Osmoregulation & Excretion, Part 1 Lecture 16 Winter 2014

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1 Osmoregulation & Excretion, Part 1 Lecture 16 Winter 2014

2 Homeostasis & Osmoregulation 1 Homeostasis The maintenance of a relatively constant chemical and physical environment within an organism Osmoregulation How animals regulate solute concentrations and balance the gain and loss of water

Water Balance Animal Cells Osmosis The diffusion of water across a selectively permeable membrane down its concentration gradient Tonicity Ability of a

3 Water Balance Animal Cells Osmosis The diffusion of water across a selectively permeable membrane down its concentration gradient Tonicity Ability of a solution to cause a cell to gain or lose water Hypotonic / Hypertonic /Isotonic Isotonic (isoosmotic) state is the functional norm for animal cells 2 See Fig. 7.13

4 Water Balance Animal Cells 3 Osmolarity Solute concentration expressed as molarity Number of moles of solute per liter of solution (mosm/l) Osmotic pressure Isoosmotic Hyperosmotic Hypoosmotic Fig. 44.2

5 Osmotic Challenges 4 Osmoregulation Osmoconformer Animal that is isoosmotic with its environment Typically stable environment Osmoregulator Animal that controls its internal osmolarity independent of the external environment

6 Osmotic Challenges 5 Stenohaline Organisms that cannot tolerate substantial changes in external osmolarity Euryhaline Organisms that can tolerate substantial changes in external osmolarity E.g., barnacles & mussels (osmoconformers); salmon (osmoregulators)

7 Osmotic Challenges: Marine Environment Ocean 1,000 mosm/l Marine osmoconformers Sponges, jelly fish, flatworms Water balance Internal osmolarity same as external osmolarity Solute balance Concentration of specific solutes differs between internal and external environment Need active transport 6

8 Osmotic Challenges: Marine Environment Marine osmoregulators Many marine vertebrates, some invertebrates E.g., Bony fish Body fluids hypoosmotic to sea water Will lose water through osmosis Will gain salt through diffusion Drink seawater Conservation of water by kidneys Excrete salt ions from gills Chloride cells Excrete salt ions from kidneys Fig

9 Osmotic Challenges: Marine Environment Marine osmoregulators e.g., Chondrichthyens (sharks, skates, rays) Body fluids slightly hyperosmotic to seawater Internal salt concentration much lower than in environment Tissue contains high concentrations of urea TMAO (trimethylamine oxide) Protects tissues from damage by urea Gains water (slowly) Does not drink seawater Kidney excretes extra water Gains salt diffusion in gills Salt excreted by kidneys Rectal gland removes salt 8

10 Removing salts Shark rectal gland (chloride cells of bony fish) 9

11 Osmotic Challenges: Freshwater Environment 10 Freshwater mosm/l Freshwater osmoregulators E.g., Bony fish Body fluids are hyperosmotic to freshwater Will gain water through osmosis Will lose salt through diffusion Does not drink water Excretes large amounts of dilute urine Salt gained through food Salt uptake through gills Chloride cells Fig. 44.4

12 11 Osmotic Challenges: Temporary Waters Anhydrobiosis Dormant state involving loss of almost all body water Need to protect cell membrane Some nematodes use sugar (trehalose) to replace water normally associated with proteins & membrane lipids Fig. 44.5

13 Osmotic Challenges: Terrestrial Environment Dehydration serious problem for land animals Lose water to environment Skin, gas exchange surfaces, urine, feces Body coverings Wax on exoskeletons Shell of land snails Keratinized skin cells (reptiles, mammals) Behavorial Nocturnal 12

14 Osmotic Challenges: Terrestrial Environment 13 Gain water through eating & drinking Gain water through metabolic activity Gain salts through eating Fig. 44.6

15 Osmotic Challenges: Seabirds 14 Many seabirds must drink salt water Must rid themselves of excess salt Nasal salt gland Fig. 44.7

16 Osmotic Challenges: Seabirds 15 Transport epithelium One or more layers of specialized epithelial cells that regulate solute movement Blood flows counter to the flow of salt excretion Counter-current exchange Fig. 44.7

17 Energetics of Osmoregulation 16 Osmoregulation requires energy expenditure Active transport of solutes Amount of energy required varies with environment 5% of resting metabolic rate of bony fish of freshwater & marine environments 30% of resting metabolic rate of crustaceans in Great Salt Lake To minimize cost of osmoregulation, body fluids adapted to be more similar to environment Marine molluscs 1,000 mosm/l Freshwater molluscs 40 m Osm/L

Osmoregulation regulates solute concentrations and balances the gain and loss of water

Ch 44 Osmoregulation & Excretion Osmoregulation regulates solute concentrations and balances the gain and loss of water Freshwater animals show adaptations that reduce water uptake and conserve solutes