Comparative Anatomy: Animal Body Systems: Excretory System AISD - 2009 Comparative Anatomy: Animal Body Systems: Excretory System

Excretory System Function: Eliminates nitrogenous wastes from the body and maintain water balance Invertebrate Organs: excretory pore, nephridia, and malpighian tubules Vertebrate Organs: Skin, kidneys, ureters, urinary bladder, urethra

Animal Excretion The main waste product created by animals is ammonia. Ammonia is a chemical that is toxic to animals and must be released through the excretory systems. Most animals have systems that eliminate ammonia quickly or convert it into a less toxic substance before it is removed from the body. Animals excretory systems can be very complex with the main organ being the kidneys to extremely simple with cells that simply pump the chemicals out.

Aquatic Invertebrate excretion Some aquatic invertebrates simply diffuse ammonia out of their bodies into the surrounding water. Example: sponges, cnidarians, and some round worms. Other aquatic invertebrates swell up with water, dilute the wastes and excrete the wastes through tiny pores in their skin.

Terrestrial Invertebrate excretion Many terrestrial invertebrates convert ammonia into urea. Urea is a simpler nitrogenous compound that is much less toxic than ammonia. This urea is eliminated from the body in urine Example: arthropods

Figure 29–11 Invertebrate Excretory Systems Flame cells Flatworm Excretory tubules Nephrostome Excretory pore Flame cell Excretory tubule Nephridia Digestive tract Annelid Malpighian tubules Arthropod

Vertebrate Excretion Aquatic vertebrate kidneys rely on gill slits to release excretory wastes into surrounding water for dilution. Terrestrial vertebrates rely on the kidneys to filter out the ammonia and change it into urea, then send it to be released in urine.

Human Excretion The kidneys filter all of the blood of the body about every 45 minutes and also receive urea from the liver. All wastes (now called urine) travel from the kidneys, through the ureter to the urinary bladder, where it is stored or released through the urethra.

The Human Urinary System Section 38-3 Vein Artery Kidney (Cross Section) Kidney Cortex Medulla Ureter Urinary bladder Urethra