Secretion, and what urine contains
Some substances are also moved from the blood into the tubule by the tubule's cells. This is secretion.
What is secreted
- Hydrogen ions (H+)
- Potassium ions (K+)
- Ammonium ions (NH4+)
- Creatinine
- Some drugs, and excess vitamin B
What is left in the tubule is urine. It passes down the collecting ducts to the pelvis and the ureter.
| Substance in urine | Approximate share |
|---|---|
| Water | 96% |
| Urea | 2% |
| Salts, uric acid, creatinine and ammonia | 2% |
Healthy urine holds no glucose and no protein. Finding either in it is a sign that something is wrong.