General Physiology — MCQs

General Physiology Indian Medical PG Practice Questions and MCQs

Question 361: Which of the following is true regarding blood pressure measurement using a sphygmomanometer?

A. May be falsely low with too narrow a cuff
B. May be falsely low in patients with badly stiffened arteries
C. May be falsely high in obese patients (Correct Answer)
D. Gives a direct reading of mean arterial pressure

Explanation: **Explanation:** The accuracy of blood pressure (BP) measurement via a sphygmomanometer depends heavily on the **cuff size** relative to the **arm circumference**. **1. Why Option C is Correct:** In obese patients, the arm circumference is larger. If a standard-sized cuff is used, the pressure applied by the inflating bladder is not transmitted efficiently to the underlying artery. Consequently, the cuff must be inflated to a much higher pressure than the actual intra-arterial pressure to occlude the artery, leading to a **falsely high (overestimated)** reading. This is often referred to as "cuff hypertension." **2. Analysis of Incorrect Options:** * **Option A:** A **narrow cuff** requires higher inflation pressure to compress the artery, leading to a **falsely high** reading, not low. (Mnemonic: Narrow = High; Wide = Low). * **Option B:** In patients with **stiffened/calcified arteries** (e.g., elderly or diabetics), the vessel wall resists compression. This requires higher cuff pressure to collapse the artery, resulting in a **falsely high** reading (Pseudohypertension). * **Option D:** A sphygmomanometer provides **indirect** measurements of Systolic (Phase I Korotkoff) and Diastolic (Phase V Korotkoff) pressures. Mean Arterial Pressure (MAP) is then calculated using the formula: $MAP = DBP + 1/3 (Pulse\ Pressure)$. **Clinical Pearls for NEET-PG:** * **Ideal Cuff Dimensions:** The bladder length should be **80%** and the width should be **40%** of the arm circumference. * **Korotkoff Sounds:** These are produced by **turbulent blood flow** through a partially occluded artery. * **Oscillometric Method:** Most automated BP monitors use this to measure oscillations and then *calculate* systolic and diastolic values using algorithms.

Question 362: What is the weight of 1 cc of air at normal pressure and temperature?

A. 0.001297 g (Correct Answer)
B. 0.002345 g
C. 0.004 g
D. 1.000 g

Explanation: **Explanation:** The weight (mass) of a substance is determined by its density at a specific temperature and pressure. In physiology and physics, **Standard Temperature and Pressure (STP)** is typically defined as 0°C (273.15 K) and 1 atmosphere (760 mmHg) of pressure. 1. **Why Option A is Correct:** The density of dry air at STP is approximately **1.293 to 1.297 kg/m³**. Since 1 cc (cubic centimeter) is equivalent to 1 mL ($10^{-6}$ m³), we convert the units: $1.297 \text{ kg/m}^3 = 0.001297 \text{ g/cm}^3$. Therefore, 1 cc of air weighs approximately **0.001297 g**. This value is a fundamental constant used when calculating gas partial pressures and understanding pulmonary mechanics. 2. **Why Other Options are Incorrect:** * **Option B (0.002345 g):** This value does not correspond to the density of any common physiological gas at STP. * **Option C (0.004 g):** This is significantly higher than the density of air; for comparison, Helium is much lighter (0.00017 g/cc), while CO₂ is heavier (0.0019 g/cc). * **Option D (1.000 g):** This is the weight of **1 cc of pure water** at 4°C. Air is roughly 773 times less dense than water. **High-Yield Clinical Pearls for NEET-PG:** * **Composition of Air:** Dry air consists of ~78% Nitrogen, ~21% Oxygen, and 0.04% CO₂. * **Water Vapor Effect:** Humidified air in the respiratory tract is *less* dense than dry air because water vapor ($H_2O$, molecular weight 18) is lighter than Nitrogen ($N_2$, MW 28) and Oxygen ($O_2$, MW 32). * **Heliox Therapy:** In severe airway obstruction (e.g., asthma or croup), a mixture of Helium and Oxygen (Heliox) is used because its lower density reduces Reynolds number, promoting **laminar flow** and decreasing the work of breathing.

