General Physiology Practice Questions

Q: Which of the following is true regarding transport across a cell membrane?

Sodium with glucose symport. **Explanation:** The correct answer is **Sodium with glucose symport (Option C)**. This process is a classic example of **Secondary Active Transport**, specifically **Cotransport (Symport)**. In this mechanism, glucose is transported against its concentration gradient by "hitching a ride" with sodium ions. Sodium moves down its electrochemical gradient (created by the Na⁺-K⁺ ATPase pump), providing the energy required to pull glucose into the cell. This occurs via specific carrier proteins known as **SGLT (Sodium-Glucose Linked Transporters)**. **Analysis of Options:** * **Option A & D:** Chloride and Potassium are not the primary ions coupled with glucose transport in human physiology. Sodium is the unique driving ion because of the steep extracellular-to-intracellular gradient maintained by the cell. * **Option B:** An **Antiport** (Counter-transport) moves substances in opposite directions (e.g., Na⁺-H⁺ exchanger). Glucose and Sodium move in the *same* direction (into the cell), making it a **Symport**. **High-Yield Clinical Pearls for NEET-PG:** 1. **SGLT-1:** Located in the **Small Intestine** (enterocytes) and the late proximal tubule of the kidney. It is responsible for glucose absorption from the gut. 2. **SGLT-2:** Located in the **Early Proximal Convoluted Tubule (PCT)** of the kidney. It reabsorbs ~90% of filtered glucose. 3. **Clinical Correlation:** **SGLT-2 Inhibitors** (e.g., Dapagliflozin) are used in Type 2 Diabetes to induce glucosuria and lower blood sugar. 4. **Oral Rehydration Therapy (ORT):** The efficacy of ORS is based on the SGLT-1 receptor; sodium and glucose are given together to maximize water absorption via osmosis.

Q: Basal metabolic rate (BMR) depends on which of the following factors?

Amount of lean body mass. **Explanation:** The **Basal Metabolic Rate (BMR)** is the minimum amount of energy required to maintain vital functions (like breathing and circulation) at complete physical and mental rest. **Why Lean Body Mass (LBM) is the correct answer:** The primary determinant of BMR is the amount of **metabolically active tissue** in the body. Lean body mass—which includes skeletal muscle, organs (liver, brain, kidneys), and bone—is highly active and consumes significantly more oxygen and energy than fat. Skeletal muscle alone accounts for a large portion of the BMR; therefore, individuals with higher LBM (e.g., athletes or males) have a higher BMR. **Analysis of Incorrect Options:** * **Body Weight:** While BMR generally increases with weight, total weight is a poor predictor because it does not differentiate between fat and muscle. Two people of the same weight can have vastly different BMRs based on their body composition. * **Body Surface Area (BSA):** Historically, BMR was expressed per square meter of BSA (the "Surface Law"). While heat loss is proportional to surface area, BSA is a *proxy* measurement rather than the underlying physiological driver. LBM remains the most accurate biological determinant. * **Adipose Tissue:** Fat is metabolically sluggish. An increase in adipose tissue (obesity) actually leads to a **decrease** in BMR relative to total body weight. **High-Yield Clinical Pearls for NEET-PG:** * **Thyroid Status:** Thyroid hormones ($T_3$ and $T_4$) are the most important hormonal regulators of BMR. * **Specific Dynamic Action (SDA):** Protein has the highest SDA (30%), meaning it increases metabolic rate the most during digestion. * **Gender & Age:** BMR is higher in males (due to more LBM) and decreases with age (due to sarcopenia/loss of muscle). * **Starvation:** BMR decreases during prolonged fasting as a compensatory mechanism to conserve energy.

Q: All of the following intercellular communications occur via extracellular chemical messengers except?

Gap junctions. ### Explanation Intercellular communication is broadly classified into two categories: **Direct communication** (physical contact) and **Indirect communication** (via chemical messengers). **Why Gap Junctions are the correct answer:** Gap junctions are specialized protein complexes (composed of **connexons**) that form direct physical bridges between the cytoplasm of adjacent cells. They allow the passage of ions and small molecules (like cAMP or $Ca^{2+}$) directly from one cell to another without the need for an extracellular chemical messenger. This allows for rapid electrical coupling and synchronized activity. **Analysis of Incorrect Options:** * **Paracrine (A):** Involves the release of chemical messengers into the interstitial fluid to act on neighboring cells (e.g., Histamine). * **Neurohormones (C):** These are chemicals released by neurons directly into the bloodstream to act on distant target cells (e.g., ADH/Oxytocin). * **Autocrine (D):** A cell secretes a chemical messenger that binds to receptors on its own surface, affecting its own function (e.g., Interleukin-1 in T-cells). All three (A, C, and D) rely on **extracellular chemical messengers** (ligands) to transmit signals. **High-Yield Facts for NEET-PG:** * **Connexon Structure:** Each gap junction is made of two connexons; each connexon is composed of **6 connexin** proteins. * **Location:** Gap junctions are vital in **cardiac muscle** (intercalated discs) and **smooth muscle** for functional syncytium. * **Juxtacrine Signaling:** Another form of direct communication where a surface protein on one cell binds to a receptor on an adjacent cell (e.g., Notch signaling). * **Speed:** Gap junctions provide the fastest mode of intercellular signal transmission.

