Endocrinology Practice Questions

Q: Glucose-mediated insulin release is primarily mediated through which mechanism?

ATP-dependent potassium channels. ### Explanation The release of insulin from pancreatic beta cells is a sophisticated process of **stimulus-secretion coupling**. **Why Option A is Correct:** When blood glucose levels rise, glucose enters the beta cell via **GLUT-2** transporters. It undergoes glycolysis and oxidative phosphorylation, leading to an increase in the **ATP/ADP ratio** within the cytoplasm. This rise in ATP triggers the closure of **ATP-sensitive Potassium ($K_{ATP}$) channels**. The resulting decrease in $K^+$ efflux causes **depolarization** of the cell membrane. This depolarization opens **Voltage-Gated Calcium Channels (VGCC)**, allowing an influx of $Ca^{2+}$, which ultimately triggers the exocytosis of insulin granules. **Why Other Options are Incorrect:** * **Option B (cAMP):** While cAMP acts as a secondary messenger that *potentiates* insulin secretion (e.g., via Incretins like GLP-1), it is not the primary mediator of glucose-induced release. * **Option C (Carrier modulators):** This is a vague term; while GLUT-2 is a carrier, the "mediation" of release refers to the signaling cascade, not just entry. * **Option D (Receptor phosphorylation):** This describes the **mechanism of action** of insulin at the target cell (Tyrosine Kinase receptor), not the mechanism of its release. **NEET-PG High-Yield Pearls:** * **Sulfonylureas** (e.g., Gliclazide) work by directly closing these $K_{ATP}$ channels, bypassing glucose metabolism to treat Type 2 Diabetes. * **Diazoxide**, used in hyperinsulinism, keeps these channels *open*, inhibiting insulin release. * The $K_{ATP}$ channel is a complex of four **Kir6.2** subunits and four **SUR1** (Sulfonylurea Receptor) subunits. * **Rate-limiting step** of glucose sensing in the beta cell: **Glucokinase** enzyme activity.

Q: Which of the anterior pituitary hormones is under tonic inhibitory control from the hypothalamus, rather than hypothalamic releasing factors?

Prolactin (PRL). **Explanation:** The secretion of most anterior pituitary hormones is primarily regulated by **hypothalamic releasing factors** (stimulatory control). However, **Prolactin (PRL)** is the unique exception as it is under **tonic inhibitory control** by the hypothalamus. **Why Prolactin is the correct answer:** The primary regulator of prolactin is **Dopamine**, which is secreted by the tuberoinfundibular neurons of the hypothalamus. Dopamine acts on **D2 receptors** on the lactotrophs of the anterior pituitary to inhibit prolactin release. If the pituitary stalk is severed (stalk effect), the levels of all other anterior pituitary hormones decrease, but **prolactin levels rise** because it has been released from this tonic inhibition. **Why the other options are incorrect:** * **LH and FSH (Options A & B):** These gonadotropins are under the positive, pulsatile control of **Gonadotropin-Releasing Hormone (GnRH)**. * **TSH (Option C):** Its secretion is primarily stimulated by **Thyrotropin-Releasing Hormone (TRH)**. While Somatostatin can inhibit TSH, the primary regulatory mode is stimulatory. **High-Yield Clinical Pearls for NEET-PG:** * **The "Stalk Effect":** Any lesion compressing the pituitary stalk (e.g., Craniopharyngioma) leads to **Hyperprolactinemia** due to the loss of dopamine delivery. * **Drug-Induced Hyperprolactinemia:** Antipsychotics (D2 antagonists) block dopamine's inhibitory effect, leading to galactorrhea and amenorrhea. * **TRH Influence:** In primary hypothyroidism, elevated TRH levels can stimulate lactotrophs, leading to secondary hyperprolactinemia. * **Prolactinoma:** The most common functioning pituitary adenoma; treated primarily with dopamine agonists like **Cabergoline** or Bromocriptine.

Q: Which of the following does not depend on insulin via GLUT4 for glucose uptake?

