Endocrinology Practice Questions

Q: A hormone acts to stimulate its neighbouring cell to divide. To which category of signaling does this hormone's action best belong?

Paracrine signaling. **Explanation:** The correct answer is **Paracrine signaling**. This mode of communication involves a cell secreting a chemical messenger (hormone or cytokine) that diffuses through the interstitial fluid to act on **neighboring or adjacent cells** of a different type. Since the question specifies the hormone acts on its "neighboring cell," it perfectly fits the definition of paracrine action. **Analysis of Options:** * **Autocrine signaling:** In this mechanism, the hormone or chemical messenger acts on the **same cell** that secreted it (self-stimulation). This is common in cancer cell proliferation and immune responses (e.g., Interleukin-2 acting on the same T-cell). * **Endocrine signaling:** This involves hormones being secreted into the **bloodstream** to act on distant target organs. This is the classic mechanism for hormones like Insulin or Thyroxine. * **Juxtacrine signaling (Related Concept):** This requires direct physical contact between the membranes of two cells (e.g., Notch signaling). **High-Yield NEET-PG Pearls:** * **Paracrine Example:** Somatostatin secreted by Delta cells of the Islets of Langerhans inhibits the secretion of Insulin (Beta cells) and Glucagon (Alpha cells) in its immediate vicinity. * **Neuroendocrine:** A variation where a neuron releases a hormone into the blood (e.g., ADH from the posterior pituitary). * **Intracrine:** A hormone acts inside the cell without ever being secreted (e.g., Steroid hormones acting on nuclear receptors). * **Key Distinction:** The primary difference between these signaling types is the **distance** the messenger travels and the **medium** (interstitial fluid vs. blood) it uses.

Q: Which hormone stimulates the production of IGF?

GH. **Explanation:** **1. Why GH is the correct answer:** Growth Hormone (GH), secreted by the somatotrophs of the anterior pituitary, does not exert most of its growth-promoting effects directly. Instead, it acts primarily by stimulating the liver (and to a lesser extent, skeletal muscle and cartilage) to produce **Insulin-like Growth Factor-1 (IGF-1)**, also known as **Somatomedin C**. The GH-IGF-1 axis is the primary pathway for longitudinal bone growth and protein synthesis. While GH has direct metabolic effects (lipolysis and anti-insulin actions), its anabolic and growth-promoting functions are mediated by IGF-1. **2. Why other options are incorrect:** * **LH (Luteinizing Hormone):** Stimulates Leydig cells in testes to produce testosterone and triggers ovulation/progesterone production in ovaries. * **PRL (Prolactin):** Primarily responsible for milk production (lactogenesis) and inhibiting GnRH; it has no significant role in IGF production. * **TSH (Thyroid Stimulating Hormone):** Stimulates the thyroid gland to synthesize and release T3 and T4, which regulate the basal metabolic rate. **3. NEET-PG High-Yield Pearls:** * **Site of Production:** The **liver** is the principal source of circulating IGF-1. * **Feedback Loop:** IGF-1 exerts negative feedback on the anterior pituitary to inhibit GH secretion and stimulates the hypothalamus to release Somatostatin (GHIH). * **Clinical Correlation:** In **Laron Dwarfism**, there is a genetic GH receptor deficiency; GH levels are high, but IGF-1 levels are low, and patients do not respond to exogenous GH. * **Diagnosis:** Serum IGF-1 levels are more stable than GH levels (which are pulsatile) and are used as the primary screening tool for **Acromegaly**.

Q: The hormone whose deficiency causes diabetes insipidus is released from which nucleus of the pituitary gland?

Supraoptic. The hormone whose deficiency causes **Diabetes Insipidus (DI)** is **Antidiuretic Hormone (ADH)**, also known as Vasopressin [1]. ADH is synthesized in the hypothalamus and transported to the posterior pituitary (neurohypophysis) for storage and release [2]. 1. **Why Option A is Correct:** While both the **Supraoptic** and **Paraventricular** nuclei synthesize ADH and Oxytocin, the **Supraoptic nucleus (SON)** is primarily responsible for the production of **ADH** (approx. 5:1 ratio) [1]. Damage to the SON or the hypothalamo-hypophyseal tract leads to Central Diabetes Insipidus, characterized by polyuria and polydipsia [1]. 2. **Why Other Options are Incorrect:** * **Paraventricular Nucleus (PVN):** Primarily responsible for the synthesis of **Oxytocin**. While it produces some ADH, it is not the predominant source [2]. * **Suprachiasmatic Nucleus:** This nucleus is the master pacemaker for **circadian rhythms** (biological clock), responding to light-dark cycles. * **Pre-optic Nucleus:** Involved in **thermoregulation** and the release of Gonadotropin-Releasing Hormone (GnRH). **High-Yield Clinical Pearls for NEET-PG:** * **Site of Synthesis vs. Release:** ADH is *synthesized* in the hypothalamus (SON) but *released* from the posterior pituitary (Pars Nervosa) [2]. * **Mechanism of Action:** ADH acts on **V2 receptors** in the late distal tubule and collecting ducts to insert **Aquaporin-2** channels, facilitating water reabsorption [3]. * **Diagnostic Test:** The **Water Deprivation Test** is used to differentiate between Central DI, Nephrogenic DI, and Primary Polydipsia [4]. * **Treatment:** Desmopressin (DDAVP) is the drug of choice for Central Diabetes Insipidus.

