One of the basic characteristics of any life form is the ability to adapt or respond to a particular environmental condition. However, there extreme conditions in the environment wherein there is seemingly impossible mechanisms in which an organism could be able to adapt. In this paper, such physiological mechanisms of adaptation and response of the human body would be discussed specifically on the thermoregulation in environmental conditions such as extreme hot and cold climactic temperatures (as experienced in high altitudes) and in SCUBA diving.
The structure and function of proteins and enzymes, which are components of cells and tissues and play significant roles as catalyst in many biological processes, are affected by many factors including temperature. These two components are only functional at optimum temperatures; otherwise their structure and consequently the function would be altered. The protein or enzyme in such case is said to be denatured, and is generally caused by exposure to high temperatures (Wenger, 2006). Similarly, cold temperatures can cause injuries to cells and tissues in a mechanism different from the previously discussed.
In extremely low temperatures, freezing might occur that can form ice in a cell or tissue. This crystallization can cause mechanical damage to the cell membrane causing leakage of the cellular or tissue components. Another mechanism for damage can occur when there is an increase in the solute concentration in the cytoplasm in the formation of ice, protein denaturation may also take place by dehydration, by increasing the ionic strength of the cytoplasm and by other physiological changes in the cytoplasmic environment (Wenger, 2006).
With these in mind, we can therefore induce that temperature plays a crucial role in the physiological process occurring in humans and in any organism. Hence, regulation or maintenance of optimum temperature levels in any biological system is essential in the continuity of vital physiological processes. All mechanisms and processes in the human body has molecular and cellular basis and unexceptionally, such are applicable in the physiological thermoregulatory response in extremely cold environment such as in Antarctica.
In 2003, two Japanese researchers dealt with the changes in the cytokines at extreme surroundings in the said location. The Antarctic region is of very high altitude averaging 2450 meters and extreme cold temperature, low pressure and low oxygen level are expected in such kind of geographical condition. Considering this condition, Otani and Kusagaya assessed the health of 7 men who joined a research group participating in the 40th Japanese Antarctic Research Expedition. The evaluation was made in viewpoint of cytokines, protein and peptide chemical signals that have important roles in adaptive immune responses.
After the subjects have underwent serial hematological examinations in 100 days at high altitudes, the researchers have found out that there was an increase in the interleukin-6 (IL-6) levels in the blood serum of a subject who suffered from severe mountain sickness (like pulmonary and brain edema). IL-6 is a pro-inflammatory cytokine that is secreted by the T-cells and macrophages that incites immunological responses particularly in damaged tissues that triggers inflammation. However, the other 6 remaining subjects were in relatively good health for a span of 3 months.
Thus, Otani and Kusagaya concluded that the human body can manage itself against the extreme conditions in the Antarctic region. There are various yet important and related bodily responses in adaptation with environments with low temperature. Generally, responses can occur as vasoconstriction, piloerection and increased body temperature (Thompson et al, 2006). Vasoconstriction refers to the retention of body heat in the core by regulation of the blood flow near organs or region of relatively low temperature such as the skin.
Piloerection is a mechanism of reduction of heat loss employing principles in air insulation of the body and power dissipation of the body which is demonstrated by “goose bumps”. Increased heat production can be achieved by shivering, which is caused by the increased contraction of muscles producing chemical and mechanical heat. If hormones trigger such phenomenon and no production of ATP, then it can be referred to as non-shivering thermogenesis. Extremely low temperatures are not only experienced in the Earth’s polar regions but also in areas of high altitude.
Many harsh conditions are present in such areas and one of the most notable is the low temperature (Kalkstein and Valimont, 1987). There are three processes that the human body employs in such condition, namely: high-altitude acclimatization, evolutionary adaptation and physiological response in extreme altitudes which refers to altitudes at about 6000 m which is known to be not suitable for human survival (West, 2006). The first process mentioned, acclimatization, is generally more related to thermoregulation.
Acclimatization refers to the short-time adaptation of the body in extreme climate conditions and temperatures. In an altitude of around 5000 m, physiological responses in the body that are taking place are hyperventilation, nearly complete renal conpensation of the respiratory alkalosis, polycythemia, increase in intracellular oxidative enzymes and reduced intercapillary diffusion distances in some tissues. Hyperventilation is the most important feature of the process, brought about by hypoxic stimulation of arterial chemoreceptors and is said to be very rigorous.
In the case of lowlanders who go to the 5000 m altitude and stay for a short period of time, there is a reduction in their alveolar partial pressure of carbon dioxide (PCO2) to 25 mmHg compared to the normal value which is 25 mmHg. The decrease in the fall in the alveolar partial pressure of oxygen (PO2) is the physiological advantage of this process, which would otherwise take place. On the other hand, polycythemia which is brought about by the release of erythropoietin, a hormone that regulates red blood cell production mainly in the kidney, in response to the low partial pressure of oxygen in the arteries.
This process was earlier known to be a more important process than hyperventilation. This event encourages the bone marrow to produce more red blood cells. The fall back of the process is that, it is slow and does not become stable in it’s the value for weeks. Those who are new in high altitude conditions often have high red blood cell concentration in their blood on the first two days but not due to the increased production of the red blood cell but on the reduced volume of the blood plasma.
As mentioned, other features in acclimatization include changes of oxidative enzymes in cells, reduction of the intercapillary distance in some peripheral tissues such as skeletal muscles and changes in oxygen affinity of hemoglobin. In the increase in 2,3-diphosphate glycerate amounts with the red blood cells, the affinity of hemoglobin is decreased with the increased to moderate altitudes but has a small effect and at 5000 m altitude, the decrease in partial pressure of carbon dioxide and consequently the occurrence respiratory alkalosis. This event further causes in the increased oxygen affinity of hemoglobin.