Concepts of Lifetime Fitness
September 1, 1997
Homeostasis is the state of equilibrium in which the internal
environment of the human body remains relatively constant. Two
excellent examples of homeostasis are how the body maintains a constant
temperature and blood pressure during strenuous physical activity or
exercise. Although there are many other activities in the body that
display homeostasis, I will only discuss these two.
Temperature in the human body is usually kept at approximately 37
degrees Celsius. To maintain such a strict temperature, the body has a
few functions to combat the outside elements. People cannot make
themselves cold as readily as make themselves hot, however I will
mention both homeostasis functions. When the external temperature
decreases, a portion of the brain called the hypothalamus detects the
drop by means of the blood. To compensate, the brain sends chemical and
electrical impulses to the muscles. These impulses tell the muscles to
begin to contract and relax at very high intervals. This is commonly
known as shivering. The production of Adenosine Triphosphate or ATP in
the mitochondria of the muscles produces heat. If the body temperature
does not rise immediately after this, then a second function begins.
The brain will signal the blood vessels near the skin to constrict or
narrow in diameter. This occurs so the heat deep in the muscles is
conserved. Since the vessels are now smaller in diameter, less blood is
needed to fill them. Since less blood is needed through the vessels,
the heart begins to slow. If the body remains in this slowed state,
hypothermia could result. Hypothermia is the condition in which
metabolic processes are inhibited. The medical world has taken
advantage of this by inducing hypothermia in patients that are
undergoing organ transplants.
To fight temperatures higher than normal, as in exercise or on hot
days, the body reacts in the opposite way than with cold. Again, the
hypothalamus detects the change of temperature in the blood. The brain
signals blood vessels not to constrict, but to dilate. This increases
the diameter of the vessels, and results in the need for more blood.
Since more blood is needed to fill the vessels, the heart pumps faster
and that causes respiration to increase. The increased respiration will
make the body exhale some of the internal heat, like placing a fan in a
window to cool a room. The blood vessels are dilated so the heat deep
in the muscles is easily released. Another commonly known mechanism to
fight heat is sweating. Sweat glands found throughout the body are
stimulated by the hypothalamus to excrete sweat and when the sweat
evaporates, the skin is cooled. If the body is not cooled by the time
all of the internal water supply is used, it could go into hypothermia.
This is when the body becomes dehydrated and proteins begin to
denature. Hypothermia can result in certain death if the water supply
is not immediately replenished. Some advantages to these mechanisms are
the cleansing effect of sweating and weight loss. Sweat, when excreted,
removes waste materials such as bacteria and water. Fat material,
during exercise, is actually "eaten" by the body thus reducing overall
weight.
The second example of homeostasis is blood pressure regulation. When
the hydrostatic pressure of blood is above normal, pressure sensors in
the blood vessels tell the brain through chemical means. The brain will
then stimulate the heart to contract or beat in slower intervals. This
will cause less blood to enter the blood vessels and that will lower the
hydrostatic pressure. If the pressure is lower than normal, the exact
opposite happens. The sensors in the vessels tell the brain and the
brain will then make the heart beat faster so more blood enters the
vessels and the pressure is raised.
The body uses many mechanisms to regulate temperature and blood
pressure. Be it stimuli to the heart from the brain or messages from
the blood, the body maintains its internal environment through a process
called homeostasis.
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