General Physiology — MCQs

General Physiology Indian Medical PG Practice Questions and MCQs

Question 71: What is the ratio of ions moving out of the cell to the number of ions moving inside the cell via the Na:K ATPase pump?

A. 2:3
B. 3:1
C. 1:3
D. 3:2 (Correct Answer)

Explanation: ### Explanation **1. Why Option D is Correct:** The **Na⁺-K⁺ ATPase pump** (also known as the Sodium-Potassium pump) is a primary active transport mechanism located in the plasma membrane of almost all animal cells. For every single molecule of ATP hydrolyzed, the pump undergoes a conformational change that transports **3 Sodium (Na⁺) ions out** of the cell and **2 Potassium (K⁺) ions into** the cell. Therefore, the ratio of ions moving out to ions moving in is **3:2**. **2. Why Other Options are Incorrect:** * **Option A (2:3):** This is the inverse of the correct ratio. While 2 and 3 are the correct numbers, the direction is wrong (2 K⁺ move in, not out). * **Option B (3:1):** This ratio is seen in the **Sodium-Calcium Exchanger (NCX)**, which typically moves 3 Na⁺ ions into the cell in exchange for 1 Ca²⁺ ion out. * **Option C (1:3):** This does not correspond to any major physiological transport pump ratio in general physiology. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Electrogenic Nature:** Because it moves 3 positive charges out for every 2 positive charges in, the pump creates a net deficit of positive ions inside the cell. This contributes to the **negative Resting Membrane Potential (RMP)**. * **Energy Consumption:** This pump accounts for approximately **30% to 70%** of the total ATP consumption in many cells, especially neurons. * **Pharmacology Link:** **Cardiac Glycosides (e.g., Digoxin, Ouabain)** specifically inhibit the Na⁺-K⁺ ATPase. This inhibition increases intracellular Na⁺, which subsequently slows the Na⁺-Ca²⁺ exchanger, leading to increased intracellular Ca²⁺ and increased cardiac contractility (positive inotropy). * **Insulin & Potassium:** Insulin stimulates Na⁺-K⁺ ATPase activity, shifting K⁺ into cells. This is why insulin/glucose infusion is used to treat **hyperkalemia**.

Question 72: What is the primary function of the basement membrane?

A. Excitation
B. Contraction
C. Filtration (Correct Answer)
D. Transport of anions

Explanation: The **basement membrane (BM)** is a specialized form of extracellular matrix that underlies all epithelial and endothelial cells. Its primary physiological function is to act as a **selective permeability barrier (Filtration)**. ### Why "Filtration" is Correct: The basement membrane, particularly in the renal glomerulus (Glomerular Basement Membrane - GBM), acts as a sophisticated filter. It regulates the passage of molecules based on two criteria: 1. **Size Selectivity:** The dense meshwork of **Type IV Collagen** and **Laminin** creates physical pores that restrict large proteins (like albumin). 2. **Charge Selectivity:** The BM is rich in **Heparan sulfate proteoglycans**, which are negatively charged. This creates an electrostatic barrier that repels other negatively charged molecules (anions). ### Why Other Options are Incorrect: * **A. Excitation:** This is a property of "excitable tissues" like neurons and muscle cells, involving rapid changes in membrane potential via ion channels. The BM is non-cellular and lacks this property. * **B. Contraction:** This is the primary function of muscle tissue (actin-myosin interaction). The BM provides structural support but cannot actively shorten or generate force. * **D. Transport of anions:** This is incorrect because the BM actually **restricts** or repels the transport of anions (like albumin) due to its negative charge. Active transport of ions is a function of the cellular plasma membrane, not the basement membrane. ### NEET-PG High-Yield Pearls: * **Composition:** The BM consists of the *Basal Lamina* (secreted by epithelial cells; contains Type IV Collagen) and the *Reticular Lamina* (secreted by fibroblasts; contains Type III Collagen). * **Goodpasture Syndrome:** Autoantibodies against the alpha-3 chain of Type IV Collagen lead to glomerulonephritis and pulmonary hemorrhage. * **Alport Syndrome:** A genetic defect in Type IV Collagen resulting in a "split" basement membrane, leading to hereditary nephritis and sensorineural deafness.

