Endocrinology Practice Questions

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 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: How does adrenaline affect insulin secretion?

Inhibition of beta cells. ***Inhibition of beta cells*** - **Adrenaline** (epinephrine) binds to **alpha-2 adrenergic receptors** on pancreatic beta cells, which are coupled to inhibitory G-proteins. - This binding leads to **decreased cAMP levels** and hyperpolarization of the beta cell membrane, ultimately inhibiting insulin release. *Stimulation of delta cells* - **Delta cells** produce **somatostatin**, which generally inhibits the secretion of insulin and glucagon. - While adrenaline can have various systemic effects, its primary direct action on insulin secretion is not through stimulating delta cells. *Stimulation of g cells* - **G cells** in the stomach produce **gastrin**, a hormone involved in gastric acid secretion. - Adrenaline's primary physiological role in glucose metabolism does not involve direct stimulation of G cells to influence insulin secretion. *Stimulation of beta cells* - **Stimulation of beta cells** would lead to increased insulin secretion. - Adrenaline's physiological role, particularly in **stress responses**, is to raise blood glucose, which is achieved in part by **reducing insulin availability** to ensure glucose enters the bloodstream rather than tissues.

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 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.

Q: All of the following are actions of cortisol EXCEPT:

Decrease blood amino acid. ***Decrease blood amino acid*** - This is **NOT** an action of cortisol, making it the correct answer for this EXCEPT question. - Cortisol actually **increases** blood amino acids through **protein catabolism** in muscle and other peripheral tissues. - The catabolic effect mobilizes amino acids from structural proteins, **elevating blood amino acid levels** during stress. *Increase blood amino acid* - This **IS** a correct action of cortisol through **protein breakdown** in peripheral tissues. - Cortisol promotes proteolysis in muscle, releasing amino acids into circulation for use in gluconeogenesis and acute phase protein synthesis. *Increase liver amino acid* - This **IS** a correct action of cortisol as it promotes **hepatic uptake** of amino acids from the bloodstream. - These amino acids are utilized for **gluconeogenesis** and synthesis of plasma proteins in the liver. *Decrease liver amino acid* - This could be considered an action in the sense that cortisol promotes rapid **utilization** of amino acids for gluconeogenesis. - However, the net effect is increased amino acid **flux through** the liver rather than a decrease in availability, as cortisol simultaneously increases hepatic uptake.

Q: After pituitary stalk resection, all hormones are affected except.

Prolactin. ***Prolactin*** - After pituitary stalk resection, prolactin is the **only anterior pituitary hormone that increases** rather than decreases, making it the exception. - Prolactin secretion is normally under **tonic inhibition** by **dopamine** from the hypothalamus, which reaches the anterior pituitary via the hypophyseal portal system. - When the pituitary stalk is severed, this **dopaminergic inhibition is lost**, resulting in **disinhibition** and a marked **increase in prolactin levels** (hyperprolactinemia). - This is in contrast to all other pituitary hormones which decrease after stalk resection. *Follicle-stimulating hormone* - FSH is an **anterior pituitary hormone** stimulated by **GnRH** from the hypothalamus. - Stalk resection interrupts GnRH delivery via the portal system, leading to **decreased FSH secretion**. - This results in hypogonadism. *Adrenocorticotropic hormone* - ACTH is an **anterior pituitary hormone** stimulated by **CRH** from the hypothalamus. - Stalk resection prevents CRH from reaching the anterior pituitary, causing **decreased ACTH production**. - This leads to secondary adrenal insufficiency. *Antidiuretic hormone (ADH)* - ADH is synthesized in the **hypothalamus** (supraoptic and paraventricular nuclei) and transported down axons to the posterior pituitary for storage and release. - Pituitary stalk resection **interrupts these axons**, initially causing **diabetes insipidus** with decreased ADH release. - While the cell bodies remain intact in the hypothalamus and some recovery may occur over time, ADH secretion is still acutely affected (decreased) by stalk resection, following the same pattern as other hormones except prolactin.

Q: What is the primary form in which testosterone circulates in the plasma?

