Principles of Endocrine Regulation — MCQs

10 questions

Receptors for thyroid hormones are present:

Diffusion of lipid-insoluble substances across the cell membrane depends on all of the following factors except which one?

Hormonal secretions are tightly controlled by the time of day due to an inbuilt biological clock in human body. This rhythmic secretion is controlled by:

All are true about hormone functions except:

Phospholipid associated with the mechanism of hormone action is

Which of the following hormones are under inhibitory control of hypothalamus?

Which of the following hormones regulates blood levels of 1,25-OH-cholecalciferol positively?

All are examples of negative feedback except

All of the following are known functions of hypothalamus except

Q10

Among the following, prolactin secretion is maximum:

Principles of Endocrine Regulation Indian Medical PG Practice Questions and MCQs

Question 1: Receptors for thyroid hormones are present:

A. On the cell membrane
B. Inside the cells (Correct Answer)
C. In association with G-proteins
D. Across the cell membrane

Explanation: ***Inside the cells*** - Thyroid hormones are **lipophilic** and can easily pass through the cell membrane to bind with receptors located in the **cytoplasm or nucleus**. - These intracellular receptors then act as **transcription factors**, regulating gene expression. *On the cell membrane* - Receptors on the cell membrane are typically for **hydrophilic hormones** (e.g., peptide hormones) that cannot freely cross the lipid bilayer. - While there are some non-genomic effects mediated by cell surface receptors, the primary action of thyroid hormones is via intracellular receptors. *In association with G-proteins* - **G-protein coupled receptors** are cell membrane receptors that transduce signals through effector enzymes or ion channels, often for peptide or catecholamine hormones. - Thyroid hormones do not primarily signal through G-protein coupled receptors for their genomic effects. *Across the cell membrane* - This option refers to transmembrane proteins that span the entire cell membrane, which are characteristic of many cell surface receptors. - **Thyroid hormone receptors** are not transmembrane proteins but are found within the cell, often in the nucleus.

Question 2: Diffusion of lipid-insoluble substances across the cell membrane depends on all of the following factors except which one?

A. Hydrated radius
B. Electrical charge
C. Lipid solubility (Correct Answer)
D. Shape

Explanation: ***Lipid solubility*** - This property is crucial for substances that **readily diffuse directly through the lipid bilayer**. - Lipid-insoluble substances, by definition, **cannot diffuse through the lipid bilayer based on their lipid solubility**, requiring other mechanisms or factors like channels or carriers. *Hydrated radius* - The **size of a hydrated ion or molecule** is a critical determinant for its ability to pass through specific protein channels or pores in the cell membrane. - A larger hydrated radius impedes passage through narrow channels, directly affecting the diffusion of lipid-insoluble substances. *Electrical charge* - For **charged lipid-insoluble substances** (ions), their movement across the membrane is significantly influenced by the **transmembrane electrical potential difference**. - The electrical gradient can either facilitate or hinder the diffusion of these substances through channels or transporters. *Shape* - The **three-dimensional configuration** of a lipid-insoluble substance can affect its ability to bind to and pass through specific protein channels or carrier proteins. - A substance's shape must complement the architecture of the transport mechanism for efficient diffusion.

Question 3: Hormonal secretions are tightly controlled by the time of day due to an inbuilt biological clock in human body. This rhythmic secretion is controlled by:

A. Ventrolateral nucleus
B. Supraoptic nucleus
C. Suprachiasmatic nucleus (Correct Answer)
D. Posterolateral nucleus

Explanation: ***Suprachiasmatic nucleus*** - The **suprachiasmatic nucleus (SCN)**, located in the hypothalamus, is the primary pacemaker of the body's **circadian rhythms**, controlling the timing of hormonal secretions, sleep-wake cycles, and other daily oscillations. - It receives direct input from the **retina** about light-dark cycles, allowing it to synchronize the body's internal clock with the external environment. *Ventrolateral nucleus* - The **ventrolateral preoptic nucleus (VLPO)** is involved in **sleep regulation** and promoting non-REM sleep, but it does not act as the primary circadian pacemaker. - It receives input from the SCN and collaborates in regulating sleep, but its role is primarily inhibitory to wakefulness. *Supraoptic nucleus* - The **supraoptic nucleus** is primarily involved in the production and secretion of **vasopressin (ADH)** and **oxytocin**, which are neurohormones regulating fluid balance and social bonding, respectively. - It does not directly control the rhythmic aspect of general hormonal secretions or act as the central circadian clock. *Posterolateral nucleus* - This term is less commonly used in the context of circadian rhythm control; however, if referring to a thalamic nucleus, the **posterolateral nucleus** is generally associated with sensory processing, particularly somatosensory information. - It has no known role as a central pacemaker for hormonal secretions or circadian rhythms.

