Osmoregulation and Excretion

1. Osmoregulation and Excretion A.P. Biology Ch. 44 Rick L. Knowles Liberty Senior High School

2. Osmoregulation • Maintaining a balance of both water and ions across a membrane/organism. Solute and water homeostasis. • Osmolarity – moles of total solute per liter of water; usually in milliosmoles/L. • Mechanism of homeostasis varies with the environment in which they’ve adapted (freshwater, saltwater, terrestrial).

3. Some Comparison Freshwater 0.5 -15 0 300 Human Plasma 1,000 Seawater 5,000 Dead Sea Distilled,deionized Water Milliosmoles/L (mosm/L)

4. Figure 44.2 • Most animals are said to be stenohaline: • And cannot tolerate substantial changes in external osmolarity; both osmoconformers and osmoregulators. • Euryhaline animals: • Can survive large fluctuations in external osmolarity. Tilapia, freshwater up to 2,000 mosm/L

5. Osmoregulation and Nitrogenous Wastes • Other waste solutes must be removed from cells and organisms. • A waste product of metabolizing amino acids and nucleic acids (deamination)- ammonia.

6. Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitat. • The type and quantity of an animal’s waste products: • May have a large impact on its water balance.

7. Ammonia • Direct by-product of protein and nucleic acids (deamination). • Very toxic to cells. • Highly soluble in water. • Molecule of choice for freshwater organisms; eliminated easily through kidneys, gill epithelia, etc. • Downside: requires a lot of water.

8. Urea • Saltwater and terrestrial mammals convert ammonia into urea. • Less toxic; accumulate more in tissue. • Less soluble in water than ammonia. • Allows conservation of water.

9. Uric Acid • Birds and reptiles accumulate waste in an egg. • Convert ammonia into uric acid. • Insoluble in water; crystallizes. • Semisolid paste-guano. • Requires less water to eliminate.

10. Nucleic acids Proteins Nitrogenous bases Amino acids –NH2 Amino groups Many reptiles (including birds), insects, land snails Most aquatic animals, including most bony fishes Mammals, most amphibians, sharks, some bony fishes O H C N C HN C O NH2 C C C O N N O NH3 NH2 H H Ammonia Urea Uric acid • Among the most important wastes • Are the nitrogenous breakdown products of proteins and nucleic acids Figure 44.8

11. Osmoconformers • Most marine protists and invertebrates. • Are isoosmotic with marine environment. • Open channels and carriers for most ion transport (Not all ions are in equilibrium). • Ex. Invertebrates like sea anemones, jellyfish, and only vertebrate, Class Agnatha- hagfish.

12. Class Agnatha- Hagfish

13. Show me a real hagfish! Video: Discovery- Blue Planet: Ocean World

14. Osmoregulators • Maintain constant osmotic concentration in body fluids and cytoplasm despite external variations. • Continuous regulation since environment and intake (diet) changes. • Evolved special mechanisms for different environments. • Ex. Most Vertebrates

15. The Problems • Freshwater Vertebrates- are hyperosmotic, water enters body, tend to lose ions. • Marine Vertebrates- are hypoosmotic, water leaves body, tend to gain ions. • Terrestrial Vertebrates- are hypoosmotic, water leaves body through respiration, perspiration, skin.

16. Freshwater Protists • Problem: hyperosmotic; impossible to become isoosmotic with dilute fresh water; tend to gain water; lose ions; no excretory organ. • Solution:Contractile Vacuoles – active transport of water out of cell; less permeable to ions • Downside: Active transport requires energy.

17. Freshwater Invertebrates • Water and wastes are passed into a collecting vessel or primitive excretory organ. • Membrane retains proteins and sugars and allows water and dissolved wastes to leave-selectively permeable. • Ex. Freshwater jellyfish, etc,

18. Concept 44.3: Diverse excretory systems are variations on a tubular theme. • Excretory systems: • Regulate solute movement between internal fluids and the external environment.

