BIOL1108 Stanger Hall FINAL Material Chapter 44 Osmoregulation Excretion pg 953 960 962 963 Homeostasis requires osmoregulation the general term for the processes by which animals control solute concentrations and balance water gain and loss In salty or dry environments like deserts and oceans organisms face potential dehydration In fresh water environments animals face problem of dilution of body uids so must absorb Dangerous metabolites produced by break down of proteins and nucleic acids need to be salts eliminated from the body Several mechanisms have evolved for excretion or the process that rids the body of nitrogenous metabolites and other metabolic waste products Systems for excretion and osmoregulation are structurally functionally related So osmoregulation helps keep certain concentrations of ions that allow for the correct functioning of muscles neurons etc also helps keep uid environment of cells tissues muscles etc 44 1 Osmoregulation balances the uptake and loss of water and solutes Osmoregulation is the process of controlled movement of solutes between internal uids and the external environment With movement of solutes water follows by osmosis Gives balance of both water as well as solutes Osmosis and Osmolarity Osmosis occurs when the osmotic pressure or osmolarity moles of solute per L of solution is different on both sides of the membrane Unit milliOsmoles per liter mOsm L Human blood 300 mOsm L Sea water 1000 mOsm L Isoosmotic two solutions separated by a membrane have the same osmolarity Hyperosmotic solution where solute concentration is greater Hypoosmotic less concentrated solution Water ows by osmosis from a hypoosmotic solution to a hyperosmotic solution BIOL1108 Stanger Hall Osmotic Challenges Animals can maintain water balance in two ways FINAL Material Osmoconformers to be isoosmotic with its environment All osmoconformers are marine animals There internal osmolarity is the same as their environment so there is NO tendency to gain or lose water Many of these animals live in environments with stable water composition so they also have a stable internal osmolarity Osmoregulators control internal osmolarity independent of that of its environment Osmoregulation allows animals to live in environments that are not suitable for osmoconformers such as fresh water terrestrial habitats To survive in hypoosmotic environment an osmoregulator must discharge water to stay alive while the opposite is true in a hyperosmotic environment Osmoregulation also allows marine animals to maintain an internal osmolarity different Most animals are called stenohaline or not able to handle extreme changes in external than their environment osmolarity Euryhaline animals can tolerate extreme changes such as barnacles who are often covered and uncovered by the sea tide Adaptations for Marine Freshwater and Terrestrial Animals Marine Animals Most marine invertebrates are osmoconformers osmolarity the same as sea water so they do not need help maintaining water balance BUT they have different concentrations of certain solutes ex Mg2 than the sea water so must use active transport to maintain homeostasis Many marine vertebrates and some marine invertebrates are osmoregulators They are so because the ocean is a dehydrating habitat Marine sh constantly lose water to osmosis They balance this loss by drinking sea water This presents a problem bc of salt Specialized chloride cells in gills actively transport Cl out and Na ions follow passively The kidneys then excrete allowing minimal loss of water excess Ca Mg and Sulfate ions Marine Sharks and other cartilaginous animals A distinct adaptation exists Like bony shes sharks have an internal osmolarity much lower than sea water so salt tends to diffuse into their bodies from the water especially across their gills However marine sharks are NOT hypoosmotic to their environment A sharks tissues have high concentrations of urea TMAO and salts and other compounds in their body uid allow them to have an osmolarity almost identical to the water around them So sometimes said to be osmoconformers BIOL1108 Stanger Hall FINAL Material Because body uid is slightly more concentrated water ows in the sharks body slowly and is disposed in the form in urine The urine also removes the salt that diffuses into the sharks body Freshwater Animals Have the opposite problem of marine animals They cannot tolerate the low solute concentrations of lake waters etc so they must be hyperosmotic to their environment This causes water to ow into their bodies which they make up for by drinking little to no water and by excreting very dilute urine Salts lost by diffusion and urine are replenished through eating Active transport is again used to transport Cl and Na ions into the freshwater sh s body across the gills Salmon and other euryhaline sh Migrate between fresh and sea water environments When living in rivers salmon osmoregulate producing large amounts of dilute urine and drinking little water but when they live in sea water the production of the hormone cortisol is increased Cortisol increases the size and number of Cl salt secreting cells As a result salmon excrete excess salt from their gills and produce little urine similar to bony shes that always live in the sea Animals That Live in Temporary Waters Desiccation or extreme hydration can occur in animals when their habitat dries up however they are still able to survive due to an adaptation Enter a dormant stage when habitats dry up called anhydrobiosis Requires adaptations that keep cell membranes intact Land Animals Ex Water bears Threat of dehydration is huge Humans can die if they lose 12 of body water Waxy cuticle on plants and coverings on animal bodies are adaptations for water loss Keratinized skin on humans BIOL1108 Stanger Hall FINAL Material Many ways to lose water urine feces sweat etc Also many ways to replenish drinking water producing water through cellular respiration etc Ex kangaroo rats can replenish 90 of water by cellular respiration and 10 from diet Energetics of Osmoregulation Costs energy to maintain the concentration gradients between external environment and animals body because diffusion tends to equalize concentrations So osmoregulators must expend energy to maintain the osmotic gradient that cause water to move in and out done so by using active transport to alter solute concentrations in their body uids The amount of energy depends on the difference in osmotic concentrations how