General Physiology Practice Questions

Q: What does the term "Meileu interior" refer to in physiology?

Extracellular fluid (ECF). **Explanation:** The term **"Milieu intérieur"** (French for "the environment within") was coined by the 19th-century French physiologist **Claude Bernard**. It refers specifically to the **Extracellular Fluid (ECF)** that surrounds and bathes the cells of multicellular organisms. **Why ECF is the correct answer:** Claude Bernard proposed that for an organism to remain healthy and independent of the external environment, its internal environment must remain constant. Since cells do not come into direct contact with the outside world, they rely on the ECF (interstitial fluid and plasma) for nutrients and waste removal. This concept laid the foundation for **Homeostasis**, a term later popularized by Walter Cannon. **Analysis of Incorrect Options:** * **Intracellular Fluid (ICF):** This is the fluid *inside* the cells. While vital, it is not the "internal environment" described by Bernard; rather, it is the environment that the *Milieu intérieur* protects and maintains. * **Plasma:** Plasma is a sub-component of the ECF (along with interstitial fluid). While it is part of the internal environment, "Milieu intérieur" encompasses the *entire* ECF. * **Lymph:** Similar to plasma, lymph is merely a specialized part of the ECF. **NEET-PG High-Yield Pearls:** * **Claude Bernard:** Known as the "Father of Modern Physiology"; he introduced the concept of *Milieu intérieur*. * **Walter Cannon:** Coined the term **Homeostasis** to describe the maintenance of a constant *Milieu intérieur*. * **ECF Composition:** ECF constitutes approximately **20%** of total body weight (15% interstitial fluid, 5% plasma). * **Total Body Water (TBW):** Roughly 60% of body weight; ICF makes up 40%, and ECF makes up 20%.

Q: Glucose and amino acids are reabsorbed from the proximal convoluted tubule or absorbed from the intestinal lumen by which transport mechanism?

Symport. ### Explanation The correct answer is **Symport** (also known as Co-transport). **1. Why Symport is Correct:** In both the Proximal Convoluted Tubule (PCT) and the small intestine, glucose and amino acids are transported against their concentration gradients. This is achieved via **Secondary Active Transport**. * **Mechanism:** The **Na⁺-K⁺ ATPase pump** (on the basolateral membrane) creates a steep electrochemical gradient for Sodium (Na⁺) to enter the cell. * **The Process:** Specialized carrier proteins (like **SGLT-1** in the gut and **SGLT-2** in the PCT) use the energy from this Na⁺ gradient to pull glucose/amino acids into the cell. Because both Na⁺ and the nutrient move in the **same direction** across the apical membrane, the mechanism is classified as **Symport**. **2. Why Other Options are Incorrect:** * **Antiport (Counter-transport):** This involves two substances moving in opposite directions (e.g., the Na⁺-H⁺ exchanger in the PCT). * **Uniport:** This involves a single substance moving down its gradient (e.g., **GLUT-2** transporting glucose out of the basolateral membrane into the blood). * **Primary Active Transport:** This refers to transport directly powered by ATP hydrolysis (e.g., Na⁺-K⁺ ATPase). While symport *depends* on this, the actual movement of glucose/amino acids is secondary. **3. High-Yield Clinical Pearls for NEET-PG:** * **SGLT-2 Inhibitors (e.g., Dapagliflozin):** A major class of drugs for Diabetes Mellitus that work by inhibiting glucose reabsorption in the PCT, causing glucosuria. * **Hartnup Disease:** A defect in the symport carrier for neutral amino acids (like Tryptophan) in the gut and kidneys. * **Renal Threshold for Glucose:** Approximately **180 mg/dL**. Beyond this plasma concentration, SGLT transporters become saturated ($T_m$ is reached), and glucose appears in the urine.

Q: What is the approximate volume of interstitial fluid in a normal adult?

