MadSci Network: Anatomy |
Hi Sam,
Wow, those are an interesting series of questions. Let me see if I
can clarify this for you. The basic idea that you are asking about is
insulation. Whether on a house, in a human, or in nature, insulation
involves the basic idea of trapping
heat.
Heat travels very poorly through certain materials, so these materials
become a shield between the user and the (typically) cold
world.
Insulation can be artificial or natural. You’ve mentioned blubber as a
natural insulator, and it is, but human fat does not fit in this category.
If humans primarily used fat as insulation, the average body
temperature of a super-model would be much less than that of a
sumo, but all human temperatures are within a couple degrees of
98.6º Fahrenheit ( or 32ishº
Celcius).
Before getting into human temperature regulation, you should
probably know that there are two types of human fat; brown and white/
Brown fat is most common in
infants.
This fat actually generates heat due to its mitochondria.
Brown fat keeps infants warmer than they would be otherwise. It also
seems to be prevalent in hibernating animals. Adult humans don’t
have this type of fat.
The more common type of fat is
white fat, which is actually more of a cream color. It is also known as
adipose tissue. This is the fat that
cushions people’s organs, serves as food storage, and adds
unsightly bulges that dieters are always trying fight. This fat doesn’t
have a large number of blood vessels and therefore is tough to lose.
Multiple factors seem to dictate how much of this fat a
person has. This fat is very poor at regulating temperature for a
variety of reasons.
Human skin, which is outside of
the fat layer, has a large amount of blood vessels in it. The blood
gives off heat to the environment, doing away with any insulating
effects the fat layer may have. Our skin, nervous system and
endocrine (hormone) systems have much more control in temperature regulation than our layer of fat.
Shivering, sweating, and the ability to walk out of the cold into a
warmer environment are far more useful to humans.
Most human temperature regulation is controlled by the nervous system. The brain and nerves cause
blood vessels to constrict or dilate, changing the amount of blood
flowing to the skin. More blood flow means that more heat is lost.
Less blood flow means that heat is conserved.
Temperature regulation is also influenced by the endocrine system.
Certain glands, such as the thyroid and hypothalmus help regulate
body temperature, but these must work within boundaries. If the
temperature gets too high, it can start to cook the body from the
inside out. This is why high fevers must be controlled. If temperature
is too low, the body starts to shut down. This is called hypothermia.
Clothing was also an item of interest to you. Do humans really need
clothing? The human body can keep its temperature regulated (even
without protective coverings) very nicely in tropical climates. You only
have to go as far as a National Geographic to show that clothing in
some regions is optional. But humans travel far in search of food or
space. To live in cooler climates, people have to maintain body
temperature somehow. Clothing is the natural answer. Humans
don’t need clothing to survive in the tropics, but we certainly find them
useful in temperate or polar regions.
Clothing traps a layer of air inside it. This air is warmed by body
heat. If the clothing is thick, it takes longer for the warm air to escape,
which is why wool feels warmer on a cold day than cotton. Fur
traps heat inside it the same way; by putting air in contact with skin
temperatures, warming the air and trapping it at the same time.
Some materials trap air better than others. A layer of plastic can also
trap heat inside, even though it’s quite thin, while even a thick layer of
mesh doesn’t do as good of a job.
Hope this satisfies some of that curiosity. Best wishes.
Picture and information from:
Georgia State University: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatreg.ht
ml
Information also from:
Encyclopædia Britannica: http://www.b
ritannica.com/eb/article?tocId=75648
The Townsend Letter for Doctors and
Patients: http://www.findarticles.com/p/articles/mi_m0ISW/is_2003_Jul
y/ai_104259134
And the Comenius University Medical School: http://nic.s
av.sk/logos/books/scientific/node45.html
Try the links in the MadSci Library for more information on Anatomy.