Question 363: In the action potential of a nerve, what is the 'overshoot'?

A. Above the iso-potential line (Correct Answer)
B. Below the iso-potential line
C. Below the resting membrane potential
D. Above the resting membrane potential

Explanation: ### Explanation **1. Why Option A is Correct:** In the context of an action potential, the **overshoot** refers to the portion of the depolarization phase where the membrane potential becomes **positive**. * The **iso-potential line** (or zero potential line) represents 0 mV. * During the rapid influx of $Na^+$ ions, the membrane potential moves from its negative resting state, crosses the zero mark, and reaches a peak (usually around +35 mV). * Therefore, any value **above the iso-potential line** is termed the overshoot. It represents the reversal of membrane polarity. **2. Why the Other Options are Incorrect:** * **Option B:** Values below the iso-potential line are simply part of the depolarization or repolarization phases within the negative range. * **Option C:** Values below the resting membrane potential (RMP) are referred to as **After-hyperpolarization** (or undershoot), caused by the slow closure of $K^+$ channels. * **Option D:** While the overshoot is technically above the RMP, this is an incomplete definition. The region between the RMP (-70 mV) and the iso-potential line (0 mV) is simply "depolarization." The specific term "overshoot" is reserved only for the positive excursion beyond 0 mV. **3. High-Yield Clinical Pearls for NEET-PG:** * **Ionic Basis:** The overshoot is primarily due to the opening of voltage-gated $Na^+$ channels. It never reaches the $Na^+$ equilibrium potential (+60 mV) because $Na^+$ channels begin to inactivate and $K^+$ channels begin to open. * **Threshold Stimulus:** For an action potential to occur, the stimulus must reach the **firing level** (usually -55 mV). * **Tetrodotoxin (TTX):** A potent toxin found in Pufferfish that blocks voltage-gated $Na^+$ channels, preventing the overshoot and the action potential entirely. * **After-hyperpolarization:** This phase is responsible for the **relative refractory period**.

Question 364: Most of the ATP generated in nerve cells is utilized to energize which of the following pumps or processes?

A. Na-Ca exchanger
B. H-ATPase in the cell membrane
C. Na-K ATPase (Correct Answer)
D. Synthesis of proteins

Explanation: **Explanation:** In nerve cells, the maintenance of the resting membrane potential (RMP) and the restoration of ionic gradients following action potentials are the most energy-demanding processes. The **Na-K ATPase (Sodium-Potassium Pump)** is responsible for this, pumping 3 Na⁺ ions out and 2 K⁺ ions into the cell against their concentration gradients. In the central nervous system, it is estimated that approximately **50% to 70% of the total ATP** generated is consumed by this pump alone to maintain cellular excitability and osmotic balance. **Analysis of Options:** * **Na-Ca Exchanger (Option A):** This is primarily a secondary active transporter (driven by the Na⁺ gradient created by Na-K ATPase) and does not consume the majority of cellular ATP directly. * **H-ATPase (Option B):** While present in certain organelles (like synaptic vesicles) and specific cell types (like renal intercalated cells), it is not the primary consumer of energy in a standard nerve cell. * **Synthesis of Proteins (Option D):** While protein synthesis is energy-intensive, it accounts for a much smaller fraction of the total energy budget in a mature neuron compared to the continuous demands of ion transport. **High-Yield Clinical Pearls for NEET-PG:** * **Electrogenic Nature:** The Na-K ATPase is electrogenic because it moves 3 positive charges out for every 2 in, contributing roughly -4 to -10 mV to the RMP. * **Digitalis/Ouabain:** These drugs specifically inhibit the Na-K ATPase by binding to the extracellular alpha subunit. * **Metabolic Rate:** The brain represents only 2% of body weight but consumes 20% of the body's total oxygen, largely to fuel the Na-K ATPase.

Question 365: Which of the following is not mediated through a negative feedback mechanism?

