共查询到20条相似文献,搜索用时 23 毫秒
1.
《Comparative biochemistry and physiology. A, Comparative physiology》1994,107(3):557-566
The preoptic anterior hypothalamus (POAH) thermoregulatory controller can be characterized by two types of control, an adjustable setpoint temperature and changing POAH thermal sensitivity. Setpoint temperatures for shivering (Tshiver) and panting (Tpant) both increased with decreasing ambient temperature (Ta), and decreased with increasing Ta. The POAH controller is twice as sensitive to heating as to cooling. Metabolic rate (MR) increased during both heating and cooling of the POAH. Resting temperature of the POAH was lower than internal body temperature (Tb) at all temperatures. This indicates the presence of some form of brain cooling mechanism. Decreased Tb during POAH heating was a result of increased heat dissipation, while higher Tb during POAH cooling was a result of increased heat production and reduced heat dissipation. The surface temperature responses indicated that foxes can actively control heat flow from body surface. Such control can be achieved by increased peripheral blood flow and vasodilation during POAH heating, and reduced peripheral blood flow and vasoconstriction during POAH cooling. The observed surface temperature changes indicated that the thermoregulatory vasomotor responses can occur within l min following POAH heating or cooling. Such a degree of regulation can be achieved only by central neural control. Only surface regions covered with relatively short fur are used for heat dissipation. These thermoregulatory effective surface areas account for approximately 33% of the total body surface area, and include the area of the face, dorsal head, nose, pinna, lower legs, and paws. 相似文献
2.
《Journal of thermal biology》1986,11(3):151-156
- 1.1. Experimental evidence is presented that short-term thermoregulatory adjustments occurring not far from thermoneutrality, involve temperature changes that are opposite in sign in different body regions. In man, exposure to hot ambient temperature (Ta), induced a decrease in esophageal and rectal temperatures. In rabbit, exposure to cold Ta induced an increase in hypothalamic temperature.
- 2.2.|Similar results could be obtained by simulation on a mathematical model of man's thermoregulatory system.
- 3.3.|The above results, as well as analogues results described in the literature, can be accounted for by a scheme of interpretation standing on current concepts of thermoregulation. If the gain of the thermoregulatory system is high, thermal stimulation of a region of the body will induce opposite temperature changes in other regions of the body.
3.
Spaceflight and its bed rest analog impair thermoregulatory responses, including elevated core temperature observed at rest and during exercise. Natural air flow has been found to increase cold sensation significantly compared to artificial constant air flow (CAF). The present study tested the hypothesis that simulated natural air flow (SNAF) ventilation would ameliorate impaired thermoregulatory function to a greater extent than CAF under simulated microgravity conditions. Seven healthy males underwent 30 days of −6° head-down bed rest (HDBR). During pre-HDBR and the day 29 of HDBR (HDBR 29), the subjects were exposed to three air flow patterns at 23 °C while in a supine posture: a still air flow control (CON), CAF, and SNAF. The mean air velocity of the latter two patterns was 0.2 m/s. Subjective perception of the thermal environment was recorded by thermal sensation vote (TSV), and rectal temperature (Tre), skin temperature (Tsk), and cutaneous vascular conductance (CVC) were also measured during the sessions. Tre was significantly elevated after 29 days of HDBR and decreased to a greater extent in SNAF than in CAF on HDBR 29. However, there was no significant difference between Tre in SNAF on HDBR 29 and that in CON on pre-HDBR. Mean Tsk, CVC, and TSV in SNAF were also significantly lower than those in CAF on HDBR 29. Moreover, TSV was close to ‘neutral’ under SNAF on HDBR 29. These data indicate that simulated natural air movement might be more effective than constant air movement at preserving core temperature at a thermoneutral ambient temperature during HDBR. 相似文献
4.
5.
- 1.1. Brain (hypothalamic), skin and body temperatures were measured in hand-reared acclimated (Acc, n = 5) and non-acclimated (NAcc, n =7) rock pigeons (Columba livia, mean body mass 237 g) exposed to increasing ambient temperatures (Ta) (30–60°C) and low humidities.
