General Physiology — MCQs

General Physiology Indian Medical PG Practice Questions and MCQs

Question 41: What is the major neurotransmitter released at the end organ effectors of the sympathetic division of the autonomic nervous system?

A. Adrenaline (Correct Answer)
B. Noradrenaline
C. Dopamine
D. Acetylcholine

Explanation: **Explanation:** The sympathetic nervous system (SNS) is characterized by a "fight or flight" response. The correct answer is **Adrenaline (Epinephrine)** because, although noradrenaline is the primary neurotransmitter at most sympathetic postganglionic nerve endings, the **adrenal medulla**—which is a modified sympathetic ganglion—releases approximately 80% adrenaline and 20% noradrenaline directly into the bloodstream to act on distant end-organ effectors. In the context of systemic sympathetic discharge, adrenaline serves as the major hormonal mediator. **Analysis of Options:** * **Noradrenaline (B):** While it is the neurotransmitter for most sympathetic postganglionic neurons (except sweat glands), adrenaline is often considered the "major" effector hormone in a global sympathetic response due to its potent action on both alpha and beta receptors. * **Dopamine (C):** This is a precursor to noradrenaline and acts as a neurotransmitter in specific CNS pathways and renal vascular smooth muscle, but it is not the primary sympathetic effector. * **Acetylcholine (D):** This is the neurotransmitter for all preganglionic autonomic fibers and parasympathetic postganglionic fibers. In the sympathetic system, it is only found at **sweat glands** (eccrine) and some blood vessels in skeletal muscle (sympathetic cholinergic fibers). **NEET-PG High-Yield Pearls:** * **Rate-limiting step** in catecholamine synthesis: Tyrosine Hydroxylase. * **PNMT (Phenylethanolamine N-methyltransferase):** The enzyme that converts noradrenaline to adrenaline, found primarily in the adrenal medulla; its activity is induced by cortisol. * **Exception Rule:** Sympathetic postganglionic fibers to sweat glands are **cholinergic** (release ACh), not adrenergic. * **Receptor Affinity:** Adrenaline has a higher affinity for $\beta_2$ receptors than noradrenaline, making it a more potent bronchodilator.

Question 42: All of the following are used to measure extracellular fluid (ECF) volume, except?

A. Sucrose
B. Sodium chloride (Correct Answer)
C. Inulin
D. Heavy water

Explanation: **Explanation:** The measurement of body fluid compartments is based on the **Indicator Dilution Principle** ($V = Q/C$). To measure a specific compartment, the indicator must distribute evenly within that compartment without entering others or being rapidly metabolized. **Why Sodium Chloride is the correct answer:** While sodium is the primary extracellular cation, **Sodium chloride (NaCl)** is not used to measure ECF volume because it is not restricted to the extracellular space. Sodium ions are actively transported and can enter cells via various channels and pumps. Furthermore, the body’s existing high concentration of NaCl makes it impossible to use as an exogenous tracer to calculate volume accurately. **Analysis of Incorrect Options:** * **Inulin & Sucrose:** These are large, inert saccharides. They distribute freely throughout the ECF (plasma and interstitial fluid) but cannot cross the cell membrane due to their size and lack of transporters. They are considered the "Gold Standard" for measuring ECF. * **Heavy Water ($D_2O$):** This is used to measure **Total Body Water (TBW)**, not ECF. It distributes uniformly across all fluid compartments (ECF + ICF). Since the question asks for an "except" regarding ECF measurement, and $D_2O$ measures TBW, it is often a distractor; however, in the context of this specific question, NaCl is the most physiologically incorrect choice for ECF measurement. **NEET-PG High-Yield Pearls:** * **Total Body Water:** Measured by Heavy water ($D_2O$), Tritiated water, or Aminopyrine. * **ECF Volume:** Measured by Inulin (Best), Sucrose, Mannitol, or Thiosulfate. * **Plasma Volume:** Measured by Evans Blue dye (T-1824) or Radio-iodinated Albumin ($RISA$). * **ICF Volume:** Cannot be measured directly. Calculated as $TBW - ECF$. * **Interstitial Fluid:** Calculated as $ECF - Plasma\ Volume$.

