Endocrinology

Endocrinology Indian Medical PG Question 1: On insulin administration, what change is expected in the extracellular fluid (ECF)?

• A. Hypoglycemia (Correct Answer)
• B. Hyperkalemia
• C. Hyponatremia
• D. Hypocalcemia

Endocrinology Explanation: **Hypoglycemia (Correct Answer)** - Insulin promotes the uptake of **glucose** from the ECF into cells, primarily muscle and adipose tissue - This action leads to a decrease in ECF **glucose concentration**, resulting in **hypoglycemia** if insulin levels are excessive or glucose intake is insufficient - This is the primary and most significant change in ECF composition after insulin administration *Hyperkalemia (Incorrect)* - Insulin actually stimulates the cellular uptake of **potassium**, moving it from the ECF into the intracellular fluid - Therefore, insulin administration typically causes **hypokalemia**, not hyperkalemia - This effect is sometimes used therapeutically to treat hyperkalemia by driving potassium into cells *Hyponatremia (Incorrect)* - Insulin primarily affects **glucose** and **potassium** metabolism and does not directly cause changes in sodium concentration in the ECF - **Hyponatremia** would be more associated with altered water balance or disorders of kidney function, not direct insulin effects - Sodium homeostasis is regulated by the renin-angiotensin-aldosterone system and ADH *Hypocalcemia (Incorrect)* - Insulin has no direct effect on **calcium** levels or its regulation in the ECF - **Calcium homeostasis** is primarily regulated by parathyroid hormone (PTH), vitamin D, and calcitonin, independent of insulin action - Changes in calcium concentration are not expected with insulin administration

Endocrinology Indian Medical PG Question 2: Which of the following can cause an increase in growth hormone levels in blood?

• A. Cortisol
• B. Glucose
• C. Hypoglycemia (Correct Answer)
• D. Methylprednisolone

Endocrinology Explanation: ***Hypoglycemia*** - **Hypoglycemia** is a potent stimulus for **growth hormone (GH) secretion**, as GH acts to raise blood glucose levels, serving as a counter-regulatory hormone. - The body perceives low blood glucose as a stressor, activating the **hypothalamic-pituitary-adrenal axis** and stimulating GH release to mobilize energy stores. *Cortisol* - **Cortisol** (a glucocorticoid) generally has an **inhibitory effect** on GH secretion at the hypothalamic and pituitary levels. - High levels of cortisol can lead to **suppression of GH pulsatility** and overall lower GH release. *Glucose* - An increase in **blood glucose** levels typically **suppresses growth hormone (GH) release**, as GH tends to increase blood glucose. - This negative feedback mechanism helps maintain **glucose homeostasis** within the body. *Methylprednisolone* - **Methylprednisolone** is a synthetic **glucocorticoid** that mimics the actions of cortisol. - Like cortisol, it suppresses GH secretion and can lead to **growth retardation** in children with chronic use.

Endocrinology Indian Medical PG Question 3: Which of the following hormones will be affected most after the change in sex hormone binding globulin?

• A. Testosterone (Correct Answer)
• B. Progesterone
• C. DHEA
• D. Estrogen

Endocrinology Explanation: ***Testosterone*** - **Sex hormone-binding globulin (SHBG)** binds primarily to **testosterone** (and dihydrotestosterone) with **high affinity**. - SHBG has approximately **5 times greater affinity** for testosterone compared to estradiol. - A change in SHBG levels will significantly impact the proportion of **free (biologically active) testosterone** available in the circulation, thus affecting its overall function and measurement. - This makes testosterone the hormone **most affected** by changes in SHBG levels. *Progesterone* - **Progesterone** is primarily bound to **albumin** and **corticosteroid-binding globulin (CBG)**, not SHBG. - Therefore, changes in SHBG would have minimal direct impact on progesterone levels or its bioavailability. *DHEA* - **Dehydroepiandrosterone (DHEA)** is mostly bound to **albumin** in the blood. - Its binding to SHBG is negligible, making changes in SHBG irrelevant to its overall circulating levels or activity. *Estrogen* - **Estrogen (estradiol)** also binds to SHBG, but with **significantly lower affinity** than testosterone (approximately 5-fold less). - While affected by SHBG changes, the impact is less pronounced than on testosterone due to the lower binding affinity and its additional binding to albumin.

Endocrinology Indian Medical PG Question 4: What is the best and most sensitive investigation for hypothyroidism ?

