dimanche 12 février 2012


Esta frio ! Mas sabe precisamente o que acontece, no corpo, quando este tem frio?
Pode ler algumas respostas neste livro digital (em inglês) sobre fisiologia humana e escrito por Paulev Zubieta, capitulo 21 : Thermo regulation, temperature and radiation.

Quando esta com frio, parece que o seu corpo quase encolhe até ao centro. Vai entender ô porque da sensaçoe, às vezes dolorosa, de se sentir tolhido (a)

Seguem-se algumas citações:

Definitions :

Body core consists of the thermoregulated deeper parts of the body and the proximal extremity portions of warm-blooded animals including man 
Body shell refers to those outer parts of the body (skin and subcutaneous tissue) that change temperature at cold exposure.

Cutaneous vasoconstriction lowers skin temperature, and thereby reduces the conductive-convective heat loss that is determined by the temperature gradient from the skin surface to the environment. Cutaneous vasoconstriction directs the peripheral venous blood back to the body core through the deep veins and the commitant veins. These veins are located around the arteries with warm blood, so that the venous blood receives part of the heat energy from the arterial blood - so-called counter current heat exchange. The vasoconstriction is so effective, that the bloodflow through the arterio-venous anastomoses in the fingers and toes can fall to below one percent of the flow at normal temperature. The cooling of the shell is immediate, and the size of the shell increases. Obviously, the shell is large for a naked person in cold air. The resistance vessels of the hands may open periodically to nourish the tissues, but the high viscosity of the cold blood can endanger the tissue nutrition and result in trench foot.
The arterio-venous shunts of the hands and feet are closed, so the bloodflow to the limbs is a nutritive minimum.
The deep arteries and veins of the limbs lie in parallel, so the arterial bloodflow loses heat to the incoming venous blood partially surrounding the arteries (Fig. 21-5). This is a typical counter-current heat exchange. In a cold environment, where vasoconstriction and heat exchange produces cold extremities, the total insulation is increased at the expense of reduced neuromuscular efficiency.
human arm