Neither hot nor cold

Considering the evolution as the process of improvement of homeostasis, we cannot be silent about the temperature of the internal environment of the organism and thermoregulation. Most chemical reactions, including biochemical associated with metabolism, proceeds more intensively at high temperatures than at low. So, if you measure the speed of oxygen consumption by different organisms depending on their temperature, the relationship between the two variables are quite the same in all living creatures and increases as the temperature of a body at all the same. However, those organisms, whose own temperature equal to ambient temperature, usually more active at sufficiently high temperatures. The easiest life, of course, those beings whose temperature is constant and independent heat or cold. In this respect was the furthest advanced of warm-blooded animals - mammals and birds.
Body temperature depends on two factors: from heat production and heat loss. At first influenced by the intensity of metabolism, and, as we have said, the metabolism is, in turn, depends on temperature; on the exchange rate effect and some hormones, especially hormones the thyroid gland and adrenal glands. You may notice that even some fish thanks to intensive metabolism, body temperature is always higher than a few degrees (!), than the water temperature, and this difference, as the reader is aware, in the summer more than winter. Vital activity of many cold-blooded depends on the heat from the outside. Hence the various features of the behavior of cold-blooded: seasonal hibernation or even a full stop living processes (for example, a frog in winter), circadian rhythms behaviour of amphibians and reptiles, related to temperature fluctuations.
Without going into the details of life cold-blooded, let us consider the peculiarities of terrestrial mammals, which is always good regulate its temperature homeostasis (however, other reptiles also have a powerful apparatus of thermoregulation).
The generation of heat in mammals occurs mainly in the liver, during chemical processing of food (about 50 % of all heat). On average, one fifth of the thermal energy allocate muscles, with intensive physical work can increase the total heat production of a man ten times, although this increase is a certain amount belongs to the muscles of the heart, respiratory, muscular, vascular muscles and the nervous tissues that are involved in the work and providing energy resources. Alone about 10 % of the heat allocates the brain and approximately as much - the heart and respiratory muscles.
Young organisms significant share in the energy formation carries brown fat - it is somewhat similar to the role of egg yolk for avian embryo.
Any such different ways heat should provide mammal constant body temperature. In humans, this temperature is about degrees above that which is measured under one arm. This higher temperature characteristic of a relatively limited area of the body, quite remote from the surface and are quite difficult for accurate measurements. This thermostable area is called the kernel and its temperature - Central temperature. It is close to the temperature of the brain and the peace of mind in a healthy person, equal to about 37,5 °N
Among small mammals body temperature is much higher, because the surface of their bodies (i.e. heat) per unit mass more, and motor activity, usually high.
Finally, on the generation of heat affected eaten food that may be high in calories or not, rich or poor, and hungry always colder than a well-fed. Has the value and emotional state, and the activity of the autonomic nervous structures influencing the generation of heat and located, according to current views, mainly in the rear part of the hypothalamus part of the brain.
So, all the heat generated in the body, should be dispersed in the environment, but at a certain speed to ensure temperature homeostasis kernel. The heat dissipation of thermal energy necessary, or else overheating and destruction.
Heat transfer occurs in several ways. This is, firstly, thermal radiation. However, one should not forget that the thermal energy radiates any body, including those surrounding body objects,the sun, hot sand, radiation comes from less heated bodies than the skin of the animal, and it radiated heat from the outside the body in varying degrees, perceives, absorbing or reflecting.
The second way of heat - convection occurring during direct contact with the external environment. The intensity of this heat loss is higher, the higher the conductivity of the skin of the body and the environment, absorbing heat, but also the speed with which moves the body in the environment (or the speed with which the environment washes the body, such as wind speed), and, of course, from the temperature difference of the skin and the environment. If the temperature of both are the same, there is no convection heat loss.
Finally, the third method of heat - moisture evaporation from the surface of the body. The amount of cooling surface depends on the boiling temperature and heat of vaporization of the liquid, but in a living organism evaporates or sweat, or the mucus of the upper respiratory tract and saliva that these features are pretty close. The sweating animals (and people) the amount of sweat loss can be very large. Our eyes working in spacesuits in extreme heat lost 10 min few liters of sweat. Thermal dyspnea y nepotisim animals, such as dogs, and even some lizards and crocodiles.
For our story, it is important that all methods of heat transfer are provided primarily by vascular reactions that occur reflex. The skin vessels are located in several layers, the United special "cranes" - shunts. If you want to increase the cooling of the body, the blood flow switches to the surface of the skin vessels, these vessels are still expanding. This increases the thermal radiation and convection. Sweating is also accompanied by the required extension of skin vessels feeding the sweat glands, and the sweat stands out due to the liquid part of blood and plasma. The salt in sweat, ensure the preservation of the normal osmotic pressure of blood.
All thermoregulatory vascular reflexes start in terminala thermoreceptors that may be sensitive to heat or cooling; thermoregulatory center there in the medulla, but the main source of centrifugal thermoregulatory pulses consider the back of hypothalamic Department of the brain.
In recent years, a number of psychologists inclined to think that the number of thermoreceptors is enormous, and even about half of all neurons are the true thermoreceptors. However, it seems more likely that these neurons have other functions, mainly related to the self-regulation of blood circulation.
Thanks to the precise interaction of heat generation and heat transfer (under the control of thermoreceptor) the core temperature of the body is quite stable.
In our research we proposed athletes load standard capacity, respectively, the mass of the muscles when the room temperature is 20 degrees C. the Duration of the work to full exhaustion ("can't!") was determined by the temperature of the core of the body" - we measured its microtimestamp on the ear drum ear, strongly insulated from the air. The temperature of rest here was average or 37.4 degrees when she reached 38,7 degrees and heard it "no Longer!". Under arms steering the Ergometer has accumulated a decent puddle of sweat. "The failure temperature has been remarkably constant in a large group of subjects. In the literature there are higher levels of working overheating, but we see them happening.
In animals there are other forms of thermoregulation, such as vcherashnie fur or feathers (piloerection). There is a group thermoregulation" - cubs or the Chicks are bunched together, saving heat. The main difference of the people in this respect - clothing. Shelter from cold to know how to build and many animals.
Let us once again the attention of the reader on brain temperature homeostasis, which must be supported by all means, not deviating from the optimum more than a degree and a half. Feverish delirium patient - evidence of cerebral homeostasis, especially temperature.
The temperature of the "core" depends very much: motivation, behavior (for example, the desire to bask running), muscle tone, which affects their heat production and grows when cooled, and Vice versa; strong cooling causes muscle tremor - a way to increase the production of thermal energy in the body.