1. Excretory Systems

2. 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 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 gut anus Malpigian tubules hemolymph HOH, solutes, wastes wastes HOH, solutes 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”

7. 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

9. Comparative anatomy of nephrons and their blood supply.

10. 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

11. 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

12. 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 NH 4, 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) NH 4 – cheap but toxic, hi HOH Urea – Int cost – low toxicity U. Acid – hi cost – not toxic, lo HOH