Q: Which of the following statements is true regarding basal metabolic rate?

Decreased by 50% in starvation. ### Explanation **Correct Answer: D. Decreased by 50% in starvation** **Understanding the Concept:** Basal Metabolic Rate (BMR) represents the minimum energy expenditure required to maintain vital functions (like breathing and circulation) at complete physical and mental rest. In states of **prolonged starvation**, the body initiates a survival mechanism to conserve energy. This leads to a significant reduction in BMR—potentially by as much as **50%**. This decrease is primarily mediated by a reduction in muscle mass (atrophy) and a decrease in the levels of circulating thyroid hormones (specifically the conversion of T4 to the more active T3) and catecholamines. **Analysis of Incorrect Options:** * **A. Increased in starvation:** This is incorrect. Starvation is a hypometabolic state. An increase in BMR is seen in conditions like hyperthyroidism, fever, and pregnancy. * **B. It is not influenced by hormonal changes:** This is false. BMR is heavily regulated by hormones. **Thyroid hormones (T3/T4)** are the primary determinants of BMR. Epinephrine, cortisol, and growth hormone also increase BMR. * **C. It is not affected by dietary changes:** This is false. Specific Dynamic Action (SDA) or the thermic effect of food increases metabolic rate after ingestion. Conversely, chronic calorie restriction leads to a compensatory drop in BMR. **High-Yield Clinical Pearls for NEET-PG:** * **Thyroid Status:** The most important factor affecting BMR. BMR increases by 50–100% in hyperthyroidism and decreases by 30–50% in hypothyroidism. * **Surface Area:** BMR is more closely related to surface area than body weight (Rubner’s Law). * **Gender & Age:** BMR is higher in males (due to higher muscle mass/testosterone) and decreases progressively with age. * **Climate:** BMR is higher in individuals living in cold climates to maintain body temperature.

Q: Which is the most potent pain-producing neurotransmitter?

Bradykinin. ### Explanation **Correct Option: C. Bradykinin** Bradykinin is considered the **most potent pain-producing chemical** (algesic agent) known. It is a nonapeptide released during tissue injury and inflammation. It acts by directly stimulating **nociceptors** (pain receptors) and sensitizing them to other stimuli (hyperalgesia). It functions via G-protein coupled receptors (B1 and B2), triggering the release of prostaglandins, which further amplifies the pain signal. **Analysis of Incorrect Options:** * **A. Acetylcholine:** While it can stimulate free nerve endings, it is primarily a neurotransmitter at the neuromuscular junction and in the autonomic nervous system. It is not a primary or potent mediator of clinical pain. * **B. Substance P:** Often confused with the "most potent" agent, Substance P is a neuropeptide released from the central terminals of primary afferent fibers in the spinal cord. Its primary role is **pain transmission** and "neurogenic inflammation" (vasodilation and edema), rather than being the most potent direct stimulator of peripheral nociceptors. * **D. Histamine:** Released from mast cells during inflammation, histamine primarily causes itching (pruritus) and vasodilation. While it can contribute to pain, its potency is significantly lower than that of Bradykinin. **NEET-PG High-Yield Pearls:** * **Triple Response of Lewis:** Mediated by Histamine (Flush, Flare, and Wheal). * **Pain Fibers:** **A-delta** (Fast pain, myelinated, glutamate) vs. **C-fibers** (Slow pain, unmyelinated, Substance P). * **Glutamate:** The major excitatory neurotransmitter for fast pain in the dorsal horn. * **Enkephalins/Endorphins:** Endogenous opioids that inhibit pain by suppressing Substance P release.

Q: Resting membrane potential is mainly due to:

K+. **Explanation:** The **Resting Membrane Potential (RMP)** is primarily determined by the equilibrium potential of the ion to which the cell membrane is most permeable at rest. **Why K+ is the correct answer:** At rest, the cell membrane is significantly more permeable to **Potassium (K+)** than to any other ion (about 50–100 times more permeable than to Na+). This is due to the presence of **non-gated K+ leak channels**, which allow K+ to diffuse out of the cell down its concentration gradient. As K+ leaves, it carries positive charges out, leaving behind immobile anions, thus creating a negative potential inside the cell. The RMP of a typical neuron (-70 mV) or muscle fiber (-90 mV) sits very close to the **Nernst equilibrium potential of K+ (-94 mV)**. **Why other options are incorrect:** * **Na+:** The membrane has very low permeability to Sodium at rest. Na+ influx is primarily responsible for the **depolarization** phase of the action potential, not the RMP. * **Cl-:** While Chloride contributes to the RMP in some cells (like skeletal muscle), its overall influence is secondary to K+ in most excitable tissues. * **Mg++:** Magnesium is an intracellular cation that acts as a cofactor for enzymes (like Na+-K+ ATPase) but does not directly contribute to the generation of the RMP. **High-Yield Facts for NEET-PG:** 1. **Goldman-Hodgkin-Katz (GHK) Equation:** Used to calculate RMP by considering the permeability and concentration gradients of all ions (Na+, K+, and Cl-). 2. **Na+-K+ ATPase Pump:** It is **electrogenic** (pumps 3 Na+ out for 2 K+ in). While it maintains the concentration gradients, it directly contributes only about -5 to -10 mV to the RMP. 3. **Gibbs-Donnan Effect:** Refers to the presence of non-diffusible intracellular proteins that contribute to the negative internal charge.

