Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 841: Which of the following statements about ghrelin is true?

A. Promotes lipolysis
B. Stimulates appetite (Correct Answer)
C. Secreted from ghrelinergic cells of fundus
D. Secreted by beta cells of pancreas

Explanation: ***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.

Question 842: What is the primary reason puberty typically does not occur before the age of 8 years?

A. The hypothalamus does not secrete GnRH in a pulsatile manner (Correct Answer)
B. Inadequate synthesis of gonadotropins by the pituitary
C. Gonads are unresponsive to gonadotropin
D. Positive feedback action of gonadal steroids on pituitary

Explanation: ***The hypothalamus does not secrete GnRH in a pulsatile manner*** - The onset of puberty is triggered by the **pulsatile secretion of gonadotropin-releasing hormone (GnRH)** from the hypothalamus. - Before age 8, the hypothalamus is **quiescent** and does not release GnRH in the frequent, high-amplitude pulses necessary to stimulate the pituitary and initiate puberty. *Inadequate synthesis of gonadotropins by the pituitary* - The pituitary gland itself is generally capable of synthesizing **gonadotropins (LH and FSH)** before puberty, but it requires stimulation by pulsatile GnRH. - The *primary issue* is the lack of hypothalamic GnRH pulse generation, not an inherent inability of the pituitary to produce gonadotropins in response to appropriate signaling. *Gonads are unresponsive to gonadotropin* - While the gonads are relatively inactive before puberty, they are generally *not unresponsive* to gonadotropins if sufficient levels were present. - The problem lies upstream in the **hypothalamic-pituitary axis**, as inadequate GnRH leads to low gonadotropin levels, which in turn leads to inactive gonads. *Positive feedback action of gonadal steroids on pituitary* - During puberty and adulthood, **gonadal steroids** exert both positive and negative feedback on the hypothalamus and pituitary. - Before puberty, there are typically very low levels of gonadal steroids, and the system is in a state of **negative feedback** (low sensitivity to inhibition) rather than the robust positive feedback seen later in development.

Question 843: Which of the following statements about the hormone leptin is false?

A. It decreases appetite.
B. It is produced by the pancreas. (Correct Answer)
C. It is produced by adipose tissue.
D. It is found in increased levels in obese individuals.

Explanation: ***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.

Question 844: All these hormones primarily use cyclic adenosine monophosphate (cAMP) as their main second messenger pathway, except:

A. Dopamine (Correct Answer)
B. Glucagon
C. vasopressin
D. Corticotropin

Explanation: ***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.

Question 845: Calcitonin is produced by which organ?

A. Thyroid (Correct Answer)
B. Pituitary
C. Pancreas
D. Hypothalamus

Explanation: ***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 846: What is the primary mechanism through which glucose stimulates insulin release?

A. Cyclic AMP signaling
B. Calcium influx (Correct Answer)
C. Insulin receptor activation
D. ATP-sensitive potassium channel activation

Explanation: ***Calcium influx*** - Glucose metabolism in pancreatic beta cells leads to increased **ATP production**, which closes **ATP-sensitive potassium channels**. - This closing causes cell membrane depolarization, opening **voltage-gated calcium channels** and leading to an influx of calcium, triggering insulin granule exocytosis. *Cyclic AMP signaling* - While **cAMP** enhances glucose-stimulated insulin secretion, it is not the primary direct trigger. - cAMP primarily modulates the sensitivity of the exocytotic machinery to calcium. *Insulin receptor activation* - **Insulin receptors** are primarily found on target cells (e.g., muscle, fat, liver) and mediate insulin's metabolic effects, not its release. - Activating insulin receptors on beta cells would typically lead to a negative feedback rather than direct stimulation of insulin release. *ATP-sensitive potassium channel activation* - **Activation** of these channels would lead to hyperpolarization and reduced insulin secretion. - The primary mechanism of glucose-stimulated insulin release involves the **inhibition** (closure) of these channels, not their activation.

Question 847: What hormone is secreted by the delta cells of the pancreas?

