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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