General Physiology — MCQs

General Physiology Indian Medical PG Practice Questions and MCQs

Question 61: Which of the following is given with iron to increase its absorption?

A. Milk
B. Antacids
C. Citrus fruits (Correct Answer)
D. Alkalies

Explanation: **Explanation:** Iron absorption is a highly regulated process occurring primarily in the duodenum and upper jejunum. The correct answer is **Citrus fruits** because they are rich in **Vitamin C (Ascorbic acid)**. **Why Citrus Fruits are Correct:** Iron exists in two forms: Ferric ($Fe^{3+}$) and Ferrous ($Fe^{2+}$). Only the **Ferrous ($Fe^{2+}$)** form is easily absorbed by the divalent metal transporter 1 (DMT1) in the intestinal mucosa. Vitamin C acts as a reducing agent, converting ferric iron to the more soluble ferrous form. Additionally, it forms a soluble iron-ascorbate complex that prevents iron from precipitating in the alkaline environment of the small intestine. **Why Other Options are Incorrect:** * **Milk:** Contains calcium and phosphates. Calcium competes with iron for transport pathways, and phosphates can form insoluble complexes with iron, significantly inhibiting absorption. * **Antacids & Alkalies:** Iron requires an acidic gastric environment to remain in its soluble ferrous state. Antacids and alkalies neutralize gastric acid, promoting the conversion of iron into insoluble ferric hydroxides, which are poorly absorbed. **NEET-PG High-Yield Pearls:** * **Promoters of Iron Absorption:** Vitamin C (Ascorbic acid), Gastric Acid (HCl), and Amino acids (Cysteine). * **Inhibitors of Iron Absorption:** Phytates (cereals), Oxalates (spinach), Tannins (tea/coffee), Calcium (milk), and Tetracyclines. * **Clinical Tip:** Patients prescribed oral iron supplements are advised to take them with orange juice and avoid tea or milk for at least 2 hours to maximize bioavailability.

Question 62: Which organelle is responsible for intracellular sorting and packing of molecules?

A. Endoplasmic Reticulum (ER)
B. Golgi apparatus (Correct Answer)
C. Ribosome
D. Nucleus

Explanation: **Explanation:** The **Golgi apparatus** is the central "post office" or "shipping hub" of the cell. Its primary function is the post-translational modification, sorting, and packaging of proteins and lipids received from the Endoplasmic Reticulum (ER). Molecules are processed within the Golgi cisternae and then packaged into membrane-bound vesicles, which are directed to their specific destinations (e.g., lysosomes, the plasma membrane, or for extracellular secretion). **Why the other options are incorrect:** * **Endoplasmic Reticulum (ER):** The Rough ER is primarily responsible for protein **synthesis** (via attached ribosomes), while the Smooth ER is involved in lipid synthesis and calcium storage. It transports molecules to the Golgi but does not perform final sorting. * **Ribosomes:** These are the sites of **translation** (protein synthesis) where mRNA is decoded into polypeptide chains. They lack the membrane structure required for packaging. * **Nucleus:** This is the control center of the cell containing genetic material (DNA). It is responsible for **transcription** and replication, not the physical packaging of cytoplasmic molecules. **High-Yield NEET-PG Pearls:** * **I-Cell Disease:** A clinical correlation where a deficiency in the enzyme *phosphotransferase* prevents the Golgi from tagging proteins with Mannose-6-Phosphate. This leads to sorting failure, causing enzymes to be secreted extracellularly rather than sent to lysosomes. * **Polarity:** The Golgi has a **Cis-face** (entry/receiving side near the ER) and a **Trans-face** (exit/shipping side). * **Clathrin:** A protein often involved in coating vesicles budding from the Trans-Golgi network for regulated secretion.

Question 63: All of the following are true about the reticular activating system except?

