General Physiology — MCQs

General Physiology Indian Medical PG Practice Questions and MCQs

Question 131: Activation of protein kinase C causes which of the following?

A. Increase in adenylyl cyclase activity
B. Phosphorylation of proteins (Correct Answer)
C. Increased cyclic AMP (cAMP) levels
D. Increased ion channel conduction

Explanation: **Explanation:** The core function of **Protein Kinase C (PKC)** is the **phosphorylation of specific serine and threonine residues** on target proteins. In the Gq-protein signaling pathway, the activation of Phospholipase C (PLC) leads to the hydrolysis of PIP₂ into Inositol trisphosphate (IP₃) and Diacylglycerol (DAG). While IP₃ increases intracellular calcium, **DAG directly activates PKC**. Once activated, PKC acts as a kinase, transferring phosphate groups from ATP to proteins, thereby altering their enzymatic activity, structural conformation, or binding properties. **Analysis of Options:** * **Option A & C:** Adenylyl cyclase activation and increased cAMP levels are characteristic of the **Gs-protein pathway** (Protein Kinase A pathway). PKC is part of the Gq pathway and does not typically stimulate cAMP production; in some tissues, PKC may actually inhibit adenylyl cyclase. * **Option D:** While phosphorylation by PKC *can* eventually modulate ion channels, "increased conduction" is not a universal or primary effect. The most direct and defining biochemical action of any kinase is the covalent modification of proteins via phosphorylation. **High-Yield NEET-PG Pearls:** * **PKC Activators:** Diacylglycerol (DAG), Calcium ($Ca^{2+}$), and Phorbol esters (experimental tools). * **G-Protein Specificity:** Remember the mnemonic **"Qis (Kiss) and Qiq (Kick) till you siq (sick) SQS"**: * **Gq:** H1, α1, V1, M1, M3 (Activates PLC $\rightarrow$ PKC). * **Gs:** β1, β2, D1, H2, V2 (Activates Adenylyl Cyclase $\rightarrow$ PKA). * **Gi:** M2, α2, D2 (Inhibits Adenylyl Cyclase). * **Tumor Promotion:** Phorbol esters act as tumor promoters because they permanently activate PKC, leading to uncontrolled cell phosphorylation and proliferation.

Question 132: Which is the most potent oxygen free radical?

A. Hydroxyl radical (Correct Answer)
B. Hydrogen peroxide
C. Superoxide radical
D. Both Hydroxyl radical and Hydrogen peroxide

Explanation: ### Explanation **1. Why Hydroxyl Radical is the Correct Answer:** The **Hydroxyl radical (OH•)** is considered the most potent and reactive oxygen free radical in biological systems. It possesses an extremely high reduction potential, meaning it has an insatiable "thirst" for electrons. Unlike other reactive oxygen species (ROS), it reacts indiscriminately and instantaneously with almost any biological molecule it encounters—including DNA, proteins, and membrane lipids—at the site of its formation. It is primarily generated via the **Fenton reaction** (where $Fe^{2+}$ reacts with $H_2O_2$) and the **Haber-Weiss reaction**. **2. Why the Other Options are Incorrect:** * **Hydrogen peroxide ($H_2O_2$):** Technically, $H_2O_2$ is **not a free radical** because it does not have unpaired electrons in its outer shell. While it is a potent oxidizing agent and a precursor to the hydroxyl radical, it is relatively stable and can diffuse across membranes. * **Superoxide radical ($O_2^{•-}$):** Although it is the "primary" ROS produced by the electron transport chain, it is less reactive than the hydroxyl radical. Its main danger lies in its role as a precursor to other more toxic species. It is neutralized by the enzyme Superoxide Dismutase (SOD). * **Option D:** Incorrect because $H_2O_2$ is neither a radical nor as potent as OH•. **3. NEET-PG High-Yield Clinical Pearls:** * **Lipid Peroxidation:** The hydroxyl radical is the chief initiator of lipid peroxidation in cell membranes, leading to cell death (ferroptosis). * **Ionizing Radiation:** The damaging effects of X-rays and Gamma rays are primarily due to the **radiolysis of water**, which generates hydroxyl radicals. * **Protective Enzymes:** Remember the triad: **SOD** (converts $O_2^{•-}$ to $H_2O_2$), **Catalase** (converts $H_2O_2$ to water), and **Glutathione Peroxidase** (neutralizes $H_2O_2$ and lipid peroxides). * **Antioxidant:** Vitamin E is the most important lipid-soluble antioxidant that protects membranes from these radicals.

