Cell Volume Regulation — MCQs
Which of the following would cause an immediate reduction in the amount of potassium leaking out of a cell?
Which of the following events does NOT occur in rods in response to light
Two solutions with equal osmotic pressures are called:
What is the freezing point of normal human plasma?
Which of the following is the primary mechanism that drives sodium reabsorption in the proximal tubule?
When two different chemicals act on two different receptors and their responses are opposite to each other on the same cell, this phenomenon is called?
Which of the following is FALSE about Ghrelin?
Which ion movement is primarily responsible for hyperpolarization of the cell membrane?
Eukaryotic pathogens differ from prokaryotic pathogens in causing infections because they have:
A child with polytrauma presents to the emergency department. What is the recommended dose of packed red blood cells for transfusion?
Cell Volume Regulation Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following would cause an immediate reduction in the amount of potassium leaking out of a cell?
- A. Hyperpolarizing the membrane potential (Correct Answer)
- B. Reducing the activity of the sodium-potassium pump
- C. Decreasing the extracellular potassium concentration
- D. Increasing the permeability of the membrane to potassium
Explanation: ***Increasing (hyperpolarizing) the membrane potential*** - **Hyperpolarizing** the membrane means making the inside of the cell more negative relative to the outside. - This increased negativity inside the cell will **electrically attract** the positively charged **potassium ions** (K+) preventing them from leaking out. *Reducing the activity of the sodium-potassium pump* - The **sodium-potassium pump** actively transports potassium into the cell, helping to maintain the concentration gradient. - Reducing its activity would lead to an accumulation of potassium outside the cell and subsequent **increase in potassium leakage**. *Decreasing the extracellular potassium concentration* - A **lower extracellular potassium concentration** would steepen the potassium concentration gradient, causing more potassium to leak out of the cell. - This effect is due to the **chemical driving force** for potassium efflux. *Increasing the permeability of the membrane to potassium* - Increasing the **permeability** to potassium, typically through opening more **potassium channels**, would facilitate the movement of potassium ions down their electrochemical gradient. - This would result in a **greater leakage** of potassium out of the cell.
Question 2: Which of the following events does NOT occur in rods in response to light
- A. Opening of Na+ channels (Correct Answer)
- B. Activation of transducin
- C. Structural changes in rhodopsin
- D. Decreased intracellular cGMP
Explanation: ***Opening of Na+ channels*** - In response to light, **rods hyperpolarize** due to the **closure of Na+ channels**, which reduces the influx of positive ions. - The opening of Na+ channels would lead to depolarization, which is the opposite of what occurs during light detection in rods. *Activation of transducin* - Light causes **conformational changes in rhodopsin**, which in turn activates the G-protein **transducin**. - Activated transducin then goes on to activate **phosphodiesterase (PDE)** as part of the phototransduction cascade. *Structural changes in rhodopsin* - When light strikes the rhodopsin molecule, the **11-cis-retinal chromophore** isomerizes to **all-trans-retinal**. - This **conformational change** in rhodopsin is the initial step that triggers the entire phototransduction pathway. *Decreased intracellular cGMP* - Activated **phosphodiesterase (PDE)**, stimulated by transducin, hydrolyzes **cGMP to GMP**. - The reduction in **cGMP levels** leads to the closure of cGMP-gated Na+ channels, causing hyperpolarization.
Question 3: Two solutions with equal osmotic pressures are called:
- A. Normal solution
- B. Hypertonic solution
- C. Isotonic solution (Correct Answer)
- D. Hypotonic solution
Explanation: ***Isotonic solution*** - **Isotonic solutions** have the same solute concentration, and therefore the same **osmotic pressure**, as another solution. - In biological systems, an isotonic solution has the same osmotic pressure as the **cytosol** inside cells, preventing net water movement. *Normal solution* - "Normal solution" is a general term often referring to a solution at standard conditions or a commonly used concentration, but it does not specifically mean equal osmotic pressure. - While **normal saline** (0.9% NaCl) is isotonic to human plasma, the term "normal solution" itself is not a direct definition of equal osmotic pressure. *Hypertonic solution* - A **hypertonic solution** has a higher solute concentration and thus a higher **osmotic pressure** compared to another solution. - When a cell is placed in a hypertonic solution, water moves out of the cell, causing it to **crenate** or shrink. *Hypotonic solution* - A **hypotonic solution** has a lower solute concentration and thus a lower **osmotic pressure** compared to another solution. - When a cell is placed in a hypotonic solution, water moves into the cell, causing it to **swell** and potentially lyse.
Question 4: What is the freezing point of normal human plasma?
