BP104T • Unit 1Topic 2 of 4⏱ 5 Min Read

2. Membrane Transport: Passive vs. Active Mechanisms

💡 Core Concept & Clinical Context:

Molecules move across the plasma membrane through either passive transport (requiring no metabolic energy, moving down a concentration or electrochemical gradient) or active transport (requiring metabolic ATP hydrolysis, moving solutes uphill against their electrochemical gradient).

Clinical Scenarios & Pharmacopoeial Examples:

1The Primary Active Sodium-Potassium Pump (Na+/K+ ATPase)

Physiological mechanism and clinical cardiac glycoside inhibition.

Step-by-Step Breakdown:

•Mechanism:

•• For every 1 molecule of ATP hydrolyzed to ADP + Pi:

•- 3 Na+ ions are pumped OUT of the intracellular fluid (ICF -> ECF).

•- 2 K+ ions are pumped INTO the intracellular fluid (ECF -> ICF).

•• Electrogenic Effect: Generates a net negative resting membrane potential (-70 mV in neurons, -90 mV in cardiac myocytes).

•Pharmacological Blockade:

•• Digoxin (Cardiac Glycoside) selectively inhibits the Na+/K+ ATPase pump in myocardium -> Intracellular Na+ rises -> Reduces Na+/Ca2+ exchanger activity -> Intracellular Ca2+ accumulates in sarcoplasmic reticulum -> Produces Positive Inotropic Effect (increases cardiac contractile force in heart failure).

📋Key Takeaways & Exam Highlights

Simple Diffusion: Movement of lipophilic solutes directly across the lipid bilayer down concentration gradient (Fick's First Law: $J = -D \frac{dC}{dx}$).
Facilitated Diffusion: Passive carrier- or channel-mediated transport down concentration gradient without ATP (e.g. GLUT-4 glucose transporters).
Primary Active Transport: Solute is pumped against gradient via direct ATP hydrolysis ($Na^+/K^+$ ATPase, $Ca^{2+}$ ATPase, $H^+/K^+$ gastric pump).
Secondary Active Transport: Couples uphill movement of solute to the downhill electrochemical gradient of $Na^+$ (e.g. SGLT-2 sodium-glucose cotransporter in renal tubules).

🇮🇳 हिन्दी व्याख्या (2. Membrane Transport: Passive vs. Active Mechanisms)

पैसिव ट्रांसपोर्ट में कण बिना ऊर्जा खर्च किए अधिक सांद्रता से कम सांद्रता की ओर बहते हैं। एक्टिव ट्रांसपोर्ट (जैसे Na+/K+ पंप) में ATP की ऊर्जा खर्च करके 3 सोडियम बाहर और 2 पोटैशियम अंदर भेजे जाते हैं।