General Physiology — MCQs

General Physiology Indian Medical PG Practice Questions and MCQs

Question 371: Which enzyme is utilized by the Na+/K+ pump?

A. ATPase (Correct Answer)
B. GTPase
C. Acetyl CoA
D. NADPH

Explanation: ### 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+).

Question 372: Anterograde axonal transport involves all except?

A. Kinesin and dynein molecular motors
B. Anterograde transport moves from the cell body toward the axon terminals
C. Nerve growth factor, toxins, and viruses are transported using kinesin (Correct Answer)
D. Mitochondria and vesicles containing neurotransmitters are transported using kinesin

Explanation: **Explanation** Axonal transport is a vital physiological process for maintaining neuronal function, categorized into **Anterograde** and **Retrograde** transport based on direction and molecular motors. **Why Option C is the Correct Answer (The "Except"):** Nerve Growth Factor (NGF), certain toxins (e.g., Tetanus toxin), and neurotropic viruses (e.g., Rabies, Herpes simplex) are classic examples of substances moved via **Retrograde transport** (from the axon terminal back to the cell body). Furthermore, retrograde transport is powered by the motor protein **Dynein**, not Kinesin. Therefore, Option C is factually incorrect regarding both the direction and the motor protein. **Analysis of Incorrect Options:** * **Option A:** While Kinesin is the primary motor for anterograde transport, some classifications of axonal transport (especially fast vs. slow) discuss both motors in the context of overall axonal flow. However, in the context of this "except" question, Option C contains a definitive physiological error. * **Option B:** This is the standard definition of **Anterograde transport**. It moves organelles and proteins from the perikaryon (cell body) toward the synaptic terminals. * **Option D:** Mitochondria, secretory vesicles, and neurotransmitter precursors are essential at the synapse and are transported via **Fast Anterograde transport** using **Kinesin**. **High-Yield Clinical Pearls for NEET-PG:** * **Kinesin:** Moves "outward" (Anterograde) toward the (+) end of microtubules. * **Dynein:** Moves "inward" (Retrograde) toward the (-) end of microtubules. * **Clinical Link:** The **Rabies virus** utilizes retrograde transport (Dynein) to reach the CNS from a peripheral bite site. * **Tetanus Toxin:** Travels via retrograde transport to reach inhibitory interneurons in the spinal cord, leading to spastic paralysis.

Question 373: What is the major ion in the extracellular compartment?

A. K+
B. Na+ (Correct Answer)
C. Cl-
D. HCO3-

Explanation: **Explanation:** The distribution of electrolytes between the intracellular fluid (ICF) and extracellular fluid (ECF) is fundamental to cellular homeostasis. **Sodium (Na+)** is the predominant cation in the extracellular compartment, with a normal plasma concentration of approximately **135–145 mEq/L**. This gradient is primarily maintained by the **Na+-K+ ATPase pump**, which actively pumps three Na+ ions out of the cell for every two K+ ions pumped in. Sodium is the chief determinant of ECF osmolality and plays a critical role in regulating blood volume and pressure. **Analysis of Incorrect Options:** * **A. K+ (Potassium):** This is the major **intracellular** cation (~140–150 mEq/L inside the cell). It is vital for maintaining the resting membrane potential. * **C. Cl- (Chloride):** While Chloride is the major extracellular **anion**, it is not the most abundant ion overall when compared to Sodium. It typically follows Sodium to maintain electrical neutrality. * **D. HCO3- (Bicarbonate):** This is an important extracellular buffer, but its concentration (~24 mEq/L) is significantly lower than that of Sodium or Chloride. **NEET-PG High-Yield Pearls:** * **Major Intracellular Cation:** K+; **Major Intracellular Anion:** PO4³⁻ (Phosphates) and proteins. * **Major Extracellular Cation:** Na+; **Major Extracellular Anion:** Cl-. * **Gibbs-Donnan Effect:** Explains why the concentration of diffusible ions is slightly different between plasma and interstitial fluid due to the presence of non-diffusible plasma proteins. * **Indicator Dilution Method:** To measure ECF volume, substances like **Inulin, Mannitol, or Sucrose** are used. To measure Plasma volume, **Evans Blue** or **Radio-iodinated Serum Albumin (RISA)** is used.

