Endocrinology Practice Questions

Q: Which hormone acts by genetic modification?

Thyroxine. **Explanation:** The mechanism of action of a hormone is determined by its chemical nature and the location of its receptors. Hormones that act via **genetic modification** (regulation of gene expression) are lipid-soluble, allowing them to cross the cell membrane and bind to intracellular receptors. **Why Thyroxine (T4) is correct:** Thyroxine is a derivative of tyrosine but behaves like a steroid hormone due to its lipophilic nature. It enters the cell and binds to **nuclear receptors** (TR-α and TR-β). The hormone-receptor complex then binds to specific DNA sequences called **Thyroid Response Elements (TREs)**. This directly stimulates or inhibits the transcription of specific genes, leading to the synthesis of new proteins (e.g., Na+/K+ ATPase, respiratory enzymes), which mediates the hormone's long-term effects. **Why other options are incorrect:** * **Insulin:** A peptide hormone that binds to a transmembrane **Tyrosine Kinase receptor**. It acts via a phosphorylation cascade (MAP kinase and PI-3 kinase pathways). * **Growth Hormone (GH):** A peptide hormone that binds to a cell surface receptor associated with the **JAK-STAT signaling pathway**. * **ACTH:** A peptide hormone that binds to G-protein coupled receptors (GPCR) on the adrenal cortex, activating the **adenylyl cyclase-cAMP** second messenger system. **High-Yield Clinical Pearls for NEET-PG:** * **Nuclear Receptors:** Remember the mnemonic **"KITE"** for hormones acting on nuclear receptors: **K**ortisol (Steroids), **I**odothyronines (T3/T4), **T**estosterone (Androgens), **E**strogen/Vitamin D/Retinoic acid. * **Speed of Action:** Hormones acting via genetic modification (Thyroid/Steroids) have a **slow onset** (hours to days) but **long duration** of action compared to peptide hormones. * **T3 vs. T4:** While T4 is secreted in higher quantities, **T3** is the active form that binds to the nuclear receptor with much higher affinity.

Q: Lesions of which of the hypothalamic nuclei cause diabetes insipidus?

Supraoptic and paraventricular nuclei. **Explanation:** **1. Why Option B is Correct:** The **Supraoptic (SON)** and **Paraventricular (PVN)** nuclei of the hypothalamus are responsible for the synthesis of **Antidiuretic Hormone (ADH)**, also known as vasopressin. ADH is synthesized in the cell bodies of these nuclei and transported via the hypothalamo-hypophyseal tract to the posterior pituitary for storage and release. * **Mechanism:** ADH acts on the V2 receptors in the collecting ducts of the kidney to increase water reabsorption. * **Lesion Effect:** Destruction of these nuclei (or the tract) leads to a deficiency of ADH, resulting in **Central Diabetes Insipidus**, characterized by polyuria (excessive dilute urine) and polydipsia. **2. Why Other Options are Incorrect:** * **A. Dorsomedial Nuclei:** Primarily involved in emotional behavior and GI stimulation (sham rage). * **C. Median Preoptic Nuclei:** Involved in thermoregulation (the "heat loss center") and bladder control. * **D. Ventromedial Nuclei:** Known as the **Satiety Center**. Lesions here lead to hyperphagia and obesity. **3. High-Yield Clinical Pearls for NEET-PG:** * **ADH vs. Oxytocin:** While both nuclei produce both hormones, the **Supraoptic** nucleus primarily produces **ADH**, while the **Paraventricular** nucleus primarily produces **Oxytocin**. * **Osmoreceptors:** These are located in the *organum vasculosum of the lamina terminalis* (OVLT), which sense plasma osmolality and signal the SON/PVN to release ADH. * **Triphasic Response:** Post-surgical trauma to this area can cause a "triphasic" response: initial DI, followed by a period of SIADH (due to leaking stored ADH), and finally permanent DI.

Q: Which of the following is a function of prolactin during lactation?

