2. Excretion Chapter 9

3. Functions of Excretory Organs Maintain solute concentrations Maintain body fluid volume Remove metabolic end products Remove foreign substances

4. Nitrogen Excretion Nitrogen-based waste compounds derived from proteins and nucleic acids Excretion classified by major waste produced –Ammonotelic – ammonia is the principle waste –Ureotelic – urea is the principle waste –Uricotelic – uric acids and urate salts are the principle wastes

5. Excretory Processes Ultrafiltration –Movement of fluid (e.g. blood) through a semipermeable membrane –Membrane allows small particles to pass with the water, large particles (proteins etc.) remain Active Transport –Movement of solutes against their electrochemical gradients (requires energy) –Secretion – movement of solute into the lumen of the excretory organ –Reabsorption – movement of solute out of lumen

6. Generalized Excretory Organs Sponges, Coelentrates and Echinoderms – none Playhelminths, Nematodes, Annelids – nephridial organs Crustaceans – antenna glands Insects – Malpighian tubules Mollusks and Vertebrates – kidneys

7. Nephridial Organs Common in invertebrates System of tubes –connected to the outside through nephridial pore Protonephridia –Found in acoelous and pseudocoelous animals (platyhelminths, nematodes, etc.) –Blind-ended tubes with flame cells or solenocytes at closed end Create current Draw fluid in from surrounding tissues (filtration) Water then reabsorbed

8. Nephridial Organs Metanephridia –Coelous Animals (e.g., annelids) –Inner cells open into coelomic cavity –Four components: Nephrostome – funnel-shaped filter Coiled tubule – secretion and absorption Bladder – storage Nephridial pore

9. Antennal Gland Crustaceans Paired glands located in the head Consist of initial sac, long coiled excretory tubule and terminal bladder –Excretory pore at base of antenna

10. Malpighian Tubules Arachnids and insects Specialized region of digestive tract –Located btw midgut and hindgut Blind-ended tubules –Blind ends locates in hemocoel –Some end near rectum

11. Malpighian Tubules and Rectum NO ultrafiltration –Active secretion of K + into lumen –H 2 O follows passively along osmotic gradient –Content altered by secretion and absorption Fluid secreted into hindgut Water and solutes reabsorbed in rectum Uric acid precipitates

12. Molluscan Kidneys Associated with pericardial cavities –Ultrafiltration from heart –Secretion/reabsorption by renopericardial canal –Stored in bladder (renal sac) –Released into mantle and expelled

13. Vertebrate Kidneys Ultrafiltration followed by reabsorption –Blood plasma is filtered, then important solutes and water reabsorbed into the blood –99% of filtered material is reabsorbed –Allows animals to filter out new substances without developing new specialized secretory mechanisms

14. Vertebrate Kidneys Consists of numerous tubular units called nephrons

15. Kidney Blood delivered into the glomerulus –Tuft of fenestrated capillaries –Site of filtration (blood pressure forces filtered plasma out) –Filtrate collected by Bowman’s capsule

16. Kidney Enters tubular structures Proximal tubule –Reabsorption of solutes and water Distal tubule –Further reabsorption and secretion Collecting duct –Join several distal tubules

17. Kidney Loop of Henle (mammals and birds) Thin, single loop between proximal and distal tubules Allows formation of hyperosmotic urine

18. Glomerular Filtration Occurs through fenestrated capillaries –Plasma with small particles filters out –Blood cells and plasma proteins remain Blood pressure must exceed colloid osmotic pressure

19. Tubular Secretion Removal of excess ions (K +, Ca 2+, Mg 2+, H + ) Removal of foreign substances Active Transport

20. Tubular Reabsorption Active transport of inorganic ions Na + Coupled transport of glucose, amino acids, etc. Osmotic uptake of water

21. Hyperosmotic Urine Mammal kidneys can excrete a hyperosmotic urine –concentrating mechanism occurs in the Loop of Henle Countercurrent Multiplication –generates osmotic gradient that draws H 2 O out of the tubules to be reabsorbed –due to active reabsorption of Na + and Cl -

22. Loop of Henle Mechanism –descending limb permeable to water –ascending limb impermeable to water lined w/ ion pumps (Na + or Cl - )

23. Loop of Henle: Ascending Limb Na and Cl actively transported out of lumen urea flows out of lumen in thin segment of ascending limb Creates osmotic gradient

24. Loop of Henle: Descending limb osmotic gradient generated btw interstitial fluid and lumen H 2 O moves out of the lumen Filtrate concentrated to hyperosmotic levels Water leaving lumen diffuses into the vasa recta (re-enters blood)

25. Loop of Henle: Ascending limb osmotic concentration  ’s as solutes are moved out of the filtrate by active Na + transport

26. Collecting Duct Water flows out as tubule descends into medulla Water leaving lumen diffuses into the vasa recta (re-enters blood) Final urine produced is hyperosmotic

27. Loop Length and Aridity Relative length of the loops is longer in animals adapted to dry habitats than in those from wetter habitats