19. Capillary 1 Filtration. The excretory tubule collects a filtrate from the blood. Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule. Excretory tubule Filtrate 2 Reabsorption. The transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids. 3 Secretion. Other substances, such as toxins and excess ions, are extracted from body fluids and added to the contents of the excretory tubule. 4 Excretion. The filtrate leaves the system and the body. Urine Excretory Processes • Most excretory systems • Produce urine by refining a filtrate derived from body fluids Figure 44.9

20. 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 Protonephridia: Flame-Bulb Systems • A protonephridium: • Is a network of dead-end tubules lacking internal openings. Figure 44.10

21. The tubules branch throughout the body: • And the smallest branches are capped by a cellular unit called a flame bulb. • These tubules excrete a dilute fluid: • And function in osmoregulation

22. Coelom Capillary network Bladder Collecting tubule Nephridio- pore Metanephridia Nephrostome Metanephridia • Each segment of an earthworm • Has a pair of open-ended metanephridia Figure 44.11

23. Metanephridia consist of tubules: • That collect coelomic fluid and produce dilute urine for excretion.

24. Terrestrial Insects • Problem: Must minimize water loss. • Solution: Use chitin as an exoskeleton.

26. Digestive tract Rectum Hindgut Intestine Malpighian tubules Midgut (stomach) Salt, water, and nitrogenous wastes Feces and urine Anus Malpighian tubule Rectum Reabsorption of H2O, ions, and valuable organic molecules HEMOLYMPH Malpighian Tubules • In insects and other terrestrial arthropods, malpighian tubules • Remove nitrogenous wastes from hemolymph and function in osmoregulation Figure 44.12

27. Malpighian Tubules K+ Hemolymph Water and K+ K+ Water and waste K+ Na+/K+-ATPase Conc. Waste Hindgut

28. Malpighian Tubules • Use Malpighian tubules- blind end tubules that extend into hemocoel (body cavity). • Cells  waste and salts into hemolymphlumen of tubule by diffusion and active transport. • K+ are actively transported into lumen; set up a gradient. • Water and other ions leave the hemolymph and follow into the lumen by passive diffusion. • Empty into hindgut; water reabsorbed; urine is concentrated. • Na+/K+-ATPase moves ions from lumen of hindgut into hemolymph.

29. Insects versus other Vertebrates • Insects use a gradient to pull water through a membrane; open circulatory system = low blood pressure. • Vertebrates- push water through a membrane; closed circulatory system = higher blood pressure.

30. More Complex Organisms Need Another Solution Introducing the Vertebrate Kidney!

31. Nephron (Tubule)

40. Gill Epithelia is Permeable

41. Hypotonic Env. Hypertonic Cells Water

42. Freshwater Bony Fishes • Problems: Water enters cells from environment, solutes leave cells. • Solutions: Drink very little water; excrete large amounts of dilute (hypoosmotic) urine with large kidneys; reabsorb ions in kidney tubules (active transport) back into blood; use chloride cells in gill epithelium (active transport).

43. 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 • Freshwater animals maintain water balance: • By excreting large amounts of dilute urine. • Salts lost by diffusion: • Are replaced by foods and uptake across the gills. Figure 44.3b (b) Osmoregulation in a freshwater fish

44. Hypotonic Cells Water Hypertonic Env.

45. Saltwater Bony Fishes • Problem: Tend to lose water, gain ions, mostly at gills. • Solutions: Drink large amount of water; kidney retains water and excretes ions (isoosmotic urine); use chloride cells in gills to actively transport some ions across gill epithelium.

46. 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 • Marine bony fishes are hypoosmotic to sea water: • Lose water by osmosis and gain salt by both diffusion and from food they eat. • These fishes balance water loss: • By drinking seawater. Figure 44.3a (a) Osmoregulation in a saltwater fish

47. Cartilaginous Fishes • Problem: Same as marine bony fishes. • Solution: Reabsorb urea from nephron tubule back into the blood; 100X blood [urea] than mammals (special protective solute,TMAO to protect proteins)blood is slightly hyperosmotic kidneys and gills do not have to remove ions; do not have to drink large volume of water.

48. Cartilaginous Fishes • Problem: Still must remove excess Na+ and Cl- that diffuse across gills, diet, etc. • Solution:Rectal Gland- uses Na+/K+-ATPase pumps to actively transport Na+ and Cl- out of blood by setting up a gradient.