Question 133: What is true about metastatic calcification?

A. Serum calcium level is normal
B. Occurs in dead or dying tissue
C. Occurs in damaged heart valves
D. Calcification starts in mitochondria (Correct Answer)

Explanation: **Explanation:** Calcification is the abnormal deposition of calcium salts in tissues. It is broadly classified into two types: **Dystrophic** and **Metastatic**. **Why Option D is Correct:** In **Metastatic Calcification**, the process typically begins in the **mitochondria** of cells. This occurs because mitochondria are the primary sites of energy production and accumulate calcium ions during states of hypercalcemia. When the intracellular calcium concentration exceeds the mitochondrial capacity, precipitation occurs, leading to cell injury and widespread calcification. **Analysis of Incorrect Options:** * **Option A (Serum calcium level is normal):** This is incorrect. Metastatic calcification occurs in **normal tissues** due to **hypercalcemia** (elevated serum calcium). Normal serum calcium levels are characteristic of *Dystrophic* calcification. * **Option B (Occurs in dead or dying tissue):** This describes **Dystrophic calcification**, which occurs in necrotic, degenerated, or damaged tissues despite normal calcium metabolism. * **Option C (Occurs in damaged heart valves):** This is a classic example of **Dystrophic calcification** (e.g., calcific aortic stenosis). Metastatic calcification typically affects healthy tissues with an alkaline internal environment, such as the gastric mucosa, kidneys, and lungs. **High-Yield Clinical Pearls for NEET-PG:** * **Favored Sites:** Metastatic calcification favors organs that excrete acid (Lungs, Stomach, Kidneys) because the resulting **internal alkalinity** predisposes them to calcium salt precipitation. * **Common Causes:** Hyperparathyroidism (most common), Vitamin D toxicity, and bone resorption (multiple myeloma or bony metastasis). * **Dystrophic vs. Metastatic:** Remember, Dystrophic = **D**amaged tissue/Normal Ca²⁺; Metastatic = **M**etabolic derangement/High Ca²⁺.

Question 134: Action potential across the cell membrane is maintained by?

A. Na+ K+ pump (Correct Answer)
B. cAMP
C. Ca++
D. Phosphodiesterase

Explanation: ### Explanation The **Na⁺-K⁺ ATPase pump** is the primary mechanism responsible for maintaining the ionic gradients and the resting membrane potential (RMP) necessary for action potentials. **1. Why Na⁺-K⁺ Pump is Correct:** The Na⁺-K⁺ pump is an **electrogenic pump** that actively transports 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell against their concentration gradients, using ATP. This activity serves two critical functions: * **Maintaining Concentration Gradients:** It ensures high [K⁺] inside and high [Na⁺] outside, which are essential for the depolarization and repolarization phases of an action potential. * **Restoring Equilibrium:** After an action potential occurs, the pump works to restore the ionic balance that was shifted during the flux of ions through voltage-gated channels. Without this pump, the gradients would dissipate, and the cell would eventually lose its excitability. **2. Why Other Options are Incorrect:** * **B. cAMP:** This is a second messenger involved in intracellular signal transduction (e.g., GPCR pathways). It does not directly maintain the membrane potential. * **C. Ca⁺⁺:** While calcium is vital for the plateau phase in cardiac action potentials and neurotransmitter release, it is not the primary ion responsible for maintaining the overall resting membrane potential or the Na⁺/K⁺ gradient. * **D. Phosphodiesterase:** This is an enzyme that breaks down cyclic nucleotides (cAMP or cGMP). It regulates signaling but has no direct role in ionic transport across the membrane. **High-Yield Clinical Pearls for NEET-PG:** * **Stoichiometry:** 3 Na⁺ Out / 2 K⁺ In. * **Inhibitor:** **Ouabain** and **Digoxin** (Cardiac glycosides) inhibit the Na⁺-K⁺ ATPase pump. * **Energy Consumption:** In a resting neuron, the Na⁺-K⁺ pump accounts for approximately **70% of the total ATP consumption**. * **Resting Membrane Potential (RMP):** While the pump contributes directly to the RMP (about -4 to -5 mV), the RMP is primarily determined by the **leakage of K⁺ ions** through non-gated channels.