10 L. **Explanation:** The distribution of body fluids is a high-yield topic in Physiology. To determine the volume of interstitial fluid, we apply the **"60-40-20 Rule"** for a standard 70 kg adult: * **Total Body Water (TBW):** 60% of body weight (≈ 42 L). * **Intracellular Fluid (ICF):** 40% of body weight (≈ 28 L). * **Extracellular Fluid (ECF):** 20% of body weight (≈ 14 L). The ECF is further divided into two main sub-compartments: **Interstitial Fluid (ISF)** and **Plasma**. Interstitial fluid constitutes approximately **3/4th of the ECF volume** (15% of body weight), while Plasma constitutes **1/4th** (5% of body weight). * Calculation: 75% of 14 L = **10.5 L** (Approx. 10 L). **Analysis of Options:** * **Option A (5 L):** This represents the approximate total **Blood Volume** (Plasma + RBCs) or roughly the Plasma volume (3.5 L) plus some transcellular fluid. * **Option B (10 L):** **Correct.** This matches the 15% body weight calculation for interstitial fluid. * **Option C (15 L):** This is close to the total **ECF volume** (14 L), not just the interstitial component. * **Option D (20 L):** This value does not correspond to a standard physiological compartment in a 70 kg adult. **NEET-PG High-Yield Pearls:** 1. **Indicator Dilution Method:** Inulin, Mannitol, and Sucrose are used to measure ECF volume. Radioactive Iodine-labeled Albumin or Evans Blue dye is used for Plasma volume. 2. **Interstitial Fluid Calculation:** It cannot be measured directly; it is calculated as **ECF volume minus Plasma volume**. 3. **Transcellular Fluid:** Includes CSF, intraocular, and synovial fluids (approx. 1–2 L); it is considered a specialized part of the ECF.

Q: Undamped oscillations are caused by:

High gain. ### Explanation **Correct Answer: C. High gain** In control systems, **Gain** refers to the efficiency or the "strength" of a feedback system in correcting a disturbance. While negative feedback is generally stabilizing, if the **gain is excessively high**, the system overcorrects for any deviation. This leads to an overshoot in the opposite direction, followed by another overcorrection. These continuous, repetitive cycles of over-adjustment result in **undamped oscillations** (vicious cycles of instability), where the system fails to return to a steady state. #### Why the other options are incorrect: * **A. Negative Feedback:** This is the most common regulatory mechanism in the body (e.g., BP or temperature control). Its primary goal is **stability** and damping of fluctuations, not causing undamped oscillations. * **B. Positive Feedback:** This leads to a "vicious cycle" or a "snowball effect" where the output increases until a climax is reached (e.g., LH surge, blood clotting, or labor). It does not typically produce oscillations; it moves the system away from the starting point. * **C. Feed-forward Control:** This is an **anticipatory** mechanism (e.g., increased heart rate before exercise). It allows the body to predict a change and act before the disturbance occurs, thereby preventing delay and minimizing oscillations. #### High-Yield NEET-PG Pearls: * **Gain Formula:** Gain = Correction / Residual Error. * **Highest Gain System:** The **Baroreceptor reflex** has a high gain, but the **CNS Ischemic Response** has the highest gain of all pressure-regulating systems (often cited as infinite or extremely high). * **Clinical Correlation:** **Cheyne-Stokes breathing** is a classic clinical example of undamped oscillations caused by a delay in the feedback loop and high gain in the respiratory centers (often seen in heart failure or brain damage).

Q: Plasma volume is best evaluated by using which substance?

Evan's blue. To measure the volume of any body fluid compartment, the **Indicator Dilution Method** ($V = Q/C$) is used. The ideal substance must be non-toxic, distribute evenly, and remain exclusively within the compartment being measured. ### Why Evan’s Blue is Correct **Evan’s Blue (T-1824)** is the gold standard for measuring **Plasma Volume**. This is because the dye binds strongly and almost instantaneously to **serum albumin**. Since albumin is too large to easily cross the capillary wall, the dye remains confined within the vascular space. Alternatively, **Radio-iodinated Serum Albumin (RISA)** can also be used for this purpose. ### Why Other Options are Incorrect * **Inulin & Mannitol (Options B & C):** These substances are small enough to cross the capillary endothelium but cannot cross the cell membrane. Therefore, they distribute throughout the entire **Extracellular Fluid (ECF)** volume (plasma + interstitial fluid). * **Radiolabeled Water (Option D):** Deuterium oxide ($D_2O$), Tritiated water ($THO$), and Aminopyrine distribute freely across all membranes. They are used to measure **Total Body Water (TBW)**. ### High-Yield NEET-PG Pearls * **Blood Volume Calculation:** Once plasma volume is determined, Total Blood Volume can be calculated using the formula: $Blood Volume = \frac{Plasma Volume}{1 - Hematocrit}$. * **Interstitial Fluid:** Cannot be measured directly. It is calculated as: $ECF - Plasma Volume$. * **Intracellular Fluid (ICF):** Cannot be measured directly. It is calculated as: $TBW - ECF$. * **Summary Table:** * **TBW:** $D_2O$, Tritiated water, Aminopyrine. * **ECF:** Inulin, Mannitol, Sucrose, Thiosulfate. * **Plasma:** Evan's Blue, RISA ($I^{131}$-albumin). * **RBC Volume:** $Cr^{51}$-labeled RBCs.

