Temperature Regulation of the Human Body

Human beings are warm-blooded animals, and can maintain a relatively constant body temperature even in extremes of arctic cold and tropical heat. This may be one reason why humans have a wider distribution across the world's surface than any other species: they are less dependent for survival on the temperature of their surroundings.

Environmental temperatures, both high and low, are not the only factors that influence your body temperature. Most of the chemical changes that take place in your body tissues during their normal functioning, in glands and muscles especially, generate heat energy. The heat your body tissues need is distributed to them by your circulatory system. If you had no way of getting rid of excess heat, your body temperature would ri se by about 1 °C every hour - even if you were not doing anything.

Constant body temperature is maintained by a balance between the heat produced and the heat lost by your body. When heat loss and gain do not balance, regulatory mechanisms in your body (which are under the control of the hypothalamus in your brain) come into action and compensate for overheating or overcooling. The temperature-regulating centers of your hypothalamus, one sensitive to heat, the other to cold, act like a thermostat, responding to information sent back from temperature receptors throughout your body.

Heat production

All your body tissues produce heat as a normal by-product of the chemical processes taking place within them. The greatest heat production is from the most active tissues -your liver, your glands and your muscles.

Muscular activity accounts for about thirty per cent of your body' s heat production, even when you are resting. During physical exercise, the amount of heat your body produces is greatly increased.

Your body also gains heat when the environmental temperature is higher than your body temperature.

Heat loss

Your body loses heat through your skin by conduction, convection and radiation. Additionally, you get rid of a small amount in the air you breathe out, and in your urine and feces.

The part of the nail you can see is its clear body or plate, which is only 0.5 millimeter (2/10 inch) thick. It rests on a living, highly sensitive area called the nail bed. and grows out of the matrix (root) which is hidden under and protected by the cuticle at the base of the nail. It is the matrix that produces the new horny cells from which your nails are made, and the cuticle (the small flap of skin curving around the base of the nail) that guides the direction in which they grow. Also at the base of each nail is the opaque crescent-shaped lunula (half-moon), which is sometimes hidden under the cuticle.

So that they can function properly, the temperature of your internal organs (the central, or core, temperature) must be kept at an almost constant level. The temperature of your skin, however, and the tissues just underneath it, can vary according to the environmental temperature -and needs to do so if your internal organs are to be protected and your vital systems safeguarded.

Radiation

Heat is transferred from your body's surface to objects nearby that are cooler; it is transferred to the skin by warmer objects.

Heat is carried from your internal organs to your skin by the bloodstream, and radiation of heat from your skin's surface can be increased greatly when the tiny blood vessels just under the surface of your skin get wider.

When the environmental temperature is higher than your body's temperature, you cannot lose heat by radiation.

Conduction

Heat is transferred from your body to any object or substance in direct contact with it. Rapid heat loss occurs when your body is in contact with good conductors of heat, like metal, or light cotton clothing, and can be minimized by wearing clothes made of wool or fur, which are poor conductors of heat.

Convection

Heat is transferred away from the body surface by the movement of the air around you. The air close to your skin is warmed by it and rises, allowing cooler air to take its place next to the skin.

 

Evaporation

Your body has to use heat to change water on the surface of your skin into water vapor. You continually lose a small amount of body heat this way by what is known as insensible perspiration, a process akin to sweating by which you get rid of about a cupful of water through your skin every twenty-four hours. You are unaware of insensible perspiration (hence its name) but it is a process that cannot be controlled for the purposes of temperature regulation.

When your body temperature rises, however, larger amounts of heat can be lost through sweating. The evaporation of sweat is a very efficient way of cooling your body, and is especially important when the environmental temperature rises to over 37°C (98.6°F) because under these conditions your body will gain heat by radiation, convection and conduction. In humid conditions, even if the air temperature is not especially high, sweat may drip off your body rather than evaporate on your skin, and therefore be useless as a coolant.