A. Involved in arousal
B. A polysynaptic pathway
C. Receives collaterals from sensory pathways
D. Does not produce EEG alerting response (Correct Answer)

Explanation: ### Explanation The **Reticular Activating System (RAS)** is a complex network of neurons located in the brainstem (extending from the medulla to the midbrain) that plays a pivotal role in maintaining consciousness and alertness. **Why Option D is the Correct Answer (The False Statement):** The RAS is directly responsible for the **EEG alerting response** (also known as desynchronization). When the RAS is stimulated, the high-amplitude, slow-wave EEG patterns (characteristic of sleep or relaxation) are replaced by low-amplitude, high-frequency **Beta waves**. Therefore, stating that it "does not produce" an alerting response is factually incorrect. **Analysis of Incorrect Options:** * **Option A (Involved in arousal):** This is the primary function of the RAS. It filters sensory input and "wakes up" the cerebral cortex, maintaining a state of wakefulness and behavioral arousal. * **Option B (A polysynaptic pathway):** Unlike the specific sensory pathways (like the dorsal column) which have few synapses, the RAS is a **nonspecific, multi-synaptic (polysynaptic)** network. This allows for the integration of diverse stimuli. * **Option C (Receives collaterals from sensory pathways):** Almost all ascending sensory systems (visual, auditory, tactile, and pain) send lateral collaterals to the RAS. This is why a loud noise or a painful stimulus can instantly wake a person from sleep. **High-Yield Clinical Pearls for NEET-PG:** * **Anatomical Location:** The core of the RAS is located in the **Midbrain Reticular Formation**. * **Neurotransmitters:** Major components include cholinergic (Acetylcholine), noradrenergic (Norepinephrine), and serotonergic projections. * **Clinical Correlation:** Damage to the RAS (e.g., midbrain strokes or severe head injury) leads to **coma**, even if the cerebral cortex itself is intact. * **Pharmacology:** Many general anesthetics work by suppressing the activity of the reticular formation.

Question 64: Which of the following statements about serotonin is true?

A. It is a sleep suppressant.
B. It increases appetite.
C. It causes vasoconstriction. (Correct Answer)
D. It causes bronchodilation.

Explanation: **Explanation:** **Serotonin (5-Hydroxytryptamine or 5-HT)** is a monoamine neurotransmitter synthesized from the amino acid **L-tryptophan**. It plays a diverse role in the central nervous system and peripheral tissues. **1. Why Option C is Correct:** Serotonin is a potent **vasoconstrictor** of large arteries and veins (acting via 5-HT₂ receptors). Its name, "serotonin," is derived from its discovery as a "serum tonic" factor that promotes hemostasis. When platelets aggregate at a site of injury, they release serotonin to cause local vasoconstriction, which helps reduce blood loss. **2. Why Other Options are Incorrect:** * **Option A:** Serotonin is actually a **sleep inducer**, not a suppressant. It is a precursor to **melatonin** in the pineal gland, which regulates the sleep-wake cycle. * **Option B:** Serotonin acts as an **anorexigenic** agent (it **decreases appetite**). Drugs that increase serotonin levels (like SSRIs or fenfluramine) are often associated with weight loss or reduced food intake. * **Option C:** In the lungs, serotonin acts as a **bronchoconstrictor** and an irritant, rather than a bronchodilator. **NEET-PG High-Yield Pearls:** * **Synthesis:** Rate-limiting enzyme is **Tryptophan hydroxylase**. * **Degradation:** Metabolized by MAO-A to **5-HIAA**. Elevated urinary 5-HIAA is a diagnostic marker for **Carcinoid Syndrome**. * **Location:** 90% of the body's serotonin is found in the **Enterochromaffin (EC) cells** of the GI tract, where it regulates intestinal motility. * **Receptors:** All 5-HT receptors are G-protein coupled except **5-HT₃**, which is a **ligand-gated ion channel** (target for anti-emetics like Ondansetron).

Question 65: Fick's law describes the rate of transport in which of the following types of diffusion?

