Twenty-four hour rhythmicity (circadian rhythm) is observed in our physiology (blood pressure and endocrine function etc.) and behavior (sleep-wake cycle) under the real world. Circadian rhythm is driven by internal autonomous clock, so called as circadian pacemaker. In mammals including humans, circadian system is organized in hierarchical multi-oscillators which consist of central circadian pacemaker in the suprachiasmatic nucleus (SCN) of hypothalamus and peripheral organs. The SCN entrains to an external light-dark cycle with a period of 24 h and adjusts autonomously our physiology and behavior. In the modern world, some people are forced to live with an irregular work schedule that becomes desynchronization between his or her circadian clock and sleep-wake cycle. Such abnormal sleep-wake cycle and poor sleep are reported to be a risk factor for metabolic dysfunction and mood disorders. In this review, I will introduce a formal property of circadian clock in humans and effect of our living environment, such as light, meal and exercise, on our internal body clock.
Soil CO2 concentrations were measured at an agricultural land and at a primary forest in Central Amazonia. During dry season with chronic sunny days, the concentrations and soil water contents decreased at sunset when the soil temperature at a depth of 10 cm peaked, and they increased from midnight to daybreak when the soil temperature decreased. These findings indicate that the phase change between soil water and water vapor caused by soil temperatures brought about the diurnal changes in concentrations. But the heat transfer was so weak at a depth of 80 cm that the concentrations did not change. Further, the diurnal variation was not clear at a soil depth of 10 cm at the forest, because the solar radiation hardly reached the forest floor, and no fluctuation was found at the soil depth of 80 cm. During rainy season, regardless of the place, the percolation of rainwater pushed up the concentration as well as soil water content at the depth of 10 cm, and after the water passed downward, the increases gradually moved down to the 80 cm layer. Therefore, diurnal variations in soil CO2 originating from soil temperatures did not appear.
The purpose of this study was to examine the thermoregulatory responses of agricultural workers at heat environmental house cultivation work in summer, and in the particularly this study screened it about a risk of the heat disorders in elderly agricultural workers.
The subjects were 25 house cultivation practitioner men, 59.6±6.7 years old in full-time agricultural workers. There were the work places to investigate in the glass type house, and type of the farming works were the making of floriculture and soil. The survey items were measured the environmental conditions, tympanic temperature, heart rate, the sweat rate, salt concentration, rehydration and thirst sensation.
WBGT was an average of 27.4 to 30.1°C. The sweat rate and salt loss quantity from sweat were 668.7±179.5 g/hr and 545±347 mg/hr. The elevation of tympanic temperature was 0.27±0.10°C/hr and the rehydration was 236.5±62.4 g/hr. Also, the dehydration rate at work was 2.15±0.72%. The thirst sensation reached 56.0±17.9% at the end of works. Furthermore, it was found that the positive correlations between the age and sweat rate, the dehydration rate, the quantity of elevation of body temperature, the salt loss of the sweat, and the negative correlation was found between age and the thirst sensation at the latter half of the work.
The results revealed that sweat rate, dehydration rate and elevation of body temperature were high because the rehydration rate was low with increase of feeling thirst with aging at the house cultivation work in summer. Therefore, to prevent heat disorders in the elderly agricultural workers at the house cultivation farming, it is necessary immediately instruct to sufficient supplementation of the rehydration including salt.