Ch. 44

1. Osmoregulation and Excretion Ch. 44

2. A Balancing Act Maintaining the fluid environment of cells, tissues, and organs is critical Achieved by… • Osmoregulation • General term for the processes by which animals control solute concentrations and balance water gain and loss • Excretion • Process that rids the body of nitrogenous metabolites and other metabolic waste products

3. Osmosis and Osmolarity Osmolarity • Total solute concentration expressed as molarity (mols of solute/liter of solution) • Isoosmotic • Equal concentrations • Hyperosmotic • The solution with greater solute • Hypoosmotic • The solution with less solute

4. Osmotic Challenges Osmoconformer • Isoosmotic with surroundings • Marine animals Osmoregulator • Control internal osmolarity independent of the environment • Freshwater and terrestrial habitats Stenohaline vs. Euryhaline

5. Animals that Live in Waters

6. Animals that Live in Temporary Waters Desiccation • Extreme dehydration is fatal for most animals Anhydrobiosis • Dormant state due to drying up of their habitat • Tardigrades (water bears)

7. Land Animals Body coverings prevent dehydration • Waxy exoskeletons, shells, keratinized skin Mainly lose water by… • Urine and feces • Across the skin • Surfaces of gas exchange organs

8. Forms of Nitrogenous Wastes Ammonia • aquatic animals • Mainly excreted by the gills; little by the kidney • unsuitable for terrestrial b/c it requires lots of water and is extremely toxic if not excreted quickly Urea • Low toxicity but energy costly • ammonia combines with CO2 in the liver

9. Forms of Nitrogenous Wastes Uric acid • land snails, insects, birds, and many reptiles • Relatively nontoxic but the most costly in energy • much less soluble in water • usually eliminated in a pastelike form along with feces

10. Excretory System

11. Diversity of Excretory Systems Flatworms • have neither a circulatory system or coelom • protonephridium instead Protonephridium • network of closed tubules lacking internal openings that branch throughout the body • smallest branches capped by flame bulbs

12. Diversity of Excretory Systems Metanephridia • most annelids • excretory tubules in each segment that have internal openings to collect body fluids • capillaries surround the metanephridium • empties outside the body through the nephridiopore

13. Diversity of Excretory Systems Malpighian tubules • insects, terrestrial arthropods • remove nitrogenous wastes from the hemolymph • empties via the rectum

14. Excretory Systems Urine production – 2 steps • Filtration of body fluids • Modification of filtrate • selective reabsorption of solutes from the filtrate back into body fluids • selective secretion of solutes from body fluids into the filtrate

15. Excretory Processes • Filtration • Water and solutes are forced by pressure out of the blood and into the excretory tubule • Reabsorption • Valuable substances are transported from the filtrate back to body fluids • Secretion • Excretion

16. Excretory Processes • Filtration • Reabsorption • Secretion • toxins, and excess ions are extracted from body fluids and added to the excretory tubule • Excretion • Altered filtrate (urine) leaves the system and the body

17. Diversity of Excretory Systems Vertebrate kidneys • compact organs • large numbers of non-segmentally arranged tubules • dense capillary network

18. Mammalian Kidneys Pair of bean shaped organs • 10 cm long Renal artery • blood enters the kidney Renal vein • blood exits the kidney Urine  ureter  u. bladder  urethra (sphincter muscles control urination)

19. Mammalian Kidneys • Renal cortex and renal medulla Nephrons • functional unit of the kidney • long tubule with associated capillaries Urine formation • Filtration • Reabsorption • Secretion

20. Mammalian Kidneys

21. Filtration • Blood pressure forces fluid (water, salts, urea, and other small molecules) into the kidneys (nephrons) • Capillaries nonselectively filter out blood cells and large molecules • Small molecules enter the nephron • Filtrate produced • glucose, salts, vitamins, nitrogenous wastes, and small molecules

22. Reabsorption • Selective transport of filtrate substances back into the interstitial fluid • Reclaims essential small molecules • sugars, vitamins, organic nutrients, water • Beneficial substances back into body and nonuseful and waste substances into kidneys for excretion

23. Secretion • Plasma is added to the filtrate • Very selective process • utilizes both active and passive transport • Collecting duct receives processed filtrate and transfers urine to renal pelvis

24. A Closer Look at the Nephron Proximal Tubule • Reabsorption of ions Descending Loop of Henle • Reabsorption of H2O (aquaporins) Ascending Loop of Henle • Impermeable to water, NaCl leaves Distal tubule • Regulates K+ and NaCl concentrations Collecting duct • Sends urine to renal pelvis • Some water reabsorption

25. Adaptations of the Vertebrate Kidney to Diverse Environments Mammals  Nephrons ability to get rid of waste and not squander water Extra long loop of Henle producing extremely concentrated urine Short loops for aquatic mammals Reptiles  Nephrons to conserve water Uric acid is the main nitrogen waste molecule Cloaca

26. Adaptations of the Vertebrate Kidney to Diverse Environments Freshwater Fishes and Amphibians  Many nephrons and long loop of Henle Must secrete excess water continuously Produce filtrate at a high rate Marine Bony Fishes  Few and small nephrons lacking a distal tubule Low filtration rate…small glomeruli

27. Hormonal Circuits (negative feedback and transduction pathways) - ADH

28. Hormonal Circuits – Renin-Angiotensin-Aldosterone System JGA- Network of specialized tissues of cells and around afferent arteriole; supplies blood to glomerulus; releases renin

29. Summary