On a hot day, or during hard exercise, the body gains heat and its core temperature begins to rise. Fig. 1.1 shows a section through the skin, which contain...

This question is about how the skin cools the body when the core temperature rises, and the consequences of heavy sweating.

(a) Sweat is produced by the sweat gland [1] (the coiled structure deep in the dermis, shown with its duct leading to the surface).

(b) When the body becomes too hot the rate of sweating increases / more sweat is produced [1].

(c) Sweating cools the body because the sweat lies on the skin surface [1]; the water in the sweat evaporates [1]; and evaporation takes heat (latent heat) energy from the skin, cooling the body [1] [3]. The heat needed to turn liquid sweat into vapour is drawn from the skin, lowering its temperature.

(d) The arterioles supplying the skin surface widen / dilate [1]; this is called vasodilation [1] [2].

(e) Because of vasodilation, more blood flows close to the skin surface [1]; so more heat is carried to the surface [1]; and more heat is lost by radiation to the surroundings [1] [3].

(f) A person may feel cold and shiver after heavy sweating because so much water and heat has been lost that the body temperature falls below normal [1]; the body then responds by shivering to generate heat and raise the temperature back towards normal [1] [2].

(g) Sweating a lot increases the need to drink because water is lost from the body in the sweat [1]; this must be replaced by drinking to keep the water content of the blood constant (osmoregulation), otherwise the blood becomes too concentrated [1] [2].