A. Blood Pressure (BP) regulation
B. Growth Hormone (GH) formation
C. Thrombus formation (Correct Answer)
D. Adrenocorticotropic Hormone (ACTH) release

Explanation: **Explanation:** The core concept tested here is the difference between **Negative Feedback** (which maintains homeostasis by reversing a change) and **Positive Feedback** (which amplifies a change, leading to an "all-or-none" event). **Why Thrombus formation is correct:** Thrombus formation (blood clotting) is a classic example of a **Positive Feedback mechanism**. When a vessel is injured, platelets adhere to the site and release chemicals (like ADP and Thromboxane A2) that attract more platelets. This cycle continues and accelerates until the plug is formed. Other examples of positive feedback include the LH surge during ovulation, uterine contractions during childbirth (Ferguson reflex), and the opening of sodium channels during an action potential. **Why the other options are incorrect:** * **BP Regulation:** Regulated primarily via the **Baroreceptor reflex**. An increase in BP triggers mechanisms to decrease it, and vice versa, to maintain a set point. * **GH Formation & ACTH Release:** Most endocrine axes operate on negative feedback. For instance, high levels of Cortisol inhibit the release of ACTH from the anterior pituitary. Similarly, GH and its mediator IGF-1 inhibit further GH secretion. **High-Yield Clinical Pearls for NEET-PG:** * **Homeostasis:** Most physiological systems in the body utilize negative feedback to ensure stability. * **Gain of Control:** The efficiency of a feedback system is called its "Gain." The baroreceptor system has a high gain, making it very effective. * **Vicious Cycle:** If a positive feedback loop is not controlled (e.g., severe hemorrhagic shock leading to decreased cardiac output and further BP drop), it can lead to death.

Question 366: Which of the following interleukins is known to cause fever?

A. IL-1 (Correct Answer)
B. IL-6
C. IL-7
D. IL-8

Explanation: ### Explanation **Correct Option: A (IL-1)** Interleukin-1 (IL-1) is a potent **endogenous pyrogen**. When the body encounters pathogens, macrophages and other immune cells release IL-1 into the bloodstream. IL-1 travels to the **anterior hypothalamus**, where it stimulates the synthesis of **Prostaglandin E2 (PGE2)** via the induction of the cyclooxygenase (COX) enzyme. PGE2 then acts on the thermoregulatory center to increase the "set-point" of body temperature, resulting in fever. While IL-6 and TNF-α also possess pyrogenic properties, IL-1 is classically recognized as the primary mediator in medical examinations. **Analysis of Incorrect Options:** * **B. IL-6:** While IL-6 is a pro-inflammatory cytokine and can contribute to the acute phase response and fever, it is primarily known for inducing the synthesis of **acute-phase reactants** (like CRP) in the liver. * **C. IL-7:** This is a hematopoietic growth factor secreted by stromal cells in the bone marrow and thymus. Its primary role is the proliferation and differentiation of **B and T cell progenitors**, not thermoregulation. * **D. IL-8:** This is a major **chemotactic factor** (chemokine). Its primary function is to recruit and activate **neutrophils** at the site of inflammation ("Neutrophils arrive at 8"). **High-Yield Clinical Pearls for NEET-PG:** * **Endogenous Pyrogens:** IL-1 (most potent), TNF-α, IL-6, and Interferons. * **Exogenous Pyrogens:** The most common is **LPS (Lipopolysaccharide)** from Gram-negative bacteria. * **Mechanism of NSAIDs:** Drugs like Paracetamol and Aspirin reduce fever by inhibiting the COX enzyme, thereby blocking PGE2 synthesis in the hypothalamus. * **Thermoregulatory Center:** Located in the **Preoptic area of the Anterior Hypothalamus**.

Question 367: Antiperistalsis is more commonly seen in which part of the gastrointestinal tract?

