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