Endocrinology Practice Questions

Q: Which of the following hormones is secreted in response to TRH stimulation?

Prolactin and TSH. **Explanation:** The correct answer is **Prolactin and TSH (Option C)**. **Underlying Medical Concept:** Thyrotropin-Releasing Hormone (TRH) is a tripeptide synthesized in the paraventricular nucleus of the hypothalamus. While its primary physiological role is to stimulate the anterior pituitary to release **Thyroid Stimulating Hormone (TSH)**, it also acts as a potent **Prolactin-Releasing Factor (PRF)**. TRH binds to G-protein coupled receptors on both thyrotropes and lactotropes, leading to the secretion of both hormones. **Analysis of Options:** * **Option A (Prolactin):** While TRH does stimulate Prolactin, this option is incomplete because TSH is also secreted. * **Option B (TSH):** This is the primary target of TRH, but choosing this alone ignores the significant stimulatory effect TRH has on Prolactin. * **Option D (None):** Incorrect, as TRH has well-documented stimulatory effects on both hormones. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Primary Hypothyroidism Connection:** In patients with primary hypothyroidism (low T3/T4), there is a compensatory increase in TRH levels due to the loss of negative feedback. This elevated TRH can lead to **hyperprolactinemia**, which clinically manifests as galactorrhea, amenorrhea, or infertility. * **Dopamine's Role:** Remember that Dopamine is the primary *inhibitor* of both Prolactin (major) and TSH (minor). * **Diagnostic Use:** The TRH stimulation test was historically used to differentiate between secondary (pituitary) and tertiary (hypothalamic) hypothyroidism.

Q: Adrenal insufficiency is not associated with which of the following?

Metabolic alkalosis. **Explanation:** Adrenal insufficiency (Addison’s disease) is characterized by the deficiency of adrenal cortical hormones: **Aldosterone** and **Cortisol**. **Why Metabolic Alkalosis is the Correct Answer:** Aldosterone normally acts on the distal convoluted tubules and collecting ducts to reabsorb sodium and water while secreting Potassium ($K^+$) and Hydrogen ions ($H^+$). In adrenal insufficiency, the lack of aldosterone leads to decreased $H^+$ secretion. This results in the retention of $H^+$ ions, leading to **Metabolic Acidosis** (specifically Normal Anion Gap Metabolic Acidosis), not alkalosis. **Analysis of Incorrect Options:** * **A. Hyponatremia:** Lack of aldosterone leads to "salt wasting" (failure to reabsorb $Na^+$), resulting in low serum sodium levels. * **B. Hyperkalemia:** Without aldosterone, the kidney cannot effectively excrete potassium, leading to its accumulation in the blood. * **C. Hypoglycemia:** Cortisol is a counter-regulatory hormone that promotes gluconeogenesis and antagonizes insulin. Its deficiency leads to impaired glucose production and increased insulin sensitivity, causing low blood sugar. **High-Yield Clinical Pearls for NEET-PG:** * **Primary vs. Secondary:** Hyperpigmentation (due to high ACTH/POMC) and mineralocorticoid deficiency (electrolyte imbalances) are features of **Primary** Adrenal Insufficiency (Addison’s), but are absent in Secondary (Pituitary) insufficiency. * **The "Addisonian Triad":** Hyponatremia, Hyperkalemia, and Metabolic Acidosis. * **Eosinophilia:** A common but often overlooked hematological finding in adrenal insufficiency. * **Gold Standard Test:** ACTH Stimulation Test (Cosyntropin test).

Q: Osteoclasts have a specific receptor for which hormone?

