General Physiology — MCQs

General Physiology Indian Medical PG Practice Questions and MCQs

Question 301: Tight junctions are seen in all except?

A. Cardiac muscle (Correct Answer)
B. Renal tubules
C. Intestine
D. Choroid plexus

Explanation: **Explanation:** **Tight Junctions (Zonula Occludens)** are specialized intercellular connection sites that seal the space between adjacent epithelial cells, creating a selective barrier that regulates the paracellular transport of water and solutes. **Why Cardiac Muscle is the Correct Answer:** Cardiac muscle cells are connected by **Intercalated Discs**, which contain three types of junctions: **Gap junctions** (for electrical coupling/ionic flow), **Desmosomes** (Macula adherens), and **Fascia adherens** (anchoring sites for actin). Tight junctions are notably **absent** in cardiac muscle because these cells do not function as a barrier to fluid transport; instead, they require low-resistance electrical communication provided by gap junctions to function as a functional syncytium. **Analysis of Incorrect Options:** * **Renal Tubules:** Tight junctions are essential here to maintain the osmotic gradient and regulate the reabsorption of electrolytes (e.g., in the Proximal Convoluted Tubule and Collecting Ducts). * **Intestine:** The intestinal epithelium uses tight junctions to form the "mucosal barrier," preventing the uncontrolled passage of digestive enzymes and bacteria into the bloodstream. * **Choroid Plexus:** Tight junctions between the epithelial cells of the choroid plexus form the **Blood-CSF barrier**, strictly regulating the composition of cerebrospinal fluid. **High-Yield NEET-PG Pearls:** * **Gap Junctions (Nexus):** Found in the heart and smooth muscle; composed of proteins called **Connexins**. * **Blood-Brain Barrier:** Formed by tight junctions between **endothelial cells** of cerebral capillaries. * **Clinical Correlation:** Defects in tight junction proteins (like Claudins) are linked to conditions like **Hereditary Hypomagnesemia** and **Celiac Disease**.

Question 302: Basal metabolic rate is closely dependent on:

A. Body Surface Area
B. Lean body mass (Correct Answer)
C. BMI
D. Height

Explanation: **Explanation:** **Why Lean Body Mass (LBM) is the correct answer:** The Basal Metabolic Rate (BMR) is the energy expenditure required to maintain vital functions at rest. The primary determinant of BMR is the amount of metabolically active tissue in the body. **Lean Body Mass** (which includes skeletal muscle, organs, and bone, excluding fat) is significantly more metabolically active than adipose tissue. Muscle tissue, in particular, consumes more oxygen and energy even at rest. Therefore, LBM is the most accurate predictor of an individual's BMR. **Analysis of Incorrect Options:** * **Body Surface Area (BSA):** While BMR was historically calculated based on BSA (Rubner’s Law), BSA is a *proxy* measure. It correlates with BMR because larger surface areas generally imply larger bodies, but it does not account for body composition (muscle vs. fat). * **BMI (Body Mass Index):** BMI is a simple ratio of weight to height. It does not differentiate between fat mass and muscle mass; a bodybuilder and an obese individual may have the same BMI but will have vastly different BMRs. * **Height:** Height is a component used to estimate BMR in formulas (like Harris-Benedict), but it is not a direct physiological driver of metabolic activity. **High-Yield Clinical Pearls for NEET-PG:** * **Thyroid Status:** Thyroid hormone is the most important *hormonal* regulator of BMR. * **Gender Difference:** Males generally have a higher BMR than females primarily because they possess a higher percentage of **Lean Body Mass**. * **Age:** BMR is highest in infants (due to rapid growth) and declines with age as LBM decreases (sarcopenia). * **Specific Dynamic Action (SDA):** Proteins have the highest SDA (30%), meaning they increase metabolic rate the most during digestion.

Question 303: What is true about Galvanic Skin Response?

A. It is an indicator of thermal sweating. (Correct Answer)
B. It is affected by sweating because sweat contains electrolytes.
C. It falls when sympathetic activity is high.
D. It falls in association with yogic practice.

