Endocrinology Practice Questions

Q: Insulin synthesis is stimulated by glucose levels above what threshold?

70 mg%. The synthesis and secretion of insulin by the pancreatic beta cells are tightly regulated by blood glucose concentrations. The correct answer is **70 mg% (70 mg/dL)** because this represents the physiological "set-point" or threshold at which the beta cells initiate the insulin response to prevent hyperglycemia [1]. Glucose enters the beta cell via **GLUT-2** transporters [3]. Once inside, it is phosphorylated by **Glucokinase** (the glucose sensor) [3]. When blood glucose levels rise above **70 mg/dL**, the rate of glycolysis increases, leading to an rise in the ATP/ADP ratio. This closes ATP-sensitive K+ channels, causing cell depolarization, calcium influx, and subsequent insulin release and synthesis [1, 3]. Below this threshold, insulin secretion is basal or suppressed to prevent hypoglycemia [1]. **Analysis of Options:** * **A, B, and C (30, 40, and 50 mg%):** These levels are considered hypoglycemic. At these concentrations, insulin synthesis is inhibited, and counter-regulatory hormones (like glucagon and epinephrine) are triggered to increase blood glucose [1]. Specifically, symptoms of hypoglycemia typically begin around 50–55 mg/dL [1]. * **D (70 mg%):** This is the recognized threshold where the metabolic machinery of the beta cell activates insulin production to maintain euglycemia. **High-Yield Clinical Pearls for NEET-PG:** * **Glucokinase:** Acts as the "glucose sensor." Mutations in this enzyme lead to **MODY-2** (Maturity-Onset Diabetes of the Young). * **Biphasic Release:** Insulin release is biphasic; the first phase is the release of stored insulin, while the second phase involves the synthesis of new insulin [2]. * **GLUT-2 vs. GLUT-4:** Remember that GLUT-2 (pancreas/liver) is insulin-independent, whereas GLUT-4 (muscle/adipose) is insulin-dependent [3].

Q: Osteoblasts express which of the following hormones?

All of the above. **Explanation:** The correct answer is **D. All of the above**. Osteoblasts are not merely bone-forming cells; they serve as the primary regulatory hub for bone remodeling by expressing receptors for various systemic hormones. 1. **Parathyroid Hormone (PTH):** Paradoxically, osteoclasts (which resorb bone) do **not** have PTH receptors. PTH binds to receptors on **osteoblasts**, stimulating them to express **RANKL** (Receptor Activator of Nuclear Factor kappa-B Ligand). RANKL then binds to osteoclasts to initiate bone resorption. 2. **Vitamin D3 (Calcitriol):** Osteoblasts possess Vitamin D receptors (VDR). Calcitriol acts on osteoblasts to stimulate the production of **osteocalcin** and alkaline phosphatase, and it also synergizes with PTH to increase RANKL expression. 3. **Glucocorticoids:** Osteoblasts have glucocorticoid receptors. Chronic exposure to steroids inhibits osteoblast proliferation and increases their apoptosis, which is the primary mechanism behind **steroid-induced osteoporosis**. **Why "All of the above" is correct:** Osteoblasts act as the "sensor" for the endocrine system to regulate bone turnover. By expressing receptors for PTH, Vitamin D, and Glucocorticoids (as well as Estrogen and Thyroid hormone), the osteoblast coordinates the balance between bone formation and resorption. **High-Yield Clinical Pearls for NEET-PG:** * **RANKL/OPG Ratio:** Osteoblasts also secrete **Osteoprotegerin (OPG)**, a decoy receptor that binds RANKL and inhibits bone resorption. The ratio of RANKL to OPG determines the rate of bone loss. * **Teriparatide (Recombinant PTH):** When given intermittently, it stimulates osteoblasts more than osteoclasts, leading to an anabolic (bone-building) effect. * **Marker of Osteoblast Activity:** Serum **Alkaline Phosphatase (ALP)** and **Osteocalcin** are high-yield biochemical markers used to assess osteoblastic function.

