How Urine Is Made
Three steps, in the right order.
Follow the fluid from the blood in the glomerulus to the urine leaving the nephron.
Tap the card that comes next
Filtration is indiscriminate — it pushes out useful things too. That is exactly why selective reabsorption has to follow it. Glucose in the urine means reabsorption has failed to keep up, which is what happens in diabetes.
Free play — put the stages in order yourself, then play the whole thing through as one continuous process. Switch to when you're ready to test yourself.
What this lesson covers
Challenges to clear
- Put the three steps and their outcome in order.
- Lay selective reabsorption in its correct place.
The task
Follow the fluid from the blood in the glomerulus to the urine leaving the nephron.
What this lesson covers
- Ultrafiltration — Blood arrives under high pressure in the glomerulus, because the afferent arteriole is wider than the efferent one. Water, urea, glucose, amino acids and salts are forced out into the Bowman's capsule. Blood cells and plasma proteins are too large to pass — they stay in the blood.
- Selective reabsorption — As the filtrate passes along the tubule, the useful substances are taken back into the blood — ALL the glucose and amino acids, most of the water, and the salts the body needs.
- Tubular secretion — Substances still left in the blood that must go — extra potassium and hydrogen ions, some drugs, and creatinine — are actively passed from the capillaries into the tubule.
- Urine collects — What remains is urine: mainly water, urea, uric acid and salts. It passes into the collecting duct, then to the ureter, bladder and out.
Hint
Filtration is indiscriminate — it pushes out useful things too. That is exactly why selective reabsorption has to follow it. Glucose in the urine means reabsorption has failed to keep up, which is what happens in diabetes.