Endocrinology Practice Questions

Q: A major causal factor in some cases of hypogonadism is:

Reduced secretion of gonadotropin-releasing hormone (GnRH). ***Reduced secretion of gonadotropin-releasing hormone (GnRH)*** - **Hypogonadotropic hypogonadism** is characterized by low levels of LH and FSH due to inadequate GnRH secretion from the hypothalamus, leading to decreased testosterone production. - This can be caused by various factors, including genetic conditions, hypothalamic tumors, or functional suppression from stress or severe illness. *Excess secretion of testicular activin by Sertoli cells* - **Activin** promotes FSH synthesis and secretion from the pituitary but is not a primary cause of hypogonadism. - While disruptions in activin/inhibin balance can affect spermatogenesis, it doesn't directly cause a systemic hypogonadal state through its direct effect on GnRH or gonadal function. *Hypersecretion of pituitary LH and FSH as the result of increased GnRH* - **Hypersecretion of LH and FSH** in response to increased GnRH would lead to **hypergonadism**, or at least eugonadism, not hypogonadism. - This scenario would stimulate excessive testosterone production, the opposite of hypogonadism. *Failure of the hypothalamus to respond to testosterone* - The hypothalamus, as well as the pituitary, are sensitive to **negative feedback from testosterone** to regulate GnRH and gonadotropin release. - A failure to respond to testosterone would typically lead to **increased GnRH and gonadotropin secretion** (as the feedback loop is broken), resulting in higher testosterone levels, which contradicts hypogonadism.

Q: What is the percentage of T4 and T3 released from the thyroid gland?

90% T4; 10% T3. ***90% T4; 10% T3*** - The thyroid gland primarily secretes **thyroxine (T4)**, which accounts for approximately **90% of its total hormone output**. - **Triiodothyronine (T3)** is released in smaller amounts, making up approximately **10% of direct thyroid secretion**. - The majority of circulating T3 (about 80%) is derived from **peripheral deiodination of T4** in tissues like liver and kidneys, not from direct thyroid secretion. *80% T4; 20% T3* - This ratio **overestimates** the direct secretion of T3 from the thyroid gland. - While some older sources cite this ratio, the more widely accepted current value is **90:10**. - The higher circulating T3 levels seen in the body are due to **peripheral conversion**, not direct glandular secretion. *50% T4; 50% T3* - This ratio is incorrect as **T4 is the predominant hormone** released directly from the thyroid gland. - Equal secretion would not align with the thyroid's primary role as a **T4-producing gland** with T4 serving as a prohormone. *25% T4; 75% T3* - This ratio is completely incorrect and would reverse the actual secretory pattern. - **T4 is quantitatively the dominant hormone** secreted by the thyroid, with T3 playing a more active role after peripheral conversion.

Q: Which of the following hormones is released from the posterior pituitary?

Antidiuretic hormone. ***Antidiuretic hormone*** - The **posterior pituitary** (neurohypophysis) stores and releases **antidiuretic hormone (ADH)** and oxytocin. - ADH, also known as **vasopressin**, is synthesized in the **hypothalamus** and transported to the posterior pituitary for release. *Luteinizing hormone* - **Luteinizing hormone (LH)** is released from the **anterior pituitary** in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus. - LH plays a crucial role in **reproduction**, triggering ovulation in females and testosterone production in males. *Growth hormone* - **Growth hormone (GH)** is synthesized and secreted by the **anterior pituitary gland**. - Its release is regulated by **growth hormone-releasing hormone (GHRH)** and **somatostatin** from the hypothalamus. *ACTH* - **Adrenocorticotropic hormone (ACTH)** is produced and secreted by the **anterior pituitary gland**. - ACTH stimulates the **adrenal cortex** to release cortisol, regulating stress responses and metabolism.

Q: All of these cause hyperglycemia except:

Insulin. ***Insulin*** - Insulin's primary function is to **lower blood glucose levels** by facilitating glucose uptake into cells and promoting glycogen synthesis. - It counters the effects of hormones that elevate blood sugar, directly leading to a **decrease in hyperglycemia**. *Catecholamines* - **Catecholamines** (e.g., epinephrine, norepinephrine) increase blood glucose by promoting **glycogenolysis** and **gluconeogenesis**. - They also **inhibit insulin secretion**, further contributing to elevated blood sugar. *Cortisol* - **Cortisol** is a **glucocorticoid** that raises blood glucose by increasing **gluconeogenesis** and reducing peripheral **glucose utilization**. - It can also decrease insulin sensitivity, leading to **hyperglycemia**. *GH* - **Growth hormone (GH)** can induce **insulin resistance** in peripheral tissues, which leads to reduced glucose uptake. - It also promotes **gluconeogenesis**, both contributing to elevated blood glucose levels.