Question 135: Which of the following is true about facilitated diffusion?

A. It is an active process.
B. It requires a carrier protein. (Correct Answer)
C. It requires ATP.
D. It occurs against the concentration gradient.

Explanation: ### Explanation **Facilitated diffusion** is a form of passive transport that allows large or polar molecules (like glucose and amino acids) to cross the cell membrane. Since these molecules are not lipid-soluble, they cannot pass through the phospholipid bilayer directly and require the assistance of specific **integral membrane proteins** known as **carrier proteins**. #### Why Option B is Correct: Facilitated diffusion relies on a **carrier-mediated mechanism**. The substance binds to a specific receptor site on the carrier protein, inducing a conformational change that moves the molecule to the other side of the membrane. This process is characterized by **specificity, competition, and saturation kinetics (Vmax)**. #### Why Other Options are Incorrect: * **Options A & C:** Facilitated diffusion is a **passive process**. It does not require metabolic energy (ATP) because the driving force is the intrinsic kinetic energy of the molecules moving down their gradient. * **Option D:** It occurs **along (down) the electrochemical or concentration gradient** (from high concentration to low concentration). Transport against a gradient is a hallmark of Active Transport. --- ### High-Yield NEET-PG Pearls: * **GLUT Transporters:** The most classic example of facilitated diffusion is the transport of glucose into cells via **GLUT-4** (insulin-dependent) and other GLUT isoforms. * **Saturation (Vmax):** Unlike simple diffusion, which increases linearly with concentration, facilitated diffusion reaches a "Transport Maximum" (Tm) when all carrier proteins are occupied. * **Stereospecificity:** These carriers are highly specific; for example, the carrier for glucose will transport **D-glucose** but not L-glucose. * **Ion Channels vs. Carriers:** While both are passive, ion channels are generally faster and do not undergo the significant conformational changes seen in carrier proteins.

Question 136: All of the following are examples of primary active transport, except:

A. The Na+/K+ ATPase in the red cell membrane
B. The H+/K+ ATPase in the parietal cell of stomach
C. Na+/ glucose symporter (Correct Answer)
D. SERCA in the skeletal muscle

Explanation: ### Explanation **Concept Overview:** Transport across cell membranes is categorized based on energy requirements. **Primary Active Transport** directly utilizes energy from ATP hydrolysis to move solutes against their electrochemical gradient. **Secondary Active Transport** (like the Na+/glucose symporter) does not use ATP directly; instead, it hitches a ride on the energy stored in an electrochemical gradient (usually Na+) created by a primary active transporter. **Why Option C is Correct:** The **Na+/glucose symporter (SGLT)** is a classic example of **Secondary Active Transport**. It moves glucose against its concentration gradient by utilizing the downward sodium gradient established by the Na+/K+ ATPase. Since it does not hydrolyze ATP itself, it is not a primary active transporter. **Analysis of Incorrect Options:** * **Option A (Na+/K+ ATPase):** The most ubiquitous primary active transporter. It pumps 3 Na+ out and 2 K+ in per ATP hydrolyzed, maintaining resting membrane potential. * **Option B (H+/K+ ATPase):** Found in gastric parietal cells, this "proton pump" uses ATP to secrete H+ into the stomach lumen in exchange for K+. It is the target of Proton Pump Inhibitors (PPIs). * **Option D (SERCA):** The **S**arco/Endoplasmic **R**eticulum **C**a2+ **A**TPase is a primary active transporter that pumps calcium from the cytosol into the SR to allow for muscle relaxation. **High-Yield NEET-PG Pearls:** 1. **P-type ATPases:** Na+/K+ ATPase, H+/K+ ATPase, and SERCA are all "P-type" because they are phosphorylated during the transport cycle. 2. **SGLT Locations:** SGLT-1 is primarily in the small intestine, while SGLT-2 is in the proximal convoluted tubule (PCT) of the kidney (target of Gliflozins). 3. **Digitalis/Ouabain:** These drugs inhibit the Na+/K+ ATPase, leading to increased intracellular Na+, which indirectly slows the Na+/Ca2+ exchanger, increasing cardiac contractility.

