Endocrinology Practice Questions

Q: In the thyroid gland, the colloid material is predominantly composed of which of the following?

Thyroglobulin. **Explanation:** **1. Why Thyroglobulin is Correct:** The thyroid follicle is the functional unit of the thyroid gland. The central lumen of these follicles is filled with **colloid**, a viscous fluid. The primary constituent of this colloid is **Thyroglobulin (Tg)** [1], a large dimeric glycoprotein synthesized by the follicular epithelial cells. Thyroglobulin acts as a scaffold for thyroid hormone synthesis and a storage form of iodine. It contains tyrosine residues that undergo iodination to eventually form T3 and T4. **2. Why Other Options are Incorrect:** * **Thyroxine (T4):** While T4 is the major hormone produced by the thyroid, it is stored *within* the thyroglobulin molecule in the colloid. It is not the "predominant material" itself but a product cleaved from Tg before secretion into the blood. * **Monoiodotyrosine (MIT) & Diiodotyrosine (DIT):** These are intermediate iodinated tyrosine residues found attached to the thyroglobulin backbone. They are precursors to T3 and T4 and do not exist independently as the bulk of the colloid. **3. High-Yield Clinical Pearls for NEET-PG:** * **PAS Staining:** Thyroid colloid is strongly **PAS (Periodic Acid-Schiff) positive** [1] due to the high carbohydrate content of thyroglobulin. * **Scalloping:** In hyperactive states (like Graves' disease), the colloid shows "peripheral scalloping" or "moth-eaten" appearance due to rapid endocytosis of thyroglobulin by follicular cells. * **Tumor Marker:** Serum thyroglobulin is used as a tumor marker to monitor the recurrence of **Papillary and Follicular thyroid carcinomas** after total thyroidectomy. * **Site of Action:** The coupling of MIT and DIT occurs at the apical surface/colloid interface, catalyzed by **Thyroid Peroxidase (TPO)**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1085-1086.

Q: A man eats a low-carbohydrate meal rich in proteins containing amino acids that stimulate insulin secretion. Which physiological response accounts for the absence of hypoglycemia?

Stimulation of glucagon secretion. **Explanation:** **1. Why the Correct Answer is Right:** When a person consumes a high-protein, low-carbohydrate meal, certain amino acids (specifically arginine and lysine) act as potent secretagogues for **both insulin and glucagon**. Under normal circumstances, insulin lowers blood glucose by promoting peripheral uptake. However, in a low-carbohydrate meal, there is no exogenous glucose to offset this insulin action. To prevent life-threatening hypoglycemia, the pancreas simultaneously secretes **glucagon**. Glucagon stimulates hepatic glycogenolysis and gluconeogenesis, ensuring a steady output of glucose into the bloodstream. This "dual secretion" maintains euglycemia while allowing insulin to perform its primary role in the protein-rich state: promoting amino acid uptake and protein synthesis in muscles. **2. Why Other Options are Incorrect:** * **Options A & B:** Growth Hormone (GH) and Somatomedin C (IGF-1) are actually **stimulated** by amino acids (like arginine) to promote growth and protein synthesis. Suppressing them would not prevent hypoglycemia; in fact, GH is a counter-regulatory hormone that helps raise blood sugar. * **Option C:** While cortisol is a diabetogenic hormone that increases blood glucose, its secretion is primarily regulated by the HPA axis in response to stress or circadian rhythms. It does not show a rapid, acute spike specifically in response to a protein meal to prevent immediate hypoglycemia. **3. NEET-PG High-Yield Pearls:** * **The "Mixed Meal" Concept:** In a mixed meal (Carbs + Protein), insulin rises and glucagon is suppressed. In a pure protein meal, **both rise**. * **Potent Amino Acids:** Arginine is the most potent stimulator of both insulin and glucagon. * **Glucagon’s Primary Target:** The liver (glycogenolysis). It has no significant effect on muscle glycogen. * **Insulin/Glucagon Ratio:** This ratio determines the net metabolic state (Anabolic vs. Catabolic).

