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Chapter 44

Chapter 44. Osmoregulation and Excretion. Overview: A Balancing Act. Physiological systems of animals operate in a fluid environment Relative concentrations of water and solutes must be maintained within fairly narrow limits.

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Chapter 44

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  1. Chapter 44 Osmoregulation and Excretion

  2. Overview: A Balancing Act • Physiological systems of animals operate in a fluid environment • Relative concentrations of water and solutes must be maintained within fairly narrow limits

  3. Freshwater animals show adaptations that reduce water uptake and conserve solutes • Desert and marine animals face desiccating (dehydrating) environments that can quickly deplete body water

  4. Osmoregulationregulates solute concentrations and balances the gain and loss of water • Excretion gets rid of metabolic wastes

  5. Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitat • The type and quantity of an animal’s waste products may greatly affect its water balance • Among the most important wastes are nitrogenous breakdown products of proteins and nucleic acids

  6. Nucleic acids Proteins HOW these waste products are excreted depends on how much water an organism needs to maintain homeostasis This is dependent on their habitat! Amino acids Nitrogenous bases —NH2 Amino groups (nitrogenous waste) Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Many reptiles (including birds), insects, land snails More H2O needed to excrete Ammonia Urea Uric acid More energy needed to excrete

  7. Forms of Nitrogenous Wastes: Ammonia • Animals that excrete nitrogenous wastes as ammonia need lots of water • So… they live in an environment where water is abundant. • They release ammonia across the whole body surface or through gills Freshwater animals Marine invertebrates

  8. Forms of Nitrogenous Wastes: Urea • Animals that produce urea have a limited source of water • The liver of mammals and most adult amphibians converts ammonia to less toxic urea • The circulatory system carries urea to the kidneys, where it is excreted

  9. If liver can’t get rid of waste, there is a buildup of uric acid in the blood. • It can crystallize in the joints and cause inflammation of the joints. • Condition is known as gout

  10. Forms of Nitrogenous Wastes: Uric Acid • Animals that excrete uric acid have a critical problem with getting water some time in their lifetime • Insects, land snails, and many reptiles, including birds, mainly excrete uric acid • Lay eggs with limited supply of water inside the egg. • Note: eggshells are impermeable to water so it won’t lose any water, but... Uric acid NH3 NH3 Uric acid NH3 Uric acid H2O H2O NH3 Uric acid No Contamination Contamination

  11. Forms of Nitrogenous Wastes: Uric Acid • Uric acid is largely insoluble in water and can be secreted as a paste with little water loss

  12. The Influence of Evolution and Environment on Nitrogenous Wastes • The kinds of nitrogenous wastes excreted depend on an animal’s evolutionary history and habitat • The amount of nitrogenous waste is coupled to the animal’s energy budget

  13. The Influence of Evolution and Environment on Nitrogenous Wastes • Remember, there are 3 general wastes products • Special cases: • Lungfish: make ammonia when there’s a lot of water, urea when pond dries out • Aquatic mollusks make ammonia, terrestrial snails make urea ammonia urea uric acid Increasing amount of water

  14. Concept 44.1: Osmoregulation balances the uptake and loss of water and solutes • Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment • Cells require a balance between osmotic gain and loss of water • Various mechanisms of osmoregulation in different environments balance water uptake and loss • Terms to remember: • Osmotic pressure: solute “pull” • Osmotic potential: water concentration • Hyper- , hypo-, iso- tonic solutions

  15. Osmotic Challenges • Osmoconformers, consisting only of some marine animals, are isoosmotic (isotonic) with their surroundings and do not regulate their osmolarity • Osmoregulatorsexpend energy to control water uptake and loss in a hyperosmotic (hypertonic) or hypoosmotic (hypotonic) environment

  16. Most animals are stenohaline; they cannot tolerate substantial changes in external osmolarity • Euryhaline animals can survive large fluctuations in external osmolarity

  17. Marine Animals • Most marine invertebrates are osmoconformers • Most marine vertebrates and some invertebrates are osmoregulators

  18. Marine bony fishes are hypoosmotic to sea water • They are in a hypertonic environment • Constantly lose water (as if they were in a desert) • They lose water by osmosis and gain salt by diffusion and from food • They balance water loss by drinking seawater Gain of water and salt ions from food and by drinking seawater Osmotic water loss through gills and other parts of body surface [hypotonic] [hypertonic] Excretion of salt ions and small amounts of water in scanty urine from kidneys Excretion of salt ions from gills Osmoregulation in a saltwater fish

  19. Transport Epithelia • Transport epithelia are specialized cells that regulate solute movement • They are essential components of osmotic regulation and metabolic waste disposal • They are arranged in complex tubular networks • An example is in salt glands of marine birds, which remove excess sodium chloride from the blood Nasal salt gland (acts as a filter) Nostril with salt secretions

  20. Freshwater Animals • Freshwater animals constantly take in water from their hypoosmotic environment • Need: get rid of extra water, keep salts • They lose salts by diffusion and maintain water balance by excreting large amounts of dilute urine • Salts lost by diffusion are replaced by foods and uptake across the gills Osmotic water gain through gills and other parts of body surface Uptake of water and some ions in food [hypotonic] [hypertonic] Uptake of salt ions by gills Excretion of large amounts of water in dilute urine from kidneys Osmoregulation in a freshwater fish

  21. Animals That Live in Temporary Waters 100 µm • Some aquatic invertebrates in temporary ponds lose almost all their body water and survive in a dormant state • This adaptation is called anhydrobiosis(“life without water”) 100 µm Dehydrated tardigrade Hydrated tardigrade

  22. Water balance in a kangaroo rat (2 mL/day) Water balance in a human (2,500 mL/day) Land Animals Ingested in food (750 mL) • Land animals manage water budgets by drinking and eating moist foods and using metabolic water Ingested in food (0.2 mL) Ingested in liquid (1,500 mL) Water gain Derived from metabolism (1.8 mL) Derived from metabolism (250 mL) Feces (100 mL) Feces (0.09 mL) Urine (1,500 mL) Urine (0.45 mL) Water loss Evaporation (900 mL) Evaporation (1.46 mL)

  23. Desert animals get major water savings from simple anatomical features 4 3 Water lost per day (L/100 kg body mass) 2 1 0 Control group (Unclipped fur) Experimental group (Clipped fur)

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