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

Thrombus formation. **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.

Q: During regulatory volume decrease, what do many cells do?

Increase efflux of K+. **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.

Q: Which enzyme is utilized by the Na+/K+ pump?

ATPase. ### Explanation The **Na+/K+ pump** (Sodium-Potassium Pump) is a classic example of **Primary Active Transport**. It moves ions against their concentration gradients—specifically pumping **3 Na+ ions out** of the cell and **2 K+ ions into** the cell. **1. Why ATPase is correct:** To move ions against a gradient, the pump requires energy. This energy is derived from the hydrolysis of Adenosine Triphosphate (ATP). The pump itself acts as an enzyme called **Na+/K+-ATPase**. It catalyzes the breakdown of ATP into ADP and inorganic phosphate (Pi), releasing the energy necessary to induce conformational changes in the protein carrier. **2. Why the other options are incorrect:** * **GTPase:** These enzymes hydrolyze GTP (not ATP). They are primarily involved in signal transduction (e.g., G-proteins) and protein synthesis, not the primary active transport of electrolytes. * **Acetyl CoA:** This is a central molecule in metabolism (Krebs cycle) that carries carbon atoms. It is a substrate, not an enzyme, and does not directly power ion pumps. * **NADPH:** This is a reducing agent used in anabolic reactions (like lipid synthesis) and the respiratory burst in neutrophils. It does not provide the phosphate-bond energy required for the Na+/K+ pump. **High-Yield Clinical Pearls for NEET-PG:** * **Stoichiometry:** 3 Na+ Out / 2 K+ In. This makes the pump **electrogenic**, contributing to the negative resting membrane potential. * **Inhibitor:** The pump is specifically inhibited by **Cardiac Glycosides** (e.g., **Ouabain** and **Digoxin**). * **Energy Consumption:** In a resting individual, this pump accounts for approximately **25-30%** of total body energy expenditure (and up to 70% in neurons). * **States:** It exists in two states: **E1** (high affinity for Na+) and **E2** (high affinity for K+).

Q: Basal Metabolic Rate (BMR) is dependent on which of the following factors?

Body surface area. **Explanation:** **Why Body Surface Area (BSA) is the Correct Answer:** The Basal Metabolic Rate (BMR) is most closely correlated with **Body Surface Area (BSA)** rather than absolute weight. This is based on the "Surface Law," which states that metabolic rate is proportional to the amount of heat lost from the body. Since heat loss occurs primarily through the skin, individuals with a larger surface area relative to their volume lose heat more rapidly and thus require a higher metabolic rate to maintain core temperature. In clinical practice and research, BMR is standardly expressed as **kcal/m²/hour**. **Analysis of Incorrect Options:** * **A. Body Weight:** While BMR increases with weight, it is not a linear or accurate predictor. Two individuals of the same weight but different heights will have different BMRs because their surface areas differ. * **C. Amount of Adipose Tissue:** Fat is metabolically inactive. An increase in adipose tissue actually **decreases** the BMR per unit of body weight. * **D. Amount of Lean Body Mass (LBM):** While LBM is the most significant *internal* determinant of BMR (as muscle is metabolically active), the standard physiological measurement and the "law" governing BMR calculation is based on **Surface Area**. **High-Yield Clinical Pearls for NEET-PG:** * **Highest BMR:** Found in infants (due to rapid growth) and males (due to higher testosterone and muscle mass). * **Hormonal Influence:** **Thyroid hormone** is the single most important regulator of BMR. Epinephrine and cortisol also increase it. * **Starvation/Hypothalamic lesions:** These significantly **decrease** BMR as a compensatory mechanism to conserve energy. * **Specific Dynamic Action (SDA):** Protein has the highest SDA (30%), meaning it increases the metabolic rate significantly during digestion.

