Biology Reference
In-Depth Information
feedback mechanism, wherein the hormone regulates its own secretion.
It is important to realize that such communications could rarely be
considered instantaneous, and mathematical models often use delay
factors to describe them.
One of the most biologically important and intriguing properties of
hormones is the pulsatile pattern of their release, and this chapter will
illustrate different conditions under which oscillations emerge in
hormone concentration profiles. To approach the topic, we outline
a formalism for mathematically modeling hormone systems and discuss
the following questions:
1. What are the biological variables essential to the oscillator?
2. How do these essential variables interact?
3. Can these interactions lead to oscillations?
4. Under what conditions will oscillations be sustained?
I. INTRODUCTION
Oscillation can be described as a pattern in the dynamic plot of a
measurable quantity (such as population size or hormone concentration
in the bloodstream) that recurs with a relatively stable waveform and
period. The important characteristics of an oscillation are the interpulse
interval and the amplitude of the individual pulses (Figure 10-1, left
panel). If the zenith-nadir difference in the amplitude of the oscillation is
continuously decreasing, we have a case of damped oscillation
(Figure 10-1, right panel). Note that the recurring pattern could be quite
different from the well-known sine- or cosine-like waveforms
(Figure 10-6). If a system contains more than one oscillating variable,
another characteristic would be the phase relationship between these
variables.
16
Interpulse interval
Zenith
8
Nadir
0
90
92
94 96
TIME
98
100 90
92
94
96
98
100
TIME
FIGURE 10-1.
Two oscillation patterns. Left panel: oscillations with constant amplitude; right panel: damped
oscillations.
