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Excretory Systems

Excretory Systems. Kidneys and their ducts. Homeostatic hormones Renin* – aids in controlling blood pressure Erythropoietin* – stimulates production of RBCs Regulates O 2 carrying capacity of blood Vitamin D** – regulates Calcium balance Ridding of Nitrogenous wastes Metabolism

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Excretory Systems

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  1. Excretory Systems

  2. Kidneys and their ducts • Homeostatic hormones • Renin* – aids in controlling blood pressure • Erythropoietin* – • stimulates production of RBCs • Regulates O2 carrying capacity of blood • Vitamin D** – regulates Calcium balance • Ridding of Nitrogenous wastes • Metabolism • Osmoregulation • Balance between solutes (salts) and water • Fresh water systems versus salt water systems • In what sort of environment did the craniate kidney evolve? * synthesized in kidney ** activated in kidney

  3. Fresh water: Kidney – enormous capacity to filter water Perceived fossil record Salt water Kidney – enormous capacity to reabsorb water (weaker argument) Updated fossil record Old thoughts – deposits – fresh HOH New thoughts – salt Hagfish are marine Malpigian tubules hemolymph HOH, solutes, wastes gut HOH, solutes wastes anus Regardless  generally conservative with highly adaptable segments

  4. Basic nephros“Archinephros”

  5. Renal corpuscle Development of corpuscle conservative variable • Above line: dorsal body wall  retroperitoneal • Below line: • No tube, celomic cavity – “external glomerulus” • Tube with connection to coelom and collecting duct – “internal glomerulus, open nephrostome” • Tube with no connection to coelom but to collecting duct – “i.g., closed nephrostome”

  6. Additional Apparatus • Regulating Anatomy: • Convoluted tubules – ciliated – move filtrate • Loop of henle – solute regulation • Size of glomerulus – hi = lots of HOH in filtrate • Collecting ducts – long = lots of absorption (with proper hormones) • Podocytes (tiny filtering structures) • Gills • Drinking • Mucus membranes on skin

  7. Comparative anatomy of nephrons and their blood supply.

  8. Environmental challenges and solutions • Freshwater • Excessive water uptake (must excrete) • Soln: Waste excreted as cheap ammonia • Problem: Toxic • Soln: Water used as solvent • Additonal cost – must actively transport solutes for retention • Examples: • Freshwater teleosts, aq. amphibians

  9. Salt Water • Prob: Excessive water loss (must conserve) • Prob: Excessive salt uptake (must excrete) • Soln 1: Become isosmotic (Hagfish, marine teleosts) • Lose glomerulus  decrease water loss • Soln 2: Become hyperosmotic (some elasmos) • Retain urea – somewhat costly, minimal toxicity (soluable in water) • Increase HOH uptake • Cost – retain glomerulus (increased metabolism) – excrete water • Soln 3: Develop special salt excretion glands (some elasmos, teleosts) • Rectal gland • Salt glands on gills

  10. Terrestrial • Prob: Dry environment • Water and salts rare  must retain both • Soln?: Return (secondarily) to water • Prob: reintroduction to above problems • Soln: N excreted in three forms • NH4, Urea, Uric Acid • Balance the costs-benefits • Soln: Reduce glomerulus (arid reptiles, anurans) • Soln: Solute recovery (develop loop of henle) (birds, mamms) • Soln: Salt glands (marine taxa) NH4 – cheap but toxic, hi HOH Urea – Int cost – low toxicity U. Acid – hi cost – not toxic, lo HOH

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