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Chapter 44: Maintaining a Constant Internal Environment (Homeostasis)

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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

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