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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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kidneys and their ducts
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

slide3
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

renal corpuscle
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”
additional apparatus
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
environmental challenges and solutions
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
slide11
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
slide12
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