General Physiology Practice Questions

Q: Activation of G-protein regulates all of the following except?

Transcription factor. **Explanation:** G-protein coupled receptors (GPCRs) are the largest family of cell surface receptors. They act as molecular switches that transmit signals from extracellular ligands to intracellular effectors via heterotrimeric G-proteins ($\alpha$, $\beta$, and $\gamma$ subunits). **Why "Transcription Factor" is the correct answer:** Transcription factors are typically regulated by **nuclear receptors** (e.g., steroid hormones) or via complex downstream kinase cascades (like the MAPK pathway). While G-protein signaling can *eventually* influence gene expression, G-proteins do not **directly** regulate transcription factors. Transcription factors are located in the nucleus, whereas G-proteins are membrane-bound peripheral proteins. **Analysis of Incorrect Options:** * **Adenyl cyclase activity:** This is a classic G-protein function. $G_s$ stimulates and $G_i$ inhibits Adenyl Cyclase, which converts ATP to cAMP (the second messenger). * **Ion channels:** G-proteins can regulate ion channels either directly (e.g., $G_{\beta\gamma}$ subunits opening $K^+$ channels in the heart) or indirectly via second messengers (e.g., cAMP-dependent phosphorylation of $Ca^{2+}$ channels). * **IP3 & DAG:** The $G_q$ protein activates Phospholipase C (PLC), which cleaves membrane phospholipids into Inositol triphosphate (IP3) and Diacylglycerol (DAG), leading to calcium release and Protein Kinase C activation. **High-Yield Clinical Pearls for NEET-PG:** * **Toxins:** *Vibrio cholerae* toxin causes permanent activation of $G_s$ (inhibits GTPase activity), leading to secretory diarrhea. *Bordetella pertussis* toxin inhibits $G_i$, leading to increased cAMP levels. * **Structure:** GPCRs are also known as **7-transmembrane** or **Serpentine receptors**. * **Termination:** The signal is terminated when the $\alpha$-subunit hydrolyzes GTP to GDP (intrinsic GTPase activity).

Q: In peripheral tissues, which of the following contains substance P?

Nerve terminal. **Explanation:** **Substance P** is an 11-amino acid neuropeptide belonging to the tachykinin family. It is primarily synthesized in the cell bodies of **primary afferent (sensory) neurons** located in the dorsal root ganglia. From there, it is transported to both the central terminals (in the spinal cord) and the **peripheral nerve terminals** (nociceptors). 1. **Why Nerve Terminal is Correct:** In the periphery, Substance P is stored in the vesicles of **unmyelinated C-fibers**. Upon stimulation (injury or inflammation), it is released from these terminals. It functions as a potent vasodilator and increases vascular permeability, contributing to **neurogenic inflammation**. 2. **Why Other Options are Incorrect:** * **Plasma Cells:** These are differentiated B-cells responsible for antibody (immunoglobulin) production, not neuropeptide storage. * **Mast Cells:** While mast cells are *activated* by Substance P (causing degranulation and histamine release), they do not synthesize or contain Substance P themselves. * **Vascular Endothelium:** The endothelium responds to Substance P via NK1 receptors to release nitric oxide, but it is not a source of the peptide. **High-Yield Clinical Pearls for NEET-PG:** * **Receptor:** Substance P acts primarily via the **NK1 (Neurokinin-1) receptor**. * **Triple Response of Lewis:** Substance P release from peripheral nerve terminals is a key mediator of the "flare" component in the triple response. * **Pain Transmission:** In the CNS, it is a major neurotransmitter for pain signals in the **Substantia Gelatinosa** of the spinal cord. * **Pharmacology:** **Aprepitant** is an NK1 receptor antagonist used clinically to manage chemotherapy-induced nausea and vomiting (CINV).

Q: What is the clearance of a drug?

