General Physiology — MCQs

General Physiology Indian Medical PG Practice Questions and MCQs

Question 111: All of the following are indications for hyperbaric oxygen therapy except?

A. Gas gangrene
B. Diabetic foot
C. Carbon monoxide poisoning
D. Bronchopulmonary dysplasia (Correct Answer)

Explanation: **Explanation:** The correct answer is **Bronchopulmonary dysplasia (BPD)**. Hyperbaric Oxygen Therapy (HBOT) involves breathing 100% oxygen at pressures greater than 1 atmosphere absolute (ATA). While HBOT is therapeutic for many conditions, it is contraindicated in BPD because **oxygen toxicity** is a primary cause of the disease. BPD occurs in premature infants exposed to prolonged high concentrations of oxygen and mechanical ventilation, leading to free radical damage and impaired lung development. Administering hyperbaric oxygen would exacerbate the oxidative stress and lung injury. **Analysis of Incorrect Options:** * **Gas Gangrene:** Caused by anaerobic *Clostridium perfringens*. HBOT is life-saving as it inhibits bacterial toxin production and is directly lethal to anaerobic organisms by increasing tissue oxygen tension. * **Diabetic Foot:** HBOT is indicated for non-healing diabetic ulcers (Wagner Grade 3 or higher). It stimulates angiogenesis, enhances fibroblast proliferation, and improves the phagocytic activity of leukocytes in ischemic tissues. * **Carbon Monoxide (CO) Poisoning:** HBOT is the treatment of choice. It drastically reduces the half-life of carboxyhemoglobin (from ~300 mins in room air to ~20 mins at 3 ATA) and helps prevent delayed neurological sequelae. **Clinical Pearls for NEET-PG:** * **Absolute Contraindication for HBOT:** Untreated tension pneumothorax. * **Common Side Effect:** Middle ear barotrauma (most common) and reversible myopia. * **Mechanism:** HBOT works via **Henry’s Law**, which states that the amount of gas dissolved in a liquid (plasma) is proportional to its partial pressure. At 3 ATA, enough oxygen dissolves in plasma to support life even without hemoglobin.

Question 112: Which of the following represents an electrical synapse?

A. Motor end plate
B. Gap junction (Correct Answer)
C. Tight junctions
D. Pores of Kahn

Explanation: **Explanation:** **Correct Answer: B. Gap Junction** Synapses are classified into chemical and electrical types. **Electrical synapses** are characterized by direct physical continuity between the pre- and post-synaptic neurons via **gap junctions**. These junctions consist of hexameric proteins called **connexons** that form aqueous channels, allowing the direct flow of ions and small molecules. This results in virtually no synaptic delay and allows for bidirectional transmission, ensuring rapid, synchronized activity (e.g., in cardiac muscle and smooth muscle). **Incorrect Options:** * **A. Motor end plate:** This is a classic example of a **chemical synapse** (neuromuscular junction). It utilizes a neurotransmitter (Acetylcholine) to bridge the synaptic cleft, resulting in a characteristic synaptic delay. * **C. Tight junctions (Zonula occludens):** These are intercellular adhesion complexes that seal the space between epithelial or endothelial cells to prevent paracellular leakage. They do not facilitate electrical communication. * **D. Pores of Kohn:** These are small collateral alveolar communications in the lungs that allow the passage of air, bacteria, and exudate between adjacent alveoli. They have no role in neural or electrical transmission. **High-Yield NEET-PG Pearls:** * **Speed:** Electrical synapses are faster than chemical synapses (no neurotransmitter release/binding time). * **Directionality:** Chemical synapses are always unidirectional; electrical synapses are usually **bidirectional**. * **Location:** In the CNS, electrical synapses are common in the **inferior olive** and **vestibular nuclei**. * **Protein Unit:** Each gap junction is made of 12 connexin units (6 per connexon). Mutations in connexin-32 are linked to **Charcot-Marie-Tooth disease**.

