMP (cGMP)**. * **Steroid/Thyroid Hormones:** These are lipid-soluble and act via **intracellular/nuclear receptors** to alter gene transcription directly.

Question 55: Central diabetes insipidus is characterized by?

A. Low plasma and low urine osmolality
B. High plasma and high urine osmolality
C. Low plasma and high urine osmolality
D. Low urine and high plasma osmolality (Correct Answer)

Explanation: **Explanation:** Central Diabetes Insipidus (CDI) is caused by a deficiency in the production or secretion of **Antidiuretic Hormone (ADH)** from the posterior pituitary. ADH normally acts on the V2 receptors in the collecting ducts of the kidney to reabsorb water. 1. **Why Option D is correct:** In the absence of ADH, the kidneys cannot reabsorb water, leading to the excretion of large volumes of dilute urine. This results in **low urine osmolality** (typically <200 mOsm/kg). The excessive loss of free water leads to hemoconcentration, resulting in **high plasma osmolality** (hypernatremia). 2. **Why other options are incorrect:** * **Option A:** Low plasma osmolality is seen in Primary Polydipsia (excessive water intake). * **Option B:** High urine osmolality occurs in dehydration where ADH is functioning normally to conserve water. * **Option C:** This pattern is physiologically impossible in DI; if urine osmolality is high, the body is conserving water, which would lower plasma osmolality. **NEET-PG High-Yield Pearls:** * **Gold Standard Diagnosis:** The **Water Deprivation Test**. In CDI, urine osmolality remains low despite dehydration but increases significantly (>50%) after administering exogenous desmopressin (differentiating it from Nephrogenic DI). * **Treatment of Choice:** Desmopressin (DDAVP), a synthetic ADH analogue. * **Most common cause:** Idiopathic, followed by head trauma or neurosurgery (transsphenoidal surgery). * **Triphasic Response:** Post-trauma/surgery, patients may show: DI phase → SIADH phase → Permanent DI phase.

Question 56: Which of the following is an amide hormone?

A. Thyroid releasing hormone (Correct Answer)
B. Melanocyte stimulating hormone
C. ACTH
D. TSH

Explanation: **Explanation:** Hormones are classified based on their chemical structure into three main categories: Steroids, Proteins/Peptides, and **Amine/Amide derivatives**. **Correct Option: A (Thyroid Releasing Hormone - TRH)** TRH is a tripeptide (Glutamate-Histidine-Proline). However, in its functional form, the C-terminus is **amidated** (prolinamide) and the N-terminus is cyclized. In many physiological classifications used in medical entrance exams, TRH is specifically highlighted for this C-terminal amidation, which is essential for its biological activity and resistance to proteolysis. **Incorrect Options:** * **B & C (MSH and ACTH):** Both are derived from the precursor molecule Pro-opiomelanocortin (POMC). They are classified as **peptide hormones**. * **D (TSH):** TSH is a **glycoprotein** hormone (consisting of alpha and beta subunits). It is much larger and more complex than simple amide or peptide hormones. **High-Yield Facts for NEET-PG:** 1. **Amine vs. Amide:** While "Amine" hormones are typically derived from Tyrosine (Thyroid hormones, Catecholamines) or Tryptophan (Melatonin), "Amide" in the context of TRH refers to the chemical modification of its peptide chain. 2. **The "P" Rule:** Most hormones from the Hypothalamus, Pituitary, Pancreas, and Parathyroid are **P**eptides/Proteins. 3. **Steroids:** Derived from cholesterol; includes Cortisol, Aldosterone, Testosterone, Estrogen, Progesterone, and Vitamin D. 4. **Water Solubility:** Peptide and Amine hormones (except Thyroid hormones) are water-soluble and bind to cell surface receptors. Steroid and Thyroid hormones are lipid-soluble and bind to intracellular receptors.

Question 57: Venous drainage from the neurohypophysis occurs through which of the following pathways EXCEPT?