Q: Elevated levels of somatostatin are pathologically associated with which of the following blood hormone levels?

Low growth hormone (GH). **Explanation:** **1. Why the Correct Answer is Right:** Somatostatin, also known as **Growth Hormone Inhibiting Hormone (GHIH)**, is a potent inhibitory peptide produced primarily by the hypothalamus and the delta cells of the pancreas. Its primary physiological role in the anterior pituitary is to **inhibit the secretion of Growth Hormone (GH)**. Therefore, pathologically elevated levels of somatostatin (such as in a somatostatinoma) will lead to the suppression of GH release, resulting in **low GH levels**. **2. Why the Other Options are Incorrect:** * **High Prolactin (PRL):** Prolactin is primarily regulated by the inhibitory action of **Dopamine**. Somatostatin does not significantly regulate prolactin; thus, elevated somatostatin would not cause high PRL. * **High TSH:** Somatostatin actually **inhibits** the release of Thyroid Stimulating Hormone (TSH). Therefore, high somatostatin would lead to *low* TSH levels, not high. * **High Cortisol:** Cortisol is regulated by the ACTH axis. Somatostatin has no major inhibitory or stimulatory effect on the secretion of ACTH or cortisol under normal physiological conditions. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Dual Inhibition:** Somatostatin inhibits both **GH and TSH** from the anterior pituitary. * **Pancreatic Action:** In the pancreas, it acts paracrinely to inhibit both **Insulin and Glucagon** secretion. * **Gastrointestinal Action:** It decreases gastric acid secretion (inhibits Gastrin), gallbladder contraction (inhibits CCK), and pancreatic enzyme secretion. * **Clinical Use:** Synthetic analogs like **Octreotide** are used clinically to treat Acromegaly (by lowering GH), secretory diarrheas (Carcinoid syndrome), and esophageal varices. * **Somatostatinoma Triad:** Steatorrhea, Diabetes Mellitus, and Cholelithiasis (due to global inhibition of GI hormones).

Q: Estrogen receptors are present in which of the following bone cells?

All of the above. **Explanation:** Estrogen plays a pivotal role in maintaining bone mineral density and regulating bone remodeling. Traditionally, it was believed that estrogen acted primarily on osteoblasts; however, molecular research has confirmed that **Estrogen Receptors (ER-α and ER-β)** are expressed in **all major types of bone cells**, making "All of the above" the correct answer. **Mechanism of Action:** 1. **Osteoblasts:** Estrogen binds to receptors on osteoblasts to increase their proliferation and differentiation. It stimulates the production of **OPG (Osteoprotegerin)**, which acts as a decoy receptor for RANKL, thereby inhibiting osteoclastogenesis. 2. **Osteoclasts:** Estrogen acts directly on osteoclasts to induce **apoptosis** and decrease their resorptive activity. It also indirectly inhibits them by reducing the expression of RANKL by T-cells and osteoblasts. 3. **Osteocytes:** Estrogen receptors in osteocytes help prevent cell death (apoptosis). Since osteocytes sense mechanical strain, estrogen helps maintain the integrity of the bone matrix through these cells. **Why other options are incorrect:** Options A, B, and C are individual components of the bone remodeling unit. While estrogen does act on each, selecting only one would be incomplete. The integrated action across all three cell types is what ensures the "anti-resorptive" effect of estrogen. **High-Yield Clinical Pearls for NEET-PG:** * **Postmenopausal Osteoporosis:** The decline in estrogen leads to an increase in RANKL and a decrease in OPG, resulting in unchecked osteoclast activity and rapid bone loss. * **Cytokine Regulation:** Estrogen suppresses pro-inflammatory cytokines like **IL-1, IL-6, and TNF-α**, which are potent stimulators of bone resorption. * **Biochemical Marker:** In estrogen deficiency, there is an increase in bone turnover markers (e.g., urinary N-telopeptide).

