ICSE Class 9 Answered

Vasoconstriction is the narrowing of blood vessels in the skin. It helps in temperature regulation of the body in cold weather.

• At low temperature, the blood vessels get narrowed or vasoconstricted. This reduces the blood supply to the skin.
• There is less loss of heat by convection, conduction and radiation. There is less loss of heat through vapourisation as reduced blood supply lowers the secretion of sweat by sweat glands.
• The person looks pale or bluish because of reduced blood supply to the skin.
• The amount of heat produced is increased by increased metabolic rate and muscular activity, which occurs in the form of shivering.

Vasodilation is the dilation of blood vessels in the skin. It helps in temperature regulation of the body in hot weather.

• At high temperature, the blood supply to the skin is increased by vasodilation or dilation of blood vessels in the skin.
• This results in greater loss of heat by convection, conduction and radiation. There is more loss of heat through vapourisation as more sweat is secreted due to the rich supply of blood to the skin.
• Heatstroke or sunstroke is a condition in which sweat production is unable to keep pace with its evaporation in very hot winds. This results in an increase in body temperature which may prove to be fatal.
• Drinking a lot of water and consuming more of salt in summer is a good precaution against sunstroke.