Going Hot and Cold: Body Temperature
At our age, most of us can probably remember that long glass thermometer that we would pop into our mouths when we were sick. A normal temperature in those days was 98.2 degrees Fahrenheit as this was the slightly cooler typical measurement for under the tongue. The accepted core body temperature internally was thought to be 98.6 degrees Fahrenheit.
Now of course we no longer need the breakable glass thermometers containing mercury, our temperature can be taken by all sorts of modern methods including plastic strips on the forehead, digital thermometers and ear thermometers. We also look at 37 (or actually 36.8) degrees centigrade rather than the old Fahrenheit numbers.
But today doctors also know that while the basis of 36.8°C as a healthy body temperature remains, there is no one exact normal body temperature. Different parts of the body produce different temperatures, but also the time of day and level of activity of a person also affect the measurements.
In healthy people, body temperature can fluctuate around 0.5°C (0.9 °F) through a day just because the requirements of the body change. Body temperature changes when someone is hungry or sleepy. The highest body temperature is often recorded at around 7pm in the early evening and falls to its lowest around 4.30am in the morning during the second half of the sleep cycle (the nadir).
Whatever the outside temperature, our bodies are geared to take action to keep our internal temperature as near to the required 36.8°C as possible.
When you exercise or are in very hot conditions, your body temperature can rise but will automatically reduce to normal quite quickly once the situation has changed. When you are fighting an infection or illness, the body goes on the defensive and the immune system is activated. Then a central nerve in the brain allows the heat inside the body to be turned up to a higher temperature which increases metabolism and prevents the increase of disease related agents.
When you get too hot, the blood vessels in your skin expand (dilate) to carry the excess heat to the skin’s surface where it is releases. Sweating releases moisture in a process that cools the skin - many of us will remember that from our school lessons on latent heat of evaporation.
At opposite ends, bodies can get too cold. When you are cold, the blood vessels in your skin narrow (contract) so that blood flow to your skin is reduced to conserve body heat. You may start shivering, which is an involuntary rapid contraction of the muscles to help generate more heat.
When a body loses more heat than it can generate and the body drops below 35°C, hypothermia is said to have set in. Hypothermia comes in different forms:
- acute hypothermia which usually occurs when the body loses heat very quickly, perhaps by sudden immersion into cold water.
- exhaustion hypothermia which occurs when a body has no energy to generate any heat; this can occur after accidents or specific activities.
- chronic hypothermia which is when heat is lost slowly over time; this is the most common problem in elderly people.
Keeping the right body temperature is crucial. Along with water balance, our blood sugar levels and our blood pH, our internal conditions need to be kept as constant as possible for the body to work properly and to ensure the stable operation of vital functions, including the brain, internal organs and main arteries. Therefore it makes sense to still keep a thermometer in your first aid kit and if you are feeling ill, checking your temperature can be a very good indicator of how you are.
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