Endocrinology Practice Questions

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.

Q: Which of the following statements regarding ghrelin is false?

None of the above. **Explanation:** Ghrelin, often referred to as the "hunger hormone," is a 28-amino acid peptide that plays a central role in energy homeostasis. The correct answer is **None of the above** because all statements (A, B, and C) are physiologically accurate. 1. **Secreted from D1 cells (Option A):** Ghrelin is primarily synthesized and secreted by the **P/D1 cells** (oxyntic cells) located in the fundus of the stomach. Smaller amounts are produced in the small intestine and the epsilon cells of the pancreas. 2. **Induces Lipolysis (Option B):** While ghrelin is orexigenic (promotes fat storage in the long term), it acutely stimulates the secretion of **Growth Hormone (GH)** from the anterior pituitary by binding to the Growth Hormone Secretagogue Receptor (GHSR). Growth hormone is a potent lipolytic agent, thereby indirectly inducing lipolysis. 3. **Stimulates Appetite (Option C):** Ghrelin is the only peripheral hormone known to stimulate food intake. It acts on the **Arcuate Nucleus** of the hypothalamus, specifically stimulating **NPY (Neuropeptide Y)** and **AgRP (Agouti-related peptide)** neurons to increase hunger. **High-Yield NEET-PG Pearls:** * **Prader-Willi Syndrome:** Characterized by extremely high ghrelin levels, leading to hyperphagia and obesity. * **Sleep Deprivation:** Increases ghrelin and decreases leptin, contributing to weight gain. * **Post-Gastric Bypass:** Ghrelin levels significantly drop, which is one mechanism for the rapid weight loss observed after bariatric surgery. * **Opponent Hormone:** **Leptin** (secreted by adipocytes) is the functional antagonist of ghrelin, as it induces satiety.

Q: Which of the following conditions would be associated with parallel changes in aldosterone and cortisol secretion?

Addison's disease. **Explanation:** The adrenal cortex is divided into three zones: the **Zona Glomerulosa** (produces Aldosterone/Mineralocorticoids) and the **Zona Fasciculata/Reticularis** (produces Cortisol/Glucocorticoids and Androgens). **Why Addison’s Disease is correct:** Addison’s disease (Primary Adrenocortical Insufficiency) involves the **destruction of the entire adrenal cortex** (most commonly due to autoimmune adrenalitis or TB). Because the whole gland is affected, there is a simultaneous deficiency of both aldosterone and cortisol. Thus, they change in **parallel** (both decrease). **Why the other options are incorrect:** * **Cushing’s Disease:** This is a secondary hypercortisolism caused by a pituitary adenoma secreting excess ACTH. ACTH primarily regulates cortisol; it has minimal effect on aldosterone (which is regulated by the Renin-Angiotensin System). Therefore, cortisol increases while aldosterone remains relatively normal. * **Cushing’s Syndrome:** This refers to hypercortisolism from any cause (e.g., adrenal tumor or exogenous steroids). Similar to Cushing's disease, the pathology is specific to glucocorticoid excess, not mineralocorticoids. * **Conn’s Syndrome:** This is Primary Hyperaldosteronism (usually a Z. Glomerulosa adenoma). It results in isolated high aldosterone levels; cortisol levels remain normal. **High-Yield Clinical Pearls for NEET-PG:** * **Regulation:** Aldosterone is primarily regulated by **Angiotensin II and Serum Potassium**, whereas Cortisol is regulated by **ACTH**. * **Electrolytes in Addison’s:** Look for the triad of **Hyponatremia, Hyperkalemia, and Metabolic Acidosis** (due to aldosterone deficiency) along with hypoglycemia (due to cortisol deficiency). * **Hyperpigmentation:** Seen in Addison’s (Primary) but NOT in Secondary Adrenal Insufficiency, due to high ACTH/MSH levels.

Q: What is the primary form of cortisol in plasma?

Bound to corticosteroid-binding globulin (CBG). ### Explanation **1. Why Option D is Correct:** Cortisol, being a steroid hormone, is lipophilic and requires transport proteins to travel through the aqueous environment of the plasma. In humans, approximately **75% to 80%** of circulating cortisol is bound to **Corticosteroid-Binding Globulin (CBG)**, also known as **Transcortin**. This high-affinity binding serves as a reservoir, protecting the hormone from rapid metabolic degradation by the liver and excretion by the kidneys, thereby extending its half-life. **2. Why Other Options are Incorrect:** * **Option A (Albumin):** About **15%** of cortisol is bound to albumin. While albumin has a high capacity, it has a much lower affinity for cortisol compared to CBG. * **Option B (Transthyretin):** Transthyretin (Prealbumin) is primarily involved in the transport of Thyroxine (T4) and Retinol (Vitamin A), not cortisol. * **Option C (Free in solution):** Only about **5% to 10%** of cortisol exists in the "free" or unbound state. However, this free fraction is the biologically active form capable of crossing cell membranes to bind to intracellular receptors. **3. NEET-PG High-Yield Clinical Pearls:** * **CBG Levels:** CBG synthesis in the liver is **increased by Estrogen** (e.g., pregnancy, OCP use) and **decreased in Liver Cirrhosis** or Nephrotic Syndrome. * **Total vs. Free Cortisol:** In pregnancy, total cortisol levels rise due to increased CBG, but the "free" (active) cortisol remains relatively normal, maintaining homeostasis. * **Diurnal Variation:** Cortisol levels peak in the early morning (approx. 8 AM) and reach their nadir around midnight. * **Metabolism:** Cortisol is metabolized in the liver and excreted in the urine as **17-hydroxycorticosteroids**.

Question 1

Which of the following stimulates insulin secretion?

Accepted Answer

All of the above

Answer

Glucose

Answer

Vagal stimulation

Answer

Acetylcholine

Question 2

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 3

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 4

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

Accepted Answer

Testosterone

Answer

Corticotropin

Answer

Dopamine

Answer

Vasopressin

Question 5

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

Accepted Answer

Insulin

Answer

Growth hormone

Answer

Cortisol

Answer

Thyroxine

Question 6

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

Accepted Answer

GLUT2

Answer

GLUT1

Answer

GLUT3

Answer

SGLT1

Question 7

Which of the following statements regarding ghrelin is false?

Accepted Answer

None of the above

Answer

Secreted from D1 cells of the fundus

Answer

Induces lipolysis

Answer

Stimulates appetite

Question 8

Which of the following conditions would be associated with parallel changes in aldosterone and cortisol secretion?

Accepted Answer

Addison's disease

Answer

Cushing's disease

Answer

Cushing's syndrome

Answer

Conn's syndrome

Question 9

Which of the following is an example of a neurohormone?

Accepted Answer

Oxytocin

Answer

ACTH

Answer

Cortisol

Answer

Somatostatin

Question 10

What is the primary form of cortisol in plasma?

Accepted Answer

Bound to corticosteroid-binding globulin (CBG)

Answer

Bound to albumin

Answer

Bound to transthyretin

Answer

Free in solution

Endocrinology — MCQs

Endocrinology — MCQs

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