- 2.2. In non-panting Acc birds, brain temperature gradually increased from 40.1 ± 0.4°C at 30°C to 41.2 ± 0.4°C at 60°C Ta. A mean body temperature (Tb) of 41.2 ± 0.2°C was measured at Ta up to 50°C; an increase of 1.1°C was observed at 60°C (Tb 42.2 ±0.6°C).
- 3.3. In Acc panting birds exposed for 2 hr to 60°C, Thy was 41.9 ± 0.8°C and Ts was somewhat (but insignificantly) higher, i.e., 42.2 ± 0.7°C. It looks as if both values were increased as a result of a slight hyperthermia that developed (Tb = 43.5 ± 0.9°C).
- 4.4. The significance of the present results for evaluating neuronal thermoresponsiveness of birds' hypothalamus is discussed.
6.
Spontaneous running in a wheel has emerged as a useful method of exercise in rodents. We investigated how exercise training
with a running wheel affects ambient temperatures (T
a) at the onset of thermoregulatory responses in rats. Female rats were allowed to run freely in the wheel for 6 months. Sedentary
control rats did not exercise during the same period. After the exercise training period, they were loosely restrained and
T
a values at the onset of tail skin vasodilation and cold- induced thermogenesis were determined by raising or lowering T
a. Resting levels of core temperature and heat production of the exercise-trained rats were significantly higher than those
of the controls. T
a values at the onset of tail skin vasodilation and cold-induced thermogenesis of the exercise-trained rats were higher than
those of the controls. The results suggest that, in rats, exercise training with a running wheel elevates ambient temperatures
for heat loss and heat production, which may then contribute to maintaining the core temperature at a high level.
Received: 20 August 1999 / Revised: 22 November 1999 / Accepted: 24 November 1999 相似文献
7.
Mohamad Rida Wafaa Karaki Nesreen Ghaddar Kamel Ghali Jamal Hoballah 《International journal of biometeorology》2014,58(9):1905-1918
The purpose of this work was to integrate a new mathematical model with a bioheat model, based on physiology and first principles, to predict thermoregulatory arterio-venous anastomoses (AVA) and cold-induced vasodilation (CIVD) reaction to local cooling. The transient energy balance equations of body segments constrained by thermoregulatory controls were solved numerically to predict segmental core and skin temperatures, and arterial blood flow for given metabolic rate and environmental conditions. Two similar AVA–CIVD mechanisms were incorporated. The first was activated during drop in local skin temperature (<32 °C). The second mechanism was activated at a minimum finger skin temperature, T CIVD, min, where the AVA flow is dilated and constricted once the skin temperature reached a maximum value. The value of T CIVD,min was determined empirically from values reported in literature for hand immersions in cold fluid. When compared with published data, the model predicted accurately the onset time of CIVD at 25 min and T CIVD,min at 10 °C for hand exposure to still air at 0 °C. Good agreement was also obtained between predicted finger skin temperature and experimentally published values for repeated immersion in cold water at environmental conditions of 30, 25, and 20 °C. The CIVD thermal response was found related to core body temperature, finger skin temperature, and initial finger sensible heat loss rate upon exposure to cold fluid. The model captured central and local stimulations of the CIVD and accommodated observed variability reported in literature of onset time of CIVD reaction and T CIVD,min. 相似文献
8.
9.
P. C. Gangwar 《International journal of biometeorology》1982,26(1):73-79
The present work was undertaken to study the changes in the thermoregulatory responses due to changing climate, androgen and TDN percent in 12 buffalo male calves from 4 months of age for a period of two years. The results obtained were: (1) The amplitudes of the diurnal cycles in rectal temperature (Tre) in each month of the experiment were very similar but longer in summer months as compared to winter months, (2) The correlation between Tre and ambient temperature (Ta) was high in all months. (3) Buffalo calves without testosterone supplementation on 70% TDN showed maximum rise in Tre by 0.076 0C per degree of ambient temperature, indicating more strain, (4) Highest respiratory frequencies occurred at 10:00 h during summer months. Subgroup 2 of group 1 showed the maximum rise by 311% in respiratory frequency in summer over winter due to least acclimatization, (5) The mean daily increase by 9.94C in ambient temperature doubled the respiratory frequency of male buffalo calves from January to April, and (6) Androgen therapy and higher TDN percent level helped the male buffalo calves to adjust better and sooner than the other calves to changing climates. 相似文献
10.
