THERMOREGULATION

In health, the human body regulates its temperature at a constant average of 37°C even though the environment temperature may vary greatly. This is maintained via a negative feedback system, in which the skin plays a major role.

The Role of Skin in Heat Loss

There are thermoreceptors (temperature-sensitive nerve endings) in the skin that detect changes in body temperature.

When the body temperature rises, nerve impulses are sent to the temperature control centre in the brain. The temperature control centre then causes a number of events which bring the body temperature back within the normal range, primarily through vasodilation and perspiration.

Vasodilation

Vasodilation is when blood vessels dilate, causing more blood to pour into the capillary network and the skin to become warm. This excess heat is lost to the environment via conduction, convection and radiation.

Perspiration

Increased temperature of the blood causes activation of the sympathetic nervous system. This stimulates sweat glands to produce perspiration (sweat). The water in sweat then evaporates from the skin. As sweat evaporates, it dissipates heat into the environment. The minimum insensible perspiration is 0.5 litre per day (Gawkrodger, 2002).
At the same time as vasodilation and perspiration occurs, the metabolic rate decreases. When the body temperature returns to normal (homeostasis), vasodilation and perspiration decreases (Tortora & Derrickson, 2013).

External temperature has a substantial influence on how body temperature is regulated. Higher temperatures coupled with high humidity can reduce the body’s ability to sweat efficiently as the air is already saturated with moisture. This means it is harder for sweat to evaporate and carry heat away. The resulting effects are discomfort and a greater risk of heat-related illnesses.

The Role of Skin in Heat Conservation

In response to a drop in body temperature, changes occur that help to conserve heat and, at the same time, promotes the production of heat at a faster rate. This is again achieved through a negative feedback response.
A drop in body temperature is detected by thermoreceptors, and nerve impulses are sent to the temperature control centre. In response to this, the hypothalamus secretes thyrotropin-releasing hormone and discharges nerve impulses. This causes several responses, which help promote heat production and conservation.

Skin plays the following role in heat conservation:

The nerve impulses from the hypothalamus stimulate sympathetic nerves, causing vasoconstriction. This decreases the flow of warm blood through the skin and therefore the amount of heat lost. At the same time, heat production is increased through the effect of thyroid hormones on metabolism, an increase in cellular metabolism and shivering (Tortora & Derrickson, 2013).