Endocrinology Practice Questions

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: The Seoli cell feedback mechanism involves:

Decreased FSH. ### Explanation The Sertoli cells of the testes play a crucial role in the negative feedback regulation of the **Hypothalamic-Pituitary-Gonadal (HPG) axis**. **Why Option B is Correct:** Sertoli cells produce a glycoprotein hormone called **Inhibin B** in response to stimulation by **Follicle-Stimulating Hormone (FSH)**. Inhibin B acts directly on the anterior pituitary gland to specifically inhibit the secretion of FSH. This creates a closed-loop feedback mechanism: high FSH levels stimulate Sertoli cells to produce Inhibin B, which then feeds back to **decrease FSH** levels, maintaining optimal spermatogenesis. **Why Other Options are Incorrect:** * **Option A (Decreased LH):** Luteinizing Hormone (LH) primarily acts on **Leydig cells** to stimulate testosterone production. Testosterone provides negative feedback to both the hypothalamus (GnRH) and the anterior pituitary (LH). Sertoli cell products do not primarily regulate LH. * **Options C & D (Decreased TRH/CRH):** Thyrotropin-releasing hormone (TRH) and Corticotropin-releasing hormone (CRH) are involved in the thyroid and adrenal axes, respectively. They are unrelated to the Sertoli cell feedback loop. **High-Yield Clinical Pearls for NEET-PG:** * **Sertoli Cells:** Often called "nurse cells"; they form the **blood-testis barrier** via tight junctions. * **Inhibin B vs. A:** In males, **Inhibin B** is the primary marker of Sertoli cell function and spermatogenesis. * **Müllerian Inhibiting Substance (MIS):** Also secreted by Sertoli cells during fetal development to cause regression of Müllerian ducts. * **Blood-Testis Barrier:** Protects germ cells from the immune system; failure can lead to anti-sperm antibodies.

Q: Endothelium-Derived Relaxing Factor (EDRF) induced vasodilatation is mediated by which of the following mechanisms?

Increased intracellular cGMP. **Explanation:** **Mechanism of Action:** Endothelium-Derived Relaxing Factor (EDRF), now known to be **Nitric Oxide (NO)**, is a potent vasodilator. The process begins when NO is synthesized in endothelial cells (from L-arginine) and diffuses into adjacent vascular smooth muscle cells. There, it binds to and activates the enzyme **Soluble Guanylyl Cyclase (sGC)**. This enzyme catalyzes the conversion of GTP to **cyclic Guanosine Monophosphate (cGMP)**. Increased intracellular cGMP activates Protein Kinase G (PKG), which leads to a decrease in intracellular calcium levels and dephosphorylation of myosin light chains, resulting in smooth muscle relaxation and vasodilation. **Analysis of Options:** * **Option A (Correct):** As described, the primary signaling pathway for NO/EDRF is the activation of the cGMP second messenger system. * **Option B:** Decreased cGMP would lead to vasoconstriction, not relaxation. * **Options C & D:** The cAMP pathway is primarily utilized by vasodilators like Prostacyclin ($PGI_2$) and $\beta_2$ agonists, not by EDRF/Nitric Oxide. **High-Yield Clinical Pearls for NEET-PG:** * **Precursor:** L-arginine is the amino acid precursor for NO synthesis via the enzyme Nitric Oxide Synthase (NOS). * **Pharmacology Link:** Nitroglycerin and Sodium Nitroprusside act as "nitrovasodilators" by releasing NO, mimicking EDRF. * **Sildenafil (Viagra):** Works by inhibiting **Phosphodiesterase-5 (PDE-5)**, the enzyme that breaks down cGMP, thereby prolonging the vasodilatory effect in the corpus cavernosum. * **Other cGMP Mediators:** Atrial Natriuretic Peptide (ANP) and Brain Natriuretic Peptide (BNP) also use cGMP, but they activate *membrane-bound* (particulate) guanylyl cyclase rather than the soluble form.

