Chapter 44

1. Chapter 44 Osmoregulation and Excretion.

2. Salvin’s Albatross

3. Concept 44.1 • The ability to regulate the intake and loss of water and solutes is called Osmoregulation. • Based on the controlled movement of solutes between the internal fluids and external environment.

4. Concept 44.1 • Osmoregulation is a problem that all animals, including humans, face. • Water is one of the most important compounds in an organism and must be balanced in order for the organism to survive.

5. Concept 44.1 • Osmoregulation is how animals regulate solute concentrations and balance the gain/loss of water. • Since animals don’t have cell walls, the cells may: swell and burst, if there’s a constant net gain, or may shrivel and die, if there’s a significant amount of water loss.

6. Osmosis • Osmosis- the movement of aqueous substances across a semi permeable membrane. • This is the basis of Osmoregulation!!!

7. Types of osmosis • Osmolarity- a difference in osmotic pressure. • The total solute concentration expressed as molarity, or moles of solute per liter of solution;

8. Osmosis and organisms • If an organism is: • Isoosmotic, it has the same solute concentration as the surrounding environment. • Hypoosmotic, it has a more diluted solution concentration than the surrounding environment. • Hyperosmotic, it has a greater concentration of solutes than its surrounding environment.

9. Osmotic challenges. • Two basic solutions to water balancing problem! • One is to be isoosmotic with the surroundings. • This is only available for marine animals. • Since it can’t adjust its osmolarity it would be consider an Osmoconformer.

10. Osmoconformers • Are marine animals • Have stable composition • Are isoosmotic and do not need to regulate their osmolarity • Often have a very constant internal osmolarity • Therefore they must be…… • Simple organisms!!!

11. Osmotic challenges • The other way an organism can regulate their osmotic problem is to control the osmolarity of its bodily fluids. • An osmoregulator must discharge excess water if it lives in a hypoosmotic environment. • It must take in the water if it lives in a hyperosmotic environment.

12. Osmotic challenges • Osmoregulation allows an animal to live in an environment that would otherwise be uninhabitable for osmoconformers. • This would be freshwater and terrestrial habitats. • Allows many marine animals to maintain internal osmolarities different than that of saltwater.

13. The costs of being complex • ENERGY!!!! • In order to maintain the osmolarity difference between the body and the external environment, the organism must extend energy. • They use active transportation to move the solute concentrations in their bodily fluids. • The amount of energy used depends on the gradient of the organism’s solute to the evironment’s solute concentration.

14. Environmental changes • Most organisms, both osmoconformers and osmoregulators, cannot survive substantial changes in the environment. • These organisms are called Stenohalines. • Derived from the Greek words stenos, meaning narrow, and haline referring to salt.

15. Environmental changes. • Some animals, however, can survive large fluctuations in solution concentration. • These are referred to as Euryhalines. • Which is derived from the Greek words Eurys, meaning broad and of course haline. • Examples are some species of Salmon and Tilapia. • Tilapia can adjust to any salt concentration between fresh water and 2,000 mosm/L, twice that of saltwater.

16. Adaptations • Most marine invertebrates are isoosmotic • Means their solute concentration is the same as their surrounding environment. • However they differ considerably from seawater in their concentrations of most specific solutes. • Thus even an osmoconformer has to regulate its concentrations.

17. Adaptations • Sharks have a slighter higher osmolarity than that of the sea water because they retain urea. • Marine bony fishes are hypoosmotic to the seawater and therefore must obtain solutes through diffuse and their food. • They (marine bony fishes) excrete their excess salt through rectal glands, gills, salt-excreting glands, or kidneys.

18. Adaptations • Unlike bony fish and despite having a relatively low internal salt concentration, marine sharks do not experience a large and continuous osmotic water loss. • Why? • Sharks maintain high concentrations of urea. • An organic solute called trimethylamine oxide or TMAO protects proteins from damage by the urea. • The sharks total osmolaric concentration would add up to just slightly above that of saltwater so therefore a shark is actually hyperosmotic to the saltwater. • Consequently, water slowly enters a shark and is disposed of in the urine produced by the kidneys.

19. LE 44-3a Gain of water and salt ions from food and by drinking seawater Osmotic water loss through gills and other parts of body surface 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

20. Adaptations • Would freshwater fish have the same problem as marine fish? • No. Freshwater fish have the opposite problem than marine fish. • Since the seawater is hyperosmotic to the marine fish, then they are constantly losing water and gaining salt, conversely since fresh water is hypoosmotic to freshwater fish then they are constantly gaining water and losing salt.

21. LE 44-3b Osmotic water gain through gills and other parts of body surface Uptake of water and some ions in food Uptake of salt ions by gills Excretion of large amounts of water in dilute urine from kidneys Osmoregulation in a freshwater fish

22. Figure 44-2

23. Adaptations • One way to prevent this salt loss is to excrete diluted urine. • The salt that is lost by diffusion and in the urine are replaced by salts in food and by picking up chloride cells in the gills. • Some fish, like salmon will exhibit traits of both marine and freshwater fish depending on the environment that they are in.

24. Life without water. • Most animals cannot survive dehydration. • However some animals can survive the dehydrated conditions by undergoing a dormant phase. • This adaptation is called anhydrobiosis (life without water) • Researchers believe that these animals have a sugar called trehalose that in the absence of water will provide the cell with membranes and proteins.

25. LE 44-4 100 µm 100 µm Dehydrated tardigrade Hydrated tardigrade

26. Adaptations • Did you know that a human dies if they lose only 12% of their body water. • The threat of dehydration for terrestrial animals is great and offers a challenge to get around. • Some animals develop waxy coverings called… • CUTICLE • Some desert dwelling animals have become nocturnal to avoid the dehydrating heat.

