Endocrinology Practice Questions

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.

Q: All the following hormones have receptors on the plasma membrane of target tissues except:

Estradiol. ***Estradiol*** - **Estradiol** is a **steroid hormone** derived from cholesterol, making it **lipid-soluble**. - Due to its lipid solubility, estradiol can readily pass through the **plasma membrane** and bind to **intracellular receptors** in the cytoplasm or nucleus. *Epinephrine* - **Epinephrine** is a **catecholamine hormone** and is **water-soluble**. - Water-soluble hormones cannot cross the lipid bilayer of the plasma membrane and thus bind to **receptors located on the cell surface**. *Glucagon* - **Glucagon** is a **peptide hormone** and is **water-soluble**. - Like other peptide hormones, it binds to **specific receptors embedded in the plasma membrane** to elicit its cellular effects via second messenger systems. *Thyrotropin* - **Thyrotropin**, also known as **Thyroid-Stimulating Hormone (TSH)**, is a **glycoprotein hormone** and is **water-soluble**. - TSH exerts its action by binding to **receptors on the plasma membrane** of thyroid follicular cells.

Q: Estradiol is a powerful inhibitor of FSH (follicle stimulating hormone). What is another factor that is a powerful inhibitor of FSH in the female?

Inhibin. ***Inhibin*** - **Inhibin** is a glycoprotein hormone primarily produced by the **granulosa cells** of the ovarian follicles. - It selectively inhibits the secretion of **FSH** from the anterior pituitary, providing negative feedback without significantly affecting LH. *LH* - **Luteinizing hormone (LH)** is primarily involved in stimulating ovulation and the production of progesterone, not directly inhibiting FSH. - While LH and FSH levels are intricately linked in the menstrual cycle, LH does not act as a primary inhibitor of FSH. *Testosterone* - **Testosterone** is an androgen primarily found at much lower levels in females compared to males and does not serve as a primary inhibitor of FSH in the female reproductive axis. - While androgens can influence follicular development, they are not a direct and potent inhibitor of FSH secretion. *Progesterone* - **Progesterone** is mainly involved in preparing the uterus for pregnancy and maintaining it, and it provides negative feedback on both LH and FSH, but its primary effect is often associated with LH suppression and the overall luteal phase regulation rather than specific, potent FSH inhibition like inhibin. - High levels of progesterone during the luteal phase do inhibit GnRH, which in turn reduces FSH and LH, but inhibin specifically targets FSH.

Q: In hypoparathyroidism:

Plasma calcium is low and inorganic phosphorous high. ***Plasma calcium is low and inorganic phosphorous high*** - **Hypoparathyroidism** is characterized by insufficient parathyroid hormone (PTH) production, leading to decreased bone resorption and reduced renal reabsorption of calcium [1]. This results in **hypocalcemia** (low plasma calcium) [1]. - PTH also promotes renal excretion of phosphate [2]. With insufficient PTH, renal phosphate excretion is impaired, leading to **hyperphosphatemia** (high inorganic phosphorus) [1]. *Plasma calcium is high and inorganic phosphorous low* - This profile is characteristic of **primary hyperparathyroidism**, where excessive PTH causes increased bone resorption and renal calcium reabsorption (high calcium), and increased renal phosphate excretion (low phosphorus). - It directly contradicts the defining features of hypoparathyroidism [1]. *Plasma calcium and inorganic phosphorous are low* - While plasma calcium is low in hypoparathyroidism, plasma inorganic phosphorus is characteristically high, not low [1]. - A combination of low calcium and low phosphorus can be seen in conditions like **vitamin D deficiency** (osteomalacia), but not directly in pure hypoparathyroidism [1]. *Plasma calcium and inorganic phosphorous are high* - This combination of high calcium and high phosphorus is uncommon and not typically seen in either hypoparathyroidism or hyperparathyroidism. - It could potentially indicate conditions like **milk-alkali syndrome** or **vitamin D intoxication**, but not hypoparathyroidism, which is defined by low calcium [1].

Q: Which of the following is a calorigenic hormone?

All of the options. ***All of the options*** - **Norepinephrine**, **epinephrine**, and **thyroid hormones** all increase the **basal metabolic rate** and **heat production**, classifying them as calorigenic. - These hormones stimulate cellular metabolism, leading to increased **oxygen consumption** and **ATP hydrolysis**, which generates heat. *Norepinephrine* - **Norepinephrine** promotes increased **thermogenesis** through its effects on various tissues, particularly brown adipose tissue. - It enhances the breakdown of **fat stores** and **glucose** to generate heat, contributing to the body's overall energy expenditure. *Epinephrine* - **Epinephrine** rapidly increases the **metabolic rate** and heat production during stress or exercise through its beta-adrenergic effects. - It stimulates **glycogenolysis** and **lipolysis**, providing substrates for energy production and subsequent heat generation. *Thyroid hormones* - **Thyroid hormones** (T3 and T4) are major regulators of the **basal metabolic rate** in nearly all body tissues. - They increase the activity of the **Na+/K+ ATPase pump** and mitochondrial oxidative phosphorylation, both of which are significant sources of heat.

Question 1

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

Accepted Answer

Vasopressin

Answer

Glucagon

Answer

Dopamine

Answer

Corticotropin

Question 2

Regarding Ghrelin, which is false?

Accepted Answer

Secreted from oxyntic cells

Answer

Stimulates appetite

Answer

Secretion increased in anorexia

Answer

Increases fat deposition

Question 3

Thyroxine causes all the following except:

Accepted Answer

Decreased cell metabolism

Answer

Increased basal metabolism

Answer

Increased pulmonary ventilation

Answer

Increased oxygen consumption

Question 4

Which of the following hormones uses cell surface receptors?

Accepted Answer

Glucagon

Answer

Thyroxine

Answer

Cortisol

Answer

Testosterone

Question 5

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 6

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

Accepted Answer

GLP-1 (7-36) amide

Answer

CCK

Answer

VIP

Answer

Serotonin

Question 7

All the following  hormones have receptors on the plasma membrane of target tissues except:

Accepted Answer

Estradiol

Answer

Epinephrine

Answer

Glucagon

Answer

Thyrotropin

Question 8

Estradiol is a powerful inhibitor of FSH (follicle stimulating hormone). What is another factor that is a powerful inhibitor of FSH in the female?

Accepted Answer

Inhibin

Answer

LH

Answer

Testosterone

Answer

Progesterone

Question 9

In hypoparathyroidism:

Accepted Answer

Plasma calcium is low and inorganic phosphorous high

Answer

Plasma calcium is high and inorganic phosphorous low

Answer

Plasma calcium and inorganic phosphorous are low

Answer

Plasma calcium and inorganic phosphorous are high

Question 10

Which of the following is a calorigenic hormone?

Accepted Answer

All of the options

Answer

Norepinephrine

Answer

Epinephrine

Answer

Thyroid hormones

Endocrinology — MCQs

Endocrinology — MCQs

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