Endocrinology Practice Questions

Q: Insulin acts through which receptor?

Enzyme-linked. ***Enzyme-linked*** - Insulin binds to an **enzyme-linked receptor**, specifically a **receptor tyrosine kinase**, to initiate its cellular effects. - Upon binding, the receptor undergoes **autophosphorylation** and then phosphorylates intracellular substrate proteins, leading to a cascade of metabolic actions. *GPCR* - **G protein-coupled receptors (GPCRs)** are integral membrane proteins that, upon ligand binding, activate intracellular G proteins, transmitting signals through second messengers. - Hormones like **glucagon** and **epinephrine** commonly act via GPCRs, not insulin. *Intracellular* - **Intracellular receptors** are typically found in the cytoplasm or nucleus and are activated by small, lipid-soluble ligands that can pass through the cell membrane, such as **steroid hormones**. - Insulin is a large peptide hormone and cannot readily cross the cell membrane to act on intracellular receptors. *Ion channel* - **Ion channel receptors** are transmembrane proteins that open or close an ion channel in response to ligand binding, leading to changes in membrane potential or ion concentration. - Neurotransmitters like **acetylcholine** often act on ligand-gated ion channels, which is not the mechanism of action for insulin.

Q: In premenopausal obese patients, which hormone is primarily formed from the peripheral conversion of androgen precursors?

Estrone (E1). **Estrone (E1)** - **Estrone** is the primary estrogen produced by the peripheral conversion of **androstenedione** in the adipose tissue of premenopausal obese women. - This conversion is facilitated by the enzyme **aromatase**, which is abundant in fat cells. *Estriol (E3)* - **Estriol** is mainly produced by the **placenta** during pregnancy and is largely considered a marker of fetal well-being. - It is a weak estrogen and is not primarily formed from peripheral conversion in non-pregnant individuals. *Estradiol (E2)* - **Estradiol** is the most potent and abundant estrogen during the reproductive years, primarily produced by the **ovaries**. - While some peripheral conversion can occur, it is not the primary estrogen formed from precursors in obese premenopausal patients. *Androgen precursor* - **Androgen precursors** (like androstenedione) are the *substrates* for estrogen production, not the estrogen itself. - These precursors are converted into estrogens, particularly estrone, in peripheral tissues.

Q: In hypoglycemia, which hormone does not increase?

Insulin. ***Correct Answer: Insulin*** - In hypoglycemia (low blood glucose), the primary goal of the body is to **raise blood glucose levels** - **Insulin** acts to lower blood glucose by promoting glucose uptake into cells - Therefore, insulin secretion is **decreased, not increased**, during hypoglycemia - This makes insulin the hormone that does NOT increase in response to hypoglycemia *Incorrect: Cortisol* - **Cortisol** is a stress hormone released during hypoglycemia - Helps **increase glucose production** through gluconeogenesis - Decreases glucose utilization by peripheral tissues - Its levels **increase** during hypoglycemic events *Incorrect: Glucagon* - **Glucagon** is the primary counter-regulatory hormone for hypoglycemia - Stimulates the liver to release stored glucose through **glycogenolysis** and **gluconeogenesis** - Its secretion **markedly increases** in response to low blood glucose - Works opposite to insulin *Incorrect: Epinephrine* - **Epinephrine** (adrenaline) is released from the adrenal medulla during hypoglycemia - Key component of **glucose counterregulation** - Increases blood glucose by promoting **glycogenolysis** and **gluconeogenesis** - Also inhibits insulin secretion and glucose uptake by peripheral tissues

Q: Calcium levels in blood are increased by:

Parathormone. ***Parathormone*** - **Parathormone (PTH)** increases blood calcium levels by stimulating **osteoclast activity**, leading to bone resorption [1]. - It also enhances **calcium reabsorption** in the kidneys and promotes the production of **calcitriol** (active vitamin D), which increases intestinal calcium absorption [1], [2]. *Calcitonin* - **Calcitonin** is a hormone that **decreases blood calcium levels** by inhibiting osteoclast activity and promoting calcium deposition in bones. - It counteracts the effects of parathormone. *Insulin* - **Insulin** primarily regulates **blood glucose levels** by facilitating glucose uptake into cells. - It does not have a direct role in the regulation of blood calcium. *TNF alpha* - **TNF-alpha (Tumor Necrosis Factor-alpha)** is a **cytokine** involved in inflammation and immune responses. - While it can indirectly affect bone metabolism in chronic inflammatory conditions, it is not a primary regulator of acute blood calcium levels.

