Human total sleep deprivation (TSD) findings up to the present show that the organ most affected is the brain, which displays psychological and some neurological decriments. The rest of the body seems to cope surprisingly well, indicating little sign of stress or malfunction. Central nervous system (CNS) effects also include some impairment to homeostatic control, particularly thermoregulation, which in humans seem to be minor, but for small mammals the outcome may be more serious. In humans, only a specific part of the lost sleep is made up, suggesting that a certain portion of a night's sleep ("obligatory" sleep) is essential to the brain, and that the remainder ("facultative" sleep) is more dispensable. Contrasting with the nominal TSD effects on the body (excluding the CNS), there are claims that sleep is necessary for general tissue growth and repair. The underlying evidence is examined, but is shown to have alternative interpretations. Anabolism may not rely so much on sleep, but on food intake and rest.