Calcitonin. **Explanation:** The correct answer is **Calcitonin**. This is a classic high-yield concept in bone physiology. **1. Why Calcitonin is Correct:** Osteoclasts are the primary target cells for calcitonin. Calcitonin receptors are G-protein coupled receptors located directly on the cell membrane of **osteoclasts**. When calcitonin binds to these receptors, it rapidly inhibits the resorptive activity of osteoclasts and decreases their number, leading to a reduction in bone resorption and a decrease in serum calcium levels. **2. Why the Other Options are Incorrect:** * **Parathyroid Hormone (PTH):** Contrary to popular belief, osteoclasts do **not** have PTH receptors. PTH acts primarily on **osteoblasts**. When PTH binds to osteoblasts, it triggers the release of **RANKL** (Receptor Activator of Nuclear Factor kappa-B Ligand), which then binds to RANK receptors on osteoclast precursors to stimulate bone resorption. * **Vitamin D3 (Calcitriol):** Like PTH, Vitamin D3 receptors (VDR) are primarily found on **osteoblasts**. Vitamin D3 promotes osteoclast differentiation indirectly via the RANKL pathway. * **Thyroxin:** While thyroid hormones influence bone turnover, they do not have specific, primary regulatory receptors on osteoclasts that govern calcium homeostasis in the same direct manner as calcitonin. **Clinical Pearls for NEET-PG:** * **The "Indirect" Rule:** Remember that most bone-resorbing factors (PTH, Vitamin D3, IL-1, TNF) act **indirectly** on osteoclasts via osteoblasts. Calcitonin is the major exception that acts **directly**. * **Marker of Osteoclasts:** Tartrate-resistant acid phosphatase (TRAP) is a key histological marker for osteoclasts. * **Therapeutic Use:** Due to its direct inhibitory effect on osteoclasts, synthetic calcitonin (Salmon calcitonin) is used clinically to treat Paget’s disease and severe hypercalcemia.

Q: What is the storage form of thyroid hormone?

Thyroglobulin. The thyroid gland is unique among endocrine glands because it stores its hormones extracellularly in the follicular lumen [1]. The correct answer is **Thyroglobulin (Tg)**, a large glycoprotein synthesized by follicular cells [1]. 1. **Why Thyroglobulin is correct:** After synthesis, Tg is secreted into the colloid. Within this colloid, iodine is attached to tyrosine residues on the Tg backbone (organification) to form MIT and DIT, which then couple to form T3 and T4 [2]. These hormones remain covalently bound to the thyroglobulin molecule, acting as a reservoir that can provide a 2–3 month supply of thyroid hormone [1]. 2. **Why other options are incorrect:** * **Tri-iodothyronine (T3):** This is the metabolically active form of the hormone, not the storage form. It is released into the blood after the proteolysis of thyroglobulin [1]. * **Tri-iodotyrosine:** This is a distractor term; it is not a standard intermediate in thyroid physiology. * **Di-iodotyrosine (DIT):** This is an intermediate precursor formed during the organification of iodine. While it is stored as part of the thyroglobulin complex, it is not the "storage form" itself but rather a building block [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Wolff-Chaikoff Effect:** A transient decrease in thyroid hormone synthesis due to the ingestion of a large amount of iodine. * **Pendred Syndrome:** Characterized by sensorineural hearing loss and goiter due to a defect in the Pendrin iodine transporter. * *Thyroglobulin Levels:** Used clinically as a **tumor marker** to monitor for recurrence in patients with differentiated thyroid cancer (Papillary or Follicular) after total thyroidectomy.

Q: Which of the following iodinated compounds is present in the maximum concentration in the thyroid?

Diiodotyrosine (DIT). **Explanation:** The synthesis of thyroid hormones occurs within the thyroid follicle through the iodination of tyrosine residues on the protein **thyroglobulin**. This process, known as organification, involves the enzyme thyroid peroxidase (TPO). **Why DIT is the correct answer:** During the synthesis process, iodine is added to tyrosine to form Monoiodotyrosine (MIT) and Diiodotyrosine (DIT). Statistically and biochemically, the coupling process favors the formation of DIT. In the thyroid gland, the ratio of DIT to MIT is approximately **2:1**. Since T3 and T4 are stored in the colloid as part of the thyroglobulin complex, and DIT is the precursor for both T4 (DIT + DIT) and T3 (MIT + DIT), **Diiodotyrosine (DIT)** remains the most abundant iodinated compound stored within the gland. **Analysis of Incorrect Options:** * **A. Monoiodotyrosine (MIT):** While present in significant amounts, its concentration is roughly half that of DIT. * **C. Triiodothyronine (T3):** T3 is the most biologically active form, but it is produced in much smaller quantities within the gland compared to its precursors. Most circulating T3 is actually derived from the peripheral conversion of T4. * **D. Reverse T3:** This is a metabolically inactive product formed primarily in peripheral tissues (not the thyroid) during states of illness or starvation. **High-Yield Clinical Pearls for NEET-PG:** * **Wolff-Chaikoff Effect:** A transient reduction in thyroid hormone synthesis caused by the ingestion of a large amount of iodine. * **Storage:** The thyroid is unique among endocrine glands because it stores its hormones extracellularly (in the colloid) in quantities sufficient to last 2–3 months. * **Coupling:** 2 DIT = T4 (Thyroxine); 1 MIT + 1 DIT = T3. Since T4 is produced in a 10:1 ratio to T3, the requirement for DIT is significantly higher.