Q: What is the osmotic pressure of 1 mole of an ideal solute in relation to pure water?

22.4 atm. **Explanation:** The osmotic pressure of a solution is determined by the number of particles (solute) present in a given volume, a principle governed by **van't Hoff’s Law**. This law states that osmotic pressure ($\pi$) is analogous to the Ideal Gas Law ($PV = nRT$). **Why Option B is Correct:** According to the laws of thermodynamics and physical chemistry, **1 mole of an ideal, non-ionizable solute** dissolved in 1 liter of water at standard temperature and pressure (0°C or 273K) exerts an osmotic pressure of **22.4 atmospheres (atm)**. This value is a constant derived from the formula $\pi = iCRT$, where: * $i$ = Van't Hoff factor (1 for ideal solute) * $C$ = Concentration (1 mol/L) * $R$ = Gas constant (0.0821 L·atm/mol·K) * $T$ = Temperature (273 K) Calculation: $1 \times 1 \times 0.0821 \times 273 \approx 22.4 \text{ atm}$. **Why Incorrect Options are Wrong:** * **Options A, C, and D:** These values (6.5, 4, and 2 atm) do not correspond to the standard physical constant for a 1-molar solution. They are arbitrary numbers that do not satisfy the $PV=nRT$ derivation for a molar concentration at standard temperature. **High-Yield Clinical Pearls for NEET-PG:** * **Osmolarity vs. Osmolality:** In clinical medicine, we usually measure *osmolality* (mOsm/kg of water) because it is independent of temperature. * **Plasma Osmotic Pressure:** Normal plasma osmolality is ~285–295 mOsm/L. * **Oncotic Pressure:** Also known as colloid osmotic pressure, it is specifically exerted by proteins (mainly albumin) and is approximately **25–28 mmHg** (not atm), crucial for preventing edema. * **Conversion:** 1 mOsm/L of a solute exerts an osmotic pressure of approximately **19.3 mmHg**.

Question 1

What does the term "Meileu interior" refer to in physiology?

Accepted Answer

Extracellular fluid (ECF)

Answer

Intracellular fluid (ICF)

Answer

Plasma

Answer

Lymph

Question 2

Glucose and amino acids are reabsorbed from the proximal convoluted tubule or absorbed from the intestinal lumen by which transport mechanism?

Accepted Answer

Symport

Answer

Antiport

Answer

Uniport

Answer

Primary active transport

Question 3

What is the approximate volume of interstitial fluid in a normal adult?

Accepted Answer

10 L

Answer

5 L

Answer

15 L

Answer

20 L

Question 4

Undamped oscillations are caused by:

Accepted Answer

High gain

Answer

Negative feedback

Answer

Positive feedback

Answer

Feed forward control

Question 5

Plasma volume is best evaluated by using which substance?

Accepted Answer

Evan's blue

Answer

Inulin

Answer

Mannitol

Answer

Radiolabeled water

Question 6

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

Accepted Answer

Thrombus formation

Answer

Blood Pressure (BP) regulation

Answer

Growth Hormone (GH) formation

Answer

Adrenocorticotropic Hormone (ACTH) release

Question 7

During regulatory volume decrease, what do many cells do?

Accepted Answer

Increase efflux of K+

Answer

Increase their volume

Answer

Increase influx of Na+

Answer

Increase synthesis of sorbitol

Question 8

Which enzyme is utilized by the Na+/K+ pump?

Accepted Answer

ATPase

Answer

GTPase

Answer

Acetyl CoA

Answer

NADPH

Question 9

Basal Metabolic Rate (BMR) is dependent on which of the following factors?

Accepted Answer

Body surface area

Answer

Body weight

Answer

Amount of adipose tissue

Answer

Amount of lean body mass

Question 10

What is the osmotic pressure of 1 mole of an ideal solute in relation to pure water?

Accepted Answer

22.4 atm

Answer

6.5 atm

Answer

4 atm

Answer

2 atm

General Physiology — MCQs

General Physiology — MCQs

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