Osmoregulation

  • Osmoregulation maintains the homeostatic balance of the bodies fluids with water and electrolytes
  • Water and electrolytes are taken from the environment through ingestion and are released back into the environment when metabolic wastes are excreted.
  • The urinary system keeps these two processes in balance
  • Osmolarity: The number of osmotically active moles of solute per litre of solution
  • Tonicity: The ability of a solution to change the volume of a cell by osmosis
    • If a cell is put in a hypertonic solution it will lose water and shrink
    • If a cell is put in a hypotonic solution it will take in water and shrink
    • If a cell is put in an isotonic solution there will be no movement of water
  • Osmotic gradient: The difference in concentration on both sides of a semipermeable membrane.
  • Osmoconformers: Have body fluids that are isotonic to seawater preventing an osmotic gradient. Most marine invertebrates
  • Osmoregulators: Maintain constant blood osmolarity while having different concentrations than their surroundings. All other vertebrates
  • When secreting nitrogenous wastes the ammonia produced from broken down amino acids is highly toxic and must be excreted quickly
    • Bony fish and tadpoles excrete ammonia through diffusion through their gills
    • Cartilaginous fish, adult amphibians, and mammals excrete urea
    • Birds and reptiles excrete uric acid
  • Flatworms have protonephridia (tubules) that branch throughout their body into flame cells. Cilia in the flame cells move fluid throughout the body. Water and metabolites are reabsorbed in flame cells and wastes are excreted through pores
  • Annelids have nephridia that open to both the inside and outside of the body. Coelomic fluid is filtered into the funnel shaped nephrostomes. As filtrate is moved salt is reabsorbed through active transport
  • Insects have Malpighian tubules that draw waste molecules and potassium ions through active transport. The resulting gradient draws water into the tubule and is later reabsorbed with the potassium ion in the hindgut. Wastes are excreted with the faeces in the form of uric acid
  • Nephron: The structural unit of the vertebral kidney. Filters blood under pressure to create tubular fluid, wastes are secreted into the fluid, and other molecules, ions, and water are reabsorbed. Molecules are them secreted from the blood
  • While this system uses more energy is can be adapted to many environments and unknown wastes can still be filtered out of the system
  • Amphibian kidneys are the same freshwater fish. They produce dilute urine and retain electrolytes through active transport of sodium ions across the skin from the water
    • Frogs have a large bladder where they store urine and reabsorb water while they are in terrestrial environments
  • Do to their environment marine reptiles lose water and absorb salt, they drink seawater and produce isotonic urine. Salt is eliminated from salt glands located around the nose or eyes.
  • Terrestrial reptiles produce uric acid as their nitrogenous waste, this requires little water that is later absorbed by their cloaca