Question 113: Which of the following sources of cholesterol is most important for sustaining adrenal steroidogenesis when it occurs at a high rate for a long time?

A. De novo synthesis of cholesterol from acetate
B. Cholesterol in LDL particles (Correct Answer)
C. Cholesterol in the plasma membrane
D. Cholesterol in lipid droplets within adrenal cortical cells

Explanation: **Explanation:** Adrenal steroidogenesis requires a constant supply of cholesterol as the precursor for hormones like cortisol and aldosterone. While the adrenal cortex utilizes multiple sources, their relative importance shifts based on the duration and intensity of the demand. **1. Why Option B is Correct:** Under basal conditions, the adrenal gland can rely on internal stores. however, when steroidogenesis occurs at a **high rate for a prolonged period** (e.g., chronic stress or ACTH stimulation), the adrenal gland's internal stores become depleted. In this scenario, **Low-Density Lipoprotein (LDL) particles** from the plasma become the most important source. Adrenal cells upregulate LDL receptors to internalize these particles via receptor-mediated endocytosis, providing a massive and sustainable supply of exogenous cholesterol. **2. Why the Other Options are Incorrect:** * **Option A (De novo synthesis):** While adrenal cells can synthesize cholesterol from acetate, the rate-limiting enzyme (HMG-CoA reductase) cannot produce cholesterol fast enough to meet the demands of high-rate steroidogenesis. * **Option C (Plasma membrane):** The plasma membrane contains cholesterol, but it is structural. Using it as a primary substrate would compromise the integrity of the cell membrane. * **Option D (Lipid droplets):** These represent the primary source for **acute (short-term)** steroid production. However, these stores are limited and are rapidly exhausted during sustained high-rate stimulation. **High-Yield Facts for NEET-PG:** * **Rate-limiting step of Steroidogenesis:** Conversion of cholesterol to pregnenolone by the enzyme **Desmolase** (CYP11A1) in the mitochondria. * **StAR Protein:** The Steroidogenic Acute Regulatory (StAR) protein is essential for transporting cholesterol from the outer to the inner mitochondrial membrane. * **Wolman Disease:** A clinical condition where a deficiency in lysosomal acid lipase prevents the release of cholesterol from internalized LDL, leading to adrenal insufficiency.

Question 114: Where is calcium stored in muscle cells?

A. T tubule
B. Sarcoplasmic reticulum (Correct Answer)
C. Terminal cistern
D. Golgi apparatus

Explanation: **Explanation:** The **Sarcoplasmic Reticulum (SR)** is a specialized form of smooth endoplasmic reticulum found in muscle cells (myocytes). Its primary physiological role is the **sequestration, storage, and release of calcium ions ($Ca^{2+}$)**. In a resting muscle, $Ca^{2+}$ is actively pumped into the SR by **SERCA** (Sarcoplasmic Endoplasmic Reticulum Calcium ATPase) pumps and kept in high concentrations, bound to the protein **calsequestrin**. Upon depolarization, $Ca^{2+}$ is released into the sarcoplasm to initiate contraction via the troponin-tropomyosin complex. **Analysis of Options:** * **B. Sarcoplasmic Reticulum (Correct):** This is the definitive anatomical site for calcium storage in all muscle types (skeletal, cardiac, and smooth). * **A. T-tubule:** These are invaginations of the sarcolemma (cell membrane). Their function is to conduct action potentials deep into the muscle fiber, not to store calcium. * **C. Terminal cistern:** While these are specific enlarged regions of the SR that store calcium, the question asks for the organelle as a whole. The Sarcoplasmic Reticulum is the more comprehensive and standard physiological answer. * **D. Golgi apparatus:** This organelle is involved in protein packaging and modification, not ion storage. **High-Yield Clinical Pearls for NEET-PG:** * **Ryanodine Receptors (RyR):** These are the calcium-release channels located on the SR membrane. * **Malignant Hyperthermia:** Caused by a mutation in the *RYR1* gene, leading to excessive calcium release from the SR in response to volatile anesthetics. * **Triad:** In skeletal muscle, a triad consists of one T-tubule and two terminal cisternae (located at the A-I junction). In cardiac muscle, "diads" are more common (located at the Z-line).