Question 374: What type of stimulus does a muscle spindle detect?

A. Tension
B. Length (Correct Answer)
C. Proprioception
D. Stretch

Explanation: **Explanation:** The **muscle spindle** is a specialized sensory receptor located within the belly of skeletal muscles. Its primary physiological function is to detect changes in **muscle length** and the rate of change in length. 1. **Why "Length" is correct:** Muscle spindles are arranged in **parallel** with extrafusal muscle fibers. When a muscle is stretched, the intrafusal fibers of the spindle are also stretched, triggering sensory signals via Type Ia and Type II afferent fibers. This information is crucial for the **stretch reflex** (myotatic reflex), which maintains muscle tone and prevents over-stretching. 2. **Why other options are incorrect:** * **Tension (Option A):** This is detected by the **Golgi Tendon Organ (GTO)**. GTOs are arranged in **series** with muscle fibers and respond to force or contraction strength to prevent tendon avulsion. * **Proprioception (Option B):** While muscle spindles *contribute* to proprioception (the sense of body position), "Proprioception" is a broad sensory category, not a specific stimulus. "Length" is the specific physical parameter detected. * **Stretch (Option D):** While "stretch" is the action that triggers the spindle, in physiological terms, the spindle is defined as a **linear length detector**. In many exams, "Length" is considered the more precise physiological answer over "Stretch." **High-Yield Clinical Pearls for NEET-PG:** * **Innervation:** Sensory (Ia - dynamic/velocity; II - static/length) and Motor (**Gamma motor neurons** - maintain spindle sensitivity during contraction). * **Alpha-Gamma Co-activation:** Ensures the muscle spindle remains sensitive even when the muscle shortens. * **Inverse Myotatic Reflex:** Mediated by the GTO to cause muscle relaxation when tension is too high.

Question 375: Basal Metabolic Rate (BMR) is dependent on which of the following factors?

A. Body weight
B. Body surface area (Correct Answer)
C. Amount of adipose tissue
D. Amount of lean body mass

Explanation: **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.

Question 376: Which drug transport process requires energy?

A. Active transport (Correct Answer)
B. Passive diffusion
C. Convective current
D. Pinocytosis

Explanation: ### Explanation **Correct Answer: A. Active transport** **1. Why Active Transport is Correct:** Active transport is the movement of molecules or ions across a cell membrane **against a concentration gradient** (from an area of lower concentration to higher concentration). Because this process moves substances "uphill," it requires the expenditure of metabolic energy, typically in the form of **ATP hydrolysis**. It involves specific carrier proteins (transporters) and exhibits properties like saturation kinetics and competitive inhibition. **2. Why Other Options are Incorrect:** * **B. Passive Diffusion:** This is the most common mechanism for drug transport. It occurs **down a concentration gradient** and does not require energy or a carrier protein. The rate is governed by Fick’s Law. * **C. Convective Current (Filtration):** This refers to the movement of drug molecules through aqueous pores (aquaporins) in the membrane, driven by hydrostatic or osmotic pressure gradients. It is a passive process. * **D. Pinocytosis:** While endocytosis (the broader category) requires energy to engulf particles, **Pinocytosis** (cell drinking) is specifically the non-specific uptake of extracellular fluid. In the context of standard pharmacology and NEET-PG classification, "Active Transport" is the primary, classic answer for energy-dependent carrier-mediated transport of drugs. **3. High-Yield Clinical Pearls for NEET-PG:** * **Primary Active Transport:** Directly uses ATP (e.g., Na+/K+ ATPase pump, P-glycoprotein). * **Secondary Active Transport:** Uses the electrochemical gradient established by primary transport (e.g., SGLT-1 for glucose absorption in the gut). * **P-glycoprotein (P-gp):** An important ATP-dependent efflux pump that pumps drugs out of cells, contributing to multi-drug resistance in cancer cells and the Blood-Brain Barrier. * **Saturation:** Unlike passive diffusion, active transport is **saturable** (follows Michaelis-Menten kinetics) because the number of carrier proteins is finite.

