The excretory system removes wastes from the body.
Cells in your body break down sugars, fats and proteins for energy. Some of these processes release waste byproducts that would be toxic in high concentrations, so cells release these wastes into the bloodstream. The excretory system plays a vital role in your body(and that of most other animals) by filtering waste and excess salt from the bloodstream and expelling it as urine.
Nitrogenous Wastes
Proteins and nucleic acids contain nitrogen, so when cells in your body break these molecules down, they remove the nitrogen in the form of ammonia (NH3). Some fish excrete ammonia in their urine; humans and other mammals, however, combine ammonia with carbon dioxide in the liver to form urea, (NH2)2CO. Like many other animals, humans also produce a small amount of a similar waste called uric acid.
Filtration
In humans and many other animals, the kidneys remove waste and excess salt from the bloodstream. Blood flows into the kidney via the renal artery and is routed into the nephrons. In each nephron, the blood travels through a ball-shaped structure called a glomerulus, where water and dissolved substances like urea, sugars, nutrients and salts can leak through the porous walls of the capillaries. The nephron removes the sugars, nutrients and some of the salt and water to return them to the bloodstream. This process leaves behind a concentrated solution of urea and salt dissolved in water.
Excretion
From the nephron, the urine flows through a duct called the ureter into the urinary bladder. A tube called the urethra links the bladder with the outside world. The sphincter muscles constrict the urethra to regulate the flow of urine so that it can be discharged at will rather than continuously.
Disorders
Gout is a disorder where the body either manufactures excess uric acid or doesn't properly filter it from the bloodstream. Unlike urea, uric acid is fairly insoluble, so it can form crystals in joints, causing pain and deformation. Urinary tract infections occur when bacteria colonize the urinary tract and can cause a variety of problems. Kidney stones are crystals of insoluble salts like calcium oxalate. They can form in the urinary tract for a number of different reasons and block the passage of urine through the tract.
Interesting Variations
Vertebrate animals inhabit a startling variety of different habitats; consequently, the excretory systems of different animals exhibit some interesting adaptations to their native environments. Freshwater fish, for example, absorb large quantities of water through osmosis, so they need to excrete large volumes of dilute urine. Saltwater fish, on the other hand, take in large quantities of salt, so their excretory systems must expel salt while conserving water. Vampire bats are perhaps the most peculiar example of a diet-specific adaptation: after consuming blood, they quickly unload much of the water from the blood meal as dilute urine. Much of the nutrition the bat can extract from the blood, however, is in the form of protein, so in breaking down these proteins the bat ends up with a large quantity of urea. After digestion, then, the bat's kidneys shift gears and start producing highly concentrated urine instead.
Tags: from bloodstream, other animals, uric acid, your body, body break, dilute urine