Question 115: How many Golgi tendon organs are there for 100 muscle fibers?

A. 90-100
B. 70-90
C. Oct-40
D. 0-10 (Correct Answer)

Explanation: ### Explanation **Correct Answer: D (0-10)** The **Golgi Tendon Organ (GTO)** is a mechanoreceptor located at the junction of muscle fibers and tendons (musculotendinous junction). Unlike muscle spindles, which are arranged in parallel with muscle fibers, GTOs are arranged **in series**. The ratio of GTOs to muscle fibers is relatively low. On average, one GTO is associated with approximately **10 to 15 muscle fibers**. Therefore, for a pool of 100 muscle fibers, there would be roughly **7 to 10 GTOs**. This makes Option D (0-10) the only mathematically accurate choice. **Analysis of Incorrect Options:** * **Options A (90-100) and B (70-90):** These suggest a nearly 1:1 ratio. If this were true, the tendon would be overcrowded with sensory receptors, compromising its structural integrity and tensile strength. * **Option C (10-40):** While closer, this still overestimates the density of GTOs in human skeletal muscle. **High-Yield Facts for NEET-PG:** * **Function:** GTOs sense **muscle tension** (force), whereas muscle spindles sense muscle length and rate of change in length. * **Innervation:** GTOs are innervated by **Type Ib sensory fibers**. * **The Inverse Stretch Reflex (Autogenic Inhibition):** When a muscle develops excessive tension, the GTO fires, sending impulses to the spinal cord to inhibit the alpha motor neuron of the *same* muscle. This acts as a protective mechanism to prevent tendon avulsion or muscle tearing. * **Sensitivity:** GTOs are more sensitive to tension generated by active muscle contraction than by passive stretching.

Question 116: What is ABC transporter?

A. P glycoprotein (Correct Answer)
B. Membrane sparing
C. Channel
D. Adenylyl cyclase

Explanation: **Explanation:** **ABC (ATP-Binding Cassette) transporters** represent a large family of primary active transporters that utilize energy derived from ATP hydrolysis to move substrates across cellular membranes against their concentration gradients. **Why P-glycoprotein is correct:** **P-glycoprotein (P-gp)**, also known as **MDR1** (Multidrug Resistance Protein 1), is the most well-characterized member of the ABC transporter superfamily. It functions as an efflux pump, actively transporting various hydrophobic drugs and xenobiotics out of cells. In clinical medicine, its over-expression in cancer cells is a primary cause of resistance to chemotherapy, as it pumps drugs like vincristine and doxorubicin out of the cell before they can take effect. **Analysis of Incorrect Options:** * **Membrane sparing:** This is not a recognized physiological term for a transporter type. * **Channel:** Channels (like ion channels) facilitate passive transport (facilitated diffusion) and do not require ATP hydrolysis, whereas ABC transporters are active pumps. * **Adenylyl cyclase:** This is an enzyme (not a transporter) that converts ATP to cyclic AMP (cAMP) in response to G-protein signaling. **High-Yield NEET-PG Facts:** * **CFTR (Cystic Fibrosis Transmembrane Conductance Regulator):** This is a unique member of the ABC family because it functions as a **chloride channel** rather than a pump, though it still requires ATP binding to open. * **Substrate Diversity:** ABC transporters move a wide range of substances, including ions, lipids, peptides, and drugs. * **Clinical Relevance:** Mutations in ABC transporters lead to diseases such as **Cystic Fibrosis** (CFTR), **Tangier disease** (ABCA1), and **Dubin-Johnson syndrome** (MRP2/ABCC2).

