Download To differentiate between the two major control systems in the body

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Homeostasis and the Body’s Systems
Introduction
Figure 1- The homeostatic mechanism
Homeostasis relies on the function and performance of several body systems that
work synchronously to keep a constant internal environment. Figure 1 summarises the
function of homeostasis. i.e., homeostatic mechanisms occur in order for the body to
keep internal fluctuations minimal even in the presence of uncontrollable external
fluctuations. Maintaining a relatively stable environment is advantageous as an
individual organism can have greater independence.
Homeostasis is the condition of equilibrium in the body’s internal environment
produced by the ceaseless interplay of the body’s regulatory processes.
(Campbell, N. A and Reece, J. B., 2005a.)
Homeostatic response is controlled by the autonomic nervous system. It regulates the
internal environment by controlling all involuntary responses of the body. These
include smooth and cardiac muscles, the different organs of the digestive, the
cardiovascular, the excretory and the endocrine systems. (Campbell, N. A and Reece,
J. B., 2005b.) Farabee summarises homeostasis,
“Any one or more of the eleven body systems are involved at a given time,
regulated by one or both of the major control systems in the body.”
(Farabee, M.J., 2000a).
This essay attempts to discuss some of the homeostatic mechanisms present in
mammals.
A constant internal environment is of particular importance in interstitial fluid.
Imbalances or large fluctuations of any nature could lead to serious, life- threatening
consequences. Detection of any deviations from the ‘normal’ functioning state is vital
to avoid this.
The two major control systems in the body (the nervous system and the endocrine
system) will be discussed in order to differentiate between them. Nervous stimuli are
received by sensors in the dermis where nerve impulses are transmitted to the spinal
cord or brain. Here they are processed and an appropriate response is initiated. The
endocrine system secretes hormones into the blood when chemical changes are
detected. Agonists are used where it is seen to be beneficial to trick the body into
responding differently a particular ailment. e.g, phenyleprine (chemical agonist)
reduces production of mucus by constricting blood vessels in the nasal mucosa. The
control system comprises a receptor which detects change, a control centre which
recognises information and an effector which responds to the nerve signal. This can
be demonstrated using the circulatory system as a model, by conducting blood
pressure.
Figure 2
Impulses (per
Second)
Relationship between baroreceptor
response and blood pressure
3000
2000
Impulses per
second
1000
0
0
100
200
300
Blood Pressure (mm Hg)
(Langley, L. L., 1966)
As the blood pressure rises, the number of impulses sent to the brain also increases. It
is clear from this that the baroreceptors are responsive over a broad range of blood
pressure, showing that they when blood pressure increases an action potential is
created (by the receptors) and inhibitory reflexes are stimulated ( by the effectors).
The vasomotor centre (medulla oblongata) changes the heart rate to return blood
pressure to acceptable levels. (UCL Department of medical Physics and
bioengineering, 1999-2005).
Homeotherms have an internal temperature that is relatively constant, though the
external temperature may fluctuate. ( Langley, L. L., 1965a.) The thermoregulatory
centre in the hypothalamus of the brain controls blood temperature (very close to
37oC). This is part of the autonomic nervous system.
The integumentary system comprises of hair, nail sweat and sebaceous glands and it
has an important role in controlling temperature regulation. Other functions include
eliminating waste, synthesis of vitamin D (with UV light) and the vitally important
function of protection. (England, S., Oct 05). Sensors in the dermal tissue detect heat
changes in the atmosphere and send impulses to the brain via the spinal cord. The
thermoregulatory centre recognises the impulse and initiates the correct response. The
brain has a programmed ‘core temperature’ which, if deviated from is corrected. An
exception to this is when there is a change to the hypothalamic set point (e.g., during a
fever) due to an infective agent, such as bacterial pyrogens. (Lynch, R., 2004).
A response to an increased temperature is the production of sweat. The hypothalamus
sends a nerve signal to the sweat glands, causing them to release about 1-2 litres of
water per hour which cools the body. (Farabee, M.J., 2000b) It is not the rate of sweat
production that enables the body to cool but the rate of evaporation. ( Langley, L. L.,
1965b.) The hypothalamus also causes vasodilation which is an increase in diameter
of the blood vessels of the skin, allowing more blood to flow into those areas. This
encourages more heat to be lost by convection. The response of the kidneys is to
produce smaller volumes of more concentrated urine to compensate for H20 loss in
this situation.
The main aim of this essay was to discuss homeostasis in relation to the body systems.
Although it has been covered to a certain depth, this essay cannot attempt to describe
homeostasis in any sufficient detail as the nature of the subject is too vast. It has,
however, elaborated on some of the intricate systems involved in regulation.
Homeostatic control of blood pressure was discussed using the circulatory system as a
model.
The integumentary system has briefly been focussed upon with emphasis on
temperature control. Although other mechanisms other than vasodilation and sweating
are involved in the homeostatic process it was useful to focus upon these topics as
they relied on other body systems to function. It would have been useful to draw on
how the arrector pili muscle has close connections with the musculoskeletal system
and how this mechanism prevents heat loss in cold temperatures.
Bibliography
Figure 1
Bishop, Dr. C., 2004. Homeostasis and Regulation [online], Bangor University.
Available from:
biology.bangor.ac.uk/.../ homeostatic_control
[Accessed 4th November 2005.]
Campbell, N. A and Reece, J. B., 2005. Biology, Seventh ed. San Francisco: Pearson
Education, 835.
England, S., Oct 05. Biology 122, Body systems and major organs.
Farabee, M.J., 2000. Animal Organ Systems and Homeostasis [online], Estrella
Mountain Community College, Arizona, USA.
Available from:
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookANIMORGSYS.html
[Accessed 4th November 2005.]
Figure 2 recreated from:
Langley, L. L., 1966. Homeostasis. Great Britain: Reinhold publishing Corporation,
22, 48.
Lynch, R., 2004. Temperature Regulation [online], University of Colorado.
Available from:
http://www.colorado.edu/epob/epob1220lynch/16temp.html#outline
[Accessed 4th November 2005.]
Tortora, G. J and Grabowski, S., R, 2000. Principles of Anatomy and Physiology.
USA: Biological Sciences Textbooks, 6.
UCL Department of medical Physics and bioengineering, 1999-2005. Blood pressure
monitoring [online], University College, London.
Available from:
http://www.medphys.ucl.ac.uk/teaching/undergrad/projects/2003/group_03/why
det.html
[Accessed 5th November 2005.]
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