Q: During fetal life, maximum growth is caused by:

Insulin. ***Insulin*** - **Insulin** is a major anabolic hormone in fetal life, primarily responsible for regulating nutrient uptake and utilization, leading to **growth and deposition of fat and glycogen**. - High levels of available nutrients from the mother stimulate fetal insulin production, which then promotes **cellular proliferation and growth**. *Growth hormone* - While essential for postnatal growth, **growth hormone** plays a relatively minor role in **fetal growth and development**. - Its effects on growth become more prominent after birth, especially during childhood and adolescence. *Cortisol* - **Cortisol** is crucial for **fetal lung maturation** and the development of other organ systems, but it generally has an **inhibitory effect on growth** rather than promoting it. - Excessive cortisol exposure in utero can lead to intrauterine growth restriction. *Thyroxine* - **Thyroid hormones (thyroxine)** are vital for normal **fetal brain development** and skeletal maturation. - However, they are **not the primary driver of overall fetal growth** in terms of size and weight gain, unlike insulin.

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

Stimulates appetite. ***Stimulates appetite*** - **Ghrelin** is often referred to as the "hunger hormone" because its primary function is to **stimulate appetite** and increase food intake. - It acts on the **hypothalamus**, particularly the arcuate nucleus, to activate NPY/AgRP neurons that promote feelings of hunger. - Ghrelin levels rise before meals and fall after eating, making it a key regulator of meal initiation. *Promotes lipolysis* - **Ghrelin** primarily promotes **lipogenesis** (fat synthesis) and fat storage, rather than lipolysis (the breakdown of fats). - It increases adiposity and reduces fat utilization, which is opposite to promoting lipolysis. - Its role is to prepare the body for energy intake and storage. *Secreted from ghrelinergic cells of fundus* - This statement is actually **largely correct** but not the best answer as it's anatomically specific rather than functional. - **Ghrelin** is predominantly secreted by **X/A-like cells** (also called ghrelin cells or P/D1 cells) located mainly in the **gastric fundus**. - The term "ghrelinergic cells" appropriately describes these ghrelin-producing enteroendocrine cells. - However, the primary distinguishing feature of ghrelin is its appetite-stimulating function rather than its anatomical source. *Secreted by beta cells of pancreas* - This is **incorrect**. Beta cells of the pancreas secrete **insulin**, not ghrelin. - Ghrelin is produced primarily in the **stomach** (fundus), with smaller amounts from the small intestine, pancreas (epsilon cells, not beta cells), and other tissues.

Q: Which of the following statements about the hormone leptin is false?

It is produced by the pancreas.. ***It is produced by the pancreas.*** - Leptin is primarily produced by **adipose tissue (fat cells)**, not the pancreas. - The pancreas produces hormones like **insulin** and **glucagon**, which regulate blood glucose. *It is produced by adipose tissue.* - This statement is **true**; white adipose tissue is the main site of **leptin synthesis** and secretion. - Leptin acts as an **adipokine**, signaling energy stores to the brain. *It decreases appetite.* - This statement is **true**; leptin acts on the **hypothalamus** to reduce hunger and inhibit food intake. - It plays a crucial role in long-term **energy homeostasis**. *It is found in increased levels in obese individuals.* - This statement is **true**; increased adipose tissue in obese individuals leads to higher leptin production. - However, obese individuals often experience **leptin resistance**, meaning their brains do not respond appropriately to the high leptin levels.

Q: All these hormones primarily use cyclic adenosine monophosphate (cAMP) as their main second messenger pathway, except:

Dopamine. ***Dopamine*** - **Dopamine** has dual signaling mechanisms depending on receptor subtype, making it unique among the listed hormones. - **D1-like receptors** (D1, D5) couple to Gs proteins and **increase cAMP** levels. - **D2-like receptors** (D2, D3, D4) couple to Gi proteins and **decrease/inhibit cAMP** production. - Since dopamine's effects are mediated through both cAMP-increasing and cAMP-decreasing pathways with significant physiological roles for both, it does **not primarily use cAMP** as a straightforward second messenger like the other hormones listed. - Therefore, dopamine is the exception as it has mixed cAMP signaling rather than primarily activating the cAMP pathway. *Corticotropin (ACTH)* - **Corticotropin** (ACTH) binds to melanocortin-2 receptors (MC2R) on the adrenal cortex and **primarily utilizes the cAMP pathway**. - Activation of adenylyl cyclase leads to increased intracellular cAMP, which activates protein kinase A (PKA). - This stimulates the synthesis and release of glucocorticoids (primarily cortisol). *Glucagon* - **Glucagon** binds to its G-protein coupled receptors on hepatocytes, leading to activation of adenylyl cyclase and increased intracellular **cAMP**. - The cAMP then activates protein kinase A, mediating glucagon's metabolic effects including **glycogenolysis and gluconeogenesis**. - This is a classic example of cAMP-mediated hormone action. *Vasopressin* - **Vasopressin** (ADH) primarily acts through **V2 receptors** in the renal collecting ducts, which use the **cAMP pathway** to increase water reabsorption (its primary physiological function). - V1 receptors (vasoconstriction) use the IP3/DAG pathway, but this is a secondary effect. - Since vasopressin's main clinical action is via cAMP-mediated V2 receptors, it primarily uses cAMP as its second messenger.

