Endocrinology — MCQs
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Secretion of prolactin is inhibited by?
What is the principal stimulus for vasopressin secretion?
Which of the following would be least likely seen 14 days after a rat is injected with a drug that kills all of its pancreatic B cells?
Which of the following hormones has its release inhibited by thyroxine?
Ghrelin stimulates the release of which hormone?
Aldosterone is produced by which of the following?
Which is the single most important factor that stimulates insulin secretion?
Estrogen action on carbohydrate metabolism:
Basophilic thyrotroph cells of pituitary secrete:
Which is the true statement about Anterior Pituitary Hormones?
Endocrinology Indian Medical PG Practice Questions and MCQs
Question 611: Secretion of prolactin is inhibited by?
- A. Dopamine (Correct Answer)
- B. Serotonin
- C. Noradrenaline
- D. Adrenaline
Explanation: ***Dopamine*** - **Dopamine**, produced by the **hypothalamus**, is the primary physiological inhibitor of **prolactin secretion** from the anterior pituitary gland. - It acts on **D2 receptors** on lactotrophs, leading to a decrease in prolactin synthesis and release. *Serotonin* - **Serotonin** generally has a stimulatory effect on **prolactin secretion**, rather than an inhibitory one. - Elevated serotonin levels can lead to **hyperprolactinemia**. *Noradrenaline* - While **noradrenaline** can have complex effects on pituitary hormones, it is not considered the primary direct inhibitor of **prolactin secretion**. - Its influence is often indirect or less potent than that of **dopamine**. *Adrenaline* - **Adrenaline** (epinephrine) is a neurotransmitter and hormone primarily involved in the **"fight or flight" response** and does not directly inhibit **prolactin secretion**. - Its effects on pituitary hormone release are typically less direct compared to **dopamine's** specific action on lactotrophs.
Question 612: What is the principal stimulus for vasopressin secretion?
- A. Hyperosmolality (Correct Answer)
- B. Hypovolemia
- C. Hypoosmolality
- D. Hypervolemia
Explanation: ***Hyperosmolality*** - An increase in **plasma osmolality**, even by a small percentage (1-2%), is the **most potent and PRINCIPAL stimulus** for ADH (vasopressin) release. - This is detected by **osmoreceptors** in the hypothalamus (particularly in the organum vasculosum of the lamina terminalis), which are extremely sensitive and respond rapidly. - This response is the primary mechanism for day-to-day regulation of water balance. *Hypovolemia* - A significant decrease in **blood volume** (typically >10%) also stimulates vasopressin release, but it is **much less sensitive** than hyperosmolality and serves as a secondary/backup mechanism. - This response is mediated by **baroreceptors** in the carotid sinuses and aortic arch. - Only activated during substantial volume loss (hemorrhage, severe dehydration). *Hypoosmolality* - **Decreased plasma osmolality** actively **inhibits** vasopressin secretion as the body aims to excrete excess water. - This helps to prevent overhydration and maintain proper fluid balance. *Hypervolemia* - **Increased blood volume** (hypervolemia) **inhibits** vasopressin secretion, as the body needs to excrete excess fluid. - This contributes to diuresis and the lowering of blood pressure.
Question 613: Which of the following would be least likely seen 14 days after a rat is injected with a drug that kills all of its pancreatic B cells?
- A. A rise in plasma osmolality
- B. A rise in the plasma H+ concentration
- C. A fall in the plasma amino acid concentration (Correct Answer)
- D. A rise in the plasma amino acid concentration
Explanation: ***A fall in the plasma amino acid concentration*** - Destruction of pancreatic **B cells** leads to a lack of **insulin**. Insulin promotes amino acid uptake and protein synthesis, so its absence would lead to a *rise*, not a *fall*, in plasma amino acids due to increased protein breakdown. - In **insulin deficiency**, the body shifts to catabolic states, breaking down proteins for energy and glucose production (gluconeogenesis), thus releasing amino acids into the plasma. *A rise in plasma osmolality* - The absence of insulin would lead to **hyperglycemia** (high blood sugar) as glucose cannot be efficiently taken up by cells. - **High plasma glucose** significantly increases plasma osmolality due to its osmotic activity. *A rise in the plasma H+ concentration* - Long-term **insulin deficiency** can lead to **diabetic ketoacidosis (DKA)**, where the body breaks down fats for energy, producing **ketone bodies**. - Ketone bodies are acids, and their accumulation increases the **plasma H+ concentration**, leading to **metabolic acidosis**. *A rise in the plasma amino acid concentration* - Without **insulin**, protein synthesis is inhibited, and protein breakdown (proteolysis) is enhanced to provide substrates for gluconeogenesis. - This results in a release of **amino acids** from muscle and other tissues into the bloodstream, increasing their plasma concentration.
Question 614: Which of the following hormones has its release inhibited by thyroxine?