A. Portal vessels to the adenohypophysis
B. Superior hypophyseal veins to ventricular tanycytes (Correct Answer)
C. Inferior hypophyseal veins to dural venous sinuses
D. Capillaries to the median eminence and hypothalamus

Explanation: The neurohypophysis (posterior pituitary) lacks a direct arterial supply like most organs; instead, it is part of a complex vascular network designed for neuroendocrine signaling. ### **Explanation of the Correct Answer** **Option B** is the correct answer because it is anatomically incorrect. The **superior hypophyseal arteries** supply the primary capillary plexus of the median eminence, not the venous drainage of the neurohypophysis. Furthermore, **tanycytes** are specialized ependymal cells that bridge the CSF in the third ventricle to the portal vessels; they are involved in transport and sensing, but they do not serve as a venous drainage pathway for the posterior pituitary. ### **Analysis of Other Options** * **Option A:** A significant portion of blood from the neurohypophysis drains into the **short portal vessels**, which carry posterior pituitary hormones (like Oxytocin and ADH) directly to the adenohypophysis. This allows for local modulation of anterior pituitary function. * **Option C:** The bulk of the venous blood from the posterior lobe is collected by the **inferior hypophyseal veins**, which then drain into the **cavernous sinus** (a dural venous sinus) to enter systemic circulation. * **Option D:** There is "retrograde" or bidirectional flow through capillary connections toward the **median eminence and hypothalamus**. This "short-loop feedback" allows pituitary hormones to directly influence the hypothalamic neurons that regulate them. ### **High-Yield NEET-PG Pearls** * **Dual Blood Supply:** The anterior pituitary has no direct arterial supply (supplied by portal vessels), while the posterior pituitary is supplied by the **inferior hypophyseal artery**. * **The Portal System:** It is a "low-pressure" system. The primary plexus is in the median eminence, and the secondary plexus is in the pars distalis. * **Tanycytes:** These are key markers for the **blood-brain barrier** interface in the circumventricular organs. They play a role in the "GnRH pulse generator" mechanism. * **Hormone Storage:** Remember, the neurohypophysis does *not* synthesize hormones; it only stores and releases ADH and Oxytocin produced in the **supraoptic and paraventricular nuclei**.

Question 58: Which of the following hormones shares a common beta subunit with TSH?

A. LH
B. FSH
C. ACTH
D. None of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **None of the above** because the question asks which hormone shares a **beta (β) subunit** with TSH. In endocrinology, it is a fundamental concept that the glycoprotein hormone family—consisting of **TSH, LH, FSH, and hCG**—shares an **identical alpha (α) subunit**. 1. **The Concept of Subunits:** These hormones are heterodimers. The **alpha (α) subunit** is common to all four (encoded by the same gene), whereas the **beta (β) subunit** is unique to each hormone. The beta subunit is what confers **biological specificity** and determines the specific receptor binding and physiological action. 2. **Why Options A and B are Incorrect:** LH and FSH share the same alpha subunit as TSH, but they have their own distinct beta subunits (LH-β and FSH-β). Therefore, they do not share a beta subunit with TSH. 3. **Why Option C is Incorrect:** ACTH is a polypeptide derived from the precursor molecule **POMC** (Pro-opiomelanocortin). It is not a glycoprotein and does not possess alpha or beta subunits. **High-Yield Clinical Pearls for NEET-PG:** * **Cross-reactivity:** Because hCG shares the same alpha subunit and a very similar beta subunit to TSH, extremely high levels of hCG (as seen in Hydatidiform mole or Choriocarcinoma) can weakly bind to TSH receptors, potentially causing **hyperthyroidism**. * **Pregnancy Tests:** Pregnancy tests specifically use antibodies against the **beta-subunit of hCG** to avoid cross-reactivity with LH, FSH, or TSH. * **Commonality:** Remember the mnemonic **"F-L-A-T"** (FSH, LH, ACTH, TSH) for anterior pituitary hormones, but distinguish that only FSH, LH, and TSH (plus placental hCG) are the glycoproteins with shared alpha subunits.

