Kidney Filtration: Nephrons (Not Ureters) Remove Waste from Blood

Correct Anatomy & Physiology

• Nephrons = functional filtering units (~1 million/kidney). Each nephron: glomerulus (filtration) + tubule (reabsorption/secretion).
• Ureters = muscular tubes (25–30 cm) transporting urine from renal pelvis → bladder.

Filtration Process (Nephron)

1. Glomerular Filtration: Blood pressure forces plasma through fenestrated endothelium → basement membrane → podocyte slit diaphragm → Bowman's space. Filtrate = water, electrolytes, glucose, amino acids, waste (urea, creatinine).
2. Tubular Reabsorption: Proximal tubule (65% Na⁺, H₂O, all glucose/AA), Loop of Henle (countercurrent multiplication), Distal tubule/Collecting duct (fine-tune Na⁺, K⁺, H⁺, H₂O via aldosterone/ADH).
3. Tubular Secretion: H⁺, K⁺, drugs, toxins → urine.

Ureter Function

• Peristaltic waves (pacemaker in renal pelvis) propel urine → bladder.
• Valveless entry at ureterovesical junction; prevents reflux via oblique tunnel.

Clinical Pearl

Obstruction (stone, stricture) → hydronephrosis → backpressure → nephron damage. Ureters transport; nephrons filter. Confusing them misattributes function.