Brain. **Explanation:** The uptake of glucose into cells is mediated by **Glucose Transporters (GLUT)**. These are divided into two categories: those that are insulin-independent and those that are insulin-dependent. **Why the Brain is the Correct Answer:** The brain is a vital organ that requires a continuous supply of glucose regardless of insulin levels. Glucose uptake in the brain (specifically across the blood-brain barrier and into neurons) is mediated primarily by **GLUT1** and **GLUT3**. These transporters are **insulin-independent**, ensuring the brain receives fuel even during fasting or hypoglycemic states. **Why the Other Options are Incorrect:** * **Skeletal Muscle & Cardiac Muscle:** These tissues primarily utilize **GLUT4**. In the resting state, GLUT4 is stored in intracellular vesicles. Upon insulin binding to its receptor, these vesicles translocate to the cell membrane to allow glucose entry. Therefore, glucose uptake here is highly **insulin-dependent**. (Note: Exercise can also trigger GLUT4 translocation in skeletal muscle via insulin-independent pathways). * **Adipose Tissue:** Like muscle, adipocytes rely on **GLUT4** for glucose uptake to facilitate triglyceride synthesis. This process is strictly regulated by insulin. **NEET-PG High-Yield Pearls:** * **GLUT4** is the **only** insulin-dependent glucose transporter. * **GLUT1:** Found in RBCs, Blood-Brain Barrier, and kidneys. * **GLUT2:** A high-capacity, bidirectional transporter found in **Liver, Pancreas (B-cells), and Small Intestine**. It acts as a glucose sensor. * **GLUT5:** Primarily a **fructose** transporter found in the small intestine and spermatozoa. * **SGLT1/2:** These are sodium-glucose co-transporters (active transport) found in the small intestine and proximal convoluted tubule of the kidney, respectively.

Q: Which of the following is NOT an appetite suppressant?

Neuropeptide Y. **Explanation:** The regulation of appetite occurs primarily in the **Arcuate Nucleus (ARC)** of the hypothalamus, which contains two distinct sets of neurons: the **Orexigenic** (appetite-stimulating) and **Anorexigenic** (appetite-suppressing) pathways. **Why Neuropeptide Y (NPY) is the correct answer:** Neuropeptide Y is one of the most potent **orexigenic** peptides known. It is co-released with Agouti-related peptide (AgRP) from the ARC. When activated, NPY stimulates food intake, reduces energy expenditure, and promotes fat storage. Therefore, it is an appetite stimulant, not a suppressant. **Analysis of Incorrect Options (Appetite Suppressants):** * **Melanocyte Stimulating Hormone (α-MSH):** This is an anorexigenic peptide derived from Pro-opiomelanocortin (POMC). It acts on MC3 and MC4 receptors in the hypothalamus to inhibit feeding. * **Corticotropin-Releasing Hormone (CRH):** Produced in the paraventricular nucleus, CRH acts as a potent anorexigenic signal, typically reducing food intake during stress responses. * **Leptin:** Produced by adipocytes, Leptin is the "satiety hormone." It crosses the blood-brain barrier to inhibit NPY/AgRP neurons (stimulants) and excite POMC neurons (suppressants), leading to long-term energy balance. **High-Yield Clinical Pearls for NEET-PG:** * **Vagus Nerve:** The primary neural pathway for short-term satiety signals (like CCK) from the gut to the brain. * **Ghrelin:** The only major peripheral hormone that **stimulates** hunger (produced by P/D1 cells of the stomach). * **POMC Deficiency:** Leads to hyperphagia, early-onset obesity, and red hair (due to lack of MSH). * **Mnemonic for ARC:** **N**PY/AgRP = **N**o (stop) fasting/Start eating; **P**OMC/CART = **P**ause eating.

Q: Calcitonin levels are increased in which of the following conditions?

Hyperparathyroidism. **Explanation:** **Correct Option: B. Hyperparathyroidism** The primary stimulus for the secretion of **Calcitonin** (produced by the parafollicular C-cells of the thyroid gland) is **Hypercalcemia**. In Hyperparathyroidism, there is an excess of Parathyroid Hormone (PTH), which leads to elevated serum calcium levels through increased bone resorption and renal calcium reabsorption. As a physiological feedback mechanism, the body increases Calcitonin levels to counteract this hypercalcemia by inhibiting osteoclast activity and promoting renal calcium excretion. **Analysis of Incorrect Options:** * **A. Hyperthyroidism:** This involves excess T3/T4 from follicular cells. While severe thyrotoxicosis can occasionally cause mild hypercalcemia due to increased bone turnover, it is not a primary or classic cause for elevated Calcitonin. * **C. Hypoparathyroidism:** This condition results in **Hypocalcemia**. Low serum calcium levels inhibit the secretion of Calcitonin. * **D. Cushing Syndrome:** Excess glucocorticoids generally lead to decreased bone formation and can cause secondary hyperparathyroidism due to decreased intestinal calcium absorption, but they do not directly stimulate Calcitonin secretion. **High-Yield Clinical Pearls for NEET-PG:** * **Tumor Marker:** Calcitonin is the most sensitive tumor marker for **Medullary Carcinoma of the Thyroid (MCT)**. * **Antagonist:** Calcitonin acts as a physiological antagonist to PTH, but its role in human calcium homeostasis is much weaker than PTH. * **Therapeutic Use:** Exogenous Calcitonin (Salmon calcitonin) is used clinically to treat **Paget’s disease** and severe hypercalcemia. * **Stimuli:** Besides hypercalcemia, GI hormones like **Gastrin** are potent stimulators of Calcitonin secretion.