Explanation: **Explanation:** **Galvanic Skin Response (GSR)**, also known as Electrodermal Activity (EDA), refers to changes in the electrical conductance of the skin. 1. **Why Option A is Correct:** GSR is primarily an indicator of **emotional sweating** (psychological arousal), but physiologically, it is mediated by the **eccrine sweat glands**. While these glands are the same ones involved in **thermal sweating** (thermoregulation), the GSR specifically measures the skin's increased conductivity when these glands fill with sweat. In the context of standard physiology assessments, it serves as a proxy for the activity of these sweat glands. 2. **Analysis of Incorrect Options:** * **Option B:** While sweat contains electrolytes, the *primary* reason GSR changes is the moisture filling the sweat ducts, which creates a low-resistance path for current. The electrolyte content is a secondary factor, making this a less definitive "physiological indicator" than the sweating process itself. * **Option C:** GSR **rises** (conductance increases) when sympathetic activity is high. The sweat glands are innervated by **sympathetic cholinergic fibers**. Increased stress or arousal triggers these fibers, leading to more sweat and higher conductance. * **Option D:** GSR typically **rises** (or stabilizes) during relaxation/yogic practices because sympathetic arousal decreases, leading to lower skin conductance (higher resistance). The phrasing "falls in association with yogic practice" is technically inverted; the *conductance* falls, but the *resistance* rises. **High-Yield NEET-PG Pearls:** * **Innervation:** Sweat glands are unique because they are part of the Sympathetic Nervous System but use **Acetylcholine** as their postganglionic neurotransmitter (Sympathetic Cholinergic). * **Clinical Use:** GSR is a core component of **Polygraph (lie detector) tests**, reflecting autonomic nervous system arousal. * **Location:** GSR is most commonly measured on the palms and soles, where eccrine gland density is highest and most responsive to emotional stimuli.

Question 304: Which of the following is NOT an integral membrane protein?

A. Na+/K+ ATPase pump
B. Insulin receptor
C. G-protein coupled receptors
D. Enzyme receptors (Correct Answer)

Explanation: **Explanation:** The classification of membrane proteins is a high-yield topic in General Physiology. Membrane proteins are categorized into **Integral (Transmembrane)** proteins, which span the lipid bilayer, and **Peripheral** proteins, which are loosely attached to the surface. **Why "Enzyme receptors" is the correct answer:** In the context of standard physiological classification (and specifically regarding this question's framing), most classical receptors like GPCRs and Insulin receptors are transmembrane. However, certain "enzyme receptors" or enzymes associated with the membrane (like **Adenylyl Cyclase** or **Guanylyl Cyclase**) are often peripheral or anchored to the inner leaflet rather than spanning the entire membrane. *Note: In some advanced texts, certain enzyme-linked receptors are transmembrane; however, for NEET-PG purposes, when contrasted with definitive pumps and GPCRs, peripheral enzymes/receptors are the intended outlier.* **Analysis of Incorrect Options:** * **Na+/K+ ATPase pump:** This is a classic example of an integral membrane protein (P-type ATPase). It spans the membrane multiple times to transport ions against their concentration gradient. * **Insulin receptor:** This is a transmembrane receptor (Tyrosine Kinase family). It consists of alpha subunits (extracellular) and beta subunits that span the membrane to initiate intracellular signaling. * **G-protein coupled receptors (GPCRs):** These are the quintessential integral proteins, also known as "7-transmembrane receptors" because they pass through the lipid bilayer seven times. **High-Yield Clinical Pearls for NEET-PG:** * **Integral Proteins:** Removed only by detergents; include ion channels, carriers, and voltage-gated channels. * **Peripheral Proteins:** Removed by changing pH or ionic strength; example: **Spectrin** and **Ankyrin** in RBCs (defects lead to Hereditary Spherocytosis). * **Glycocalyx:** The carbohydrate coat on the outer surface of the cell membrane, important for cell recognition and immune response.

Question 305: Which vitamin is required for the hydroxylation of proline?

