Endocrinology Practice Questions

Q: All of the following hormones accelerate the release of free fatty acids (FFA) from adipose tissue, EXCEPT:

Insulin. **Explanation:** The mobilization of free fatty acids (FFA) from adipose tissue is primarily regulated by the enzyme **Hormone-Sensitive Lipase (HSL)**. This enzyme catalyzes the breakdown of stored triglycerides into glycerol and FFAs (lipolysis). **1. Why Insulin is the Correct Answer:** Insulin is the most potent **anti-lipolytic** hormone. It inhibits HSL through the activation of phosphodiesterase, which lowers intracellular cAMP levels. Furthermore, insulin promotes glucose uptake into adipocytes (via GLUT-4) and stimulates **alpha-glycerophosphate** production, which favors the re-esterification of FFAs back into triglycerides. Therefore, insulin decreases the release of FFA into the plasma. **2. Why the Other Options are Incorrect:** * **Epinephrine & Norepinephrine (Catecholamines):** These are potent stimulators of lipolysis. They bind to **$\beta_3$-adrenergic receptors** on adipocytes, increasing cAMP levels, which activates Protein Kinase A (PKA). PKA then phosphorylates and activates HSL, accelerating FFA release. * **Vasopressin (ADH):** While its primary role is water reabsorption, at higher concentrations, vasopressin exerts a "pressor" effect and has been shown to stimulate lipolysis in adipose tissue via V1a receptors. **Clinical Pearls for NEET-PG:** * **Lipolytic Hormones (The "Stress" Hormones):** Glucagon, Epinephrine, Norepinephrine, Cortisol, Growth Hormone, and ACTH all increase FFA release. * **Rate-Limiting Enzyme:** Hormone-Sensitive Lipase (HSL) is the rate-limiting step for lipolysis. * **Insulin's Dual Action:** It inhibits HSL (preventing breakdown) and stimulates **Lipoprotein Lipase (LPL)** in capillary walls (promoting storage). * **Ketogenesis Connection:** In states of absolute insulin deficiency (like DKA), unchecked HSL activity leads to a massive influx of FFAs to the liver, providing the substrate for ketone body synthesis.

Q: Orexins play an important role in eating disorders. All of the following are orexins, EXCEPT?

Leptin. **Explanation:** The regulation of appetite is controlled by the hypothalamus through two types of signals: **Orexigenic** (appetite-stimulating) and **Anorexigenic** (appetite-suppressing). **Why Leptin is the correct answer:** Leptin is an **anorexigenic** hormone produced by adipocytes (fat cells). It acts on the arcuate nucleus of the hypothalamus to inhibit hunger and stimulate satiety. Therefore, it is not an orexin; rather, it is an "anti-orexin" or satiety factor. **Analysis of incorrect options:** * **Orexin-A and Orexin-B:** These are neuropeptides produced in the lateral hypothalamus (the "feeding center"). They strongly stimulate food intake and play a vital role in regulating wakefulness. * **Hypocretin 1 and 2:** These are alternative names for Orexin-A and Orexin-B, respectively. The terms are used interchangeably in medical literature (Hypocretin-1 = Orexin-A; Hypocretin-2 = Orexin-B). Since they promote feeding, they are true orexins. **High-Yield Clinical Pearls for NEET-PG:** * **Narcolepsy Connection:** A deficiency of orexin (hypocretin) producing neurons in the hypothalamus is the primary cause of **Narcolepsy Type 1** (associated with cataplexy). * **The "Satiety Center":** The **Ventromedial Nucleus (VMN)** of the hypothalamus is the satiety center (lesion leads to obesity). * **The "Feeding Center":** The **Lateral Hypothalamus (LHA)** is the feeding center where orexins are produced (lesion leads to anorexia/starvation). * **Ghrelin:** Known as the "hunger hormone," it is the only peripheral orexigenic hormone (produced by the stomach).

Q: Catecholamine hormones are synthesized in which location?