- A. LH
- B. TSH (Correct Answer)
- C. GH
- D. PRL
Explanation: ***TSH*** - **Thyroid-stimulating hormone (TSH)** release from the anterior pituitary is **inhibited by thyroxine** (T4) through a negative feedback loop. - When **thyroxine levels are high**, they signal the pituitary to produce less TSH. *LH* - **Luteinizing hormone (LH)** is primarily regulated by **gonadotropin-releasing hormone (GnRH)** and inhibited by sex steroids (estrogen, progesterone, testosterone), not directly by thyroxine. - Imbalances in thyroid hormones can indirectly affect LH, but **thyroxine does not directly inhibit its release**. *GH* - **Growth hormone (GH)** secretion is regulated by **growth hormone-releasing hormone (GHRH)** and **somatostatin**, as well as other factors like IGF-1. - While thyroid hormones can indirectly influence GH secretion, **thyroxine does not directly inhibit GH release**. *PRL* - **Prolactin (PRL)** release is primarily inhibited by **dopamine** from the hypothalamus. - Although hypothyroidism can sometimes lead to hyperprolactinemia, **thyroxine does not directly inhibit prolactin release**.
Question 615: Ghrelin stimulates the release of which hormone?
- A. LH
- B. PTH
- C. Prolactin
- D. Growth hormone (Correct Answer)
Explanation: ***Growth hormone*** - **Ghrelin** is a **neuropeptide** that acts as a potent **growth hormone-releasing peptide (GHRP)**. - It stimulates **growth hormone (GH)** secretion from the anterior pituitary, primarily by acting on the **growth hormone secretagogue receptor (GHS-R)** in the hypothalamus and pituitary. *LH* - **Luteinizing hormone (LH)** release is primarily stimulated by **gonadotropin-releasing hormone (GnRH)**, not ghrelin. - While ghrelin can have some modulatory effects on reproductive hormones, its primary role is not the direct stimulation of LH. *PTH* - **Parathyroid hormone (PTH)** is released in response to **low serum calcium levels**, acting to raise calcium levels. - Ghrelin has no direct established role in stimulating PTH secretion. *Prolactin* - **Prolactin** release is primarily regulated by the inhibition of **dopamine** from the hypothalamus. - Although ghrelin has been shown to a minor extent to stimulate prolactin, growth hormone is the main hormone that ghrelin stimulates.
Question 616: Aldosterone is produced by which of the following?
- A. Posterior pituitary gland
- B. Hypothalamus
- C. Adrenal gland (Correct Answer)
- D. Anterior pituitary gland
Explanation: ***Adrenal gland*** - Aldosterone is a **mineralocorticoid hormone** primarily produced by the **zona glomerulosa** of the **adrenal cortex**, which is the outer layer of the adrenal gland. - Its main role is to regulate **sodium and potassium balance** and thereby influence blood pressure. *Posterior pituitary gland* - The posterior pituitary gland stores and releases **oxytocin** and **antidiuretic hormone (ADH)**, which are produced by the hypothalamus. - It does not synthesize its own hormones, and specifically, it does not produce aldosterone. *Hypothalamus* - The hypothalamus produces various **releasing and inhibiting hormones** that control the anterior pituitary, as well as ADH and oxytocin which are transported to the posterior pituitary. - While it plays a role in regulating many endocrine functions, it does not directly produce aldosterone. *Anterior pituitary gland* - The anterior pituitary gland produces several hormones, including **growth hormone**, **prolactin**, **thyroid-stimulating hormone (TSH)**, **adrenocorticotropic hormone (ACTH)**, **follicle-stimulating hormone (FSH)**, and **luteinizing hormone (LH)**. - Aldosterone production is not among its functions, although ACTH from the anterior pituitary can indirectly influence aldosterone synthesis.
Question 617: Which is the single most important factor that stimulates insulin secretion?
- A. Increased plasma glucose concentration stimulates insulin release. (Correct Answer)
- B. Increased plasma potassium concentration stimulates insulin release.
- C. Increased plasma fatty acid concentration stimulates insulin release.
- D. Increased amino acid concentration stimulates insulin release.
Explanation: **Increased plasma glucose concentration stimulates insulin release.** - **Glucose** is the primary physiological stimulus for **insulin secretion** from the pancreatic Langerhans beta-cells. - High plasma glucose levels trigger a cascade of events within the beta-cells, leading to **ATP production** and subsequent **insulin exocytosis**. *Increased plasma potassium concentration stimulates insulin release.* - While changes in ion concentrations can affect cell function, **potassium** does not play a primary role in directly stimulating **insulin release** under normal physiological conditions. - Its effects are typically indirect and not comparable to glucose's role. *Increased plasma fatty acid concentration stimulates insulin release.* - **Fatty acids** can stimulate some insulin release, particularly chronically, but their acute effect is much weaker than that of glucose. - Prolonged exposure to high fatty acid levels can also contribute to **insulin resistance**. *Increased amino acid concentration stimulates insulin release.* - **Amino acids**, especially certain ones like leucine and arginine, can stimulate **insulin release**, sometimes significantly. - However, their combined effect is generally less potent than that of **glucose** in a healthy individual after a meal.