Q: The syndrome of growth failure, rash, and hypogonadism is due to deficiency of which essential nutrient?

Zinc. **Explanation:** The correct answer is **Zinc (Option C)**. Zinc is an essential trace element that acts as a cofactor for over 300 enzymes, including those involved in DNA synthesis, protein metabolism, and cell division. **Why Zinc is correct:** Zinc deficiency classically presents with a triad of **growth retardation (stunting)**, **hypogonadism (delayed sexual maturation)**, and **dermatitis**. * **Growth Failure:** Zinc is vital for the action of Growth Hormone and IGF-1. * **Hypogonadism:** It is essential for testosterone production and spermatogenesis. * **Rash:** Deficiency leads to a characteristic periorificial and acral dermatitis (classically seen in the genetic disorder *Acrodermatitis Enteropathica*). It also causes impaired wound healing and immune dysfunction. **Why other options are incorrect:** * **Calcium:** Deficiency primarily leads to rickets in children, osteomalacia in adults, and tetany due to neuromuscular irritability, but not typically a specific rash or hypogonadism. * **Copper:** Deficiency causes microcytic anemia (refractory to iron), neutropenia, and skeletal abnormalities. *Menkes Kinky Hair Syndrome* is the classic genetic deficiency. * **Magnesium:** Deficiency results in neuromuscular irritability (tremors, seizures) and cardiac arrhythmias, often associated with hypocalcemia and hypokalemia. **High-Yield Clinical Pearls for NEET-PG:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder of zinc absorption. * **Zinc & Taste:** Deficiency causes **hypogeusia** (decreased taste acuity). * **Zinc & Vision:** It is required for the enzyme retinol dehydrogenase; deficiency can contribute to night blindness. * **Diarrhea:** Zinc supplementation is a WHO-recommended standard of care to reduce the duration and severity of pediatric diarrhea.

Q: Triiodothyronine (T3) as compared to T4:

Is shorter acting. **Explanation:** The thyroid gland primarily secretes **Thyroxine (T4)**, which acts as a pro-hormone, while **Triiodothyronine (T3)** is the biologically active form. The differences in their pharmacokinetics and pharmacodynamics are high-yield topics for NEET-PG. **Why the correct answer is right:** T3 is **shorter acting** because it has a significantly lower affinity for plasma proteins (like Thyroxine-Binding Globulin) compared to T4. This results in a much shorter **half-life** (approx. 1 day for T3 vs. 6–7 days for T4). Because it is not "stored" in the blood by proteins, it is cleared and metabolized more rapidly. **Analysis of Incorrect Options:** * **A. Is more plasma protein bound:** Incorrect. T4 is 99.98% bound, whereas T3 is only 99.8% bound. The higher free fraction of T3 contributes to its rapid action and clearance. * **C. Is less potent:** Incorrect. T3 is **3 to 5 times more potent** than T4. It has a much higher affinity for the nuclear thyroid hormone receptors. * **D. Has delayed action:** Incorrect. T3 has a **rapid onset of action** (latent period of 6–12 hours) compared to T4 (latent period of 2–3 days). **High-Yield Clinical Pearls for NEET-PG:** * **Peripheral Conversion:** About 80% of T3 is derived from the peripheral deiodination of T4 by the enzyme **5'-deiodinase**. * **Reverse T3 (rT3):** This is the metabolically inactive form produced during states of illness or starvation. * **Potency vs. Quantity:** T4 is secreted in larger quantities (ratio 20:1), but T3 is the functional mediator of metabolic effects. * **Thyroid Storm:** Proportions of T3 increase significantly, necessitating rapid-acting treatments like PTU which also inhibits peripheral conversion.

