Lesson 7: How Do We Know When We're Sick? PDF

LESSON 7 How do we know when we’re sick? You might say, “I feel sick,” or “I don’t feel well.” But what does “sick” mean? For that matter, what does it mean to feel “well”? From the perspective of your body, it means that a number of critical characteristics are being maintained within fairly narro...

LESSON 7 How do we know when we’re sick? You might say, “I feel sick,” or “I don’t feel well.” But what does “sick” mean? For that matter, what does it mean to feel “well”? From the perspective of your body, it means that a number of critical characteristics are being maintained within fairly narrow ranges. Those characteristics include body temperature, and when our body temperature climbs higher than normal, we call it a fever, one of the most recognizable symptoms of illness. What is “normal” body temperature? But what is “normal” healthy body temperature, anyway? You may have learned that a “normal” body temperature for humans is 98.6°F, or 37°C. This is based on a study conducted in 1869. A more recent study found that the average temperature in a group of men and women was 97.7°F, or 36.5°C. This temperature not only varied from individual to individual, but also varied depending on the time of day for any one individual. This finding emphasizes that a healthy body temperature is not just one point, but exists within a range of temperatures. Nevertheless, most healthy people have an average body temperature between 96°F (35.6°C) and 99°F (37.2°C). Healthy body temperature range for humans. Recent studies indicate that the average human body temperature is 97.7°F, lower than previously thought. The traditional 98.6°F, however, is within the healthy temperature range (left). Within any individual, body temperature also fluctuates over the course of each day (right). If you are in a cold external environment, nerve cells in your skin sense this and relay the message to your brain. The brain then triggers your body to respond. You begin shivering, which generates some heat for your body. On the other hand, if you are outside on a hot day, the nerve cells in your skin sense this also and send a message to your brain that body temperature is in danger of increasing above the healthy range. Your body responds by sweating and diverting blood flow away from internal organs so that they are not damaged by excess heat. Shivering and sweating are ways the body attempts to return our internal body temperature to the healthy range even as the external environment becomes colder or hotter. Homeostasis The body’s attempts to stay within the normal healthy range can be referred to as the process of homeostasis. Even though small changes and fluctuations may occur as the external environment changes, the body is usually able to maintain relative stability. Symptoms and tests Taking our temperature and seeing a number that is higher than our normal range reveals a fever. Any time our body’s levels deviate from normal can be an indicator that we’re sick. In fact, if they are concerned about the possibility of an infection, doctors often look at a variety of immune cells and molecules in the bloodstream by ordering blood tests. Each of these tests has a certain range within which most healthy people fall, and levels much higher or lower may indicate infection.