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Chapter 44: Maintaining a Constant Internal Environment (Homeostasis) 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) Heat Gain/Loss 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) 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 Endotherms/Ectotherms 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 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 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 Insulation Hair Feathers Blubber, fat Reduces the loss of heat Allows maintenance of higher body temps Insulation Thermoregulation in Humans Thermoregulation in Humans Heat receptors in skin Receptors send hot/cold signal to hypothalamus (brain) Hypothalamus regulates vasodilation and vasoconstriction 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 Hibernation Bears, squirrels go into a deep sleep during winter in order to avoid harsh conditions Very low energy demands Very low metabolic rate Hibernation 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]) 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 Osmoregulation 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 Nitrogenous Waste 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 Malpighian Tubules Remove nitrogenous wastes from open circulatory system of insects 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 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 Human Kidney 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 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 Kidneys Kidneys give terrestrial vertebrates the ability to regulate their osmotic balance Without kidneys, life on land would not be possible