The volume of plasma cleared of drug per unit of time.. **Explanation** Clearance ($Cl$) is a fundamental pharmacokinetic parameter defined as the **volume of plasma** from which a drug is completely removed per unit of time (usually expressed in mL/min or L/hr). It represents the efficiency of drug elimination from the body. The mathematical formula is: $Cl = \frac{\text{Rate of elimination}}{\text{Plasma concentration } (C_p)}$ **Why Option A is correct:** Clearance does not measure the *amount* of drug removed; rather, it measures the *volume of fluid* (plasma) that would need to be entirely freed of the drug to account for the elimination. This is a constant value for drugs following first-order kinetics. **Why other options are incorrect:** * **Option B:** The amount of drug in urine is the "excretion rate," not clearance. Clearance relates this excretion to the plasma concentration. * **Option C:** This describes the "metabolic rate." While metabolism contributes to total clearance (Hepatic Clearance), it is only one component and is measured in mass/time (e.g., mg/min), not volume/time. * **Option D:** Incorrect because clearance specifically refers to the volume of distribution cleared, not the mass of the drug. **NEET-PG High-Yield Pearls:** 1. **Total Body Clearance:** Sum of Renal + Hepatic + Pulmonic + Other clearances. 2. **First-Order Kinetics:** Clearance remains constant regardless of drug concentration. 3. **Zero-Order Kinetics:** Clearance decreases as plasma concentration increases (e.g., Phenytoin, Alcohol, Aspirin at high doses). 4. **Clinical Significance:** Clearance is the most important parameter for determining the **Maintenance Dose** of a drug. * *Maintenance Dose = Target $C_p \times Cl$*

Q: What is hypertrophy?

Increase in cell size. **Explanation:** **Hypertrophy** is defined as an increase in the size of cells, which subsequently leads to an increase in the size of the involved organ. This process occurs due to the increased synthesis of structural proteins and organelles within the cell. It is the primary response to increased workload in cells that have a limited capacity to divide (permanent cells). **Analysis of Options:** * **Option B (Correct):** Hypertrophy specifically refers to **cellular enlargement**. A classic physiological example is the skeletal muscle growth seen in bodybuilders, while a pathological example is Left Ventricular Hypertrophy (LVH) due to hypertension. * **Option A (Incorrect):** An increase in the number of cells is termed **Hyperplasia**. This occurs in tissues capable of replication (e.g., uterine growth during pregnancy involves both hypertrophy and hyperplasia). * **Option C & D (Incorrect):** A decrease in cell number or size is characteristic of **Atrophy**, which results in the shrinkage of an organ or tissue. **High-Yield NEET-PG Pearls:** 1. **Permanent Cells:** Cardiac myocytes and skeletal muscle cells undergo *only* hypertrophy, not hyperplasia, because they cannot divide. 2. **Mechanism:** Triggered by mechanical sensors (stretch), growth factors (IGF-1), and vasoactive agents (Endothelin-1, Angiotensin II). 3. **Subcellular Hypertrophy:** An example is the hypertrophy of the Smooth Endoplasmic Reticulum (SER) in hepatocytes when exposed to drugs like barbiturates (leading to drug tolerance). 4. **Key Distinction:** Hypertrophy (Size) vs. Hyperplasia (Number). Both result in increased organ volume.

Q: What does the term "Meileu interior" refer to in physiology?

Extracellular fluid (ECF). **Explanation:** The term **"Milieu intérieur"** (French for "the environment within") was coined by the 19th-century French physiologist **Claude Bernard**. It refers specifically to the **Extracellular Fluid (ECF)** that surrounds and bathes the cells of multicellular organisms. **Why ECF is the correct answer:** Claude Bernard proposed that for an organism to remain healthy and independent of the external environment, its internal environment must remain constant. Since cells do not come into direct contact with the outside world, they rely on the ECF (interstitial fluid and plasma) for nutrients and waste removal. This concept laid the foundation for **Homeostasis**, a term later popularized by Walter Cannon. **Analysis of Incorrect Options:** * **Intracellular Fluid (ICF):** This is the fluid *inside* the cells. While vital, it is not the "internal environment" described by Bernard; rather, it is the environment that the *Milieu intérieur* protects and maintains. * **Plasma:** Plasma is a sub-component of the ECF (along with interstitial fluid). While it is part of the internal environment, "Milieu intérieur" encompasses the *entire* ECF. * **Lymph:** Similar to plasma, lymph is merely a specialized part of the ECF. **NEET-PG High-Yield Pearls:** * **Claude Bernard:** Known as the "Father of Modern Physiology"; he introduced the concept of *Milieu intérieur*. * **Walter Cannon:** Coined the term **Homeostasis** to describe the maintenance of a constant *Milieu intérieur*. * **ECF Composition:** ECF constitutes approximately **20%** of total body weight (15% interstitial fluid, 5% plasma). * **Total Body Water (TBW):** Roughly 60% of body weight; ICF makes up 40%, and ECF makes up 20%.