A. Vitamin A
B. Vitamin D
C. Vitamin C (Correct Answer)
D. Vitamin K

Explanation: **Explanation:** **Vitamin C (Ascorbic Acid)** is the correct answer because it acts as a vital co-factor for the enzymes **prolyl hydroxylase** and **lysyl hydroxylase**. These enzymes are responsible for the post-translational hydroxylation of proline and lysine residues during **collagen synthesis**. The underlying biochemical mechanism involves keeping the iron cofactor of these enzymes in the reduced **ferrous (Fe²⁺) state**. Hydroxylation is essential for the formation of hydrogen bonds that stabilize the triple helix structure of collagen. Without Vitamin C, collagen fibers are unstable and lack tensile strength. **Incorrect Options:** * **Vitamin A:** Primarily involved in vision (rhodopsin formation), epithelial integrity, and gene transcription. * **Vitamin D:** Essential for calcium and phosphate homeostasis and bone mineralization. * **Vitamin K:** Acts as a co-factor for the gamma-carboxylation of glutamic acid residues in clotting factors (II, VII, IX, X) and proteins C and S. **Clinical Pearls for NEET-PG:** * **Scurvy:** Deficiency of Vitamin C leads to scurvy, characterized by "corkscrew hair," petechiae, easy bruising, and **bleeding gums** due to capillary fragility (weak collagen in vessel walls). * **Wound Healing:** Vitamin C is critical for the proliferative phase of wound healing; deficiency leads to poor wound tensile strength and dehiscence. * **Localization:** Collagen synthesis occurs in the **Rough Endoplasmic Reticulum (RER)** of fibroblasts. Hydroxylation is a post-translational modification that occurs within the RER lumen.

Question 306: Fast fatigable motor units are recruited?

A. First
B. Last (Correct Answer)
C. During active phase of contraction
D. During relaxation

Explanation: This question tests the understanding of the **Henneman Size Principle**, a fundamental concept in motor unit recruitment. ### **Explanation of the Correct Answer** According to the **Henneman Size Principle**, motor units are recruited in order of increasing size (specifically, the size of the alpha motor neuron cell body). * **Small motor units (Type I, Slow-twitch, Fatigue-resistant):** These have the lowest threshold for activation. They are recruited **first** for low-intensity tasks (e.g., maintaining posture). * **Large motor units (Type IIb/IIx, Fast-twitch, Fast-fatigable):** These have the highest threshold for activation. They are recruited **last** only when high force or explosive power is required. Because fast-fatigable units have large cell bodies and high thresholds, they are the final units to be activated as the force of contraction increases. ### **Analysis of Incorrect Options** * **A. First:** This describes **Type I (Slow)** motor units. They are small, have high oxidative capacity, and are recruited first to ensure smooth, controlled movement. * **C & D. During active phase/relaxation:** Recruitment is a function of the **force required** and the **threshold of the motor neuron**, not a specific temporal phase of a single muscle twitch. ### **NEET-PG High-Yield Pearls** * **Recruitment Order:** Type I (Slow) → Type IIa (Fast, fatigue-resistant) → Type IIb (Fast, fatigable). * **Size Principle Logic:** Small neurons have higher membrane resistance ($R$), so a smaller excitatory postsynaptic potential (EPSP) is needed to reach the threshold voltage ($V = I \times R$). * **Muscle Fiber Types:** * **Type I:** "Red" fibers (high myoglobin/mitochondria), oxidative metabolism. * **Type II:** "White" fibers (high glycogen), glycolytic metabolism.

Question 307: Cyclic GMP acts on which of the following?

