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Tears

 

Overview

Tears flow from tear glands into your eyes through tiny tear ducts. The tear glands are located under your upper lids, and when stimulated, produce tears to form a thin film over your eyeballs. Every time you blink the film spreads over your eyes to keep them moist and free of dust and other irritants. Whether you are awake or asleep, happy or sad, this salty fluid is always flowing from the tear glands. Besides protecting your eyes, the tear glands produce more fluid when your eyes are irritated. These extra tears are called reflex or irritant tears. And, when something makes you happy or sad, your tear glands will produce emotional tears. Used tears then drain down into two tiny openings on the brim of your upper and lower eyelids at the inner edge of your eyes, which lead to the nasolacrimal tear ducts next to the bridge of your nose. From there, they are channeled into your nasal cavity where they are swallowed or blown out with other nasal fluids. If there are too many tears, they will overflow your lower lid and run down your cheeks. Some people have to help stimulate the production of natural tears. This disease is called Dry Eye Syndrome or Sjogren's Syndrome . People who have diseases like rheumatoid arthritis or lupus often have this condition. They must use artificial tears up to every 10 to 15 minutes, and apply other medications to their eyes before going to bed as part of the treatment to improve the condition of their eyes.

Activity

In this activity, you will determine the average number of times humans blink in one minute and the range of how the number of blinks per minute varies from one person to another. Materials:
  • Stopwatch or clock with a second hand
  • Pencil/paper
  • Chart for data collection
1. Ask at least 10 people to help you gather information (data) on blinking. You will want to observe everyone under the same conditions. This is called controlling the variables. You should control for time, temperature and location. 2. Count how many times each person blinks in a minute. Enter your data in a chart. 3. Add the number of blinks from all the people you observed. Divide the sum by the total number of people observed to determine the average number of blinks. 4. To find the range, look for the person with the lowest number of blinks and the person with the most blinks per minute. The difference between the fewest and the most is called the range. For example, if George had five blinks and Juanita had 13, than the range is from five to 13.

Resources

  • Frey, William H. and Lanseth, Muriel. Crying, the Mystery of Tears. Minneapolis: Winston Press, 1985.
  • Kapit, Wynn and Elson, Lawrence M. The Anatomy Coloring Book. NY: Harper and Row, 1977.