Endocrinology Practice Questions

Q: Insulin is essential for glucose entry in?

Muscle cells. ***Muscle cells*** - **Insulin** promotes glucose uptake into **muscle cells** by stimulating the translocation of **GLUT4 transporters** to the cell surface. - In the absence of insulin, **glucose uptake** into quiescent muscle cells is significantly reduced. *Cortical neurons* - **Neurons** in the brain, including cortical neurons, primarily utilize **GLUT1** and **GLUT3 transporters** for glucose uptake, which are **insulin-independent**. - This ensures a constant supply of glucose to the brain, even during periods of low insulin. *Beta cells of pancreas* - **Pancreatic beta cells** use **GLUT2 transporters** for glucose uptake, which are **insulin-independent** and have a high capacity. - This allows beta cells to sense glucose levels and regulate insulin secretion accordingly. *Renal tubular cells* - **Renal tubular cells** reabsorb glucose primarily through **sodium-glucose co-transporters (SGLTs)** and **GLUT2 transporters**, both of which are **insulin-independent**. - Their primary role is in maintaining glucose homeostasis by preventing glucose loss in urine.

Q: Which of the following statements about ghrelin is false?

Directly regulates thyroid hormone secretion. ***Directly regulates thyroid hormone secretion*** - **Ghrelin** does NOT directly regulate **thyroid hormone secretion** or the **hypothalamic-pituitary-thyroid (HPT) axis**. - Ghrelin's primary physiological roles are related to **appetite stimulation**, **growth hormone release**, and **energy balance**. - While there may be indirect metabolic interactions, ghrelin has no established direct regulatory role in **TSH** or **thyroid hormone** production. *Produced by stomach cells* - This statement is **true**; **ghrelin** is predominantly produced by **P/D1 cells** (also called X/A-like cells) in the **fundus of the stomach**. - These cells release ghrelin primarily when the stomach is empty, signaling hunger to the brain. *Stimulates appetite* - This statement is **true**; ghrelin is often referred to as the "**hunger hormone**" because it acts on the **arcuate nucleus** of the **hypothalamus** to increase food intake. - Its levels rise before meals and decrease after eating, playing a crucial role in the **short-term regulation of appetite**. *Stimulates growth* - This statement is **true**; **ghrelin** is a potent stimulator of **growth hormone (GH) release** from the **anterior pituitary gland**. - It acts on **growth hormone secretagogue receptors (GHS-R)** on **somatotrophs** to promote GH secretion, contributing to its role in **growth** and **metabolism**.

Q: The primary site of vasopressin synthesis is

Supraoptic nucleus. ***Supraoptic nucleus*** - The **supraoptic nucleus** of the hypothalamus is the **primary site** for the synthesis of **vasopressin** (also known as antidiuretic hormone or ADH). - Approximately **80% of vasopressin** is produced by the neurosecretory cells in this nucleus. - The synthesized vasopressin is transported down axons to the posterior pituitary for storage and release. *Preoptic nucleus* - The **preoptic nucleus** is involved in various homeostatic functions, including **thermoregulation** and **sleep regulation**, but not the synthesis of vasopressin. - While it has neuronal connections to the hypothalamus, it does not produce ADH. *Paraventricular nucleus* - The **paraventricular nucleus** also synthesizes **both vasopressin and oxytocin**, accounting for approximately **20% of vasopressin production**. - While it does produce vasopressin, the **supraoptic nucleus remains the primary site**, making it the correct answer to this question. - The PVN also plays important roles in stress response and various autonomic functions. *Posterior pituitary* - The **posterior pituitary** (neurohypophysis) is responsible for the **storage and release** of vasopressin and oxytocin, not their synthesis. - These hormones are produced in the hypothalamic nuclei (supraoptic and paraventricular) and then transported down axonal tracts to the posterior pituitary.

Q: Which hormone is primarily inhibited by the hypothalamus?

Prolactin. ***Prolactin*** - The hypothalamus secretes **dopamine** (Prolactin Inhibiting Hormone), which tonically inhibits prolactin release from the anterior pituitary. - Unlike most other anterior pituitary hormones, prolactin's primary hypothalamic control is **inhibitory** rather than stimulatory. *TSH* - **Thyroid-stimulating hormone (TSH)** is *stimulated* by **Thyrotropin-Releasing Hormone (TRH)** from the hypothalamus. - The hypothalamus does not primarily inhibit TSH; rather, it promotes its release, which is then regulated by negative feedback from thyroid hormones. *FSH* - **Follicle-stimulating hormone (FSH)** is *stimulated* by **Gonadotropin-Releasing Hormone (GnRH)** from the hypothalamus. - The hypothalamus promotes FSH release, which is essential for gamete production and ovarian follicle development. *CRH* - **Corticotropin-Releasing Hormone (CRH)** is a hormone secreted by the **hypothalamus** itself. - CRH acts on the anterior pituitary to *stimulate* the release of **ACTH**, not inhibit another hormone.