Q: All the following mediate their action using cAMP as second messenger except:

Vasopressin. ***Vasopressin (ADH)*** - Vasopressin has **dual signaling mechanisms** depending on receptor type: - **V2 receptors** (kidney collecting duct): Use **Gs-protein → cAMP pathway** for water reabsorption via aquaporin-2 insertion - **V1 receptors** (vascular smooth muscle): Use **Gq-protein → IP3/DAG pathway** for vasoconstriction - In the context of this question, vasopressin is considered the exception because it has **significant non-cAMP mediated actions** through V1 receptors, unlike the other hormones listed which **predominantly or exclusively** use cAMP - **Note**: This is a teaching point about receptor subtypes; vasopressin DOES use cAMP at V2 receptors *Glucagon* - **Exclusively uses cAMP pathway** in hepatocytes and adipocytes - Binds to **glucagon receptor** (GPCR) → **Gs-protein** → adenylyl cyclase activation → **increased cAMP** → PKA activation - Promotes glycogenolysis, gluconeogenesis, and lipolysis *Dopamine* - **D1 and D5 receptors** are **Gs-coupled** → **stimulate adenylyl cyclase** → **increase cAMP** - Important for neurotransmission (motor control, reward) and renal vasodilation - D2-family receptors (D2, D3, D4) inhibit cAMP but D1-family predominates in many physiological contexts *Corticotropin (ACTH)* - Binds to **melanocortin-2 receptor (MC2R)** on adrenal cortex - **Gs-protein coupled** → adenylyl cyclase activation → **increased cAMP** → PKA activation - Stimulates steroidogenesis and cortisol secretion - **Exclusively cAMP-dependent mechanism**

Q: Regarding Ghrelin, which is false?

Secreted from oxyntic cells. ***Secreted from oxyntic cells*** - Ghrelin is **NOT** secreted from oxyntic cells (parietal cells). - It is primarily secreted by **P/D1 cells (X/A-like cells)** in the **gastric fundus**. - Oxyntic cells produce **hydrochloric acid** and **intrinsic factor**, not ghrelin. - This is the **FALSE** statement. *Stimulates appetite* - Ghrelin is known as the "**hunger hormone**" and is the primary **orexigenic hormone**. - It acts on **NPY/AgRP neurons** in the arcuate nucleus of the hypothalamus. - Ghrelin levels **rise before meals** and **fall after eating**, directly stimulating appetite and food intake. *Secretion increased in anorexia* - In **anorexia nervosa** and states of **negative energy balance**, ghrelin levels are **elevated**. - This represents a **compensatory physiological response** to stimulate appetite and restore energy balance. - Paradoxically, despite high ghrelin, appetite remains suppressed in anorexia due to central resistance. *Increases fat deposition* - Ghrelin has **anabolic effects** and promotes **adipogenesis** (fat storage). - It reduces **fat oxidation** and increases **lipid accumulation** in adipocytes. - Beyond stimulating food intake, ghrelin has direct metabolic effects favoring a positive energy balance and fat deposition.

Q: Thyroxine causes all the following except:

Decreased cell metabolism. ***Decreased cell metabolism*** - **Thyroid hormones**, including thyroxine, are known to **increase the metabolic rate** of most body cells. - Therefore, a decrease in cell metabolism is contrary to the primary action of thyroxine. - This is the correct answer as thyroxine does NOT cause decreased cell metabolism. *Increased basal metabolism* - **Thyroxine** (T4) and triiodothyronine (T3) are crucial for regulating the body's **basal metabolic rate**. - They enhance **cellular oxygen consumption** and the production of ATP, leading to increased energy expenditure. *Increased pulmonary ventilation* - The elevated **metabolic rate** induced by thyroxine leads to an increased demand for oxygen and production of carbon dioxide. - This physiological response stimulates the respiratory centers, resulting in **increased pulmonary ventilation** to meet the body's gas exchange needs. *Increased oxygen consumption* - One of the principal actions of **thyroxine** is to stimulate **mitochondrial activity** and the electron transport chain in most tissues. - This directly leads to an increase in cellular oxygen utilization and overall **oxygen consumption** throughout the body.

Q: Which of the following hormones uses cell surface receptors?

Glucagon. ***Glucagon*** - **Glucagon** is a **peptide hormone** that cannot pass through the **hydrophobic cell membrane**. - It binds to specific **G protein-coupled receptors** on the surface of target cells (e.g., hepatocytes) to exert its effects. *Thyroxine* - **Thyroxine (T4)** is a **tyrosine-derived (amino acid-derived) hormone** that is lipid-soluble and can readily cross the cell membrane. - It acts on **intracellular receptors** in the nucleus to regulate gene expression. *Cortisol* - **Cortisol** is a **steroid hormone** that is lipid-soluble and can diffuse through the cell membrane. - It primarily binds to **intracellular receptors** in the cytoplasm or nucleus to modulate gene transcription. *Testosterone* - **Testosterone** is a **steroid hormone** that is lipid-soluble and can easily pass through the cell membrane. - Its receptors are located **intracellularly**, usually in the cytoplasm, forming a complex that moves to the nucleus to regulate gene expression.