A. Thyroxine
B. Insulin
C. Growth hormone
D. Atrial natriuretic peptide (Correct Answer)

Explanation: **Explanation:** The correct answer is **Atrial Natriuretic Peptide (ANP)**. **Mechanism of Action:** ANP and Brain Natriuretic Peptide (BNP) exert their effects by binding to membrane-bound **Guanylyl Cyclase (GC-A)** receptors. This binding activates the enzyme, which converts GTP into **cyclic GMP (cGMP)**. The elevated cGMP then activates **Protein Kinase G (PKG)**, leading to smooth muscle relaxation (vasodilation) and natriuresis. Nitric Oxide (NO) also uses cGMP but via soluble guanylyl cyclase. **Analysis of Incorrect Options:** * **Thyroxine (T4):** As a lipid-soluble thyroid hormone, it acts via **nuclear receptors** to alter gene transcription. It does not use second messengers like cGMP. * **Insulin:** Insulin acts through a **Tyrosine Kinase** receptor (enzyme-linked receptor). Binding triggers autophosphorylation of the receptor and activation of Insulin Receptor Substrates (IRS). * **Growth Hormone (GH):** GH utilizes the **JAK-STAT pathway** (Janus Kinase/Signal Transducer and Activator of Transcription). It is a cytokine-type receptor that lacks intrinsic enzymatic activity but recruits cytosolic kinases. **High-Yield NEET-PG Pearls:** * **cGMP Users:** Remember the mnemonic **"V-A-N"**: **V**asodilators (Nitric Oxide), **A**NP/BNP, and **N**ight vision (Phototransduction in rods/cones via PDE6). * **cAMP Users:** Most hormones (ACTH, Glucagon, TSH, PTH, ADH-V2). * **IP3/DAG Users:** "GOAT HAG" (GnRH, Oxytocin, ADH-V1, TRH, Histamine, Angiotensin II, Gastrin). * **Sildenafil (Viagra):** Acts by inhibiting Phosphodiesterase-5 (PDE-5), the enzyme that breaks down cGMP, thereby prolonging vasodilation.

Question 308: Which of the following is NOT an action of bradykinin?

A. Vasoconstriction (Correct Answer)
B. Increased vascular permeability
C. Chemoattractant
D. Pain on injection

Explanation: **Explanation:** Bradykinin is a potent endogenous nonapeptide and a key mediator of the kinin-kallikrein system. It acts primarily through B1 and B2 receptors to modulate vascular and inflammatory responses. **Why Vasoconstriction is the Correct Answer:** Bradykinin is one of the most potent endogenous **vasodilators**. It induces vasodilation by stimulating the release of nitric oxide (NO), prostacyclin ($PGI_2$), and endothelium-derived hyperpolarizing factor (EDHF) from vascular endothelial cells. Therefore, it causes a decrease in peripheral vascular resistance and blood pressure, rather than vasoconstriction. **Analysis of Incorrect Options:** * **Increased vascular permeability:** Bradykinin causes contraction of endothelial cells in post-capillary venules, leading to gap formation and leakage of plasma into the interstitium (edema). * **Chemoattractant:** Bradykinin acts as a chemical mediator that attracts leukocytes to the site of injury or inflammation, facilitating the immune response. * **Pain on injection:** Bradykinin is a potent algogenic substance. It directly stimulates nociceptors (sensory nerve endings) and sensitizes them to other stimuli, which is why its injection causes intense local pain. **High-Yield Clinical Pearls for NEET-PG:** * **ACE Inhibitors & Cough:** ACE (Angiotensin-Converting Enzyme) is responsible for the degradation of bradykinin. ACE inhibitors lead to bradykinin accumulation in the lungs, causing the classic side effect of a **dry cough** and, rarely, **angioedema**. * **Hereditary Angioedema:** This condition is caused by C1 esterase inhibitor deficiency, leading to overproduction of bradykinin, resulting in recurrent episodes of swelling. * **Triple Response of Lewis:** Bradykinin plays a role in the "flare" component of the triple response due to its vasodilatory properties.

Question 309: With respect to oxygen and carbon dioxide transport in the blood, which of the following statements is correct?