Q: Glucose transport in myocytes is stimulated by insulin. Which glucose transporter is involved?

GLUT-4. **Explanation:** The correct answer is **GLUT-4**. This question tests the fundamental concept of insulin-dependent versus insulin-independent glucose uptake in human tissues. **Why GLUT-4 is correct:** GLUT-4 is the only **insulin-responsive** glucose transporter. It is primarily expressed in **skeletal muscle (myocytes)** and **adipose tissue**. In the resting state, GLUT-4 remains sequestered in intracellular vesicles. Upon insulin binding to its receptor, a signaling cascade (via PI3-kinase) triggers the translocation of these vesicles to the plasma membrane, facilitating glucose uptake. **Analysis of Incorrect Options:** * **GLUT-1:** Responsible for basal (insulin-independent) glucose uptake. It is found in almost all tissues but is most highly concentrated in **RBCs** and the **Blood-Brain Barrier**. * **GLUT-2:** A high-capacity, low-affinity transporter found in the **Liver, Pancreatic beta cells, and Kidney**. It acts as a "glucose sensor" in the pancreas and allows bidirectional transport in the liver. * **GLUT-3:** A high-affinity transporter found primarily in **Neurons** (Brain), ensuring glucose uptake even during low blood sugar levels. **High-Yield Clinical Pearls for NEET-PG:** * **Exercise & GLUT-4:** Muscle contraction during exercise can trigger GLUT-4 translocation to the membrane **independent of insulin**. This is why exercise helps lower blood glucose in diabetic patients. * **SGLT vs. GLUT:** Remember that SGLT-1 (Intestine) and SGLT-2 (Kidney) use **secondary active transport** (sodium-dependent), whereas all GLUT transporters use **facilitated diffusion**. * **GLUT-5:** Specifically transports **Fructose** and is located in the small intestine and spermatozoa.

Q: Which of the following hormones act through nuclear receptors?

None of the above. **Explanation:** The mechanism of hormone action is determined by the chemical nature of the hormone. Hormones that are lipid-soluble (lipophilic) can cross the cell membrane and bind to **nuclear or cytoplasmic receptors**, while water-soluble (hydrophilic) hormones bind to **cell surface (membrane) receptors**. **1. Why "None of the above" is correct:** For an option to be correct, *all* hormones listed in that group must act via nuclear receptors. In this question, every option contains at least one hormone that acts via a cell surface receptor (using second messengers like cAMP or IP3/DAG). **2. Analysis of Incorrect Options:** * **Option A:** Estrogen and Thyroxine (T4) act via nuclear receptors. However, **Glucagon** is a peptide hormone that acts via a G-protein coupled receptor (GPCR) and the cAMP second messenger system. * **Option B:** Estrogen and Thyroxine use nuclear receptors. **TSH (Thyroid Stimulating Hormone)**, despite acting on the thyroid gland, is a glycoprotein that binds to membrane-bound GPCRs. * **Option C:** Estrogen uses nuclear receptors. Both **TSH and GnRH** act via cell surface receptors (GnRH uses the Gq-IP3/DAG pathway). **High-Yield NEET-PG Clinical Pearls:** * **Nuclear Receptor Superfamily:** Includes Steroid hormones (Estrogen, Progesterone, Testosterone, Cortisol, Aldosterone), Thyroid hormones (T3, T4), Vitamin D, and Retinoic acid. * **Thyroid Exception:** Unlike most lipid-soluble hormones that bind in the cytoplasm, Thyroid hormone receptors are already bound to DNA in the nucleus even in the absence of the hormone. * **Speed of Action:** Hormones acting via nuclear receptors have a **slow onset** (hours to days) because they require gene transcription and protein synthesis, whereas membrane-receptor hormones (like Epinephrine or Insulin) act almost instantaneously.

Q: Prolactin secretion is inhibited by which of the following?

