Endocrinology Practice Questions

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**.

Q: Which of the following is a known effect of catecholamines?

Decrease gut motility. **Explanation:** Catecholamines (Epinephrine and Norepinephrine) are the primary mediators of the **"Fight or Flight" response**, acting via alpha (α) and beta (β) adrenergic receptors to prepare the body for acute stress. **1. Why Option A is Correct:** Catecholamines **decrease gut motility** and secretions while causing the contraction of sphincters. This occurs through: * **β2 receptors:** Relaxation of the smooth muscles in the intestinal wall. * **α2 receptors:** Inhibition of acetylcholine release from parasympathetic nerve terminals (presynaptic inhibition). In a stressful state, the body diverts energy and blood flow away from the digestive system toward the heart and skeletal muscles. **2. Analysis of Incorrect Options:** * **B. Bronchoconstriction:** Incorrect. Catecholamines cause **bronchodilation** via **β2 receptors**. This reduces airway resistance to maximize oxygen intake during stress. * **C. Decrease plasma glucose:** Incorrect. Catecholamines are **hyperglycemic** hormones. They increase plasma glucose by stimulating glycogenolysis (liver/muscle) and gluconeogenesis via β2 and α1 receptors. * **D. Inhibit lipolysis:** Incorrect. Catecholamines **stimulate lipolysis** in adipose tissue (primarily via **β3 receptors**), breaking down triglycerides into free fatty acids to be used as an alternative energy source. **High-Yield Clinical Pearls for NEET-PG:** * **Receptor Rule:** Generally, **α1** is excitatory (vasoconstriction), **β1** is excitatory (increased heart rate/contractility), and **β2** is inhibitory (bronchodilation, vasodilation in muscles, gut relaxation). * **Metabolic Effect:** Epinephrine is more potent than Norepinephrine in stimulating metabolism and hyperglycemia. * **Clinical Link:** Beta-blockers (like Propranolol) are contraindicated in asthmatics because they block β2 receptors, leading to bronchospasm.

Q: Which of the following is NOT essential for normal biosynthesis of thyroid hormone?

Ferritin. **Explanation:** The biosynthesis of thyroid hormones (T3 and T4) is a complex process occurring within the thyroid follicles, requiring specific substrates and regulatory factors. **Why Ferritin is the Correct Answer:** **Ferritin** is the primary intracellular storage protein for **iron**. While iron is a necessary cofactor for the enzyme *Thyroid Peroxidase (TPO)*, ferritin itself is not a direct substrate or an essential component of the thyroid hormone synthetic pathway. Its presence or absence in the follicular lumen does not govern the immediate biosynthesis of T3 and T4. **Why the other options are essential:** * **Iodine (A):** This is the fundamental raw material. It must be trapped from the blood and oxidized to be incorporated into tyrosine residues. * **Thyroglobulin (C):** This large glycoprotein acts as the scaffold. Synthesis occurs on the tyrosine residues of thyroglobulin within the follicular lumen (colloid). * **TSH (D):** Secreted by the anterior pituitary, TSH is the primary stimulator of every step of thyroid hormone synthesis, including the iodine pump (NIS), thyroglobulin synthesis, and the coupling reaction. **High-Yield Clinical Pearls for NEET-PG:** * **Thyroid Peroxidase (TPO):** The most critical enzyme, responsible for oxidation, organification, and coupling. It is the target of antithyroid drugs like Propylthiouracil (PTU) and Methimazole. * **Wolff-Chaikoff Effect:** A transient reduction in thyroid hormone synthesis caused by the ingestion of a large amount of iodine. * **Pendred Syndrome:** A genetic defect in the *Pendrin* transporter (iodide-chloride exchanger) leading to sensorineural hearing loss and goiter.

Q: Which one of the following central controllers of appetite does not decrease the appetite?

Melanin concentrating hormone (MCH). The regulation of appetite occurs primarily in the **Arcuate Nucleus (ARC)** of the hypothalamus, which integrates peripheral signals to control food intake via two distinct neuronal populations: the **Orexigenic** (appetite-stimulating) and **Anorexigenic** (appetite-suppressing) pathways. ### **Explanation of the Correct Answer** **C. Melanin Concentrating Hormone (MCH):** This is an **orexigenic** peptide produced in the lateral hypothalamic area. It acts as a potent stimulator of feeding behavior. When MCH levels increase, appetite and food intake increase, leading to energy storage. Therefore, it does *not* decrease appetite. ### **Explanation of Incorrect Options** * **A. CART (Cocaine-and-Amphetamine-Regulated Transcript):** These neurons are located in the ARC and are **anorexigenic**. Activation of CART pathways significantly decreases food intake and increases energy expenditure. * **B. GLP-1 (Glucagon-Like Peptide-1):** (Note: Likely intended as GLP-1 in the question). This is an incretin hormone that acts both peripherally and centrally to induce **satiety** and slow gastric emptying, thereby decreasing appetite. * **D. α-MSH (Alpha-Melanocyte Stimulating Hormone):** Derived from Pro-opiomelanocortin (POMC), α-MSH is the primary central **anorexigenic** mediator. It binds to MC3 and MC4 receptors to inhibit feeding. ### **High-Yield Clinical Pearls for NEET-PG** * **Orexigenic (Hunger) Signals:** Neuropeptide Y (NPY), Agouti-related peptide (AgRP), MCH, Orexins, and **Ghrelin** (the only major peripheral hunger hormone). * **Anorexigenic (Satiety) Signals:** POMC, α-MSH, CART, Leptin, Insulin, CCK, and PYY. * **The "Hunger Center":** Lateral Hypothalamus (Lesion leads to aphagia/starvation). * **The "Satiety Center":** Ventromedial Hypothalamus (Lesion leads to hyperphagia/obesity).

