Each kidney has about a million nephrons. Each one filters blood and turns the filtrate into urine.
Glomerulus
A ball of capillaries filters water and small molecules out of the blood. The filtering rate is the GFR, the main measure of kidney function.
Proximal tubule
Takes back most of the water, sodium, glucose and bicarbonate. Glucose spills into urine when blood glucose is very high.
Loop of Henle
Concentrates the urine. Loop diuretics (for example furosemide) act here.
Distal tubule and collecting duct
Fine-tune sodium, potassium and water. Aldosterone saves sodium and loses potassium; antidiuretic hormone saves water.
At the bedside
Low urine output, rising creatinine and abnormal potassium are signs the nephrons are struggling. Many drug doses depend on GFR.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).