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 Excretory / Urinary System

 q       Body must maintain osmotic balance and dispose of nitrogen wastes

q       Nitrogenous wastes which must be disposed of varies from organism to organism, and include the following:

o       Ammonia (mostly aquatic animals)

o       Urea (mostly terrestrial animals)

o       Uric Acid (water insoluble, mostly in snails, insects, birds & reptiles)

q       Organisms use many different structures to remove N wastes.

o       Gills – very effective in removing soluble wastes like ammonia

o       Protoneophridia (flame / bulb systems) - Filter interstitial fluids of primitive worms.

o       Metanephridia – Found frequently in annelid worms.  More complex system in which N wastes diffuse into collection tubes from the blood, passes to a bladder, and then excreted.

o       Malpighian tubules – are more complex systems in which nitrogenous wastes are collected, passed into the gut and eliminated with the feces.  This system is excellent in preventing water loss

q       Humans Utilize a kidney to dispose of nitrogenous wastes

o       Kidney is a complex organ

o       Humans have 2 kidneys located dorsally, and adjacent to major arteries and veins.

§         Each kidney is served by a renal artery and a renal vein.

o       Kidney has several important regions

§         Renal cortex: Outermost region of kidney tissues

§         Renal medulla: More central region of tissue.  Contains the kidney’s functional unit, the nephron.

§         Renal pelvis: collection point for wastes requiring disposal

§         Ureters: Collect and transport wastes to the urinary bladder.

Kidney Function:

q       Functional units are the nephrons located in the renal medulla

q       Blood flows into the glomerulus of the bowman’s capsule.

q       Wastes, H2O, minerals etc… diffuse into the capsule and into the proximal tubule.

q       Liquid continues down the tubule, and water is reclaimed

q       Liquid continues around the loop of henule and into the ascending limb.  Here NaCl is reclaimed

q       Liquid continues to the distal tubule where more water, NaCl and HCO₃^- is reclaimed.

q       Liquid continues to the collecting duct, and is generally passed to the Renal pelvis, the ureters and the urinary bladder

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Mr. Stanley

Last updated: 03/11/2004