Excretion
Videos
Excretion is elimination of metabolic waste, which is an essential process in all organisms. In vertebrates, this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with sec
Mammals excrete urine through the urinary system.
White cast of uric acid defecated along with the dark feces by a lizard. Insects, birds and some other reptiles also use a similar mechanism.
Urine
Videos
Urine is the fluid excreted by the kidneys of vertebrates to clear the bloodstream of excess water and metabolic by-products including urea, uric acid, and creatinine.
Excretion
…and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell. For example, placental mammals expel urine from the bladder through the urethra, which is part of the excretory system. Unicellular organisms discharge waste products directly through the surface…
Sample of human urine
Tigers spray small quantities of urine to mark their territories.
Urine containing uric acid crystals under the microscope
Medical experts have long connected urine colour with certain medical conditions. A medieval chart showing the medical implications of different urine color