Decreased estrogen. **Explanation:** The correct answer is **D. Decreased estrogen**. **Mechanism:** Prolactin, primarily known for stimulating milk production (lactogenesis), exerts a potent inhibitory effect on the hypothalamic-pituitary-gonadal (HPG) axis. High levels of prolactin during lactation inhibit the pulsatile release of **Gonadotropin-Releasing Hormone (GnRH)** from the hypothalamus. This suppression leads to a decrease in the secretion of **FSH (Follicle-Stimulating Hormone)** and **LH (Luteinizing Hormone)** from the anterior pituitary. Consequently, the ovaries are not stimulated to produce **estrogen**, leading to a state of temporary hypogonadism known as **lactational amenorrhea**. **Analysis of Incorrect Options:** * **A. Increased FSH:** Prolactin suppresses GnRH, which leads to a *decrease* in FSH levels, not an increase. * **B. Increased libido:** Estrogen and testosterone are key drivers of libido. Since prolactin suppresses these sex steroids, it typically results in *decreased* libido. * **C. Increased testosterone:** In both males and females, hyperprolactinemia inhibits the HPG axis, leading to *decreased* production of testosterone. **Clinical Pearls for NEET-PG:** * **Lactational Amenorrhea Method (LAM):** This physiological suppression of ovulation serves as a natural (though not 100% reliable) form of contraception postpartum. * **Prolactinoma:** In non-lactating patients, a prolactin-secreting tumor presents with galactorrhea, infertility, and decreased bone density (due to chronic low estrogen). * **Dopamine Connection:** Dopamine is the primary "Prolactin-Inhibiting Factor." Drugs that block dopamine (like antipsychotics) can cause hyperprolactinemia.

Q: Pheochromocytoma predominantly secretes which hormone?

Norepinephrine. ### Explanation **Pheochromocytoma** is a catecholamine-secreting tumor derived from the chromaffin cells of the adrenal medulla. **Why Norepinephrine is Correct:** In the normal adrenal medulla, approximately 80% of the secretion is Epinephrine and 20% is Norepinephrine. This is because the enzyme **PNMT** (Phenylethanolamine N-methyltransferase), which converts norepinephrine to epinephrine, is induced by high concentrations of cortisol draining from the adrenal cortex. However, in a **Pheochromocytoma**, the tumor cells often lack sufficient contact with cortical cortisol or lose the ability to express PNMT efficiently. Consequently, the predominant hormone secreted into the circulation is **Norepinephrine**. **Analysis of Incorrect Options:** * **A. Serotonin:** This is primarily secreted by enterochromaffin cells of the GI tract and is the hallmark of Carcinoid Syndrome, not Pheochromocytoma. * **B. Epinephrine:** While secreted by the normal adrenal medulla and some specific pheochromocytomas (especially those associated with MEN 2 syndrome), it is not the *predominant* secretion in sporadic cases. * **D. Dopamine:** Though a precursor in the catecholamine pathway, it is rarely the primary secretion. High dopamine levels are more characteristic of neuroblastomas or extra-adrenal paragangliomas. **High-Yield Clinical Pearls for NEET-PG:** * **Rule of 10s:** 10% bilateral, 10% malignant, 10% pediatric, 10% extra-adrenal (Paraganglioma). * **Diagnosis:** Best initial screening test is **24-hour urinary fractionated metanephrines** and VMA. * **Management:** Always give **Alpha-blockers (Phenoxybenzamine)** before Beta-blockers to prevent a hypertensive crisis (unopposed alpha-1 stimulation). * **Associated Syndromes:** MEN 2A, MEN 2B, von Hippel-Lindau (VHL), and NF-1.

