osmoregulation

• Excretion


  The process of eliminating waste products of metabolism and other materials that are not useful to the body
• Primary metabolic waste products in animals

  • Water
  • Carbon dioxide
  • Nitrogenous wastes
• Ammonia


  Highly toxic nitrogen-containing waste product
• Uric acid


  Insoluble in water, forms crystals when excreted as a paste, important adaptation in many terrestrial animals for water conservation
• Protonephridia of planaria


  1. Water enters flame cells

  2. Cilia propel water to tubules

  3. Excess water and waste materials leave through excretory pores

  
• Metanephridia


  • Tubules open on both ends, inner end opens into body cavity, outer end opens to outside
• Osmoconformers


  Organisms whose body osmolarity matches their environment
• Osmoregulators


  Organisms whose internal environment remains constant despite osmotic pressure changes in their environment
• Osmoregulation in saltwater fish


  1. Constantly lose water to environment

  2. Drink seawater to replace water loss

  3. Actively transport salt from blood into surrounding water

  4. Produce small volume of urine to conserve water

  
• Freshwater fishes


  Live in a hypotonic environment, meaning their bodies have higher salt concentration than the environment they are in
• Saltwater fishes


  Live in a hypertonic environment, the salt concentration in their bodies is way lower than the environment they are in
• Marine cartilaginous fishes (sharks and rays)


  • Tolerate and accumulate urea in concentrations that may already be harmful to some organisms
  • The high urea concentrations in their body fluids make them more hypertonic than the surrounding environment, resulting in a net inflow of water

  
• Marine mammals (whales, dolphins)


  • Water intake happens along food intake
  • Their kidneys produce concentrated urine that is much saltier than seawater
• Marine mammals


  • Physiologically significant especially for carnivores whose high protein diet produces a large amount of urea and must be removed from the body without the expense of losing too much water
• Euryhaline organisms


  Spend part of their life in freshwater and part in saltwater as certain phases of their developmental stages dictate

  
• Amphibian kidneys function similarly to that of freshwater fishes, they excrete large amount of dilute urine and have active transport of salt in their skin
• On land, amphibians conserve body fluid through water reabsorption across the epithelium of their urinary bladder and excrete urea as a nitrogenous waste

  
• Birds


  • Have efficient kidneys but the nephrons do not extend far into the medulla, so they cannot concentrate urine to the high osmolarities achieved by mammalian kidneys
  • Produce uric acid as a nitrogenous waste, which is excreted as a paste and reduces water loss
• Terrestrial vertebrates


  • The lungs, skin, and organs of the digestive system work collaboratively in the disposal of metabolic wastes and regulation of body salt concentration
  • Carbon dioxide is excreted mainly through the lungs during respiration, and to some extent water also goes with it
  • The sweat glands of humans and other mammals also contribute by excreting perspiration which comprises about five to ten percent of all metabolic wastes
  • The liver produces urea and uric acid which are processed by the kidneys