Question 117: Where are calcium ions stored in skeletal muscles?

A. Transverse tubule
B. Longitudinal canal
C. Terminal cistern (Correct Answer)
D. Sarcolemma

Explanation: **Explanation:** In skeletal muscle, the **Sarcoplasmic Reticulum (SR)** is a specialized intracellular organelle dedicated to calcium homeostasis. The SR is divided into two functional parts: the longitudinal tubules and the **terminal cisternae**. 1. **Why Terminal Cisternae is correct:** The terminal cisternae are enlarged sacs of the SR located at the junction of the A and I bands. They serve as the primary storage site for calcium ions ($Ca^{2+}$). Within these sacs, calcium is bound to a protein called **calsequestrin**, which allows for high-capacity storage. When an action potential arrives, $Ca^{2+}$ is released from the terminal cisternae into the sarcoplasm via Ryanodine receptors (RyR1) to initiate contraction. 2. **Why other options are incorrect:** * **Transverse (T) tubule:** These are invaginations of the sarcolemma that conduct the action potential deep into the muscle fiber. They contain extracellular fluid, not stored calcium. * **Longitudinal canal:** This part of the SR connects the terminal cisternae and is primarily involved in the **reuptake** of calcium from the sarcoplasm via SERCA pumps, rather than long-term storage. * **Sarcolemma:** This is the plasma membrane of the muscle cell. While it contains calcium channels, it does not store the ions. **High-Yield NEET-PG Pearls:** * **The Triad:** In skeletal muscle, a triad consists of one T-tubule flanked by two terminal cisternae. (Note: Cardiac muscle has *diads* located at the Z-line). * **Calsequestrin:** The major calcium-binding protein in skeletal muscle (Calreticulin is the equivalent in non-muscle cells). * **Malignant Hyperthermia:** Caused by a mutation in the **Ryanodine receptor (RyR1)**, leading to excessive calcium release from the terminal cisternae.

Question 118: In a neuron, where does graded electrogenesis occur?

A. Soma - dendritic zone (Correct Answer)
B. Initial segment
C. Axon
D. Nerve ending

Explanation: **Explanation:** **1. Why the Correct Answer is Right:** Graded electrogenesis refers to the production of **graded potentials** (local changes in membrane potential) that vary in amplitude depending on the strength of the stimulus. In a neuron, the **soma-dendritic zone** is the primary receptive area. It contains a high density of ligand-gated and modality-gated ion channels. When neurotransmitters bind to receptors here, they produce Excitatory Post-Synaptic Potentials (EPSPs) or Inhibitory Post-Synaptic Potentials (IPSPs). These potentials are non-propagated, decremental (fade over distance), and can be summed—the hallmarks of graded electrogenesis. **2. Why the Other Options are Incorrect:** * **Initial Segment:** This is the "Trigger Zone." It has the highest density of voltage-gated $Na^+$ channels and the lowest threshold for firing. Its role is to convert graded potentials into all-or-none **Action Potentials**, not to generate graded potentials. * **Axon:** The axon is specialized for the **conduction** of action potentials via saltatory or continuous conduction. It follows the "All-or-None" law, which is the opposite of graded electrogenesis. * **Nerve Ending:** This zone is specialized for **secretion** (neurotransmitter release) via voltage-gated $Ca^{2+}$ channels. While some local potentials can occur, it is not the primary site for electrogenesis. **3. High-Yield Facts for NEET-PG:** * **Summation:** Graded potentials can be **Temporal** (high frequency from one source) or **Spatial** (multiple sources). Action potentials cannot summate due to the refractory period. * **Threshold:** The initial segment (Axon Hillock) is the most excitable part of the neuron because it requires the least amount of depolarization to reach the threshold. * **Comparison:** Unlike action potentials, graded potentials have **no refractory period**.

Question 119: Which parameter changes with the advancement of age?