Question 43: Common for both simple and facilitated diffusion is:

A. Can be blocked by specific inhibitors
B. Follows Fick's Law
C. Follows saturation kinetics
D. Transport along the concentration gradient (Correct Answer)

Explanation: ### Explanation **Concept Overview:** Both simple and facilitated diffusion are forms of **passive transport**. The fundamental driving force for any passive process is the electrochemical or concentration gradient. Since neither process requires metabolic energy (ATP), molecules must move from an area of higher concentration to an area of lower concentration ("downhill"). **Why Option D is Correct:** By definition, all diffusion processes involve the movement of solutes **along the concentration gradient** until equilibrium is reached. This is the only shared characteristic between simple and facilitated diffusion. **Analysis of Incorrect Options:** * **A. Can be blocked by specific inhibitors:** This is a feature of **facilitated diffusion** only. Because facilitated diffusion relies on specific carrier proteins or channels, competitive or non-competitive inhibitors can bind to these proteins and block transport. Simple diffusion occurs through the lipid bilayer and cannot be "inhibited" in this manner. * **B. Follows Fick’s Law:** This law states that the rate of diffusion is directly proportional to the concentration gradient and surface area. While **simple diffusion** linearly follows this law, facilitated diffusion deviates from it because the rate is limited by the number of available carriers. * **C. Follows saturation kinetics ($V_{max}$):** This is unique to **facilitated diffusion**. As the concentration gradient increases, the carrier proteins eventually become saturated, reaching a maximum transport velocity ($V_{max}$). Simple diffusion does not show saturation; its rate increases linearly with the concentration gradient. **NEET-PG High-Yield Pearls:** * **GLUT Transporters:** Classic example of facilitated diffusion (e.g., GLUT-4 in muscle/adipose). * **Simple Diffusion:** Used by gases ($O_2, CO_2$), steroid hormones, and lipid-soluble drugs. * **Key Distinction:** If a question mentions "carrier-mediated" but "no ATP," it is always facilitated diffusion. If it mentions "carrier-mediated" and "against gradient," it is active transport.

Question 44: What is the predominant cation in intracellular fluid?

A. Na+
B. K+ (Correct Answer)
C. Ca+2
D. H+

Explanation: **Explanation:** The distribution of electrolytes across the cell membrane is a fundamental concept in physiology. The correct answer is **Potassium (K+)**, which is the primary intracellular cation. 1. **Why K+ is correct:** In a steady state, the intracellular concentration of Potassium is approximately **140–150 mEq/L**, compared to only 4–5 mEq/L in the extracellular fluid (ECF). This gradient is primarily maintained by the **Na+-K+ ATPase pump**, which actively pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell against their concentration gradients. 2. **Analysis of Incorrect Options:** * **Na+ (Sodium):** This is the predominant cation of the **Extracellular Fluid (ECF)** (~142 mEq/L). Intracellularly, it is kept low (~10–14 mEq/L). * **Ca+2 (Calcium):** While vital for signaling, free cytosolic calcium is kept extremely low (~10⁻⁷ mol/L) to prevent cell toxicity and unintended signaling. Most intracellular calcium is sequestered in the sarcoplasmic reticulum or mitochondria. * **H+ (Hydrogen):** Hydrogen ion concentration determines pH. While it exists in both compartments, its concentration is measured in nanomoles, making it a minor component in terms of total cationic bulk. **NEET-PG High-Yield Pearls:** * **Predominant Intracellular Anion:** Phosphate and negatively charged proteins (not Chloride). * **Predominant Extracellular Anion:** Chloride (Cl-). * **Gibbs-Donnan Effect:** Explains why the presence of non-diffusible intracellular proteins leads to a higher concentration of diffusible cations (K+) inside the cell. * **Resting Membrane Potential (RMP):** Is primarily determined by the K+ equilibrium potential because the resting membrane is most permeable to K+.

Question 45: Positive feedback is seen in all except?

