Endocrinology Practice Questions

Q: Which hormone is secreted by alpha-cells in the pancreas in response to low blood glucose levels?

Glucagon. **Explanation:** The pancreas functions as both an exocrine and endocrine gland. The endocrine component consists of the **Islets of Langerhans**, which contain several distinct cell types. **1. Why Glucagon is Correct:** **Glucagon** is synthesized and secreted by the **alpha (α) cells**, which constitute about 20% of the islet cells. Its primary stimulus is **hypoglycemia** (low blood glucose). Glucagon acts as a counter-regulatory hormone to insulin; it increases blood glucose levels by stimulating **glycogenolysis** (breakdown of glycogen) and **gluconeogenesis** (synthesis of glucose from non-carbohydrate sources) in the liver. **2. Why Other Options are Incorrect:** * **Insulin:** Secreted by **beta (β) cells** (the most abundant type, ~65-70%). It is released in response to *high* blood glucose levels to facilitate glucose uptake into cells. * **Epinephrine:** While it also raises blood glucose, it is secreted by the **adrenal medulla**, not the pancreas. It acts during the "fight or flight" response. * **Somatostatin:** Secreted by **delta (δ) cells**. Its primary role is paracrine inhibition, suppressing the secretion of both insulin and glucagon. **3. NEET-PG High-Yield Pearls:** * **Major Stimulus:** The most potent stimulator for glucagon is a fall in blood glucose, but **increased amino acids** (especially arginine and alanine) also stimulate its release. * **Inhibitors:** Glucagon secretion is inhibited by hyperglycemia, insulin, and somatostatin. * **Glucagonoma:** A rare tumor of alpha cells characterized by the "4 Ds": Diabetes, Dermatitis (Necrolytic migratory erythema), Deep vein thrombosis, and Depression. * **Clinical Use:** Intramuscular glucagon is used as emergency treatment for severe hypoglycemia in diabetic patients.

Q: Disorganized lesions in which of the following locations would affect the release of ADH and oxytocin from the posterior pituitary?

Supraoptic and paraventricular nuclei. **Explanation:** The posterior pituitary (neurohypophysis) does not synthesize hormones; instead, it stores and releases hormones produced in the hypothalamus. **1. Why Option A is Correct:** The hormones **Antidiuretic Hormone (ADH/Vasopressin)** and **Oxytocin** are synthesized in the cell bodies of magnocellular neurons located in the **Supraoptic (SON)** and **Paraventricular (PVN)** nuclei of the hypothalamus. * **SON** primarily synthesizes ADH. * **PVN** primarily synthesizes Oxytocin. These hormones are transported down the axons via the hypothalamo-hypophyseal tract (bound to carrier proteins called **neurophysins**) and are stored in terminal nerve endings (Herring bodies) in the posterior pituitary until release. Therefore, lesions in these nuclei directly disrupt the production and subsequent release of these hormones. **2. Why Other Options are Incorrect:** * **B. Ventromedial Nucleus:** Known as the **Satiety Center**. Lesions here lead to hyperphagia and obesity. * **C. Lateral Hypothalamus:** Known as the **Feeding Center**. Lesions here lead to aphagia and weight loss. * **D. Posterior Hypothalamus:** Primarily involved in **thermogenesis** (response to cold) and sympathetic regulation. Lesions result in poikilothermia (inability to regulate body temperature). **High-Yield Clinical Pearls for NEET-PG:** * **Diabetes Insipidus (DI):** Central DI occurs due to a deficiency of ADH, often resulting from trauma or lesions to the SON/PVN or the pituitary stalk. * **Neurophysins:** Neurophysin I is associated with Oxytocin, while Neurophysin II is associated with ADH. * **V2 Receptors:** ADH acts on V2 receptors in the collecting ducts of the kidney to insert Aquaporin-2 channels for water reabsorption.

Q: Diabetes insipidus is due to hyposecretion of which hormone?

Arginine Vasopressin/ AVP. **Explanation:** **Diabetes Insipidus (DI)** is a clinical syndrome characterized by the excretion of large volumes of dilute urine (polyuria) and excessive thirst (polydipsia). It occurs due to a deficiency in the action of **Arginine Vasopressin (AVP)**, also known as Antidiuretic Hormone (ADH). 1. **Why Arginine Vasopressin (AVP) is correct:** AVP is synthesized in the hypothalamus and stored in the posterior pituitary. Its primary role is to maintain water homeostasis by binding to V2 receptors in the renal collecting ducts, promoting the insertion of aquaporin-2 channels. This allows water reabsorption. **Hyposecretion** of AVP (Central DI) or resistance to its action (Nephrogenic DI) leads to an inability to concentrate urine, resulting in the hallmark symptoms of DI. 2. **Why other options are incorrect:** * **Insulin:** Hyposecretion of insulin leads to **Diabetes Mellitus**, characterized by hyperglycemia and osmotic diuresis due to glycosuria. * **Angiotensin:** Part of the RAAS pathway, Angiotensin II is a potent vasoconstrictor and stimulates aldosterone release; its deficiency does not cause DI. * **Aldosterone:** A mineralocorticoid responsible for sodium reabsorption and potassium excretion. Deficiency (as in Addison’s disease) leads to hyponatremia and hyperkalemia, not DI. **High-Yield Clinical Pearls for NEET-PG:** * **Water Deprivation Test:** The gold standard for diagnosing DI and differentiating it from primary polydipsia. * **Desmopressin (dDAVP):** A synthetic analog of AVP used to differentiate Central DI (responds to dDAVP) from Nephrogenic DI (no response). * **Urine Osmolality:** In DI, urine is characteristically dilute (typically <300 mOsm/kg).