Chromaffin cells of the adrenal medulla. **Explanation:** **1. Why Option A is Correct:** Catecholamines (Epinephrine, Norepinephrine, and Dopamine) are synthesized in the **Chromaffin cells** of the **adrenal medulla**. These cells are embryologically derived from the **neural crest** and act as modified postganglionic sympathetic neurons. Within these cells, the amino acid Tyrosine is converted into catecholamines through a series of enzymatic steps. The final step (Norepinephrine to Epinephrine) is catalyzed by the enzyme **PNMT** (Phenylethanolamine N-methyltransferase), which is uniquely induced by high concentrations of cortisol draining from the adrenal cortex. **2. Why Other Options are Incorrect:** Options B, C, and D refer to the **Adrenal Cortex**, which is mesodermal in origin and produces **steroid hormones**, not catecholamines. * **Zona Glomerulosa (B):** The outermost layer, responsible for secreting mineralocorticoids (primarily **Aldosterone**). * **Zona Fasciculata (C):** The middle and widest layer, responsible for secreting glucocorticoids (primarily **Cortisol**). * **Zona Reticularis (D):** The innermost layer of the cortex, responsible for secreting adrenal androgens (e.g., **DHEA**). **3. NEET-PG High-Yield Pearls:** * **Rate-limiting enzyme:** Tyrosine hydroxylase is the rate-limiting step in catecholamine synthesis. * **VMAT-2:** This transporter packages catecholamines into granules (inhibited by Reserpine). * **Tumor Correlation:** **Pheochromocytoma** is a tumor of the chromaffin cells, leading to episodic hypertension due to excessive catecholamine release. * **Rule of 10s:** Pheochromocytoma is 10% bilateral, 10% malignant, and 10% extra-adrenal (where they are called Paragangliomas).

Q: Which of the following stimulates insulin secretion?

All of the above. **Explanation:** Insulin secretion from the pancreatic beta cells is a highly regulated process influenced by metabolic, neural, and hormonal factors. 1. **Glucose (Option A):** This is the most potent physiological stimulus. Glucose enters beta cells via **GLUT-2** transporters and undergoes glycolysis, increasing the ATP/ADP ratio. This closes ATP-sensitive K+ channels, leading to depolarization, calcium influx, and subsequent insulin exocytosis. 2. **Vagal Stimulation & Acetylcholine (Options B & C):** The pancreas receives extensive parasympathetic innervation via the **Vagus nerve**. During the cephalic and gastric phases of digestion, vagal efferents release **Acetylcholine**, which binds to **M3 muscarinic receptors** on beta cells. This activates the Gq-phospholipase C pathway, increasing intracellular calcium and stimulating insulin release. This "anticipatory" response ensures the body is prepared for the incoming glucose load. Since all three factors independently and synergistically promote insulin release, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Incretin Effect:** Oral glucose stimulates more insulin secretion than intravenous glucose due to the release of GIP and GLP-1 from the gut. * **Adrenergic Influence:** While Parasympathetic (ACh) stimulates insulin, Sympathetic stimulation primarily **inhibits** it via **α2 receptors** (dominant effect), though β2 stimulation can increase it. * **Amino Acids:** Arginine and Lysine are also potent stimulators of insulin. * **Biphasic Release:** Insulin is released in two phases; the first phase is the release of pre-formed granules, and the second is the synthesis of new insulin.

Q: Which of the following hormones can cause hyperglycemia without known effects on glycogen or gluconeogenesis?

Thyroxine. **Explanation:** The correct answer is **Thyroxine (T4)**. While most "anti-insulin" hormones increase blood glucose by stimulating glycogenolysis or gluconeogenesis, Thyroxine has a unique primary mechanism for inducing hyperglycemia. **1. Why Thyroxine is Correct:** Thyroxine increases blood glucose levels primarily by **increasing the rate of glucose absorption from the gastrointestinal tract**. While it does have some permissive effects on catecholamines, its direct and most distinct hyperglycemic action—independent of hepatic glucose production pathways—is the acceleration of intestinal hexose transport. **2. Why the Other Options are Incorrect:** * **Epinephrine:** This is a potent stimulator of **glycogenolysis** in both the liver (increasing blood glucose) and muscle (increasing lactate). It also stimulates gluconeogenesis. * **Glucocorticoids (e.g., Cortisol):** These are classic "diabetogenic" hormones that primarily increase blood glucose by inducing the synthesis of key enzymes involved in **gluconeogenesis** (e.g., PEPCK) and by decreasing peripheral glucose uptake. * **Epidermal Growth Factor (EGF):** This is a signaling protein involved in cell growth and proliferation; it does not play a primary or significant role in systemic glucose homeostasis. **3. NEET-PG High-Yield Pearls:** * **Hyperthyroidism & Diabetes:** Patients with hyperthyroidism often show abnormal glucose tolerance tests (GTT) because the rapid absorption of glucose leads to a high postprandial peak (lag storage curve). * **Growth Hormone:** Also causes hyperglycemia by decreasing peripheral glucose utilization (anti-insulin effect). * **Glucagon:** The primary hormone for acute glucose elevation via hepatic glycogenolysis and gluconeogenesis. * **Key Enzyme:** Glucocorticoids increase the expression of **Glucose-6-Phosphatase**, the final common enzyme for both gluconeogenesis and glycogenolysis.

