<unk>  emphasizes that regulation must be efficient, whereas homeostasis makes no reference to efficiency. In addition,<unk>  recognizes that efficiency requires predicting bodily needs to prevent errors, whereas homeostasis emphasizes detecting errors and correcting them–– responding like a thermostat. Prediction requires the brain to: (i) collect information across all spatial and temporal scales; (ii) analyze, integrate, and decide what will be needed; (iii) exert feedforward control of all parameters. Naturally, many needs are somewhat unpredictable, so errors are inevitable; and for those errors, homeostatic mechanisms––feedback control––are available to correct them. Allostatic (predictive) regulation allows the brain to prioritize needs, for example, by sending more oxygen and nutrients to organs that need it most. For this example, during peak exercise muscle requires an 18-fold increase in oxygenated blood, but the heart can increase its capacity only 3.5-fold. Therefore, the brain temporarily borrows blood from the digestive system and kidney rerouting it to muscle. It later repays the debt when muscle's increased need subsides. Without the ability to prioritize trade-offs between organ systems, the heart and lungs would need to be far larger while much of this costly extra capacity would go unused. Predictive regulation also occurs at the cellular and systems levels. When humans are chronically stressed, the brain chronically raises blood pressure; then arterial muscles predict higher pressure and respond with hypertrophy (like skeletal muscles when we lift weights). Gradually the whole cardiovascular system adapts to life at an elevated pressure level. This is known as chronic hypertension, which elevates mortality from cardiovascular disease and stroke. Similarly, a chronically high carbohydrate diet requires chronically high blood glucose and leads to chronically high levels of insulin that increase in anticipation of the need to manage the high level of carbohydrates. Cells that express insulin receptors, predicting high insulin, adapt by reducing their sensitivity (like photoreceptors in bright light). This leads to type 2 diabetes and elevated mortality from many causes. Although physicians term this response insulin resistance, it can be better understood as consequent to predictive regulation. Every system evolves to operate over a particular range. For example, cone photoreceptors evolved to sense daylight over a 10,000-fold range of intensities, whereas rod photoreceptors evolved a different design to sense moonlight and starlight down to detection of single photons. To function optimally across their wide operating ranges, all systems adapt their sensitivities. A rod photoreceptor adapts to bright moonlight and requires minutes to increase its sensitivity to starlight. When a system is chronically forced beyond its intended operating range – as by chronic high carbohydrate diet or other stress – the limits of adaptation are exceeded, and systems break down. This condition was termed by Bruce McEwen as allostatic load. The health of an organism is maintained when operating within certain parameters, but having dynamic variability of range.<unk>  can be carried out by means of alteration in HPA axis hormones, the autonomic nervous system, cytokines, or a number of other systems, and is generally adaptive in the short term.<unk>  is essential in order to maintain internal viability amid changing conditions.<unk>  provides compensation for various problems, such as in compensated heart failure, compensated kidney failure, and compensated liver failure. However, such allostatic states are inherently fragile, and decompensation can occur quickly, as in acute decompensated heart failure.
Allostasis
Vasospasm
Vasoactivity
Venous cutdown
Cluttering
Venospasm
Premastication
Irritation