Endocrinology — MCQs

Endocrinology Indian Medical PG Practice Questions and MCQs

Question 661: All of the following are increased in Acute stress except

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

Explanation: ***Insulin*** - During acute stress, **insulin secretion is actively suppressed** by catecholamines (epinephrine and norepinephrine) acting on **alpha-2 adrenergic receptors** on pancreatic beta cells. - This suppression is crucial for the stress response, as it allows **unopposed action of counter-regulatory hormones** to mobilize glucose and raise blood glucose levels. - The body prioritizes **immediate energy availability** (high blood glucose) over storage, making insulin the hormone that is **decreased, not increased**, during acute stress. *Growth hormone* - **Growth hormone** is a counter-regulatory hormone that **increases during acute stress** to mobilize energy stores, particularly by promoting lipolysis and gluconeogenesis. - Its actions contribute to the stress-induced elevation of **blood glucose levels**. *Epinephrine* - **Epinephrine** (adrenaline) is a primary catecholamine released during acute stress, leading to a rapid **fight or flight response**. - It significantly **increases heart rate**, blood pressure, and **glucose mobilization** through glycogenolysis and gluconeogenesis. *Glucagon* - **Glucagon** is a key hormone involved in **maintaining glucose homeostasis** and is significantly **increased during acute stress**. - It primarily acts on the liver to **stimulate glycogenolysis** and **gluconeogenesis**, thereby raising blood glucose levels to provide energy.

Question 662: Testis is not the source for which of the following?

A. Dehydroepiandrosterone (Correct Answer)
B. Testosterone
C. Dihydrotestosterone
D. Androstenodione

Explanation: ***Correct: Dehydroepiandrosterone (DHEA)*** - **DHEA is primarily produced by the adrenal glands**, specifically the zona reticularis of the adrenal cortex - It is an important **adrenal androgen** that serves as a precursor for sex hormones - The **testes are NOT a significant source** of DHEA production or secretion - This makes DHEA the correct answer to what the testis does NOT produce *Incorrect: Dihydrotestosterone (DHT)* - While most DHT in the body is formed by **peripheral conversion** of testosterone via 5-alpha-reductase in target tissues (prostate, skin, hair follicles) - The **testes do produce small amounts of DHT directly** from testosterone - Therefore, the testes ARE a source of DHT, making this option incorrect *Incorrect: Testosterone* - The testes are the **primary site of testosterone production** in males - **Leydig cells** synthesize and secrete testosterone in response to luteinizing hormone (LH) - Testosterone is essential for male sexual development, spermatogenesis, and secondary sexual characteristics *Incorrect: Androstenedione* - **Androstenedione is produced in the testes** as an intermediate in steroidogenesis - It serves as a precursor for both testosterone and estrogens - Also produced in adrenal glands and ovaries, but the testes ARE a definite source

Question 663: All are true for oxytocin EXCEPT:

A. Causes ejection of milk
B. Secreted by anterior pituitary (Correct Answer)
C. Polypeptide
D. Secreted in both sexes

Explanation: ***Secreted by anterior pituitary*** - Oxytocin is synthesized in the **hypothalamus** (specifically the paraventricular and supraoptic nuclei) and then transported down axons to the **posterior pituitary gland**, where it is stored and released. - The **anterior pituitary** produces and secretes hormones like growth hormone, prolactin, TSH, ACTH, FSH, and LH, but not oxytocin or vasopressin. *Causes ejection of milk* - Oxytocin acts on **myoepithelial cells** surrounding the alveoli of the mammary glands, causing them to contract and eject milk during lactation. - This is known as the **milk ejection reflex** or "let-down" reflex, which is stimulated by suckling. *Polypeptide* - Oxytocin is a **peptide hormone** composed of nine amino acids, making it a small polypeptide. - Its specific amino acid sequence is **Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2**, with a disulfide bond between the cysteine residues. *Secreted in both sexes* - While most recognized for its roles in childbirth and lactation in females, oxytocin is also produced and secreted in **males**. - In males, it is involved in various functions including **sperm transport**, sexual arousal, ejaculation, and social bonding behaviors.