Testosterone bound to sex-hormone-binding globulin. ***Testosterone bound to sex-hormone-binding globulin*** - The majority of circulating **testosterone** (approximately **60-70%**) is bound to **sex-hormone-binding globulin (SHBG)**, making this the **primary specific form** in which testosterone circulates. - **SHBG** is a high-affinity binding protein that tightly regulates testosterone bioavailability and maintains a stable hormone reservoir. - This is the standard answer in medical physiology when asked about the primary circulating form of testosterone. *Bound testosterone* - While it is true that approximately **98%** of total testosterone is protein-bound (SHBG + albumin combined), this option is too **general** and lacks the specificity expected in medical examination questions. - When asking for the "primary form," medical education refers to the **single largest specific fraction**, which is SHBG-bound testosterone. *Free testosterone* - Only **1-2%** of circulating testosterone is in the **free** (unbound) form. - While this is the **biologically active** fraction that can enter cells and bind to androgen receptors, it represents only a small minority of circulating testosterone. *Dihydrotestosterone bound to sex-hormone-binding globulin* - **Dihydrotestosterone (DHT)** is a potent **metabolite** of testosterone formed by 5α-reductase in peripheral tissues. - DHT is not the primary circulating form of **testosterone** itself; it is a different, more potent androgen present in much smaller quantities in plasma.

Q: Conversion of chondrocytes into osteogenic cells is caused by

IGF-1. ***IGF-1*** - **Insulin-like Growth Factor 1 (IGF-1)** is the primary direct mediator in endochondral ossification, stimulating chondrocyte proliferation, differentiation, and hypertrophy in the growth plate. - IGF-1 acts directly on chondrocytes to promote their maturation and the subsequent invasion of osteoprogenitor cells that form bone. - It plays a crucial role in longitudinal bone growth by regulating various cellular processes in the growth plate and promoting the replacement of cartilage with bone tissue. *Insulin* - While insulin has anabolic effects on bone and can interact with IGF-1 receptors due to structural similarity, its primary role is in **glucose metabolism** rather than direct regulation of chondrocyte activity in endochondral ossification. - Insulin may have supportive effects on bone formation but is not the primary hormone driving growth plate chondrocyte function. *Growth hormone* - **Growth hormone (GH)** stimulates the production of IGF-1 both systemically (from the liver) and locally (from chondrocytes and other skeletal tissues). - GH acts upstream by increasing IGF-1 levels, which then directly mediates the effects on chondrocytes. - While GH is essential for normal bone growth, IGF-1 is considered the direct effector molecule on chondrocytes. *Thyroxine* - **Thyroxine (T4)** is essential for normal skeletal development and bone maturation, particularly in regulating the timing of growth plate fusion and overall metabolic support for bone growth. - However, it does not directly regulate chondrocyte proliferation and differentiation in the growth plate during endochondral ossification. - Thyroid hormone deficiency causes growth retardation, but thyroxine is not the primary hormonal driver of chondrocyte activity.

Question 1

The primary site of vasopressin synthesis is

Accepted Answer

Supraoptic nucleus

Answer

Preoptic nucleus

Answer

Paraventricular nucleus

Answer

Posterior pituitary

Question 2

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 3

How does adrenaline affect insulin secretion?

Accepted Answer

Inhibition of beta cells

Answer

Stimulation of delta cells

Answer

Stimulation of G cells

Answer

Stimulation of beta cells

Question 4

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 5

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 6

Laron dwarfism is due to:

Accepted Answer

GH receptor resistance

Answer

GH deficiency

Answer

GHRH deficiency

Answer

IGF-1 deficiency

Question 7

All of the following are actions of cortisol EXCEPT:

Accepted Answer

Decrease blood amino acid

Answer

Increase blood amino acid

Answer

Increase liver amino acid

Answer

Decrease liver amino acid

Question 8

After pituitary stalk resection, all hormones are affected except.

Accepted Answer

Prolactin

Answer

Follicle-stimulating hormone

Answer

Adrenocorticotropic hormone

Answer

Antidiuretic hormone (ADH)

Question 9

What is the primary form in which testosterone circulates in the plasma?

Accepted Answer

Testosterone bound to sex-hormone-binding globulin

Answer

Free testosterone

Answer

Bound testosterone

Answer

Dihydrotestosterone bound to sex-hormone-binding globulin

Question 10

Conversion of chondrocytes into osteogenic cells is caused by

Accepted Answer

IGF-1

Answer

Insulin

Answer

Thyroxine

Answer

Growth hormone

Endocrinology — MCQs

Endocrinology — MCQs

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