Which segment of the nephron is the most common site of reabsorption of filtered glucose and amino acids?

Explanation

## Glucose and Amino Acid Reabsorption **Key Point:** The proximal convoluted tubule (PCT) is the primary and most common site where filtered glucose and amino acids are reabsorbed via active transport mechanisms. ### Mechanism of Reabsorption 1. **Active Transport Process** - Both glucose and amino acids are filtered at the glomerulus - Reabsorption occurs via secondary active transport (symport with Na^+^) - Requires intact mitochondrial function and ATP 2. **Epithelial Features of PCT** - Tall columnar epithelium with abundant mitochondria - Dense brush border (microvilli) increases surface area - Basolateral Na^+^/K^+^-ATPase pumps maintain Na^+^ gradient ### Comparison of Nephron Segments | Segment | Glucose Reabsorption | Amino Acid Reabsorption | Primary Function | | --- | --- | --- | --- | | **Proximal Convoluted Tubule** | **Nearly 100%** | **Nearly 100%** | **Selective reabsorption** | | Loop of Henle | Minimal | Minimal | Countercurrent multiplier | | Distal Convoluted Tubule | Minimal | Minimal | Fine-tuning of reabsorption | | Collecting Duct | None | None | Water & electrolyte balance | **High-Yield:** Under normal conditions, all filtered glucose and amino acids are reabsorbed in the PCT; their presence in urine indicates either glomerular damage (proteinuria) or tubular dysfunction (Fanconi syndrome). **Clinical Pearl:** In diabetes mellitus, when plasma glucose exceeds the renal threshold (~180 mg/dL), the reabsorptive capacity of the PCT is saturated, leading to glucosuria despite normal glomerular filtration. **Mnemonic:** **AAGG** — Amino acids and Glucose are reabsorbed in the **Ascending** (proximal) segment of the tubule.