The kidneys
1. Renal cortex 2. Renal artery
3. Renal vein 4. Urether
5. Renal medulla
The kidneys' function is to remove waste products from your blood and to regulate the body's acidity-alkali equilibrium, the blood pressure and fluid balance.
Each kidney contains one million nephrons that are found in the kidney tissue and filter your blood. Every day, your kidneys filter about 180 litres of fluid. What isn't returned to the blood is removed as urine. You produce about 2 litres of urine a day.
Under normal circumstances, your body produces about 1 ml of urine per kilo of body wieght an hour. When you consume large quantities of liquid, this production can increase to 15 ml per kilo an hour.
If we take an adult that weighs 70 kg (155 pounds), under normal circumstances this would mean about 1.7 litres of urine a day.
Ureters
To prevent urine from flowing back up to your kidneys, the ureters empty into your bladder at a slope. In the transition from ureter to bladder you find a "valve" that prevents the urine from being pressed back up to the kidneys.