A. LH surge
B. Entry of calcium into sarcoplasmic reticulum
C. Gastric secretion (Correct Answer)
D. Thrombus formation

Explanation: **Explanation:** In physiology, **Positive Feedback** is a mechanism where the output of a system intensifies the original stimulus, leading to an "amplification" or "vicious cycle" until a specific endpoint is reached. Most physiological processes, however, rely on **Negative Feedback** to maintain homeostasis. **Why Gastric Secretion is the Correct Answer:** Gastric acid secretion is primarily regulated by **negative feedback**. As the pH of the stomach falls (becomes more acidic), D-cells in the antrum are stimulated to release **Somatostatin**. Somatostatin then inhibits the release of Gastrin from G-cells and Histamine from ECL cells, thereby decreasing further HCL production. This prevents the stomach from becoming excessively acidic. **Analysis of Incorrect Options (Examples of Positive Feedback):** * **LH Surge:** Increasing levels of Estrogen (above a threshold) exert positive feedback on the anterior pituitary, causing a massive release of Luteinizing Hormone (LH), which triggers ovulation. * **Entry of Calcium into Sarcoplasmic Reticulum (SR):** This refers to **Calcium-Induced Calcium Release (CICR)**. In cardiac muscle, a small amount of trigger calcium entering the cell causes a massive release of calcium from the SR, amplifying the signal for contraction. * **Thrombus Formation:** When a vessel is injured, activated platelets release chemicals that attract and activate more platelets. This cascade continues until a stable plug is formed. **High-Yield Clinical Pearls for NEET-PG:** * **Most common feedback in the body:** Negative Feedback (e.g., BP regulation, Thyroid hormone axis). * **Other Positive Feedback examples:** Parturition (Oxytocin), Nerve Action Potential (Hodgkin cycle/Sodium influx), and the Blood Clotting Cascade. * **Exception to LH:** Low levels of Estrogen exert *negative* feedback; only high, sustained levels trigger the *positive* feedback LH surge.

Question 46: What is the primary sensory function of the Pacinian corpuscle?

A. Crude touch
B. Deep pressure
C. Vibration (Correct Answer)
D. Pricking pain

Explanation: **Explanation:** The **Pacinian corpuscle** is a rapidly adapting (phasic) mechanoreceptor located deep in the dermis and subcutaneous tissue. Its primary sensory function is the detection of **vibration** (specifically high-frequency vibration between 60–400 Hz) and rapid changes in mechanical displacement. **Why Vibration is Correct:** The unique "onion-like" lamellated structure of the Pacinian corpuscle acts as a mechanical filter. When a constant pressure is applied, the fluid between the lamellae redistributes, quickly neutralizing the stimulus. However, it responds vigorously to the onset and offset of pressure. This makes it exquisitely sensitive to repetitive, oscillating stimuli—clinically perceived as vibration. **Analysis of Incorrect Options:** * **A. Crude touch:** This is primarily mediated by **Meissner’s corpuscles** (fine touch) and free nerve endings. These signals are carried via the anterior spinothalamic tract. * **B. Deep pressure:** While Pacinian corpuscles respond to the *initiation* of pressure, **Ruffini endings** are the primary receptors for sustained deep pressure and skin stretch due to their slow-adapting nature. * **C. Pricking pain:** This is mediated by **A-delta fibers** (fast pain) and free nerve endings, not encapsulated mechanoreceptors. **High-Yield Clinical Pearls for NEET-PG:** * **Adaptation:** Pacinian corpuscles are the **fastest adapting** mechanoreceptors in the body. * **Pathway:** Vibration and proprioception are carried via the **Dorsal Column-Medial Lemniscal (DCML) pathway**. * **Clinical Testing:** Vibration sense is often the first modality lost in peripheral neuropathies (e.g., Diabetes Mellitus) and Vitamin B12 deficiency (Subacute Combined Degeneration of the spinal cord). It is tested using a **128 Hz tuning fork**.

Question 47: Which of the following describes the oxidative or respiratory burst phenomenon?

