The kidneys are the main organs of the urinary system. They function chiefly to filter blood in order to remove wastes and excess water. The waste and water are excreted as urine. The kidneys also reabsorb and return to the blood needed substances, including amino acids, sugar, sodium, potassium, and other nutrients.
But many popular brands actually contain considerably less than an old-fashioned cup of black coffee. An 8.4-ounce serving of Red Bull, for instance, has a relatively modest 76 to 80 mg of caffeine, compared to the 95 to 200 mg in a typical cup of coffee, the Mayo Clinic reports.
Your Average Cup. A 12-ounce cup of coffee that you brew at home contains about 100 to 160 milligrams of caffeine. Use a coffee maker with coffee pods and you're likely to get between 75 and 150 milligrams per cup.Instant coffee contains between 135 and 148 milligrams per cup.ach day about 75 percent of Americans consume coffee, which contains the world's most popular stimulant -- caffeine -- reports Rice University. Although caffeine is generally considered safe, certain people, such as pregnant women or people on certain medications, may need to monitor their intake.