A. Simple diffusion (Correct Answer)
B. Facilitated diffusion
C. Non-ionic diffusion
D. Secondary active transport

Explanation: ### Explanation **1. Why Simple Diffusion is Correct:** Fick’s Law of Diffusion states that the net rate of diffusion ($J$) is directly proportional to the concentration gradient ($\Delta C$), the surface area of the membrane ($A$), and the diffusion coefficient ($D$), while being inversely proportional to the thickness of the membrane ($\Delta X$). **Formula:** $J = -DA \frac{\Delta C}{\Delta X}$ This law applies specifically to **Simple Diffusion**, where substances move down their electrochemical gradient without the requirement of a carrier protein or metabolic energy. Since there are no carriers involved, the rate of transport increases linearly with the concentration gradient and does not show "saturation kinetics." **2. Why the Other Options are Incorrect:** * **Facilitated Diffusion:** Unlike simple diffusion, this requires a carrier protein. Because the number of carriers is finite, the transport rate follows **Michaelis-Menten kinetics** and reaches a maximum limit ($V_{max}$), a phenomenon known as **saturation**. It does not follow the linear relationship described by Fick's Law. * **Non-ionic Diffusion:** This refers to the diffusion of uncharged (non-ionized) molecules across a membrane. While it is a form of simple diffusion, Fick’s Law is the broader governing principle for all simple diffusion, making Option A the most accurate and fundamental choice. * **Secondary Active Transport:** This process requires energy (derived from an ion gradient, usually $Na^+$) and a carrier protein (symporters or antiporters). It moves solutes against a concentration gradient, which contradicts the passive nature of Fick’s Law. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Factors increasing Diffusion:** High lipid solubility (high oil/water partition coefficient), increased surface area (e.g., microvilli), and increased temperature. * **Factors decreasing Diffusion:** Increased membrane thickness (e.g., Pulmonary Fibrosis increases the diffusion distance for $O_2$, leading to hypoxia). * **Graham’s Law:** The diffusion coefficient ($D$) is inversely proportional to the square root of the molecular weight. Smaller molecules diffuse faster. * **Key Distinction:** Simple diffusion is the only transport mechanism that is **not** carrier-mediated and therefore **cannot** be saturated.

Question 66: An open wound contracts by what mechanism?

A. Stretching of surrounding tissues
B. Epithelial growth
C. Skin grafting
D. Fibroblast proliferation (Correct Answer)

Explanation: **Explanation:** The contraction of an open wound is a critical physiological process aimed at reducing the surface area of the defect. This is primarily mediated by **myofibroblasts**, which are specialized cells derived from **fibroblast proliferation** and differentiation. 1. **Why Fibroblast Proliferation is Correct:** During the proliferative phase of wound healing (typically days 3–14), fibroblasts migrate into the wound. Under the influence of cytokines like TGF-β, these fibroblasts transform into myofibroblasts. These cells contain smooth muscle-like actin filaments (alpha-smooth muscle actin), allowing them to exert contractile forces that pull the wound edges together. 2. **Why Other Options are Incorrect:** * **Stretching of surrounding tissues:** While the surrounding skin may stretch to accommodate the closure, it is a *result* of the contraction, not the primary mechanism driving it. * **Epithelial growth:** This refers to **epithelialization**, where keratinocytes migrate from the edges to cover the surface. This provides a barrier but does not physically pull the wound edges together (contraction). * **Skin grafting:** This is a surgical intervention used to close large wounds; it is not a natural physiological mechanism of contraction. **Clinical Pearls for NEET-PG:** * **Key Cell:** The **Myofibroblast** is the hallmark cell of wound contraction. * **Primary Intention vs. Secondary Intention:** Wound contraction is much more pronounced in healing by **secondary intention** (open wounds). * **Complication:** Excessive contraction can lead to **contractures**, commonly seen after severe burn injuries, which can restrict joint mobility. * **Growth Factor:** **TGF-β** is the most important cytokine stimulating fibroblast-to-myofibroblast differentiation.

Question 67: Ubiquitin is a key molecule in protein degradation. Ubiquitinated proteins are degraded by which cellular component?

