How the Body Handles Heat
The human body,
being warm blooded, maintains a fairly constant internal temperature, even though it is being exposed to varying environmental temperatures. To keep internal body temperatures within safe limits, the body must get rid of its excess heat, primarily through varying the rate and amount of blood circulation through the skin and the release of fluid onto the skin by the sweat glands. These automatic responses usually occur when the temperature of the blood exceeds 98.6oF and are kept in balance and controlled by the brain.
In this process of lowering internal body temperature, the heart begins to pump more blood, blood vessels expand to accommodate the increased flow, and the microscopic blood vessels (capillaries) which thread through the upper layers of the skin begin to fill with blood. The blood circulates closer to the surface of the skin, and the excess heat is lost to the cooler environment.
If heat loss from increased blood circulation through the skin
is not adequate, the brain continues to sense overheating and signals the sweat glands in the skin to shed large quantities of sweat onto the skin surface. Evaporation of sweat cools the skin, eliminating large quantities of heat from the body.
As environmental temperatures approach normal skin temperature, cooling of the body becomes more difficult. If air temperature is as warm as or warmer than the skin, blood brought to the body surface cannot lose its heat. Under these conditions, the heart continues to pump blood to the body surface, the sweat glands pour liquids containing electrolytes onto the surface of the skin and the evaporation of the sweat becomes the principal effective means of maintaining a constant body temperature. Sweating does not cool the body unless the moisture is removed from the skin by evaporation. Under conditions of high humidity, the evaporation of sweat from the skin is decreased and the body's efforts to maintain an acceptable body temperature may be significantly impaired.
http://www.cdc.gov/niosh/hotenvt.html
Mealen özetle:
Sıcak ortamda kalan vücut bu ısıyla baş etmek için çeşitli önlemler alır;
Kalp daha fazla kan pompalamaya başlar
Kan damarları artan kan miktarına uyum sağlamak için genişler
Üst deriye yakın yerlerdeki kılcal kan damarları kanla dolar
Kan dolaşımı deriye yakın yerlerde daha fazla olur
Bunlar yeterli gelmezse beyin terleme emrini verir
Bütün bunların olabilmesi için ise vücut enerji harcar.
Body Temperature/Health
For every increase of 0.5C in internal temperature of the body, the BMR increases by about 7 percent. The chemical reactions in the body actually occur more quickly at higher temperatures. So a patient with a fever of 42C (about 4C above normal) would have an increase of about 50 percent in BMR.
Short Term Factors Affecting BMR
Illnesses such as a fever, high levels of stress hormones in the body and
either an increase or decrease in the environmental temperature will result in an increase in BMR. Fasting, starving or malnutrition all result in a lowering of BMR. This lowering of BMR can be one side effect of following a diet and nothing else. Solely dieting , i.e. reducing the amount of calories the body takes on, will not be as affective as dieting and increased exercise. The negative effect of dieting on BMR can be offset with a positive effect from increased exercise.
http://www.shapefit.com/basal-metabolic-rate.html
Mealen özetle:
Vücut sıcaklığındaki her 0,5 derecelik artış bazal metabolizma hızında ortalama yüzde 7 lik bir artışa neden olur. Vücut sıcaklığı 42 dereceye ulaşan bir insanın bazal metabolizma hızı ortalama yüzde 50 oranında yükselir.
Ortamın sıcaklığındaki yükseliş ve düşüşler bazal metabolizma hızında yükselmelere neden olurlar.
Daha birçok kaynak var ama tıbbi terimler oldukça fazla olduğundan daha normal dile yakın olanları seçmeye çalıştım.