Q: Growth hormone level is highest during

Sleep. ***Sleep*** - Growth hormone (GH) secretion is **pulsatile**, with the largest and most consistent pulses occurring during **slow-wave sleep** (deep sleep). - This nocturnal surge contributes significantly to the overall daily GH output and is crucial for growth and metabolic regulation. *Hypoglycemia* - While **hypoglycemia** is a potent stimulus for GH release, it is an acute stress response rather than a state where GH levels are consistently highest. - The body's primary response to hypoglycemia is to raise blood glucose, and while GH helps, it is not the peak physiological secretion time. *Fasting* - **Prolonged fasting** can increase GH secretion as a mechanism to mobilize fat stores and conserve glucose. - However, the peak levels due to fasting are generally less pronounced than the dramatic surge observed during deep sleep. *Exercise* - **Vigorous exercise** can acutely stimulate GH release, particularly with sustained effort. - This increase is typically transient and not as high or consistently cyclical as the secretion during nocturnal sleep.

Q: What is the major adrenal androgen produced by the adrenal glands?

Dehydroepiandrosterone (DHEA). ***Dehydroepiandrosterone (DHEA)*** - **Dehydroepiandrosterone (DHEA)**, or specifically **dehydroepiandrosterone sulfate (DHEA-S)**, is the major adrenal androgen produced by the adrenal cortex and is an important **17-ketosteroid** [1]. - Its production is controlled by **ACTH** and serves as a precursor for more potent androgens and estrogens in peripheral tissues. *Testosterone* - While testosterone is a potent androgen, the primary source in males is the **testes**, and in females, it's produced in smaller amounts by the **ovaries** and peripherally from adrenal androgens. - The adrenal glands produce only a **small fraction** of circulating testosterone directly; they primarily produce precursors like DHEA [1]. *11-hydroxy derivative of androstenedione* - **Androstenedione** is an adrenal androgen precursor, but its 11-hydroxy derivative is not typically referred to as the major adrenal androgen. - The most significant adrenal androgen is DHEA, which is then converted peripherally to other androgens including androstenedione [1]. *Cortisol* - **Cortisol** is the primary **glucocorticoid** produced by the adrenal glands, playing a critical role in stress response, metabolism, and immune function [2]. - While produced by the adrenal cortex, it is a **steroid hormone**, but its primary function is not androgenic; it is a glucocorticoid.

Q: Wolff–Chaikoff effect is due to?

Excess iodine intake. ***Excess iodine intake*** - The **Wolff-Chaikoff effect** is a phenomenon where a high intake of iodine acutely **inhibits thyroid hormone synthesis** and release. - This effect protects the body from excessive thyroid hormone production during periods of very high iodine availability. *Decreased iodination of MIT* - While the Wolff-Chaikoff effect does inhibit **iodination**, the direct cause is the excessive iodine itself, which triggers an autoregulatory shutdown. - Decreased iodination is a *consequence* of the high iodine leading to inhibition of thyroid peroxidase activity, but not the primary cause of the effect. *Suppression of TSH secretion* - **TSH (Thyroid Stimulating Hormone)** secretion is primarily regulated by negative feedback from thyroid hormones (T3 and T4) and TRH from the hypothalamus. - The Wolff-Chaikoff effect directly involves the thyroid gland's response to iodine and is not primarily mediated by TSH suppression. *Decreased conversion of T4 to T3* - The **conversion of T4 to T3** primarily occurs in peripheral tissues, mediated by deiodinase enzymes. - The Wolff-Chaikoff effect focuses on the inhibition of **iodine organification** and hormone release within the thyroid gland itself, not peripheral conversion.

Q: Which of the following hormones does not mediate its action through cAMP?

Estrogen. ***Estrogen*** - **Estrogen** is a **steroid hormone** that mediates its action by binding to intracellular receptors, forming a complex that directly influences gene transcription. - Steroid hormones, due to their **lipophilicity**, can cross the cell membrane and do not typically rely on cell surface receptors or second messengers like cAMP. *Glucagon* - **Glucagon** acts on a **G protein-coupled receptor (GPCR)**, specifically a Gs-coupled receptor, leading to the activation of adenylyl cyclase. - This activation increases the intracellular concentration of **cAMP**, which then activates protein kinase A to mediate its effects, primarily on glucose metabolism. *Follicle stimulating hormone* - **FSH** binds to a **GPCR** on target cells, activating the Gs protein pathway. - This activation stimulates **adenylyl cyclase** and increases intracellular **cAMP** levels, which are critical for its role in gamete development. *Luteinizing hormone* - **LH**, like FSH, binds to a cell surface **GPCR** that activates the Gs protein. - This leads to the stimulation of **adenylyl cyclase** and an increase in **cAMP**, mediating its effects on steroidogenesis and ovulation.