Question 4: All are true about hormone functions except:

A. Cortisol regulates plasma volume (Correct Answer)
B. Thyroid hormones regulate metabolism
C. ADH regulates blood osmolality
D. Insulin regulates blood glucose

Explanation: ***Cortisol regulates plasma volume*** - While cortisol plays a role in fluid balance by influencing **renal perfusion** and the action of other hormones like ADH, its primary role is not the direct regulation of plasma volume. - **Aldosterone** is the primary hormone directly responsible for regulating plasma volume through its effects on sodium and water reabsorption in the kidneys. *Thyroid hormones regulate metabolism* - **Thyroid hormones** (T3 and T4) are crucial for regulating the body's metabolic rate, influencing factors like energy production, protein synthesis, and cellular oxygen consumption. - They impact the metabolism of **carbohydrates, fats, and proteins**, affecting nearly every cell in the body. *ADH regulates blood osmolality* - **Antidiuretic hormone (ADH)**, also known as vasopressin, primarily regulates blood osmolality by controlling the reabsorption of water in the renal collecting ducts. - It increases the permeability of collecting ducts to water, thus concentrating urine and **reducing plasma osmolality** when it's high. *Insulin regulates blood glucose* - **Insulin** is a key hormone produced by the pancreas that regulates blood glucose levels by facilitating the uptake of glucose into cells for energy or storage. - It plays a crucial role in lowering blood glucose after meals by promoting **glucose utilization** and inhibiting glucose production by the liver.

Question 5: Phospholipid associated with the mechanism of hormone action is

A. Phosphatidylcholine
B. Phosphatidylethanolamine
C. Plasmalogen
D. Phosphatidylinositol (Correct Answer)

Explanation: ***Phosphatidylinositol*** (Correct) - **Phosphatidylinositol (PI)** and its phosphorylated derivatives, particularly **PIP2 (phosphatidylinositol 4,5-bisphosphate)**, are critical in signal transduction pathways activated by many hormones. - Hormones binding to **G protein-coupled receptors** can activate phospholipase C, which cleaves PIP2 into **inositol triphosphate (IP3)** and **diacylglycerol (DAG)**, leading to increased intracellular calcium and protein kinase C activation, respectively. *Phosphatidylcholine* (Incorrect) - **Phosphatidylcholine** is a major component of cell membranes and is involved in membrane structure and fluidity. - While it can be a source of signaling molecules like **lysophosphatidic acid**, it is not primarily associated with the initial intracellular signaling events of hormone action in the same way as phosphatidylinositol. *Phosphatidylethanolamine* (Incorrect) - **Phosphatidylethanolamine** is another abundant membrane phospholipid primarily involved in membrane structure and stability. - It can be a precursor for other lipids, but it does not directly participate in the **second messenger systems** triggered by most hormones as a primary signaling molecule. *Plasmalogen* (Incorrect) - **Plasmalogens** are a unique class of phospholipids containing an ether bond at the sn-1 position. - They are abundant in certain tissues, particularly nervous and cardiovascular tissues, and are thought to have antioxidant properties, but they are not directly involved in the initiating events of **hormone signaling pathways**.

Question 6: Which of the following hormones are under inhibitory control of hypothalamus?

A. Growth hormone only
B. Prolactin only
C. Both prolactin and growth hormone (Correct Answer)
D. Neither prolactin nor growth hormone

Explanation: ***Both prolactin and growth hormone*** - The hypothalamus exerts **inhibitory control over prolactin release** primarily through **dopamine** (prolactin-inhibiting hormone/PIH). - Growth hormone (GH) secretion is inhibited by **somatostatin** (growth hormone-inhibiting hormone/GHIH), which is also secreted by the hypothalamus. - These are the **only two anterior pituitary hormones** predominantly under tonic inhibitory control from the hypothalamus. *Growth hormone only* - While **somatostatin** from the hypothalamus does inhibit growth hormone, this option is incomplete. - **Prolactin** is also under hypothalamic inhibitory control via dopamine, making this the wrong answer. *Prolactin only* - The hypothalamus does exert inhibitory control over prolactin via **dopamine**, making this statement partially correct. - However, **growth hormone** is also under inhibitory control by **somatostatin**, so this option is incomplete. *Neither prolactin nor growth hormone* - This is incorrect because both prolactin and growth hormone are under inhibitory hypothalamic control. - All other anterior pituitary hormones (TSH, ACTH, FSH, LH) are primarily under **stimulatory control** from the hypothalamus.

Question 7: Which of the following hormones regulates blood levels of 1,25-OH-cholecalciferol positively?