Q: Which of the following receptors is NOT found in the nucleus?

Androgen receptor. To answer this question correctly, it is essential to distinguish between the two types of intracellular receptors: **Cytoplasmic** and **Nuclear**. ### **Why Androgen Receptor is the Correct Answer** The **Androgen receptor (Option B)**, along with Glucocorticoid, Mineralocorticoid, and Progesterone receptors, is primarily located in the **cytoplasm** in its inactive state. These receptors are bound to heat shock proteins (HSPs). Upon ligand binding, the receptor dissociates from the HSP, undergoes dimerization, and translocates into the nucleus to act as a transcription factor. ### **Analysis of Incorrect Options** * **Estrogen Receptor (Option A):** Unlike other steroid receptors, the Estrogen receptor is predominantly located **inside the nucleus**, even in its unbound state. * **Thyroxine (T3/T4) Receptor (Option C):** Thyroid hormone receptors are classic examples of **constitutive nuclear receptors**. They are always bound to DNA (Thyroid Response Elements), often acting as repressors until the hormone binds. * **Vitamin D Receptor (Option D):** Similar to Thyroid and Retinoic acid receptors, the Vitamin D receptor (VDR) is located **within the nucleus**. ### **High-Yield NEET-PG Pearls** * **Mnemonic for Cytoplasmic Receptors:** **"M-A-G-P"** (Mineralocorticoid, Androgen, Glucocorticoid, Progesterone). * **Nuclear Receptors:** Remember **"T-E-V-R"** (Thyroid, Estrogen, Vitamin D, Retinoic Acid). * **Mechanism:** All these receptors belong to the **Steroid Hormone Receptor Superfamily** and regulate gene expression by binding to specific DNA sequences called Hormone Response Elements (HREs). * **Exception:** While Estrogen is a steroid, its receptor is a notable exception as it resides in the nucleus, not the cytoplasm.

Q: Which hormone is secreted by the posterior pituitary gland?

Antidiuretic Hormone (ADH). **Explanation:** The posterior pituitary gland (neurohypophysis) does not synthesize hormones; instead, it stores and releases two hormones produced by the hypothalamus: **Antidiuretic Hormone (ADH/Vasopressin)** and **Oxytocin**. ADH is synthesized primarily in the **supraoptic nucleus**, while Oxytocin is synthesized in the **paraventricular nucleus**. They travel down the hypothalamo-hypophyseal tract and are released into the systemic circulation from the posterior pituitary in response to physiological triggers like increased plasma osmolarity. **Analysis of Incorrect Options:** * **A, B, and D (GH, TSH, FSH):** These are all synthesized and secreted by the **Anterior Pituitary (Adenohypophysis)**. The anterior pituitary contains specialized glandular cells (Somatotrophs for GH, Thyrotrophs for TSH, and Gonadotrophs for FSH/LH) regulated by hypothalamic releasing hormones. **NEET-PG High-Yield Pearls:** * **Storage Site:** Hormones in the posterior pituitary are stored in terminal nerve endings called **Herring Bodies**. * **ADH Receptors:** * **V1 receptors:** Located on vascular smooth muscle (cause vasoconstriction). * **V2 receptors:** Located in the late distal tubule and collecting ducts (increase water reabsorption via **Aquaporin-2** channels). * **Clinical Correlation:** A deficiency in ADH secretion or action leads to **Diabetes Insipidus**, characterized by polyuria and polydipsia. * **Mnemonic:** Remember **"FLAT PIG"** for Anterior Pituitary hormones (FSH, LH, ACTH, TSH, Prolactin, GH). If it’s not on this list, it’s likely Posterior Pituitary.

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.

Question 1

Which hormone is secreted by alpha-cells in the pancreas in response to low blood glucose levels?

Accepted Answer

Glucagon

Answer

Insulin

Answer

Epinephrine

Answer

Somatostatin

Question 2

Disorganized lesions in which of the following locations would affect the release of ADH and oxytocin from the posterior pituitary?

Accepted Answer

Supraoptic and paraventricular nuclei

Answer

Ventromedial part of the hypothalamus

Answer

Lateral hypothalamus

Answer

Posterior hypothalamus

Question 3

Diabetes insipidus is due to hyposecretion of which hormone?

Accepted Answer

Arginine Vasopressin/ AVP

Answer

Insulin

Answer

Angiotensin

Answer

Aldosterone

Question 4

Which of the following statements is true regarding calcium and phosphorus metabolism?

Accepted Answer

Calcitriol increases phosphate reabsorption in the proximal convoluted tubule.

Answer

Parathormone increases phosphate reabsorption in the proximal convoluted tubule.

Answer

Parathormone increases calcium reabsorption in the proximal convoluted tubule.

Answer

Calcitriol decreases phosphate absorption in the intestine.

Question 5

Which of the following receptors is NOT found in the nucleus?

Accepted Answer

Androgen receptor

Answer

Estrogen receptor

Answer

Thyroxine receptor

Answer

Vitamin D receptor

Question 6

Which hormone is secreted by the posterior pituitary gland?

Accepted Answer

Antidiuretic Hormone (ADH)

Answer

Growth Hormone (GH)

Answer

Thyroid Stimulating Hormone (TSH)

Answer

Follicle Stimulating Hormone (FSH)

Question 7

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 8

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 9

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 10

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

Endocrinology — MCQs

Endocrinology — MCQs

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