Q: Pulsatile release of GnRH is important for?

Gonadotrophin stimulation. **Explanation:** The secretion of **Gonadotropin-Releasing Hormone (GnRH)** from the hypothalamus is inherently **pulsatile**. This intermittent release is physiological and essential for the stimulation of the anterior pituitary to secrete LH (Luteinizing Hormone) and FSH (Follicle-Stimulating Hormone). **1. Why Option A is Correct:** The pituitary GnRH receptors require a "rest period" between pulses to remain sensitive. Pulsatile GnRH (occurring every 60–90 minutes) prevents the internalization of receptors, thereby maintaining the synthesis and release of **Gonadotrophins**. **2. Why Other Options are Incorrect:** * **Option B:** While pulsatile GnRH eventually leads to ovulation, its *direct* physiological function is the stimulation of gonadotrophs. Ovulation is a secondary downstream effect of the LH surge. * **Option C:** Feedback inhibition is primarily mediated by ovarian/testicular steroids (estrogen, progesterone, testosterone) acting on the hypothalamus and pituitary, not by the pulsatility of GnRH itself. * **Option D:** **Continuous (non-pulsatile)** administration of GnRH leads to the **downregulation** and desensitization of GnRH receptors. This suppresses the pituitary-gonadal axis. **Clinical Pearls for NEET-PG:** * **GnRH Agonists (e.g., Leuprolide, Goserelin):** When given continuously, they cause "chemical castration." This is used clinically to treat **prostate cancer, endometriosis, and precocious puberty**. * **Kallmann Syndrome:** Characterized by the failure of GnRH neurons to migrate, leading to hypogonadotropic hypogonadism and anosmia. * **Pulse Frequency:** High-frequency pulses favor **LH** release, while low-frequency pulses favor **FSH** release.

Question 1

Glucose-mediated insulin release is primarily mediated through which mechanism?

Accepted Answer

ATP-dependent potassium channels

Answer

Cyclic adenosine monophosphate (cAMP)

Answer

Carrier modulators

Answer

Receptor phosphorylation

Question 2

Which of the anterior pituitary hormones is under tonic inhibitory control from the hypothalamus, rather than hypothalamic releasing factors?

Accepted Answer

Prolactin (PRL)

Answer

Luteinizing hormone (LH)

Answer

Follicle-stimulating hormone (FSH)

Answer

Thyroid-stimulating hormone (TSH)

Question 3

Which of the following does not depend on insulin via GLUT4 for glucose uptake?

Accepted Answer

Brain

Answer

Skeletal muscles

Answer

Cardiac muscles

Answer

Adipose tissue

Question 4

Thyroid-stimulating hormone (TSH) secreted from the pituitary gland is under control by which of the following mechanisms?

Accepted Answer

Thyrotropin-releasing hormone (TRH) and negative feedback from T3 and T4

Answer

Releasing factors similar to those controlling cortisol secretion

Answer

Releasing factors that bypass the neurohypophysis to act on the anterior pituitary

Answer

Thyrotropin-releasing hormone (TRH) only

Question 5

Which of the following is NOT an appetite suppressant?

Accepted Answer

Neuropeptide Y

Answer

Melanocyte stimulating hormone

Answer

Melanocyte corticotropic releasing hormone

Answer

Leptin

Question 6

Calcitonin levels are increased in which of the following conditions?

Accepted Answer

Hyperparathyroidism

Answer

Hyperthyroidism

Answer

Hypoparathyroidism

Answer

Cushing Syndrome

Question 7

The blood glucose level in diabetes mellitus is decreased by the removal of which endocrine gland?

Accepted Answer

Anterior pituitary

Answer

Thyroid

Answer

Parathyroids

Answer

Posterior pituitary

Question 8

Pulsatile release of GnRH is important for?

Accepted Answer

Gonadotrophin stimulation

Answer

Ovulation induction

Answer

GnRH feedback inhibition

Answer

Gonadotropin downregulation

Question 9

Steroid hormones exert their effects by binding to which of the following?

Accepted Answer

Transcription factors

Answer

Cell surface receptors

Answer

G proteins

Answer

Cyclic adenosine monophosphate (AMP)

Question 10

All of the following developmental events are dependent on the production of maternal or fetal glucocorticoids, except?

Accepted Answer

Functional hypothalamic pituitary axis

Answer

Induction of thymic involution

Answer

Production of surfactant by type II alveolar cells

Answer

Functional thyroid

Endocrinology — MCQs

Endocrinology — MCQs

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