Question 59: Which of the following hormones is not secreted by the kidney?

A. Renin
B. Angiotensin I (Correct Answer)
C. Erythropoietin
D. 1,25-dihydroxycholecalciferol

Explanation: **Explanation:** The kidney functions as both an excretory and an endocrine organ. The correct answer is **Angiotensin I** because it is not secreted by the kidney; rather, it is produced in the **circulating blood**. 1. **Why Angiotensin I is the correct answer:** Angiotensin I is a decapeptide produced when **Renin** (secreted by the kidney) acts upon **Angiotensinogen** (a plasma protein synthesized by the liver). This conversion occurs in the systemic circulation, not within the renal parenchyma. Angiotensin I is subsequently converted to Angiotensin II by the Angiotensin-Converting Enzyme (ACE), primarily in the pulmonary capillaries. 2. **Why other options are incorrect:** * **Renin:** Secreted by the **Juxtaglomerular (JG) cells** of the afferent arteriole in response to low blood pressure or low sodium delivery. * **Erythropoietin (EPO):** Produced by **interstitial cells in the peritubular capillary bed** of the renal cortex. It stimulates RBC production in the bone marrow in response to hypoxia. * **1,25-dihydroxycholecalciferol (Calcitriol):** The kidney contains the enzyme **1-alpha-hydroxylase** (in the proximal convoluted tubule), which converts 25-hydroxyvitamin D into its active form, Calcitriol. **High-Yield Clinical Pearls for NEET-PG:** * **Renin** is an enzyme, but it is often functionally classified as a hormone in the RAAS axis. * **Thrombopoietin** is primarily produced by the liver, but a small amount is also secreted by the kidney. * **Prostaglandins (PGE2 and PGI2)** are produced in the renal medulla and act as local vasodilators to maintain renal blood flow. * In **Chronic Kidney Disease (CKD)**, the deficiency of Erythropoietin leads to normocytic normochromic anemia, and the deficiency of Calcitriol leads to secondary hyperparathyroidism (Renal Osteodystrophy).

Question 60: What is the number of primordial follicles in the ovary at birth?

A. 2 million (Correct Answer)
B. 7 million
C. 10 million
D. 20 million

Explanation: ### Explanation The number of primordial follicles in the human ovary follows a specific pattern of attrition throughout a woman's life, a process known as **follicular atresia**. **1. Why Option A (2 million) is Correct:** During fetal development, the number of germ cells increases rapidly via mitosis. At birth, the total number of primordial follicles in both ovaries is approximately **1 to 2 million**. These follicles remain in a state of meiotic arrest (prophase of Meiosis I) until puberty. **2. Why the Other Options are Incorrect:** * **Option B (7 million):** This is the **peak number** of germ cells (oogonia) reached at the **20th week of intrauterine life**. After this peak, massive atresia begins even before birth. * **Options C & D (10 and 20 million):** These values are physiologically inaccurate and exceed the maximum germ cell count ever recorded in human fetal development. **3. High-Yield NEET-PG Clinical Pearls:** * **At Puberty:** The number of follicles drops to approximately **300,000 to 400,000**. * **Reproductive Span:** Only about **400 to 500** follicles will actually ovulate during a woman's reproductive life; the rest undergo atresia. * **Menopause:** Occurs when the follicle count falls below a critical threshold (usually <1,000). * **Meiotic Arrest:** Primordial follicles are arrested in the **Diplotene stage of Prophase I** (often called the Dictyate stage) until ovulation. * **Key Concept:** The ovary does not produce new follicles after birth; the "ovarian reserve" only diminishes over time.

Practice by Chapter

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Growth Hormone and Growth Factors

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Assessment of Endocrine Function

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