Endocrinology Practice Questions

Q: Which hormone is primarily responsible for lowering blood glucose levels and is most critical in glucose homeostasis?

Insulin. ***Insulin*** - **Insulin** is a peptide hormone produced by the **beta cells of the pancreatic islets** that plays the most critical role in **lowering blood glucose levels**. - It is the **only hormone that decreases blood glucose** by facilitating the uptake of **glucose into cells from the blood**, promoting its storage as **glycogen in the liver and muscles** and conversion into fat. - **Insulin deficiency or resistance** leads to **diabetes mellitus**, the most common disorder of glucose homeostasis, highlighting its primary importance. - While multiple hormones can raise glucose (glucagon, cortisol, epinephrine, growth hormone), **only insulin lowers it**, making it the primary regulator. *Glucagon* - **Glucagon** is produced by the **pancreatic alpha cells** and acts as the primary **counter-regulatory hormone** to insulin. - Its role is to **raise blood glucose levels** by stimulating **glycogenolysis** (breakdown of glycogen) and **gluconeogenesis** (synthesis of glucose) in the liver. - While equally important in glucose homeostasis, it is not the "primary" regulator since multiple other hormones can also raise glucose. *Cortisol* - **Cortisol** is a **steroid hormone** produced by the **adrenal cortex** involved in the stress response and chronic metabolic regulation. - It **increases blood glucose levels** by promoting **gluconeogenesis** and reducing glucose uptake in some tissues, but acts over longer time periods. - Its role is secondary to insulin and glucagon in acute glucose regulation. *Epinephrine* - **Epinephrine** (adrenaline) is a **catecholamine hormone** produced by the **adrenal medulla** in response to acute stress. - It rapidly **increases blood glucose levels** by promoting **glycogenolysis** in the liver and muscle as part of the "fight or flight" response. - Its effect is typically short-lived and situational, not involved in basal glucose regulation.

Q: Hyperpigmentation is seen with which hormone?

ACTH. ***ACTH*** - In conditions like **Addison's disease**, the adrenal glands' inability to produce cortisol leads to increased **ACTH** (adrenocorticotropic hormone) secretion due to a lack of negative feedback [3], [4]. - ACTH is derived from proopiomelanocortin (POMC), which also gives rise to alpha-melanocyte-stimulating hormone (α-MSH). Elevated ACTH levels can thus stimulate melanocytes, causing **hyperpigmentation** in skin folds, buccal mucosa, and pressure points [4]. *FSH* - **FSH** (follicle-stimulating hormone) primarily regulates the development of **follicles in the ovaries** and sperm production in the testes [1]. - There is no known direct association between excessive FSH levels and **hyperpigmentation**. *TSH* - **TSH** (thyroid-stimulating hormone) stimulates the **thyroid gland** to produce thyroid hormones (T3 and T4) [1]. - While thyroid disorders can affect skin texture and moisture, there is no direct link between elevated TSH and **hyperpigmentation**. *LH* - **LH** (luteinizing hormone) plays a key role in **ovulation** in females and testosterone production in males [2]. - High LH levels are not associated with **hyperpigmentation**.

Q: Which of the following cell types is considered insulin-dependent?

Myocytes. ***Myocytes*** - **Myocytes** (skeletal muscle cells) are **insulin-dependent** and represent the **largest site of insulin-mediated glucose disposal** in the body - Insulin promotes translocation of **GLUT4 transporters** to the cell membrane, enabling glucose uptake - Skeletal muscle accounts for approximately **70-80% of postprandial glucose disposal**, making it the most quantitatively significant insulin-dependent tissue *Adipocytes* - **Adipocytes** (fat cells) are also **insulin-dependent** and utilize **GLUT4 transporters** for glucose uptake - Insulin stimulates glucose uptake and conversion to triglycerides for storage - However, adipose tissue accounts for only **10-15% of glucose disposal**, making it less quantitatively significant than skeletal muscle - Both myocytes and adipocytes are considered the two major insulin-dependent tissues in the body *Pituitocytes* - **Pituitocytes** are supporting cells in the pituitary gland - They use **insulin-independent glucose transporters** (GLUT1/GLUT3) - The pituitary gland requires constant glucose supply independent of insulin status *RBCs* - **Red blood cells** lack mitochondria and depend entirely on **anaerobic glycolysis** - Glucose uptake occurs via **insulin-independent GLUT1 transporters** - RBCs must maintain glucose uptake at all times, regardless of insulin levels

Q: What is the nature of the relationship between insulin and glucose concentration in the human body?

