LE 40-12River otter (endotherm)Largemouth bass (ectotherm)Ambient (environmental) temperature (°C)0 10 20304040Body temperature (°C)302010LE 40-10800,000Endotherms340,000Annual energy expenditure (kcal/yr)Basal(standard)metabolismReproductionTemperatureregulationGrowthActivity60-kg female humanfrom temperate climate4-kg male Adélie penguinfrom Antarctica (brooding)4,0000.025-kg female deer mousefrom temperateNorth America4-kg female pythonfrom Australia8,000EctothermTotal annual energy expenditures. The slices of the pie charts indicate energy expenditures for various functions.Energy expenditures per unit mass (kcal/kg•day). Comparing the daily energy expendituresper kg of body weight for the four animals reinforces two important concepts ofbioenergetics. First, a small animal, such as a mouse, has a much greater energy demandper kg than does a large animal of the same taxonomic class, such as a human (bothmammals). Second, note again that an ectotherm, such as a python, requires much lessenergy per kg than does an endotherm of equivalent size, such as a penguin.Energy expenditure per unit mass(kcal/kg•day)43823336.55.5PythonHumanDeer mouseAdélie penguinLE 40-21Thermostat inhypothalamusactivates coolingmechanisms.Increased bodytemperature (suchas when exercisingor in hotsurroundings)Body temperaturedecreases;thermostatshuts off coolingmechanisms.Sweat glands secretesweat that evaporates,cooling the body.Blood vesselsin skin dilate:capillaries fillwith warm blood;heat radiates fromskin surface.Body temperatureincreases;thermostatshuts off warmingmechanisms.Decreased bodytemperature(such as whenin coldsurroundings)Blood vessels in skin constrict, diverting bloodfrom skin to deeper tissuesand reducing heat lossfrom skin surface.Skeletal muscles rapidlycontract, causing shivering,which generates heat.Thermostat in hypothalamusactivateswarmingmechanisms.Homeostasis:Internal body temperatureof approximately 36–38°CHomeostatic mechanismsmanage an animal’s energybudget• Nearly all of an animal’s ATP generation is based onoxidation of energy-rich molecules: carbohydrates,proteins, and fatsGlucose Regulation as anExample of Homeostasis• Animals store excess calories as glycogenin the liver and muscles and as fat• Glucose is a major fuel for cells• Hormones regulate glucose metabolism• When fewer calories are taken in than areexpended, fuel is taken from storage andoxidizedLE 41-3STIMULUS:Blood glucoselevel risesafter eating.STIMULUS:Blood glucoselevel dropsbelow set point.Homeostasis:90 mg glucose/100 mL bloodAn animal’s diet must supplycarbon skeletons and essentialnutrients• An animal must obtain carbon skeletonsfrom its food to build complex molecules• Besides fuel and carbon skeletons, adiet must supply essential nutrients inpreassembled form• A malnourished animal is missing oneor more essential nutrients in its dietHow do we know whichnutrients are essential?Beriberi• Japanese sailors around the turn of thecentury fell victim, in large numbers, tothis disease• Characterized by emaciation,weakness, emotional disturbance, andeventually heart failureBeriberi• Sailors adhering to the British naval dietdidn’t develop the disease• In a Manila prison, prisoners that hadbeen switched from the crude brownrice diet to a more pleasing polishedwhite rice diet developed beriberi• Beriberi is caused by a lack of thevitamin Thiamine• Scurvy is caused by a lack of Vitamin
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