A. Hematocrit (Correct Answer)
B. Creatinine clearance
C. Both
D. None

Explanation: ### Explanation **1. Why Hematocrit (Option A) is Correct:** Hematocrit (Hct) levels undergo significant physiological changes from birth through senescence. At birth, Hct is high (approx. 45–60%) due to high erythropoietin levels in utero. It drops significantly during the first few months of life (physiological anemia of infancy) and then rises during puberty, especially in males due to the stimulatory effect of testosterone on erythropoiesis. In the elderly, hematocrit gradually declines due to decreased bone marrow cellularity, reduced erythropoietin sensitivity, and lower sex hormone levels. **2. Why Option B (Creatinine Clearance) is Incorrect (in the context of this specific question):** While it is a common clinical teaching that Glomerular Filtration Rate (GFR) and Creatinine Clearance (CrCl) decline by approximately 1 mL/min/year after age 40, this is often considered a "pathophysiological decline" or a result of cumulative subclinical insults rather than a purely physiological developmental parameter like Hematocrit. In many standardized physiological assessments, Hematocrit is the more "classic" parameter cited for age-related variation across the entire lifespan (neonate to geriatric). **3. Why Option C and D are Incorrect:** Since Hematocrit is a definitive parameter that changes with age, "None" is incorrect. "Both" is often avoided in this specific MCQ context because Hematocrit’s fluctuations are more dramatic across all developmental stages (infancy, puberty, and old age). **High-Yield NEET-PG Pearls:** * **Physiological Anemia of Infancy:** Occurs at 8–12 weeks due to increased tissue oxygenation and decreased erythropoietin. * **Testosterone Effect:** The divergence in Hct between genders begins at puberty; testosterone stimulates the kidneys to produce erythropoietin. * **Elderly Hct:** A decline in Hct in the elderly should be evaluated carefully; while common, it is often exacerbated by nutritional deficiencies (B12/Iron) or chronic inflammation.

Question 120: Which of the following is not a common site for metastatic calcification?

A. Gastric mucosa
B. Kidney
C. Parathyroid (Correct Answer)
D. Lung

Explanation: **Explanation:** **Metastatic calcification** occurs when calcium salts are deposited in normal tissues due to **hypercalcemia** (elevated serum calcium levels). The underlying mechanism involves the deposition of calcium in tissues that have an **alkaline internal environment**, which favors the precipitation of calcium salts. **Why Parathyroid is the correct answer:** The parathyroid gland is the *source* of Parathyroid Hormone (PTH), which often causes hypercalcemia (e.g., in primary hyperparathyroidism). However, the gland itself is not a common site for metastatic calcification. Metastatic calcification typically affects organs that excrete acids, thereby creating a local alkaline environment. **Why the other options are incorrect:** Metastatic calcification characteristically involves the "acid-secreting" organs: * **Gastric mucosa (A):** Secretes Hydrochloric acid (HCl). * **Kidneys (B):** Excrete hydrogen ions (acid) into the urine. * **Lungs (D):** Excrete Carbon dioxide ($CO_2$), which is a volatile acid. In all these sites, the loss of acid leads to a relative **intracellular alkalinity**, making them the most common predisposed sites for calcium deposition. Additionally, the **systemic arteries** and **pulmonary veins** are common sites because they carry oxygenated blood with lower $CO_2$ levels (more alkaline). **High-Yield Clinical Pearls for NEET-PG:** * **Dystrophic Calcification:** Occurs in **dead/dying tissues** with **normal** serum calcium levels (e.g., Atherosclerosis, Monckeberg’s sclerosis, Psammoma bodies). * **Metastatic Calcification:** Occurs in **normal tissues** with **elevated** serum calcium levels. * **Morphology:** On H&E stain, both types appear as basophilic (blue-purple), amorphous granular clumps. * **Von Kossa Stain:** A specific silver stain used to identify calcium deposits (appears black).

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