A. Chaperone
B. Protease
C. Proteasome (Correct Answer)
D. Caspase

Explanation: ### Explanation **Correct Answer: C. Proteasome** The **Ubiquitin-Proteasome Pathway (UPP)** is the primary mechanism for the targeted degradation of short-lived, misfolded, or damaged intracellular proteins. 1. **Ubiquitination:** The process begins when a small regulatory protein called **Ubiquitin** is covalently attached to a target protein (tagging). 2. **Recognition:** Poly-ubiquitinated proteins are specifically recognized by the **26S Proteasome**, a large, barrel-shaped multi-enzyme complex. 3. **Degradation:** The proteasome acts as a "cellular garbage disposal," unfolding the protein and breaking it down into small peptides, while the ubiquitin molecules are recycled. --- ### Why the other options are incorrect: * **A. Chaperones:** These are proteins that assist in the **folding** or refolding of proteins. They prevent aggregation but do not degrade proteins. * **B. Protease:** While proteasomes contain protease activity, "protease" is a general term for any enzyme that breaks down proteins (e.g., pepsin, trypsin). The specific cellular component responsible for the ubiquitin-mediated pathway is the proteasome. * **C. Caspases:** These are specialized cysteine proteases involved specifically in **Apoptosis** (programmed cell death), not the routine degradation of ubiquitinated proteins. --- ### NEET-PG High-Yield Pearls: * **Energy Requirement:** Unlike lysosomal degradation, the Ubiquitin-Proteasome pathway is **ATP-dependent**. * **Clinical Correlation:** **Bortezomib** is a proteasome inhibitor used in the treatment of **Multiple Myeloma**. It works by preventing the degradation of pro-apoptotic factors, leading to cancer cell death. * **Parkinson’s Disease:** Mutations in the *Parkin* gene (an E3 ubiquitin ligase) lead to the accumulation of misfolded proteins, contributing to neurodegeneration.

Question 68: What is the approximate volume of intracellular fluid (ICF) in the body, expressed as a fraction of body weight?

A. 0.2 * body weight
B. 0.4 * body weight (Correct Answer)
C. 0.6 * body weight
D. 0.8 * body weight

Explanation: ### Explanation The distribution of body water is a fundamental concept in physiology, often governed by the **"60-40-20 Rule."** **1. Why Option B is Correct:** In an average healthy adult (70 kg), **Total Body Water (TBW)** accounts for approximately **60% (0.6)** of the total body weight. This water is distributed into two main compartments: * **Intracellular Fluid (ICF):** This is the fluid contained within the cells. It constitutes **two-thirds (2/3)** of the TBW, which equates to approximately **40% (0.4) of the total body weight.** * **Extracellular Fluid (ECF):** This is the fluid outside the cells, constituting the remaining **one-third (1/3)** of TBW, or **20% (0.2) of the body weight.** **2. Analysis of Incorrect Options:** * **Option A (0.2):** This represents the **Extracellular Fluid (ECF)** volume, not the intracellular volume. * **Option C (0.6):** This represents the **Total Body Water (TBW)** in a standard adult male. * **Option D (0.8):** This value is too high for an adult; however, TBW can reach up to 75-80% in **neonates**, making them highly susceptible to dehydration. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Gender Variation:** Women have a lower percentage of TBW (~50%) compared to men (~60%) because they generally have a higher proportion of **adipose tissue** (fat is hydrophobic and contains very little water). * **Indicator Dilution Method:** To measure these volumes clinically: * **TBW** is measured using Tritiated water or Deuterium oxide ($D_2O$). * **ECF** is measured using Inulin, Mannitol, or Sucrose. * **Plasma Volume** is measured using Evans Blue dye or Radio-iodinated Albumin. * **ICF** cannot be measured directly; it is calculated as **TBW minus ECF.**

Question 69: Repolarization is due to the opening of which ion channels?

