Endocrinology Practice Questions

Q: Which of the following is NOT a physiologic change of thyroid metabolism during pregnancy?

TSH level is highest during the first trimester. **Explanation:** The correct answer is **D**. During pregnancy, thyroid physiology undergoes significant changes driven by rising levels of **Human Chorionic Gonadotropin (hCG)** and **Estrogen**. 1. **Why Option D is the correct (incorrect statement):** hCG shares a common alpha-subunit with TSH and can directly stimulate the TSH receptor. During the **first trimester**, hCG levels peak, leading to a transient increase in free T4. This rise in T4 exerts negative feedback on the pituitary, causing **TSH levels to reach their lowest point** (nadir) during the first trimester, not the highest. 2. **Why the other options are wrong (correct physiologic changes):** * **Option B:** High estrogen levels stimulate the liver to increase the synthesis of **Thyroxine-Binding Globulin (TBG)** and decrease its clearance. * **Option A:** Because TBG levels are elevated, more T4 and T3 are bound. To maintain a constant level of "free" (active) hormone, the total pool of thyroid hormones increases. Thus, **Total T4 and T3 are elevated**, while Free T4/T3 remain largely within normal limits. * **Option C:** hCG is a structural analog of TSH. At high concentrations (especially weeks 8–12), it acts as a weak thyrotropin, stimulating the thyroid gland. **High-Yield Clinical Pearls for NEET-PG:** * **Total T4** in pregnancy is roughly **1.5 times** the non-pregnant value. * The **TSH reference range is lower** in pregnancy (Lower limit ~0.1 mIU/L; Upper limit ~2.5–3.0 mIU/L in the first trimester). * **Iodine requirements increase** during pregnancy due to increased glomerular filtration rate (renal loss) and fetal transfer. * **Thyroid size** may increase slightly (goitrogenesis) due to hCG stimulation and iodine deficiency, but significant goiter is always pathologic.

Q: A 16-year-old female patient presents to the OPD with hirsutism and masculinization. Which of the following hormones of the adrenal cortex is the likely culprit?

Dehydroepiandrosterone (DHEA). ### Explanation **Correct Option: A. Dehydroepiandrosterone (DHEA)** The clinical presentation of **hirsutism** (excessive male-pattern hair growth) and **masculinization** (virilization) in a female indicates an excess of androgens. The adrenal cortex produces weak androgens, primarily **Dehydroepiandrosterone (DHEA)** and its sulfate form (DHEA-S), in the **Zona Reticularis**. In conditions like Congenital Adrenal Hyperplasia (CAH) or androgen-secreting adrenal tumors, these androgens are overproduced. While weak, they are converted peripherally into potent testosterone, leading to clitomegaly, deepening of the voice, and hirsutism. **Why other options are incorrect:** * **B. Aldosterone:** Produced in the *Zona Glomerulosa*, it regulates sodium and potassium balance. Excess leads to hypertension and hypokalemia (Conn’s Syndrome), not virilization. * **C. Cortisol:** Produced in the *Zona Fasciculata*, it regulates glucose metabolism and stress response. Excess (Cushing’s Syndrome) causes weight gain and "moon face." While Cushing’s can coexist with androgen excess, cortisol itself is not androgenic. * **D. Epinephrine:** This is a catecholamine produced by the **adrenal medulla**, not the cortex. It regulates the "fight or flight" response. **High-Yield NEET-PG Pearls:** * **Layers of Adrenal Cortex (Outer to Inner):** **G**lomerulosa (Salt/Aldosterone), **F**asciculata (Sugar/Cortisol), **R**eticularis (Sex/Androgens) — Mnemonic: **"GFR"**. * **DHEA-S** is the most specific marker for adrenal androgen production because the ovaries do not produce it. * The most common cause of virilizing CAH is **21-hydroxylase deficiency**, which shunts precursors toward the androgen pathway.

Q: By the time of implantation in the uterine endometrium, into how many cells has the fertilized ovum typically divided?

16. **Explanation:** The process of early embryonic development follows a specific chronological sequence as the zygote travels from the fallopian tube to the uterus. 1. **The Correct Answer (C):** After fertilization in the ampulla, the zygote undergoes rapid mitotic divisions called **cleavage**. By day 3–4, it reaches the **16-cell stage**, known as the **Morula** (resembling a mulberry). Implantation typically begins around day 6 post-fertilization. By this time, the morula has transformed into a **Blastocyst**, which consists of approximately **16 to 64 cells** (though 16 is the classic textbook milestone for the transition into the uterine cavity prior to attachment). 2. **Why other options are incorrect:** * **A & B (2 and 4 cells):** These represent the very early stages of cleavage occurring within the first 24–48 hours while the embryo is still in the upper portion of the fallopian tube. * **D (750 cells):** This number is far too high for the initial stage of implantation. A blastocyst at the time of attachment generally contains between 100–200 cells, but the physiological "division milestone" associated with the transition to the uterus in standard medical curriculum is the 16-cell morula. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Fertilization:** Ampulla of the fallopian tube. * **Time of Implantation:** Begins on **Day 6** and is completed by **Day 10–12**. * **Window of Implantation:** The period when the endometrium is most receptive (usually days 20–24 of a typical menstrual cycle), regulated by **Progesterone**. * **HCG Secretion:** Begins once the trophoblast cells of the blastocyst invade the endometrium, usually detectable in maternal serum by day 8–9 post-ovulation.

