The Development of Circadian Rhythms in Human Infants

11.6 Ordering of physiological events in postnatal months
Is there any suggestion of ordering/timing of physiological events in human
infants in the first postnatal months?
The reported analysis and resultant graphical representation regarding the
relationships between the timing of physiological events (Table 10.1 and Figure 10.1)
must be highlighted as being exploratory and is presented primarily in a visual manner
in order to provide a platform for discussion, further work and investigation. These
first few postnatal weeks are a time of rapid change and this change in itself could
confer vulnerability to the developing infant. If this is coupled with an insult such as
an episode of illness, any delay in physiological maturation could be detrimental or at
its worst, fatal (Bajanowski et al., 2007).
From the graphical plots it appears that diurnal pattern of cortisol emerges first at 8
weeks. This may be linked to the fact life cannot be sustained without cortisol
(although survival is related to its presence in the body not necessarily the body‟s
ability to secrete it in a diurnal fashion). The emergence of a diurnal pattern of
secretion for melatonin seems to occur next at 9 weeks of age. Physiological stability
maybe conferred by the achievement of a mature core temperature rhythm. This is
then followed by the sinusoidal pattern of peripheral cycling genes which may reflect
stability of the peripheral oscillators at a cellular level at 10 weeks of age.
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