What are the two basic processes controlling sleep timing and sleep quality and, therefore, contributing to anterior pituitary hormone cycling in a 24-hour period?
The following should serve as a framework for understating these two time-honored processes. For more in-depth rendering, please see selected references. The first process is called process-C , for circadian process ( circadian from Latin “approximately a day”), and is regulated by the hypothalamic suprachiasmatic nuclei (SCN). This nucleus receives input from environmental cues, the strongest of which is light. Process-C is the broader of the two processes and transmits circadian output to coordinate behavioral, physiologic, and genetic rhythms. The second process is sleep–wake homeostasis (SWH), also known as process-S . SWH is dependent on process-C but the circadian process is not dependent on SWH. SWH is presently conceptualized as a process relating the amount and intensity of sleep to the duration of prior wakefulness; however, the actual basis of SWH and its anatomic location remain elusive. So, if one has 24 hours with no sleep, there is increased pressure to sleep. The pressure to sleep is least when a person is most rested. This pressure increases during the day and peaks just before midnight. The continuous interaction between these two processes, process-C and process-S, influences the hypothalamic generators to release or inhibit hormones from the anterior pituitary, which, in turn, contributes to the 24-hour hormone profile.