Q: Which of the following hormones is released from the hypothalamus?

Cortisol releasing hormone. The hypothalamus acts as the primary neuroendocrine control center, secreting "releasing" and "inhibiting" hormones that regulate the anterior pituitary gland via the hypophyseal portal system. ### **Explanation of the Correct Answer** **B. Cortisol Releasing Hormone (CRH):** This is the correct answer. CRH (also known as Corticotropin-Releasing Hormone) is synthesized by the parvocellular neurosecretory cells of the **paraventricular nucleus (PVN)** of the hypothalamus. It stimulates the anterior pituitary to release Adrenocorticotropic Hormone (ACTH), which in turn stimulates the adrenal cortex to produce cortisol. ### **Analysis of Incorrect Options** * **A. Orexin (Hypocretin):** While produced in the lateral hypothalamus, it functions primarily as a **neurotransmitter** regulating wakefulness and appetite, rather than a classical endocrine hormone released into the portal circulation. * **C. Neuropeptide Y (NPY):** This is a potent orexigenic (appetite-stimulating) peptide. While found in the arcuate nucleus of the hypothalamus, it is classified as a **neuromodulator/neurotransmitter** involved in energy homeostasis. * **D. Ghrelin:** Known as the "hunger hormone," it is primarily secreted by the **P/D1 cells of the stomach fundus**. It acts on the hypothalamus to increase appetite but is not produced there. ### **High-Yield Clinical Pearls for NEET-PG** * **The "Releasing" Rule:** Almost all hormones with "Releasing" in their name (GHRH, TRH, GnRH, CRH) originate from the hypothalamus. * **Posterior Pituitary Connection:** ADH (Vasopressin) and Oxytocin are *synthesized* in the hypothalamus (Supraoptic and Paraventricular nuclei) but *stored and released* by the posterior pituitary. * **Dopamine:** It is the primary **Prolactin-Inhibiting Hormone (PIH)** secreted by the hypothalamus. A deficiency in hypothalamic dopamine leads to hyperprolactinemia.

Q: Which of the following is an orexigenic hormone?

Ghrelin. ***Ghrelin (Correct Answer)*** - Ghrelin is often termed the "hunger hormone" as it acts primarily as a powerful **orexigenic signal**, stimulating appetite and food intake. - It is primarily produced by specialized cells in the **stomach**, and its levels typically rise before meals. *Melanocyte-stimulating hormone (Incorrect)* - MSH, specifically **alpha-MSH**, is released from **proopiomelanocortin (POMC) neurons** in the hypothalamus. - It acts to suppress appetite and is classified as an **anorexigenic hormone**. *Cholecystokinin (Incorrect)* - CCK is a **satiety hormone** released in response to fat and protein entering the duodenum and jejunum. - It acts on the brainstem and peripheral nerves to inhibit gastric emptying and induce short-term feelings of **satiety** (anorexigenic effect). *Leptin (Incorrect)* - Leptin is produced mainly by **adipocytes (fat cells)** and signals the brain about long-term energy stores. - High circulating levels of leptin act on the hypothalamus to **inhibit appetite** and increase energy expenditure, making it an **anorexigenic hormone (satiety signal)**.

Q: Which of the following tissues will not be able to take up glucose in insulin resistance/insulin absence/diabetes mellitus?