27. LE 44-5 Water balance in a kangaroo rat (2 mL/day) Water balance in a human (2,500 mL/day) Ingested in food (750 mL) 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)

28. Land adaptations • Even with these adaptations animals still lose water through their gas exchange organs, in their urine and feces, and across their skin. • Land animals replenish their water balance by drinking water and obtaining it in their food.

29. Transport Epithelia • In most animals there are one or more different kinds of transport epithelium or a layer/layers of specialized epithelial cells that regulate solute movements. • These are essential components of osmotic regulation and metabolic waste disposal. • They move specific solutes in controlled amounts in specific directions. • Some epithelia face outward towards the environment while others line channels connected to the outside by an opening on the body’s surface.

30. LE 44-6 4 3 Water lost per day (L/100 kg body mass) 2 1 0 Control group (Unclipped fur) Experimental group (Clipped fur)

31. Epithelia • Are joined by impermeable tight junctions • Form a barrier at the tissue-environment boundary • Are arranged into complex tubular networks with extensive surface areas.

32. LE 44-7b Lumen of secretory tubule Vein Capillary Artery Secretory tubule NaCl Transport epithelium Direction of salt movement Blood flow Secretory cell of transport epithelium Central duct

33. Nitrogenous waste and phylogeny/habitat. • The type and quantity of an animal’s waste may have a large impact on its water balance. • Metabolic processes of an organism produces a nitrogenous waste ammonia. • Most mammals convert ammonia to urea, which is less toxic to the body. • The urea is carried to the kidneys and concentrated it is excreted with a minimal loss of water.

34. Ammonia • In fish the ammonia is lost as ammonium ions, while the kidneys only excrete a minor amount of nitrogenous waste. • The gill epithelium takes up Na+ in exchange for the ammonium ions • This helps to maintain a higher amount of Na in the body fluids than in the surrounding waters.

35. Urea • Transferring through the skin is good for fish but not so beneficial for land animals because ammonia has to be transported in large amounts of diluted solutions. • The reason why land dwelling organisms don’t use this type of excretion is that it requires a huge amount of water and most land animals simply do not have a sufficient amount of water.

36. LE 44-8 Nucleic acids Proteins Amino acids Nitrogenous bases —NH2 Amino groups Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes Many reptiles (including birds), insects, land snails Ammonia Urea Uric acid

37. Urea • Mammals, sharks and some amphibians produce urea by a metabolic process in the liver that combines ammonia with carbon dioxide.

38. Main advantages • Less toxic; about 100,000 times less toxic than ammonia • This allows urea to be transported safely at high concentrations. • Little water is lost in the excretion

39. Main disadvantages • ENERGY!!! • It takes energy to convert the ammonia to urea. • Many amphibians produce ammonia in their aqueous stage and then produce urea in their terrestrial phase.

40. Uric Acid • Insects, land snails, and many reptiles including birds excrete uric acid. • Similarly uric acid is less toxic than ammonia • Unlike urea and ammonia, uric acid is insoluble in water and can be excreted in a semi-solid form. • High energy cost!!! More so than making urea. Requires a considerable amount of ATP for synthesis from ammonia

41. Nitrogenous wastes • In general the kind of nitrogenous waste depends on the organism’s evolutionary history, habitat and availability of water. • In some species individuals can change forms of nitrogenous wastes when environmental conditions change. • Over time evolution determines the limits of physiological responses for a species, but during their lives, individual organisms make physiological adjustments within these evolutionary constraints. • Finally the amount of waste produced is coupled with the amount and what the animal consumes.

42. Diverse excretory systems are variations on a tubular theme.

43. Excretory systems • Excretory systems produce urine by refining a filtrate derived from body fluids. • The key functions of excretory systems are filtration and the production of urine from the filtrate by selective reabsorption, and secretion.

44. Key functions • Filtration- pressure-filtering of body fluids, producing a filtrate. • Production of urine form the filtrate by selective reabsorption- reclaiming valuable solutes from the filtrate • Secretion- addition of toxins and other solutes from the body fluids to the filtrate.

45. LE 44-9 Capillary Filtration Excretory tubule Filtrate Reabsorption Secretion Urine Excretion

46. Excretory varieties of Flatworms • A Protenephridium is a network of dead end tubules lacking internal openings. • The tubules branch throughout the body and the smallest branches are capped by a cellular unit called a flame bulb. • The flame bulb has cilia that draw water and solutes from the interstitial fluid through the flame bulb and then moves the urine outward through the tubules until they empty into the environment through pores called nephridiopores.

47. Flame bulbs • The tubules reabsorb most solutes before the urine exits the body. • Function mainly in osmoregulation • Most metabolic wastes diffuse out of the animal through the body surface or are excreted into the gastrovascular cavity and eliminated through the mouth.

48. LE 44-10 Nucleus of cap cell Cilia Interstitial fluid filters through membrane where cap cell and tubule cell interdigitate (interlock) Tubule cell Flame bulb Protonephridia (tubules) Tubule Nephridiopore in body wall

49. Metaphridia • Another type of excretory system is called Metanephridia. • Found in most annelid • Each segment of an earthworm contains a pair of metaphridia, which are emmersed in coelomic fluid and enveloped by a capillary network. • The internal opening is surrounded by a ciliated funnel called the nephrostome.

50. LE 44-11 Coelom Capillary network Bladder Collecting tubule Nephridio- pore Nephrostome Metanephridium