Q: Which of the following binds to intracellular receptors?

Estrogen. ***Estrogen*** - **Estrogen** is a **steroid hormone** that, due to its **lipophilic nature**, can easily pass through the cell membrane to bind to **intracellular receptors** in the cytoplasm or nucleus. - This binding leads to the formation of a **hormone-receptor complex** that acts as a transcription factor, regulating **gene expression**. *Growth hormone* - **Growth hormone** is a **peptide hormone** and therefore **hydrophilic**, meaning it cannot freely cross the cell membrane. - It binds to **transmembrane receptors** on the cell surface, initiating intracellular signaling cascades through pathways like the **JAK/STAT pathway**. *Vitamin E* - **Vitamin E** is a **lipid-soluble vitamin** and an important **antioxidant**, but it does not function as a signaling molecule that binds to intracellular receptors to regulate gene expression in the same manner as steroid hormones. - While it diffuses across membranes due to its lipophilicity, its primary role is to protect cell membranes from **oxidative damage**. *Insulin* - **Insulin** is a **protein hormone** that is **hydrophilic** and cannot pass through the cell membrane. - It binds to **tyrosine kinase receptors** on the cell surface, triggering a cascade of intracellular events like the **PI3K/Akt pathway** to regulate glucose metabolism.

Q: Calcitonin is produced by which organ?

Thyroid. ***Thyroid*** - **Calcitonin** is a hormone primarily produced by the **parafollicular cells** (C cells) of the **thyroid gland**. - Its main function is to lower **blood calcium levels** by inhibiting osteoclast activity and increasing renal calcium excretion. *Pituitary* - The **pituitary gland** produces various hormones that regulate other endocrine glands, but it does not produce calcitonin. - Hormones like **growth hormone**, **TSH**, **ACTH**, and **prolactin** are examples of pituitary secretions. *Pancreas* - The **pancreas** primarily produces hormones such as **insulin** and **glucagon**, which are involved in blood glucose regulation. - It also produces digestive enzymes, but not calcitonin. *Hypothalamus* - The **hypothalamus** is a brain region that links the nervous system to the endocrine system via the pituitary gland. - It produces **releasing and inhibiting hormones** that control pituitary function, but not calcitonin.

Question 1

Insulin acts through which receptor?

Accepted Answer

Enzyme-linked

Answer

GPCR

Answer

Intracellular

Answer

Ion channel

Question 2

In premenopausal obese patients, which hormone is primarily formed from the peripheral conversion of androgen precursors?

Accepted Answer

Estrone (E1)

Answer

Estriol (E3)

Answer

Estradiol (E2)

Answer

Androgen precursor

Question 3

In hypoglycemia, which hormone does not increase?

Accepted Answer

Insulin

Answer

Glucagon

Answer

Epinephrine

Answer

Cortisol

Question 4

Calcium levels in blood are increased by:

Accepted Answer

Parathormone

Answer

Calcitonin

Answer

Insulin

Answer

TNF alpha

Question 5

During fetal life, maximum growth is caused by:

Accepted Answer

Insulin

Answer

Thyroxine

Answer

Growth hormone

Answer

Cortisol

Question 6

Which of the following statements about ghrelin is true?

Accepted Answer

Stimulates appetite

Answer

Promotes lipolysis

Answer

Secreted from ghrelinergic cells of fundus

Answer

Secreted by beta cells of pancreas

Question 7

Which of the following statements about the hormone leptin is false?

Accepted Answer

It is produced by the pancreas.

Answer

It decreases appetite.

Answer

It is produced by adipose tissue.

Answer

It is found in increased levels in obese individuals.

Question 8

All these hormones primarily use cyclic adenosine monophosphate (cAMP) as their main second messenger pathway, except:

Accepted Answer

Dopamine

Answer

Glucagon

Answer

vasopressin

Answer

Corticotropin

Question 9

Which of the following binds to intracellular receptors?

Accepted Answer

Estrogen

Answer

Growth hormone

Answer

Vitamin E

Answer

Insulin

Question 10

Calcitonin is produced by which organ?

Accepted Answer

Thyroid

Answer

Pituitary

Answer

Pancreas

Answer

Hypothalamus

Endocrinology — MCQs

Endocrinology — MCQs

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