Q: Which of the following hormones is orally active?

Thyroxine. **Explanation:** The oral activity of a hormone depends primarily on its chemical structure and its ability to withstand digestion by proteolytic enzymes in the gastrointestinal tract. **1. Why Thyroxine (T4) is correct:** Thyroxine is an **iodinated derivative of the amino acid tyrosine**. Unlike protein or peptide hormones, it is a small, non-peptide molecule that is not degraded by gastric acid or proteases (like pepsin, trypsin, or chymotrypsin). It is efficiently absorbed in the small intestine (primarily the ileum and jejunum), making it highly effective when administered orally. This property is the basis for its use in the lifelong management of hypothyroidism. **2. Why the other options are incorrect:** * **TSH (Thyroid Stimulating Hormone), GH (Growth Hormone), and Prolactin** are all **peptide/protein hormones**. * If taken orally, these hormones would be denatured by stomach acid and hydrolyzed into their constituent amino acids by digestive enzymes before they could be absorbed into the bloodstream. * Therefore, these hormones must be administered parenterally (e.g., subcutaneous or intramuscular injections) to maintain their biological activity. **Clinical Pearls for NEET-PG:** * **Steroid Hormones** (e.g., Estrogen, Progesterone, Cortisol) are also orally active because they are lipid-soluble and resistant to digestive enzymes. * **Insulin** is a classic example of a peptide hormone that cannot be given orally (requires SC injection). * **Absorption Tip:** Oral Thyroxine absorption is decreased by food, calcium supplements, and iron; hence, it is clinically advised to be taken on an empty stomach. * **Exceptions:** Some small peptides like **Desmopressin** can be administered via oral/buccal routes using high doses or specialized formulations, but standard peptide hormones are generally not orally active.

Q: Which one of the following pituitary hormones is an opioid peptide?

Beta endorphin. **Explanation:** The correct answer is **Beta-endorphin**. The underlying concept lies in the post-translational processing of the precursor molecule **Pro-opiomelanocortin (POMC)**. POMC is a large pro-hormone synthesized in the anterior and intermediate lobes of the pituitary gland. It undergoes tissue-specific enzymatic cleavage by prohormone convertases to produce several biologically active peptides. **Beta-endorphin** is one of these derivatives and is classified as an **endogenous opioid peptide**. It acts primarily on $\mu$-opioid receptors to produce analgesic effects and a sense of well-being. **Analysis of Options:** * **ACTH (Adrenocorticotropic Hormone):** While derived from POMC, ACTH is a polypeptide hormone that stimulates the adrenal cortex to produce cortisol; it does not possess opioid activity. * **Alpha and Beta-MSH (Melanocyte Stimulating Hormones):** These are also derivatives of POMC (formed by the cleavage of ACTH and Beta-lipotropin, respectively). Their primary function is stimulating melanin production in melanocytes; they are not opioid peptides. **High-Yield Clinical Pearls for NEET-PG:** * **POMC Derivatives:** Remember the "family" — ACTH, $\beta$-endorphin, $\alpha$-MSH, $\beta$-MSH, and $\gamma$-MSH. * **Common Origin:** Because ACTH and MSH share the same precursor (POMC), conditions with high ACTH (like Addison’s disease or Nelson’s Syndrome) often present with **hyperpigmentation**. * **Opioid Receptors:** Beta-endorphin has the highest affinity for **$\mu$ (mu) receptors**. * **Site of Synthesis:** POMC is mainly produced in the **corticotrophs** of the anterior pituitary.

Q: Excess of growth hormone does not cause which of the following conditions?

Obesity. **Explanation:** The correct answer is **Obesity**. Growth Hormone (GH) is a potent **lipolytic hormone**; it stimulates the breakdown of triglycerides into free fatty acids. Consequently, an excess of GH typically leads to a reduction in adipose tissue rather than an increase. **Why the other options are incorrect:** * **Gigantism:** This occurs when GH excess occurs **before the fusion of epiphyseal plates** in children, leading to excessive linear bone growth and tall stature. * **Acromegaly:** This occurs when GH excess occurs **after epiphyseal fusion** in adults. It is characterized by the enlargement of hands, feet, and facial bones (membranous bone growth). * **Diabetes:** GH is a **diabetogenic hormone**. It decreases peripheral glucose uptake (anti-insulin effect) and increases hepatic gluconeogenesis. Chronic excess leads to "Pituitary Diabetes." **High-Yield Clinical Pearls for NEET-PG:** 1. **Metabolic Effects:** GH increases protein synthesis (anabolic), increases blood glucose (diabetogenic), and decreases fat stores (lipolytic). 2. **Mediator:** Most growth-promoting effects of GH are mediated by **IGF-1 (Somatomedin C)**, primarily produced in the liver. 3. **Diagnosis:** The gold standard screening test for Acromegaly is measuring **Serum IGF-1 levels**. The definitive confirmatory test is the **Oral Glucose Tolerance Test (OGTT)**; normally, glucose suppresses GH, but in acromegaly, GH levels remain high or show a paradoxical rise. 4. **Visual Field:** A GH-secreting pituitary adenoma can compress the optic chiasm, leading to **bitemporal hemianopia**.