Question 73: What does the PR interval on an ECG represent in terms of electrical conduction time from the SA node to the AV node?

A. PR interval (Correct Answer)
B. ST segment
C. QT interval
D. Cannot be determined by ECG

Explanation: **Explanation:** The **PR interval** represents the time taken for electrical impulses to travel from the onset of atrial depolarization (SA node) to the onset of ventricular depolarization. It encompasses the conduction through the atria, the AV node (where the physiological delay occurs), the Bundle of His, and the Purkinje system. * **Why Option A is correct:** The PR interval specifically measures the time from the beginning of the P wave to the beginning of the QRS complex. Since the AV node is the primary site of conduction delay, the PR interval is the clinical marker used to assess the speed of conduction from the atria to the ventricles. * **Why Option B is incorrect:** The **ST segment** represents the period when the ventricles are completely depolarized (plateau phase of the action potential) and is used to identify myocardial ischemia or infarction. * **Why Option C is incorrect:** The **QT interval** represents the total time for ventricular depolarization and repolarization (electrical systole). * **Why Option D is incorrect:** While the ECG cannot visualize the SA node firing directly, the PR interval is the standard indirect measurement for this conduction time. **High-Yield NEET-PG Pearls:** 1. **Normal Duration:** 0.12 to 0.20 seconds (3-5 small squares). 2. **AV Nodal Delay:** The majority of the PR interval is due to the slow conduction in the AV node (0.09s), which allows for optimal ventricular filling (atrial kick). 3. **Clinical Correlation:** A PR interval >0.20s indicates **First-degree Heart Block**, whereas a short PR interval (<0.12s) is characteristic of **Wolff-Parkinson-White (WPW) syndrome** due to accessory pathways (Bundle of Kent).

Question 74: Who coined the term "Milieu intérieur"?

A. Knut Schmidt-Nielsen
B. George Bartholomew
C. Claude Bernard (Correct Answer)
D. Walter Cannon

Explanation: **Explanation:** The correct answer is **Claude Bernard**. **1. Why Claude Bernard is correct:** Claude Bernard, a French physiologist often called the "Father of Modern Physiology," introduced the concept of **"Milieu intérieur"** (Internal Environment) in the mid-19th century. He proposed that for an organism to remain healthy and independent of the external environment, its internal fluids (interstitial fluid and plasma) must remain constant. This concept laid the foundational groundwork for what we now understand as physiological regulation. **2. Analysis of Incorrect Options:** * **Walter Cannon:** He is the most common distractor. While Bernard coined "Milieu intérieur," Walter Cannon later (1926) coined the term **"Homeostasis"** to describe the processes by which this internal constancy is maintained. He also described the "Fight or Flight" response. * **Knut Schmidt-Nielsen:** A prominent figure in comparative physiology known for his work on how animals survive in extreme environments (e.g., camels in deserts) and scaling in biology. * **George Bartholomew:** A pioneer in physiological ecology who focused on the relationship between an animal's physiology and its natural environment. **3. NEET-PG High-Yield Pearls:** * **Claude Bernard:** Coined "Milieu intérieur"; discovered the glycogenic function of the liver. * **Walter Cannon:** Coined "Homeostasis"; "Fight or Flight" response; "Emergency theory" of the adrenal glands. * **Homeostasis:** Maintenance of a nearly constant internal environment. Most systems use **Negative Feedback** (e.g., blood pressure regulation). * **Positive Feedback:** Usually pathological (e.g., heart failure), but physiological in specific cases: **LH surge** (ovulation), **Oxytocin** (childbirth), and **Blood clotting cascade**.

Question 75: Skeletal muscle primarily utilizes which glucose transporter for uptake?

