Chapter 40 Lecture 13 Living Systems and Temperature Dr. Alan McElligott

Living Systems and Temperature Aims: To examine how temperature affects living systems To understand how animals exchange heat with their environment To examine regulation of body temperature by mammals

Aims: To examine how temperature affects living systems To understand how animals exchange heat with their environment To examine regulation of body temperature by mammals These lecture aims form part of the knowledge required for learning outcome 4. Appreciate how the physiology of an organism fits it for its environment (LOC 4). Living Systems and Temperature

Essential reading pages Pages Living Systems and Temperature 40.2 How Does Temperature Affect Living Systems? 40.3 How Do Animals Alter Their Heat Exchange with the Environment? 40.4 How Do Mammals Regulate Their Body Temperatures?

40.2 How Does Temperature Affect Living Systems? Physiological processes are temperature-sensitive and increase their rate at higher temperatures. Q 10 describes temperature-sensitivity as the quotient of the rate of a reaction at one temperature divided by the rate of the same reaction at a lower temperature.

Figure 40.8 Q 10 and Reaction Rate

40.2 How Does Temperature Affect Living Systems? Body temperature of some animals is coupled to environmental temperature. In winter, a fish will acclimatize to colder water by expressing different isozymes. Isozymes that are optimized at different temperatures can catalyze the same metabolic reaction.

40.3 How Do Animals Alter Their Heat Exchange with the Environment? Thermal classification of animals can be based on source of heat. Ectotherms have external sources of heat. Endotherms regulate temperature by producing heat metabolically or by actively losing heat. Heterotherms can behave either as an ectotherm or an endotherm.

40.3 How Do Animals Alter Their Heat Exchange with the Environment? Major differences between ectotherms and endotherms: Resting metabolic rate Total energy expenditure when at rest Response to changes in environmental temperatures

Figure 40.9 Ectotherms and Endotherms React Differently to Environmental Temperatures

40.3 How Do Animals Alter Their Heat Exchange with the Environment? An endotherm will increase its metabolic rate to maintain its body temperature in cold conditions. Both endotherms and ectotherms may use behavioral regulation to maintain body temperature. Example: moving into sun

Figure Ectotherms and Endotherms Use Behavior to Regulate Body Temperature

40.3 How Do Animals Alter Their Heat Exchange with the Environment? Both ectotherms and endotherms can alter heat exchange between their bodies and the environment. Body temperature is determined by the balance between internal heat production and four types of heat exchange.

40.3 How Do Animals Alter Their Heat Exchange with the Environment? Radiation: heat transfer via infrared radiation. Conduction: heat transfer by direct contact. Convection: heat transfer through a surrounding medium. Evaporation: heat transfer through evaporation of water from a surface.

Figure Animals Exchange Heat with the Environment

40.3 How Do Animals Alter Their Heat Exchange with the Environment? The energy budget is the balance of heat production and heat exchange. Heat entering through solar radiation and metabolism must equal loss via radiation, convection, conduction, and evaporation.

40.3 How Do Animals Alter Their Heat Exchange with the Environment? Blood flow to the skin helps endotherms and ectotherms maintain body temperature. Increased blood flow to the skin increases heat loss and lowers body temperature. Constriction of blood vessels to the skin results in less heat loss.

Figure Some Ectotherms Regulate Blood Flow to the Skin

40.3 How Do Animals Alter Their Heat Exchange with the Environment? Fur on animals acts as insulation that retains body heat. When animals are active and must lose excess heat, special blood vessels carry the heat to hairless skin surfaces.

40.4 How Do Mammals Regulate Their Body Temperatures? Endotherms can respond to changes in temperature by changing their metabolic rate—the rate at which they consume O 2 and produce CO 2. In the thermoneutral zone the metabolic rate is low and independent of temperature.

40.4 How Do Mammals Regulate Their Body Temperatures? The basal metabolic rate (BMR) is the metabolic rate of a resting animal at a temperature within the thermoneutral zone.

40.4 How Do Mammals Regulate Their Body Temperatures? The basal metabolic rate (BMR) is correlated with body size and environmental temperature. However, the BMR per gram of tissue increases as animals get smaller. Example: a gram of mouse tissue uses energy at a rate 20 times greater than a gram of elephant tissue.