Q: Which of the following hormones uses cGMP as a second messenger?

Atrial natriuretic peptide (ANP). ***Atrial natriuretic peptide (ANP)*** - **ANP** binds to a receptor that has **guanylyl cyclase activity**, directly converting **GTP to cGMP**. - **cGMP** then acts as a second messenger, leading to vasodilation and increased sodium and water excretion. *Insulin* - **Insulin** primarily signals through a **tyrosine kinase receptor**, leading to phosphorylation cascades. - It does not directly use **cGMP** as a second messenger for its main effects. *Thyroxine* - **Thyroxine (T4)** and **triiodothyronine (T3)** are **thyroid hormones** (amino acid derivatives) that act directly on **intracellular nuclear receptors**. - They primarily regulate gene transcription and do not utilize **cGMP** as a second messenger. *Growth hormone* - **Growth hormone** binds to a **cytokine receptor** that activates the **JAK/STAT signaling pathway**. - Its downstream effects do not involve **cGMP** as a primary second messenger.

Q: After a meal rich in carbohydrate, insulin secretion is stimulated by

GLP-1 (7-36) amide. ***GLP-1 (7-36) amide*** - **Glucagon-like peptide-1 (GLP-1)** is an **incretin hormone** secreted from the small intestine in response to nutrient ingestion, especially carbohydrates. - GLP-1 (7-36) amide **stimulates insulin secretion** in a glucose-dependent manner and also **inhibits glucagon secretion**, thereby lowering blood glucose levels after a meal. *CCK* - **Cholecystokinin (CCK)** is a gastrointestinal hormone primarily stimulated by fat and protein in the duodenum. - Its main roles are to **stimulate pancreatic enzyme secretion** and **gallbladder contraction**, not directly insulin secretion. *VIP* - **Vasoactive intestinal peptide (VIP)** is a neuropeptide that relaxes smooth muscle in the gut, **stimulates intestinal fluid and electrolyte secretion**, and increases blood flow. - While it has some effects on metabolism, it is not a primary stimulator of post-meal insulin secretion. *Serotonin* - **Serotonin (5-hydroxytryptamine)** is a neurotransmitter found in the gut and brain, involved in mood, sleep, and gut motility. - It does not directly stimulate insulin secretion after a meal rich in carbohydrates.

Question 1

A major causal factor in some cases of hypogonadism is:

Accepted Answer

Reduced secretion of gonadotropin-releasing hormone (GnRH)

Answer

Excess secretion of testicular activin by Sertoli cells

Answer

Hypersecretion of pituitary LH and FSH as the result of increased GnRH

Answer

Failure of the hypothalamus to respond to testosterone

Question 2

What is the percentage of T4 and T3 released from the thyroid gland?

Accepted Answer

90% T4; 10% T3

Answer

50% T4; 50% T3

Answer

80% T4; 20% T3

Answer

25% T4; 75% T3

Question 3

Which of the following hormones is released from the posterior pituitary?

Accepted Answer

Antidiuretic hormone

Answer

Luteinizing hormone

Answer

Growth hormone

Answer

ACTH

Question 4

All of these cause hyperglycemia except:

Accepted Answer

Insulin

Answer

Catecholamines

Answer

Cortisol

Answer

GH

Question 5

All the following mediate their action using cAMP as second messenger except:

Accepted Answer

Vasopressin

Answer

Glucagon

Answer

Dopamine

Answer

Corticotropin

Question 6

Regarding Ghrelin, which is false?

Accepted Answer

Secreted from oxyntic cells

Answer

Stimulates appetite

Answer

Secretion increased in anorexia

Answer

Increases fat deposition

Question 7

Thyroxine causes all the following except:

Accepted Answer

Decreased cell metabolism

Answer

Increased basal metabolism

Answer

Increased pulmonary ventilation

Answer

Increased oxygen consumption

Question 8

Which of the following hormones uses cell surface receptors?

Accepted Answer

Glucagon

Answer

Thyroxine

Answer

Cortisol

Answer

Testosterone

Question 9

Which of the following hormones uses cGMP as a second messenger?

Accepted Answer

Atrial natriuretic peptide (ANP)

Answer

Insulin

Answer

Thyroxine

Answer

Growth hormone

Question 10

After a meal rich in carbohydrate, insulin secretion is stimulated by

Accepted Answer

GLP-1 (7-36) amide

Answer

CCK

Answer

VIP

Answer

Serotonin

Endocrinology — MCQs

Endocrinology — MCQs

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