These sensors also formulate input for cell-specific homeostatic plasticity regulation systems. Endotherms control body temperature by internal homeostatic mechanisms. This is possibly due to homeostatic synaptic scaling. The depressive phase ends with homeostatic upregulation potentially restarting the cycle over again. One physiological characteristic of sleep goes by the name of "homeostatic regulation". However, some relatively simple homeostatic mechanisms are generally accepted. The cells of the lens epithelium regulate most of the homeostatic functions of the lens. It also stimulates basophils to release B cell homeostatic factors. The organism returns to homeostatic regulation almost immediately after REM sleep ends. PTH is responsible for maintaining a homeostatic calcium concentration in the blood. However, the common ostrich shows no nasal glandular function in regard to this homeostatic process. The diving reflex is a response to immersion that overrides the basic homeostatic reflexes. They give rise to a variety of cells, are capable of self-renewal and homeostatic control. Under homeostatic conditions, Galectin-8 associates with active mTOR. An internal stimulus is often the first component of a homeostatic control system.