Sigmoidal. ***Sigmoidal*** - The relationship between insulin and glucose concentration is best described as **sigmoidal**, characterized by a slow initial rise in insulin secretion at low glucose levels, followed by a steep increase at physiological glucose concentrations, and then a plateau at very high glucose levels. - This shape reflects the **beta cell's sensitivity to glucose**, where a minimal threshold of glucose is required to trigger insulin release, and then a maximal release capacity is reached. *Linear* - A **linear relationship** would imply that for every unit increase in glucose, there is a constant, proportional increase in insulin secretion, which is not physiologically accurate. - While insulin secretion does increase with glucose, the rate of increase varies significantly across different glucose concentrations. *Hyperbola* - A **hyperbolic relationship** typically suggests a rapid initial response that then gradually plateaus, often seen in enzyme kinetics. - While there is a plateau in insulin secretion at high glucose levels, the initial phase is not as rapid or proportionally inverse as a hyperbolic function would suggest. *Bell Shaped* - A **bell-shaped curve** describes a relationship where there is an optimal point, and deviations in either direction lead to a decrease in the response (e.g., enzyme activity vs. pH). - This is not characteristic of insulin secretion, as insulin levels generally continue to rise or plateau at higher glucose concentrations and do not decrease beyond an optimal point.

Q: Somatomedin-C deficiency causes?

Growth retardation. ***Growth retardation*** - **Somatomedin-C** (also known as **Insulin-like Growth Factor 1 or IGF-1**) is a crucial mediator of **growth hormone's** effects on growth. - A deficiency in Somatomedin-C, therefore, directly leads to **impaired growth** and **stature**, manifesting as **growth retardation**. *Genetic dwarfism* - This term generally refers to dwarfism caused by various **genetic conditions** (e.g., achondroplasia), which may or may not involve the **growth hormone/IGF-1 axis**. - While Somatomedin-C deficiency can be genetic, "genetic dwarfism" is a broader term and not the most precise answer for the direct consequence. *Congenital hypothyroidism* - This condition results from **deficient thyroid hormone production** from birth. - It leads to neurological impairment and **growth failure**, but it is due to **thyroid hormone deficiency**, not Somatomedin-C deficiency. *Type 1 diabetes mellitus* - This is an **autoimmune disease** characterized by the **destruction of pancreatic beta cells**, leading to **insulin deficiency**. - It is entirely unrelated to **Somatomedin-C** or the growth hormone axis.

Q: Which of the following statements about insulin-mediated transport of glucose is correct?

Seen in adipose tissue. ***Seen in adipose tissue*** - **Adipose tissue** and **skeletal muscle** are the primary sites where glucose uptake from the bloodstream is significantly enhanced by insulin. - Insulin stimulates the translocation of **GLUT4 transporters** to the cell membrane in these tissues, increasing glucose entry. *Occurs primarily in the brain* - Glucose uptake into the **brain** is largely **insulin-independent**, primarily mediated by **GLUT1** and **GLUT3 transporters**. - The brain requires a constant supply of glucose and does not rely on insulin to facilitate its entry. *Via GLUT-2* - **GLUT2** is a **low-affinity, high-capacity** glucose transporter primarily found in the **liver**, **pancreatic beta cells**, kidneys, and small intestine. - It allows for rapid equilibration of glucose across membranes but is not directly involved in the **insulin-mediated uptake** seen in peripheral tissues. *Main mechanism in RBCs* - **Red blood cells (RBCs)** primarily use **GLUT1** for glucose transport, which is an **insulin-independent** process. - RBCs do not contain mitochondria and rely on glycolysis for energy, so they require a continuous, insulin-independent supply of glucose.

Q: Intestinal absorption of calcium is mainly increased by?

Calcitriol. ***Calcitriol*** - **Calcitriol** (1,25-dihydroxyvitamin D3) is the hormonally active form of vitamin D, which is essential for increasing **calcium absorption** from the intestines. - It stimulates the synthesis of **calcium-binding proteins** in intestinal epithelial cells, facilitating active transport of calcium. *Parathormone* - **Parathormone (PTH)** primarily regulates calcium by increasing its reabsorption in the **kidneys** and stimulating its release from **bones**. - While it indirectly promotes calcitriol synthesis, its *direct* effect on intestinal calcium absorption is minimal compared to calcitriol. *Glucocorticoids* - **Glucocorticoids** generally have an *inhibitory* effect on calcium absorption in the intestine and can also increase renal excretion of calcium. - Prolonged use can lead to **osteoporosis** due to their negative impact on bone formation and calcium balance. *ACTH* - **ACTH (adrenocorticotropic hormone)** primarily stimulates the adrenal cortex to produce **cortisol** and other glucocorticoids. - It has **no direct role** in regulating calcium absorption from the intestines.

Q: What is the half-life of the thyroid hormone triiodothyronine (T3)?