Q: Which of the following is the active form of calcium in the body?

Ionized calcium. **Explanation:** Calcium in the plasma exists in three distinct fractions: **Ionized (free) calcium (~50%)**, **Protein-bound calcium (~40%)**, and **Complexed calcium (~10%)**. **1. Why Ionized Calcium is the Correct Answer:** Ionized calcium ($Ca^{2+}$) is the only **physiologically active** form. It is the form that is regulated by parathyroid hormone (PTH) and calcitinin, and it is responsible for vital cellular processes including neuromuscular excitability, cardiac contractility, blood coagulation, and enzyme activation. The body maintains the concentration of ionized calcium within a very narrow range to ensure normal physiological function. **2. Analysis of Incorrect Options:** * **Bound to Albumin:** This is the largest fraction of non-diffusible calcium. While it serves as a reservoir, it is physiologically inactive. Clinical Tip: Hypoalbuminemia decreases *total* calcium but usually leaves *ionized* calcium (the active part) unaffected. * **Complexed with Phosphate/Oxalates:** These represent the "complexed" fraction where calcium is bound to small anions (citrate, phosphate, bicarbonate). While diffusible, these complexes are not immediately available for cellular signaling or physiological action. **3. High-Yield NEET-PG Pearls:** * **Acid-Base Balance:** Alkalosis (e.g., hyperventilation) increases calcium binding to albumin, **decreasing ionized calcium** levels. This can trigger tetany even if total serum calcium is normal. * **The Formula:** Corrected Calcium = Measured Total Calcium + [0.8 × (4.0 - Patient's Albumin)]. * **Storage:** 99% of total body calcium is stored in the bone as **hydroxyapatite crystals**.

Question 1

A hormone acts to stimulate its neighbouring cell to divide. To which category of signaling does this hormone's action best belong?

Accepted Answer

Paracrine signaling

Answer

Autocrine signaling

Answer

Endocrine signaling

Answer

None of the above

Question 2

Which hormone stimulates the production of IGF?

Accepted Answer

GH

Answer

LH

Answer

PRL

Answer

TSH

Question 3

Which is the single most important factor that stimulates insulin secretion?

Accepted Answer

Increased plasma glucose concentration stimulates insulin release

Answer

Decreased plasma glucose concentration inhibits insulin release

Answer

Decreased plasma glucose concentration stimulates insulin release

Answer

Increased plasma glucose concentration inhibits insulin release

Question 4

The hormone whose deficiency causes diabetes insipidus is released from which nucleus of the pituitary gland?

Accepted Answer

Supraoptic

Answer

Pre optic

Answer

Suprachiasmatic

Answer

Paraventricular

Question 5

Elevated levels of somatostatin are pathologically associated with which of the following blood hormone levels?

Accepted Answer

Low growth hormone (GH)

Answer

High prolactin (PRL)

Answer

High TSH

Answer

High cortisol

Question 6

Estrogen receptors are present in which of the following bone cells?

Accepted Answer

All of the above

Answer

Osteoblasts

Answer

Osteoclasts

Answer

Osteocytes

Question 7

Which of the following hormones is orally active?

Accepted Answer

Thyroxine

Answer

TSH

Answer

GH

Answer

Prolactin

Question 8

Which one of the following pituitary hormones is an opioid peptide?

Accepted Answer

Beta endorphin

Answer

ACTH

Answer

Alpha melanocyte stimulating hormone

Answer

Beta melanocyte stimulating hormone

Question 9

Excess of growth hormone does not cause which of the following conditions?

Accepted Answer

Obesity

Answer

Gigantism

Answer

Acromegaly

Answer

Diabetes

Question 10

Which of the following is the active form of calcium in the body?

Accepted Answer

Ionized calcium

Answer

Complexed with phosphate

Answer

Complexed with oxalates

Answer

Bound to albumin

Endocrinology — MCQs

Endocrinology — MCQs

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