Question 664: Which of the following causes hypocalcemia:

A. 1, 25-dihydroxycholecalciferol
B. Parathormone
C. Thyroid hormones
D. Calcitonin (Correct Answer)

Explanation: ***Calcitonin*** - **Calcitonin** is a hormone secreted by the **parafollicular cells (C cells)** of the thyroid gland. - It **lowers serum calcium levels** by **inhibiting osteoclast activity** (preventing bone resorption) and **increasing renal calcium excretion**. - This is the only hormone among the options that causes hypocalcemia. *1,25-dihydroxycholecalciferol* - This is the **active form of vitamin D** (calcitriol), which **increases serum calcium levels**. - It promotes intestinal calcium absorption, enhances bone resorption, and increases renal calcium reabsorption. - Deficiency of this hormone leads to hypocalcemia, but the hormone itself raises calcium. *Parathormone* - **Parathyroid hormone (PTH)** is the primary regulator that **increases serum calcium levels**. - It stimulates **osteoclast activity** (releasing calcium from bone), increases renal calcium reabsorption, and promotes synthesis of 1,25-dihydroxycholecalciferol. - PTH acts opposite to calcitonin in calcium homeostasis. *Thyroid hormones* - **Thyroxine (T4) and triiodothyronine (T3)** primarily regulate metabolism and have **no direct role in calcium homeostasis**. - While severe thyroid dysfunction can indirectly affect bone turnover, thyroid hormones do not directly cause hypocalcemia.

Question 665: Neuroendocrine glands means:

A. Substance is released into the blood from the nerve (Correct Answer)
B. Those acting at peripheral nervous system
C. Chemical acting at the synapse
D. Substance acts on the cells that release it.

Explanation: ***Substance is released into the blood from the nerve*** - Neuroendocrine glands are specialized neurons that synthesize and release **hormones** directly into the bloodstream, integrating the nervous and endocrine systems. - This **neurosecretion** allows neurons to exert widespread, long-lasting effects on target cells throughout the body. *Those acting at peripheral nervous system* - This describes the general function of peripheral nerves, which can be **motor**, **sensory**, or **autonomic**, but doesn't specifically define a neuroendocrine gland. - Neuroendocrine cells are typically found within the central and peripheral nervous systems but their defining characteristic is release into the **blood**, not just acting within the PNS. *Chemical acting at the synapse* - This describes a **neurotransmitter**, which is released from a neuron and acts locally on a postsynaptic neuron or effector cell across a synaptic cleft. - Unlike hormones, neurotransmitters exert their effects over very **short distances** and typically have a rapid, short-lived action. *Substance act on the cells that release it.* - This describes **autocrine signaling**, where a cell produces and secretes an extracellular mediator that binds to its own surface receptors. - While some neuroendocrine cells may exhibit autocrine regulation, their primary definition involves releasing substances into the **bloodstream** to act on distant targets, not solely on themselves.

Question 666: A patient with a pheochromocytoma is secreting large amounts of norepinephrine into the bloodstream. In a normal individual, this compound is usually released from the adrenal medulla in response to which of the following?

A. Acetylcholine (Correct Answer)
B. Normetanephrine
C. Metanephrine
D. Epinephrine

Explanation: ***Acetylcholine*** - **Acetylcholine** is the primary neurotransmitter released by **preganglionic sympathetic fibers** that innervate the adrenal medulla. - Upon binding to **nicotinic receptors** on chromaffin cells, acetylcholine stimulates the release of catecholamines, including norepinephrine and epinephrine, into the bloodstream. *Normetanephrine* - **Normetanephrine** is a metabolite of **norepinephrine**, not a hormone that triggers its release. - It is formed by the action of **catechol-O-methyltransferase (COMT)** on norepinephrine. *Metanephrine* - **Metanephrine** is a metabolite of **epinephrine**, not a substance that stimulates catecholamine release from the adrenal medulla. - Like normetanephrine, it is also formed by the action of **COMT**. *Epinephrine* - **Epinephrine** (adrenaline) is a hormone primarily produced and released by the **adrenal medulla**, alongside norepinephrine. - While both are catecholamines, epinephrine does not trigger its own release or the release of norepinephrine in this context; instead, their release is stimulated by acetylcholine.

Question 667: Which of the following can cause an increase in growth hormone levels in blood?