1 day. ***1 day*** - The **half-life of T3 (triiodothyronine)** is approximately **1 day (24 hours)**, making its biological effects relatively rapid compared to T4. - This shorter half-life contributes to its quicker onset and offset of action. *8 hours* - While reflecting a relatively short duration, **8 hours** is not the accepted half-life for T3. - This value is too short for T3, which has a more sustained biological effect. *6 hours* - A half-life of **6 hours** is too short for T3, which has a more sustained effect than such a rapid clearance would suggest. - This would imply a much faster metabolic turnover than observed clinically. *10 days* - **10 days** is longer than the actual **half-life of T4 (thyroxine)**, which is approximately **7 days**. - T4 serves as a prohormone and is more extensively protein-bound, contributing to its prolonged presence in circulation compared to T3.

Q: Which of the following does not stimulate growth hormone (GH) release?

Free fatty acids. ***Free fatty acids*** - High levels of **free fatty acids** in the bloodstream inhibit growth hormone (GH) secretion. - This occurs through a **negative feedback loop** at the level of the hypothalamus and pituitary gland. *Fasting* - **Fasting** (especially prolonged) is a potent stimulus for GH release, helping to mobilize fat stores and maintain **glucose homeostasis**. - During fasting, ghrelin levels increase, which further promotes GH secretion. *Exercise* - **Physical exercise** is a well-known physiological stimulus for GH release, contributing to muscle growth and repair. - The intensity and duration of exercise can influence the magnitude of GH secretion. *Stress* - Various forms of **stress**, including physical (e.g., trauma, surgery) and psychological stress, stimulate GH release. - This response is mediated in part by the **sympathetic nervous system** and increased cortisol levels.

Q: Which of the following hormones is not stored in cells?

Cortisol. ***Cortisol*** - Cortisol is a **steroid hormone** that is synthesized from **cholesterol** on demand and is **not stored** in secretory vesicles or elsewhere within cells. - Being **lipophilic**, it diffuses freely across cell membranes immediately after synthesis. - Its release is regulated by the **hypothalamic-pituitary-adrenal (HPA) axis**, with synthesis and immediate secretion occurring upon stimulation. *Insulin* - Insulin is a **peptide hormone** synthesized as **proinsulin** and then cleaved into active insulin. - It is **stored in secretory granules** within pancreatic beta cells, allowing for rapid release in response to elevated blood glucose. *Thyroxine* - Thyroxine (T4) is a **thyroid hormone** that is synthesized from tyrosine and iodine. - It is **stored extracellularly** within the thyroid gland's follicles as part of a large protein called **thyroglobulin**. - Unlike cortisol (which is never stored), thyroxine has a **substantial storage pool** that can last weeks, though the storage is extracellular rather than intracellular. *Renin* - Renin is an **enzyme** produced by the **juxtaglomerular cells** of the kidney. - It is **stored in secretory granules** within these cells and released in response to decreased renal perfusion pressure or sympathetic stimulation.

Question 1

Which hormone is primarily responsible for lowering blood glucose levels and is most critical in glucose homeostasis?

Accepted Answer

Insulin

Answer

Epinephrine

Answer

Glucagon

Answer

Cortisol

Question 2

Hyperpigmentation is seen with which hormone?

Accepted Answer

ACTH

Answer

TSH

Answer

FSH

Answer

LH

Question 3

Which of the following cell types is considered insulin-dependent?

Accepted Answer

Myocytes

Answer

Pituitocytes

Answer

Adipocytes

Answer

RBCs

Question 4

What is the nature of the relationship between insulin and glucose concentration in the human body?

Accepted Answer

Sigmoidal

Answer

Linear

Answer

Hyperbola

Answer

Bell Shaped

Question 5

Somatomedin-C deficiency causes?

Accepted Answer

Growth retardation

Answer

Genetic dwarfism

Answer

Congenital hypothyroidism

Answer

Type 1 diabetes mellitus

Question 6

Which of the following statements about insulin-mediated transport of glucose is correct?

Accepted Answer

Seen in adipose tissue

Answer

Via GLUT-2

Answer

Main mechanism in RBCs

Answer

Occurs primarily in the brain

Question 7

Intestinal absorption of calcium is mainly increased by?

Accepted Answer

Calcitriol

Answer

Parathormone

Answer

Glucocorticoids

Answer

ACTH

Question 8

What is the half-life of the thyroid hormone triiodothyronine (T3)?

Accepted Answer

1 day

Answer

8 hours

Answer

6 hours

Answer

10 days

Question 9

Which of the following does not stimulate growth hormone (GH) release?

Accepted Answer

Free fatty acids

Answer

Exercise

Answer

Fasting

Answer

Stress

Question 10

Which of the following hormones is not stored in cells?

Accepted Answer

Cortisol

Answer

Thyroxin

Answer

Renin

Answer

Insulin

Endocrinology — MCQs

Endocrinology — MCQs

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