A. Gastrin
B. Insulin
C. Cholecystokinin
D. Somatostatin (Correct Answer)

Explanation: ***Somatostatin*** - **Delta cells** (δ cells) of the pancreas are responsible for secreting **somatostatin**. - Somatostatin acts as a general **inhibitory hormone**, suppressing the release of other hormones, including insulin and glucagon, and regulating gastrointestinal function. *Cholecystokinin* - **Cholecystokinin (CCK)** is primarily produced by cells in the **duodenum** and jejunum, not the pancreas. - It stimulates the release of **bile** and **pancreatic enzymes** in response to fats and proteins. *Gastrin* - **Gastrin** is secreted by **G cells** mainly in the **antrum of the stomach**, not the pancreas. - It stimulates the secretion of **gastric acid** and promotes mucosal growth in the stomach. *Insulin* - **Insulin** is secreted by the **beta cells** (β cells) of the pancreatic islets, which are distinct from the delta cells. - Its primary role is to lower blood glucose levels by promoting glucose uptake into cells.

Question 848: Which hormone is primarily synthesized by the supraoptic nucleus of the hypothalamus?

A. Antidiuretic hormone (Correct Answer)
B. Oxytocin
C. Growth hormone
D. Adrenocorticotropic hormone

Explanation: ***Antidiuretic hormone*** - The **supraoptic nucleus** of the hypothalamus is the primary site for the synthesis of **antidiuretic hormone (ADH)**, also known as vasopressin. - Approximately **80% of supraoptic neurons** produce ADH, making it the predominant hormone synthesized by this nucleus. - ADH is crucial for **water reabsorption** in the kidneys, regulating plasma osmolality and blood pressure. *Oxytocin* - While **oxytocin** is also synthesized in the supraoptic nucleus (approximately 20% of neurons), it is produced in much greater quantities by the **paraventricular nucleus**. - The paraventricular nucleus is the **primary source** of oxytocin, which is important for **uterine contractions** during labor and **milk ejection** during lactation. *Growth hormone* - **Growth hormone (GH)** is produced by the **anterior pituitary gland** under the control of **growth hormone-releasing hormone (GHRH)** and **somatostatin** from the hypothalamus. - It is not synthesized by the supraoptic nucleus. *Adrenocorticotropic hormone* - **Adrenocorticotropic hormone (ACTH)** is secreted by the **anterior pituitary gland** in response to **corticotropin-releasing hormone (CRH)** from the hypothalamus. - The supraoptic nucleus is not involved in its synthesis or direct regulation.

Question 849: Which hormone is released when serum calcium levels decrease?

A. Parathormone (Correct Answer)
B. Calcitonin
C. Thyroxine
D. Adrenaline

Explanation: ***Parathormone*** - **Parathormone (PTH)** is released from the **parathyroid glands** in response to **low serum calcium levels**. - Its primary function is to **increase serum calcium** by stimulating bone resorption, increasing renal reabsorption of calcium, and enhancing intestinal absorption of calcium (indirectly via vitamin D activation). *Calcitonin* - **Calcitonin** is released from the **thyroid gland** in response to **high serum calcium levels**. - Its main action is to **lower serum calcium** by inhibiting osteoclast activity and increasing renal calcium excretion. *Thyroxine* - **Thyroxine (T4)** is a thyroid hormone primarily involved in **metabolism**, growth, and development. - It does **not directly regulate** serum calcium levels. *Adrenaline* - **Adrenaline (epinephrine)** is a hormone released from the **adrenal glands** in response to stress. - It plays a role in the "fight or flight" response, affecting heart rate, blood pressure, and glucose metabolism, but **not calcium regulation**.

Question 850: Growth hormone secretion is increased by what?

A. Somatostatin
B. Obesity
C. Hyperglycemia
D. Hypoglycemia (Correct Answer)

Explanation: ***Hypoglycemia*** - **Hypoglycemia** (low blood glucose) is a **potent stimulus for growth hormone secretion**. - GH acts as a counter-regulatory hormone to raise blood glucose by promoting gluconeogenesis and reducing glucose uptake in peripheral tissues. - This is a physiological response to maintain blood glucose homeostasis during fasting or hypoglycemic states. *Somatostatin* - **Somatostatin** (also known as growth hormone-inhibiting hormone) directly **inhibits the release of growth hormone** from the anterior pituitary. - It acts as a negative regulator of GH secretion, not a stimulator. *Hyperglycemia* - **Hyperglycemia** (high blood glucose levels) **inhibits growth hormone secretion**. - This negative feedback mechanism prevents excessive GH-mediated glucose elevation when blood glucose is already high. *Obesity* - **Obesity** is associated with **reduced basal and stimulated growth hormone secretion**. - Multiple mechanisms contribute to this, including increased free fatty acids, altered hypothalamic-pituitary function, and increased negative feedback from IGF-1.

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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