Temperature, Osmotic Regulation, and the Urinary System

• Homeostasis – the ability of living organisms to maintain internal conditions within an optimal range– a steady-state physiological condition,

extremely important for the proper functioning of cells

Homeostasis

• Thermoregulation (temperature)• Osmoregulation (solute and water balance)• Excretion (rids system of nitrogen-containing

metabolic byproducts)

Thermoregulation

• The rate of any chemical reaction is affected by temperature

• The rate of reaction increases with increasing temperature

• The rate of reaction decreases with decreasing temperature

• Q10 is a quantitative examination of how reaction rates vary with temperature

Thermoregulation, Q10

• Q10 – the ratio between the rates of a reaction at two temperatures that differ by 10°C

Q10 = RT+10 / RT

• For example, if Q10 = 2, then for every 10°C increase in temperature, the rate of reaction doubles (increases by a factor of 2)

Thermoregulation, Q10

• For most enzymes, Q10 = 2

• Q10 can also be applied to metabolism (the set of all chemical reactions that occur in living organisms in order to maintain life)

• In most organisms, the Q10 of metabolism is 2-3

• In some organisms, their Q10 is close to 1

– Little to no change in metabolic rate with temperature

Thermoregulation

• The reactions in your body that make up your metabolism are constantly producing heat– Can be dissipated or used to raise internal

body temperature– Metabolic rate and body temperature are

inter-related• Lower body temperatures do not permit high

metabolic rates

Thermoregulation

• External temperatures affect metabolism as well

• As external temperatures decrease, tremendous heat loss can occur

• As body temperatures are reduced, it becomes more difficult to generate metabolic heat

Thermoregulation

• Internal body heat = heat produced + heat transferred or Body heat = heat produced + (heat gained –

heat lost)

Thermoreguation

• Four mechanisms of heat transfer– Radiation: no direct contact; e.g., Sun– Conduction: direct transfer of heat from one

object to another– Convection: involves movement of gas or

liquid– Evaporation: energy loss, conversion of liquid

gas

Thermoregulation

Thermoregulation: Ectothermy vs. Endothermy

Endothermy vs. Ectothermy

• Ectothermy– Lower energy requirements (more efficient at

converting energy into biomass)– Typically limited to diurnal environments,

tropical and semi-tropical environments, short bursts of activity

• Endothermy– May be active at night; in tropics to the poles– Very high energy requirements

Thermoregulation

• Organisms have evolved adaptations to regulate their body temperature (and reduce heat loss to their environment)– Changes in surface area, temperature

difference and heat conduction– In Ectotherms

• Presence of ’antifreeze’ (cold temps)• Different enzyme systems (hot temps)

Thermoregulation – In Endotherms

• Increase muscular activity; shivering (cold temps)

• Adjusting blood flow through skin (cold or hot)

• Adjusting amount of heat loss through evaporation

• Adjusting amount of insulation• Adjusting proportion of body parts in order

to reduce or increase surface area

Thermoregulation

www.flickr.com/photos/hearman/9884614/

http://dive.scubadiving.com/d2d_archive/read.php?f=1&t=920399&a=2&

www.flickr.com/photos/80835774@N00/2096697676/

Thermoregulation• Adaptations to regulating temperatures

can be both physiological and behavioral

• Most invertebrates (ectodermic) use behavior to adjust their temperature– Orientation of body

towards sun– Shivering

www.flickr.com/photos/fxd/2760414614/

Countercurrent Heat Exchange

• Vertebrate ectoderms, as well as some endodermic birds and mammals regulate their internal body temperature by way of a counter-current heat exchange system– Warm blood pumped from within the body is

used to warm the cooler blood returning from the extremities

– Ingenious! Blood leaving the warm interior loses its heat to returning vessels just before they enter (cooler) extremities

Countercurrent Heat Exchange

Countercurrent Heat Exchange in Action!!!

Countercurrent Heat Exchange in Action!!!

• Marine birds do this as well!

Countercurrent Heat Exchange

Common dolphin dorsal fin

Common dolphin dorsal fin

Common dolphin dorsal fin

artery vein

Thermoregulation

• In general, ectotherms have low metabolic rates, which has the advantage of correspondingly low intake of food

• Some endoderms can prevent overheating by perspiring (sweating) and panting

• Mud baths are particularly useful in preventing overheating

Adaptations to Temperature Extremes

• When temperatures fall below a critical threshold, the animal must resort to thermogenesis, the use of normal energy metabolism to produce heat– Shivering (muscular activity)– Nonshivering thermogenesis

• Occurs primarily in brown fat (hibernating animals, babies, arctic mammals)

Adaptations to Temperature Extremes

• In mammals, thermoregulation is controlled by the hypothalamus

• When the temperature of blood exceeds 98.6°F, neurons in the hypothalamus detect the temperature change, stimulates its heat-losing center– Causes dilation of peripheral blood vessels,

bringing more blood to the surface to dissipate heat

– Stimulates sweating; suppression of metabolism-stimulating hormones

Adaptations to Temperature Extremes

• When the temperature of blood falls below 98.6°F, the heat promoting center of the hypothalamus is stimulated– Causes constriction of blood vessels– Inhibit sweating– Epinephrine produced by adrenal medulla to

stimulate metabolism

Adaptations to Temperature Extremes

• Torpor – decrease of metabolic rate over a relatively short period of time– Reduces the need for food intake by reducing

metabolism– More common in smaller animals; larger

animals have too much mass to effectively cool

Adaptations to Temperature Extremes

• Hibernation – drastic decrease in metabolic rate over a long period of time, in response to colder temperatures

• Effective only in midsize animals– Too big; costs more energy to increase

temperature than what is saved over winter– Too small: can’t store enough energy – Estivation – large decrease in metabolic rate

over a long period of time, in response to hotter temperatures (& food, water supplies)

Thermoregulation

• Fever – an increase in body temperature to levels above normal

• Considered to be one of the body’s (normal) immune mechanisms to inhibit the growth of bacteria or viruses

• Extremely high fevers, however, are detrimental and can result in seizures and hallucinations