Question 377: Which substance best estimates the Extracellular Fluid (ECF) volume?

A. Mannitol
B. Inulin (Correct Answer)
C. Deuterium oxide (D2O)
D. Evan's blue

Explanation: **Explanation:** The volume of a body fluid compartment is measured using the **Indicator Dilution Method** ($V = Q/C$). To measure the **Extracellular Fluid (ECF)** volume, a substance must be able to freely cross capillary walls but be **unable to cross cell membranes**, thus remaining confined to the interstitial space and plasma. **Why Inulin is the Correct Answer:** Inulin (a polysaccharide) is considered the **gold standard** for ECF measurement because it is physiologically inert, not metabolized, and strictly confined to the ECF. While **Mannitol** is also used to estimate ECF, Inulin is more precise in experimental and clinical physiology contexts. **Analysis of Incorrect Options:** * **A. Mannitol:** While it can be used to measure ECF, it is slightly less accurate than Inulin as it can be metabolized to a small extent. * **C. Deuterium oxide ($D_2O$):** Also known as "heavy water," it distributes uniformly across all fluid compartments (ECF + ICF). Therefore, it is used to measure **Total Body Water (TBW)**. * **D. Evan's blue:** This dye binds strongly to serum albumin and remains confined to the vascular system. It is used to measure **Plasma Volume**. **High-Yield Clinical Pearls for NEET-PG:** * **Total Body Water (60% of BW):** Measured by $D_2O$, Tritiated water, or Aminopyrine. * **ECF (20% of BW):** Measured by Inulin (Best), Mannitol, Sucrose, or Thiosulfate. * **Plasma Volume:** Measured by Evan’s Blue (T-1824) or Radio-iodinated Albumin ($RISA$). * **ICF Volume:** Cannot be measured directly. It is calculated as: $ICF = TBW - ECF$. * **Interstitial Fluid:** Calculated as: $ECF - Plasma\ Volume$.

Question 378: Which of the following glands primarily exhibits serous secretion?

A. Pancreas
B. Parotid gland (Correct Answer)
C. Submandibular salivary gland
D. Minor salivary glands

Explanation: ### Explanation The classification of exocrine glands is based on the nature of their secretions: **serous** (watery, protein-rich, containing enzymes), **mucous** (viscous, rich in mucin), or **mixed**. **1. Why Parotid Gland is Correct:** The **Parotid gland** is a purely **serous** gland (in adults). Its secretions are watery and contain high concentrations of salivary amylase (ptyalin), which initiates starch digestion. Histologically, it is characterized by serous acini with narrow lumina and central nuclei. **2. Analysis of Incorrect Options:** * **Pancreas (Option A):** While the exocrine pancreas is a serous gland (secreting digestive enzymes), in the context of "salivary vs. general glands" questions in Physiology, the Parotid is the classic textbook example of a purely serous gland. Furthermore, the pancreas has an endocrine component, making it a heterocrine gland. * **Submandibular Gland (Option B):** This is a **mixed** gland, though it is predominantly serous (roughly 80% serous, 20% mucous). It produces the majority of the total daily salivary volume. * **Minor Salivary Glands (Option D):** Most minor salivary glands (lingual, buccal, palatal) are **predominantly mucous**, with the notable exception of **Von Ebner’s glands** (which are serous). **3. High-Yield Clinical Pearls for NEET-PG:** * **Sublingual Gland:** Predominantly **mucous** (the opposite of the Submandibular). * **Von Ebner’s Glands:** These are the only purely serous minor salivary glands, located around circumvallate papillae; they secrete lingual lipase. * **Mumps:** A viral infection primarily affecting the serous acini of the parotid gland. * **Stensen’s Duct:** The excretory duct of the parotid gland, opening opposite the maxillary second molar.