《Journal of thermal biology》2001,26(4-5):249-253
(1) Primordial lesioning and stimulation experiments established a thermoregulatory centre in the rostral brain stem at the end of the 19th century. (2) A major landmark in understanding how deep-body temperature (Tc) is sensed, came in 1912 when Barbour found that changing rostral brain stem temperature inversely raised or lowered Tc, ultimately leading to a mono-centric concept of hypothalamic thermoregulation, prevailing for about 50 years. (3) The discovery of extrahypothalamic sites of temperature signal generation in the 1960s led to the multiple-input, multiple-controller concept of thermoregulation. (4) During the last 40 years, concepts concerning thermosensory specificity have radically changed from viewing bimodal peripheral thermoreceptors and hypothalamic thermoreceptors as the only relevant signal generators towards a complex picture including monomodality of peripheral warm and cold thermoreceptors and multimodality of deep-body thermosensors. 相似文献
11.
Seasonal variations in ambient temperature (Ta) require changes in thermoregulatory responses of endotherms. These responses vary according to several factors including taxon and energy constraints. Despite a plethora of studies on chiropteran variations in thermoregulation, few have examined African species. In this study, we used the Wahlberg's epauletted fruit bat (Epomophorus wahlbergi, body mass≈115 g) to determine how the thermoregulatory abilities of an Afrotropical chiropteran respond to seasonal changes in Ta. Mass specific Resting Metabolic Rates (RMRTa) and basal metabolic rate (BMR) were significantly higher in winter than in summer. Furthermore, winter body mass was significantly higher than summer body mass. A broad thermoneutral zone (TNZ) was observed in winter (15–35 °C) compared with summer (25–30 °C). This species exhibited heterothermy (rectal and core body temperature) during the photophase (bats' rest-phase) particularly at lower Tas and had a low tolerance of high Tas. Overall, there was a significant seasonal variation in the thermoregulatory abilities of E. wahlbergi. The relative paucity of data relating to the seasonal thermoregulatory abilities of Afrotropical bats suggest further work is needed for comparison and possible effects of climate change, particularly extreme hot days. 相似文献
12.
G. Heldmaier T. Ruf 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1992,162(8):696-706
During daily torpor and hibernation metabolic rate is reduced to a fraction of the euthermic metabolic rate. This reduction is commonly explained by temperature effects on biochemical reactions, as described by Q
10 effects or Arrhenius plots. This study shows that the degree of metabolic suppression during hypothermia can alternatively be explained by active downregulation of metabolic rate and thermoregulatory control of heat production. Heat regulation is fully adequate to predict changes in metabolic rate, and Q
10 effects are not required to explain the reduction of energy requirements during hibernation and torpor.Abbreviations BMR
basal metabolic rate
- BW
body weight
- C
thermal conductance
- CHL
thermal conductance as derived from HL
- CHP
thermal conductance as derived from HP
- HL
heat loss
- HP
heat production
- MR
metabolic rate
- RQ
respiratory quotient
- Ta
ambient temperature
- Tb
body temperature 相似文献
13.
F. Aujard M. Perret G. Vannier 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(7):540-548
The lesser mouse lemur, a small Malagasy primate, is exposed to strong seasonal variations in ambient temperature and food
availability in its natural habitat. To face these environmental constraints, this nocturnal primate exhibits biological seasonal
rhythms that are photoperiodically driven. To determine the role of daylength on thermoregulatory responses to changes in
ambient temperature, evaporative water loss (EWL), body temperature (T
b) and oxygen consumption, measured as resting metabolic rate (RMR), were measured in response to ambient temperatures ranging
from 5 °C to 35 °C, in eight males exposed to either short (10L:14D) or long (14L:10D) daylengths in controlled captive conditions.
In both photoperiods, EWL, T
b and RMR were significantly modified by ambient temperatures. Exposure to ambient temperatures below 25 °C was associated
with a decrease in T
b and an increase in RMR, whereas EWL remained constant. Heat exposure caused an increase in T
b and heat loss through evaporative pathways. Thermoregulatory responses to changes in ambient temperature significantly differed
according to daylength. Daily variations in T
b and EWL were characterized by high values during the night. During the diurnal rest, lower values were found and a phase
of heterothermia occurred in the early morning followed by a spontaneous rewarming. The amplitude of T
b decrease with or without the occurrence of torpor (T
b < 33 °C) was dependent on both ambient temperature and photoperiod. This would support the hypothesis of advanced thermoregulatory
processes in mouse lemurs in response to selective environmental pressure, the major external cue being photoperiodic variations.
