Main article: Renal physiology Urea structure Most animals have excretory systems for elimination of soluble toxic wastes. In humans, soluble wastes are excreted primarily by the urinary system and, to a lesser extent in terms of urea , removed by perspiration. The system produces urine by a process of filtration , reabsorption , and tubular secretion. The kidneys extract the soluble wastes from the bloodstream, as well as excess water, sugars, and a variety of other compounds.
Your Urinary System
Your Urinary System (for Kids) - Nemours KidsHealth
See all videos for this article In most mammals, including humans, the formation of urine begins in the nephrons of the kidneys by filtration of blood plasma into the nephron; the fluid found within the nephron is essentially the same as blood plasma without the macromolecules e. As the fluid passes along the nephron tube, water and useful plasma components such as amino acids, glucose, and other nutrients are reabsorbed into the bloodstream, leaving a concentrated solution of waste material called final, or bladder, urine. It consists of water, urea from amino acid metabolism , inorganic salts, creatinine, ammonia , and pigmented products of blood breakdown, one of which urochrome gives urine its typically yellowish colour. In addition, any unusual substances for which there is no mechanism of reabsorption into the blood remain in the urine. The products of nucleic acid breakdown are present as allantoin in most mammals and as uric acid in man and, through a quirk of breeding, in the Dalmatian dog. In most birds, reptiles, and terrestrial insects, the end product of amino acid metabolism is not water-soluble urea but insoluble uric acid. The urine of birds and reptiles is a whitish, aqueous suspension of uric acid crystals that is passed into the cloaca and mixed with fecal material before being expelled.
Now that you're older, you can understand much more about the amazing yellow stuff called pee. Parts of the Urinary Tract You drink, you pee. But urine is more than just that drink you had a few hours ago.
Anatomy of the bladder and outlet The interior of the bladder Main articles: Urinary bladder and Urethra The main organs involved in urination are the urinary bladder and the urethra. The smooth muscle of the bladder, known as the detrusor , is innervated by sympathetic nervous system fibers from the lumbar spinal cord and parasympathetic fibers from the sacral spinal cord. Part of the urethra is surrounded by the male or female external urethral sphincter , which is innervated by the somatic pudendal nerve originating in the cord, in an area termed Onuf's nucleus. Further along the urethra is a sphincter of skeletal muscle, the sphincter of the membranous urethra external urethral sphincter.