EXCRETORY SYSTEMS C All work in the same basic way: Body fluid is filtered by a special organ. Selectively permeable membranes remove urea or uric acid. Osmolarity is controlled by selective reabsorption/secretion. C 5 types of excretory systems: None in porifera, cnidaria Protonephridia in planaria & rotifers Metanephridia in annelids Malpighian tubules in terrestrial arthropods Kidneys (with nephrons) in vertebrates
Protonephridia Have flame bulbs, tubules, and nephridopores. C Flame bulbs selectively filter body fluid to nitrogenous waste. C Fluid collects in tubules and drips outside through the nephridopore.
Metanephridia are found in annelids. C Nephrostomes collect and filter body fluid. C Waste concentrates inside the collecting tubules, which are wrapped by capillaries. Capillaries reabsorb water. C Concentrated waste drips down the tubules and outside the body via a nephridopore. C The bottom line: wash your hands after handling worms!
Malpighian tubules are found in insects.
C Malpighian tubules filter body fluid, collecting nitrogenous waste, salt and water. C Contents of the tubules are dumped into the intestines. C Intestine reabsorbs water, ions and nutrients. C Nitrogen wastes are eliminated along with feces - very efficient!
KIDNEYS C Nephron is the functional unit. C Nephron spans the cortex and medulla. C Nephrons are wrapped by a capillary network. C Nutrients are returned to the bloodstream by active transport. C Water and salt are returned to the blood via the capillary network, in concentrations that preserve blood osmolarity.
Pathway for urine: Blood vessels enter glomerulus Fluid is filtered into Bowman’s capsule. Fluid flows through: proximal tubule loop of Henle distal tubule collecting duct ureter Along the way, fluid volume decreases, salts and nutrients are returned to the bloodstream, [urea] increases.
HOW A NEPHRON WORKS There is a very strong concentration gradient between the nephron tubules and the...
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