Dopamine excess. **Explanation:** The regulation of prolactin (PRL) is unique among anterior pituitary hormones because it is under **tonic inhibitory control** by the hypothalamus. **1. Why Option A is Correct:** The primary Prolactin Inhibiting Factor (PIF) is **Dopamine**. Dopamine is secreted by the tuberoinfundibular neurons into the hypophyseal portal system. It binds to **D2 receptors** on the lactotrophs in the anterior pituitary, leading to the inhibition of prolactin synthesis and release. Therefore, an excess of dopamine directly suppresses prolactin levels. **2. Why the Other Options are Incorrect:** * **B. Metoclopramide:** This is a dopamine (D2) receptor antagonist. By blocking the inhibitory effect of dopamine, it causes a rise in prolactin levels (hyperprolactinemia). * **C. Hypothyroidism:** In primary hypothyroidism, low levels of thyroid hormones lead to a compensatory increase in **Thyrotropin-Releasing Hormone (TRH)**. TRH acts as a potent prolactin-releasing factor; thus, hypothyroidism is a common cause of hyperprolactinemia. * **D. Emotional Stress:** Prolactin is a stress-responsive hormone. Physical or emotional stress stimulates the release of prolactin via various neuroendocrine pathways. **High-Yield Clinical Pearls for NEET-PG:** * **Prolactinoma:** The most common secretory tumor of the pituitary. Treatment of choice is medical (Dopamine agonists like **Cabergoline** or Bromocriptine), not surgery. * **Stalk Effect:** Any lesion compressing the pituitary stalk prevents dopamine from reaching the pituitary, leading to elevated prolactin (the only pituitary hormone that increases when the stalk is cut). * **Hook Effect:** In cases of extremely high prolactin (giant prolactinomas), lab assays may show falsely low levels; serial dilution is required for accurate diagnosis.

Q: Primary Adrenal Insufficiency causes all of the following, except?

Increased protein breakdown. **Explanation:** Primary Adrenal Insufficiency (Addison’s Disease) is characterized by the destruction of the adrenal cortex, leading to a deficiency of both **Mineralocorticoids (Aldosterone)** and **Glucocorticoids (Cortisol)**. **Why "Increased protein breakdown" is the correct answer:** Cortisol is a catabolic hormone. Its primary role in protein metabolism is to stimulate the breakdown of proteins in peripheral tissues (like muscle) to provide amino acids for gluconeogenesis. In adrenal insufficiency, there is a **deficiency of cortisol**, which leads to **decreased protein breakdown** and impaired gluconeogenesis. Therefore, increased protein breakdown does not occur. **Analysis of incorrect options:** * **Low Blood Pressure:** Aldosterone deficiency leads to "pressure natriuresis" (loss of sodium and water), resulting in hypovolemia. Additionally, cortisol is required to maintain the sensitivity of blood vessels to catecholamines. Lack of both leads to hypotension. * **Decrease in ECF:** The loss of sodium (and consequently water) due to lack of aldosterone directly reduces the extracellular fluid volume. * **Decreased sodium-potassium ratio:** Aldosterone normally causes Na+ reabsorption and K+ excretion. Its absence leads to **Hyponatremia** and **Hyperkalemia**, which mathematically decreases the Na+:K+ ratio (a classic diagnostic marker). **High-Yield Clinical Pearls for NEET-PG:** * **Hyperpigmentation:** Seen only in *Primary* Adrenal Insufficiency due to compensatory increase in ACTH (which shares a precursor with MSH, POMC). * **Electrolyte Triad:** Hyponatremia, Hyperkalemia, and Metabolic Acidosis. * **Gold Standard Test:** ACTH Stimulation Test (Cosyntropin test). * **Crisis Management:** Immediate IV Hydrocortisone and aggressive fluid resuscitation with Normal Saline.

Q: Laron dwarfism is caused by which of the following?

