In an unacclimatised person suddenly exposed to cold atmosphere, changes seen are
|A||Increase in systolic BP|
|B||Shift of blood from shell to core|
|C||Non — thermogenic shivering|
Body responses on exposure to cold:
Keep its internal temperature constant by increasing heat production or by reducing heat loos.
a. Heat loss in reduced by cutaneous vasoconstriction this reduces the amount of heat transferred by the blood from the body core to the body surface (shell). This may raised the B.P. Heat loss is also reduced by piloerection
b. Heat production ↑ed by:
c. ↑es the metabolic rate
d. ↑ Adrenaline secretion → chemical thermogenesis or non shivering thermogenesis from brown fat (by uncouple oxidative phosphorylation). Since brown fat almost absent in adult, so it is not important in adult. But important in neonates, in which non shivering thermogenesis, increases the heat production by 100%
i. Increased thyroxin productin as a long term cause of increased Heat production → it requires several weak
ii. Shivering → during maximal shivering body heat production can rise to four to five times normal → shivering centre located in dorsomedial portion of the posterior hypothalamus
iii. Voluntary muscular activity.