A. Colon
B. Jejunum
C. Ileum
D. Duodenum (Correct Answer)

Explanation: **Explanation:** **Antiperistalsis** (reverse peristalsis) refers to wave-like muscular contractions that move luminal contents in an oral direction rather than aboral. **Why Duodenum is Correct:** The duodenum is the most common site for physiological antiperistalsis. This occurs primarily to facilitate the **mixing of chyme** with pancreatic enzymes and bile, and to neutralize gastric acid by pushing bicarbonate-rich secretions back toward the pylorus. Furthermore, during the vomiting reflex, strong antiperistaltic waves originate in the duodenum and jejunum, pushing intestinal contents back into the stomach before expulsion. **Analysis of Incorrect Options:** * **Jejunum & Ileum:** While reverse peristalsis can occur here during pathological states (like intestinal obstruction), it is not a frequent physiological feature. The primary motility patterns here are segmentation (mixing) and orthograde peristalsis (propulsion). * **Colon:** The colon primarily exhibits **haustral churning** and **mass movements**. While "antiperistaltic" like waves occur in the ascending colon to delay transit and enhance water absorption, they are less frequent and less characteristic than the functional reverse waves seen in the duodenum. **High-Yield Clinical Pearls for NEET-PG:** * **Vomiting Center:** Located in the **Area Postrema** (medulla), it triggers the antiperistaltic rush. * **Duodenal Ulcers:** Often associated with rapid gastric emptying; however, normal duodenal motility requires these reverse waves for acid neutralization. * **Migrating Motor Complex (MMC):** The "intestinal housekeeper" waves that occur during fasting; these move in the **aboral** direction (stomach to ileum), unlike antiperistalsis.

Question 368: If the plasma concentration of a freely filterable substance is 2 mg/mL, GFR is 100 mL/min, urine concentration of the substance is 10 mg/mL, and urine flow rate is 5 mL/min, what can be concluded about the kidney tubules?

A. Reabsorbed 150 mg/min (Correct Answer)
B. Reabsorbed 200 mg/min
C. Secreted 50 mg/min
D. Secreted 150 mg/min

Explanation: To solve this problem, we must compare the **Filtered Load** of the substance with its **Excretion Rate**. ### 1. Calculation * **Filtered Load:** This is the amount of substance filtered at the glomerulus per minute. * Formula: $GFR \times \text{Plasma Concentration } (P_x)$ * Calculation: $100\text{ mL/min} \times 2\text{ mg/mL} = \mathbf{200\text{ mg/min}}$ * **Excretion Rate:** This is the amount of substance actually leaving the body in urine per minute. * Formula: $\text{Urine Flow Rate } (V) \times \text{Urine Concentration } (U_x)$ * Calculation: $5\text{ mL/min} \times 10\text{ mg/mL} = \mathbf{50\text{ mg/min}}$ ### 2. Interpretation Since the **Filtered Load (200 mg/min)** is greater than the **Excretion Rate (50 mg/min)**, it means that 150 mg of the substance was "lost" during its passage through the tubules. Therefore, the tubules must have **reabsorbed** the difference. * **Net Transport = Filtered Load – Excretion Rate** * $200 - 50 = \mathbf{150\text{ mg/min (Reabsorbed)}}$ ### 3. Why Incorrect Options are Wrong * **B (Reabsorbed 200 mg/min):** This would imply an excretion rate of zero (complete reabsorption, like glucose in a healthy individual). * **C & D (Secreted):** Secretion occurs only when the Excretion Rate is **greater** than the Filtered Load (e.g., PAH or Creatinine). Here, the excretion is much lower than the filtration. ### 4. NEET-PG High-Yield Pearls * **Clearance Ratio:** If $C_x / C_{\text{inulin}} < 1$, the substance is reabsorbed. If $> 1$, the substance is secreted. * **Freely Filterable:** This term implies the substance's concentration in the Bowman’s space equals its concentration in the plasma (no protein binding). * **Glucose:** At normal plasma levels, filtered load = reabsorption rate (Excretion = 0). Glucosuria occurs only when the filtered load exceeds the $T_m$ (Transport Maximum) of SGLT transporters.

Question 369: During regulatory volume decrease, what do many cells do?

