Nephrons: Location and Function in the Kidney

Location

• Renal cortex: Glomeruli, proximal and distal convoluted tubules, cortical collecting ducts
• Renal medulla: Loops of Henle, vasa recta, medullary collecting ducts (pyramids)
• Each kidney contains ~1–1.5 million nephrons

Structure and Function

Segment	Key Functions
Glomerulus	Filtration (GFR ~120 mL/min)
Proximal tubule	Reabsorbs 65% Na⁺, H₂O, glucose, amino acids, HCO₃⁻; secretes H⁺, drugs
Loop of Henle	Countercurrent multiplication → medullary gradient; reabsorbs 25% Na⁺/H₂O
Distal tubule	Fine-tunes Na⁺, K⁺, Ca²⁺, pH (aldosterone, PTH sensitive)
Collecting duct	Final water reabsorption (ADH); acid-base balance (intercalated cells)

Nephron Types

• Cortical (85%): Short loops, glomeruli in outer cortex
• Juxtamedullary (15%): Long loops deep into medulla; critical for urine concentration

Clinical Relevance

Nephron loss leads to CKD; hyperfiltration in remaining nephrons causes further damage (Brenner hypothesis). ACE inhibitors and ARBs protect by reducing intraglomerular pressure.