Download Thermoregulation

Animal Physiology
Topic: Thermoregulation
Chong Yee Ling
BSc.(UPM), MSc.(UNIMAS),PhD(PennState) – Wildlife Virology and Evolution
Department of Zoology
Faculty of Resource Science & Technology
Universiti Malaysia Sarawak
This OpenCourseWare@UNIMAS and its related course materials are licensed under a Crea<ve Commons A>ribu<on-­‐NonCommercial-­‐ShareAlike 4.0 Interna<onal License. At the end of the unit, you should be able to: 1. Define thermoregula:on and how temperature influence the metabolic and physiological processes of living organism. 2. Differen:ate between endotherm and ectotherm. 3. Calculate temperature coefficient, Q10. 4. Discuss how body temperature heat is transferred. 5. Describe factors that could be responsible for death at high temperature and factors that allow animals to survive at extreme cold temperature. 6. Explain the temperature regula:on of various animals in different environment. Thermoregula:on is defined as the process of regula<on of body temperature to ensure the body physiological state is at normal/
constant level (homeostasis).  Animal body temperature is controlled mainly by hypothalamus and spinal cord thermoreceptors with the help of other organ systems (nega<ve feedback mechanism).  “Thermoregulate” animals can regulate their body temperature.  Birds have higher average body temperature (38-­‐41oC) compared to mammals (35-­‐38oC). The core body temperature normally fluctuates within 2oC.  Animals that are unable to control their body temperature are called “thermoconform”; their body temperature fluctuates with external temperature. Ectotherm versus endotherm Ectotherm: Animals that keep their body temperature by gaining heat from external source.  Almost all animals (e.g. many fish, most invertebrates, amphibians; except birds and mammals).  Ectotherms also produce low metabolic heat but their body temperature does not differ much from environment temperature.  Thus, food requirement is less to maintain its body temperature.  Enzyme ac<vi<es are not at op<mal; may compromise some physiological mechanisms (e.g. diges<on, excre<on, locomo<on, etc.). Ectotherm versus endotherm Endotherm: Animals that maintain their fairly constant body temperature via metabolic heat produc:on.  All birds and mammals, a few rep<les and fish, some insects.  Endotherms usually maintain large differences in their body temperature compared to external temperature.  Need a lot of food and energy to maintain its high body temperature via aerobic respira<on compared to ectotherm of equivalent body size.  Enzyme ac<vi<es are usually maintained at op<mal. Temperature Coefficient, Q10 • The rates of biochemical reac:ons (e.g. enzyma<c ac<on) and physiological processes (respira<on, heart beat, gill movement, etc.) due to the changes of body temperature. • Increase in Q10 due to 10oC increase in temperature. However, Q10 fall off if temperature is outside the range that an animal can tolerate. • Important for cold blooded organisms in which the body temperatures depend on the external environmental fluctua<on and biological mechanism. 10 Q10 = Temperature (oC) R2 (t2 – t1) R1 Fish Respiratory rate 12 80 20 150 R: Rate of biochemical/physiological reac<on T: Temperature (degree Celsius or Kelvins) 10 Q10 = 150 (20
– 12) = 2.194 80 Usually between 2 and 3. THINK ABOUT THIS: How animal body temperature heat is transferred? How body temperature heat is transferred? 1) Conduc:on Physical contact between two surfaces of different temperature lead to direct heat transfer. Animal fur and feathers are poor conductors but good insulators. 2) Convec:on Occurs at fluid phase with different densi<es (warm fluid have lower density) or movement of airstream (e.g. wind). 3) Radia:on All objects receive and emit electromagne:c waves of specific wavelength. Hot surface temperature emits short wavelength of radia<on with large energy or heat. 4) Evapora:on Changes of water from liquid to vapour (gas) phase require heat taken from the contact surface. E.g. swea<ng is a mean of body heat loss via evapora<on by animals. Efficient when there is low humidity of the surrounding air. Different animal species have different range of temperature tolerance. High temperature is fatal for almost all animals. Why? Different animal species have different range of temperature tolerance. High temperature is fatal for almost all animals. Why? (answer)  Temperature above 45-­‐55⁰C will denature protein.  High temperature inac<vate enzyme reac<on.  High temperature increases metabolism, thus the demand of O2 is also increases, especially cold-­‐blood animals.  Deple<on or over-­‐accumula<on of metabolites and wastes.  Q10 fall off at high temperature.  