A. Increase their volume
B. Increase influx of Na+
C. Increase efflux of K+ (Correct Answer)
D. Increase synthesis of sorbitol

Explanation: **Explanation:** Cell volume regulation is a critical homeostatic process. When a cell is placed in a hypotonic environment, water enters the cell via osmosis, causing it to swell. To prevent lysis, the cell undergoes **Regulatory Volume Decrease (RVD)**. **1. Why Option C is Correct:** The primary mechanism of RVD is the rapid **efflux of intracellular osmolytes**. Cells activate specific channels to allow **K+ and Cl-** to exit the cytoplasm. As these ions leave the cell, water follows them osmotically, effectively reducing the cell volume back to its original state. This is primarily mediated by swell-activated K+ channels and Cl- channels. **2. Why the other options are incorrect:** * **Option A:** RVD is a compensatory mechanism to *decrease* volume after initial swelling; increasing volume would be counterproductive. * **Option B:** Increasing Na+ influx would increase intracellular osmolarity, drawing more water *into* the cell and worsening the swelling. (Na+ influx is typically seen in Regulatory Volume Increase/RVI). * **Option C:** Sorbitol is an "organic osmolyte." Cells increase the synthesis or uptake of organic osmolytes (like sorbitol, betaine, or inositol) during **Regulatory Volume Increase (RVI)** to protect against shrinkage in hypertonic environments (e.g., in the renal medulla). **High-Yield Clinical Pearls for NEET-PG:** * **RVD (Regulatory Volume Decrease):** Response to hypotonicity $\rightarrow$ Efflux of K+, Cl-, and organic solutes. * **RVI (Regulatory Volume Increase):** Response to hypertonicity $\rightarrow$ Influx of Na+, Cl-, and synthesis of organic osmolytes (Sorbitol). * **Brain Adaptation:** In chronic hyponatremia, the brain cells perform RVD by losing organic osmolytes. Rapid correction with hypertonic saline can lead to **Osmotic Demyelination Syndrome (Central Pontine Myelinolysis)** because the cells cannot regain these osmolytes fast enough.

Question 370: Peripheral cell membrane proteins are:

A. Pumps
B. Channels
C. Adhesion molecules (Correct Answer)
D. Enzyme receptors

Explanation: ### Explanation Cell membrane proteins are classified into two main categories based on their location and attachment: **Integral (Transmembrane)** and **Peripheral** proteins. **1. Why Adhesion Molecules are the Correct Answer:** Peripheral proteins do not span the entire lipid bilayer; instead, they are loosely attached to the inner or outer surfaces of the membrane via electrostatic interactions or covalent bonds with integral proteins. **Adhesion molecules** (such as certain selectins or components of the cytoskeleton like spectrin and ankyrin) often function as peripheral proteins, providing structural support and facilitating cell-to-cell or cell-to-matrix interactions. **2. Why the Other Options are Incorrect:** * **A. Pumps (e.g., Na+-K+ ATPase):** These are **Integral proteins**. They must span the entire membrane to transport ions from one side to the other against a concentration gradient. * **B. Channels (e.g., Aquaporins, Voltage-gated Na+ channels):** These are **Integral proteins**. They form a continuous pore across the hydrophobic lipid bilayer to allow the passage of water or ions. * **C. Enzyme Receptors (e.g., Insulin receptor, GPCRs):** These are **Integral proteins**. They require an extracellular domain for ligand binding and an intracellular domain for signal transduction, necessitating a transmembrane structure. **3. NEET-PG High-Yield Clinical Pearls:** * **Fluid Mosaic Model:** Proposed by Singer and Nicolson (1972), it describes the membrane as a "sea of lipids" with "floating proteins." * **Spectrin & Hereditary Spherocytosis:** Spectrin is a classic example of a **peripheral protein** in the RBC membrane. A deficiency in spectrin leads to Hereditary Spherocytosis, where RBCs become fragile and spherical. * **Glycocalyx:** The carbohydrate coat on the outer surface of the cell membrane (involved in immune recognition) is formed by glycoproteins and glycolipids. * **Integral vs. Peripheral:** Integral proteins can only be removed by detergents (disrupting the bilayer), whereas peripheral proteins can be removed by changing pH or salt concentration.

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