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

Explanation: ***Parathormone*** - **Parathormone (PTH)** directly stimulates the **renal 1-alpha-hydroxylase** enzyme, which converts 25-hydroxycholecalciferol to its active form, **1,25-dihydroxycholecalciferol (calcitriol)**. - This activation is crucial for increasing **calcium absorption** from the gut and maintaining calcium homeostasis. *Thyroxine* - **Thyroxine** (thyroid hormone) primarily regulates **metabolism**, growth, and development. - It does not have a direct positive regulatory effect on the synthesis or blood levels of **1,25-OH-cholecalciferol**. *Calcitonin* - **Calcitonin** is a hormone that **lowers blood calcium levels** by inhibiting osteoclast activity and decreasing renal calcium reabsorption. - It does not positively regulate the production of **1,25-OH-cholecalciferol**; in fact, its actions are generally antagonistic to those influenced by active vitamin D. *Insulin* - **Insulin** is a key hormone in **glucose metabolism**, facilitating glucose uptake by cells and promoting glycogen synthesis. - It plays no direct role in the regulation or synthesis of **1,25-OH-cholecalciferol**.

Question 8: All are examples of negative feedback except

A. Regulation of blood CO2 level
B. Regulation of pituitary hormones
C. Regulation of blood pressure
D. Coagulation of the blood (Correct Answer)

Explanation: ***Coagulation of the blood*** - **Blood coagulation** is a classic example of **positive feedback**, where the initial clotting process amplifies itself until bleeding stops - Platelets aggregate and release factors that promote further platelet aggregation and activation of the clotting cascade, thereby **accelerating the response** rather than diminishing it - This is the exception among the options, as it represents positive feedback while all others are negative feedback *Regulation of blood CO2 level* - The regulation of **blood CO2 levels** is a vital example of **negative feedback**, where an increase in CO2 stimulates breathing to expel excess CO2 - This mechanism works to return the blood CO2 concentration to its homeostatic set point, thus **counteracting the initial stimulus** - Central and peripheral chemoreceptors detect elevated CO2 and trigger increased ventilation *Regulation of pituitary hormones* - The regulation of **pituitary hormones** involves **negative feedback loops**, where high levels of target gland hormones inhibit the release of stimulating hormones from the pituitary and hypothalamus - For example, high thyroid hormone levels inhibit TSH release from the pituitary and TRH from the hypothalamus - This effectively **reduces the initial stimulus** and maintains hormonal balance *Regulation of blood pressure* - The regulation of **blood pressure** is primarily controlled by **negative feedback mechanisms** involving baroreceptors, which detect changes in pressure - If blood pressure rises, baroreceptors in the carotid sinus and aortic arch signal the medulla to reduce heart rate and dilate blood vessels - This response **lowers the pressure back to the set point**, maintaining cardiovascular homeostasis

Question 9: All of the following are known functions of hypothalamus except

A. Temperature regulation
B. Hypophyseal control
C. Food intake
D. Increase in heart rate with exercise (Correct Answer)

Explanation: ***Increase in heart rate with exercise*** - The **hypothalamus** has an indirect role in cardiovascular responses during exercise, primarily through its influence on the **autonomic nervous system** to maintain homeostasis. - However, the primary control of increased heart rate during exercise originates from the **medulla oblongata** and the **motor cortex**, which directly modulates the sympathetic nervous system to increase cardiac output. *Temperature regulation* - The **hypothalamus** contains thermoregulatory centers that monitor and adjust body temperature through mechanisms such as **sweating** and **shivering**. - This function is a fundamental aspect of maintaining **homeostasis**. *Hypophyseal control* - The **hypothalamus** directly controls the **pituitary gland** (hypophysis) by producing releasing and inhibiting hormones that regulate the secretion of pituitary hormones. - This neuroendocrine function is crucial for controlling various **endocrine axes**. *Food intake* - The **hypothalamus** plays a key role in regulating appetite and satiety, with specific nuclei like the **arcuate nucleus** integrating signals related to hunger and fullness. - This control is essential for maintaining **energy balance**.

Question 10: Among the following, prolactin secretion is maximum:

A. During REM sleep
B. After 2 hours of running
C. 24 hrs after delivery (Correct Answer)
D. 24 hours after ovulation

Explanation: ***Correct: 24 hrs after delivery*** - Prolactin levels are highest in the initial **24 hours postpartum**, especially during and after **breastfeeding sessions**, which act as a powerful stimulus for prolactin release. - This peak prolactin level is crucial for initiating and maintaining **lactation** following childbirth. - The postpartum prolactin surge represents the **maximum physiological level** of this hormone under normal circumstances. *Incorrect: During REM sleep* - While prolactin secretion does exhibit a **circadian rhythm** with nocturnal peaks, the highest levels do not specifically occur during **REM sleep**; rather, they are elevated throughout the sleep cycle. - Though prolactin does rise during sleep, the magnitudes are **not comparable** to the surges seen postpartum or after intense suckling. *Incorrect: After 2 hours of running* - Exercise, particularly prolonged and intense physical activity, can cause a transient increase in prolactin levels due to **stress response** and hormonal changes. - However, this exercise-induced increase is generally **modest** compared to the physiological surge observed after delivery. *Incorrect: 24 hours after ovulation* - Prolactin levels show a slight increase during the **luteal phase** of the menstrual cycle, which follows ovulation, primarily due to rising progesterone levels. - This elevation is significantly **lower** than the dramatic rise seen immediately postpartum needed for milk production.

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