Q: Calcitonin is released by:

Parafollicular cells of thyroid. **Explanation:** **Calcitonin** is a 32-amino acid peptide hormone primarily involved in calcium homeostasis. It is synthesized and secreted by the **Parafollicular cells (also known as C-cells)** of the thyroid gland. These cells are neuroendocrine in origin (derived from the neural crest) and are located in the connective tissue between the thyroid follicles. Calcitonin acts to lower plasma calcium levels by inhibiting osteoclast activity and decreasing renal calcium reabsorption, effectively acting as a physiological antagonist to Parathyroid Hormone (PTH). **Analysis of Incorrect Options:** * **B. Chief cells of thyroid:** This is a distractor. Chief cells are found in the **Parathyroid glands**, where they secrete Parathyroid Hormone (PTH), not in the thyroid gland. * **C. Granular cells of adrenal gland:** There are no specific "granular cells" defined as a major secretory unit in the adrenal gland. The adrenal medulla contains Chromaffin cells which secrete catecholamines. * **D. Stratum fasciculata of adrenal gland:** This is the middle layer of the adrenal cortex responsible for secreting **Glucocorticoids** (primarily Cortisol), not calcitonin. **High-Yield Clinical Pearls for NEET-PG:** * **Stimulus for Release:** The primary stimulus for calcitonin secretion is **hypercalcemia**. * **Tumor Marker:** Calcitonin serves as a critical tumor marker for **Medullary Thyroid Carcinoma (MTC)**, which arises from the Parafollicular C-cells. * **Therapeutic Use:** Exogenous calcitonin (often salmon calcitonin) is used clinically to treat Paget’s disease of the bone and severe hypercalcemia. * **Developmental Origin:** While thyroid follicular cells arise from the endoderm (thyroglossal duct), the Parafollicular C-cells originate from the **ultimobranchial body** (derived from the 4th/5th pharyngeal pouches).

Q: Insulin acts by stimulation of which type of receptor?

Enzymatic receptor. **Explanation:** The insulin receptor belongs to the **Enzymatic receptor** family, specifically the **Receptor Tyrosine Kinase (RTK)** class. It is a heterotetramer consisting of two extracellular alpha-subunits (binding site) and two transmembrane beta-subunits. When insulin binds to the alpha-subunits, it triggers autophosphorylation of the beta-subunits. This activates the intrinsic tyrosine kinase activity, which then phosphorylates **Insulin Receptor Substrates (IRS)**, leading to downstream metabolic effects like glucose uptake via GLUT-4 translocation. **Analysis of Options:** * **A. Ionotropic receptors:** These are ligand-gated ion channels (e.g., Nicotinic ACh receptors) that change membrane potential. Insulin does not directly open an ion channel. * **C. Metabotropic receptors:** These are G-Protein Coupled Receptors (GPCRs) that act via second messengers like cAMP or IP3/DAG (e.g., Glucagon, Epinephrine). Insulin does not utilize G-proteins. * **D. Nuclear receptors:** These are intracellular receptors for lipid-soluble hormones (e.g., Steroids, Thyroid hormone) that act as transcription factors. Insulin is a peptide hormone and cannot cross the lipid bilayer. **High-Yield Clinical Pearls for NEET-PG:** * **GLUT-4:** The only insulin-dependent glucose transporter, found primarily in skeletal muscle and adipose tissue. * **MAP Kinase Pathway:** Mediates the growth-promoting (mitogenic) effects of insulin. * **PI3-Kinase Pathway:** Mediates the metabolic effects (glucose transport and glycogen synthesis). * **Downregulation:** Chronic hyperinsulinemia (as seen in Type 2 Diabetes) leads to "internalization" of receptors, contributing to insulin resistance.

Q: What is the primary mechanism through which catecholamines stabilize blood glucose concentration in response to hypoglycemia?

