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 fluids, so must absorb salts.- Dangerous metabolites produced by break down of proteins and nucleic acids need to be 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 fluid 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 fluids 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 flows by osmosis from a hypoosmotic solution to a hyperosmotic solution**BIOL1108: Stanger-Hall! FINAL Material- Osmotic Challenges- Animals can maintain water balance in two ways:- 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 than their environment. - Most animals are called stenohaline, or not able to handle extreme changes in external 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 fish 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 fishes” 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 fluid 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 fluid is slightly more concentrated, water flows 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 flow 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 fishʼs body across the gills. - Salmon and other euryhaline fish:- 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 fishes 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. - Ex. Water bears- Land Animals - 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