A healthy person's urine is amber-colored and slightly acid. Urine is a little heavier than water with an average specific gravity of 1.022. Urine consists mainly of water. It also contains urea, creatinine, uric acid, and such inorganic salts as sodium, potassium, ammonia, calcium, and magnesium.
Blood reaches the kidneys through the renal arteries.
Waste matter and water removed from this blood passes from the kidneys to the urinary bladder through two small tubes, the ureters. Urine is stored in the bladder until urination occurs. The urine then is expelled to the outside through another tube, the urethra. During sleep, the amount is smaller and more concentrated. Less urine is produced when a person is dehydrated, and more when a person drinks large amounts of liquid.