General Physiology Practice Questions

Q: Na+-K+ ATPase is which type of pump?

Electrogenic. ### Explanation The **Na⁺-K⁺ ATPase** (Sodium-Potassium Pump) is a primary active transporter found in the plasma membrane of almost all animal cells. **Why "Electrogenic" is the Correct Answer:** The pump moves **3 Na⁺ ions out** of the cell and **2 K⁺ ions into** the cell for every molecule of ATP hydrolyzed. Because there is an unequal exchange of cations (3 positive charges out vs. 2 positive charges in), it creates a net deficit of positive charge inside the cell. This directly contributes to the negativity of the **Resting Membrane Potential (RMP)**, typically contributing about -5 to -10 mV. Any pump that creates a net charge imbalance across the membrane is termed **electrogenic**. **Analysis of Incorrect Options:** * **A. Secondary active:** The Na⁺-K⁺ ATPase is a **Primary Active Transporter** because it derives energy directly from the hydrolysis of ATP (it is a P-type ATPase). Secondary active transport (like SGLT) relies on the gradient created by primary active transport. * **C. Symport:** This pump is an **Antiport** (counter-transport) mechanism because it moves the two ions in opposite directions across the cell membrane. * **D. All of the above:** Incorrect, as options A and C are physiologically inaccurate descriptions of this specific pump. **High-Yield Clinical Pearls for NEET-PG:** * **Inhibitor:** The pump is specifically inhibited by **Cardiac Glycosides** (e.g., Digoxin and Ouabain), which bind to the extracellular side of the alpha subunit. * **Structure:** It is a heteromer composed of an **alpha subunit** (catalytic, contains binding sites for Na⁺, K⁺, and ATP) and a **beta subunit** (essential for membrane trafficking). * **Functions:** It maintains cell volume, provides the driving force for secondary active transport, and is crucial for maintaining the steep Na⁺ and K⁺ gradients necessary for excitable tissues.

Q: Which of the following is NOT a major calcium-binding protein?

Actinin. **Explanation:** The correct answer is **Actinin (Option C)**. **Why Actinin is the correct answer:** Actinin (specifically $\alpha$-actinin) is a **structural protein**, not a calcium-binding protein. Its primary role is to anchor actin filaments to the Z-discs in skeletal muscle and to dense bodies in smooth muscle. It belongs to the spectrin superfamily and functions as a cross-linking protein to maintain the architectural integrity of the sarcomere. **Analysis of Incorrect Options:** * **Troponin (Option A):** Specifically, **Troponin C** is a major calcium-binding protein in striated muscle. Upon binding $Ca^{2+}$, it undergoes a conformational change that moves tropomyosin away from the myosin-binding sites on actin, initiating contraction. * **Calmodulin (Option B):** This is the most ubiquitous calcium-binding messenger protein. It mediates various cellular processes (like activating Myosin Light Chain Kinase in smooth muscle) by forming a $Ca^{2+}$-calmodulin complex. * **Calcineurin (Option D):** Also known as Protein Phosphatase 2B, it is a calcium and calmodulin-dependent serine/threonine protein phosphatase. It plays a critical role in T-cell activation and cardiac hypertrophy. **High-Yield Clinical Pearls for NEET-PG:** * **Calsequestrin:** The major $Ca^{2+}$-binding protein located inside the **Sarcoplasmic Reticulum** (SR) that allows for high-capacity $Ca^{2+}$ storage. * **Calbindin:** A vitamin D-dependent calcium-binding protein found in the intestines and kidneys that facilitates $Ca^{2+}$ absorption/reabsorption. * **Clinical Correlation:** Calcineurin inhibitors (e.g., **Cyclosporine, Tacrolimus**) are potent immunosuppressants used to prevent organ transplant rejection.

Q: What is the term for the transport of sodium and potassium in opposite directions?

Antiport. **Explanation:** The correct answer is **Antiport** (also known as counter-transport). This is a type of secondary active transport (or mediated transport) where two different molecules or ions are moved across a cell membrane in **opposite directions** simultaneously. In the context of sodium and potassium, an example is the Na⁺-H⁺ exchanger or specific Na⁺-K⁺ exchangers found in certain tissues, where one ion moves down its electrochemical gradient to provide the energy for the other to move against its gradient. **Analysis of Options:** * **A. Symport:** Also known as co-transport, this involves the movement of two substances in the **same direction** (e.g., SGLT-1 moving Sodium and Glucose together into the intestinal cell). * **B. Na-K ATPase:** While this pump does move Na⁺ and K⁺ in opposite directions (3 Na⁺ out, 2 K⁺ in), it is a specific **primary active transport mechanism** (a protein pump), not the general term for the directional classification of transport. * **C. Neutral transport:** This is a non-specific term. In physiology, it usually refers to the movement of uncharged molecules or a transport process that does not result in a net change in charge across the membrane (electroneutral). **High-Yield Clinical Pearls for NEET-PG:** * **Primary vs. Secondary:** Na-K ATPase is **Primary** active transport (uses ATP directly). Antiport/Symport are usually **Secondary** active transport (use the gradient created by primary transport). * **Electrogenicity:** The Na-K ATPase is **electrogenic** because it pumps 3 positive charges out for every 2 it brings in, contributing to the resting membrane potential. * **Inhibitor:** Digitalis (Digoxin) inhibits the Na-K ATPase, leading to increased intracellular Na⁺, which subsequently slows the Na⁺-Ca²⁺ exchanger (an antiport), increasing intracellular Calcium and cardiac contractility.