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: Norepinephrine is produced by which of the following structures?

Adrenal medulla. **Explanation:** The adrenal gland is divided into two distinct functional units: the outer **adrenal cortex** and the inner **adrenal medulla**. **Why the Adrenal Medulla is Correct:** The adrenal medulla is embryologically derived from the **neural crest cells** and functions as a modified sympathetic ganglion. It contains **chromaffin cells** (pheochromocytes) that synthesize catecholamines. In response to preganglionic sympathetic stimulation, these cells secrete **Epinephrine (80%)** and **Norepinephrine (20%)** directly into the bloodstream. The conversion of norepinephrine to epinephrine is catalyzed by the enzyme *Phenylethanolamine N-methyltransferase (PNMT)*, which is induced by cortisol. **Why the Other Options are Incorrect:** The adrenal cortex is divided into three zones, which exclusively produce steroid hormones (corticosteroids), not catecholamines: * **A. Zona Fasciculata:** The middle and widest layer; it primarily secretes **Glucocorticoids** (e.g., Cortisol). * **B. Zona Glomerulosa:** The outermost layer; it secretes **Mineralocorticoids** (e.g., Aldosterone) under the influence of Angiotensin II. * **C. Zona Reticularis:** The innermost layer of the cortex; it secretes **Androgens** (e.g., Dehydroepiandrosterone or DHEA). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Cortex Layers:** **G-F-R** (Glomerulosa, Fasciculata, Reticularis) corresponds to **Salt, Sugar, Sex** (Aldosterone, Cortisol, Androgens). * **Pheochromocytoma:** A tumor of the chromaffin cells of the adrenal medulla that leads to excessive secretion of norepinephrine and epinephrine, presenting with the classic triad of episodic headache, sweating, and tachycardia. * **VMA (Vanillylmandelic Acid):** The major urinary metabolite of norepinephrine and epinephrine, used as a diagnostic marker for catecholamine-secreting tumors.

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

A 35-year-old woman presents with swelling of the small joints of the hands. On examination, swan neck deformity is present. Labs show elevated rheumatoid factor levels and high anti-CCP levels. She is diagnosed with rheumatoid arthritis and started on steroids for a short duration. What is the mechanism by which steroids reduce inflammation?

Accepted Answer

Inhibition of phospholipase A2

Answer

Inhibition of cyclo-oxygenase

Answer

Inhibition of lipoprotein lipase activity

Answer

Inhibition of lipogenase

Question 2

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

Accepted Answer

Insulin

Answer

Growth hormone

Answer

Cortisol

Answer

Thyroxine

Question 3

The Seoli cell feedback mechanism involves:

Accepted Answer

Decreased FSH

Answer

Decreased LH

Answer

Decreased TRH

Answer

Decreased CRH

Question 4

Endothelium-Derived Relaxing Factor (EDRF) induced vasodilatation is mediated by which of the following mechanisms?

Accepted Answer

Increased intracellular cGMP

Answer

Decreased intracellular cGMP

Answer

Increased extracellular cAMP

Answer

Decreased intracellular cAMP

Question 5

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

Accepted Answer

GLUT2

Answer

GLUT1

Answer

GLUT3

Answer

SGLT1

Question 6

Norepinephrine is produced by which of the following structures?

Accepted Answer

Adrenal medulla

Answer

Zona fasiculata

Answer

Zona glomerulosa

Answer

Zona reticularis

Question 7

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 8

Which of the following is an example of a neurohormone?

Accepted Answer

Oxytocin

Answer

ACTH

Answer

Cortisol

Answer

Somatostatin

Question 9

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

Question 10

A 43-year-old female presents with galactorrhea. Investigations show increased prolactin levels. Which of the following conditions can cause increased prolactin secretion?

Accepted Answer

Dopamine

Answer

Sleep

Answer

Pregnancy

Answer

Stress

Endocrinology — MCQs

Endocrinology — MCQs

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