Q: All of the following use cyclic AMP (c-AMP) as a second messenger except?

Testosterone. **Explanation:** The mechanism of hormone action is determined by the hormone's chemical nature. Hormones are broadly classified into **water-soluble** (peptides and catecholamines) and **lipid-soluble** (steroids and thyroid hormones). **Why Testosterone is the correct answer:** Testosterone is a **steroid hormone**. Steroid hormones are lipophilic and can easily cross the cell membrane. Therefore, they do not require cell-surface receptors or second messengers like c-AMP. Instead, they bind to **intracellular (cytoplasmic or nuclear) receptors**, forming a hormone-receptor complex that acts as a transcription factor to alter gene expression directly. **Analysis of Incorrect Options:** * **Corticotropin (ACTH):** A peptide hormone that binds to G-protein coupled receptors (GPCRs) on the adrenal cortex, activating adenylyl cyclase to increase **c-AMP**. * **Dopamine:** Acts via D1 and D2 receptors. D1-like receptors stimulate adenylyl cyclase to increase **c-AMP**, while D2-like receptors inhibit it. Regardless, it utilizes the c-AMP pathway. * **Vasopressin (ADH):** Acts via two main receptors. While V1 receptors use the IP3/DAG pathway, **V2 receptors** (located in the renal collecting ducts) utilize the **c-AMP** pathway to insert aquaporin-2 channels. **NEET-PG High-Yield Pearls:** * **c-AMP users (FLAT ChAMP):** **F**SH, **L**H, **A**CTH, **T**SH, **C**RH, **h**CG, **A**DH (V2), **M**SH, **P**TH, and Glucagon. * **IP3/DAG users (GOAT):** **G**nRH, **O**xytocin, **A**DH (V1), **T**RH. * **Intracellular/Nuclear Receptors:** All Steroids (Glucocorticoids, Mineralocorticoids, Androgens, Estrogen, Progesterone), Thyroid hormones (T3/T4), and Vitamin D.

Q: Fetal growth is maximally affected by which of the following hormones?

Insulin. **Explanation:** In fetal life, the regulation of growth differs significantly from postnatal life. **Insulin** is the primary anabolic hormone responsible for fetal growth and macrosomia. **1. Why Insulin is Correct:** Insulin promotes cell division (hyperplasia) and protein synthesis in fetal tissues. It acts as a major growth promoter because fetal growth is largely independent of the Growth Hormone (GH)-IGF-1 axis. Instead, it is driven by **Insulin and IGF-2**. Clinical evidence for this is seen in **Infants of Diabetic Mothers (IDM)**; maternal hyperglycemia leads to fetal hyperinsulinemia, resulting in macrosomia (excessive birth weight). **2. Why the other options are incorrect:** * **Growth Hormone (GH):** While GH is the primary regulator of linear growth *after* birth, it has a negligible role in utero. Fetuses with anencephaly or pituitary agenesis (lacking GH) often have near-normal birth weights. * **Thyroxine (T4):** Thyroid hormones are crucial for **fetal brain development** and skeletal maturation (bone age), but they do not significantly influence overall somatic growth or birth weight. * **Cortisol:** Cortisol is primarily involved in the **maturation of fetal organs** (especially surfactant production in lungs) rather than promoting growth. In fact, excess glucocorticoids can lead to intrauterine growth restriction (IUGR). **High-Yield NEET-PG Pearls:** * **Primary growth promoter in utero:** Insulin / IGF-2. * **Primary growth promoter postnatally:** Growth Hormone / IGF-1. * **Thyroid hormone deficiency in utero:** Leads to Cretinism (mental retardation), but birth weight is usually normal. * **Laron Dwarfism:** Caused by GH receptor insensitivity; birth weight is normal, but postnatal growth is severely retarded.