Q: What is the approximate osmolarity of human plasma?

290 mOsm/L. **Explanation:** The osmolarity of human plasma is a measure of the concentration of osmotically active particles in a liter of solution. In a healthy adult, the normal range for plasma osmolarity is approximately **280 to 295 mOsm/L**, making **290 mOsm/L** the most accurate representative value among the choices. **Why the correct answer is right:** Plasma osmolarity is primarily determined by electrolytes, specifically **Sodium (Na⁺)** and its associated anions (Chloride and Bicarbonate), which account for nearly 90% of the total osmotic pressure. Glucose and Urea contribute the remaining fraction. The body tightly regulates this value via the hypothalamus-pituitary-adrenal axis (ADH secretion) and the thirst mechanism to maintain cellular volume and homeostasis. **Why the incorrect options are wrong:** * **A (190 mOsm/L):** This value represents extreme hypotonicity. Such low osmolarity would cause massive water shift into cells (cerebral edema), leading to seizures or death. * **C & D (390 & 490 mOsm/L):** These values represent severe hypertonicity. High osmolarity (seen in conditions like Hyperosmolar Hyperglycemic State or severe dehydration) causes cellular shrinkage and neurological dysfunction. **High-Yield NEET-PG Pearls:** 1. **Calculated Osmolarity Formula:** $2 \times [Na^+] + \frac{[Glucose]}{18} + \frac{[BUN]}{2.8}$. 2. **Osmolar Gap:** The difference between measured and calculated osmolarity. A gap **>10 mOsm/L** suggests the presence of unmeasured osmoles (e.g., Ethanol, Methanol, Ethylene glycol). 3. **Osmolality vs. Osmolarity:** While often used interchangeably in clinical practice, *Osmolality* (mOsm/kg) is more accurate as it is independent of temperature and pressure. Normal plasma osmolality is similarly ~285–295 mOsm/kg.

Q: The Lewis Triple Response is mediated by which of the following?

Histamine. **Explanation:** The **Lewis Triple Response** is a characteristic cutaneous reaction that occurs following firm stroking of the skin or intradermal injection of certain substances. It is primarily mediated by the release of **Histamine** from mast cells. **1. Why Histamine is the Correct Answer:** Histamine is the central chemical mediator of this response. When the skin is injured, mast cells degranulate, releasing histamine which acts on H1 receptors to produce three distinct stages: * **Red Reaction (Flush):** Localized capillary dilatation (occurs within seconds). * **Flare:** A spreading redness beyond the site of injury caused by arteriolar dilatation. This is mediated by the **axon reflex**, but histamine is the trigger that initiates this neural pathway. * **Wheal:** Localized edema due to increased capillary permeability (exudation of fluid). **2. Analysis of Incorrect Options:** * **Option B (Axon Reflex):** While the "Flare" component is specifically mediated by the axon reflex (antidromic conduction), the axon reflex itself is a *mechanism* triggered by histamine. Histamine is the primary *mediator* for the entire triple response. * **Option C (Injury to endothelium):** While endothelial changes occur (contraction of endothelial cells leading to gaps), the response is a physiological reaction to chemical mediators rather than a direct mechanical injury to the endothelium itself. **High-Yield Clinical Pearls for NEET-PG:** * **Dermatographism:** An exaggerated triple response where even light pressure causes a wheal; it is a form of physical urticaria. * **Antidromic Conduction:** The flare is unique because the impulse travels "backwards" along sensory nerve fibers without involving the spinal cord. * **Substance P:** This neuropeptide is often released alongside histamine during the axon reflex to further promote vasodilation.

Q: What is the daily insensible water loss through the respiratory tract?