Q: Which of the following substances moves most rapidly across a cell membrane?

Carbon dioxide. **Explanation:** The movement of substances across a cell membrane is primarily governed by the **lipid solubility** and the **size** of the molecule. The cell membrane is a phospholipid bilayer; therefore, lipid-soluble (hydrophobic) substances can dissolve directly into the membrane and diffuse rapidly via simple diffusion. **1. Why Carbon Dioxide (CO₂) is Correct:** CO₂ is a small, non-polar, and highly **lipid-soluble** gas. According to Fick’s Law of Diffusion, lipid solubility is a major determinant of the diffusion coefficient. CO₂ is approximately 20 times more soluble than Oxygen (O₂), allowing it to pass through the lipid bilayer almost instantaneously without the need for channels or carriers. **2. Why the other options are incorrect:** * **Water (B):** Although water molecules are small, they are highly **polar** (insoluble in lipids). They move through the membrane via specialized channels called **aquaporins**. While this process is fast, it is not as rapid as the direct lipid diffusion of CO₂. * **Glucose (C):** Glucose is a large, polar molecule. It is completely lipid-insoluble and requires **facilitated diffusion** via specific carrier proteins (GLUT transporters), making its transport significantly slower. * **Urea (D):** Urea is a small, polar molecule. While it can permeate the membrane, its lipid solubility is much lower than that of dissolved gases, resulting in a slower rate of diffusion compared to CO₂. **High-Yield NEET-PG Pearls:** * **Permeability Order:** Hydrophobic molecules (O₂, CO₂, N₂, Steroids) > Small uncharged polar molecules (H₂O, Urea) > Large uncharged polar molecules (Glucose) > Ions (Na⁺, K⁺). * **Clinical Correlation:** The high solubility of CO₂ is the reason why, in respiratory failure, CO₂ retention (hypercapnia) often occurs later than hypoxia; CO₂ diffuses across the alveolar-capillary membrane much more efficiently than O₂.

Question 1

Which of the following is true regarding transport across a cell membrane?

Accepted Answer

Sodium with glucose symport

Answer

Chloride with glucose symport

Answer

Sodium with glucose antiport

Answer

Potassium with glucose symport

Question 2

Which of the following is NOT an integral membrane protein?

Accepted Answer

Enzyme receptors

Answer

Na+/K+ ATPase pump

Answer

Insulin receptor

Answer

G-protein coupled receptors

Question 3

Basal metabolic rate (BMR) depends on which of the following factors?

Accepted Answer

Amount of lean body mass

Answer

Body weight

Answer

Body surface area

Answer

Amount of adipose tissue

Question 4

All of the following intercellular communications occur via extracellular chemical messengers except?

Accepted Answer

Gap junctions

Answer

Paracrine

Answer

Neurohormones

Answer

Autocrine

Question 5

Which of the following statements is true regarding basal metabolic rate?

Accepted Answer

Decreased by 50% in starvation

Answer

Increased in starvation

Answer

It is not influenced by hormonal changes

Answer

It is not affected by dietary changes

Question 6

Total body water differences between males and females are not observed at which age range?

Accepted Answer

18-25 years

Answer

Above 60 years

Answer

40-60 years

Answer

10-18 years

Question 7

Which is the most potent pain-producing neurotransmitter?

Accepted Answer

Bradykinin

Answer

Acetylcholine

Answer

Substance P

Answer

Histamine

Question 8

Resting membrane potential is mainly due to:

Accepted Answer

K+

Answer

Na+

Answer

Cl-

Answer

Mg++

Question 9

What is the effect on the resting membrane potential when the extracellular concentration of potassium is decreased?

Accepted Answer

Increased negativity of the RMP

Answer

Increased magnitude of RMP

Answer

Decreased magnitude of RMP

Answer

Decreased negativity of the RMP

Question 10

Which of the following substances moves most rapidly across a cell membrane?

Accepted Answer

Carbon dioxide

Answer

Water

Answer

Glucose

Answer

Urea

General Physiology — MCQs

General Physiology — MCQs

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