Biology Reference
In-Depth Information
Life is a constant oscillation between the sharp horns of dilemmas.
Henry Louis Mencken (1880-1956)
In their article ''What is a Biological Oscillator?'' Friesen
and Block wrote: ''There can be little doubt that
oscillations are an essential property of living systems.
From primitive bacteria to the most sophisticated life
forms, rhythmicity plays a vital role in providing for
intercellular communication, locomotion, and behavioral
regulation. Although the presence of biological rhythms
has been recognized since antiquity, only recently has the
origin of these rhythms been systematically addressed. At
present, there are numerous descriptions of biochemical,
biophysical, and physiological oscillations in the scientific
literature ....Mostrecently, mathematical analysis has
been applied to biological oscillators as well. . . .'' (from
Friesen and Block [1984], used with permission of the
American Journal of Physiology-Regulatory, Integrative, and
Comparative Physiology).
Chapter 10
ENDOCRINE
NETWORK MODELING:
FEEDBACK LOOPS
AND HORMONE
OSCILLATIONS
Since this was written, the importance of applying
mathematical methods to examining the source, nature,
mechanism, and stability of biologic oscillations has
intensified considerably. In particular, the efforts to
describe, explain, and predict oscillatory hormonal
behavior are fundamentally interdisciplinary, with
mathematics contributing its own arsenal of methods to
the more traditional methods of biochemistry and
physiology (see, for example, Farhy and Veldhuis [2005];
Farhy et al. [2002]; Wagner et al. [1998]; Keenan and
Veldhuis [2001]; Farhy [2004]).
Introduction
Symbolic Scheme Representations of
Theoretical Models and Modeling Goals
Evolution and Control of Hormone
Concentration
Oscillations Driven by a Single-System
Feedback Loop
In Chapter 9, we described some statistical methods for
examining the pulsatile nature of hormone release and
quantifying the notion of secretion peaks. However,
we did not discuss how the secretion events are regulated
by the endocrine system. In this chapter, we construct
and study mathematical models of hormone networks.
The goal is to explore some of the endocrine mechanisms
that control the secreting glands and cell groups to
ensure precise hormone release with regard to amount,
secretion times, and long-term secretion patterns. By
these mechanisms, called feedback mechanisms, the body
can sense that the concentration of a certain hormone has
decreased and communicate to the secreting gland the
amount of the additional hormone needed. The secretion
rate will then be increased. This is an example of a
Networks with Multiple Feedback Loops
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