![]() ![]() Changes in heat balance require autonomic (e.g., sweating) and behavioral (e.g., seeking shade) thermoeffector initiation to maintain thermal homeostasis. Temperature sensitive receptors in the skin and deep body enable the detection of the external and internal environment, including the perception of thermal stimuli. Thus, the thermosensitivity of myogenic tone is tuned to tissue temperature and serves as a fundamental mechanism to regulate local blood flow. Elevations in temperature are known to increase tissue perfusion by altering blood viscosity remarkably, we demonstrate that thermosensitive tone counterbalances this effect. Further, we reveal key roles for heat-sensitive channels TRPV1 and TRPM4 in heat-induced myogenic tone in the skeletal muscle, both in vitro and in vivo. In skeletal muscle arteries, we show that temperature and intraluminal pressure are sensed largely independently yet integrated to trigger contractility. Further, the temperatures for half-maximal tone correspond closely to resting tissue temperatures, indicating that arterial tone is sensitive to small thermal fluctuations. ![]() Heating steeply activates tone in mouse skeletal muscle, brain, gut, and skin arteries with a temperature co-efficient ( Q 10 ) of ~11-20, reflecting a highly thermosensitive process. Here, we show that in addition to pressure, temperature is a critical determinant of myogenic tone. This autoregulatory property, known as myogenic tone, helps maintain a constant capillary pressure, which is important for tissue perfusion, fluid balance and vessel integrity. The smooth muscle cells surrounding small arteries and arterioles sense changes in local blood pressure and reflexively adjust their contractility to regulate vessel caliber. The auxiliary feedback (which can be negative or positive, +/−) is shown in red. (c) The same negative feedback control loop (as in panel a) is supplemented by auxiliary feedback control (from skin temperature). The feedforward control signal is shown in red. (b) Deep body temperature is controlled by the same negative feedback loop (from deep body temperature) supplemented by a feedforward signal (ambient temperature). (a) Deep body temperature is controlled via a negative (−) feedback loop. The active elements of each loop (in principal, thermoreceptors and the thermoeffector) are marked as the active system the passive system (processes of heat transfer) is marked as heat transfer. The three hypothetical schematics show how body temperature may be regulated within an individual thermoeffector loop. The multisensory, multieffector thermoregulation system can be described as a federation of relatively independent thermoeffector loops (Romanovsky 2007b). Implications of these principles to thermopharmacology, a new approach to achieving biological effects by blocking temperature signals with drugs, are discussed.įeedback and feedforward in thermoregulation. Thermoregulatory behaviours use both feedback and feedforward signals. ![]() Autonomic (physiological) thermoregulation does not use feedforward signals. Non-hairy skin also contributes to the feedback for thermoregulation, but this contribution is limited. Their main thermosensory-related role is to assess local temperatures of objects explored these local temperatures are feedforward signals for various behaviours. In thermoregulation, these organs are primarily effectors. the hand), which are also used to explore the environment. Non-hairy (glabrous) skin covers specialized heat-exchange organs (e.g. ![]() It is explained that this feedback is auxiliary, both negative and positive, and that it reduces the system's response time and load error. Thermal signals from hairy skin represent a temperature of the insulated superficial layer of the body and provide feedback to the thermoregulation system. The body is covered mostly by hairy (non-glabrous) skin, which is typically insulated from the environment (with clothes in humans and with fur in non-human mammals). This review analyses whether skin temperature represents ambient temperature and serves as a feedforward signal for the thermoregulation system, or whether it is one of the body's temperatures and provides feedback. ![]()
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