350 ml. **Explanation:** Insensible water loss refers to the continuous, unavoidable loss of water that occurs without the individual's awareness, primarily through the skin (diffusion) and the respiratory tract (evaporation). **1. Why 350 ml is correct:** In a healthy adult under normal conditions, the total daily insensible water loss is approximately **700 ml**. This is divided almost equally between the skin and the lungs. As air enters the respiratory tract, it is humidified to a vapor pressure of about 47 mmHg before reaching the alveoli. This process of humidification results in a daily loss of approximately **300–400 ml** (average **350 ml**) of water through exhalation. **2. Analysis of Incorrect Options:** * **A (100 ml):** This value is too low for respiratory loss. However, 100 ml is the typical daily volume of water lost in **feces** under normal conditions. * **B (200 ml):** This is an underestimate for respiratory loss but may represent sweat loss in a sedentary individual in a temperate climate. * **D (700 ml):** This represents the **total** daily insensible water loss (Skin + Lungs). The question specifically asks for the respiratory component only. **High-Yield Clinical Pearls for NEET-PG:** * **Effect of Temperature:** In cold weather, atmospheric vapor pressure decreases to nearly zero, increasing the gradient for evaporation; this explains the "foggy breath" and increased respiratory water loss in winter. * **Clinical Significance:** Insensible loss is **solute-free water**. In patients with extensive burns, the "insensible" loss through the skin can increase from 350 ml to 3–5 Liters/day due to the loss of the cornified layer. * **Fever:** For every 1°C rise in body temperature, insensible water loss increases by approximately 10–15%.

Q: Along with acetylcholine, what is released from sweat gland secretions?

Vasoactive intestinal peptide. **Explanation:** The correct answer is **Vasoactive intestinal peptide (VIP)**. **1. Why VIP is correct:** Sweat glands are unique in the autonomic nervous system. While they are anatomically part of the **sympathetic nervous system**, their postganglionic fibers are **cholinergic** (releasing Acetylcholine). In these specific fibers, **Vasoactive Intestinal Peptide (VIP)** is co-released with Acetylcholine (ACh). * **Mechanism:** ACh acts on muscarinic receptors to stimulate sweat secretion. VIP acts as a potent vasodilator, increasing local blood flow to the sweat glands, which provides the necessary fluid for sweat production and aids in thermoregulation by facilitating heat loss. **2. Why other options are incorrect:** * **A. Neuropeptide Y (NPY):** This is typically co-released with **Norepinephrine** in sympathetic adrenergic neurons. It acts as a vasoconstrictor, the opposite of what is required for active sweating. * **B. Enkephalin:** These are endogenous opioids primarily involved in pain modulation and are found in the adrenal medulla and CNS, not typically associated with sweat gland innervation. * **C. Substance P:** While involved in neurogenic inflammation and pain transmission, it is not the primary co-transmitter for thermoregulatory sweat glands. **Clinical Pearls & High-Yield Facts:** * **Exception to the Rule:** Most sympathetic postganglionic neurons release Norepinephrine; sweat glands (and some blood vessels in skeletal muscle) are the major exceptions, releasing ACh. * **Cotransmission:** This concept describes a single nerve terminal releasing multiple transmitters. In the ANS, the ACh-VIP pair is the classic example for parasympathetic-like sympathetic fibers. * **Clinical Correlation:** In **Lambert-Eaton Syndrome** or **Botulism**, ACh release is impaired, leading to anhidrosis (lack of sweating) alongside muscle weakness.

Question 1

Na+-K+ ATPase is which type of pump?

Accepted Answer

Electrogenic

Answer

Secondary active

Answer

Symport

Answer

All of the above

Question 2

Which of the following is NOT a major calcium-binding protein?

Accepted Answer

Actinin

Answer

Troponin

Answer

Calmodulin

Answer

Calcineurin

Question 3

Saltatory conduction in myelinated axons results from the fact that:

Accepted Answer

Voltage-gated sodium channels are concentrated at the nodes of Ranvier

Answer

Salt concentration is increased beneath the myelin segments

Answer

Non-gated ion channels are present beneath the segments of myelin

Answer

Membrane resistance is decreased beneath the segments of myelin

Question 4

What is the term for the transport of sodium and potassium in opposite directions?

Accepted Answer

Antiport

Answer

Symport

Answer

Na-K ATPase

Answer

Neutral transport

Question 5

What is the approximate osmolarity of human plasma?

Accepted Answer

290 mOsm/L

Answer

190 mOsm/L

Answer

390 mOsm/L

Answer

490 mOsm/L

Question 6

The Lewis Triple Response is mediated by which of the following?

Accepted Answer

Histamine

Answer

Axon reflex

Answer

Injury to endothelium

Answer

None of the above

Question 7

What is the daily insensible water loss through the respiratory tract?

Accepted Answer

350 ml

Answer

100 ml

Answer

200 ml

Answer

700 ml

Question 8

Along with acetylcholine, what is released from sweat gland secretions?

Accepted Answer

Vasoactive intestinal peptide

Answer

Neuro peptide Y

Answer

Enkephalin

Answer

Substance P

Question 9

Synaptic conduction is mostly orthodromic because?

Accepted Answer

Chemical mediators are located only in the presynaptic terminal.

Answer

Dendrites cannot be depolarized.

Answer

Once repolarized, an area cannot be depolarized.

Answer

The strength of the antidromic impulse is less.

Question 10

Most peptide and protein hormones are synthesized as what?

Accepted Answer

A preprohormone

Answer

A secretagogue

Answer

A pleiotropic hormone

Answer

Proopiomelanocortin (POMC)

General Physiology — MCQs

General Physiology — MCQs

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