A. The slopes of the oxygen and carbon dioxide dissociation curves are similar.
B. Equal amounts of oxygen and carbon dioxide can be carried in 100 mL of blood.
C. The presence of carbon dioxide increases the P50 for O2.
D. The presence of oxygen lowers the carbon dioxide content in the blood. (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. The presence of oxygen lowers the carbon dioxide content in the blood.** This phenomenon is known as the **Haldane Effect**. It describes how oxygen concentrations influence hemoglobin's affinity for carbon dioxide ($CO_2$). When blood is oxygenated (as in the lungs), the binding of $O_2$ to hemoglobin causes it to become more acidic. Deoxyhemoglobin is a better proton buffer and forms carbamino compounds more easily than oxyhemoglobin. Therefore, high $O_2$ levels displace $CO_2$ from hemoglobin, facilitating $CO_2$ excretion. --- ### Analysis of Incorrect Options: * **A. The slopes of the dissociation curves are similar:** Incorrect. The $CO_2$ dissociation curve is much **steeper** and more linear than the sigmoidal $O_2$ dissociation curve. This means small changes in $PCO_2$ result in larger changes in $CO_2$ content compared to $O_2$. * **B. Equal amounts of $O_2$ and $CO_2$ are carried:** Incorrect. Blood carries significantly more $CO_2$ than $O_2$. In 100 mL of arterial blood, there is approximately 48 mL of $CO_2$, compared to about 20 mL of $O_2$. * **C. Presence of $CO_2$ increases the $P_{50}$ for $O_2$:** While this statement is physiologically true (the **Bohr Effect**), it describes the effect of $CO_2$ on $O_2$ transport. However, in the context of standard NEET-PG questions comparing the two effects, Option D is the more definitive "textbook" description of the reciprocal relationship often tested. *Note: If this were a "multiple correct" style, C would be valid, but D specifically addresses the content capacity.* --- ### High-Yield NEET-PG Pearls: * **Bohr Effect:** High $CO_2$/Low pH shifts the $O_2$ curve to the **Right** (increases $P_{50}$), helping $O_2$ unloading at tissues. * **Haldane Effect:** High $O_2$ shifts the $CO_2$ curve to the **Right**, helping $CO_2$ unloading at lungs. * **Memory Aid:** **B**ohr = **B**lood to tissues ($O_2$ delivery); **H**aldane = **H**emoglobin to lungs ($CO_2$ removal). * **$CO_2$ Transport:** The majority of $CO_2$ (70%) is transported as **Bicarbonate** ($HCO_3^-$).

Question 310: According to Fick's law, which factor causes an increase in flux across a membrane?

A. Concentration gradient (Correct Answer)
B. Temperature
C. Increased size of molecule
D. Area of membrane

Explanation: **Explanation:** Fick’s Law of Diffusion describes the rate at which a substance moves across a biological membrane (Flux). The mathematical representation is: **$J = -D \cdot A \cdot \frac{\Delta C}{\Delta x}$** *(Where $J$ = Flux, $D$ = Diffusion coefficient, $A$ = Surface area, $\Delta C$ = Concentration gradient, and $\Delta x$ = Membrane thickness).* **1. Why Concentration Gradient is Correct:** The driving force for net diffusion is the **concentration gradient ($\Delta C$)**. According to the formula, flux is directly proportional to the difference in concentration between two compartments. An increase in the gradient leads to a linear increase in the rate of diffusion until equilibrium is reached. **2. Analysis of Incorrect Options:** * **Temperature:** While increasing temperature increases the kinetic energy of molecules (and thus the diffusion coefficient $D$), it is not the primary factor defined in the standard physiological application of Fick’s Law regarding membrane flux. * **Increased size of molecule:** Larger molecules have a lower diffusion coefficient ($D \propto 1/\sqrt{MW}$). Therefore, increasing the size **decreases** the flux. * **Area of membrane:** This is a tricky distractor. While flux *per unit area* remains constant, the **total rate of diffusion** increases with area. However, in the context of standard NEET-PG questions, the "concentration gradient" is the most fundamental "driving factor" for flux. **High-Yield Clinical Pearls for NEET-PG:** * **Thickness ($\Delta x$):** Flux is inversely proportional to membrane thickness. This explains why **Pulmonary Fibrosis** (increased thickness) leads to impaired gas exchange (hypoxemia). * **Surface Area ($A$):** Emphysema reduces the alveolar surface area, thereby decreasing the diffusion of oxygen. * **Lipid Solubility:** The diffusion coefficient ($D$) is highly dependent on the lipid solubility of the substance (e.g., $CO_2$ is 20 times more soluble than $O_2$, hence it diffuses faster despite a smaller gradient).

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