The Body and Sleep
Although brain function is emphasized here, other organ systems demonstrate significant changes during sleep, in different sleep stages, and as part of a normal circadian oscillation synchronized with the sleep-wake cycle. There are clear alterations in thermoregulatory, cardiovascular, respiratory, and gastrointestinal physiological activity. A generalized parasympathetic predominance during NREM sleep is interrupted by autonomic swings during REM sleep. Dramatic endocrine changes are associated with sleep and circadian rhythms. This is evident particularly in the hypothalamic-pituitary axis. For instance, human growth hormone is secreted primarily during sleep, especially when SWS is most intense. Prolactin also is secreted mostly during sleep. Major circadian changes in cortisol and thyroid-stimulating hormone (TSH) normally occur during sleep. In each of these hormonal systems, changes with sleep (e.g., sleep deprivation) can influence the timing, pattern, and amount of the hormone released. Sleep also plays a role in the regulation of glucose levels. Even a moderate degree of sleep deprivation can lead to elevations on a glucose tolerance test (Spiegel, Leproult, and Van Cauter, 1999).
Accumulating evidence indicates that immune system function may be impaired with sleep deprivation. Accordingly, normal sleep may play an important role in maintaining host defenses on a regular basis. With infection, there often is an increase in the sleepiness drive. Immune mechanisms that promote recovery may be enhanced directly as a result of sleep (Moldofsky, 1995).
Normal sleep seems to be important for the cardiovascular system. During most of a normal night of sleep, there are significant reductions in heart rate and blood pressure. Both the lowered rate and afterload reduction seem to decrease the workload on the heart. This reduction of the blood pressure during the night seems to help maintain a normal daytime blood pressure in healthy individuals. It has been argued that severe sleepdisrupted breathing prevents the blood pressure drop and thereby contributes to the hypertension that is very common in this patient population.
Source: David N. Neubauer, “Understanding Sleeplessness: Perspectives on Insomnia,” The Johns Hopkins University Press, Baltimore 2003
Republished by Health Care Programs