Excretory Systems
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
• 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 marinegut
anus
Malpigian tubuleshemolymph
HOH, solutes, wastes
wastesHOH, solutes
Regardless generally conservative with highly adaptable segments
Basic nephros“Archinephros”
Renal corpuscleDevelopment of corpuscle
conservative
variable
Above line: dorsal body wall retroperitonealBelow 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”
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
Comparative anatomy of nephrons and their blood supply.
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
• 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
• 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 HOHUrea – Int cost – low toxicityU. Acid – hi cost – not toxic, lo HOH