Question 137: Acclimatization does NOT include which of the following?

A. Hyperventilation
B. Decreased concentration of 2,3-DPG in RBC (Correct Answer)
C. Increased erythropoiesis
D. Kidneys excrete more alkali

Explanation: **Explanation:** Acclimatization refers to the physiological adjustments the body undergoes to adapt to low oxygen levels (hypoxia) at high altitudes. **Why Option B is Correct:** In response to high-altitude hypoxia, the concentration of **2,3-Diphosphoglycerate (2,3-DPG)** in Red Blood Cells **increases**, not decreases. 2,3-DPG binds to hemoglobin and shifts the oxygen-dissociation curve to the **right**. This reduces the affinity of hemoglobin for oxygen, thereby facilitating the unloading of oxygen into the peripheral tissues where it is needed most. Therefore, a "decreased concentration" is physiologically incorrect in the context of acclimatization. **Analysis of Incorrect Options:** * **A. Hyperventilation:** Low partial pressure of oxygen ($PO_2$) stimulates peripheral chemoreceptors, leading to an immediate increase in alveolar ventilation to bring in more oxygen. * **C. Increased erythropoiesis:** Hypoxia stimulates the kidneys to release **erythropoietin**, which acts on the bone marrow to increase RBC production (polycythemia). This increases the oxygen-carrying capacity of the blood. * **D. Kidneys excrete more alkali:** Hyperventilation causes respiratory alkalosis (due to $CO_2$ washout). To compensate, the kidneys excrete excess bicarbonate ($HCO_3^-$) to restore the blood pH toward normal. **High-Yield Clinical Pearls for NEET-PG:** * **Shift to the Right:** Remember the mnemonic **"CADET, face Right!"** (increased **C**O2, **A**cid/H+, **D**PG, **E**xercise, and **T**emperature all shift the curve to the right). * **Pulmonary Vasoconstriction:** Unlike systemic vessels, pulmonary vessels undergo vasoconstriction in response to hypoxia, which can lead to High-Altitude Pulmonary Edema (HAPE). * **Acetazolamide:** This drug is used for prophylaxis in mountain sickness because it inhibits carbonic anhydrase, forcing bicarbonate excretion and inducing a mild metabolic acidosis that counteracts respiratory alkalosis and stimulates breathing.

Question 138: Who is considered the Father of Physiology?

A. Herophilus of Chalcedon
B. Claude Bernard (Correct Answer)
C. Louis Pasteur
D. Robin Virchow

Explanation: **Explanation:** **Claude Bernard (Option B)** is widely recognized as the "Father of Physiology" due to his pioneering work in establishing the scientific method in medicine. His most significant contribution is the concept of **"Milieu Intérieur"** (internal environment), which posits that the stability of the internal environment is the condition for free and independent life. This concept laid the foundational groundwork for the later development of the theory of **Homeostasis** by Walter Cannon. Bernard was also the first to describe the glycogenic function of the liver and the role of pancreatic juice in digestion. **Analysis of Incorrect Options:** * **Herophilus of Chalcedon (Option A):** Known as the "Father of Anatomy." He was the first to perform systematic human dissections and distinguished between sensory and motor nerves. * **Louis Pasteur (Option C):** Known as the "Father of Microbiology." He developed the germ theory of disease, pasteurization, and vaccines for rabies and anthrax. * **Rudolf Virchow (Option D):** Known as the "Father of Modern Pathology." He is famous for the cell theory principle *"Omnis cellula e cellula"* (every cell originates from another cell). **High-Yield Facts for NEET-PG:** * **Walter Cannon:** Coined the term **"Homeostasis"** and described the "Fight or Flight" response. * **Guyton:** Often associated with modern medical physiology education, but Bernard holds the historical title. * **Milieu Intérieur:** Focuses on the ECF (Extracellular Fluid) acting as a protective buffer for cells against external changes.

