Temperature Regulation and Water Balance

1. Temperature Regulation and Water Balance

2. Ectotherm Vs. Endotherm Ectotherms –have a body temperature that is more or less determined by the temperature of the surrounding environment Endotherms – have a relatively constant body temperature that is usually higher than the surrounding environment temperature

3. Ectotherms: • ‘Ecto’ – mean outside • ‘Therm’ – means heat • Generally if the climate is hot ectotherms including their blood is hot. If the climate is cold so to is the animal including the blood. This information dispels the idea that reptiles are cold blooded. • Some ectotherms alter their behaviours to maintain body temperature. For example reptiles are inactive in cold weather and in the warmer weather can often be seen out in the sunshine warming up. The warming up of the body temperature results in an increase in activity level. • Some ectotherms also produce heat through extensive movement such as flying and swimming. • Ectotherms include: • Snakes • Lizards • Fish • Frogs

4. Endotherms: • ‘Endo’ – means inside • ‘Therm’ – means heat • Endotherms produce a large amount od heat internally. They also have insulating structures such as feathers, fur and fat layers to reduce and slow the loss of heat to the environment. • Keeping warm however costs energy for these animals. The cost is also high in smaller animals who have a large surface area to lose heat and less tissue to produce heat. Due to this small animals require more food than larger animals to keep up with energy demands. • In endotherms more than 6 degrees above core temperature is lethal. Temperatures can drop significantly if the animal can survive the reduced blood flow and reduced cellular metabolism (such as hibernation). • Endotherms include: • Birds • Mammals • Humans

5. Temperature Regulating Pathways: The regulation of temperature in humans is an example of the way different sensory detectors work together to produce an integrated response. Arterial blood has the most constant temperature. The relatively constant temperature of other body parts is an indicator of a good arterial blood supply In endotherms a group of temperature-sensitive cells in the hypothalamus act as misalignment detectors, triggering homeostatic responses if blood temperature deviated from optimum range. Temperature receptors are also found in the skin. A decrease in temperature will initiate responses such as a decrease in blood flow to the skin to reduce the amount of heat lost to the environment. Skin detectors are an example of a disturbance detector, detecting and responding to environmental temperature change before there is a change in the core body temperature.

6. Regulating Heat Exchange: • Factors which are involved in regulating the rate of heat exchange between an animal and its environment include: • The effective temperature difference between the two • The area of exposed surface • The efficiency of any insulation against heat exchange • Physiological process involving evaporation and circulatory changes

7. Heat Loss: When environmental temperature is lower than body temperature animals tend to lose heat by radiation, evaporation, conduction and direct loss through body fluids If temperature of the environment is higher than body temperature the only way that animal will lose heat is through evaporation (sweating, panting and the licking of fur) Heat gain: Heat is generated by metabolism in cells. Endothermic animals have insulation and physiological mechanisms that allow them to reattain this heat in order to maintain a constant body temperature Insulation: Endotherms have fur and feathers for insulation which reduce heat exchange with the environment. Fur and feathers trap a layer of warm air next to the body which reduces to gradient between the temperature of the climate and the body. This decrease in temperature gradient reduces heat loss

8. Countercurrent Heat Exchange: Countercurrent heat exchange works by way of warm blood in the arteries moving parallel and very close to the cooler venous return. The proximity of two fluids of different temperatures creates the necessary conditions for the exchange of heat. Heat is transferred from the warmer arterial flow into the cooler venous flow which then returns the warm blood to the body's core. The now somewhat cooler arterial flow proceeds to the relatively poorly insulated appendages. The net result is that the core remains warm and the appendages perpetually cool. Countercurrent heat-exchangers acting to conserve core heat are commonly found in the extremities of animals living in cold habitats, particularly in the legs or flippers of polar and cool temperate birds and mammals. http://www.biology.ualberta.ca/facilities/multimedia/uploads/zoology/counter%20current.html

10. Behavioural regulation: • Behaviours that regulate heat exchange: • Curling up to sleep in the cold (reduces surface areas for heat loss) • Huddling together (to reduce surface area for heat loss) • Moving out of the sun (to reduce heat gain) • Moving underground (to reduce heat gain) • Restricting activity to night-time (to reduce heat loss or gain) • Altering the amount of clothing being worn (to increase surface area for heat loss or to decrease it) • Altering body temperature (to either increase of decrease heat gain) • Controlling heat production: • It is more energy efficient to reduce heat loss and increase heat gain that to use up food and oxygen to increase metabolic heat production • Metabolic heat can be increased by shivering or increasing cellular activity in brown fat.

11. Water Balance and Salt Levels: Maintaining water balance is necessary to control salt concentrations. Salts form ions in solution and cells require the concentration of ions to be held within narrow limits for biochemical processes to occur efficiently Some ions are important for regulating pH which is critical for enzyme functioning. Water balance is a result of water intake and water loss. In organisms net movement of water occurs as a result of osmosis which is governed by solute concentration.

12. Water Balance in Aquatic Animals: Invertebrates: Invertebrates have body fluids with an osmotic concentration equal to that of sea water. They therefore do not need to expend energy to maintain osmotic balance. Bony fish:

13. Cartilaginous fish: Marine fishes such as sharks and rays retain an extraordinarily high amount of urea in their blood. This retention increases their osmotic gradient to equal that of sea water. This means that no energy needs to be spent to maintain osmotic balance Amphibians: The majority of amphibians are freshwater, particularly in the Laval stage and during breeding. Freshwater amphibians lose salt and gain water via osmosis through their skin.

14. Terrestrial Organisms – Coping with Limited Water • Water gain in animals can be achieved through: • Actively seeking out water however, this may lead to further water loss in some environments, this will require energy • Food intake (all food contains some water), this will require energy • Cellular respiration also create metabolic water , this will require energy • Water loss in animals: • Respiratory surfaces must be moist so air breathers always lose water from evaporation (less water is lost from humid air) • Cool air carries less water than warm air • Water is also lost form the kidneys when expelling nitrogenous wastes, as well as from the gut when expelling faeces • The kidney in mammals allows for water balance by creating concentrated urine

15. Glossary: Ectotherm Endotherm Hibernate Core body temperature Misalignment detector Disturbance detector Heat exchange Insulation Countercurrent flow Metabolic heat Brown fat Water balance Osmosis kidneys

16. Complete the following: Key Questions: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 Chapter Review Questions: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11