Q: Glucose increases plasma insulin by a process that involves which of the following?

GLUT2. **Explanation:** The secretion of insulin from pancreatic beta cells is a highly regulated process triggered by rising blood glucose levels. The correct answer is **GLUT2** because it serves as the specific glucose sensor for the beta cell. **Why GLUT2 is correct:** GLUT2 is a high-capacity, low-affinity glucose transporter. Its high $K_m$ (Michaelis constant) ensures that glucose entry into the beta cell is proportional to the plasma glucose concentration within the physiological range. Once inside, glucose is phosphorylated by **Glucokinase** (the rate-limiting step), leading to ATP production. The increased ATP/ADP ratio closes **ATP-sensitive $K^+$ channels**, causing membrane depolarization. This opens **voltage-gated $Ca^{2+}$ channels**, leading to calcium influx and the subsequent exocytosis of insulin granules. **Why other options are incorrect:** * **GLUT1:** Found primarily in RBCs and the blood-brain barrier; it provides basal glucose uptake but does not act as the primary sensor for insulin release. * **GLUT3:** Primarily located in neurons; it has a very low $K_m$ (high affinity), ensuring glucose uptake even during hypoglycemia, which is unsuitable for a regulatory sensing role. * **SGLT1:** This is a sodium-glucose co-transporter found in the small intestine and proximal renal tubules (S3 segment) for active transport, not involved in the pancreatic insulin secretion mechanism. **High-Yield Clinical Pearls for NEET-PG:** * **Glucokinase** is often called the "Glucose Sensor" of the body; mutations in this enzyme lead to **MODY type 2** (Maturity-Onset Diabetes of the Young). * **GLUT4** is the only insulin-dependent transporter (found in skeletal muscle and adipose tissue). * **Sulfonylureas** (oral hypoglycemics) work by directly closing the ATP-sensitive $K^+$ channels, bypassing the glucose metabolism step to stimulate insulin release.

Question 1

All of the following hormones accelerate the release of free fatty acids (FFA) from adipose tissue, EXCEPT:

Accepted Answer

Insulin

Answer

Epinephrine

Answer

Norepinephrine

Answer

Vasopressin

Question 2

Orexins play an important role in eating disorders. All of the following are orexins, EXCEPT?

Accepted Answer

Leptin

Answer

Orexin-A

Answer

Hypocretin 1

Answer

Hypocretin 2

Question 3

Catecholamine hormones are synthesized in which location?

Accepted Answer

Chromaffin cells of the adrenal medulla

Answer

Zona glomerulosa of the adrenal cortex

Answer

Zona fasciculata of the adrenal cortex

Answer

Zona reticularis of the adrenal cortex

Question 4

The occurrence of hypothyroidism following administration of supplemental iodine to subjects with endemic iodine deficiency goiter is known as:

Accepted Answer

Wolff-Chaikoff effect

Answer

Jod-Basedow effect

Answer

Rafetoff Syndrome

Answer

Pendred Syndrome

Question 5

Which of the following stimulates insulin secretion?

Accepted Answer

All of the above

Answer

Glucose

Answer

Vagal stimulation

Answer

Acetylcholine

Question 6

Which of the following hormones can cause hyperglycemia without known effects on glycogen or gluconeogenesis?

Accepted Answer

Thyroxine

Answer

Epinephrine

Answer

Glucocorticoids

Answer

Epidermal growth factor

Question 7

When NaCl is injected into the internal carotid artery, it causes the release of ADH by acting on which nucleus?

Accepted Answer

Supraoptic nucleus

Answer

Paramedian nucleus

Answer

Anterior pituitary

Answer

Paraventricular nucleus

Question 8

All of the following use cyclic AMP (c-AMP) as a second messenger except?

Accepted Answer

Testosterone

Answer

Corticotropin

Answer

Dopamine

Answer

Vasopressin

Question 9

Fetal growth is maximally affected by which of the following hormones?

Accepted Answer

Insulin

Answer

Growth hormone

Answer

Cortisol

Answer

Thyroxine

Question 10

Glucose increases plasma insulin by a process that involves which of the following?

Accepted Answer

GLUT2

Answer

GLUT1

Answer

GLUT3

Answer

SGLT1

Endocrinology — MCQs

Endocrinology — MCQs

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