Q: All of the following statements concerning Atrial Natriuretic Peptide (ANP) are true except:

Its effects are mediated by decreased cyclic AMP. **Explanation:** The correct answer is **D** because the effects of Atrial Natriuretic Peptide (ANP) are mediated by an **increase in cyclic GMP (cGMP)**, not a decrease in cAMP. ANP binds to its receptor (NPR-A), which has intrinsic **guanylyl cyclase** activity. This converts GTP to cGMP, which then activates Protein Kinase G (PKG) to produce physiological effects like vasodilation and natriuresis. **Analysis of Options:** * **Option A (Incorrect):** This is a true statement. The primary stimulus for ANP release is the **stretching of atrial myocytes** caused by increased blood volume or high atrial pressure. * **Option B (Incorrect):** This is a true statement. ANP increases GFR by **dilating afferent arterioles** and **constricting efferent arterioles**. It also increases the capillary surface area for filtration by relaxing glomerular mesangial cells. * **Option C (Incorrect):** This is a true statement. ANP acts as a natural antagonist to the Renin-Angiotensin-Aldosterone System (RAAS). It directly inhibits the release of **renin** from juxtaglomerular cells and **aldosterone** from the adrenal cortex. **High-Yield Clinical Pearls for NEET-PG:** * **Second Messenger:** ANP and Nitric Oxide (NO) both use **cGMP** as a second messenger. * **Brain Natriuretic Peptide (BNP):** Secreted by ventricles in response to pressure overload; used clinically as a marker for **Congestive Heart Failure (CHF)**. * **Nesiritide:** A recombinant form of BNP used in the treatment of acute decompensated heart failure. * **Net Effect:** ANP is "heart-protective" as it lowers blood pressure and reduces fluid volume (natriuresis and diuresis).

Q: Insulin synthesis is stimulated by glucose levels above what threshold?

70 mg%. The synthesis and secretion of insulin by the pancreatic beta cells are tightly regulated by blood glucose concentrations. The correct answer is **70 mg% (70 mg/dL)** because this represents the physiological "set-point" or threshold at which the beta cells initiate the insulin response to prevent hyperglycemia [1]. Glucose enters the beta cell via **GLUT-2** transporters [3]. Once inside, it is phosphorylated by **Glucokinase** (the glucose sensor) [3]. When blood glucose levels rise above **70 mg/dL**, the rate of glycolysis increases, leading to an rise in the ATP/ADP ratio. This closes ATP-sensitive K+ channels, causing cell depolarization, calcium influx, and subsequent insulin release and synthesis [1, 3]. Below this threshold, insulin secretion is basal or suppressed to prevent hypoglycemia [1]. **Analysis of Options:** * **A, B, and C (30, 40, and 50 mg%):** These levels are considered hypoglycemic. At these concentrations, insulin synthesis is inhibited, and counter-regulatory hormones (like glucagon and epinephrine) are triggered to increase blood glucose [1]. Specifically, symptoms of hypoglycemia typically begin around 50–55 mg/dL [1]. * **D (70 mg%):** This is the recognized threshold where the metabolic machinery of the beta cell activates insulin production to maintain euglycemia. **High-Yield Clinical Pearls for NEET-PG:** * **Glucokinase:** Acts as the "glucose sensor." Mutations in this enzyme lead to **MODY-2** (Maturity-Onset Diabetes of the Young). * **Biphasic Release:** Insulin release is biphasic; the first phase is the release of stored insulin, while the second phase involves the synthesis of new insulin [2]. * **GLUT-2 vs. GLUT-4:** Remember that GLUT-2 (pancreas/liver) is insulin-independent, whereas GLUT-4 (muscle/adipose) is insulin-dependent [3].

Q: Osteoblasts express which of the following hormones?

