OSMOREGULATION & EXCRETION

1. OSMOREGULATION & EXCRETION Chapter 44

2. OVERVIEW • Osmoregulation • Relative concentrations of water and solutes must be maintained in a variety of environments (land, freshwater, marine) • Excretion • Metabolism creates waste that must be expelled from the body • Proteins and nucleic acids present a problem because ammonia (primary waste product) is toxic

3. 44.1 ~ OSMOREGULATION • Balancing the uptake and loss of water and solutes over time. If they don’t osmosis will cause animal cells to swell and burst or shrivel and die. • Isoosomotic = two solutions with the same osmolarity • Hyperosmotic = solution with the greater concentration of solutes • Hyposomotic = solution with the more dilute concentration of solutes • Water flows from a hyposomotic solution to a hyperosmotic one.

4. TWO BASIC SOLUTIONS • #1 (only available to marine animals) is to be isoosomotic with the environment. • Osmoconformer • Does not adjust its internal osmolarity • Live in water that is fairly stable • #2 (available to any animal) is to control its internal osmolarity because body fluids are NOT isoosmotic with the outside environment. • Osmoregulator • Body fluids are not isoosomotic with surroundings • Enables animals to live in diverse environments • Has an energy cost (active transport of solutes)

5. COST OF OSMOREGULATION • Depends on: • How different osmolarity is from the surroundings • How easily water & solutes move across the animal’s surface • How much work is required to pump solutes across the membranes • Ranges from 5% to 30% of total resting metabolic rate

6. STENOHALINE VS. EURYHALINE • Stenohaline – narrow salt; Most animals cannot tolerate substantial changes in external osmolarity • Euryhaline – broad salt; Animals that can survive large fluctuations in external osmolarity. • Examples: Salmon, Talapia

7. MARINE ANIMALS • Most marine invertebrates are osmoconformers • Marine vertebrates and some invertebrates are osmoregulators • Ocean is strongly dehydrating because it is much saltier than than internal fluids and water is lost by osmosis • Balance water loss by drinking large amounts of seawater • Salt is actively pumped out of gills and passed through urine

8. FRESHWATER ANIMALS • Problems are opposite those of marine animals • Freshwater animals are constantly gaining water by osmosis and losing salt by diffusion • Maintain water balance by excreting large amounts of very dilute urine and taking in salt by the gills

10. TEMPORARY WATERS • Anhydrobiosis “life without water” – animals can survive in a dormant state when their habitats dry up • Water bears • Survive for a decade or more in inactive state

11. LAND ANIMALS • Desiccation “drying up” is a huge problem for land animals • Adaptations that help land animals avoid drying up: • Waxy layers of insects exoskeleton • Shells of land snails • Layers of dead keratinized skin • Nocturnal • Drinking and eating moist foods • Using metabolic water (water produced during cellular respiration)

12. 44.2 ~ NITROGENOUS WASTES • When proteins and nucleic acids are broken down nitrogenous wastes are produced • When these macromolecules are broken apart for energy ammonia (NH3) is produced which is very toxic • Three forms of ammonia that animals secrete • Ammonia • Urea • Uric acid

13. AMMONIA • Very soluble but only tolerated at low concentrations so must be released in lots of water • Aquatic species (fish)

14. UREA • Substance produced in the vertebrate liver by metabolic cycle that combines ammonia with carbon dioxide • System carries urea to kidneys where it is excreted • Mammals, adult amphibians, sharks, marine bony fishes, turtles • Advantage: low toxicity and requires less water • Disadvantage: expend energy to produce it from ammonia

15. URIC ACID • Largely insoluble in water and can be excreted as a semi solid paste with very little water loss • Insects, land snails, reptiles, birds • Relatively non-toxic • Requires considerable ATP to produce (more than Urea)

17. EVOLUTION & ENVIRONMENT ON WASTE • Uric acid can be stored within the reptilian egg as a harmless solid left behind when the animal hatches • Type of waste produced by vertebrates depends on habitat

18. 44.3 ~ STEPS OF URINE PRODUCTION • 1. Filtration – body fluids are filtered to keep the good stuff in the body fluids and put the bad stuff in the filtrate • 2. Reabsorption – filtering the filtrate to make sure none of the “good stuff” is kept in the filtrate (active transport to reclaim valuable substances in body fluids) • 3. Secretion – filtering the body fluid to make sure all of the “bad stuff” is in the filtrate • 4. Excretion – filtrate leaves the body (urine)

20. Good stuff: cells, proteins, large molecules, valuable solutes such as glucose, • Bad stuff: water, small solutes such as salts, sugars, amino acids, and nitrogenous wastes. Nonessential solutes and wastes

21. SURVEY OF EXCRETORY SYSTEMS • Protonephridia: Flame-bulb system • Flatworms • Functions in osmoregulation (wastes diffuse out through body surface)

22. Metanephridia • Annelids

23. Malpighian Tubules • Insects and terrestrial arthropods

24. Vertebrate Kidneys • Function in osmoregulation and excretion

25. 44.4 ~ MAMMALIAN KIDNEY • Site of water balance, salt regulation and excretion • Pair of kidneys • Each 10 cm long (kidney bean shaped) • Supplied with blood by a renal artery and drained by a renal vein • Urine exits through ureter and drains into urinary bladder • Urine is excreted from urinary bladder through the urethra

26. STRUCTURE & FUNCTION OF NEPHRON • 2 regions to the kidney • Outer renal cortex • Inner renal medulla • Functional unit of the kidney is the nephron – consists of single long tubule and a ball of capillaries called the glomerulus • Bowman’s capsule – cup shaped swelling that surrounds the glomerulus • Each human kidney contains a million nephrons

28. Filtration happens as blood pressure forces fluid from the blood in the glomerulus into the Bowman’s capsule. • Filtration is nonselective and filtrate contains: salts, glucose, amino acids, vitamins, nitrogenous wastes and other small molecules • Pathway of filtrate – see figure 44.14

30. Between 1,100 to 2,000 L of blood flows through a pair of human kidney’s each day. • Nephrons process about 180 L of initial filtrate • Nearly all sugar, vitamins, other organic nutrients and about 99% of the water are reabsorbed into the blood leaving only about 1.5 L of urine to be voided per day • 4 steps are completed in: • Proximal tubule • Descending limbo of the loop of Henle • Ascending limb of the loop of Henle • Distal tubule • Collecting duct

31. 44.5 ~ WATER CONSERVATION IS A KEY TO TERRESTRIAL ADAPTATION • As the filtrate flows in the collecting duct past interstitial fluid of increasing osmolarity, more water moves out of the duct by osmois, thereby concentrating the solutes, including urea, that are left behind in the filtrate.

32. REGULATION OF KIDNEY FUNCTION • If a lot of salt is brought in with low water availability the mammal can excrete urea and salt with little water loss in hyperosmotic urine. • If salt is scarce and fluid intake is high the kidney can get rid of the excess water with little salt loss by producing large volumes of hypoosmotic urine • Regulated through nervous and hormonal controls • ADH – antidiuretic hormone • RAAS – renin-angiotensin-aldosterone system • ANF – atrial natriuretic factor

34. ADH is a response to an increase in the osmolarity of the blood – when the body is dehydrated. • RAAS – responds when a situation that causes an excessive loss of both salt and body fluids (injury, severe diarrhea)

35. 44.6 ~ DIVERSE ADAPTATIONS