A. Cortisol
B. Glucose
C. Hypoglycemia (Correct Answer)
D. Methylprednisolone

Explanation: ***Hypoglycemia*** - **Hypoglycemia** is a potent stimulus for **growth hormone (GH) secretion**, as GH acts to raise blood glucose levels, serving as a counter-regulatory hormone. - The body perceives low blood glucose as a stressor, activating the **hypothalamic-pituitary-adrenal axis** and stimulating GH release to mobilize energy stores. *Cortisol* - **Cortisol** (a glucocorticoid) generally has an **inhibitory effect** on GH secretion at the hypothalamic and pituitary levels. - High levels of cortisol can lead to **suppression of GH pulsatility** and overall lower GH release. *Glucose* - An increase in **blood glucose** levels typically **suppresses growth hormone (GH) release**, as GH tends to increase blood glucose. - This negative feedback mechanism helps maintain **glucose homeostasis** within the body. *Methylprednisolone* - **Methylprednisolone** is a synthetic **glucocorticoid** that mimics the actions of cortisol. - Like cortisol, it suppresses GH secretion and can lead to **growth retardation** in children with chronic use.

Question 668: Steroid hormone that directly binds to intracellular cytoplasmic receptors

A. Glucocorticoids (Correct Answer)
B. Thyroxine
C. Calcitonin
D. Vasopressin

Explanation: ***Glucocorticoids*** - **Glucocorticoids** are **steroid hormones** that are **lipid-soluble** and can easily pass through the cell membrane to bind to **intracellular cytoplasmic receptors**. - This binding leads to the formation of a hormone-receptor complex that translocates to the nucleus to regulate **gene expression**. - This is the classic mechanism of action for steroid hormones. *Thyroxine* - **Thyroxine (T4)** is a **thyroid hormone**, **not a steroid hormone** - it is derived from tyrosine amino acids. - Although it does bind to intracellular receptors, it does not meet the criteria of being a steroid hormone as asked in the question. - Thyroxine primarily binds to nuclear receptors rather than cytoplasmic receptors. *Calcitonin* - **Calcitonin** is a **peptide hormone**, not a steroid hormone, that primarily binds to **cell surface receptors** on target cells like osteoclasts and renal tubule cells. - As a large, **water-soluble** molecule, it cannot directly cross the cell membrane to bind to intracellular receptors. *Vasopressin* - **Vasopressin**, also known as **antidiuretic hormone (ADH)**, is a **peptide hormone**, not a steroid hormone, that acts on **cell surface receptors** in the kidneys and blood vessels. - Its **hydrophilic** nature prevents it from penetrating the cell membrane to bind to intracellular receptors.

Question 669: All of the following hormones have cell surface receptors except:

A. Thyroxine (Correct Answer)
B. Insulin
C. Adrenalin
D. Growth Hormone

Explanation: ***Thyroxine*** - **Thyroxine** (T4) is a **lipid-soluble thyroid hormone** that readily crosses the cell membrane to bind to **intracellular nuclear receptors** in the nucleus. - This binding leads to changes in gene expression, which then mediates its metabolic effects. - Unlike peptide hormones, thyroid hormones do not require cell surface receptors. *Insulin* - **Insulin** is a **peptide hormone** that binds to specific **cell surface receptors** (tyrosine kinase receptors) on target cells. - This binding initiates a signaling cascade that regulates glucose uptake and metabolism. *Adrenalin* - **Adrenalin** (epinephrine) is a **catecholamine hormone** that binds to **G protein-coupled receptors (GPCRs)** on the cell surface. - This binding triggers intracellular signaling pathways, leading to the "fight-or-flight" response. *Growth Hormone* - **Growth hormone** is a **protein hormone** that binds to **cell surface receptors** (cytokine receptors) on target cells. - This interaction activates the JAK-STAT signaling pathway, promoting growth and metabolism.

Question 670: The anterior pituitary is mainly composed of which of the following secretory cells?

A. Lactotrope
B. Corticotrope
C. Somatotrope (Correct Answer)
D. Thyrotrope

Explanation: ***Somatotrope*** - **Somatotropes** are the most abundant cell type in the anterior pituitary, constituting about 50% of the gland's cells. - They produce and secrete **growth hormone (GH)**, which is crucial for growth, metabolism, and body composition. *Lactotrope* - **Lactotropes** produce **prolactin (PRL)**, which is involved in lactation. - They make up about 15-20% of the anterior pituitary cells, a significant but not the main proportion. *Corticotrope* - **Corticotropes** secrete **adrenocorticotropic hormone (ACTH)**, which stimulates the adrenal glands. - They constitute approximately 15-20% of the anterior pituitary cells, similar to lactotropes. *Thyrotrope* - **Thyrotropes** produce **thyroid-stimulating hormone (TSH)**, regulating thyroid function. - They are the least abundant cell type, making up only about 5% of the anterior pituitary cells.

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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