Flatworms
- Have an excretory system called a Protonephridia.
- During filtration the cilia beats water and solute through the flame bulb releasing filtrate into the tubule network
- Then the filtrate moves throughout the tubules and empties as urine
- If the urine is excreted by a freshwater flatworm then the urine will have low solute concentration for osmoregulation
Earthworms
- Have excretory organs, metanephridia, which collect fluids from the coelom or body.
- When the cilia beats, the filtrate is drawn into a collecting tubule, which includes a storage bladder that opens to the outside
- During the time the urine is moving through the body to be excreted out, the transport epithelium, by the lumen, reabsorbs most solutes to give to the blood.
- The earthworms receive water through their skin, so the metanephridia produces more solute in the urine for homeostasis.
Vertebrates
- Have organs called malpighian tubules that remove nitrogenous waste
- They don’t have the filtration step like other excretory systems
- Instead the transport epithelium secretes certain solutes from the hemolymph into the lumen of the tubule.
- The fluids flow into the rectum because of water flow and osmosis.
- In the rectum most solutes are pumped back into the hemolymph and water reabsorption by osmosis follows next.
- Then all the waste is eliminated from the anus.