Question 139: What is the most serious complication of a prolonged sitting position?

A. Venous air embolism (Correct Answer)
B. Dysrhythmias
C. Hypotension
D. Nerve palsies

Explanation: **Explanation:** The **sitting position** is frequently utilized in neurosurgery (e.g., posterior fossa surgery) to improve surgical access and venous drainage. However, its most serious and potentially fatal complication is **Venous Air Embolism (VAE)**. **Why Venous Air Embolism is the correct answer:** In the sitting position, the surgical site (the head/neck) is significantly higher than the level of the heart. This creates a **negative pressure gradient** between the atmospheric air and the open non-collapsible dural venous sinuses. If a vein is breached, air is sucked into the venous circulation. This air can travel to the right heart, causing an "air lock" in the pulmonary artery, leading to acute right heart failure, cardiovascular collapse, and death. **Analysis of Incorrect Options:** * **Hypotension:** This is the *most common* complication due to venous pooling in the lower extremities, but it is generally manageable with fluids and vasopressors, making it less "serious" than a fatal embolism. * **Dysrhythmias:** These can occur due to surgical manipulation of cranial nerves or brainstem structures, but they are usually transient. * **Nerve Palsies:** Prolonged sitting can cause peripheral nerve injuries (e.g., sciatic or ulnar nerve) due to pressure or stretch, but these are morbidities rather than life-threatening emergencies. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for Detection:** **Precordial Doppler** ultrasound (placed at the 4th/5th intercostal space, right sternal border) is the most sensitive non-invasive monitor for VAE. * **Most Sensitive Monitor:** **Transesophageal Echocardiography (TEE)** is the overall most sensitive but is invasive. * **Early Sign:** A sudden drop in **End-Tidal CO2 (EtCO2)** is a classic capnographic sign of VAE. * **Management:** Place the patient in **Durant’s position** (Left lateral decubitus with Trendelenburg) and aspirate air via a central venous catheter.

Question 140: Which of the following is an effect of acetylcholine?

A. Relaxes the lower esophageal sphincter (LES)
B. Contracts the lower esophageal sphincter (LES) (Correct Answer)
C. Constricts the blood vessels
D. Relaxes the bronchial muscles

Explanation: **Explanation:** Acetylcholine (ACh) is the primary neurotransmitter of the parasympathetic nervous system. In the gastrointestinal tract, it generally acts to stimulate motility and secretions. **1. Why Option B is Correct:** The Lower Esophageal Sphincter (LES) is regulated by the autonomic nervous system. Acetylcholine acts on **M3 muscarinic receptors** located on the smooth muscle of the LES, causing **contraction**. This increases the resting tone of the sphincter, preventing gastroesophageal reflux. Conversely, relaxation of the LES is mediated by non-adrenergic, non-cholinergic (NANC) neurons releasing Nitric Oxide (NO) and Vasoactive Intestinal Peptide (VIP). **2. Why the Other Options are Incorrect:** * **Option A:** As stated above, ACh contracts the LES. Relaxation is primarily mediated by NO and VIP during the swallowing reflex. * **Option C:** In most vascular beds, ACh causes **vasodilation** (not constriction) by stimulating the release of Endothelium-Derived Relaxing Factor (EDRF/Nitric Oxide) from endothelial cells. * **Option D:** ACh acts on M3 receptors in the lungs to cause **bronchoconstriction** and increased mucus secretion. Bronchodilation is a sympathetic effect mediated by $\beta_2$ receptors. **Clinical Pearls for NEET-PG:** * **Achalasia Cardia:** Characterized by failure of the LES to relax due to loss of inhibitory (NO/VIP) neurons in the myenteric plexus. * **Atropine:** An anticholinergic drug that decreases LES pressure, potentially worsening GERD. * **SLUDGE Syndrome:** A mnemonic for cholinergic excess (Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis).

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