- A. 0° C
- B. –0.54° C (Correct Answer)
- C. –1.54° C
- D. 4° C
Explanation: ***–0.54° C*** - The **freezing point depression** of normal human plasma is approximately **–0.54° C**, which is a key physical property used to assess plasma osmolality. - This specific value reflects the **total concentration of solutes** (like electrolytes, glucose, and urea) in the plasma. *0° C* - This is the freezing point of **pure water**, which does not account for the dissolved solutes in human plasma. - Due to the presence of solutes, the freezing point of plasma is **depressed below 0° C**. *–1.54° C* - This value represents a significantly **lower freezing point depression**, suggesting a much higher concentration of solutes than found in normal human plasma. - Such a low freezing point would indicate a state of **severe hyperosmolality**. *4° C* - This temperature is above the freezing point of water and human plasma, typically used for **refrigeration** rather than indicating freezing point. - Plasma would be in a **liquid state** at this temperature.
Question 5: Which of the following is the primary mechanism that drives sodium reabsorption in the proximal tubule?
- A. Sodium reabsorption through cotransport with amino acids at the luminal membrane.
- B. Sodium reabsorption through cotransport with glucose at the luminal membrane.
- C. Sodium reabsorption through countertransport with hydrogen ions at the luminal membrane.
- D. Active sodium transport via the Na+-K+-ATPase pump at the basolateral membrane. (Correct Answer)
Explanation: ***Active sodium transport via the Na+-K+-ATPase pump at the basolateral membrane.*** - This pump **actively transports sodium out of the cell** into the interstitial fluid, creating a low intracellular sodium concentration. - The **Na+-K+-ATPase** is the primary driver of sodium reabsorption throughout the nephron, creating the electrochemical gradient for other sodium transporters. *Sodium reabsorption through cotransport with amino acids at the luminal membrane.* - While **sodium-amino acid cotransport** does occur in the proximal tubule, it accounts for only a fraction of total sodium reabsorption. - The primary driving force for this cotransport is the **low intracellular sodium concentration** maintained by the Na+-K+-ATPase. *Sodium reabsorption through cotransport with glucose at the luminal membrane.* - **Sodium-glucose cotransporters (SGLTs)** are crucial for glucose reabsorption in the proximal tubule, moving glucose into the cell along with sodium. - However, glucose cotransport represents a specific mechanism for glucose handling, not the overarching mechanism for sodium reabsorption. *Sodium reabsorption through countertransport with hydrogen ions at the luminal membrane.* - The **Na+-H+ exchanger (NHE3)** is significant for exchanging sodium for hydrogen ions at the luminal membrane in the proximal tubule. - This mechanism is important for **acid-base balance** and some sodium reabsorption, but it is secondary to the Na+-K+-ATPase in driving the overall sodium gradient.
Question 6: When two different chemicals act on two different receptors and their responses are opposite to each other on the same cell, this phenomenon is called?
- A. Physiological antagonism (Correct Answer)
- B. Chemical antagonism
- C. Reversible antagonism
- D. Competitive antagonism
Explanation: ***Physiological antagonism*** - This occurs when two drugs act on **different receptors** to produce **opposite physiological effects** within the same system or cell, effectively canceling each other out [1]. - A classic example is the opposing actions of **histamine** (causing bronchoconstriction) and **adrenaline** (causing bronchodilation) on the bronchi [1]. *Chemical antagonism* - This involves a direct **chemical interaction** between two drugs that results in the **inactivation of one or both** of them. - An example is the binding of **chelating agents** to heavy metals, forming an inert complex. *Reversible antagonism* - This describes antagonism where the antagonist binds to the receptor and can be **displaced by a higher concentration of the agonist**. - It does not specifically describe antagonists acting on different receptors or producing opposing physiological effects. *Competitive antagonism* - This occurs when an antagonist directly **competes with an agonist for the same binding site** on a receptor [1]. - The antagonist, while not producing a response itself, prevents the agonist from binding and activating the receptor.
Question 7: Which of the following is FALSE about Ghrelin?
- A. Stimulates growth
- B. Produced by stomach cells
- C. Is related to regulation of thyroid hormone (Correct Answer)
- D. Increased appetite
Explanation: ***Is related to regulation of thyroid hormone*** - **Ghrelin** is primarily involved in **appetite regulation** and **growth hormone secretion**, not direct regulation of thyroid hormones. - While metabolic processes are interconnected, ghrelin does not have a direct, established role in the synthesis or release of **thyroid hormones**. *Stimulates growth* - Ghrelin is a potent **stimulator of growth hormone (GH) release** from the pituitary gland. - This action indirectly contributes to **growth processes** and metabolic regulation. *Produced by stomach cells* - The majority of ghrelin is produced by **P/D1 cells** (also known as enterochromaffin-like cells) primarily located in the **fundus of the stomach**. - Smaller amounts are also produced in the intestine, pancreas, and brain. *Increased appetite* - Ghrelin is often referred to as the "**hunger hormone**" because it stimulates appetite, promoting food intake. - Its levels typically **rise before meals** and fall after meals.