Accepted: 4 August 1998 相似文献
14.
J. R. Coelho A. J. Ross 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,166(1):68-76
In spite of the abundance and broad distribution of social wasps, little information exists concerning thermoregulation by individuals. We measured body temperatures of the yellowjackets Vespula germanica and V. maculifrons and examined their thermoregulatory mechanisms. V. germanica demonstrated thermoregulation via a decreasing gradient between thorax temperature and ambient temperature as ambient temperature increased. V. maculifrons exhibited a constant gradient at lower ambient temperatures but thorax temperature was constant at high ambient temperatures. Head temperature exhibited similar patterns in both species. In spite of low thermal conductances, a simple heat budget model predicts substantial heat loads in warm conditions in the absence of thermoregulation. Both species regurgitated when heated on the head. A smaller volume of regurgitant was produced at lower head temperatures and a larger volume at higher head temperatures. Small regurgitations resulted in stabilization of head temperature, while large ones resulted in 4°C decreases in head temperature. Regurgitation was rare when wasps were heated upon the thorax. Abdomen temperature was 3–4°C above ambient temperature, and approached ambient temperature under the hottest conditions. No evidence was found for shunting of hot hemolymph from thorax to abdomen as a cooling mechanism. The frequency of regurgitation in workers returning to the nest increased with ambient temperature. Regurgitation may be an important thermoregulatory strategy during heat stress, but is probably not the only mechanism used in yellowjackets.Abbreviations
M
b
body mass
-
M
th
thorax mass
-
T
a
ambient temperature
-
T
ab
abdomen temperature
-
T
b
body temperature
-
T
h
head temperature
-
T
th
thorax temperature
-
C
t
thermal conductance 相似文献
15.
The purpose of the present study was to analyze simultaneously the temporal relationship between the changes of circadian rhythms of brown adipose tissue (BAT) thermogenesis and core temperature (Tc) by dual probe telemetric monitoring transmitters and to determine the role of endogenous arginine vasopressin (AVP) in the circadian rhythms of BAT temperature (TBAT) and Tc in male rats. The key observations in this study are: (1) Increase in TBAT commenced approximately 8 min before Tc increases at the start of transition from the light to dark phase. Whereas at the start of transition from the dark to light phase, decrease in TBAT commenced approximately 3 min before Tc decreases. The data show that circadian changes of BAT thermogenesis do indeed play a significant role in the overall maintenance of the circadian rhythm of core temperature. (2) The plasma AVP level was significantly elevated when core temperature decreases during the light phase, suggesting that endogenous AVP is involved in thermoregulatory processes during the light phase. V1a receptor antagonist could elevate core and BAT temperature during the light period, suggesting that endogenous AVP, acting through V1a receptor, could be involved in tonic thermoregulatory processes.V1a receptor antagonist can increase the blood lipid metabolism, suggesting that the mechanism of endogenous AVP in tonic thermoregulatory processes during light period could involve the suppression of lipolysis in BAT and other peripheral tissues. In summary, this study demonstrated that endogenous vasopressin contributes to reduced BAT themogenesis and body temperature in the light phase of the circadian cycle. 相似文献
16.