Q: Insulin-dependent glucose uptake is not seen in which of the following tissues?

Kidney. **Explanation:** The uptake of glucose into cells is mediated by **Glucose Transporters (GLUT)**. The core concept tested here is the distinction between insulin-dependent and insulin-independent glucose transport. **Why Kidney is the Correct Answer:** Glucose uptake in the **Kidney** (specifically the proximal convoluted tubules) and the **Small Intestine** occurs via **SGLT (Sodium-Glucose Co-transporters)** for active transport and **GLUT-2** for facilitated diffusion. Neither of these transporters requires insulin to function. This ensures that the body can reabsorb glucose from glomerular filtrate regardless of insulin levels. **Why the Other Options are Incorrect:** * **Skeletal Muscle & Heart (Options A & B):** These tissues primarily utilize **GLUT-4**. GLUT-4 is the only insulin-responsive glucose transporter. In the resting state, GLUT-4 is stored in intracellular vesicles; insulin binding to its receptor triggers the translocation of these transporters to the cell membrane. * **Adipose Tissue (Option C):** Like muscle, adipocytes rely on **GLUT-4** for glucose uptake to provide the glycerol backbone for triglyceride synthesis. Therefore, it is highly insulin-dependent. **High-Yield Clinical Pearls for NEET-PG:** * **GLUT-4 (Insulin-Dependent):** Found in Skeletal muscle, Cardiac muscle, and Adipose tissue. * **GLUT-1:** Responsible for basal glucose uptake (Brain, RBCs, Placenta). * **GLUT-2:** High-capacity, low-affinity transporter found in the **Liver, Pancreatic beta cells, and Kidney**. It acts as a "glucose sensor." * **GLUT-3:** Primary transporter in **Neurons** (highest affinity for glucose). * **GLUT-5:** Specifically transports **Fructose** (found in Jejunum and Spermatozoa). * **Exercise** can trigger GLUT-4 translocation in skeletal muscle even in the absence of insulin, which is why exercise helps manage blood sugar in Diabetics.

Q: Somatostatin is produced by:

D cell. **Explanation:** The Islets of Langerhans in the pancreas are composed of several distinct endocrine cell types, each secreting specific hormones that regulate glucose metabolism [1]. **Correct Answer: C. D cell (Delta cells)** Somatostatin is synthesized and secreted by the **D cells** of the pancreatic islets (as well as by cells in the gastrointestinal tract and the hypothalamus). In the pancreas, somatostatin acts primarily as a potent **inhibitor** [2]. It functions via paracrine signaling to inhibit the secretion of both Insulin and Glucagon, thereby modulating the glycemic response [1], [3]. **Analysis of Incorrect Options:** * **A. A cell (Alpha cells):** These cells comprise about 20% of the islet and are responsible for secreting **Glucagon**, which increases blood glucose levels via glycogenolysis and gluconeogenesis [1]. * **B. B cell (Beta cells):** These are the most numerous cells (approx. 65-70%) and secrete **Insulin**, which lowers blood glucose, and **Amylin**. * **D. F cell (PP cells):** These cells secrete **Pancreatic Polypeptide**, which plays a role in regulating exocrine pancreatic secretions and gallbladder contraction [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Somatostatinoma:** A rare neuroendocrine tumor of D cells characterized by the "Inhibitory Syndrome": Diabetes mellitus (low insulin), Cholelithiasis (low CCK/gallbladder motility), and Steatorrhea (low pancreatic enzymes). * **Octreotide:** A synthetic long-acting analog of somatostatin used clinically to treat acromegaly, carcinoid syndrome, and acute variceal bleeding. * **Universal Inhibitor:** Remember Somatostatin as the "Great Inhibitor"—it decreases GH, TSH, Insulin, Glucagon, and Gastrin [3].

Question 1

Which of the following hormones is orally active?

Accepted Answer

Thyroxine

Answer

TSH

Answer

GH

Answer

Prolactin

Question 2

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 3

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

Accepted Answer

Obesity

Answer

Gigantism

Answer

Acromegaly

Answer

Diabetes

Question 4

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

Question 5

Which of the following is a known effect of catecholamines?

Accepted Answer

Decrease gut motility

Answer

Bronchoconstriction

Answer

Decrease plasma glucose

Answer

Inhibit lipolysis

Question 6

Which of the following is NOT essential for normal biosynthesis of thyroid hormone?

Accepted Answer

Ferritin

Answer

Iodine

Answer

Thyroglobulin

Answer

TSH

Question 7

Which one of the following central controllers of appetite does not decrease the appetite?

Accepted Answer

Melanin concentrating hormone (MCH)

Answer

CART

Answer

GRP-1

Answer

MSH-alpha

Question 8

Insulin-dependent glucose uptake is not seen in which of the following tissues?

Accepted Answer

Kidney

Answer

Skeletal muscles

Answer

Heart

Answer

Adipose tissue

Question 9

Insulin facilitates glucose uptake in all of the following tissues except:

Accepted Answer

Heart

Answer

Liver

Answer

RBC

Answer

Kidney

Question 10

Somatostatin is produced by:

Accepted Answer

D cell

Answer

A cell

Answer

B cell

Answer

F cell

Endocrinology — MCQs

Endocrinology — MCQs

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