Lecture Notes for General Biology BI 101 - Excretory Systems


I Excretory System

	A) Function - overcome problem of water balance and buildup of toxic wastes in the 
		body
		1) maintain stable levels of water and salts in the blood
		2) Excrete nitrogenous wastes from the body
	B) Problems for different organisms
		1) Freshwater fish - plenty of water, problems with diffusion, constantly urinating 
				and not drinking
		2) Marine fish - problems with diffusion (water loss), constantly drinking water
		3) Terrestrial organsims - face water loss and dessication
	C) How does it accomplish this?
		1) Excretes nitrogenous waste products in a water solution
			a) Ammonia in fish
			b) Uric acid in birds and insects
			c) dilute urea in mammals, amphibians, sharks
		2) Physiological strategies
			a) freshwater fish
			b) saltwater fish
			c) flatworms - flame cells
			d) insects - Malphigian tubules
			e) Vertebrates -  kidney
				basic unit of the human/vertebrate kidney - nephron


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