I’d Lick My Balls For It.

(O.K., Web readers, The titles were sometimes strange. The professor did not want to read 30 papers with the same exact title, so we had a contest running among students for the "best" title's. I won this week!!)

Introduction: Heterotrophic homeothermic endothermic mammals utilize outside food sources to provide them with the energy they need to survive and maintain a body temperature at which the animal functions most efficiently. There are measures that a mammal can take when faced with an environment that is either too warm or too cold for proper metabolic functioning. The experiment is to quantitatively measure the amount of oxygen that a mouse uses during respiration indifferent environments.

Materials and Methods: This experiment is carried out with a lab mouse, an Erlenmeyer flask with water and carbon dioxide absorbing chemicals. A graduated glass tube and a thermometer attached to an airtight stopper on top of the Erlenmeyer. A bubble solution is used on the graduated glass tube to measure the amount of respiration from mouse. A hot and cold bath large enough for the flasks is needed to change the temperature of the flask.

Results: The experiment consisted of measuring the amount of time it took the mouse to use five milliliters of oxygen. This was measured by watching a soap bubble fall down the graduated glass tube. The measurements were taken three times at each of the following temperatures: 1= 11°C, 2= 24.5°C, and 3= 31.5°C. The results are given in Graph 1 and the metabolic rate (MR) is given in (calories/gram*hour).

Graph 1. Shows the metabolic rate of a mouse under different environmental temperatures.

Graph 2. An average of Graph #1. The Temperatures are 1=11°C, 2=24.5°C, 3=31.5°C.

Discussion:

The class results were fairly good. When graphs of environmental temperature to metabolic rate (Graphs 1 and 2) are constructed, you see what is to be expected. The metabolic rate increases under both hot and cold conditions. The Metabolic rate was not significantly different between the cold and the normal (P value = 0.129), but was significant between hot and normal (P value = 0.023). If the mouse had just eaten (hypothetically), the differences would be less because the mouse’s metabolism at the room temperature would be raised because of the meal. Of course we are using indirect methods of obtaining this information since we are relying on gas exchange outside of the animal and assuming that all of the CO₂ is absorbed by the Soda Lime, and that this is a typical oxygen metabolizing laboratory rodent (i.e. not an alien). Another method could be to measure heart rate since it correlates with metabolic rate fairly well. A shaved Hamster would have a higher metabolism at the cooler and the room temperatures because of a higher rate of heat loss than his furred friend. The bald Hamster would have a lower metabolism at the higher temperature for the same rationale. Larger animals have larger surface to volume ratios than smaller animals therefore the heat loss is less per volume and the metabolic rate is less as well (also seen in heart rates increasing with smaller size). Two graphs. (8&9)

8. Mass of an animal.

9. Body weight of a mouse.

Humidity and fur are the two main factors that affect the heat transfer between the mouse and his/her environment. Since the animal cannot “naturally” affect the surrounding humidity (by air-conditioning units the way humans do), is has to increase insulation in cold environments (piloerection of fur), curl up and lessen the blood flow to the outer parts of the body. In warmer environments, the animal must use evaporative cooling (sweating, panting or licking their testicles), spread out and expose uninsulated portions of the body, or lessen the amount of insulation.

Heterotrophic homeothermic endotherms (such as Mice or shaved Hamsters) utilize outside food sources to provide them with the energy they need to survive and maintain a body temperature at which the animal functions most efficiently. There are definite advantages associated with being an endotherm, such as always being able to carry out necessary body functions most efficiently at a fairly constant temperature, but to receive this luxury, the organism expends a great deal of energy in heat regulation processes. Cold-blooded as I am, I also see the benefits of being an ectotherm. Being immersed in the reptile world you find that they are extremely successful under the right conditions. Because they use the environment to raise their body temperature, they save a tremendous amount of energy, which an endotherm would expend to raise its core temperature. This is evident when you can have some species of snake that can easily go a year without food and still be in reasonable health. Most species routinely go for periods between 3 and 6 months without eating during pregnancy (gravidity for egg laying species), at which times they not only survive, but also expend significant amounts of energy on offspring production. The drawback here is that not every environment is warm enough to survive without an internal heat source. Many people don’t know that many species of snakes (pythons) can actually raise their body temperatures up to 13°C above the environment by friction during muscle contraction (i.e. Shivering). This is only used in the brooding of eggs and is not sufficient to allow these reptiles to stay warm in cold environments.

According to Rachel Theriault, our mouse’s thermostat is located in his testicles. This comes from long observations, during the different environmental temperatures. When it is cold, the mice testicles get drawn towards the body and act as a signal that it is cold outside. When it gets hotter, the mice testicles swell. This signifies a warmer environmental temperature and the mouse acts accordingly. You can learn a lot from watching a mouse. My final final conclusion is that I am finished with the lab report and lab in general. Thanx J.

I’d Lick My Balls For It

Bryan Hummel

Vert. Physiology 99

December 3, 1999.

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