. The state of blood vessels also powerful govern me hue or color of the skin and has been discussed

processes of the cell, into other Celts of the epidermis in the people of the colored races (Asians, Negroes) although the number of melanocytes is not higher, the amount of melanin produced is higher. The state of blood vessels also powerful govern me hue or color of the skin and has been discussed In details elsewhere in this book (coetaneous circulation chi 10. sec V). in short, vasoconstriction, (due to. say, sympathetic over activity) toads to pale skin or pallor, where as In a comfortably warm atmosphere (where the vessels of the dermis are well dilated). the color of me skin is reddish If the blood of the dermis. due to any reason is extraordinary reduced, color of the overlying epidermis that is color of the Skin' (at that region) also becomes blue, a condition called cyanosed. Cyanosis has been discussed in greater detail, in ch. 7, sec IV. FUNCTIONS OF THE SKIN These may be discussed under four headings (i) temperature regulation, (ii) sense perception(iii) protective function, and (iv) water balance. Temperature regulation Temperature regulation has been discussed in the section dealing will neurophysiology (Thermal regulation, sec XD, chap. 2). In short, me major functions or the skin in relation to the temperature regulation are as follows: The different organs of the body, notably the liver, generates large Quantities of heat. The interior of the body, called the core, thus produces the heat Now. if the core becomes too hot, -some of its heat is discharged through the Skin which forms part of’ shell' This is done by cutaneousvas dilatation, heat from the core comes, to the shell (_ skin and subcutaneous tissue) via the blood, reaches the skin and passes into the environment (provided, the environment has a lower temperature than that of the body). Coetaneous vasodilatation (which , mediated via the hypothalamus), is thus a fundamental mechanism to keep the body cool On the other hand, in a fold climate, when it is necessary to heap the body warm, there is coetaneous vasoconstriction. so that the core heat cannot be dissipated and the causes preservation of body heat Coetaneous vasoconstriction is also due to the hypothalamic activity In an environment where the environmental temperature is hotter than that of the body, there cannot be any dissipation of coetaneous heat try ordinary methods (Like conduct on/convection /radiation) Now, the sweat glands, (the echini glands) sweat. the sweat is evaporated, taking the latent heat of evaporation from the body and the body is cooled .Temperature regulation is a fundamental homeostatic process Excessive body temperature can kill the subject Subnormal temperature, also, can kill Sense perception This has been discussed in greater detail in sensory physiology. In short, skin contains nerve endings, as well as various receptors for touch and temperature. Afferent nerves emerge from them carrying specific sensation and ultimately convey those sensations to proper areas of the brain so that the subject feels (perceives) The sense. Touch, pain and temperature are coetaneous sense aborts Protective function (1) Ultraviolet (UV) rays of the sun cause damage of the skin called ultraviolet ray injury Melanin and the thick stratum come together prevents such injury Exposure to UV rays stimulate more melanin production and melanin adsorbs the light of all wave lengths. The stratum cornea also thickens when it is chronically exposed to sun rays The stratum corneum absorbs waves mostly which are less than 320mu (UV light = light waves having less than 360 mg lengths) Such naves are often cancer producing There is an interesting theory which states that in the distant past, in Europe, all the persons n whom melanin production was excessive,