Question 618: Estrogen action on carbohydrate metabolism:
- A. Glycolysis increases
- B. Increasing central adipose deposition
- C. Worsening of NIDDM
- D. Increases uptake of glucose through increase in insulin sensitivity (Correct Answer)
Explanation: ***Increases uptake of glucose through increase in insulin sensitivity*** - Estrogen generally improves **insulin sensitivity**, leading to better glucose uptake by cells and reduced peripheral insulin resistance - This effect contributes to a lower incidence of type 2 diabetes in premenopausal women compared to men - Protection against insulin resistance is one of the key metabolic benefits of estrogen *Glycolysis increases* - While estrogen has complex effects on glucose metabolism, its primary role in carbohydrate metabolism is related to **insulin sensitivity** rather than a direct, general increase in glycolysis - Increased glycolysis typically occurs in response to high glucose levels; estrogen's effect is more about improving cellular response to glucose *Increasing central adipose deposition* - Estrogen is typically associated with **peripheral fat distribution** (gynoid pattern) rather than central (android) adipose deposition - A decrease in estrogen, such as during menopause, is linked to an increase in central adiposity - This explains why postmenopausal women develop more central fat distribution *Worsening of NIDDM* - Estrogen generally **improves insulin sensitivity**, which reduces the risk or severity of Type 2 Diabetes Mellitus (NIDDM), not worsens it - The metabolic protection provided by estrogen explains lower diabetes rates in premenopausal women compared to age-matched men
Question 619: Basophilic thyrotroph cells of pituitary secrete:
- A. GH
- B. LH
- C. Prolactin
- D. TSH (Correct Answer)
Explanation: ***TSH*** - **Basophilic thyrotroph cells** of the anterior pituitary gland are responsible for synthesizing and secreting **Thyroid-Stimulating Hormone (TSH)**. - TSH then acts on the thyroid gland, stimulating it to produce **thyroid hormones (T3 and T4)**. *GH* - **Growth Hormone (GH)** is secreted by **acidophilic somatotroph cells** in the anterior pituitary, not basophilic thyrotrophs. - GH plays a crucial role in growth, metabolism, and body composition. *LH* - **Luteinizing Hormone (LH)** is secreted by **basophilic gonadotrophs** of the anterior pituitary, which also secrete Follicle-Stimulating Hormone (FSH). - LH is involved in reproductive functions in both males and females. *Prolactin* - **Prolactin** is produced by **acidophilic lactotroph (mammotroph) cells** in the anterior pituitary, not basophilic thyrotrophs. - Its primary function is to stimulate milk production in mammary glands.
Question 620: Which is the true statement about Anterior Pituitary Hormones?
- A. The hypophyseal portal veins are associated with the posterior lobe of the pituitary gland.
- B. No hormones are secreted before 28 weeks of gestation except prolactin
- C. Most of the pituitary hormones are secreted by the posterior lobe
- D. Secretion of anterior pituitary hormones is pulsatile (Correct Answer)
Explanation: ***Secretion of anterior pituitary hormones is pulsatile*** - The **anterior pituitary** releases its hormones in a **pulsatile fashion**, meaning in bursts rather than a continuous stream. - This pulsatile secretion is crucial for maintaining the sensitivity of target tissues and for proper endocrine regulation. *The hypophyseal portal veins are associated with the posterior lobe of the pituitary gland.* - The **hypophyseal portal veins** are part of the **hypothalamic-hypophyseal portal system**, which primarily regulates the **anterior pituitary gland**. - The **posterior pituitary** is regulated by direct neural connections from the hypothalamus, not by a portal venous system. *No hormones are secreted before 28 weeks of gestation except prolactin* - Several **anterior pituitary hormones**, including **growth hormone**, **TSH**, and **ACTH**, are secreted much earlier in gestation, typically by the end of the first trimester. - While **prolactin** is also secreted early, it is not the *only* anterior pituitary hormone produced before 28 weeks. *Most of the pituitary hormones are secreted by the posterior lobe* - The **anterior pituitary** (adenohypophysis) is responsible for secreting most of the pituitary hormones, including **GH, TSH, ACTH, FSH, LH, and prolactin**. - The **posterior pituitary** (neurohypophysis) only releases two hormones: **oxytocin** and **antidiuretic hormone (ADH)**, which are produced in the hypothalamus.
Practice by Chapter
Principles of Endocrine Regulation
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Hypothalamus and Pituitary Gland
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Thyroid Physiology
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Adrenal Cortex and Medulla
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Pancreatic Hormones and Glucose Metabolism
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Calcium and Phosphate Homeostasis
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Growth Hormone and Growth Factors
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Endocrine Regulation of Metabolism
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Hormone Receptors and Signaling
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Assessment of Endocrine Function
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