Chapter 44: Maintaining a Constant Internal Environment (Homeostasis)

1. Chapter 44:Maintaining a Constant Internal Environment (Homeostasis)

2. Body Temperature • Enzymes: Rxn rates inc. 2-3 times with each 100 C temp. inc. (until denatured) • Each species has an optimal temp. range for metabolic rxns to be efficient • Thermoregulation Organisms maintain their body temp within optimal range (various methods)

3. Heat Gain/Loss

4. Heat Gain/Loss (HIGH to LOW) • Conduction = molecule to molecule (ie: hot concrete and feet in summer) • Convection = heat transfer b/t object and H2O or air moving across it • Radiation = electromagnetic waves transferred as heat (ie: suns rays) • Evaporative Cooling = lowers temp by releasing H2O as vapor (ie: sweating)

5. Ectotherms and Endotherms • Ectotherms (“cold-blooded”) maintain a temperature close to external temp. • Low metabolic requirements (little heat generated) • Most fish, reptiles, amphibians • Endotherms (“warm-blooded”) maintain a constant temp. that may vary significantly from external temp (species dependent) • High metabolic rate (lots of heat!) • Humans, other mammals, and birds

6. Endotherms/Ectotherms

7. Endothermic Advantages • Higher temp allows for inc. metabolic rate • More energy is generated • Can perform more vigorous activities for more sustained periods • Allows terrestrial life (more temp. fluctuations than H2O) • Disadvantage : Require more frequent meals for higher aerobic resp. rate

8. Vasodilation and Vasoconstriction • Vasodilation Blood vessels dilate (expand) in order to release more heat • Vasoconstriction  Blood vessels constrict in order to limit heat loss in the cold

9. Behavioral Controls • Basking in the sun to raise body temp • Hibernation • Migration to different climates (birds) • Inc or dec metabolic rate in hot/cold temps • Certain insects huddle to generate more heat

10. Insulation • Hair • Feathers • Blubber, fat • Reduces the loss of heat • Allows maintenance of higher body temps

11. Insulation

12. Thermoregulation in Humans

13. Thermoregulation in Humans • Heat receptors in skin • Receptors send hot/cold signal to hypothalamus (brain) • Hypothalamus regulates vasodilation and vasoconstriction

14. Extreme Hot/Cold Environments • Cryoprotectants Certain organisms (some frog eggs, arctic fish) have a biologically produced antifreeze • Heat shock proteins  Produced in response to heat. Bind to enzymes and other proteins to inhibit denaturization

15. Hibernation • Bears, squirrels go into a deep sleep during winter in order to avoid harsh conditions • Very low energy demands • Very low metabolic rate

16. Hibernation

17. Osmoregulation (Water Balance) • Organisms must balance their water and solute concentrations • Water uptake and loss must remain essentially equal • Cells could swell or shrivel • Water flows from high water potential (low [solute]) to low water potential (high [solute])

18. Osmoregulators/Osmoconformors • Osmoregulators maintain a constant solute concentration different from that of ext. environment • Freshwater, terrestrial, some marine • Costs energy (active transport) • Osmoconformers maintain solute concentration equal to that of surroundings • Many marine invertebrates

19. Osmoregulation

21. Waste Disposal • Elimination of toxic materials is needed to maintain homeostasis • Nitrogenous wastes are very toxic to living cells • Urea Many terrestrial organisms, lowest toxicity, high energy requirement (humans) • Uric Acid  Birds, insects reptiles, least water lost • Ammonia  Fish, aquatic organisms, most toxic

22. Nitrogenous Waste

23. Selective Reabsorption and Secretion • Organisms will filter their wastes and reabsorb anything that may be of use • Accomplished in tubules (present in human kidneys) • May also secrete more waste materials into urine

24. Malpighian Tubules Remove nitrogenous wastes from open circulatory system of insects

25. Vertebrate Urinary System • Kidneys • Function in osmoregulation and reabsorption • Contain a network of tubules • Renal Artery Blood to kidney • Renal Vein Blood from kidney • Ureter  Carries urine to bladder • Bladder  Stores urine • Urethra  Tube that exits the body

26. Vertebrate Kidneys • Two regions • Renal cortex and renal medulla • Contains millions of nephrons • Microscopic tubules • Glomerulus Network of capillaries serving each nephron with a blood supply • Bowman’s Capsule  End of tubule that surrounds the glomerulus

27. Human Kidney

28. Kidneys • nephron and collecting duct are lined by a transport epithelium • process filtrate to form urine • reabsorb solutes and water • sugar, vitamins, and other organic nutrients from the initial filtrate and about 99% of the water • reduce 180 L of initial filtrate to about 1.5 L of urine to be voided

30. Kidney Function • Proximal Tubule NaCl and H2O reabsorption and pH regulation • Descending Loop of Henle  H2O reabsorption • Ascending Loop of Henle  NaCl reabsorption • Distal Tubule  K+ and NaCl balance, pH regulation, some H2O reabsorbed • Collecting Duct  NaCl reabsorption, H2O reabsorption • As it moves through the kidney, urine becomes more concentrated with unusable waste

31. Kidneys • Kidneys give terrestrial vertebrates the ability to regulate their osmotic balance • Without kidneys, life on land would not be possible