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Explore the mechanisms of homeostasis including regulating body temperature, coping with fluctuations, and osmoregulation in different organisms. Learn about the advantages and disadvantages of endothermy, methods of thermoregulation, and adaptation to varying environments.
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Chapter 44 Regulating the Internal Environment
Homeostasis • Thermoregulation • Osmoregulation • Excretion
Homeostasis • All organisms must maintain a constant internal environment to function properly • Temperature • pH • ion levels • hormones
Negative Feedback Body Temperature Regulation
Coping with Environmental Fluctuations Regulating: Endotherms are thermoregulators Fundulus-osmoregulator Conforming: Ectotherms Many inverts- nonregulator
Regulators & Conformers Spider crab Libinia
Four physical processes account for heat gain or loss • Heat exchange by: • Conduction- transfer of heat between objects in direct contact with each other • Convection- heat is conducted away from an object of high temp to low temp • - Rate varies with different materials • Radiation- transfers heat between objects not in direct contact • - sun energy • Evaporation- change of liquid to vapor • - cooling
Advantages of Endothermy : • Maintains stable body temp • Cooling & heating the body • cooling and heating the body • high levels of aerobic metabolism • sustains vigorous activity for much longer than ectotherms • Long distance running • Flight
Disadvantages of Endothermy : • Greater food consumption to meet metabolic needs • Human metabolic mate at 200C & at rest • 1,300 to 1,800 kcal per day. • American alligator metabolic rate at 200C & at rest • 60 kcal per day at 200C.
Mechanisms for thermoregulation • Insulation • Fur • Hair • Feathers • Fat • Blubber • Evaporative cooling • sweating, panting, bathing • Shivering • Nonshivering thermogenesis & brown fat • Circulation adaptations • Countercurrent exchange • Vasodilatation (cooling) • Vasoconstriction (heat conservation) • Behavioral responses
Countercurrent heat exchangers Goose leg Dolphin flipper
Evaporative Cooling Hippos bathing
Brown Fat & Non-shivering Thermogenesis • Brown fat- generates heat • important in neonates, small mammals in cold environments, and animals that hibernate • Located in neck and in inner scapula area • Non-shivering Thermogenesis • Larges amts of heat produced by oxidizing fatty acids in the mitochondria
Acclimatizationto New Env. Temps. • Endotherms (birds and mammals): grow a thicker fur coat in the winter and shedding it in the summer - and sometimes by varying the capacity for metabolic heat production seasonally. • Ectotherms compensate for changes in body temperature through adjustments in physiology and temperature tolerance. • For example, winter-acclimated catfish can only survive temperatures at high as 28oC, but summer-acclimated fish can survive temperatures to 36oC.
Some ectotherms that experience subzero body temperatures protect themselves by producing “antifreeze” compounds (cryoprotectants) that prevent ice formation in the cells. • In cold climates, cryoprotectants in the body fluids let overwintering ectotherms, such as some frogs and many arthropods and their eggs, withstand body temperatures considerably below zero. • Cyroprotectants are also found in some Arctic and Antarctic fishes, where temperatures can drop below the freezing point of unprotected body fluids (about -0.7oC).
Cells can often make rapid adjustments to temperature changes. • For example, marked increases in temperature or other sources of stress induce cells grown in culture to produce stress-induced proteins, including heat-shock proteins, within minutes. • These molecules help maintain the integrity of other proteins that would be denatured by severe heat. • These proteins are also produced in bacteria, yeast, and plants cells, as well as other animals. • These help prevent cell death when an organism is challenged by severe changes in the cellular environment.
Hibernation:long-term torpor as an adaptation to long-term winter cold and food shortage • Torpor in Ground Squirrels • Body temperature: 37oC • Metabolic rate: 85 kcal per day. • During the eight months the squirrel is in hibernation, its body temperature is only a few degrees above burrow temperature and its metabolic rate is very low.
Body Temperature and metabolism during hibernation of Belding’s ground squirrel
Osmoregulation Osmoregulation- the control of the concentration of body fluids. Diffusion- movement of substance from an area of greater concentration to an area of lower concentration Osmosis- diffusion of water through a semipermeable membrane
Adaptation to Marine Environment • Reducing salt • Seabird and marine iguana- nasal salt secreting gland • Sea snake- sublingual gland • Crocodile- lacrimal gland • Fish gills- chloride cells • Shark- rectal gland
Nitrogenous Waste Excretion • Ammonia- toxic • Excrete directly into water- jellies • Detoxifyurea • Urea- need lots of water to get rid of • Uric Acid- birds & reptiles • more costly to produce than urea, but needs less water to be removed
Balancing NaCl in Blood • Osmoconformer: isoosmotic • Osmoregulator: hyper-, hypo-, ureoosmotic • Euryhaline: wide tolerance range • Stenohaline: narrow tolerance range Osmols- total solute concentration in moles of solute/liter of solution
Marine Fish: hypoosmotic Less salt than external environment H2O continually leaves body continually drinks seawater excretes salt through gills produces small amts of dilute urine
Freshwater Fish: hyperosmotic H2O continually enters body does not drinks water More salt than external environment produces large amts of dilute urine
Shark and Coelacanth: ureoosmotic Maintains high levels of urea and TMAO in blood excretes salt through rectal gland coelacanth Rana cancrivora
Hagfish: ionosmotic nonregulator Seawater concentration = internal concentration
Osmolarity in Freshwater and Saltwater Osmolarity- measure of total solutes(dissolved particles) Ions FW m osmol/l SW m osmol/l Na+ 1 470 Cl- 1 550 Ca++ variable 10 Total 10 1000
Habitat Na+ Cl- Urea seawater sw 478 558 hagfish (Myxine) sw 537 542 lamprey fw 120 96 Goldfish (Carassius) fw 115 107 Toadfish (Opsanus) sw 160 Crab-eating frog (Rana) sw 252 227 350 Dogfish sw 287 240 354 freshwater ray fw 150 149 <1 coelacanth sw 197 199 350 Concentration of Ions
Adaptations to Dry Environment • Many desert animals don’t drink water • Kangaroo rats lose so little water that they can recover 90% of the loss from metabolic water and gain the remaining 10% in their diet of seeds. • Also have long loop of Henle
Most excretory systems produce a filtrate by pressure-filtering body fluids into tubules.
Diverse excretory systems are variations on a tubular theme • Flatworms have an excretory system called protonephridia, consisting of a branching network of dead-end tubules. • The flame bulb draws water and solutes from the interstitial fluid, through the flame bulb, and into the tubule system.
Metanephridia consist of internal openings that collect body fluids from the coelom through a ciliated funnel, the nephrostome, and release the fluid through the nephridiopore. • Found in most annelids, each segment of a worm has a pair of metanephridia.
Insects and other terrestrial arthropods have organs called Malpighian tubules that remove nitrogenous wastes and also function in osmoregulation. • These open into the digestive system and dead-end at tips that are immersed in the hemolymph.
