Lecture 5: Thermoregulation PDF

Biol 224.3 – Animal Body Systems Lecture 5: Thermoregulation Dr Joan Forder Supplementary Textbook Reading: Textbook (5th Edition, Chapter 39, page 1043- 1053)...

Biol 224.3 – Animal Body Systems Lecture 5: Thermoregulation Dr Joan Forder Supplementary Textbook Reading: Textbook (5th Edition, Chapter 39, page 1043- 1053) 1 Where we are headed Thermoregulation in Ectotherms Thermal Acclimatization Thermoregulation in Endotherms Negative Feedback: Hypothalamus Negative Feedback: Endocrine system Keeping Warm Keeping Cool Torpor Thermoregulation Animals maintain body temperature at a level that provides optimal physiological performance. Organismal performance: the rate and efficiency of an animal’s biochemical, physiological, and whole-body processes 3 Ectotherms: Review Obtain heat energy primarily from the external environment Most fish, amphibians, and reptiles are Ectotherms Migrating Salmon 4  Thermal Acclimatization Definition: A structural or metabolic change in the limits of tolerable temperatures as the environment alternates between warm and cool seasons. Allows animal to attain good physiological performance at both winter and summer temperatures Could be an increase in specific enzymes that work better at different temperatures Could be a change in phospholipids saturation and cholesterol levels (recall Bio 120) 5 Surviving Freezing Spruce Budworm effects Use of ANTIFREEZE proteins Icefish & Wood Frog 6 Fig. 39.22, p. 1047 Endotherms: Review Obtain heat energy primarily from internal reactions Maintain body temperature over a narrow range Balance internal heat production against heat loss from body surface 7 Temperature Regulation Focus on Birds and Mammals Example of how changes in skin temperature cause changes in core temperature and the body’s attempt to thermoregulate Thermoreceptors detect the change in temperature The Hypothalamus is referred to as the body’s thermostat 8 Fig. 39.23, p. 1048 Hypothalamus: Negative Feedback NOTE: disruption of normal feedback leads to a disease (goiter) 9 Hypothalamus Hypothalamus maintains core homeostatic functions (more than temp). Thyroid - front of throat, wide range of effects through hormones. TRH = thyroid-releasing hormone. TSH = Thyroid stimulating hormone. T3 = triiodothyronine. T4 = thyroxine Iodine needed for thyroid to produce T3 and T4. Too little and thyroid grows larger in an attempt to make more thyroid hormone 10  Effects of Iodine Deficiency Hyper - too much; Hypo - too little Hypo or hyperthyroidism refers to T3 and T4 production, not thyroid size. Do low levels of T3 and T4 cause hypothyroidism? YES! Iodine deficiency results in hypothyroidism. Without iodine, thyroid cannot make T3 and T4 in response to stimulation by TSH. Low T3 and T4 remain low but TSH continues to be secreted, overstimulating the thyroid and making it grow in size while still not being able to make T3 and T4 Negative Feedback: Endocrine System Calcium Regulation Sodium Regulation 12  The Skin and Endothermy Organ of heat transfer Blood vessels of the skin regulate heat loss by constricting (vasoconstriction) or dilating (vasodilation). Skin is water-impermeable, reducing heat lost by direct evaporation of body fluids. An insulating fatty tissue layer under blood vessels limits losses to heat carried by blood. 13 Keeping Warm When thermoreceptors signal a fall in core temperature below the set point, the hypothalamus triggers compensating responses by sending signals through the autonomic nervous system. Immediate responses include the constriction of the arterioles in the skin (vasoconstriction), which reduces the flow of blood to the skin’s capillary networks. (89) VASODILATION and VASOCONSTRICTION _ - YouTube.mhtml 14  Examples of Keeping Warm Many mammals (dogs, for example) have an uneven distribution of fur. Birds and mammals have veins and arteries to their legs. Whales and seals have adjustments of blood flow. Countercurrent Circulation in the 15 Leg of an Arctic Wolf Keeping Cool When the core temperature rises above the set point, the hypothalamus sends signals through the autonomic system to trigger responses that lower body temperature. As an immediate response, the signals relax smooth muscles of arterioles in the skin (vasodilation), increasing blood flow and with it the heat lost from the body surface. 16 Examples of Keeping Cool Birds fly with their legs extended. Penguins expose featherless patches of skin. Elephants dissipate heat from their large ears. 17 Structural and Behavioural Adaptations Penguins Husky dog Jackrabbit Elephants 18 Fig. 39.26, p. 1051 Temperature Variations Deer Mouse The temperature set point in many birds and mammals varies in daily and seasonal patterns. During cooler conditions, a lowered set point is accompanied by torpor. Daily torpor Seasonal torpor Hibernation: Extended torpor of small mammals during winter Torpor: a state of physical or mental inactivity; lethargy. 19  What happens if core temperature gets too high? What happens during a fever? Temporary increase in body temperature, usually due to infection Foreign bodies signal hypothalamus to increase internal temperature set point. Turns on the immune system to help fight infection (symptomatic) Mild fever ok, high fever can be deadly.