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