Q: Hypoxia causes vasoconstriction in which of the following locations?

Lungs. ### Explanation The correct answer is **Lungs (Option B)**. **Underlying Concept: Hypoxic Pulmonary Vasoconstriction (HPV)** In most systemic tissues, hypoxia (low oxygen) acts as a potent **vasodilator** to increase blood flow and oxygen delivery to oxygen-starved cells. However, the pulmonary circulation exhibits a unique phenomenon known as **Hypoxic Pulmonary Vasoconstriction (HPV)**. When alveolar oxygen levels drop, the smooth muscles of the pulmonary arterioles constrict. This is a protective mechanism designed to **shunt blood away** from poorly ventilated areas of the lung toward well-ventilated areas, thereby optimizing **ventilation-perfusion (V/Q) matching** and preventing systemic hypoxemia. **Why the other options are incorrect:** * **Muscle (A):** In skeletal muscle, hypoxia and the accumulation of metabolic byproducts (like adenosine, $K^+$, and $CO_2$) cause **vasodilation** to meet the increased metabolic demand. * **Liver (C) and Spleen (D):** These systemic organs follow the general rule where hypoxia leads to vasodilation to maintain tissue oxygenation. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** HPV is mediated by the inhibition of oxygen-sensitive $K^+$ channels in pulmonary artery smooth muscle cells, leading to depolarization and $Ca^{2+}$ influx. * **Clinical Correlation:** Chronic hypoxia (e.g., in COPD or at high altitudes) leads to generalized pulmonary vasoconstriction, resulting in **Pulmonary Hypertension** and eventually **Right Heart Failure (Cor Pulmonale)**. * **Fetal Circulation:** In the fetus, the lungs are hypoxic and collapsed, leading to high pulmonary vascular resistance, which shunts blood through the ductus arteriosus.

Q: What is the twitch of a single motor unit called?

Fasciculation. **Explanation:** The correct answer is **Fasciculation**. **1. Why Fasciculation is correct:** A **motor unit** consists of a single alpha motor neuron and all the muscle fibers it innervates. A **fasciculation** is defined as the spontaneous, involuntary contraction of all muscle fibers within a single motor unit. Because an entire motor unit is involved, these twitches are often visible under the skin as brief ripples or flickers, though they are usually insufficient to move a joint. They typically result from pathological irritation of the lower motor neuron (LMN) or its axon. **2. Why the other options are incorrect:** * **Myoclonic jerk:** These are sudden, brief, shock-like involuntary movements caused by muscular contractions (positive myoclonus) or sudden loss of muscle tone (negative myoclonus). Unlike fasciculations, these involve large groups of muscles and result in visible limb movement. * **Tremor:** This is a rhythmic, oscillatory movement produced by alternating or synchronous contractions of antagonist muscles. It is not a single twitch but a repetitive movement. * **Fibrillation:** This is the spontaneous contraction of a **single muscle fiber**. Because only one fiber is contracting, fibrillations are **not visible** to the naked eye and can only be detected via Electromyography (EMG). They occur when a muscle fiber loses its nerve supply (denervation hypersensitivity). **3. High-Yield Clinical Pearls for NEET-PG:** * **Fasciculations vs. Fibrillations:** Fasciculations are visible; Fibrillations are invisible (EMG only). * **LMN Lesions:** Both fasciculations and fibrillations are classic signs of Lower Motor Neuron (LMN) lesions (e.g., Amyotrophic Lateral Sclerosis or Polio). * **Benign Fasciculations:** These can occur in healthy individuals due to fatigue, caffeine, or electrolyte imbalances (e.g., eyelid twitching).