Q: Hypocalcemia due to calcitonin is caused by which of the following mechanisms?

Decreased bone resorption. **Explanation:** Calcitonin is a peptide hormone secreted by the **parafollicular cells (C-cells)** of the thyroid gland. Its primary physiological role is to lower plasma calcium levels, acting as a functional antagonist to Parathyroid Hormone (PTH). **Why Option B is Correct:** The most potent and immediate effect of calcitonin is the **inhibition of osteoclastic bone resorption**. Calcitonin binds to specific receptors on osteoclasts, leading to a decrease in their absorptive activity and a reduction in their formation rate. By preventing the breakdown of the bone matrix, it stops the release of calcium and phosphate into the blood, thereby inducing hypocalcemia. **Why Other Options are Incorrect:** * **Options A & D:** While calcitonin does have a minor effect on the kidneys by increasing the excretion of calcium and phosphate (by decreasing reabsorption in the tubules), this effect is **clinically insignificant** and transient compared to its profound effect on bone. * **Option C:** Calcitonin has no significant direct effect on the intestinal absorption of calcium. Intestinal absorption is primarily regulated by Vitamin D3 (Calcitriol). **High-Yield Clinical Pearls for NEET-PG:** * **Stimulus:** Calcitonin secretion is stimulated by an increase in plasma calcium levels and the hormone **Gastrin**. * **Clinical Use:** Due to its ability to inhibit osteoclasts, synthetic calcitonin (Salmon calcitonin) is used therapeutically in **Paget’s disease**, severe hypercalcemia, and postmenopausal osteoporosis. * **Tumor Marker:** Serum calcitonin is a highly specific tumor marker for **Medullary Thyroid Carcinoma (MTC)**. * **Escape Phenomenon:** Prolonged exposure to calcitonin leads to a downregulation of receptors, causing the hormone to lose its effectiveness over time.

Q: Central osmoreceptors are located in which part of the hypothalamus?

Anterior hypothalamus. **Explanation:** The regulation of water balance is primarily controlled by **osmoreceptors** located in the **Anterior Hypothalamus**. Specifically, these receptors are found in the circumventricular organs—the **Organum Vasculosum of the Lamina Terminalis (OVLT)** and the **Subfornical Organ (SFO)**. These areas lack a blood-brain barrier, allowing them to sense changes in plasma osmolality directly. When osmolality rises, these neurons shrink, triggering a signal to release Antidiuretic Hormone (ADH) and stimulate the thirst center. **Analysis of Options:** * **Anterior Hypothalamus (Correct):** This region houses the OVLT and SFO, the primary sites for osmoreception. * **Supraoptic (SON) and Paraventricular (PVN) Nuclei:** While these nuclei **synthesize** ADH (Vasopressin) and Oxytocin, they are not the primary sensors for osmolality. They receive neural inputs from the osmoreceptors in the anterior hypothalamus to release ADH into the posterior pituitary. * **Lateral Hypothalamus:** This is primarily the **"Feeding Center."** Stimulation leads to hyperphagia, while lesions lead to aphagia/starvation. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Stimulus:** A mere **1-2% increase** in plasma osmolality is sufficient to trigger ADH release. * **ADH Synthesis vs. Storage:** ADH is synthesized in the SON/PVN (Hypothalamus) but stored and released from the **Posterior Pituitary (Neurohypophysis)**. * **Thirst Center:** Also located in the anterior hypothalamus; it is stimulated by increased osmolality or decreased ECF volume (via Angiotensin II). * **V2 Receptors:** ADH acts on V2 receptors in the collecting ducts of the kidney to insert **Aquaporin-2** channels, facilitating water reabsorption.

Q: Which of the following physiological states or substances promotes the secretion of Growth Hormone?

Glucagon. **Explanation:** Growth Hormone (GH) secretion is regulated by a complex interplay of hypothalamic factors (GHRH and Somatostatin) and metabolic signals. **Why Glucagon is Correct:** Glucagon is a potent stimulator of Growth Hormone secretion. While the exact mechanism is multifaceted, it is believed that glucagon stimulates the hypothalamus to release GHRH. Clinically, this is utilized in the **Glucagon Stimulation Test**, where glucagon is administered to provoke GH release to diagnose GH deficiency in children and adults. **Analysis of Incorrect Options:** * **Cortisol:** Chronic or high levels of glucocorticoids generally **inhibit** GH secretion by increasing somatostatin tone and decreasing GHRH sensitivity. * **REM Sleep:** GH secretion is characteristically associated with **Deep Sleep (Stage N3/Slow-wave sleep)**, typically occurring in the first 90 minutes of sleep. In contrast, GH secretion is inhibited during REM (Rapid Eye Movement) sleep. * **Glucose:** Hyperglycemia **inhibits** GH secretion. Conversely, hypoglycemia is one of the most potent physiological stimuli for GH release (used in the Insulin Tolerance Test). **High-Yield Clinical Pearls for NEET-PG:** * **Stimulators of GH:** Hypoglycemia, Fasting/Starvation, Exercise, Deep sleep, Amino acids (Arginine), and Ghrelin. * **Inhibitors of GH:** Hyperglycemia, Free fatty acids, Obesity, Somatostatin, and IGF-1 (via negative feedback). * **Gold Standard Test:** The **Insulin Tolerance Test (ITT)** is the gold standard for diagnosing GH deficiency, as it induces hypoglycemia to trigger GH release. * **Screening Test:** IGF-1 levels are used for screening acromegaly because GH is secreted in pulsatile bursts and has a short half-life.