A. Sodium (Na+)
B. Bicarbonate (HCO3-)
C. Potassium (K+) (Correct Answer)
D. Chloride (Cl-)

Explanation: **Explanation:** The Action Potential (AP) consists of two primary phases: depolarization and repolarization. **Repolarization** is the process by which the cell membrane potential returns to its negative resting state after depolarization. **Why Potassium (K+) is correct:** During the peak of an action potential, voltage-gated Na+ channels close (inactivate) and **voltage-gated K+ channels open**. Because the concentration of K+ is much higher inside the cell than outside, K+ ions rapidly exit the cell (efflux) down their electrochemical gradient. This loss of positive charge from the intracellular compartment restores the negative resting membrane potential. **Analysis of Incorrect Options:** * **Sodium (Na+):** The opening of voltage-gated Na+ channels leads to Na+ influx, which causes **Depolarization** (making the cell interior more positive). * **Bicarbonate (HCO3-):** This ion is primarily involved in acid-base balance and CO2 transport; it does not play a primary role in the rapid phases of the neuronal or muscular action potential. * **Chloride (Cl-):** The entry of Cl- into a cell typically causes **Hyperpolarization** (Inhibitory Post-Synaptic Potential - IPSP), making the cell less likely to fire, rather than driving the standard repolarization phase. **High-Yield Facts for NEET-PG:** * **Hyperkalemia:** Increases membrane excitability initially (brings RMP closer to threshold) but can eventually lead to paralysis due to persistent inactivation of Na+ channels. * **After-hyperpolarization:** Occurs because voltage-gated K+ channels are slow to close, allowing the membrane potential to briefly become more negative than the resting level. * **Cardiac Repolarization:** In cardiac ventricular muscle, Phase 2 (Plateau) is due to Ca2+ influx, while **Phase 3 (Rapid Repolarization)** is due to K+ efflux.

Question 70: Which of the following pigments are involved in free radical injury?

A. Lipofuscin (Correct Answer)
B. Melanin
C. Bilirubin
D. Hematin

Explanation: **Explanation:** **Lipofuscin** is known as the "wear-and-tear" or "aging" pigment. It is the correct answer because its formation is directly linked to **lipid peroxidation**—a hallmark of free radical injury. When reactive oxygen species (ROS) attack the polyunsaturated lipids of subcellular membranes, they undergo peroxidation, forming malondialdehyde. This reacts with proteins to create insoluble, brownish-yellow granular polymers (lipofuscin) that accumulate within lysosomes, particularly in permanent cells like neurons and cardiac myocytes. **Analysis of Incorrect Options:** * **Melanin (B):** An endogenous, non-hemoglobin derived black-brown pigment produced by melanocytes. Its primary function is protection against UV radiation, not a byproduct of free radical damage. * **Bilirubin (C):** A yellow breakdown product of normal heme catabolism. While it has some antioxidant properties, it is not a marker or product of free radical-induced cellular injury. * **Hematin (D):** An oxidation product of hemoglobin (specifically the ferric form of heme). It is typically seen in malarial parasites (hemozoin) or as an artifact, but is not the characteristic pigment of lipid peroxidation. **Clinical Pearls for NEET-PG:** * **Morphology:** Lipofuscin appears as fine, yellow-brown intracytoplasmic granules, often seen in a perinuclear distribution. * **Brown Atrophy:** Massive accumulation of lipofuscin in the heart or liver of elderly or malnourished patients leads to an organ appearance known as "brown atrophy." * **Key Association:** Always associate Lipofuscin with **Lipid Peroxidation** and **Autophagy**. It is a tell-tale sign of past free radical insult.

Practice by Chapter

Cell Structure and Function

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Membrane Transport Mechanisms

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Bioelectric Phenomena

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Homeostasis and Feedback Mechanisms

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Body Fluid Compartments

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Signal Transduction Mechanisms

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Cell-to-Cell Communication

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Principles of Physiological Measurement

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Osmosis and Osmotic Pressure

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Physiological Adaptation Mechanisms

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