Man (Homo Sapiens)
A human's, much like all other chordata, uses the kidney to rid its body of waste. Humans each have two kidneys, yet are able to survive properly with one. The kidney filters its bloodstream for any toxins, unnecessary minerals, excess liquid, et cetera. The mixture of liquid and minerals then goes through tubes called the ureters. The ureter transfers the mixture, mostly consisting of urea and ammonia, to the bladder, a muscular sac where urine is stored prior to urination. The urine is finally excreted through the genital region going through as well the urethra. The human body also excretes through the use of sweat. The apocrine sweat glands within humans work to excrete various substances from the human body, mainly within the underarm region, rather than just cool the body down. These pores on the human epidermis are larger than other forms of sweat glands due to its function of releasing larger substances instead of simply producing sweat.
Tuna (Thunnus albacares)
The tuna fish is very similar to other , has a less structured excretory system, compared to mammals, such as humans. They do have kidney which filters the blood, but the way it releases this waste is vastly different. Diffusion through the gills rids fish of most of its waste. Also, because the tuna fish is also a salt water fish, it loses water through osmosis, excreting excess liquid that way. The waste produced by the tuna fish, much like most fish is, though, ammonia.
Dog (Canis lupus)
The dog's excretory system, is very closely related to that of a human's. They both have fundamentally the same system. The dog has two kidneys, as most mammals do, which filters the blood from waste and excess fluid.The excretory system then transfers the waste to the ureter. This then goes to the bladder, where it eventually is excreted by the urethra, located in the genital region for both males and females.