Organismal Physiology Lecture No. 2: Endothermy
Thursday September 13 , 2012
-The explored temperature range for the environment may vary from -238°C (the surface of the moon)
to 5,430°C (the Earth’s core). We, along with most of the organisms on Earth, live within the aquatic
environment of the hydrosphere where there is a 4°C temperature range. The greatest range for oceanic
organisms lies in places such as the deep sea vents and the polar seas.
- As human beings are classified as homeothermic endotherms, and are thus responsible for regulating
their body temperature, they (along with birds and other mammals) can live in higher temperature
ranges that often fluctuate. E.g. Terrestrial temperatures.
-As mentioned previously, mammals and birds can survive wide temperature ranges on Earth. Other
ectothermic organisms such as turtles have a much slower metabolism in colder temperatures. What is
remarkable is the fact that both mammals and birds have evolved their endothermic traits
independently of each other; depicting physiological convergence as a solution to the thermal problem.
What is important to note is that core/body temperature does not change in endothermic
Effect Of Temperature On Endothermic Homeotherms:
-This can be observed by examining an organism’s metabolic rate over an n range in temperature. In the
thermoneutral zone metabolic rate is maintained at a very stable interval. The size of the zone varies for
different homeothermic species. Large animals will exhibit a naturally large thermoneutral zone, while
small animals, a small one.
-Once within the thermoneutral zone, the organism will experience the modulation of insulation and
blood flow. Outside the thermoneutral zone, species will exhibit increased energy consumption due to
heat generation at colder temperatures and increased energy consumption due to heat loss at higher
temperatures. Regulation of body temperature in homeotherms requires a set point for which there are
many biological sensors like: the skin, spinal cord, back of the brain, hypothalamus, and scrotum (in
-In Antoine Lavoisier’s experiment, a guinea pig’s thermal heat was measured from drops of water that
trickled from a double-ice barrier calorimeter. The outer ice barrier protects the inner ice from
environmental temperatures. -Because of water’s high heat capacity, a swimmer’s heat is lost through conduction and he/she find the
need to shiver between swims. This shivering involves uncoordinated muscle contractions, performs no
muscle contractions and uses ATP in order to generate heat for body temperature regulation.
-In an experiment, rats that were placed in 6°C environments shivered uncontrollably at first, but given
time they ceased shivering a