Skeletal muscle. ### **Explanation** The uptake of glucose into cells is mediated by **Glucose Transporters (GLUT)**. The fundamental concept here is the distinction between **Insulin-Dependent** and **Insulin-Independent** glucose uptake. **1. Why Skeletal Muscle is Correct:** * **Skeletal muscle** (and adipose tissue) primarily utilizes **GLUT-4**, which is the only **insulin-dependent** glucose transporter. * In the absence of insulin or in states of insulin resistance, GLUT-4 remains sequestered in intracellular vesicles and cannot translocate to the cell membrane. Consequently, these tissues cannot take up glucose effectively, leading to post-prandial hyperglycemia. **2. Why the Other Options are Incorrect:** * **Kidney (Option A):** Uses **GLUT-2** (basolateral membrane) and **SGLT-1/2** (apical membrane) for glucose reabsorption. These are insulin-independent. * **Brain (Option C):** Relies on **GLUT-1** and **GLUT-3**. The brain requires a continuous supply of glucose regardless of insulin levels to maintain metabolic function. * **Red Blood Cells (Option D):** Utilize **GLUT-1** for constitutive glucose uptake, which does not require insulin. --- ### **High-Yield Clinical Pearls for INI-CET** * **GLUT-4 Locations:** Remember the "Big Three": **Skeletal muscle**, **Cardiac muscle**, and **Adipose tissue**. * **Exercise Exception:** During exercise, skeletal muscle can take up glucose **independently of insulin** because muscle contraction triggers GLUT-4 translocation via the **AMPK pathway**. This is why exercise is a key management strategy for Type 2 Diabetes. * **GLUT-2:** Found in the **Liver, Pancreatic beta cells, and Small Intestine**. It acts as a "glucose sensor" due to its high $K_m$ (low affinity). * **SGLT:** These are **Secondary Active Transporters** (Sodium-Glucose Linked Transporters) found in the kidneys and small intestine, not to be confused with the facilitated diffusion of GLUTs.

Question 1

Which of the following hormones is secreted in response to TRH stimulation?

Accepted Answer

Prolactin and TSH

Answer

Prolactin

Answer

TSH

Answer

None of the above

Question 2

What is true about insulin action?

Accepted Answer

Required for the transport of glucose, amino acids, K+, and Na+

Answer

Causes gluconeogenesis

Answer

Not useful for growth and development

Answer

Catabolic hormone

Question 3

Adrenal insufficiency is not associated with which of the following?

Accepted Answer

Metabolic alkalosis

Answer

Hyponatremia

Answer

Hyperkalemia

Answer

Hypoglycemia

Question 4

Osteoclasts have a specific receptor for which hormone?

Accepted Answer

Calcitonin

Answer

Parathyroid hormone

Answer

Thyroxin

Answer

Vitamin D3

Question 5

What is the storage form of thyroid hormone?

Accepted Answer

Thyroglobulin

Answer

Tri-iodotyrosine

Answer

Tri-iodothyronine

Answer

Di-iodotyrosine

Question 6

Which of the following iodinated compounds is present in the maximum concentration in the thyroid?

Accepted Answer

Diiodotyrosine (DIT)

Answer

Monoiodotyrosine (MIT)

Answer

Triiodothyronine (T3)

Answer

Reverse T3

Question 7

Which of the following hormones is released from the hypothalamus?

Accepted Answer

Cortisol releasing hormone

Answer

Orexin

Answer

Neuropeptide

Answer

Ghrelin

Question 8

Which of the following is an orexigenic hormone?

Accepted Answer

Ghrelin

Answer

Melanocyte-stimulating hormone

Answer

Cholecystokinin

Answer

Leptin

Question 9

Which of the following mechanisms is used by the marked structure to influence neighboring cells?

Accepted Answer

Paracrine

Answer

Nerve mediated

Answer

Vein mediated

Answer

Autocrine

Question 10

Which of the following tissues will not be able to take up glucose in insulin resistance/insulin absence/diabetes mellitus?

Accepted Answer

Skeletal muscle

Answer

Kidney

Answer

Brain

Answer

Red blood cells

Endocrinology — MCQs

Endocrinology — MCQs

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