A. It is due to antimicrobial proteins called defensins.
B. It occurs during diapedesis.
C. It involves the activation of NADPH oxidase associated with an increase in oxygen uptake and metabolism in neutrophils. (Correct Answer)
D. It leads to the production of HOCl and HOBr from Cl- and Br- respectively by the action of myeloperoxidase.

Explanation: ### Explanation **Concept Overview:** The **oxidative (respiratory) burst** is a critical mechanism used by phagocytes (neutrophils and macrophages) to kill ingested pathogens. It is characterized by a rapid increase in non-mitochondrial oxygen consumption, which is utilized to generate reactive oxygen species (ROS). **Why Option C is Correct:** The process is initiated by the activation of the multi-subunit enzyme **NADPH oxidase** (nicotinamide adenine dinucleotide phosphate oxidase) located in the phagosomal membrane. This enzyme transfers electrons from NADPH to molecular oxygen ($O_2$), reducing it to **superoxide anion** ($O_2^-$). This sudden surge in oxygen uptake is the "burst" that provides the precursors for microbial killing. **Analysis of Incorrect Options:** * **Option A:** Defensins are antimicrobial peptides that create pores in bacterial membranes; they are part of the **non-oxidative** killing mechanism. * **Option B:** Diapedesis is the process of leukocytes squeezing through endothelial junctions to enter tissues. While it precedes phagocytosis, it does not involve the respiratory burst. * **Option D:** While myeloperoxidase (MPO) does produce HOCl (hypochlorous acid), this step is technically **downstream** of the initial respiratory burst. The "burst" specifically refers to the oxygen consumption phase mediated by NADPH oxidase, not the subsequent enzymatic reactions of MPO. **High-Yield Clinical Pearls for NEET-PG:** * **Chronic Granulomatous Disease (CGD):** Caused by a genetic deficiency in **NADPH oxidase**. Patients suffer from recurrent infections with **catalase-positive** organisms (e.g., *S. aureus*, *Aspergillus*). * **Nitroblue Tetrazolium (NBT) Test:** Used to diagnose CGD. Normal neutrophils turn blue (positive), while CGD neutrophils remain colorless (negative). * **Sequence of ROS:** $O_2 \xrightarrow{\text{NADPH Oxidase}} O_2^- \xrightarrow{\text{Superoxide Dismutase}} H_2O_2 \xrightarrow{\text{MPO}} HOCl$.

Question 48: What is Charles's Law?

A. PV = constant
B. V/T = constant (Correct Answer)
C. PV = nRT
D. None of the above

Explanation: **Explanation:** **Charles’s Law** states that for a fixed mass of gas at a **constant pressure**, the volume (V) is directly proportional to its absolute temperature (T). Mathematically, this is expressed as **V ∝ T** or **V/T = constant**. In physiological terms, as the temperature of a gas increases, the kinetic energy of the molecules increases, causing the gas to expand and occupy a larger volume. **Analysis of Options:** * **Option B (Correct):** Reflects Charles’s Law. In clinical anesthesia, this explains why a gas expands when it moves from a cool environment (like an anesthetic vaporizer) into the warmer environment of a patient’s lungs. * **Option A (Incorrect):** This is **Boyle’s Law**, which states that at a constant temperature, pressure and volume are inversely proportional (P ∝ 1/V). This is the principle behind the mechanism of breathing (inspiration/expiration). * **Option C (Incorrect):** This is the **Ideal Gas Law**, which combines Boyle’s, Charles’s, and Avogadro’s laws into a single equation to describe the behavior of a theoretical ideal gas. **Clinical Pearls for NEET-PG:** 1. **BTPS Conditions:** Lung volumes are typically measured at Body Temperature, ambient Pressure, and Saturated with water vapor (BTPS). Because of Charles's Law, the volume of air expired into a cool spirometer will be less than the volume it occupied in the warm lungs. 2. **Mnemonic:** Remember **"Charles is under Pressure"** (Pressure is constant) and **"Boyle is at a Boil"** (Temperature is constant). 3. **Application:** Charles's Law is essential for calculating the correct dosage of volatile anesthetics and understanding the function of gas-filled equipment in varying climates.

