Topics:
Animal Physiology, Animal Refresher
Major Site of Electrolyte and Water Reabsorption
About 65% of sodium, potassium, calcium and water reabsorption occurs at:
- PCT (Proximal Convoluted Tubule) — Correct Answer
- Thick limb of loop of Henle
- DCT (Distal Convoluted Tubule)
- Collecting duct
Explanation:
Correct Answer: PCT (Proximal Convoluted Tubule)
The Proximal Convoluted Tubule (PCT) is the workhorse of tubular reabsorption. Approximately 65% of filtered Na⁺, K⁺, Ca²⁺, and water are reabsorbed here, along with virtually all filtered glucose and amino acids.
What Is Reabsorbed at PCT
- ~65% of Na⁺, K⁺, Ca²⁺, Cl⁻, HCO₃⁻
- ~65–70% of water (follows Na⁺ osmotically)
- ~100% of glucose (under normal blood glucose levels)
- ~100% of amino acids
- Most of filtered urate, phosphate, and other organic solutes
Structural Features That Enable High Reabsorption
- Brush border (microvilli): Greatly increases luminal surface area
- Rich in mitochondria to power Na⁺-K⁺-ATPase
- Highly leaky tight junctions allowing paracellular transport
Reabsorption at Other Segments
- Thick ascending limb of loop of Henle: Active reabsorption of Na⁺, K⁺, Cl⁻ (NKCC2 cotransporter) — no water
- DCT: Na⁺-Cl⁻ cotransporter; Ca²⁺ under PTH; fine-tuning
- Collecting duct: Na⁺ under aldosterone; water under ADH
📚 About this Topic — Animal Physiology
This multiple choice question is from Animal Physiology, Animal Refresher. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Animal Physiology to strengthen your preparation.