Question 379: All are true about hemolytic disease of the newborn except?

A. Hemolytic anemia
B. Hydrops fetalis
C. Kernicterus
D. Anti-Rh agglutinins are of IgM type (Correct Answer)

Explanation: **Explanation:** Hemolytic Disease of the Newborn (HDN), or **Erythroblastosis Fetalis**, occurs due to Rh-incompatibility between an Rh-negative mother and an Rh-positive fetus. **Why Option D is the correct answer (the "Except" statement):** The hallmark of HDN is the placental transfer of maternal antibodies. **IgM antibodies** are pentameric and large, making them **incapable of crossing the placenta**. In HDN, the mother’s immune system produces **IgG type anti-Rh agglutinins** (specifically anti-D) following sensitization. IgG is monomeric and can cross the placental barrier to attack fetal RBCs. Therefore, stating they are IgM is incorrect. **Analysis of other options:** * **A. Hemolytic anemia:** This is the primary pathology. Maternal IgG coats fetal RBCs, leading to their destruction (hemolysis) in the fetal spleen. * **B. Hydrops fetalis:** Severe hemolysis leads to profound anemia, which causes high-output cardiac failure, generalized edema (anasarca), and ascites. This is the most severe form of the disease. * **C. Kernicterus:** Rapid hemolysis produces high levels of unconjugated bilirubin. In neonates, the blood-brain barrier is immature, allowing bilirubin to deposit in the basal ganglia, leading to permanent neurological damage known as kernicterus. **High-Yield NEET-PG Pearls:** * **Sensitization:** Usually occurs during the first delivery; hence, the first child is typically unaffected, but subsequent Rh+ pregnancies are at risk. * **Prophylaxis:** Administer **Anti-D (RhoGAM)** to Rh-negative mothers at 28 weeks gestation and within 72 hours of delivery to neutralize fetal Rh+ cells before the mother’s immune system reacts. * **Diagnosis:** **Direct Coombs Test** is used on the newborn’s cord blood to detect antibodies bound to RBCs.

Question 380: What is the genotype of blood group A?

A. AB
B. AO (Correct Answer)
C. OO
D. BO

Explanation: **Explanation:** The ABO blood group system is determined by the presence of specific antigens on the surface of red blood cells, which are inherited via three alleles: **A, B, and O**. 1. **Why AO is correct:** The inheritance of blood groups follows Mendelian genetics. The A and B alleles are **co-dominant**, while the O allele is **recessive**. For an individual to have the **phenotype** (expressed blood group) of "A," their **genotype** can be either homozygous (**AA**) or heterozygous (**AO**). Since "AO" is the only valid genotype for Group A provided in the options, it is the correct answer. In AO, the A allele masks the expression of the recessive O allele. 2. **Analysis of Incorrect Options:** * **AB:** This represents the genotype for Blood Group AB. Due to co-dominance, both A and B antigens are expressed on the RBC surface. * **OO:** This is the genotype for Blood Group O. Since O is recessive, it must be homozygous to be expressed. * **BO:** This is the genotype for Blood Group B (heterozygous state). **High-Yield Clinical Pearls for NEET-PG:** * **The H-Antigen:** The H gene (Chromosome 19) is the precursor for A and B antigens. In the rare **Bombay Phenotype (hh)**, the H-antigen is absent, meaning the person will test as Group O regardless of their ABO genotype. * **Universal Donor/Recipient:** Group O negative is the universal donor (no antigens); Group AB positive is the universal recipient (no antibodies). * **Genetics:** The ABO gene is located on the long arm of **Chromosome 9**. * **Antibodies:** ABO antibodies (Isoagglutinins) are typically **IgM** and do not cross the placenta, unlike Rh antibodies which are **IgG**.

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