Jain Vidyalay Hirak Jayanti Granth

SR No.: 012029
Original Sutra Author: N/A
Author: Kameshwar Prasad
Publisher: Jain Vidyalaya Calcutta
Publication Year: 1994
Total Pages: 270
Language: Hindi, English
Classification: Smruti_Granth & Articles
File Size: 11 MB

Page 223

had well developed hair.
Heat loss :- Various agencies are responsible for control of the heat loss. The convection from the surface of the body can be controlled by changing the position of the hair. The skin contains devices for losing as well as for retaining heat. The sweat glands are derived from the Epidermis but lie deeply in Dermis. They tubular glands much coiled at their inner ends and surrounded by myo-epithelial cells contain contractile fibries and serve to expel the secretion. The sweat is watery solution, whose evaporation serves to cool the body. The amount of liquid (sweat) produced is controlled by the action of nerve fibres of the sympathetic nervous system. Sweat glands are not properly developed in all the mammals e.g. in cats these glands are confied to the pads of the feet. In man they occur all over the body, most abundantly in the axilla and groin. They are altogether absent from the skin of whales and sea cows.
temperature which may reach as high as 42°C. It is not clear how these various heat regulating centres are related
If cooled blood reaches one of these regions the shivering mechanism is set in action; conversely perfusion of the Carotid arteries with overwarm blood causes sweating or panting. Heat producing systems other than muscles may be called upon. The Liver and other organs give out heat in the course of their work and it is possible that during periods of sleep they may be stimulated to increased activity and greater heat output. Thyroid secretion increases the basal metabolism and thus the amount of secretion produced by the Thyroid affects the temperature. Other Endocrine glands are probably also involved.
Heat Conservation - Hair tends to trap a layer of air, which insulates the body, reducing heat exchange with the Environment. The air retaining capacity is increased in some mammals by a roughening of the surfaces of the hair, which causes them to stick together to make a pelt. The hair are not of the same kind all over the surface of the body: often longstiff hair are found mingled with softer fur. In many mammals the hair changes according to the time of year so as to provide a thicker covering in winter than in summer.
The hair do not grow straight out from the skin but are placed obliquely, so that they all set in a particular direction, giving the coat its characteristic reaction to brushing. It has been suggested that the primary direction of the hair provides a backward slope, which would prevent them from catching in grasses. The reasons for the deviations from this direction, which occur in many mammals are not understood
Not all mammals use an air layer for the retention of heat. In the whales and walruses the body is covered with a thick layer of fat called Blubber in the Dermis of their skin, the hair are reduced to a few vibrissae. In man, hair are present over most parts of the body, but their function is mainly tactile and heat is conserved mainly by a layer of fat in the skin. Very large mammals, such as Elephants or Rhinoceros have little need to minimize heat loss, since their surface is small relative to the large heat producing volume the hair are accordingly reduced. Related species that existed during glacial periods
The amount of heat lost from the surface is also controlled by regulating the flow of blood. When the whole capillary bed is used the skin becomes flushed and loses much heat, also the sweat glands receive more blood. In cold conditions a set of Arterio-venous anastomoses is opened up so that the blood short circuits the capillaries and the skin becomes blue or white. These processes are influenced by the hypothalamus. The surface of the lungs also provides a means of heat loss. Animals such as dogs which have few sweat glands resort to panting.
Large animals use special means for losing heat, for instance the African elephant increases its total surface area by nearly one-sixth (1/6) when it raises its ears. The flapping movements of ears are more frequent in large elephants than small. The flow of blood to the ears is increased in hot weather. The ears are used for heat loss in smaller animals also. In North America the hares have longer ears in the warmer southern regions.
Assistant Teacher Shree Jain Vidyalaya, Calcutta
हीरक जयन्ती स्मारिका
अध्यापक खण्ड/२६