Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 801: Which hormone is primarily responsible for lowering blood glucose levels and is most critical in glucose homeostasis?

A. Epinephrine
B. Insulin (Correct Answer)
C. Glucagon
D. Cortisol

Explanation: ***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.

Question 802: Which of the following statements about insulin-mediated transport of glucose is correct?

A. Via GLUT-2
B. Main mechanism in RBCs
C. Seen in adipose tissue (Correct Answer)
D. Occurs primarily in the brain

Explanation: ***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.

Question 803: Somatomedin-C deficiency causes?

A. Growth retardation (Correct Answer)
B. Genetic dwarfism
C. Congenital hypothyroidism
D. Type 1 diabetes mellitus

Explanation: ***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.

Question 804: What is the nature of the relationship between insulin and glucose concentration in the human body?

A. Linear
B. Hyperbola
C. Sigmoidal (Correct Answer)
D. Bell Shaped

Explanation: ***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.

Question 805: Intestinal absorption of calcium is mainly increased by?

A. Calcitriol (Correct Answer)
B. Parathormone
C. Glucocorticoids
D. ACTH

Explanation: ***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.

Question 806: Which of the following actions of growth hormone (GH) is primarily mediated by insulin-like growth factor 1 (IGF-1)?

A. Lipolysis
B. Sodium retention
C. Linear growth and bone development (Correct Answer)
D. Insulin resistance

Explanation: ***Linear growth and bone development*** - **IGF-1 (Somatomedin C)** is the primary mediator of growth hormone's effects on **linear growth and skeletal development** - IGF-1 is produced primarily in the liver in response to GH stimulation - Acts on **epiphyseal growth plates** to promote chondrocyte proliferation and differentiation - Mediates **protein synthesis, muscle growth, and bone mineralization** - This represents the classic **somatomedin hypothesis** - GH stimulates IGF-1 production, which then mediates growth effects *Lipolysis* - Growth hormone **directly** promotes lipolysis through GH receptors on adipocytes - This leads to breakdown of triglycerides into free fatty acids and glycerol - This is a **direct metabolic effect** of GH, independent of IGF-1 *Insulin resistance* - GH **directly** induces insulin resistance through its own receptors - This is one of the **diabetogenic effects** of GH - While IGF-1 can influence insulin sensitivity, insulin resistance is primarily a **direct GH effect** *Sodium retention* - GH has **direct effects** on renal tubules to promote sodium and water retention - This antinatriuretic effect occurs through GH receptors in the kidney - Not primarily mediated by IGF-1

Question 807: Which hormone acts on JAK-STAT kinase receptor?

A. TSH
B. Thyroxine
C. GH (Correct Answer)
D. FSH

Explanation: ***GH*** - **Growth Hormone (GH)** binds to a **cytokine receptor** that lacks intrinsic tyrosine kinase activity and instead signals through associated **JAK-STAT kinases**. - This binding leads to **JAK phosphorylation**, which then phosphorylates and activates **STAT proteins**, regulating gene expression. *TSH* - **Thyroid-stimulating hormone (TSH)** acts on a **G protein-coupled receptor** to stimulate thyroid hormone production and release. - Its signaling pathway primarily involves the activation of **adenylyl cyclase** and increases in **cAMP**, not the JAK-STAT pathway. *Thyroxine* - **Thyroxine (T4)** is a **thyroid hormone** that primarily acts by binding to **intracellular nuclear receptors**, which then regulate gene transcription. - It directly influences gene expression, rather than signaling through cell surface receptors and kinase pathways like JAK-STAT. *FSH* - **Follicle-stimulating hormone (FSH)**, like TSH, signals through a **G protein-coupled receptor** on target cells in the gonads. - This activation primarily leads to an increase in **intracellular cAMP levels** to mediate its effects on gamete production and hormone synthesis.

Question 808: Which of the following does not stimulate growth hormone (GH) release?

A. Exercise
B. Free fatty acids (Correct Answer)
C. Fasting
D. Stress

Explanation: ***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.

Question 809: Which hormone increases with age?

A. GH
B. Prolactin
C. Parathormone (Correct Answer)
D. Insulin

Explanation: ***Parathormone*** - **Parathormone (PTH)** levels in the blood tend to increase with age, often due to a decline in renal function and reduced vitamin D synthesis, leading to compensatory hyperparathyroidism. - This age-related increase in PTH can contribute to **bone demineralization** and an increased risk of osteoporosis. *GH* - **Growth hormone (GH)** levels generally **decrease with age**, leading to a condition known as somatopause. - Reduced GH contributes to changes in body composition, such as increased adiposity and decreased lean muscle mass, as well as reduced bone density. *Prolactin* - **Prolactin** levels typically remain relatively stable or may slightly decrease with age in men, while in women they can fluctuate due to hormonal changes like menopause but do not show a consistent increase with age. - High prolactin levels are often associated with specific pathological conditions like **prolactinomas** rather than normal aging. *Insulin* - While **insulin resistance** often increases with age, leading to higher fasting insulin levels in some individuals, the overall picture of insulin secretion can be complex and is often influenced by factors such as diet, exercise, and genetics rather than solely age. - A *decline in pancreatic beta-cell function* with age can also lead to impaired insulin secretion in some elderly individuals, complicating the simple relationship between age and insulin levels.

Question 810: During starvation, which hormone level increases?

A. Leptin
B. MSH
C. Insulin
D. Ghrelin (Correct Answer)

Explanation: ***Ghrelin*** - **Ghrelin** is often referred to as the "hunger hormone" because its levels typically rise during fasting or periods of starvation. - It stimulates **appetite** and signals the brain to increase food intake, playing a crucial role in energy balance. *Leptin* - **Leptin** is a hormone produced by **adipose tissue** that signals satiety and helps regulate long-term energy balance. - During starvation, **leptin levels typically decrease** as fat stores are depleted, which further increases appetite and reduces energy expenditure. *MSH* - **Melanocyte-stimulating hormone (MSH)** is involved in skin pigmentation and appetite regulation, but its levels do not primarily increase in response to starvation. - While MSH can influence appetite, it is often seen to decrease appetite when present in higher concentrations, which is counterintuitive during starvation. *Insulin* - **Insulin** is a hormone produced by the **pancreas** that helps regulate blood glucose levels by promoting glucose uptake into cells. - During starvation, blood glucose levels decrease, leading to a **reduction in insulin secretion** to preserve glucose for vital organs like the brain.

Practice by Chapter

Principles of Endocrine Regulation

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Hypothalamus and Pituitary Gland

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Thyroid Physiology

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Adrenal Cortex and Medulla

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Pancreatic Hormones and Glucose Metabolism

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Calcium and Phosphate Homeostasis

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Growth Hormone and Growth Factors

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Endocrine Regulation of Metabolism

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Hormone Receptors and Signaling

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Assessment of Endocrine Function

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