COMPARATIVE COMPARATIVE ANATOMY:ANATOMY:ANIMAL BODY ANIMAL BODY SYSTEMS:SYSTEMS:EXCRETORY SYSTEMEXCRETORY SYSTEM

AISD - 2009

Excretory SystemExcretory 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 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 Aquatic Invertebrate excretionexcretionSome 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 Terrestrial Invertebrate excretionexcretionMany 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

Annelid

Arthropod

Flatworm

Malpighian tubules

Digestive tract

Nephridia

Excretory pore

Excretory tubule

Flame cell

Flamecells

Excretorytubules

Nephrostome

Figure 29–11Figure 29–11

 Invertebrate Excretory Systems Invertebrate Excretory Systems

Vertebrate ExcretionVertebrate ExcretionAquatic 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 ExcretionHuman ExcretionThe 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.

Kidney (Cross Section)

Cortex

Medulla

Vein Artery

Kidney

Ureter

Urinary bladder

Urethra

The Human Urinary The Human Urinary SystemSystem

Section 38-3