All of the above. **Explanation:** The correct answer is **D. All of the above**. Osteoblasts are not merely bone-forming cells; they serve as the primary regulatory hub for bone remodeling by expressing receptors for various systemic hormones. 1. **Parathyroid Hormone (PTH):** Paradoxically, osteoclasts (which resorb bone) do **not** have PTH receptors. PTH binds to receptors on **osteoblasts**, stimulating them to express **RANKL** (Receptor Activator of Nuclear Factor kappa-B Ligand). RANKL then binds to osteoclasts to initiate bone resorption. 2. **Vitamin D3 (Calcitriol):** Osteoblasts possess Vitamin D receptors (VDR). Calcitriol acts on osteoblasts to stimulate the production of **osteocalcin** and alkaline phosphatase, and it also synergizes with PTH to increase RANKL expression. 3. **Glucocorticoids:** Osteoblasts have glucocorticoid receptors. Chronic exposure to steroids inhibits osteoblast proliferation and increases their apoptosis, which is the primary mechanism behind **steroid-induced osteoporosis**. **Why "All of the above" is correct:** Osteoblasts act as the "sensor" for the endocrine system to regulate bone turnover. By expressing receptors for PTH, Vitamin D, and Glucocorticoids (as well as Estrogen and Thyroid hormone), the osteoblast coordinates the balance between bone formation and resorption. **High-Yield Clinical Pearls for NEET-PG:** * **RANKL/OPG Ratio:** Osteoblasts also secrete **Osteoprotegerin (OPG)**, a decoy receptor that binds RANKL and inhibits bone resorption. The ratio of RANKL to OPG determines the rate of bone loss. * **Teriparatide (Recombinant PTH):** When given intermittently, it stimulates osteoblasts more than osteoclasts, leading to an anabolic (bone-building) effect. * **Marker of Osteoblast Activity:** Serum **Alkaline Phosphatase (ALP)** and **Osteocalcin** are high-yield biochemical markers used to assess osteoblastic function.

Q: Glucose transport in myocytes is stimulated by insulin. Which glucose transporter is involved?

GLUT-4. **Explanation:** The correct answer is **GLUT-4**. This question tests the fundamental concept of insulin-dependent versus insulin-independent glucose uptake in human tissues. **Why GLUT-4 is correct:** GLUT-4 is the only **insulin-responsive** glucose transporter. It is primarily expressed in **skeletal muscle (myocytes)** and **adipose tissue**. In the resting state, GLUT-4 remains sequestered in intracellular vesicles. Upon insulin binding to its receptor, a signaling cascade (via PI3-kinase) triggers the translocation of these vesicles to the plasma membrane, facilitating glucose uptake. **Analysis of Incorrect Options:** * **GLUT-1:** Responsible for basal (insulin-independent) glucose uptake. It is found in almost all tissues but is most highly concentrated in **RBCs** and the **Blood-Brain Barrier**. * **GLUT-2:** A high-capacity, low-affinity transporter found in the **Liver, Pancreatic beta cells, and Kidney**. It acts as a "glucose sensor" in the pancreas and allows bidirectional transport in the liver. * **GLUT-3:** A high-affinity transporter found primarily in **Neurons** (Brain), ensuring glucose uptake even during low blood sugar levels. **High-Yield Clinical Pearls for NEET-PG:** * **Exercise & GLUT-4:** Muscle contraction during exercise can trigger GLUT-4 translocation to the membrane **independent of insulin**. This is why exercise helps lower blood glucose in diabetic patients. * **SGLT vs. GLUT:** Remember that SGLT-1 (Intestine) and SGLT-2 (Kidney) use **secondary active transport** (sodium-dependent), whereas all GLUT transporters use **facilitated diffusion**. * **GLUT-5:** Specifically transports **Fructose** and is located in the small intestine and spermatozoa.

Q: Which of the following hormones act through nuclear receptors?

