Chapter 50 Temperature, osmotic regulation and the urinary system

Regulating body temperature Q10 is the ratio of reaction at two temperatures 10degreeC apart. Body temperature is determined by internal factors such as metabolism and external factors that affect heat transfer. Body heat = heat produced + heat transferred In biological systems, the heat transfer takes place by radiation, conduction, convection and evaporation Surface area, temperature difference and specific heat conduction are other factors influencing heat transfer

Classification of animals based on heat source Ectotherms/cold blooded/poikilotherms maintain a body temperature that conforms to ambient temperature and do not use metabolism to produce heat. Endotherms/warm blooded/homeotherms use metabolism to generate body heat and maintain their temperatures above ambient temperature. These have insulating mechanisms Heterotherms falls between the two categories

How do ectotherms regulate temperature? Invertebrates regulate temperature via behavior. Example: Butterflies must reach a certain body temperature before they can fly Countercurrent heat exchange-Some fishes can maintain their body temperature at higher temperature than that of water How do endotherms regulate temperature? When temperatures are cold, the organism can keep itself warm by generating internal heat via high metabolic rate When temperatures are warm, the organism can keep itself cool by dissipating heat energy in form of sweating or panting Smaller animals consume more energy per unit body mass than larger animals (high metabolic rate) and require more insulation in colder environments.

What is thermogenesis? Thermogenesis is the use of normal energy metabolism to produce heat (when endothermic responses are not sufficient to warm an animal) Two forms: Shivering and Non-shivering thermogenesis Non-shivering – fat deposits are used to provide heat Shivering thermogenesis – Some insects uses muscles to generate heat – Flight muscles in butterflies warm up How mammalian thermoregulation is controlled by hypothalamus? When temperature goes beyond 37 degree, then heat-losing centre in hypothalamus gets stimulated, blood vessels dilate and sweat is released When temperature goes below 37 degree, then heat-promoting centre gets stimulated, blood vessels constrict to reduce heat transfer and raise temperature of body

Various osmoregulatory organs of different animals Invertebrates use specialized cells and tubules - Flatworms draw fluids from their bodies into flame cells, water and metabolites are reabsorbed, excreted substances are expelled through pores in the body wall (figure 50.7) In earthworms, the internal fluid is collected in the nephrostomes and filtered, NaCl is reabsorbed by active transport (figure 50.8) The Malpighian tubules of insects secrete potassium ions into the gut which pull body fluids and waste past their filtering apparatus (figure 50.9) Vertebrates use the pressure-driven filtration system of the kidney. Certain small molecules (glucose, aminoacids, and vitamins etc) are selectively reabsorbed in the kidneys to help conserve water (figure 50.10)

Different forms of excretion of nitrogenous wastes (figure 50.13) Catabolism of amino acids and nucleic acids forms ammonia as by-product. Ammonia is directly eliminated in fish Mammals, Amphibians and cartilaginous fishes excrete urea Birds and reptiles excrete uric acid (ammonia converted to uric acid). Energy is lost but saves water Some mammals have uricase enzyme which convert uric acid to (soluble) allantoin

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