Catecholamines stimulate gluconeogenesis in the liver.. **Explanation:** The primary goal of catecholamines (Epinephrine and Norepinephrine) during hypoglycemia is to increase blood glucose levels rapidly. This is achieved through the activation of **$\beta_2$ and $\alpha_1$ receptors** in the liver. **Why Option D is correct:** Catecholamines are potent counter-regulatory hormones. They stimulate **gluconeogenesis** (the synthesis of glucose from non-carbohydrate precursors like lactate and amino acids) and **glycogenolysis** (breakdown of glycogen) in the liver. By increasing the expression of key enzymes like PEPCK (Phosphoenolpyruvate carboxykinase), they ensure a sustained release of glucose into the systemic circulation to protect the brain. **Why other options are incorrect:** * **Option A:** While catecholamines do stimulate glycogen phosphorylase in muscles, **muscle lacks the enzyme Glucose-6-Phosphatase**. Therefore, muscle glycogen is converted to lactate (via glycolysis) rather than free glucose, and cannot directly contribute to blood glucose levels. * **Option B:** Catecholamines **stimulate** liver glycogenolysis; inhibiting it would worsen hypoglycemia. * **Option C:** Catecholamines actually **inhibit insulin release** (via $\alpha_2$ receptors) and stimulate glucagon release (via $\beta_2$ receptors) to prevent further glucose uptake by peripheral tissues. **High-Yield NEET-PG Pearls:** * **Dual Action:** Catecholamines increase glucose **production** (liver) and decrease glucose **utilization** (peripheral tissues like muscle/adipose) to spare glucose for the CNS. * **Receptor Specificity:** Hepatic glucose production is mediated by both $\alpha_1$ and $\beta_2$ receptors, but the **inhibition of insulin** is primarily an **$\alpha_2$ effect**. * **Hierarchy:** In the defense against hypoglycemia, Glucagon is the first line of defense, followed closely by Epinephrine. Cortisol and Growth Hormone act much later.

Question 1

Which hormone acts by genetic modification?

Accepted Answer

Thyroxine

Answer

Insulin

Answer

Growth Hormone (GH)

Answer

Adrenocorticotropic Hormone (ACTH)

Question 2

Lesions of which of the hypothalamic nuclei cause diabetes insipidus?

Accepted Answer

Supraoptic and paraventricular nuclei

Answer

Dorsomedial nuclei

Answer

Median preoptic nuclei

Answer

Ventromedial nuclei

Question 3

Which of the following is a function of prolactin during lactation?

Accepted Answer

Decreased estrogen

Answer

Increased FSH

Answer

Increased libido

Answer

Increased testosterone

Question 4

Pheochromocytoma predominantly secretes which hormone?

Accepted Answer

Norepinephrine

Answer

Serotonin

Answer

Epinephrine

Answer

Dopamine

Question 5

Calcitonin is released by:

Accepted Answer

Parafollicular cells of thyroid

Answer

Chief cells of thyroid

Answer

Granular cells of adrenal gland

Answer

Stratum fasciculata of adrenal gland

Question 6

Which of the following is NOT an action of calcitriol?

Accepted Answer

Calcitriol increases the excretion of calcium and phosphate through the kidney.

Answer

Calcitriol increases the intestinal absorption of calcium.

Answer

Calcitriol stimulates calcium uptake for deposition as calcium phosphate in the osteoblasts of bone.

Answer

Calcitriol's action is similar to steroid hormones.

Question 7

Glucose-dependent release of insulin is mediated by which mechanism?

Accepted Answer

Cyclic AMP

Answer

Carrier's modulators

Answer

Receptor phosphorylation

Answer

ATP-dependent K+ channel

Question 8

Insulin acts by stimulation of which type of receptor?

Accepted Answer

Enzymatic receptor

Answer

Ionotropic receptor

Answer

Metabotropic receptor

Answer

Nuclear receptor

Question 9

In a transection between the hypothalamus and the anterior pituitary, the production of which hormone remains unaffected?

Accepted Answer

Oxytocin

Answer

Testosterone

Answer

Thyroxine

Answer

Cortisol

Question 10

What is the primary mechanism through which catecholamines stabilize blood glucose concentration in response to hypoglycemia?

Accepted Answer

Catecholamines stimulate gluconeogenesis in the liver.

Answer

Catecholamines stimulate glycogen phosphorylase to release glucose from muscle.

Answer

Catecholamines inhibit glycogenolysis in the liver.

Answer

Catecholamines stimulate the release of insulin from the pancreas.

Endocrinology — MCQs

Endocrinology — MCQs

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