Figure The Mouse-to-Elephant Curve

40.4 How Do Mammals Regulate Their Body Temperatures? A curve showing BMR versus ambient temperature represents an integrated response of an animal. The thermoneutral zone is bounded by a lower and an upper critical temperature.

Figure Environmental Temperature and Mammalian Metabolic Rates

40.4 How Do Mammals Regulate Their Body Temperatures? Inside the thermoneutral zone an animal can adapt to changes without using much energy. Outside the thermoneutral zone responses to temperature changes require bigger metabolic increases.

40.4 How Do Mammals Regulate Their Body Temperatures? Endotherms respond to cold by producing heat and reducing heat loss. Mammals produce heat in two ways: Shivering: skeletal muscles contract and release energy from ATP as heat. Nonshivering: occurs in adipose tissue called brown fat. The protein thermogenin causes heat release by altering ATP production.

Figure Brown Fat

40.4 How Do Mammals Regulate Their Body Temperatures? Reducing heat loss is important in cold climates. Some cold-climate species have a smaller surface area than warm- climate relatives. Rounder body shapes and shorter appendages reduce surface area-to- volume ratios.

40.4 How Do Mammals Regulate Their Body Temperatures? Other adaptations to reducing heat loss include: Increased thermal insulation with fur, feathers, or fat. Ability to decrease blood flow to the skin by constricting blood vessels. Use of countercurrent heat exchange in blood flow to appendages.

Figure Adapting to Hot and Cold Climates

40.4 How Do Mammals Regulate Their Body Temperatures? A rise in environmental temperature results in increased blood flow to the skin to dissipate heat. If temperature exceeds the upper critical temperature, overheating is possible. Evaporation of water through sweating or panting increases heat loss, but is an active process that also generates some heat.

40.4 How Do Mammals Regulate Their Body Temperatures? The regulatory system that controls body temperature depends on feedback and acts as a thermostat. In vertebrates a brain structure, the hypothalamus, is the major center of the thermostat. The temperature of the hypothalamus can be the main feedback to the thermostat.

40.4 How Do Mammals Regulate Their Body Temperatures? Cooling the hypothalamus can cause body temperature to rise by: Constricting blood vessels to the skin Increasing metabolic rate Warming the hypothalamus can lower body temperature by: Dilating blood vessels to the skin Sweating or panting

Figure The Hypothalamus Regulates Body Temperature (Part 1)

Figure The Hypothalamus Regulates Body Temperature (Part 2)

Figure The Hypothalamus Regulates Body Temperature

40.4 How Do Mammals Regulate Their Body Temperatures? The temperature of the hypothalamus is a negative feedback signal; variability from its set point can trigger thermoregulatory responses. Other factors can change hypothalamic set points: Change in skin temperature Wakefulness or sleep Circadian rhythm: a daily internal cycle

40.4 How Do Mammals Regulate Their Body Temperatures? Fever is a rise in body temperature caused by pyrogens. Exogenous pyrogens come from foreign substances; bacteria or viruses. Endogenous pyrogens are produced by immune cells in response to infection. Pyrogens cause a rise in the set point for metabolic heat production.

40.4 How Do Mammals Regulate Their Body Temperatures? Hypothermia is a state of below-normal temperature. Regulated hypothermia is a means of survival. Small endotherms, like hummingbirds, can lower their temperature during inactive periods to conserve energy, known as daily torpor. Long-lasting regulated hypothermia is called hibernation.

Figure A Ground Squirrel Enters Repeated Bouts of Hibernation during Winter

Check out 40.2 RECAP, page CHAPTER SUMMARY, page RECAP, page 866, first question only 40.4 RECAP, page CHAPTER SUMMARY, page 871, See WEB/CD Activity 40.1 Self Quiz page 871-2: Chapter 40, questions 2-8 For Discussion page 872: Chapter 40, question 4 Living Systems and Temperature

Key terms: acclimatization, basal metabolic rate (BMR), conduction, convection, ectotherm, endogenous, endotherm, evaporation, exogenous, fever, heterotherm, hibernation, homeostasis, homeotherm, hypothalamus, hypothermia, poikilotherm, pyrogen, quotient, Q 10, radiation, thermogenesis, thermoneutral zone Living Systems and Temperature