What purpose do tears have?

Tears are the secretion of the lacrimal glands. They continually bathe the cornea, the tough outer layer of the eyeball. They help to clear it of foreign particles, such as dust and hairs, and keep it from drying out, which would result in blindness. Two lacrimal glands, one over each eye, lie behind the eyelid. They pour out their fluid through several small ducts in the underside of the eyelid. Each time a person blinks an eyelid, it sucks a little fluid from the glands. When a person feels some emotion very strongly, such as grief or anger, the muscles around the lacrimal glands may tighten up and squeeze out the tear fluid. After the tears pass across the eyeball, they flow out through two lacrimal ducts that open at the inner corner of each eye.

Fact File

Mostly a salt solution, lacrimal fluid also contains substances that fight bacteria, and proteins that help make the eye immune to infection.

Why do our pupils change size?

In the middle of the iris is a round opening called the pupil, which looks like a black circle. The size of the pupil regulates the amount of light that enters the eye. Two muscles in the iris automatically adjust the size of the pupil to the level of the light. In dim light, the dilator muscle enlarges the pupil, so as much light as possible can then enter the eye. In bright light, the sphincter muscle makes the pupil smaller, which prevents too much light from entering the eye. The pupil also becomes smaller when the eye looks at a nearby object, thus bringing the image into sharp focus.

Fact file

Birds have the keenest sight of all animals, including human beings. An osprey can see a dead animal on the ground from a height of up to 4km.

What causes hiccups?

“Hic!” You’ve just hiccupped for what seems like the 10th time since you finished your big dinner. Wonder where these funny noises are coming from? The part to blame is your diaphragm. This is a dome-shaped muscle at the bottom of your chest and all hiccups start here.

The diaphragm almost always works perfectly. It pulls down when you inhale to help pull air into the lungs, and it pushes up when you exhale to help push air out of the lungs. But sometimes the diaphragm becomes irritated, and when this happens, it pushes up in a jerky way that makes your breath come out differently from how it normally does. When this irregular breath hits your voice box, you’re left with a big hiccup.

Some things that irritate the diaphragm are eating too quickly or too much, an irritation in the stomach or the throat, or feeling nervous or excited. Almost all cases of the hiccups last only a few minutes. Some cases of the hiccups can last for days or weeks, but this is very unusual, and it’s usually a sign of another medical problem.

You’ve probably heard lots of suggestions for how to get rid of hiccups, and maybe you’ve even tried a few. Holding your breath and counting to 10 is one way some people can get rid of their hiccups; other people say that drinking from the “wrong” side of a glass of water is the way to become hiccup-free. Putting sugar under your tongue might work, too. And maybe the most famous treatment – having someone jump out and scare you when you’re not expecting it – helps some people wave good-bye to their hiccups.

http://www.kidshealth.org/kid/talk/qa/hiccup.html