A. GLUT-1 transporter
B. GLUT-2 transporter
C. GLUT-3 transporter
D. GLUT-4 transporter (Correct Answer)

Explanation: **Explanation:** The correct answer is **GLUT-4 transporter**. **1. Why GLUT-4 is correct:** GLUT-4 is the primary glucose transporter found in **skeletal muscle** and **adipose tissue**. It is unique because it is **insulin-dependent**. In the resting state, GLUT-4 molecules are stored in intracellular vesicles. Upon insulin stimulation (or during exercise), these vesicles translocation to the cell membrane, allowing glucose to enter the cell via facilitated diffusion. This mechanism is crucial for post-prandial glucose lowering. **2. Why other options are incorrect:** * **GLUT-1:** This is an insulin-independent transporter found in almost all tissues, but it is the primary transporter for the **Blood-Brain Barrier (BBB)** and **RBCs**. It maintains basal glucose uptake. * **GLUT-2:** A high-capacity, low-affinity transporter found in the **Liver, Pancreas (beta cells), and Kidney**. It acts as a "glucose sensor" in the pancreas and allows bidirectional transport in the liver. * **GLUT-3:** Found primarily in **Neurons** and the placenta. It has a very high affinity for glucose, ensuring the brain receives priority supply even during hypoglycemia. **3. High-Yield Clinical Pearls for NEET-PG:** * **Exercise & GLUT-4:** Muscle contraction during exercise can trigger GLUT-4 translocation *independent* of insulin. This is why exercise is a key management strategy for Type 2 Diabetes. * **GLUT-5:** This is a specialized transporter for **Fructose**, located primarily in the small intestine and spermatozoa. * **SGLT vs. GLUT:** Remember that SGLT (Sodium-Glucose Linked Transporters) perform **active transport** (secondary), whereas all GLUT transporters perform **facilitated diffusion** (passive).

Question 76: Across the cell membrane of a skeletal muscle cell in the resting state with a non-electrogenic pump, what is the relationship between the rates of ion movement?

A. Both sodium and potassium are in electrochemical equilibrium.
B. The rate of sodium influx is equal to the rate of potassium efflux. (Correct Answer)
C. The rate of sodium influx is much less than the rate of potassium efflux.
D. The rate of sodium influx is much greater than the rate of potassium efflux.

Explanation: ### Explanation **1. Why Option B is Correct: The Concept of Steady State** In a resting skeletal muscle cell, the membrane potential is stable (Resting Membrane Potential or RMP). For the RMP to remain constant, the net charge movement across the membrane must be zero. Even at rest, the membrane is slightly permeable to ions. Sodium ($Na^+$) leaks into the cell (influx) down its electrochemical gradient, while Potassium ($K^+$) leaks out of the cell (efflux). To maintain stability, the **$Na^+$-$K^+$ ATPase pump** must counteract these leaks. Since the question specifies a **non-electrogenic pump** (a theoretical scenario where the pump moves ions in a 1:1 ratio), the rate of $Na^+$ entering must exactly equal the rate of $K^+$ leaving to prevent a change in the membrane charge. In a steady state, **Net Flux = 0**. **2. Why Other Options are Incorrect:** * **Option A:** Neither ion is in electrochemical equilibrium at RMP. If they were, their respective equilibrium potentials ($E_{Na} \approx +65mV$, $E_K \approx -90mV$) would equal the RMP ($\approx -90mV$ for muscle). Only $K^+$ is *near* equilibrium, but $Na^+$ is far from it. * **Options C & D:** If influx and efflux were unequal, the RMP would not be "resting"; the cell would either progressively depolarize or hyperpolarize until it reached a new steady state or became non-functional. **3. NEET-PG High-Yield Pearls:** * **Real-world Pump:** In physiological conditions, the $Na^+$-$K^+$ ATPase is **electrogenic**, pumping **3 $Na^+$ out for every 2 $K^+$ in**, contributing about -5 to -10 mV directly to the RMP. * **Permeability:** At rest, the membrane is **50–100 times more permeable to $K^+$** than to $Na^+$. This is why the RMP is closest to the Equilibrium Potential of $K^+$. * **Gibbs-Donnan Effect:** This describes the behavior of charged particles near a semi-permeable membrane that sometimes fail to distribute evenly due to the presence of non-diffusible ions (like intracellular proteins).

Question 77: What is the hardest tissue in the human body?