Q: Glucose is transported in the pancreas through which receptor?

GLUT 2. **Explanation:** The correct answer is **GLUT 2**. In the pancreas, specifically within the **beta cells of the Islets of Langerhans**, glucose entry is the rate-limiting step for insulin secretion. **Why GLUT 2 is the correct answer:** GLUT 2 is a high-capacity, low-affinity (high $K_m$) glucose transporter. Because of its low affinity, the rate of glucose transport into the beta cell is directly proportional to the blood glucose concentration within the physiological range. This allows the pancreas to act as a **"glucose sensor."** Once inside, glucose is phosphorylated by **Glucokinase**, leading to ATP production, closure of ATP-sensitive $K^+$ channels, depolarization, and subsequent insulin release. **Analysis of Incorrect Options:** * **GLUT 1:** Found primarily in **RBCs and the Blood-Brain Barrier**. It provides basal glucose uptake required to sustain respiration in these cells. * **GLUT 3:** Found mainly in **neurons** and the placenta. It has a very high affinity (low $K_m$), ensuring glucose uptake even during hypoglycemia. * **GLUT 4:** This is the only **insulin-dependent** transporter. It is sequestered in intracellular vesicles and moves to the cell membrane only in the presence of insulin. It is found in **skeletal muscle and adipose tissue**. **High-Yield Clinical Pearls for NEET-PG:** * **Bidirectional Flow:** GLUT 2 is also found in the **liver, small intestine, and renal tubular cells**, where it allows for the bidirectional flux of glucose. * **Maturity-Onset Diabetes of the Young (MODY):** Mutations in **Glucokinase** (the enzyme following GLUT 2 transport) lead to MODY type 2. * **SGLT vs. GLUT:** Remember that SGLTs (Sodium-Glucose Linked Transporters) are active transporters (secondary active), whereas all GLUTs facilitate **passive diffusion**.

Question 1

The principle of "Wolff-chaikoff effect" is utilized in which of the following clinical scenarios?

Accepted Answer

Administration of iodide for thyrotoxic patients before surgery

Answer

Administration of iodide for thyrotoxic patients after surgery

Answer

Stimulation of hormone synthesis

Answer

Increased vascularity of the thyroid gland

Question 2

Which of the following is NOT a physiologic change of thyroid metabolism during pregnancy?

Accepted Answer

TSH level is highest during the first trimester

Answer

Increased levels of total T4 and T3

Answer

Elevated levels of serum TBG

Answer

hCG acts at the TSH receptor

Question 3

A 16-year-old female patient presents to the OPD with hirsutism and masculinization. Which of the following hormones of the adrenal cortex is the likely culprit?

Accepted Answer

Dehydroepiandrosterone (DHEA)

Answer

Aldosterone

Answer

Cortisol

Answer

Epinephrine

Question 4

By the time of implantation in the uterine endometrium, into how many cells has the fertilized ovum typically divided?

Accepted Answer

16

Answer

2

Answer

4

Answer

750

Question 5

Hypocalcemia due to calcitonin is caused by which of the following mechanisms?

Accepted Answer

Decreased bone resorption

Answer

Increased excretion in the kidney

Answer

Decreased intestinal absorption

Answer

Decreased renal reabsorption

Question 6

Regarding myxedema, which of the following statements is true EXCEPT:

Accepted Answer

Increased basal metabolic rate (BMR)

Answer

Swollen, edematous look of the face

Answer

Impotency, amenorrhea

Answer

Dullness, loss of memory

Question 7

Central osmoreceptors are located in which part of the hypothalamus?

Accepted Answer

Anterior hypothalamus

Answer

Supraoptic nuclei

Answer

Paraventricular nuclei

Answer

Lateral hypothalamus

Question 8

Which of the following is NOT a physiological action of insulin?

Accepted Answer

Activation of lipoprotein lipase

Answer

Increased lipogenesis

Answer

Increased amino acid entry into the cell

Answer

Activation of key enzymes of glycolysis

Question 9

Which of the following physiological states or substances promotes the secretion of Growth Hormone?

Accepted Answer

Glucagon

Answer

Cortisol

Answer

REM sleep

Answer

Glucose

Question 10

Glucose is transported in the pancreas through which receptor?

Accepted Answer

GLUT 2

Answer

GLUT 1

Answer

GLUT 3

Answer

GLUT 4

Endocrinology — MCQs

Endocrinology — MCQs

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