Destroy membrane structure (i.e. disrup<on of phospholipid bilayer at high temperature). THINK ABOUT THIS: How animals survive at extreme low temperature? How animals survive at extreme low temperature? Freeze-­‐tolerance:  Many aqua<c invertebrates (e.g. insects, gastropods, larvae, etc.) can survive even ice forma<on occurs in their bodies.  Examples: glycoprotein and carbohydrate-­‐free polypep<des, nuclea<ng agents.  They allow freezing (ice forma<on) occurs only at the animal’s extracellular fluid while withdraw water from intracellular fluid. Thus, intracellular fluid is very concentrated but remain unfrozen and this will protect the cells from rupturing. An:-­‐freeze compounds:  Arc<c or Antarc<c fish (freeze-­‐intolerant) avoid freezing by the produc<on of an<-­‐freeze compounds (largely by amino acid alanine). These an<-­‐freeze compounds can lower the freezing point by preven<ng the entering of water molecule into the ice crystal lajce, hence ice crystal will not grow in size.  The glycerol concentra<on usually increase just before winter and the minimum freezing point temperature of glycerol is at −37.8 °C. THINK ABOUT THIS: How animals keeping their body warm in the cold? How animals keeping their body warm in the cold?  Increase metabolic heat produc<on via voluntary muscular ac:vity (e.g. exercise).  Shivering (involuntary muscle contrac:on and relaxa:on repe<<vely) will increase body heat produc<on (e.g. preflight warm-­‐up shivering in hawkmoth, bumblebee, etc. to prepare muscles for take off).  Vasoconstric:on (constric<on of blood vessels thus reducing blood flow near the surface of the body and reducing heat loss from the skin surface).  Piloerec:on (erector pili muscles contract and cause skin hairs to stand in order to trap warm air surrounding the skin surface). Other example is bird feather fluffing. How animals keeping their body warm in the cold? (cont..)  Non-­‐shivering thermogenesis increase metabolic heat produc<on (occurs in brown adipose <ssues in mammals).  Smaller mammals (e.g. squirrels) become fat and hide in burrows or hibernate (long-­‐term torpor) during cold weather. Some huddle together (e.g. penguins and honeybees).  Bumblebee has superficial hairs that act as insula<on in keeping body warm.  Larger mammals (i.e. polar bear) increase their fur thickness and subcutaneous fat during cold winter.  Endotherms produce more metabolic heat than ectotherms as they posses different types of mitochondria and concentra<on level. How animals keeping their body warm in the cold? (cont..)  Many grasshoppers bask in the sun to warm their body. Grasshoppers also develop dark pigmenta:on to increase net environmental heat gain.  Birds cover their feet with feathers for external insula<on. Most of them migrate to warmer climate.  Aqua<c animals (e.g. whales and seals) also have thick layer of fat for internal insula<on and increase their metabolic rates.  Prevent excessive heat loss at appendages that are not insulated (e.g. flippers & fins of whales, legs of bird, horns of ungulates, etc.) via counter-­‐
current heat exchange mechanism (to reduce temperature gradient). THINK ABOUT THIS: How animals keeping their body cold in the heat? How animals keeping their body cold in the heat?  Vasodila:on (dila<on of blood vessels thus increase blood flow near the body surface and increase body heat loss).  Some animals swea:ng (sweat evaporates thus cooling the body).  Smaller ungulates, dog, and birds pan:ng to allow cooling of blood to the brain.  Elephants flap their ears (remove heat via convec<on) or spray their body with water (evapora<ve cooling). How animals keeping their body cold in the heat? (cont..)  Camels increase their fur thickness to insulate their body. Their body temperature is higher (~41⁰C) than the surrounding air during the later aqernoon compared to early morning (~34⁰C). Heat is stored in the body during the day and in the cool night the stored heat is released by conduc:on or radia:on. Higher body temperature during the day also decrease the net environmental heat gain, thus reduce the water usage due to evapora<on.  Small animals living at desert hide in burrows during the day to conserve water and avoid over-­‐hea<ng. They are ac<ve during the night to find food and mates.  Marsupials lick their body with saliva for cooling. Further Reading: Rastogi, S.C. (2007). Essen<als of Animal Physiology, 4th Edi<on. New Delhi: New Age Interna<onal Publishers. Campbell and Reece (2005). Biology, 7th Edi<on. Benjamin Cummings. Willmer, P., Stone, G., Johnston, I. (2005). Environmental Physiology of Animals., 2nd Edi<on. Blackwell Science. Schmidt-­‐Nielsen, K. (1997). Animal Physiology: Adapta<on and environment, 5th Edi<on. Cambridge University Press. Prosser, C.L. (1950). Compara<ve Animal Physiology. Philadelphia: W.B. Saunders Company.