A. Enamel (Correct Answer)
B. Bone
C. Muscle
D. Skin

Explanation: **Explanation:** **1. Why Enamel is the Correct Answer:** Enamel is the most highly mineralized and hardest substance in the human body. Its extreme hardness is attributed to its composition: it consists of approximately **96% inorganic material**, primarily in the form of **hydroxyapatite crystals** (calcium phosphate). Unlike other tissues, enamel is acellular and does not contain collagen in its mature state. It is designed to withstand the significant mechanical stresses of mastication (chewing) and to protect the underlying dentin and pulp. **2. Why Other Options are Incorrect:** * **Bone:** While bone is a rigid connective tissue, it is significantly less mineralized than enamel (containing about 65-70% inorganic matter). The presence of organic collagen fibers provides bone with flexibility and tensile strength, but reduces its overall hardness compared to enamel. * **Muscle:** Muscle is a soft tissue composed of contractile proteins (actin and myosin). It has no mineralization and is flexible. * **Skin:** Skin is the largest organ of the body, composed of epithelial and connective tissue. It is soft, pliable, and lacks the mineral density required to be considered "hard." **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Embryological Origin:** Enamel is derived from **Ectoderm** (specifically from the Enamel Organ/Ameloblasts), whereas dentin, cementum, and bone are derived from Mesoderm/Ectomesenchyme. * **Regeneration:** Because **Ameloblasts** are lost after tooth eruption, enamel cannot regenerate or repair itself biologically. * **Fluoride Action:** Fluoride prevents dental caries by replacing the hydroxyl group in hydroxyapatite to form **Fluorapatite**, which is even more resistant to acid dissolution. * **Hardness Scale:** On the Mohs scale of mineral hardness, enamel ranks around 5, while bone is significantly lower.

Question 78: Which of the following would cause a decrease in stroke volume when compared with the normal resting value?

A. Reduction in afterload
B. An increase in end-diastolic pressure
C. Stimulation of the vagus nerves
D. Electrical pacing to a heart rate of 200 beats/min (Correct Answer)

Explanation: **Explanation** Stroke Volume (SV) is determined by the formula: **SV = End-Diastolic Volume (EDV) – End-Systolic Volume (ESV)**. Any factor that significantly decreases EDV or increases ESV will reduce stroke volume. **Why Option D is Correct:** At extremely high heart rates (e.g., **200 beats/min**), the duration of the cardiac cycle shortens significantly. Since diastole is shortened disproportionately more than systole, there is **inadequate time for ventricular filling**. This leads to a marked decrease in **End-Diastolic Volume (EDV)**. According to the Frank-Starling Law, reduced filling leads to a weaker contraction and a subsequent drop in stroke volume. **Analysis of Incorrect Options:** * **A. Reduction in afterload:** Decreasing the resistance against which the heart pumps (afterload) allows the ventricle to empty more effectively, thereby **increasing** stroke volume. * **B. Increase in end-diastolic pressure:** An increase in filling pressure (preload) increases the initial stretching of myocardial fibers, which **increases** the force of contraction and stroke volume (Frank-Starling mechanism). * **C. Stimulation of the vagus nerves:** Vagal stimulation primarily decreases heart rate (negative chronotropy) but has minimal effect on ventricular contractility. While it may decrease Cardiac Output ($CO = HR \times SV$), it does not directly decrease stroke volume; in fact, the resulting slower HR might slightly increase filling time and SV. **High-Yield Clinical Pearls for NEET-PG:** * **Frank-Starling Law:** Stroke volume increases in response to an increase in the volume of blood filling the heart (EDV), within physiological limits. * **Tachycardia Paradox:** While moderate increases in HR increase Cardiac Output, extreme tachycardia (usually >160-180 bpm) causes CO to fall because the drop in SV outweighs the increase in HR. * **Filling Time:** Diastole is divided into three phases of filling. At high heart rates, the "diastasis" (slow filling) phase is eliminated first, followed by encroachment into the rapid filling phase.

Question 79: All of the following are true regarding the Donnan effect EXCEPT?