None of the above. **Explanation:** The mechanism of hormone action is determined by the chemical nature of the hormone. Hormones that are lipid-soluble (lipophilic) can cross the cell membrane and bind to **nuclear or cytoplasmic receptors**, while water-soluble (hydrophilic) hormones bind to **cell surface (membrane) receptors**. **1. Why "None of the above" is correct:** For an option to be correct, *all* hormones listed in that group must act via nuclear receptors. In this question, every option contains at least one hormone that acts via a cell surface receptor (using second messengers like cAMP or IP3/DAG). **2. Analysis of Incorrect Options:** * **Option A:** Estrogen and Thyroxine (T4) act via nuclear receptors. However, **Glucagon** is a peptide hormone that acts via a G-protein coupled receptor (GPCR) and the cAMP second messenger system. * **Option B:** Estrogen and Thyroxine use nuclear receptors. **TSH (Thyroid Stimulating Hormone)**, despite acting on the thyroid gland, is a glycoprotein that binds to membrane-bound GPCRs. * **Option C:** Estrogen uses nuclear receptors. Both **TSH and GnRH** act via cell surface receptors (GnRH uses the Gq-IP3/DAG pathway). **High-Yield NEET-PG Clinical Pearls:** * **Nuclear Receptor Superfamily:** Includes Steroid hormones (Estrogen, Progesterone, Testosterone, Cortisol, Aldosterone), Thyroid hormones (T3, T4), Vitamin D, and Retinoic acid. * **Thyroid Exception:** Unlike most lipid-soluble hormones that bind in the cytoplasm, Thyroid hormone receptors are already bound to DNA in the nucleus even in the absence of the hormone. * **Speed of Action:** Hormones acting via nuclear receptors have a **slow onset** (hours to days) because they require gene transcription and protein synthesis, whereas membrane-receptor hormones (like Epinephrine or Insulin) act almost instantaneously.

Question 1

In the thyroid gland, the colloid material is predominantly composed of which of the following?

Accepted Answer

Thyroglobulin

Answer

Thyroxine

Answer

Monoiodotyrosine

Answer

Diiodotyrosine

Question 2

A man eats a low-carbohydrate meal rich in proteins containing amino acids that stimulate insulin secretion. Which physiological response accounts for the absence of hypoglycemia?

Accepted Answer

Stimulation of glucagon secretion

Answer

Suppression of growth hormone (GH) secretion

Answer

Suppression of somatomedin C secretion

Answer

Stimulation of cortisol secretion

Question 3

The syndrome of growth failure, rash, and hypogonadism is due to deficiency of which essential nutrient?

Accepted Answer

Zinc

Answer

Calcium

Answer

Copper

Answer

Magnesium

Question 4

Triiodothyronine (T3) as compared to T4:

Accepted Answer

Is shorter acting

Answer

Is more plasma protein bound

Answer

Is less potent

Answer

Has delayed action

Question 5

Insulin acts on glucose metabolism by:

Accepted Answer

Increasing glucose permeability across cell membrane against the glucose gradient

Answer

Increasing glucose permeability across cell membrane

Answer

Increasing glucose permeability of renal cells

Answer

Increasing glucose transport to the brain

Question 6

All of the following statements concerning Atrial Natriuretic Peptide (ANP) are true except:

Accepted Answer

Its effects are mediated by decreased cyclic AMP

Answer

Its secretion is increased by an increase in blood volume

Answer

It increases glomerular filtration rate

Answer

It inhibits renin secretion

Question 7

Insulin synthesis is stimulated by glucose levels above what threshold?

Accepted Answer

70 mg%

Answer

30 mg%

Answer

40 mg%

Answer

50 mg%

Question 8

Osteoblasts express which of the following hormones?

Accepted Answer

All of the above

Answer

Parathyroid hormone (PTH)

Answer

Vitamin D3

Answer

Glucocorticoid

Question 9

Glucose transport in myocytes is stimulated by insulin. Which glucose transporter is involved?

Accepted Answer

GLUT-4

Answer

GLUT-1

Answer

GLUT-2

Answer

GLUT-3

Question 10

Which of the following hormones act through nuclear receptors?

Accepted Answer

None of the above

Answer

Estrogen, thyroxine, and glucagon

Answer

Estrogen, thyroxine, and TSH

Answer

Estrogen, TSH, and Gonadotropin releasing hormone (GnRH)

Endocrinology — MCQs

Endocrinology — MCQs

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