• A. T3, T4 levels
• B. TRH levels
• C. Radioactive I2 uptake
• D. TSH levels (Correct Answer)

Endocrinology Explanation: TSH levels - **Thyroid-Stimulating Hormone (TSH)** is the most sensitive and specific test for diagnosing **primary hypothyroidism** because even slight decreases in thyroid hormone levels cause significant increases in TSH [1]. - TSH is released from the **pituitary gland** and acts as a direct feedback mechanism to regulate thyroid hormone production [1]. A high TSH level indicates that the thyroid gland is not producing enough hormones. *T3, T4 levels* - While **T3 (triiodothyronine)** and **T4 (thyroxine)** levels are direct measures of thyroid hormones, their values may remain within the normal range in early or subclinical hypothyroidism [1]. - They are less sensitive than TSH for initial screening and often become abnormal only after hypothyroidism is well-established [1]. *TRH levels* - **Thyrotropin-Releasing Hormone (TRH)** is produced by the hypothalamus and stimulates TSH release from the pituitary [1]. - Measuring TRH levels is generally not used as a primary diagnostic test for hypothyroidism due to its complexity and lack of direct clinical utility in routine screening. *Radioactive I2 uptake* - **Radioactive iodine uptake (RAIU)** measures the thyroid gland's ability to take up iodine, which is used to produce thyroid hormones. - It is primarily used to differentiate causes of hyperthyroidism (e.g., Graves' disease vs. thyroiditis), not as a diagnostic test for hypothyroidism [1].

Endocrinology Indian Medical PG Question 5: Which of the following statements about nateglinide is correct?

• A. It is a long-acting oral hypoglycemic drug
• B. It can be used in patients with renal impairment with caution.
• C. It acts by blocking K+ channels in pancreatic beta-cells.
• D. Taken just before a meal, it limits postprandial hyperglycemia in type 2 diabetes mellitus (Correct Answer)

Endocrinology Explanation: ***Correct: Taken just before a meal, it limits postprandial hyperglycemia in type 2 diabetes mellitus*** - **Nateglinide** is a **meglitinide analog** designed to stimulate rapid, short-duration insulin release - Specifically taken **just before meals** (preprandially) to manage postprandial glucose spikes - Its **rapid onset** (within 20 minutes) and **short duration** (approximately 4 hours) make it ideal for controlling **postprandial hyperglycemia** in type 2 diabetes - This is the **primary clinical indication** and most characteristic feature of nateglinide *Incorrect: It is a long-acting oral hypoglycemic drug* - Nateglinide is actually a **short-acting** oral hypoglycemic, not long-acting - Peak action occurs within **1 hour** and duration is only **3-4 hours** - This short duration distinguishes it from sulfonylureas like **glimepiride** or **glibenclamide** which have longer durations *Incorrect: It can be used in patients with renal impairment with caution* - Nateglinide is **hepatically metabolized** but its metabolites are **renally excreted** - Requires **dose adjustment** in moderate to severe renal impairment (CrCl <30 mL/min) - **Repaglinide** (another meglitinide) is preferred in renal impairment due to predominantly biliary excretion - Not the safest or most characteristic feature of nateglinide *Incorrect: It acts by blocking K+ channels in pancreatic beta-cells* - While nateglinide does **close ATP-dependent K+ channels** on pancreatic beta-cells (leading to depolarization and insulin release), this mechanism is **shared by all sulfonylureas and meglitinides** - This is not a **distinguishing feature** of nateglinide specifically - The question asks what is correct "about nateglinide" - while mechanistically true, this doesn't distinguish it from other insulin secretagogues

Endocrinology Flashcard 1 of 5

Question: One major effect of thyroid hormone is increased _____ with a resultant increase in BMR and body temperature, due to increased Na/K+-ATPase activity

Answer: O2 consumption

Endocrinology Flashcard 2 of 5

Question: How is the action of peptide hormones terminated?_____

Answer: proteolysis or diffusing away

Endocrinology Flashcard 3 of 5

Question: The _____ cell system is also called the diffuse neuroendocrine system.

Answer: APUD

Endocrinology Flashcard 4 of 5

Question: Glucagon causes a(n) _____ in growth hormone secretion

Answer: increase

Endocrinology Flashcard 5 of 5

Question: Obesity _____ the conversion of T4 to T3, thus increasing the amount of active hormone

Answer: increases