It has been speculated that the control of core temperature is modulated by physiological demands. We could not prove the modulation because we did not have a good method to evaluate the control. In the present study, the control of core temperature in mice was assessed by exposing them to various ambient temperatures (Ta), and the influence of circadian rhythm and feeding condition was evaluated. Male ICR mice (n=20) were placed in a box where Ta was increased or decreased from 27 °C to 40 °C or to −4 °C (0.15 °C/min) at 0800 and 2000 (daytime and nighttime, respectively). Intra-abdominal temperature (Tcore) was monitored by telemetry. The relationship between Tcore and Ta was assessed. The range of Ta where Tcore was relatively stable (range of normothermia, RNT) and Tcore corresponding to the RNT median (regulated Tcore) were estimated by model analysis. In fed mice, the regression slope within the RNT was smaller in the nighttime than in the daytime (0.02 and 0.06, respectively), and the regulated Tcore was higher in the nighttime than in the daytime (37.5 °C and 36.0 °C, respectively). In the fasted mice, the slope remained unchanged, and the regulated Tcore decreased in the nighttime (0.05 and 35.9 °C, respectively), while the slopes in the daytime became greater (0.13). Without the estimating individual thermoregulatory response such as metabolic heat production and skin vasodilation, the analysis of the Ta–Tcore relationship could describe the character of the core temperature control. The present results show that the character of the system changes depending on time of day and feeding conditions. 相似文献
17.
The present study aims to understand the effects of interindividual differences in thermal comfort on the relationship between the preferred temperature and the thermoregulatory responses to ambient cooling. Thirteen young women subjects chose the preferred ambient temperature (preferred Ta) in a climate chamber and were categorized into the H group (preferring ≥29 °C; n=6) and the M group (preferring <29 °C; n=7). The H group preferred warmer sensations than the M group (P<0.05) and the average of preferred Ta was 27.6 °C and 30.2 °C in the M group and H group, respectively. Then all subjects were exposed to temperature variations in the climate chamber. During Ta variations from 33 °C to 25 °C, the H group felt colder than the M group, although no difference was noted in the Tsk (mean skin temperature) and Ts-hand between the 2 groups. From the view of the relationship between the Tsk and thermal sensation, although the thermal sensitivity to the Tsk was almost similar in the H and M groups, the H group might have lower threshold to decreasing Ta than the M group. 相似文献
18.
19.
Extreme environmental conditions present challenges for thermoregulation in homoeothermic organisms such as mammals. Such challenges are exacerbated when two stressors are experienced simultaneously and each stimulus evokes opposing physiological responses. This is the case of cold, which induces an increase in thermogenesis, and hypoxia, which suppresses metabolism conserving oxygen and preventing hypoxaemia. As an initial approach to understanding the thermoregulatory responses to cold and hypoxia in a small mammal, we explored the effects of acclimation to these two stressors on the body temperature (Tb) and the daily and ultradian Tb variations of Sprague-Dawley rats. As Tb is influenced by sleep-wake cycles, these Tb variations reflect underlying adjustments in set-point and thermosensitivity. The Tb of rats decreased precipitously during initial hypoxic exposure which was more pronounced in cold (Tb=33.4±0.13) than in room temperature (Tb=35.74±0.17) conditions. This decline was followed by an increase in Tb stabilising at a new level ~0.5 °C and ~1.4 °C below normoxic values at room and cold temperatures, respectively. Daily Tb variations were blunted during hypoxia with a greater effect in the cold. Ultradian Tb variations exhibited daily rhythmicity that disappeared under hypoxia, independent of ambient temperature. The adjustments in Tb during hypoxia and/or cold are in agreement with the hypothesis that an initial decrease in the Tb set-point is followed by its partial re-establishment with chronic hypoxia. This rebound of the Tb set-point might reflect cellular adjustments that would allow animals to better deal with low oxygen conditions, diminishing the drive for a lower Tb set-point. Cold and hypoxia are characteristic of high altitude environments. Understanding how mammals cope with changes in oxygen and temperature will shed light into their ability to colonize new environments along altitudinal clines and increase our understanding of how Tb is regulated under stimuli that impose contrasting physiological constraints. 相似文献
20.
The European red squirrel Sciurus vulgaris inhabits areas which undergo profound seasonal declines in food availability and ambient temperature. We measured the body temperature (Tb) of free-ranging S. vulgaris over the course of one year to examine its thermoregulatory strategies and found no evidence of heterothermy, with Tb never dropping below 36.7 °C. A lower average Tb and a reduced active phase are likely to have resulted in some energetic savings, sufficient for survival during the particularly mild winter with unhindered access to food stores. We cannot exclude that a different Tb pattern may be seen in energetically more demanding years, but we can confirm that heterothermy is not an obligatory behaviour in this species to counter energetic bottlenecks. Either S. vulgaris is indeed a strict homeotherm, or the need for torpor is flexibly adjusted. 相似文献