Q: What is the primary use of kinesiomyography?

Monitoring of neuromuscular function. **Explanation:** **Kinesiomyography (KMG)** is a method used for the quantitative monitoring of **neuromuscular function**, particularly during general anesthesia. It operates on the principle of **mechanomyography**, using a piezo-electric sensor (accelerometer) to measure the mechanical movement or displacement of a muscle (usually the adductor pollicis) in response to a nerve stimulus. This allows clinicians to objectively assess the degree of neuromuscular blockade and ensure safe recovery before extubation. **Analysis of Options:** * **Option A (Exercise capacity):** This is typically assessed using Cardiopulmonary Exercise Testing (CPET) or the 6-minute walk test, which measure VO2 max and metabolic parameters, not muscle displacement. * **Option C (Muscle spindle activity):** Muscle spindle activity (proprioception and stretch reflex) is evaluated via Electromyography (EMG) or H-reflex studies, which measure electrical potentials rather than mechanical motion. * **Option D (CSF pressure):** This is monitored via lumbar puncture manometry or intracranial pressure (ICP) transducers. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** While KMG is common in clinical practice, **Acceleromyography (AMG)** is currently the most widely used objective monitor in anesthesia. * **Train-of-Four (TOF) Ratio:** In neuromuscular monitoring, a TOF ratio of **>0.9** is the clinical benchmark required to safely exclude residual paralysis. * **Site of Placement:** The most common site for monitoring is the **Ulnar nerve**, observing the contraction of the **Adductor pollicis** muscle. * **KMG vs. EMG:** EMG measures the *electrical* action potential of the muscle, whereas KMG/AMG measures the *mechanical* response.

Question 1

Activation of G-protein regulates all of the following except?

Accepted Answer

Transcription factor

Answer

Adenyl cyclase activity

Answer

Ion channels

Answer

IP3 & DAG

Question 2

In peripheral tissues, which of the following contains substance P?

Accepted Answer

Nerve terminal

Answer

Plasma cell

Answer

Mast cell

Answer

Vascular endothelium

Question 3

What is the clearance of a drug?

Accepted Answer

The volume of plasma cleared of drug per unit of time.

Answer

The amount of drug excreted in urine.

Answer

The amount of drug metabolized per unit of time.

Answer

All of the above.

Question 4

The transmembrane region of a protein is likely to have which of the following?

Accepted Answer

A stretch of hydrophobic amino acids

Answer

A stretch of hydrophilic amino acids

Answer

A disulphide loop

Answer

Alternating hydrophilic and hydrophobic amino acids

Question 5

All of the following are associated with increased aging, except?

Accepted Answer

Enlargement of telomere

Answer

Decrease in number of mitochondria

Answer

Glycosylation of DNA

Answer

Glycosylation of RNA

Question 6

What is hypertrophy?

Accepted Answer

Increase in cell size

Answer

Increase in cell number

Answer

Decrease in cell number

Answer

Decrease in cell size

Question 7

What does the term "Meileu interior" refer to in physiology?

Accepted Answer

Extracellular fluid (ECF)

Answer

Intracellular fluid (ICF)

Answer

Plasma

Answer

Lymph

Question 8

Hypoxia causes vasoconstriction in which of the following locations?

Accepted Answer

Lungs

Answer

Muscle

Answer

Liver

Answer

Spleen

Question 9

What is the twitch of a single motor unit called?

Accepted Answer

Fasciculation

Answer

Myoclonic jerk

Answer

Tremor

Answer

Fibrillation

Question 10

What is the primary use of kinesiomyography?

Accepted Answer

Monitoring of neuromuscular function

Answer

Monitoring of exercise capacity

Answer

Monitoring of muscle spindle activity

Answer

Monitoring of cerebrospinal fluid pressure changes

General Physiology — MCQs

General Physiology — MCQs

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