Question 8: Which ion movement is primarily responsible for hyperpolarization of the cell membrane?
- A. Chloride (Cl-) influx
- B. Potassium (K+) efflux (Correct Answer)
- C. Sodium (Na+) influx
- D. None of the options
Explanation: ***Potassium (K+) efflux*** - **Potassium efflux** (K+ leaving the cell) is the **primary mechanism** responsible for hyperpolarization of the cell membrane across most cell types. - When K+ channels open, positive charges leave the cell, making the intracellular environment more negative relative to the extracellular space, thereby **hyperpolarizing** the membrane. - This mechanism is responsible for: - **Afterhyperpolarization** following action potentials - Setting the **resting membrane potential** close to the K+ equilibrium potential (-90 mV) - **Repolarization and hyperpolarization phases** of action potentials - Examples include delayed rectifier K+ channels and calcium-activated K+ channels. *Chloride (Cl-) influx* - While Cl- influx can cause hyperpolarization (especially through **GABA-A receptors** in neurons), it is a **secondary or specialized mechanism**, not the primary one. - In many mature neurons, the Cl- equilibrium potential is close to the resting potential, limiting its hyperpolarizing effect. - This mechanism is important in **inhibitory neurotransmission** but not universally across all cell types. *Sodium (Na+) influx* - **Sodium influx** through voltage-gated sodium channels is responsible for the **depolarization phase** of an action potential. - This makes the inside of the cell significantly more positive (+30 to +40 mV), which is the opposite of hyperpolarization. *None of the options* - This option is incorrect because **potassium efflux** is indeed the primary mechanism for membrane hyperpolarization.
Question 9: Eukaryotic pathogens differ from prokaryotic pathogens in causing infections because they have:
- A. Highly structured cell with organized cell organelles (Correct Answer)
- B. Evolutionarily ancient
- C. Divide by binary fission
- D. Do not have all organelles
Explanation: ***Highly structured cell with organized cell organelles*** - **Eukaryotic cells** are characterized by a **true nucleus** and other **membrane-bound organelles** (e.g., mitochondria, endoplasmic reticulum, Golgi apparatus) that compartmentalize cellular functions. - This complex internal organization allows for specialized functions and metabolic pathways that distinguish them from prokaryotes, influencing how they cause infection and how they are targeted by treatments. *Evolutionarily ancient* - **Prokaryotes** (bacteria and archaea) are considered **evolutionarily ancient** and were the first forms of life on Earth. - **Eukaryotes** evolved from prokaryotic ancestors and are therefore more recent in evolutionary terms. *Divide by binary fission* - **Binary fission** is the primary mode of asexual reproduction for **prokaryotes**, where one cell divides into two identical daughter cells. - **Eukaryotic pathogens** reproduce through more complex processes like **mitosis** (for asexual reproduction) or meiosis (for sexual reproduction). *Do not have all organelles* - The statement "Do not have all organelles" is more characteristic of **prokaryotic cells**, which lack membrane-bound organelles. - **Eukaryotic cells**, by definition, possess a comprehensive set of organelles, differentiating them from prokaryotes.
Question 10: A child with polytrauma presents to the emergency department. What is the recommended dose of packed red blood cells for transfusion?
- A. 20 ml/kg
- B. 10 ml/kg (Correct Answer)
- C. 30 ml/kg
- D. 40 ml/kg
Explanation: ***10 ml/kg*** - The standard recommended initial dose of **packed red blood cells (PRBCs)** for transfusion in pediatric trauma patients is **10 ml/kg** according to **ATLS** and **PALS** guidelines. - This dose is aimed at rapidly restoring intravascular volume and oxygen-carrying capacity in the setting of significant blood loss from polytrauma. - The dose can be **repeated** based on the patient's clinical response and ongoing blood loss, with reassessment after each bolus. - This approach allows for **controlled volume resuscitation** while minimizing the risk of transfusion-related complications. *20 ml/kg* - While **20 ml/kg** may eventually be transfused in severe hemorrhage, it typically represents **two sequential 10 ml/kg boluses** rather than a single initial dose. - Giving the full 20 ml/kg as a single initial bolus without reassessment between doses is not standard practice and may increase the risk of volume overload. *30 ml/kg* - A dose of **30 ml/kg** of PRBCs is excessive for an initial bolus and could lead to **Transfusion-Associated Circulatory Overload (TACO)**, especially in children. - Such high volumes are only considered in **massive transfusion protocols** with appropriate monitoring and staged administration. *40 ml/kg* - **40 ml/kg** is an excessively high dose for PRBC transfusion in pediatric trauma and would carry significant risk of volume overload and other transfusion-related complications. - This volume far exceeds standard trauma resuscitation guidelines and would only be reached through multiple sequential boluses with careful monitoring in cases of ongoing massive hemorrhage.
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