Question 49: Which EEG wave is recorded in a subject who is awake with eyes closed?

A. Alpha waves (Correct Answer)
B. Beta waves
C. Theta waves
D. Delta waves

Explanation: **Explanation:** The Electroencephalogram (EEG) records electrical activity of the cerebral cortex. The correct answer is **Alpha waves** because they are the characteristic rhythm of an adult who is **awake, relaxed, and has their eyes closed**. * **Alpha waves (8–13 Hz):** These are best recorded from the occipital cortex. They represent a state of "relaxed wakefulness." The defining feature for NEET-PG is **Alpha Blockade (Desynchronization)**: as soon as the subject opens their eyes or focuses on a mental task, alpha waves are replaced by low-voltage, high-frequency beta waves. * **Beta waves (14–30 Hz):** These occur during **active mental concentration**, alertness, or when the eyes are open. They have the highest frequency and lowest amplitude (desynchronized). * **Theta waves (4–7 Hz):** These are normal in children but in adults, they signify **Stage N1 sleep** (light sleep) or emotional stress. Presence in an awake adult may indicate brain disorders. * **Delta waves (<3.5 Hz):** These are the slowest waves with the highest amplitude. They are characteristic of **Stage N3 (Deep/Slow-wave sleep)** and are also seen in infancy or severe organic brain disease. **High-Yield Clinical Pearls for NEET-PG:** 1. **Frequency Order:** Beta > Alpha > Theta > Delta (Mnemonic: **BAT-D**). 2. **REM Sleep:** EEG shows Beta-like activity (paradoxical sleep) despite the patient being asleep. 3. **Epilepsy:** EEG is the gold standard for diagnosis (e.g., 3 Hz spike-and-wave pattern in Absence seizures). 4. **Brain Death:** Characterized by a "flat" or isoelectric EEG.

Question 50: Gap junctions are found in which of the following tissues?

A. Intestine
B. Brain
C. Kidney
D. Cardiac muscles (Correct Answer)

Explanation: **Explanation:** **Gap junctions** (also known as nexus or communicating junctions) are specialized intercellular connections composed of proteins called **connexins**. Their primary function is to allow the direct passage of ions and small molecules between adjacent cells, facilitating **electrical and metabolic coupling**. **Why Cardiac Muscle is Correct:** In the heart, gap junctions are concentrated in the **intercalated discs**. They are essential for the rapid, synchronized spread of action potentials across the myocardium. This electrical coupling allows the heart to function as a **functional syncytium**, ensuring that the atria and ventricles contract in a coordinated manner. **Why Other Options are Incorrect:** * **Intestine:** While some smooth muscle in the GI tract contains gap junctions (single-unit smooth muscle), the predominant cell-to-cell junctions in the intestinal epithelium are **tight junctions** (zonula occludens), which regulate paracellular permeability and maintain the mucosal barrier. * **Brain:** While gap junctions exist in specific areas (electrical synapses and glial cells), the brain is primarily characterized by **chemical synapses** and the Blood-Brain Barrier, which relies heavily on tight junctions. * **Kidney:** The renal tubular epithelium is primarily characterized by **tight junctions** that vary in "leakiness" to regulate the reabsorption of water and electrolytes. **High-Yield NEET-PG Pearls:** 1. **Connexon Structure:** Six connexin subunits form one hemichannel (connexon); two connexons from adjacent cells align to form a complete gap junction. 2. **Permeability:** They allow molecules smaller than **1000 Daltons** (e.g., $Ca^{2+}$, $IP_3$, cAMP) to pass. 3. **Regulation:** Gap junctions close in response to **high intracellular $Ca^{2+}$** or **low intracellular pH** (acidosis) to prevent the spread of damage from injured cells. 4. **Clinical Correlation:** Mutations in connexin genes are linked to conditions like **Charcot-Marie-Tooth disease** (Cx32) and **congenital deafness** (Cx26).

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