Directions: Complete the following passage by using the words in the box. Each word can only be used once. Note that there is one word more than you need.
A. contact B. serve C. weakening D. form E. consciously F. swell G. leisurely H. proportion I. randomly J. grasp K. normal |
Why do fingers get wrinkly after a long bath or swim?
We know skin wrinkles as you get older or when you pinch it between two fingers. But it’s been somewhat of a mystery why skin gets wrinkly and even sometimes changes color after you take a 16 bath or spend too long in the swimming pool.
Often people assume that these wrinkles form because the skin absorbs water, which makes it 17 up and buckle. To be honest, I did too for a long time.
But researchers back in the 1930s discovered that in people with nerve damage in their fingers, the post-bath wrinkles didn’t 18 . Wrinkly fingers can’t just be due to water absorption then, or this would be a universal phenomenon, no matter how well your nerves are or aren’t working.
To explain what is happening, first you need to know a bit about the autonomic nervous system – the involuntary part of how your body works. Functions like breathing, blinking, your heart pumping or your pupils constricting in the sun all happen without your needing to 19 control them, thanks to the autonomic nervous system.
It also automatically controls the expansion and contraction of your blood vessels. This contraction of your blood vessels is also what causes the skin to wrinkle after a lengthy swim.
When your hands and feet come into 20 with water for more than a few minutes, the sweat ducts (汗腺管) in your skin open, allowing water to flow into the skin tissue. This added water decreases the 21 of salt inside the skin. Nerve fibers send a message about lower salt levels to your brain, and the autonomic nervous system responds by constricting the blood vessels.
When tiny blood vessels inside the skin contract, they pull the skin’s surface down, forming the wrinkles you see after a long bath.
But does this skin wrinkling-when-wet 22 any purpose?
Researchers have found that wrinkled skin has added grip underwater in comparison to unwrinkled skin. Better grip lets you 23 objects more firmly. It makes walking along an underwater surface easier, with less likelihood of slipping.
Prolonged immersion in water makes skin more likely to break, but this 24 can take weeks to occur. Just don’t stay in the swimming pool too long and your pruney digits will go back to 25 once you’ve dried off.