GH receptor defect. **Explanation:** **Laron Dwarfism (Laron Syndrome)** is an autosomal recessive condition characterized by a mutation in the **Growth Hormone Receptor (GHR)** gene. In this condition, the body produces normal or even elevated levels of Growth Hormone (GH), but the receptors are non-functional. Consequently, the liver cannot produce **Insulin-like Growth Factor-1 (IGF-1)** in response to GH. Since IGF-1 is the primary mediator of GH’s growth-promoting effects on bone and cartilage, its absence leads to severe short stature. **Analysis of Options:** * **Option B (Correct):** The primary pathology is a **GH receptor defect** (insensitivity to GH). Laboratory findings typically show **High GH** and **Low IGF-1**. * **Option A:** Deficiency of GH causes **Pituitary Dwarfism**. Unlike Laron syndrome, these patients respond to exogenous GH therapy. * **Option C:** Deficiency of thyroxin in childhood leads to **Cretinism**, characterized by stunted growth and significant mental retardation. * **Option D:** Thyroxin receptor defects lead to **Thyroid Hormone Resistance Syndrome (Refetoff Syndrome)**, which presents with features of hypothyroidism or goiter, but is not the cause of Laron dwarfism. **High-Yield Clinical Pearls for NEET-PG:** * **Hallmark Lab Profile:** ↑ GH, ↓ IGF-1, and ↓ GH-Binding Protein (GHBP). * **Clinical Feature:** Patients often have a characteristic "doll-like" face (prominent forehead, depressed nasal bridge) and a high-pitched voice. * **Metabolic Paradox:** Interestingly, individuals with Laron syndrome have a significantly **reduced risk of developing cancer and Type 2 Diabetes Mellitus**, despite their growth deficits. * **Treatment:** Since the defect is at the receptor level, exogenous GH is ineffective. Treatment requires **recombinant IGF-1 (Mecasermin)**.

Question 1

Insulin synthesis is stimulated by glucose levels above what threshold?

Accepted Answer

70 mg%

Answer

30 mg%

Answer

40 mg%

Answer

50 mg%

Question 2

Osteoblasts express which of the following hormones?

Accepted Answer

All of the above

Answer

Parathyroid hormone (PTH)

Answer

Vitamin D3

Answer

Glucocorticoid

Question 3

Glucose transport in myocytes is stimulated by insulin. Which glucose transporter is involved?

Accepted Answer

GLUT-4

Answer

GLUT-1

Answer

GLUT-2

Answer

GLUT-3

Question 4

Which of the following hormones act through nuclear receptors?

Accepted Answer

None of the above

Answer

Estrogen, thyroxine, and glucagon

Answer

Estrogen, thyroxine, and TSH

Answer

Estrogen, TSH, and Gonadotropin releasing hormone (GnRH)

Question 5

Which of the following statements about calcitonin is incorrect?

Accepted Answer

It plays a major role in the regulation of calcium levels in humans.

Answer

It inhibits osteoclast-mediated bone resorption.

Answer

It increases phosphate excretion in the kidneys.

Answer

It is useful in treating acute hypercalcemic crisis.

Question 6

Prolactin secretion is inhibited by which of the following?

Accepted Answer

Dopamine excess

Answer

Metoclopramide

Answer

Hypothyroidism

Answer

Emotional stress

Question 7

Which one of the following statements regarding Growth Hormone (GH) secretion is true?

Accepted Answer

GH secretion increases after exercise, stress, and hypoglycemia.

Answer

GH secretion is maximum during the evening.

Answer

GH is produced equally in all age groups.

Answer

GH decreases circulating IGF and somatostatin.

Question 8

Aldosterone secretion is controlled by all of the following except:

Accepted Answer

Increase in ECF volume

Answer

ACTH

Answer

Increase in potassium ion concentration in ECF

Answer

Decrease in the sodium ion concentration in ECF

Question 9

Primary Adrenal Insufficiency causes all of the following, except?

Accepted Answer

Increased protein breakdown

Answer

Low Blood Pressure

Answer

Decrease in Extracellular Fluid (ECF)

Answer

Decreased sodium-potassium ratio

Question 10

Laron dwarfism is caused by which of the following?

Accepted Answer

GH receptor defect

Answer

Deficiency of Growth Hormone (GH)

Answer

Deficiency of thyroxin

Answer

Thyroxin receptor defect

Endocrinology — MCQs

Endocrinology — MCQs

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