I have trouble with my fingers and toes in cold weather. I am a retired doctor, and an outdoor athlete all year. I want to share my knowledge about this problem with anyone who is interested.

Your brain is the most important part of your body, and your body knows it. Your body’s most important job is to keep your brain alive by keeping your core temperature near 98.6 degrees.

When a doctor or nurse takes your temperature by putting a thermometer under your tongue, they are actually trying to take your “core” temperature. Your core is your abdominal viscera, your spinal cord, and your brain. The space under your tongue is the place to which they have the easiest access to a temperature similar to your “core” without generating discomfort or embarrassment. If your core temperature goes too low or too high, your heart will pump blood that is too hot or cold to your brain and hence will cause your brain to malfunction.

The autonomic system controls your body temperature, as well as many other bodily functions, such as heart rate, blood pressure, and how much pee you make. It does so automatically, most of the time, without you being aware.

Let’s concentrate on how the autonomic system regulates temperature. For simplicity, I will discuss only cold temperatures. The system works in reverse for high temperatures. (Maybe I will write another op-ed for “sweating” next summer!)

Unlike many digital systems with which we are familiar, the “computer” that governs the autonomic system is not digital and it is not at all central. It is analog, and it is spread over a great deal of your brain, spinal column, general nervous system and organs. It has many inputs. Sensors, including temperature sensors, are located all over your body. They are all connected eventually to your autonomic system. But not all of them are connected directly to your brain. For example, there are pressure sensors in your bowels. If you have a bowel obstruction, you may not be able to tell exactly what is going on because sensors in your bowels do not have direct connections to your brain the way your fingers do.

If any temperature sensor gets cold, your autonomic system knows it. If enough of them get cold, it compensates by slowing down or stopping blood flow to “unimportant” and exposed organs, like your fingers and toes, and maybe your ears and your nose. It tries to conserve heat for your brain.

The algorithm that your autonomic system uses for deciding how to handle temperature variations has different variables for different people, and the algorithms change as the individual ages. When you are 13 years old, you might easily tolerate wearing shorts on a 20-degree day. But not if you are 75.

The most important statistic that your autonomic system calculates is the ratio of how much heat you are generating compared to how much heat you are losing, or heat generated divided by heat lost. You are playing the game very well if the heat you are generating is equal to the heat you are losing. The ratio then equals 1. But if the heat you are generating is less than the heat you are losing, the ratio is less than 1, you are losing the game, and you had better do something about it.

If your fingers and/or toes get cold when you are sitting in your living room reading a book, your body is telling you something. It is trying to conserve heat by shutting off blood flow to your “unimportant” small parts (that are extremely exposed). You can raise their temperature by changing the ratio of heat generated to heat lost by:

— Raising the target temperature on your thermostat (thereby reducing the heat lost from your body to the environment). This is a reasonable strategy when the outdoor temperature is extremely low, since the walls of your house get colder as the outdoor temperature goes down, and your body loses more heat to the house’s walls through infrared radiation. (Yes, Hot-Stuff, you do radiate infrared.)

— Wearing more insulation (another fleece or coat, long underwear, insulated pants, gloves or a hat) again to reduce heat lost to the environment. The increased insulation does not have to be on the body part that gets cold. A hat is always a good idea because a very large fraction of heat lost to the environment goes through your head. Your autonomic system will probably respond to the overall preservation of body heat by increasing blood flow where it has previously reduced it.

— Exercising. Walking around or climbing stairs.

Please, do not expect to get relief in a minute. Heat moves slowly through the human body.

In thinking about this op-ed for months, I have started climbing stairs to warm up. I bought new high-top furry shoes. And I bought heated gloves. They all help. In fact, the gloves make my toes warmer!

Ben Lounsbury lives in Auburn.