A. The Donnan effect helps prevent cell rupture.
B. There is no Donnan effect on diffusible ion movement across the capillary wall.
C. A non-diffusible ion on one side of a membrane affects the distribution of other diffusible ions. (Correct Answer)
D. The Donnan effect causes a decrease in both the concentrations of cations and the colloid osmotic pressure in the capillary lumen.

Explanation: ### Explanation **Gibbs-Donnan Effect** describes the behavior of charged particles near a semi-permeable membrane when one or more ionic species are non-diffusible (e.g., intracellular proteins or plasma proteins). **1. Why Option C is the "Correct" (Incorrect Statement) Answer:** The question asks for the **EXCEPT** statement. Option C is actually a **true** statement: the presence of a non-diffusible ion (like protein) forces diffusible ions (like $Na^+$ and $Cl^-$) to distribute unevenly to maintain electrical neutrality. Since the question asks for the false statement, and the provided key marks C as correct, there is a likely error in the source's keying or phrasing. In standard physiology, **Option A is the most false statement.** **2. Analysis of Options:** * **Option A (False):** The Donnan effect actually **promotes** cell swelling. Because proteins are trapped inside cells, they attract extra diffusible cations and increase the total number of particles (osmotic load). This draws water into the cell, potentially causing **cell rupture** unless countered by the $Na^+$-$K^+$ ATPase pump. * **Option B (False):** There **is** a Donnan effect at the capillary wall. Plasma proteins (anions) are non-diffusible, causing a slightly higher concentration of cations ($Na^+$) and a lower concentration of diffusible anions ($Cl^-$) in the plasma compared to interstitial fluid. * **Option D (False):** The Donnan effect **increases** the concentration of cations and **increases** the colloid osmotic pressure (by about 6-7 mmHg) in the capillary lumen due to the extra ions attracted by proteins. **3. Clinical Pearls for NEET-PG:** * **Donnan Equilibrium Formula:** $[Cation]_{in} \times [Anion]_{in} = [Cation]_{out} \times [Anion]_{out}$. * **Plasma vs. Interstitial Fluid:** Due to Donnan effect, plasma has ~5% more cations and ~5% fewer anions than interstitial fluid. * **Cell Volume Regulation:** The $Na^+$-$K^+$ pump is essential to counteract the Donnan effect; if the pump fails, the Donnan effect leads to hydropic swelling and cell death.

Question 80: Passive transfer of solvent occurs in which process?

A. Diffusion
B. Active transport
C. Osmosis (Correct Answer)
D. Pinocytosis

Explanation: **Explanation:** The correct answer is **Osmosis (Option C)**. **Why Osmosis is correct:** Osmosis is defined as the net movement of **solvent molecules** (usually water in biological systems) across a semi-permeable membrane. This movement occurs from a region of lower solute concentration (higher water potential) to a region of higher solute concentration (lower water potential). It is a passive process, meaning it requires no energy (ATP) and is driven solely by the osmotic pressure gradient. **Why other options are incorrect:** * **Diffusion (Option A):** This refers to the passive movement of **solute particles** (not solvent) from an area of higher concentration to lower concentration. * **Active Transport (Option B):** This process moves molecules against their concentration gradient and requires **energy (ATP)**. It is not a passive process. * **Pinocytosis (Option D):** Also known as "cell drinking," this is a form of endocytosis where the cell membrane invaginates to engulf extracellular fluid. It is an **active process** involving vesicle formation. **High-Yield NEET-PG Pearls:** * **Aquaporins:** These are specialized water channels (integral membrane proteins) that facilitate rapid osmosis in tissues like the renal collecting ducts (regulated by ADH). * **Osmotic Pressure vs. Oncotic Pressure:** While osmotic pressure is exerted by all solutes, **Oncotic pressure** (Colloid Osmotic Pressure) is specifically exerted by plasma proteins (mainly Albumin) and is crucial in preventing edema. * **Van’t Hoff’s Law:** Osmotic pressure is proportional to the molar concentration of the solute and the absolute temperature. * **Gibbs-Donnan Effect:** Describes the behavior of charged particles near a semi-permeable membrane that sometimes fails to distribute evenly, influencing osmotic balance.

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