1. Osmoregulation and Excretion

2. 44.1 OSMOSIS Cells require a balance between osmotic gain and loss of water Water uptake and loss are balanced by being isoosmotic, hyperosmotic, or hypoosmotic

3. Osmotic Challenges  Osmoconformers—only marine animals, do not regulate their osmolarity  Osmoregulators

4. Transport Epithelia  ultimate function of osmoregulation is to maintain the composition of cellular cytoplasm  water balance and waste disposal depend on this  Components of transport epithelia are essential for tempering changes in body fluid and metabolic waste disposal

5. 44.2 Forms of Nitrogenous Waste  Ammonia  Most common in aquatic species—requires the use of large amts. of water  Can be excreted and transported only in large volumes of very dilute solutions

6. Urea  mammals, adult amphibians, sharks and other marine bony fishes, and turtles excrete by urea  main advantage: low toxicity—allows animals to transport and store urea safely at high concentrations  main disadvantage: animals must use up energy to produce urea from ammonia

7. Uric Acid  excreted by land snails, insects, and many reptiles, including birds  largely insoluble in water and can be excreted as a semi-solid paste with very little water loss  Good for animals with little access to water

8. 44.3 Excretory Processes  1. body fluid is collected (blood, coelomic fluid, or hemolymph)  -involves filtration  - new fluid is filtrate  -Excretory system produces urine from the filtrate after extracting valuable solutes from it and concentrating it  2. selective reabsorption  3. secretion  4. Excretion. Filtrate leaves the system and body

9. Survey of Excretory Systems  Protonephridia:Flame-Bulb Systems  excreted urine is very dilute in freshwater flatworms, helping balance the osmotic uptake of water from the environment  flame-bulb systems function mainly in osmoregulation  found in flatworms rotifers, some annelids, the larvae of molluscs, and lancelets--which are invertebrate chordates

10. Metanephridia  -Malpighian tubule: an excretory organ of insects that empties into the digestive tract, removes nitrogenous wastes from the hemolymph, and functions in osmoregulation  -highly effective in conserving water

11. Vertebrate Kidneys  -function in both excretion and osmoregulation  -made of tubules

12. 44.4 Structure and Function of the Nephron and Associated Structures  Pathway of the Filtrate  filtrate passes through the proximal tubule, loop of the Henle, and the distal tubule  collecting duct: location in the kidney where filtrate from renal tubules is collected; filtrate called urine  only mammals and birds have JGA’s. nephrons of other vertebrates lack loops of Henle  enable mammals to produce urine that is hyperosmotic to body fluids—adaptation important for the conservation of water

13. Blood Vessels Associated with the Nephrons  afferent arteriole  efferent arteriole  peritubular capillaries  vasa recta  excretory tubules and surrounding capillaries do not exchange materials directly  exchange facilitated by the relative direction of blood flow and filtrate flow in the nephrons

14. From Blood Filtrate to Urine: A Closer Look  1. Proximal Tubule.  most important function is reabsorption of most of the NaCl and water from the huge initial filtrate volume  salt and water now diffuse from interstitial fluid into peritubular capillarie 2. Descending on the loop of Henle. - here the transport epithelium is freely permeable to water but not very permeable to salt and other small solutes

15. Cont…  3.Ascending limb of the loop of Henle.  permeable to salt but not water  2 specialized regions: thin segment near loop tip, and thick segment adjacent to distal tubule 4. Distal Tubule. -key role in regulating the K+ and NaCl concentration of body fluids by changing the amount of K+ that is secreted into the filtrate and the amt. of NaCl reabsorbed from the filtrate

16. Cont…  5. Collecting duct.  in inner medulla duct becomes permeable to urea  some urea diffuses out of duct into interstitial fluid because of high urea concentration  high osmolarity allows mammalian kidney to conserve water by excreting urine that is hyperosmotic to general body fluids

17. 44.5 Solute Gradients and Water Conservation  Kidney is a water conserving organ  loop of Henle has several qualities of a countercurrent multiplier system  maintains a high salt concentration in the interior of kidney  enables the kidney to form concentrated urine -2 primary solutes in this molarity gradient: urea, and NaCl

18. Regulation of Kidney Function  kidney can adjust the volume and osmolarity of urine, depending on animals water and salt balance and rate of urea production  can get rid of excess water with little salt loss by producing large volumes of hypoosmotic urine  ADH promotes water retention by kidneys  part of complex feedback scheme that helps regulate the osmolarity of the blood

19. Cont…  if a large intake of water has reduced blood osmolarity below set point, little ADH is released  ADH and RAAS increase water reabsorption but counter different osmoregulatory problems  ADH, RAAS, and ANF provide a system of checks and balance

20. 44.6 Diverse adaptations of the vertebrate kidney have evolved in different environments  form and function of nephrons in various vertebrates are related mostly to the requirements of omsoregulation in the animal’s habitat