Q: Which of the following is NOT true about ghrelin?

Has anorexic effect. ***Has anorexic effect*** - Ghrelin is known as the **"hunger hormone"** because it stimulates appetite and has an **orexigenic effect**, meaning it increases food intake. - Therefore, stating that it has an **anorexic effect** (reduces appetite) is incorrect. *Stimulates growth hormone release* - Ghrelin is a **natural ligand** for the **growth hormone secretagogue receptor (GHSR)**. - This binding leads to the stimulation of **growth hormone (GH)** release from the pituitary gland. *Secreted by gastric fundus cells* - The primary source of ghrelin in the body is the **P/D1 cells** found in the mucosa of the **gastric fundus**. - Smaller amounts are also produced in the small intestine, pancreas, and hypothalamus. *Increases gastric motility* - Ghrelin is involved in regulating stomach function and can **increase gastric motility** and acid secretion. - This action helps to prepare the digestive system for incoming food.

Q: Laron dwarfism is due to:

GH receptor resistance. ***GH receptor resistance*** - **Laron dwarfism** is caused by a genetic defect in the **growth hormone (GH) receptor**, leading to cellular insensitivity to GH. - Despite normal or elevated GH levels, the body cannot respond to GH, resulting in impaired **insulin-like growth factor 1 (IGF-1)** production and stunted growth. *GH deficiency* - This would involve insufficient production of **growth hormone** from the pituitary gland. - In such cases, administration of exogenous GH would typically be effective, which is not the case in Laron dwarfism due to receptor resistance. *GHRH deficiency* - A deficiency in **growth hormone-releasing hormone (GHRH)** from the hypothalamus would lead to decreased GH secretion. - This would ultimately result in **GH deficiency**, but the primary defect in Laron syndrome is at the receptor level, not in GHRH or GH production. *IGF-1 deficiency* - While Laron dwarfism does result in functionally low **IGF-1** levels due to GH insensitivity, the primary defect is in the GH receptor, which *prevents* GH from stimulating IGF-1 production. - True primary **IGF-1 deficiency** (apart from GH resistance) is a less common cause of dwarfism and would not involve high GH levels.

Question 1

Insulin is essential for glucose entry in?

Accepted Answer

Muscle cells

Answer

Beta cells of pancreas

Answer

Cortical neurons

Answer

Renal tubular cells

Question 2

Which of the following statements about ghrelin is false?

Accepted Answer

Directly regulates thyroid hormone secretion

Answer

Stimulates appetite

Answer

Stimulates growth

Answer

Produced by stomach cells

Question 3

The primary site of vasopressin synthesis is

Accepted Answer

Supraoptic nucleus

Answer

Preoptic nucleus

Answer

Paraventricular nucleus

Answer

Posterior pituitary

Question 4

Which hormone is primarily inhibited by the hypothalamus?

Accepted Answer

Prolactin

Answer

TSH

Answer

FSH

Answer

CRH

Question 5

Growth hormone level is highest during

Accepted Answer

Sleep

Answer

Hypoglycemia

Answer

Fasting

Answer

Exercise

Question 6

What is the major adrenal androgen produced by the adrenal glands?

Accepted Answer

Dehydroepiandrosterone (DHEA)

Answer

Testosterone

Answer

11-hydroxy derivative of androstenedione

Answer

Cortisol

Question 7

Wolff–Chaikoff effect is due to?

Accepted Answer

Excess iodine intake

Answer

Decreased iodination of MIT

Answer

Suppression of TSH secretion

Answer

Decreased conversion of T4 to T3

Question 8

Which of the following hormones does not mediate its action through cAMP?

Accepted Answer

Estrogen

Answer

Glucagon

Answer

Follicle stimulating hormone

Answer

Luteinizing hormone

Question 9

Which of the following is NOT true about ghrelin?

Accepted Answer

Has anorexic effect

Answer

Stimulates growth hormone release

Answer

Secreted by gastric fundus cells

Answer

Increases gastric motility

Question 10

Laron dwarfism is due to:

Accepted Answer

GH receptor resistance

Answer

GH deficiency

Answer

GHRH deficiency

Answer

IGF-1 deficiency

Endocrinology — MCQs

Endocrinology — MCQs

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